Listado de Artículos Publicados 2011
Los artículos están ordenados por el factor de impacto reflejado en el 'Journal Citation Reports 2010'.
Infinite penetration of a projectile into a granular medium
F. Pacheco-Vázquez. G. A. Caballero-Robledo, J. M. Solano-Altamirano, E. Altshuler, A. J. Batista-Leyva, and J. C. Ruiz-Suárez.
Phys Rev Lett . F. I. 7.622. 106, 218001- 218004. (2011)
An object falling in a fluid reaches a terminal velocity when the drag force and its weight are balanced. Contrastingly, an object impacting into a granular medium rapidly dissipates all its energy and comes to rest always at a shallow depth. Here we study, experimentally and theoretically, the penetration dynamics of a projectile in a very long silo filled with expanded polystyrene particles. We discovered that, above a critical mass, the projectile reaches a terminal velocity and, therefore, an endless penetration
Multicommutation flow techniques in the hydride generation-atomic fluorescence determination of arsenic
Leal, LO; Ferrer, L; Forteza, R; Cerda, V
Trac-Trend Anal Chem. F. I. 6.602. 30, 761-770. (2011)
This review outlines automated methodologies developed for measuring arsenic in environmental samples. We report the state of the art of the most significant methods exploiting multicommutation flow techniques coupled to hydride generation-atomic fluorescence determination. We review analytical methods used and present a comparative evaluation of them. We also discuss the on-line pre-concentration procedure as being of particular interest in the development of fully automated methods.
Synthesis, Structural Characterization, and Electrical Properties of (Sr(0.5)Ca(0.5))(Ca(0.5)Sb(0.5))O(3-delta) Double Perovskites
Moreno, B; Urones-Garrote, E; Chinarro, E; Fuentes, L; Moran, E.
Chem Mater. F. I. 6.4. 23, 1779-1784. (2011)
Double perovskites which exhibit 1:2 B-site ordering are under focus because of their interesting structure property relationships and high chemical versatility. Perovskites with a big cation, such as Sr(2+) or Ca(2+), occupying the octahedral B site are very scarce because the calculated Goldschmidt tolerance factor becomes quite small as these types of cations usually occupy the A-site. This work describes the synthesis and structural and microstructural characterization of a new calcium and strontium antimoniate which shows face-centered cubic symmetry and a rock-salt ordered distribution of Sb(s+) and Sr(2+). The ordered-cation distribution occurs due to the differences in both the ionic sizes and the bonding character of the two B-site cations. As a consequence of the cation stoichiometry of the title phase and assuming a pentavalent state for Sb, a large concentration of oxygen vacancies are created (y similar to 0.25). Diffraction studies reveal that these vacancies tend to arrange in a short-ordered way and are related to oxygen ionic conductivity (10(-3) S/cm at 700 degrees C) which makes these materials potential candidates to be used as electrolytes in solid oxide fuel cells (SOFC).
A comparison of the effects of multi-wall and single-wall carbon nanotube additions on the properties of zirconia toughened alumina composites
Bocanegra-Bernal, MH; Echeberria, J Ollo; García-Reyes; Domínguez-Ríos, ; Reyes-Rojas, A; Aguilar-Elguezabal, A.
Carbon. F. I. 4.896. 49, 1599-1607. (2011)
The use of multi-wall carbon nanotubes (MWCNTs) or single-wall carbon nanotubes (SWCNTs) as filler in ceramic matrices could create composites with exceptional mechanical properties. We have prepared dense monolithic alumina (Al(2)O(3)) and zirconia-toughened alumina (ZTA) composites with additions of 0.01 wt% of MWCNTs or 0.01 wt% of SWCNTs by conventional sintering and have demonstrated that the mechanical properties depend on (a) the distribution of CNTs in the matrix and (b) the interaction between the ceramic phases and CNTs. The fracture toughness of Al(2)O(3) ceramics reinforced with SWCNTs was significantly better than those reinforced with MWCNTs. However, fracture toughness in MWCNT-reinforced ZTA increased 41% over ZTA free of the toughening agent and 44% over ZTA reinforced with SWCNTs. A well dispersed and small amount of MWCNTs was enough to produce an increase of fracture toughness in ZTA composites.
Nanostructured polyethylene glycol-titanium oxide composites as solvent-free viscous electrolytes for electrochromic devices
Mendoza, N; Paraguay-Delgado, F; Hechavarria, L ; Nicho, ME; Hu, HL.
Sol Energ Mat Sol C. F. I. 4.746. 95, 2478-2484. (2011)
Composites of polyethylene glycol (PEG) and titanium oxide compounds have been prepared by sol-gel method using different molar ratio between PEG and titanium isopropoxide. Transmission electron microscope (TEM) images and UV-vis absorption spectra of these composites indicate that titanium oxide particles or clusters were formed inside the composite materials and their maximum sizes were between 1.8 and 7 nm for PEG:Ti molar ratio changing from 24:1 to 4:1. Fourier Transform Infrared spectroscopy analysis of the same PEG-Ti composites suggests the presence of tetragonal titanium oxide compounds and its association with ether oxygen atoms of PEG molecules. As lithium iodide salt was added into PEG-Ti composites, iodide ions were oxidized into iodine and tri-iodides and, at the same time, titanium oxide compounds should be reduced. Color change speeds of tungsten oxide thin films were significantly improved when PEG-Ti-Lil composites were used as electrolytes compared to salt-in-polymer one (PEG-Lil); the bleaching time of tungsten oxide was reduced from 22 to 2.5 s under +1.0 V polarization, and the coloring time under -1.5 V lowered from 16 to 2.2 s. The transfer of negative charges from smaller iodide ions onto longer or crosslinked PEG-Ti macromolecules could be the origin of faster lithium ion transport/insertion speeds in PEG-Ti composite electrolyte based electrochromic devices.
New Fe(3+)/Cr(3+) Perovskites with Anomalous Transport Properties: The Solid Solution La(x)Bi(1-x)Fe(0.5)Cr(0.5)O(3) (0.4 <= x <= 1)
Villafuerte-Castrejon, ME; García-Guaderrama, M; Fuentes, L; Prado-Gonjal, J; Gonzalez, AM; de la Rubia, MA; García-Hernández, M; Moran, E.
Inorg Chem. F. I. 4.326. 50, 8340-8347. (2011)
In this work, the sol gel synthesis, structural characterization, and transport properties of a new solid solution of the general formula La(x)Bi(1-x)Fe(0.5)Cr(0.5)O(3) (0.4 <= x <= 1) are presented. The solubility limit x has been determined and variation of the lattice parameters measured through profile fitting. The cell parameters, space group, and atomic positions, as obtained by the Rietveld refinement of X-ray diffraction data, are reported. This analysis and electron diffraction studies as well do not reveal any evidence of Fe/Cr ordering. Regarding the transport properties, magnetic and electric characterizations are described. The electrical response with the temperature and frequency has been studied, and a "positive temperature coefficient" for the resistivity has been found for temperatures between 270 and 400 degrees C. The magnetic behavior is striking because, for all materials studied, zero-field-cooling curves appear above field-cooling ones, an anomalous feature that is interpreted as being due to complex ferromagnetic/antiferromagnetic interactions in the B perovskite sublattice.
PdCo supported on multiwalled carbon nanotubes as an anode catalyst in a microfluidic formic acid fuel cell
D. Morales-Acosta, M.D. Morales-Acosta, L.A. Godínez, L. Álvarez-Contreras, S.M. Duron-Torres, J. Ledesma-García, L.G. Arraiga.
J Power Sources. F. I. 4.29. 196, 9270-9275. (2011)
This work reports the synthesis of Pd-based alloys of Co and their evaluation as anode materials in a microfluidic formic acid fuel cell (mu FAFC). The catalysts were prepared using the impregnation method followed by thermal treatment. The synthesized catalysts contain 22 wt.% Pd on multiwalled carbon nanotubes (Pd/MWCNT) and its alloys with two Co atomic percent in the sample with 4 at.% Co (PdCo1/MWCNT) and 10 at.% Co (PdCo2/MWCNT). The role of the alloying element was determined by XRD and XPS techniques. Both catalysts were evaluated as anode materials in a mu FAFC operating with different concentrations of HCOOH (0.1 and 0.5 M), and the results were compared to those obtained with Pd/MWCNT. A better performance was obtained for the cell using PdCo1/MWCNT (1.75 mW cm(-2)) compared to Pd/MWCNT (0.85 mW cm(-2)) in the presence of 0.5 M HCOOH. By means of external electrode measurements, it was also possible to observe shifts in the formic acid oxidation potential due to a fuel concentration increment (ca. 0.05 V for both PdCo1/MWCNT and PdCo2/MWCNT catalysts and 0.23 V for Pd/MWCNT) that was attributed to deactivation of the catalyst material. The maximum current densities obtained were 8 mA cm(-2) and 5.2 mA cm(-2) for PdCo2/MWCNT and Pd/MWCNT, respectively. In this way, the addition of Co to the Pd catalyst was shown to improve the tolerance of intermediates produced during formic acid oxidation that tend to poison Pd, thus improving the catalytic activity and stability of the cell.
Tuning high aqueous phase uptake in nonionic w/o microemulsions for the synthesis of Mn-Zn ferrite nanoparticles: phase behavior, characterization and nanoparticle synthesis
Carolina Aubery, Conxita Solans, and Margarita Sánchez-Domínguez.
Langmuir. F. I. 4.269. 27, 14005-14013. (2011)
In this work, the formation of water-in-oil (w/o) microemulsions with high aqueous phase uptake in a nonionic surfactant system is investigated as potential media for the synthesis ofMn Zn ferrite nanoparticles. A comprehensive study based on the phase behavior of systems containing precursor salts, on one hand, and precipitating agent, on the other hand, was
carried out to identify key regions on (a) pseudoternary phase diagrams at constant temperature (50 C), and (b) pseudobinary phase diagrams at constant surfactant (S):oil(O) weight ratio (S:O) as a function of temperature. The internal structure and dynamics of microemulsions were studied systematically by conductivity and selfdiffusion coefficient determinations (FT PGSE 1H NMR). It was found that nonpercolated w/o microemulsions could be obtained by appropriate tuning of composition variables and temperature, with aqueous phase concentrations as high as 36 wt%for precursor salts and 25 wt%for precipitating agent systems. Three compositions with three different dynamic behaviors (nonpercolated and percolated w/o, as well as bicontinuous microemulsions) were selected for the synthesis of Mn Zn ferrites, resulting in nanoparticles with different characteristics. Spinel structure and superparamagnetic behavior were obtained. This study sets firm basis for a systematic study of Mn Zn ferrite nanoparticle synthesis via different scenarios of microemulsion dynamics, which will contribute to a better understanding on the relationship of the characteristics of the obtained materials with the properties of the reaction media.
The software package ANAELU for X-ray diffraction analysis using two-dimensional patterns
Fuentes-Montero, L; Montero-Cabrera, ME; Fuentes-Cobas, L.
J Appl Crystallogr. F. I. 3.794. 44, 241-246. (2011)
A new software package for interpreting two-dimensional diffraction diagrams is presented. The application capabilities include representation of single- and polycrystal structures with an inverse pole figure treatment of texture phenomena, measurement and analysis of diffraction signals, and different approaches to the modelling of two-dimensional diffraction patterns obtained from both single-crystal and polycrystalline samples. Particular consideration is given to the effect of axially symmetric textures on two-dimensional diffraction patterns. An example showing the capabilities of the software is presented.
Ultra-low thermal conductivity thermal barrier coatings from recycled fly-ash cenospheres
Chavez-Valdez, A; Arizmendi-Morquecho, A; Vargas, G; Almanza, JM; Álvarez-Quintana, J .
Acta Mater. F. I. 3.791. 59, 2256-2263. (2011)
Thermal conductivity of electrophoretically deposited fly ash (FA) and fly-ash cenosphere (FAC) coatings was measured in the range 100-500 K by the 3 omega method. The room temperature thermal conductivity in FAC coatings is found to be as low as 0.08 W m K(-1) and slightly higher for FA coatings. The reduction in the thermal conductivity is related mainly to the air-filled core of the cenospheres and the coating's porosity, which produces a strong heat barrier. The sintering process of the FAC and FA coatings at 1000, 1100 and 1200 degrees C slightly increases the thermal conductivity as a result of changes in microstructure. The temperature dependence of the effective thermal conductivity of the coatings was modeled within the framework of the self-consistent field concept and a modified Maxwell equation. These results suggest a route for obtaining suitable thermal barrier coatings for high-temperature applications.
Caloric effects induced by magnetic and mechanical fields in a Ni(50)Mn(25-x)Ga(25)Co(x) magnetic shape memory alloy
Castillo-Villa, PO; Soto Parra, DE; Matutes-Aquino, JA; Ochoa-Gamboa, RA; Planes, A; Manosa, L Manosa, Lluis; Gonzalez-Alonso, David; Stipcich, Marcelo; Romero, Ricardo; Rios-Jara, D; Flores-Zuniga, H.
Phys Rev B. F. I. 3.774. 83, 174109-1 a 174109-6. (2011)
We have studied the elastocaloric effect in a Co-doped Ni-Mn-Ga magnetic Heusler shape memory alloy in the vicinity of its martensitic transition. Measurements of the length change as a function of temperature have been carried out across the transition under applied compression stresses and magnetic fields. The isothermal stress-induced entropy changes have been computed from the experimental data. Results evidence a significant elastocaloric effect associated with the large entropy change of the structural phase transition. The alloy also exhibits a magnetocaloric effect at low applied magnetic fields. It is shown that application of a magnetic field below 1 T increases the estimated elastocaloric relative cooling power by about 20%. A comparison of elasto-and magnetocaloric properties indicates that a similar relative cooling power is reached under application of 10 MPa or 0.8 T.
Carbon nanotubes as catalyst support in a glucose microfluidic fuel cell in basic media
M. Guerra-Balcázara, F.M. Cuevas-Muñiz, F. Castanedaa, R. Ortegaa, L. Álvarez-Contreras, J. Ledesma-García, L.G. Arriaga.
Electrochim Acta. F. I. 3.65. 56, 8758-8762. (2011)
Au/MWCNTs previous termcatalystsnext term were synthesised by chemical reduction and tested as anode electrodes in previous termanext termprevious termglucosenext termprevious termmicrofluidicnext termprevious termfuelnext termprevious termcellnext term as previous termanext term function of time at different temperatures. Physicochemical characterisation of Au/MWCNTs showed an average particle size of approximately 4 nm with high dispersion among the MWCNTs previous termsupportnext term. The use of MWNTCs as previous termsupportnext term provides chemical stability and good performance for previous termmicrofluidicnext termprevious termfuelnext termprevious termcellsnext term. The maximum power density reached with Au/MWCNTs was 0.28 mW cm−2. Chronoamperometric testing (4 h) at three operating temperatures (15, 25 and 35 °C) demonstrated that the use of Au/MWCNTs as anode electrodes showed better stability compared with that of Au/C.
Biopolymers-based nanocomposites: Membranes from propionated lignin and cellulose for water purification
Nevarez, LM ; Casarrubias, LB; Canto, OS ; Celzard, A; Fierro, V; Gomez, RI; Sánchez, GG.
Carbohyd Polym. F. I. 3.463. 86, 732-741. (2011)
Nanocomposite membranes for water treatment were prepared by vapor-induced phase separation method from propionated lignin and cellulose triacetate (CIA). Three kinds of lignin were used: Kraft. Organosolv and Hydrolytic, which were propionated for improving their compatibility with CIA. Such chemical lignin modification was analyzed by FTIR. UV spectrophotometry and GPC. Morphology (through FE-SEM and AFM), mechanical properties (DMA), and surface potential (SPKM) were investigated for all membranes obtained. For determining membrane performance, groundwater from Chihuahua (México) containing high concentrations of fluoride, arsenic, calcium, sodium and magnesium, was filtrated. Membrane rejection was 15-35% for anions present, and 12-42% and 27-54% for monovalent and divalent cations, respectively. Arsenic and fluoride removal by membranes was found to be affected by ionic and organic matter present in groundwater.
Thermal and microstructural characterization of biodegradable films prepared by extrusion–calendering process
Galicia-García, T; Martínez-Bustos, F; Jiménez-Arévalo, O; Martínez, AB; Ibarra-Gómez, R; Gaytán-Martínez, M; Mendoza-Duarte, M.
Carbohyd Polym. F. I. 3.463. 83, 354-361. (2011)
Native starch (corn, potato and waxy corn) and phosphorylated corn starch blended with bagasse fiber and glycerol were used for the preparation of previous termbiodegradablenext termprevious termfilmsnext term. The processing previous termextrusionnext term variables were: feed moisture FM (18.25–20.5%), fiber content FC (0–10%) and type of starch TS (native or phosphorylated). The analysis of infrared spectroscopy showed OH and C–O bands at 2750–3250 and 550–1000 cm−1, related to plasticizer–starch interactions. previous termFilmsnext term processed without fiber revealed peaks of low intensity associated to the plastizicing of starch. Differential scanning calorimeter displayed some changes in calorific capacity that could be attributed to molecular excitations and the mobility of polymeric chains (Tg) in a range of temperature between 40 and 80 °C. The dynamic mechanical analyses presented a decrease in the loss modulus at a temperature lower than 100 °C associated to a more structural mobility of bonds indicating a previous termfilmnext term with more flexibility. The previous termthermalnext term and previous termmicrostructuralnext termprevious termcharacterizationnext term of previous termfilmsnext term showed appropriate functional properties in the development of packing materials or flexible containers type bag.
Surface versus volume effects in luminescent ceria nanocrystals synthesized by oil in- water microemulsion method
C. Tiseanu, V. I. Parvulescu, M. Boutonnet, B. Cojocaru, P. A. Primus, C. Teodorescu, C. Solans, M. Sánchez-Domínguez.
Phys Chem Chem Phys. F. I. 3.454. 13, 17135-17145. (2011)
Pure and europium (Eu(3+)) doped cerium dioxide (CeO(2)) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce(4+) sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce(4+) relative to Ce(3+) ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.
CO(2) corrosion inhibition of X-120 pipeline steel by a modified imidazoline under flow conditions
Ortega-Toledo, DM; González-Rodríguez, JG ; Casales, M; Martínez, L; Martínez-Villafañe, A. .
Corros Sci. F. I. 3.265. 53, 3780-3787. (2011)
A study of the effect of flow conditions on the performance of a carboxyethyl-imidazoline as CO(2)-corrosion inhibitor for API X-120 pipeline steel has been evaluated. Testing techniques include polarization curves, linear polarization resistance, electrochemical impedance spectroscopy and electrochemical noise measurements under stirred conditions (0, 250, 500, 1000 and 2500 rpm). All these techniques show that for the uninhibited solution, corrosion rate increases with an increase in the rotation speed, but for the inhibited solution, the lowest corrosion rate is obtained at 500 rpm, and it increases at lower or higher rotation speeds.
New organometallic salts as precursors for the functionalization of carbon nanotubes with metallic nanoparticles
Alonso-Nunez, G; de la Garza, LM; Rogel-Hernández, E; Reynoso, E; Licea-Claverie, A; Felix-Navarro, RM; Berhault, G; Paraguay-Delgado, F.
J Nanopart Res. F. I. 3.253. 13, 3643-3656. (2011)
New organometallic salts were synthesized in aqueous solution and were used as precursors for the functionalization of carbon nanotubes (CNT) by metallic nanoparticles. The precursors were obtained by reaction between HAuCl(4), (NH(4))(2)PtCl(6), (NH(4))(2)PdCl(6), or (NH(4))(3)RhCl(6) with cetyltrimethylammonium bromide (CTAB). The as-obtained (CTA) (n) Me (x) Cl (y) salts (with Me = Au, Pt, Pd, Rh) were characterized by Fourier-transform infra-red (FTIR) spectroscopy, (1)H nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis. These precursors were then used to synthesize metallic nanoparticles of Au, Pt, Pd, and Rh over multiwalled carbon nanotubes (MWCNT). Characterization by scanning transmission electron microscopy (STEM) and thermogravimetric analysis under air reveals that the CNT-supported catalysts exhibit high loading and good dispersion of the metallic nanoparticles with small average particle sizes. The present preparation procedure therefore allows obtaining high densities of small metallic nanoparticles at the surface of MWCNT.
Biopolymer-based nanocomposites: effect of lignin acetylation in cellulose triacetate films
Nevarez, LAM; Casarrubias, LB; Celzard; Fierro, V; Munoz, VT; Davila, AC; Lubian, JRT; Sánchez, GG.
Sci Technol Adv Mat . F. I. 3.226. 12, DOI: 10.1088/1468-6996/12/4/045006. (2011)
We have prepared all-biopolymer nanocomposite films using lignin as a filler and cellulose triacetate (CTA) as a polymer matrix, and characterized them by several analytical methods. Three types of lignin were tested: organosolv, hydrolytic and kraft, with or without acetylation. They were used in the form of nanoparticles incorporated at 1 wt% in CTA. Self-supported films were prepared by vapor-induced phase separation at controlled temperature (35-55 degrees C) and relative humidity (10-70%). The efficiency of acetylation of each type of lignin was studied and discussed, as well as its effects on film structure, homogeneity and mechanical properties. The obtained results are explained in terms of intermolecular filler-matrix interaction at the nanometer scale, for which the highest mechanical resistance was reached using hydrolytic lignin in the nanocomposite.
Occurrence and treatment of arsenic in groundwater and soil in northern México and southwestern USA
Camacho, LM; Gutierrez, W; Alarcon-Herrera, MT; Villalba, MD; Deng, SG.
Chemosphere. F. I. 3.155. 83, 211-225. (2011)
This review focuses on the occurrence and treatment of arsenic (As) in the arid region of northern México (states of Chihuahua and Coahuila) and bordering states of the southwestern US (New México, Arizona. and Texas), an area known for having high As concentrations. Information assembled and assessed includes the content and probable source of As in water, soil, and sediments and treatment methods that have been applied in the area. High As concentrations were found mainly in groundwater, their source being mostly from natural origin related to volcanic processes with significant anthropogenic contributions near mining and smelting of ores containing arsenic. The affinity of As for solid phases in alkaline conditions common to arid areas precludes it from being present in surface waters, accumulating instead in sediments and shifting its threat to its potential remobilization in reservoir sediments and irrigation waterways. Factors such as oxidation and pH that affect the mobility of As in the subsurface environment are mentioned. Independent of socio-demographic variables, nutritional status, and levels of blood lead. cognitive development in children is being affected when exposed to As. Treatments known to effectively reduce As content to safe drinking water levels as well as those that are capable of reducing As content in soils are discussed. Besides conventional methods, emergent technologies, such as phytoremediation, offer a viable solution to As contamination in drinking water.
Effect of gamma-irradiation on the growth of ZnO nanorod films for photocatalytic disinfection of contaminated water
Julio Alarcón, Silvia Ponce, Francisco Paraguay-Delgado, Juan Rodríguez.
The rate of crystal growth on the seed layer during the thermal bath treatment was kept constant. The resulting materials were characterized morphologically by scanning electron and atomic force microscopies; X-ray diffraction was used to study their morphology and structure and ultraviolet–visible spectroscopy to determine their absorbance. The obtained seed films were morphologically dependent on the radiation dose and this was correlated with the ZnO nanorod films which presented a texture in the (002) direction perpendicular to the substrate. The rods have a hexagonal mean cross section between 20 and 140 nm. Using these rods, the photocatalytic degradation of Escherichia coli bacteria in water was studied; a positive influence of the crystalline texture on the degradation rate was observed.
J Colliod Interf Sci. F. I. 3.068. 364, 49-55. (2011)
TiO(2) doped with Sm(3+) by sol-gel: Synthesis, characterization and photocatalytic activity of diuron under solar light
de la Cruz, D; Arevalo, JC; Torres, G; Margulis, RGB; Ornelas, C; Aguilar-Elguezabal, A.
Catal Today. F. I. 2.993. 8, 152-158. (2011)
A simple method to synthesize highly dispersed Sm(3+) on TiO(2) by sol-gel which induced significant changes in the photocatalytic properties, Eg values, specific surface areas, and crystal size of pure TiO(2), is reported. As is well known, thermal treatment of anatase TiO(2) at 600 degrees C leads to the transformation to rutile phase, however for Sm(3+) doped photocatalyst here reported, a significant amount of anatase phase remained even after thermal treatment at 800 degrees C, showing an interesting photocatalytic activity under sunlight degradation of diuron. TiO(2) doped with 0.3 wt% Sm(3+) and calcined at 500 degrees C showed the best performance for the photocatalytic degradation of diuron herbicide.
Performance of Eleocharis Macrostachya and its importance for arsenic retention in constructed Wetlands
Mario A. Olmos-Marquez, Ma.Teresa Alarcon-Herrera, Alejandro Benavides-Montoya, Ignacio R. Martín Domínguez.
Environ Sci Pollut R. F. I. 2.87. *, 21935698. (2011)
Arsenic (As) can be removed from water via rhizofiltration using phytostabilizing plants. The aim of this study was to investigate the performance of Eleocharis macrostachya in constructed wetland prototypes, as well as the plant's arsenic mass retention and the distribution of As along the wetland flow gradient and the soil in the wetland mesocosmos.
Chloride Ion Penetrability and Corrosion Behavior of Steel in Concrete with Sustainability Characteristics
Corral-Higuera, R; Arredondo-Rea, SP; Neri-Flores, MA; Gomez-Soberon, JM; Almaral-Sánchez, JL ; Castorena-Gonzalez, JH; Martinez-Villafane, A; Almeraya-Calderon, F.
Int J Electrochem Sc. F. I. 2.808. 6, 958-970. (2011)
As a contributive strategy in the sustainability concrete industry, the durability improving of reinforced concrete structures is currently investigated, as well as the partial or total replacement of its components for recycled materials. For the steel bars, the corrosion is the principal problem of durability in reinforced concrete. Coarse Recycled Concrete Aggregates (RCA), Supplementary Cementing Materials (SCM) byproducts of industrial processes such as fly ash and silica fume were used to produce concrete with sustainability characteristics and for the evaluation of its behavior when it is exposed to chlorides. From the resulting test specimens: electrical resistivity, resistance to charge transfer and resistance to chloride ion penetration, were determined; these parameters specify the minimum necessary properties for concretes, according to regulations, to guarantee their durability when they are exposed to chlorides. The results obtained concluded that the concrete manufactured with 100% RCA and SCM, improves its performance in durability compared with those of conventional concrete.
Corrosion Behavior of Ni-Al-Cu Alloys in Simulated Human Body Solution.
Castaneda, IE; Gonzalez-Rodriguez, JG; Domínguez-Patino, G; Sandoval-Jabalera, R; Neri-Flores, M. A.; Chacón-Nava, JG; Martinez-Villafane, A.
Int J Electrochem Sc. F. I. 2.808. 6, 404-418. (2011)
An investigation about the corrosion resistance of Ni-Al-Cu intermetallic alloys in simulated human body fluid environments has been carried out by using electrochemical techniques. Tested alloys included 50 (wt %) Ni-(20 and 25) Al-(20 and 25) Cu using the Hank's solution. For comparison, 316L type stainless steel has also been evaluated. Electrochemical techniques included potentiodynamic polarization curves, linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and electrochemical noise measurements, EN. Different techniques have shown that, generally speaking, Ni-Al-Cu alloys showed a lower corrosion resistance than conventional 316L type stainless steel only during a few days. Their corrosion resistance decreased as the Cu content in the alloy decreased. The alloys were susceptible to pitting type of corrosion on the. gamma'-(Ni, Cu)(3)Al Cu-rich phases.
Corrosion Behavior of Ni-Cr Based Coatings in Simulated Human Body Fluid Environment
C.D. Arrieta-González, J. Porcayo-Calderon , V.M. Salinas-Bravo, J.G. Chacón-Nava, A. Martinez-Villafane, J.G. Gonzalez-Rodriguez.
Int J Electrochem Sc. F. I. 2.808. 6, 3644-3655. (2011)
Potentiodynamic polarization and linear polarization resistance electrochemical techniques were used to assess the corrosion behavior of Ni20(% wt.)Cr, NiCrAl, NiCrAlY2O3, NiCrAlCoY2O3 and Cr2C3-Ni20Cr metallic coatings in simulated body fluid environment. Hank´s solution was used for simulating body fluid environment. Coatings were deposited on to AISI 304-type stainless steel by the High Velocity Oxygen Fuel (HVOF) system. All coatings were evaluated in the as deposited and grinded with 600 grade emery paper conditions. Corrosion behavior of all coatings was affected by both its chemical composition and surface finish. Scanning electron microscopy was used to observe the surface features of coatings before and after exposure in the corrosive media. Corrosion tests showed that by adding Al to the NiCr coating system in the as deposited condition decreased its corrosion potential whereas the corrosion current density (icorr) increased in the order NiCrAl > NiCrAlYCo > Ni20Cr > NiCrAlY > Cr3C2(NiCr). Corrosion potential of coatings in the grinded condition nobler than coatings in the as coated condition whereas the icorr value increased in the order NiCrAlY > NiCrAlYCo > NiCrAl > Cr3C2(NiCr) > Ni20Cr. The coating with the highest pitting potential value was NiCrAl, whereas the most susceptible to pitting type of corrosion was Cr3C2(NiCr). All coatings showed a crevice localized type of corrosion, and only NiCrAlY and Cr3C2(NiCr) coatings showed a repasivation, protection potential.
Corrosion Behavior of Steel Embedded in Ternary Concrete Mixtures
E. P. Reyes-Diaz, E.Maldonado B., F. Almeraya, D. M. Bastidas, M. Baltazar Z, J. Chacón N., A. Martínez-Villafañe, J. M. Bastidas, C. Gaona T.
Int J Electrochem Sc. F. I. 2.808. 6, 1892-1905. (2011)
The main reason for the premature failure of reinforced concrete structures is corrosion of the reinforcements. The use of new mortars based on ternary mixtures, an alternative to ordinary Portland cement (OPC), requires extensive research in order to check its passivating properties for reinforcements and the instability or permanence of the passive state achieved. Pozzolans and slag extend the market for concrete by improving specific properties of concrete products, allowing them to be constructed with other materials or placed in environments that would have precluded the use of Portland cement alone. In properly formulated concrete mixtures, pozzolans and slag have been shown to enhance long-term strength, decrease permeability, increase durability, and reduce thermal cracking of bulk concrete. Steel reinforcements have been exposed for 13 months in mortars immersed in a 3.5% NaCl solution. The effect of mortar composition using ternary mixtures of fly-ash (FA), microsilica (MS), and granulated blast furnace slag (GBFS) was tested. OPC was also tested as a reference. Electrochemical characterization was performed, measuring corrosion potential, linear polarization resistance, and electrochemical noise resistance. The best passivating properties were shown by the mixture of 10% FA and 10% GBFS.
Corrosion Fatigue of Road Bridges: a review.
F.J. Olguin Coca, M.U. Loya Tello, C. Gaona-Tiburcio, J.A. Romero, A. Martínez-Villafañe. E. Maldonado B, F. Almeraya-Calderón.
Int J Electrochem Sc. F. I. 2.808. 6, 3438-3451. (2011)
In this paper a review is presented about studies involving the fatigue and the corrosion of bridge elements. Reviewed reports include steel structures and steel-reinforced concrete bridges, classified as experimental and theoretical approaches. A special section has been dedicated to particular studies that deny any corrosion–fatigue relationship, thus involving pure corrosion or pure fatigue approaches. Most of the reports deal with the uncoupled corrosion – fatigue, in which the corrosion environment and cyclic loading do no coexist during the experiments. Most of the studies consider the exposition to the aggressive environment, followed by the strength or fatigue testing of the corroded material. Results from these approaches reveal that in some cases the strain level is more significant (up to 85 times more), while in others the corrosion level is the most significant factor (up to 11 times more). The studies that considered the coupled corrosion-fatigue phenomenon, whether circumstantially or systematically, reveal the greatest effects (from 20 to 30% reductions in fatigue strength). Furthermore, it is found that a realistic loading time-history has not been applied, regardless of the approach selected. Future works should focus on coupled corrosion – fatigue phenomenon, proposing standard procedures for structure design. Also, realistic force time-histories should be considered
Corrosion of Carbon Steel in Presence of Hydrocarbon
L. D. López León, M. A. Veloz Rodríguez, V. E. Reyes Cruz, F. Almeraya Calderón*, S. A. Pérez García .
Int J Electrochem Sc. F. I. 2.808. 6, 3497 – 3507. (2011)
In this work the study of the behaviour AISI 1018 in a buffered solution like NACETM177 with and without hydrocarbon. Polarisation curves indicated slopes changing with the hydrocarbon presence enhancing the reduction reaction and inhibiting oxidation. EIS technique shows high activity of steel in the solution at low frequencies, establishing that interaction of the ions in solution with the metal is enhanced by hydrocarbon, where the adsorption processes are governing the corrosion mechanism. The adsorption of corrosive agents prevents the formation and growth of a passive layer, even in the presence of hydrocarbon and the corrosion rate is high
Electrochemical Behavior of Fe3Al Modified with Ni in Hank´s Solution
C.D Arrieta-Gonzalez, J. Porcayo-Calderon, V.M. Salinas-Bravo, J.G. Gonzalez-Rodriguez, J.G. Chacón-Nava.
Int J Electrochem Sc. F. I. 2.808. 6, 4016-4031. (2011)
An investigation about the corrosion resistance of Fe3Al-type intermetallic alloys in Hank´s solution was carried out via electrochemical techniques. The Fe3Al intermetallic alloy was modified with additions of Ni and evaluated in the as cast and thermal treated conditions. For comparison, Titanium and 316-L stainless steel were also evaluated. For evaluation purposes, electrochemical techniques included potentiodynamic polarization curves, open circuit potential measurements, linear polarization resistance curves and cyclic polarization curves were employed. Results shown that the 316-L stainless steel and titanium are the materials with greater corrosion resistance in chloride-rich environments showing an active-passive behavior and are susceptible to pitting corrosion. Compared to 316-L SS and Titanium, intermetallic Fe3Al alloys had greater susceptibility to pitting corrosion. Ni addition changed the corrosion potential of the intermetallic base Fe3Al to more noble values. Ni addition and thermal treatment improved the corrosion resistance of Fe3Al-base alloy owing to an increased stability of the passive layer
Electrochemical Characterization of Modified Concretes with Sugar Cane Bagasse Ash E
E. Maldonado-Bandala, V. Jiménez- Quero, F. J. Olguin-Coca, L. G. Lizarraga M, M. A. Baltazar-Zamora, A.Ortiz-C., F. Almeraya C., P. Zambrano R. C. Gaona-Tiburcio García.
Int J Electrochem Sc. F. I. 2.808. 6, 4915 - 4926. (2011)
Corrosion is one of the most serious causes that reduce service life of Reinforced Concrete Structures (RCS). This is why it is necessary to create concrete mixtures that add durability for steel and that reduce impact on the environment. The use of agro-industrial waste materials rich in SiO2, Al2O3 and Fe2O3, added to concrete, has been the subject of research in recent years, because these pozzolanic materials improves o mecharacteristics of concrete, as mechanical strength, sulfate resistance and lower permeability. Binary Concretes were made and evaluated in the impact of Sugar Cane Bagasse Ash (SCBA) as a partial substitute for Portland cement, with the aim of reducing gtherate of corrosion induced by chloride ions and sulfate. The behavior of corrosion was monitored for 14 months in two aqueous solutions of NaCl and Na2SO4 both at 3.5%, using electrochemical techniques of corrosion potential (Ecorr) and linear polarization resistance (Rp). Under the conditions of study, the binary mixture that showed a better corrosion protection was the one that contained 80% from sugar Cane bagasse ash and 20% Portland cement.
Electrochemical Corrosion and Electrical Resistivity of Reinforced Recycled Aggregate Concrete
Corral-Higuera, R; Arredondo-Rea, SP; Neri-Flores, MA; Gomez-Soberon, JM; Almaral-Sánchez, JL; Castorena-Gonzalez, JH; Martinez-Villafane, A; Almeraya-Calderon, F.
Int J Electrochem Sc. F. I. 2.808. 6, 475-483. (2011)
It is planned to improve the durability of reinforced concrete structures and the total or partial replacement of their components by the use of recyclable materials; as strategies to contribute to the concrete industry sustainability. The electrical resistivity and its relationship with the microstructure and electrochemical corrosion resistance in reinforced concrete manufactured with sustainable characteristics, that is, with recycled aggregates and supplementary cementitious materials; was evaluated in this study. The electrical resistivity in reinforced concretes is closely related to the microstructure of the cementitious matrix, and with the pore structure and distribution. As a consequence of the their components nature, it is assumed that the proposed sustainable concretes present different microstructure and porosity than the conventional concretes; because of this, the electrical and electrochemical response of those systems was analyzed with the help of the electrochemical impedance spectroscopy technique.
Electrochemical impedance spectroscopy investigation of alloy inconel 718 in molten salts at high temperature.
Trinstancho-Reyes, J; Sánchez-Carrillo, M; Sandoval-Jabalera, R; Orozco-Carmona, VM; Almeraya-Calderon, F; Chacón-Nava, JG; Gonzalez-Rodriguez, JG; Martinez-Villafane, A. .
Int J Electrochem Sc. F. I. 2.808. 6, 419-431. (2011)
The corrosion behavior in molten salts of Inconel 718 (IN 718) superalloy was investigated by Electrochemical Impedance Spectroscopy (EIS). The corrosion test temperatures used were salt melting points of Na(2)SO(4), 80V(2)O(5)-20Na(2)SO(4), NaVO(3) and natural ash (collected in a power plant). Different experimental runs were made attempting to establish the material behavior. The results showed that the corrosion process was controlled by activation and in some cases by diffusion. The aggressiveness of the salts increased with temperature, as indicated for the corrosion rates values derived. On the whole, the corrosion rates were somewhat similar at the lowest test temperatures. However at 588 degrees C the 80V(2)O(5)- 20Na(2)SO(4) salt showed a much higher corrosion rate than that recorded for Na(2)SO(4) or natural ash. The results obtained from electrochemical measurements correlated well with those corrosion degradation observed by SEM, and comments on the behavior found are made.
Hot Corrosion Behaviour of NiCrFeNbMoTiAl Coating in Molten Salts at 700 degrees c by Electrochemical Techniques
Tristancho-Reyes, JL; Chacón-Nava, JG; Pena-Ballesteros, DY;Gaona-Tiburcio, C; Gonzalez-Rodriguez, JG; Martinez-Villafane, A; Almeraya-Calderon, F.
Int J Electrochem Sc. F. I. 2.808. 6, 432-441. (2011)
This research studied the behavior of NiCrFeNbMoTiAl metallic coating under corrosive attack by molten salts 80% Na(2)SO(4) - 20%V(2)O(5) and 80%K(2)SO(4) - 20%V(2)O(5) deposited by non- transfer arc plasma- assisted thermal spraying (APS) at a temperature of 700 degrees C. Corrosion rate were determined by means of linear polarization resistance (LPR), electrochemical techniques, and electrochemical impedance spectroscopy (EIS). The results obtained showed a high severity of attack from the 80% Na(2)SO(4) - 20%V(2)O(5) mixture. Nyquist plots show a trend that the load transfer mechanism was the predominant factor in the process activation.
Hydrodynamic Effects on the CO(2) Corrosion Inhibition of X-20 Pipeline Steel by Carboxyethyl-imidazoline
Ortega-Toledo, DM; Gonzalez-Rodriguez, JG ; Casales, M; Caceres, A; Martinez, L.
Int J Electrochem Sc. F. I. 2.808. 6, 778-792. (2011)
The effect of flow conditions on the performance of carboxyethylimidazoline as CO(2)-corrosion inhibitor for API X-120 pipeline steel has been evaluated by using electrochemical techniques. Techniques includes polarization curves, linear polarization resistance, electrochemical impedance spectroscopy and electrochemical noise measurements, whereas the rotation speed were 0, 250, 500, 1000 and 2500 rpm. Different techniques show that for uninhibited solution, the corrosion rate increases with an increase in the rotating speed, but for the inhibited solution, the lowest corrosion rate is obtained at 1000 rpm, but it increases with a further increase in the rotating speed. Electrochemical noise measurements shows that in absence of inhibitor, the steel is susceptible to uniform corrosion, whereas when the inhibitor is present, the steel is highly susceptible to localized type of corrosion.
Inhibition on Carbon Steel Corrosion in Presence of Hydrocarbon
L. D. López León, M. A. Veloz Rodríguez, V. E. Reyes Cruz, S. A. Pérez García, A.L. López León.
Int J Electrochem Sc. F. I. 2.808. 6, 5134-5145. (2011)
In this work the study of electrochemical behaviour of organic compounds as corrosion inhibitors is being done over a carbon steel AISI 1018 immersed in a corrosive synthetic environment (brine type NACE 1D196), in the absence and presence of hydrocarbon. The techniques used were the electrochemical Polarisation curves and electrochemical impedance spectroscopy. In the Polarisation curves, the presence of corrosion inhibitors in the system shows that increasing of the concentration affects both the anodic and the cathodic stages of the corrosion process, showing that the obtained currents are lower by increasing the concentration of the inhibitor. On the other hand the inhibitor efficiency decreases with the presence of hydrocarbon in different systems. Electrochemical impedance spectroscopy shows that steel has high activity in the environments studied, being more remarkable at low frequencies and in the presence of hydrocarbon since the spectra shows flattened semicircles, with low values of real impedance and inductive trends. This establishes that the interaction of ions in the solution with the metal, where adsorption processes are governing the corrosion mechanism, is favoured by the presence of hydrocarbon.
Platinum Nanoparticles Synthesis Supported in Mesoporous Silica and Its Effect in M C M-41 Lattice
I. Alonso-Lemus Y. Verde-Gómez L. Álvarez-Contreras.
Int J Electrochem Sc. F. I. 2.808. 6, 4176-4187. (2011)
Platinum nanoparticles were incorporated in MCM-41 mesoporous support. Two different ways to incorporate metallic nanoparticles were evaluated (i) Pt wetness impregnation in MCM-41 previously synthesized and (ii) Pt incorporated in situ during MCM-41 synthesis in alkaline (iia) and acid (iib) media. Synthesis conditions influence was studied by X-Ray diffraction, nitrogen adsorption analysis and electron microscopy. High surface areas (up to 900 m2/g) were obtained in all methods. However, high Pt loading were observed only in wetness impregnation and in situ incorporation in alkaline media methods. Additionally, composites Pt/MCM-41-black carbon were prepared and their electrocatalytic activity and electrical bulk resistance were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. An interesting behaviour was observed in the samples where the platinum was in situ incorporated; the samples show structural and textural properties modifications compared to raw MCM-41.Hydrogen oxidation reaction by CV was observed in high Pt loading samples. On the other hands, EIS results indicate that Pt/MCM-41 materials synthesized by in situ incorporation methods have lower electrical bulk resistance than the samples prepared by wetness impregnation method.
Sulfate Attack and Reinforcement Corrosion in Concrete with Recycled Concrete Aggregates and Supplementary Cementing Materials
Corral-Higuera, R; Arredondo-Rea, SP; Neri-Flores, MA; Gomez-Soberon, JM; Calderon, FA; Castorena-Gonzalez, JH; Almaral-Sánchez, JL.
Int J Electrochem Sc. F. I. 2.808. 6, 613-621. (2011)
As strategies to contribute to the concrete industry sustainability, reinforced concrete was fabricated using recycled concrete coarse aggregate and replacing partially portland cement with supplementary cementing materials as fly ash and silica fume. On test specimens, partially immersed in 3.5% Na(2)SO(4) aqueous solution, the effect of the recycled and supplementary materials against sulfate attack and reinforcement corrosion was evaluated. For such aim, weight loss of concrete and corrosion potentials, corrosion current density of reinforcement were determined by means of electrochemical techniques as open circuit potential and linear polarization resistance, respectively.
Transient Analysis of Electrochemical Noise for 316 and Duplex 2205 Stainless Steels Under Pitting Corrosion.
F.H. Estupiñán-López, F. Almeraya-Calderón, R.G. Bautista M, M.A. Baltazar Z, A. Martínez-Villafañe, J. Uruchurtu Ch, C. Gaona-Tiburcio.
Int J Electrochem Sc. F. I. 2.808. 6, 1785-1796. (2011)
The use of electrochemical noise (EN) technique for the investigation and monitoring of corrosion has allowed many interesting advances in the corrosion science in recent years. A special advantage of EN measurements includes the possibility to detect and analyses the early stages of localized corrosion. However, the understanding of the electrochemical information included in the EN signal is actually very limited. This work shows the results obtained from EN measurements for different materials that exhibit pitting corrosion. The obtained transients in potential and current time, correlates with the scanning electron microscopy (SEM) surface analysis. Electrochemical measurements were made at different exposure times in order to obtain any correlation. The used materials were austenitic 316 stainless steel and 2205 duplex alloy, immersed in ferric chloride (FeCl(3)) and sodium chloride (NaCl) electrolytes. SEM analysis shows that the observed transients in the time series really correspond to the activity of pit nucleation developed on the surface of the electrodes.
Growth of vertically aligned ZnO nanorods using textured ZnO films
F. Solís-Pomar, E. Martínez-Guerra, M.F. Meléndrez, E. Pérez-Tijerina.
Nanoscale Res Lett. F. I. 2.56. 6, 10.1186/1556-276X-6-524. (2011)
A hydrothermal method to grow vertical-aligned ZnO nanorod arrays on ZnO films obtained by atomic layer deposition (ALD) is presented. The growth of ZnO nanorods is studied as function of the crystallographic orientation of the ZnO films deposited on silicon (100) substrates. Different thicknesses of ZnO films around 40 to 180 nm were obtained and characterized before carrying out the growth process by hydrothermal methods. A textured ZnO layer with preferential direction in the normal c-axes is formed on substrates by the decomposition of diethylzinc to provide nucleation sites for vertical nanorod growth. Crystallographic orientation of the ZnO nanorods and ZnO-ALD films was determined by X-ray diffraction analysis. Composition, morphologies, length, size, and diameter of the nanorods were studied using a scanning electron microscope and energy dispersed x-ray spectroscopy analyses. In this work, it is demonstrated that crystallinity of the ZnO-ALD films plays an important role in the vertical-aligned ZnO nanorod growth. The nanorod arrays synthesized in solution had a diameter, length, density, and orientation desirable for a potential application as photosensitive materials in the manufacture of semiconductor-polymer solar cells.
Synthesis of polypyrrole nanoparticles by oil-in-water microemulsion polymerization with narrow size distribution
Ovando-Medina, VM; Peralta, RD; Mendizábal, E; Martínez-Gutierrez, H; Lara-Ceniceros, TE; Ledezma-Rodríguez, R.
Colloid Polym Sci. F. I. 2.443. 289, 759-765. (2011)
Conductive spherical polypyrrole nanoparticles were obtained by polymerization in oil-in-water (o/w) microemulsions using sodium dodecyl sulfate (SDS) as anionic surfactant, ethanol as co-surfactant, and potassium persulfate (KPS, 0.017 wt.%) as oxidizing agent. The average particle diameter (Dp) of the nanoparticles was between 38 and 45 nm with narrow particle size distributions (D (w)/D (n) < 1.2). Dp increases with the ethanol concentration due to the intercalation between the polar heads of SDS, promoting instability of the nanoparticles and some coagulation. In this work, low surfactant concentration was used, and the molar ratio of the oxidizing agent to monomer was 8.5 x 10(-3), a value much lower compared with others reported in the literature. Increasing the ethanol concentration in the recipes enhanced the conductive properties of the polymers due to the high pi-conjugation length obtained.
Amphiphilic Block Copolymer from Hydroxyl-Terminated Polymers Functionalized with TEMPO. A New Synthetic Method Using Oxoammonium Salt
José Bonilla-Cruz, Tania E. Lara-Ceniceros, D. G. Ramírez-Wong,Enrique Saldívar-Guerra, F. Pérez-Rodríguez, Uriel Márquez-Lamas.
Macromol Chem Physic. F. I. 2.437. 212, 1654-1662. (2011)
A simple approach for the end-functionalization of hydroxyl-terminated polymers with nitroxide moieties using oxoammonium salts (OS) is presented. The functionalization is carried out using only one synthetic pathway in which high levels of functionalization (90%) are found. A mechanism for the functionalization with TEMPO moieties using OS is proposed in which the formation of peroxide groups is suggested. The structures of the functionalized polymers are characterized in detail by 1H NMR, 13C NMR, DQF-COSY, and HETCOR. Bifunctional macroalkoxyamines are used to demonstrate how to extend the polymer chain for the synthesis of amphiphilic triblock copolymers by polymerizing St in a second block mediated by a nitroxide radical which provides the block length control.
Nickel Nanoparticles Dispersion on Carbon Molecular Sieve by Electroless Deposition by Electroless Deposition
Figueroa-Torres, MZ; Saenz, LD; Rios, CD; Torres-Sánchez, R; Aguilar-Elguezabal, A.
Top Catal. F. I. 2.359. 54, 568-571. (2011)
This work presents a novel one step process to synthesize nickel nanoparticles dispersed on activated carbon. This technique is widely used for the plating of metal surfaces and consists of the immersion of substrate on a stabilized bath that contains the metal precursor, a complexing agent, an additive for pH control, and chemical stabilizer to avoid the spontaneous reduction of metal in bath solution. By this process, nickel was dispersed on chemical activated carbon (carbon molecular sieve, CMS) obtaining a catalyst which showed better catalytic activity on benzene dehydrogenation than the observed for unsupported nickel nanoparticles and a commercial catalyst composed by nickel nanoparticles supported in Al(2)O(3)-SiO(2).
Symmetry breaking and electrical conductivity of La(0.7)Sr(0.3)Cr(0.4)Mn(0.6)O(3-delta) perovskite as SOFC anode material
Reyes-Rojas, A; Alvarado-Flores, J; Esparza-Ponce, H; Esneider-Alcala, M; Espitia-Cabrera, I; Torres-Moye.
Mater Chem Phys. F. I. 2.356. 126, 773-779. (2011)
This work is focused on nanocrystalline solid oxide fuel cell synthesis and characterization (SOFC) anodes of La(0.7)Sr(0.3)Cr(0.4)Mn(0.6)O(3-delta) (perovskite-type) with Nickel. Perovskite-type oxide chemical reactivity, nucleation kinetics and phase composition related with La(0.7)Sr(0.3)Cr(0.4)Mn(0.6)O(3-delta)-NiO to La(0.7)Sr(0.3)Cr(0.4)Mn(0.6)O(3-delta)-Ni transformation have been analyzed. SOFC anode powders were obtained by sol-gel synthesis, using polyvinyl alcohol as an organic precursor to get a porous cermet electrode after sintering at 1365 degrees C and oxide reduction by hydrogen at 800 degrees C/1050 degrees C for 8 h in a horizontal tubular reactor furnace under 10% H(2)/N(2) atmosphere. Composite powders were compressed into 10-mm diameter discs with 25-75 wt% Ni. Electrical and structural characterization by four-point probe method for conductivity, scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS). X-ray diffraction (XRD), and Rietveld method were carried out. Symmetry-breaking by phase transition from high temperature aristotype R (3) over barc to hettotype 14/mmm has been identified and confirmed by XRD and Rietveld method which can be produced by introducing Ni(2+) cations in the perovskite solid solution. Rietveld analysis suggests that Ni contents are directly proportional to a(0.7)Sr(0.3)Cr(0.4)Mn(0.5)NiO(3.95) tetragonal structure cell volume and inversely proportional to Ni cubic structure cell volume after reduction at 1050 degrees C. Kinetic analysis indicated that the Johnson-Mehl-Avrami equation is able to provide a good fit to phase transformation kinetics. The variation of electrical conductivity reveals the presence of two types of behavior in samples reduced at 1050 degrees C. First, at low Ni concentration (25%), p resistivity decreases when increasing the temperature; then, for Ni concentration higher than 25% rho resistivity increases.
Fluorescence and conformation in water-soluble bis(pyrenyl amide) receptors derived from polyaminopolycarboxylic acids
Pérez-Gonzalez, R; Machi, L; Inoue, M; Sánchez, M; Medrano F.
J Photoch Photobio A. F. I. 2.243. 219, 90-100. (2011)
Fluorescent responses and conformational changes against pH were studied on four new water-soluble 1-pyrene and 1-methylpyrene bichromophores, (tthal py)H(4), (edta1 mpy)H(2), (dtpa1 mpy)H(3) and (tthalmpy)H(4), with the objective of modifying pH-fluorescence profiles and other solution properties of 1-pyrene bichromophores, (edtal py)H(2) and (dtpa1py)H(3), developed previously by our group; the abbreviations with acidic protons stand for pyrenyl moieties interlinked by an EDTA, DTPA (diethylenetriaminepentacetic acid) or TTHA (triethylenetetraminehexaacetic acid) chain through amide linkages. The new derivatives exhibit emission bands of monomeric pyrene and an intense structureless excimer band; the latter responds to pH sensitively. The pH dependence of the emission intensity of the DTPA and TTHA derivatives is well correlated with species distribution determined by potentiometry. In every derivative, the completely deprotonated species L(n-) is the most efficient for excimer emission, followed by the corresponding monoprotonated species LH((n-1)-). In the latter, the acidic hydrogen is located on the central amine, as confirmed by (1)H NMR. The resulting hydrogen bond between amino nitrogen atoms makes the aliphatic chain rigid. Further protonation stretches the interlinking chain due to electrostatic repulsion. These conformational changes with protonation result in fluorescent on-off cycles against pH window. The switching cycles of the methylpyrene derivatives are reverse to those of the corresponding pyrene derivatives, as the CH(2) spacer between the amide and aromatic groups defines the orientation of pyrene rings. The sensitiveness of amide group to environment leads to a sharp change in excimer emission above pH similar to 11. The combined functions of amide and amino groups lead to the novel pH-responses.
CO(2) corrosion inhibition of X-70 pipeline steel by carboxyamido imidazoline
Ortega-Sotelo, DM; Gonzalez-Rodriguez, JG; Neri-Flores, MA; Casales, M; Martinez, L; Martinez-Villafane, A..br/>J Solid State Electr. F. I. 2.234. 15, 1997-2004. (2011)
The corrosion inhibition of X-70 pipeline steel in saltwater saturated with CO(2) at 50 A degrees C with carboxyamido imidazoline has been evaluated by using electrochemical techniques. Techniques included polarization curves, linear polarization resistance, electrochemical impedance, and electrochemical noise measurements. Inhibitor concentrations were 0, 1.6 x 10(-5), 3.32 x 10(-5), 8.1 x 10(-5), 1.6 x 10(-4), and 3.32 x 10(-4) mol l(-1). All techniques showed that the best corrosion inhibition was obtained by adding 8.1 x 10(-5) mol l(-1) of carboxyamido imidazoline. For inhibitor concentrations higher than 8.1 x 10(-5) mol l(-1) a desorption process occurs, and an explanation has been given for this phenomenon.
Observation and formation mechanism of individual graphene foils inside multi-walled carbon nanotubes
Alonso-Nunez, G; Avalos-Borja, M ; Lara-Romero, J; Berhault, G; Marquez-Lucero, A.
Mater Res Bull. F. I. 2.146. 46, 658-661. (2011)
The formation of individual graphene foils (GF) has been evidenced in the present study inside multi-walled carbon nanotubes. The graphene foils are attached on one side to a catalyst nanoparticle and on the other side to the internal walls of the nanotube. Moreover, results suggest that a necking process occurs in which internal carbon walls are deformed until formation of the graphene foil. A possible mechanism for the GF formation is then proposed.
Microstructure of NiCoAlFeCuCr Multi-Component Systems Synthesized by Mechanical Alloying
Gómez-Esparza, CD; Ochoa-Gamboa, RA; Estrada-Guel, I; Cabañas-Moreno, JG; Barajas-Villarruel, JI; Arizmendi-Morquecho, A; Herrera-Ramírez, JM; Maríinez-Sánchez, R.
J Alloy Compd. F. I. 2.138. 509, S279-S283. (2011)
The present study uses the mechanical alloying method to produce series of binary to senary alloys based on Ni, Co, Al, Fe, Cu, Cr. Milling times are 0, 10, 20 and 30 h and experiments are performed in a high energy ball mill. The results of this investigation show that an FCC solid solution is formed in all the studied systems, but a different phase formation response is presented in each system. A mixture of FCC and BCC solid solutions in quaternary to senary systems, is formed for short milling times. Apparently, the dissolution rate of Fe and Cr into the FCC solid solution, is low. Moreover, it is observed that additions of these elements promote the formation of BCC solid solution, which is stable at temperatures up to -1273 K. Finally, it is observed that the heat treated products present a mixture of FCC and BCC solid solutions with lattice parameters close to those found in the milled products.
Synthesis of Aluminum Alloy 7075-graphite Composites by Milling Processes and Hot Extrusion
Deaquino-Lara, R; Estrada-Guel I; Hinojosa-Ruiz, G; Flores-Campos, R; Herrera-Ramírez, JM; Martinez-Sánchez, R.
J Alloy Compd. F. I. 2.138. 509, S284-S289. (2011)
Aluminum alloy 7075 (Al(7075)) and composites of Al(7075) with different concentrations of graphite particles (Al(7075)-G) were synthesized from elemental powders by a milling process. Milled products were consolidated by pressureless-sintering followed by hot extrusion. The mechanical properties of the sintered specimens were evaluated by tension tests and hardness measurements. Variation of Zn and graphite contents and their effect on mechanical properties was characterized. The results obtained show that the yield strength (sigma(y)), the maximum strength (sigma(max)) and the Vickers microhardness (mu HV) were enhanced as a function of graphite particles content and milling time, but the elongation was reduced significantly in some cases.
Synthesis, microstructural characterization and optical properties of undoped, V and Sc doped ZnO thin films
P. Amézaga-Madrid, W. Antúnez-Flores, J. E. Ledezma-Sillas, J.G. Murillo-Ramírez, O. Solís-Canto, O. E. Vega-Becerra, R. Martínez-Sánchez, and M. Miki-Yoshida.
J Alloy Compd. F. I. 2.138. 509, S490-S495. (2011)
Many semiconductor oxides (ZnO, TiO2, SnO2) when doped with a low percentage of non-magnetic (V, Sc) or magnetic 3d (Co, Mn, Ni, Fe) cation behave ferromagnetically. They have attracted a great deal of interest due to the integration of semiconducting and magnetic properties in a material. ZnO is one of the most promising materials to carry out these tasks in view of the fact that it is optically transparent and has n or p type conductivity. Here, we report the synthesis, microstructural characterization and optical properties of undoped, V and Sc doped zinc oxide thin films. ZnO based thin films with additions of V and Sc were deposited by the Aerosol Assisted Chemical Vapour Deposition method. V and Sc were incorporated separately in the precursor solution. The films were uniform, transparent and non-light scattering. The microstructure of the films was characterized by Grazing Incidence X-ray Diffraction, Scanning Electron Microscopy, and Scanning Probe Microscopy. Average grain size and surface rms roughness were estimated by the measurement of Atomic Force Microscopy. The microstructure of doped ZnO thin films depended on the type and amount of dopant material incorporated. The optical properties were determined from specular reflectance and transmittance spectra. Results were analyzed to determine the optical constant and band gap of the films. An increase in the optical band gap with the content of Sc dopant was obtained.
Characterization of Al2O3NP-Al2024and AgCNP-Al2024Composites Prepared by Mechanical Processing in a High Energy Ball Mill
C. Carreño-Gallardoa, b, I. Estrada-Guel, M. Romero-Romob, R. Cruz-Garcíac, C. López-Meléndeza, d, R. Martínez-Sánchez, .
J Alloy Compd. F. I. 2.134. *, 1016. (2011)
Mechanical alloying was used to produce two kinds of metal matrix composites based on 2024 aluminum alloy. The nanocomposites were reinforced with different percentages of Al2O3 and AgC nanoparticles. The content of nanoparticles has an important role on the mechanical properties of the nanocomposites. A milling time of 10 h is enough to form the Al2024nanocomposites. The thermograms obtained by differential scanning calorimeter show the temperatures of phase precipitation, which were identified by X-ray diffraction. The results revealed that mechanical alloying is an excellent route for the incorporation and distribution of nanoparticles into Al2024.
In vitro bioactivity of chitosan/poly (d,l-lactide-co-glycolide) composites
Martel-Estrada, SA; Martínez-Pérez, CA; Chacón-Nava, JG; García-Casillas, PE; Olivas-Armendáriz, I. .
Mater Lett. F. I. 2.12. 65, 137-141. (2011)
Porous composites scaffolds of chitosan/poly(D L-lactide-co-glycolide) were fabricated for tissue engineering applications by thermally induced phase separation and lyophilization techniques The in vitro bioactivity evaluation of the scaffolds was carried out by analyzing the apatite layers produced on them using SBF is incubation medium The apatite formation was analyzed using FTIR spectroscopy and Field emission scanning electron microscopy coupled to energy-dispersive electron X-ray spectroscopy The cumulative results obtained from the IR spectra and SEM-EDS suggest that the developed composites might have potential applications in tissue engineering
Spectrally and temporarily resolved luminescence study of short-range order in nanostructures amorphous ZrO2.
C. Tiseanu, V. I. Parvulescu, M.Sánchez-Domínguez, M. Boutonnet.
J Appl Phys. F. I. 2.079. 110, 103521–103524. (2011)
The local structure amorphous ZrO2 doped with europium (Eu3+) and its evolution during crystallization was investigated by using spectrally and temporally resolved luminescence of europium. A small contribution of a crystalline, tetragonal-like local phase emission to the overall broad/amorphous emission could be observed in the amorphous state before calcination. Also, a non- negligible amount of amorphous type emission was still detectable with the crystalline europium-doped ZrO2 obtained on calcination at 500 and 1000 °C being assigned to a disordered, monoclinic-like local phase.
Analysis of polyelectrolyte complexes formed with jicama pectic polysaccharide and water-soluble chitosan
Ramos-de-la-Pena, AM; Rangel-Rodriguez, AM; Casas-Gonzalez, MR; Balagurusamy, N; Sanudo-Barajas, JA; Carrillo-Castillo, A; Contreras-Esquivel, JC.
Polym Int. F. I. 2.056. 60, 916-919. (2011)
Jicama (Pachyrhizus erosus L.) is a root-based legume that has been cultivated in México for centuries. Pectic polysaccharide from de-starched jicama pomace was extracted using an autoclave-assisted process and physicochemically characterized. The extracted polysaccharide (1.0 g L(-1)) was used for the formation of polyelectrolyte complexes (PECs) with water-soluble chitosan (WSCh; 0.5, 1.0 and 2.0 g L(-1)). The extraction yield of jicama pectic polysaccharide was 22.8 wt% (dry basis) and infrared spectroscopic analysis showed that it was methoxylated to a small degree. Thermogravimetric analysis indicated that this biopolymer was very stable, its weight loss being 51.2% after heating at 479. C. Anion-exchange chromatography showed it to have a wide and heterogeneous charge density. The yield of the PECs was dependent on the concentration of WSCh used, it being 13.3, 26.7 and18.3% withWSChat 0.5, 1.0 and 2.0 g L(-1), respectively. The PECs had higher thermostability compared with WSCh and this confirmed the complex formation between WSCh and jicama polysaccharide. WSCh is a promising polycation able to interact with low-methoxylated pectic polysaccharide from jicama to produce PECs with uses in a wide variety of specialized applications such as food technology and medicine.
A layerwise finite element for multilayers with imperfect interfaces
Duong, VA; Diaz, AD; Chataigne; Caron, JF. .
Compos Struct. F. I. 2.036. 93, 3262-3271. (2011)
This article is aimed at proposing a new development of a layer-wise 2D finite-element method for multilayers considering the laminated plate as a superposition of Reissner plates coupled by interfacial stresses. Here, despite the 2D description of the laminates, the interfaces show a particular behavior, elastic or elastoplastic (Von-Mises criterion). The finite element formulation is derived and an eight-node multiparticle element is detailed. The application example of a double lap joint with an elastoplastic adhesive is then considered. The adhesive layer is modeled as an interface. The loading scheme is a load-unload-load one. Interface shear and normal stresses are compared to 3D finite element results. A good agreement between both techniques is observed, particularly for the prediction of the history of the slip between the two adherends and the plastic strains in the adhesive.
Non-linear characterization of PP/Twaron laminates based on a model of plasticity with damage
Mena-Tun, JL; Diaz-Diaz, A; Gonzalez-Chi, PI.
Compos Struct. F. I. 2.036. 93, 2808-2816. (2011)
The non-linear stress-strain response of thermoplastic laminates was investigated for a polypropylene matrix composite reinforced with continuous Twaron fibers. Tensile tests were performed on unidirectional composites with a fiber orientation of [O](5), (5), (5), (5) and (5) and also on a [+/- 45](2S) laminate. The inelastic strains of these materials were described with a modification made to a model of plasticity with damage, originally proposed by Ladeveze (1992). This approach considers the longitudinal plasticity and stiffening behavior of a thermoplastic composite, and models the damaged elastoplastic stress-strain response of the material. The theoretical stress-strain curves and experimental results from the model composites (5), (5) and [+/- 45](2S) were compared, demonstrating that the model can be used as a designing tool for laminated thermoplastic composites.
Many-body forces and stability of the alkaline-earth tetramers
Diaz-Torrejon, CC; Kaplan, IG.
Chem Phys . F. I. 2.017. 381, 67-71. (2011)
The comparative study of the interaction energy and its many-body decomposition for Be(4), Mg(4), and Ca(4) at the all-electron CCSD(T)/aug-cc-pVQZ level is performed. For study of dependence of the binding energy and the orbital population on the cluster size the corresponding dimers and trimers were also calculated at the same level of theory. In comparison with weakly bound dimers, the binding energy in trimers and, especially, in tetramers drastically increases; e. g., E(b)/N in Be(3) is 7 times larger and in Be(4) is 18.4 times larger than in Be(2). This sharp increase is explained as a manifestation of many-body forces. As follows from the many-body decomposition, the tetramers, and trimers as well, are stabilized by the three-body forces, whereas the two-and four-body forces are repulsive. The attractive contribution to the three-body forces has a three-atom electron exchange origin. The latter benefits the promotion of ns-electrons to np-orbitals. The natural bond orbital (NBO) population analysis reveals a relatively large np-population in trimers and tetramers (in Be(4) it is equal to 2p(0.44)). The population of the valence np-orbitals leads to the sp-hybridization providing the covalent bonding.
Thermal analysis and prediction of phase equilibria in the TiO(2)-Bi(2)O(3) system
Lopez-Martinez, J; Romero-Serrano, A; Hernández-Ramírez, A; Zeifert, B; Gomez-Yanez, C; Martinez-Sánchez, R.
Thermochim Acta. F. I. 1.908. 516, 35-39. (2011)
A thermodynamic study on the TiO(2)-Bi(2)O(3) system was carried out using differential thermal analysis (DTA) and X-Ray diffraction (XRD) techniques covering the composition range from 65 to 90 mol% Bi(2)O(3). From the XRD results the only two intermediate compounds in the Bi(2)O(3) rich region were Bi(4)Ti(3)O(12) and Bi(12)TiO(20). The Bi(4)Ti(3)O(12) phase presents the well known plate-like morphology. The experimentally determined phase transition temperatures with DTA technique were compared with thermodynamic calculated results and good agreement was obtained. The DTA results also showed that the limit of the peritectic reaction between liquid and Bi(4)Ti(3)O(12) occurs approximately at 90 mol% Bi(2)O(3).
The phase diagram of the TiO(2)-Bi(2)O(3) system was calculated using a quasichemical model for the liquid phase. The thermodynamic properties of the intermediate compounds were estimated from the data of TiO(2) and Bi(2)O(3) pure solids. In this manner, data for this binary system have been analysed and represented with a small adjustable parameter for the liquid phase.
Thermal conductivity of thin single-crystalline germanium-on-insulator structures
Álvarez-Quintana, J; Rodriguez-Viejo, J; Álvarez, FX; Jou, D.
Int J Heat Mass Tran. F. I. 1.899. 53, 1959-1962. (2011)
We report on the effective cross-plane thermal conductivity of single-crystal Ge layers from 42 to 100 nm on a SiO(2)/Si substrate in the temperature range 30-300 K. We observe a drastic reduction of the thermal conductivity compared to bulk germanium. A large contribution to the temperature rise in the Ge layer is due to the interfacial thermal resistance between c-Ge/SiO(2). The use of a size-dependent intrinsic thermal conductivity of the Ge layer instead of the bulk thermal conductivity improves the consistency with values of the thermal boundary resistance derived from the diffusive mismatch model. Ultrathin films of Ge suffer from a lower reduction of the thermal conductivity compared to ultrathin films of Si, which makes germanium-on-insulator structures promising candidates for devices with reduced self-heating effects compared to silicon-on-insulator structures.
Characterization of Al2024-CNTs composites produced by mechanical alloying
R., Pérez Bustamante F., Pérez-Bustamante I., Estrada-Guel, C.R., Santillán-Rodríguez, J.A., Matutes-Aquino, J.M., Herrera-Ramírez, M., Miki-Yoshida, R., Martínez-Sánchez.
Powder Technol. F. I. 1.887. 212, 390-396. (2011)
In the present work, the 2024 aluminum alloy (Al2024) alloy has been previous termproducednext term by previous termmechanicalnext termprevious termalloyingnext term (MA). The alloy was then strengthened by dispersion of carbon nanotubes (previous termCNTsnext term) during different times. Thus, the effect of previous termCNTsnext term concentration and milling time on the microstructure of the Al2024-previous termCNTsnext termprevious termcompositesnext term was studied. The results show a homogeneous dispersion of previous termCNTsnext term into the Al-matrix phase by previous termmechanicalnext term milling (MM). It was observed that the increment in the milling time, for a fixed amount of previous termCNTsnext term, causes a reduction of the particle size of powders resulting from MA. The finest particle size was obtained at 20 h of milling. These observations were confirmed by scanning and transmission electron microscopy. After 10 h of milling, Cu, Mg and other previous termalloyingnext term elements constituting the Al2024 alloy, form a solid solution and only some remnant Mn particles were observed but not detected by X-ray diffraction.
Computational characterization of sodium selenite using density functional theory
Barraza-Jimenez, D; Flores-Hidalgo, MA; Galvan, DH; Sánchez, E; Glossman-Mitnik, D.
J Mol Model. F. I. 1.871. 17, 701-708. (2011)
In this theoretical study we used density functional theory to calculate the molecular and crystalline structures of sodium selenite. Our structural results were compared with experimental data. From the molecular structure we determined the ionization potential, electronic affinity, and global reactivity parameters like electronegativity, hardness, softness and global electrophilic index. A significant difference in the IP and EA values was observed, and this difference was dependent on the calculation method used (employing either vertical or adiabatic energies). Thus, values obtained for the electrophilic index (2.186 eV from vertical energies and 2.188 eV from adiabatic energies) were not significantly different. Selectivity was calculated using the Fukui functions. Since the Mulliken charge study predicted a negative value, it is recommended that AIM should be used in selectivity characterization. It was evident from the selectivity index that sodium atoms are the most sensitive sites to nucleophilic attack. The results obtained in this work provide data that will aid the characterization of compounds used in crop biofortification.
Computational Molecular Characterization of the Flavonoid Morin and Its Pt(II), Pd(II) and Zn(II) Complexes
Payan-Gomez, SA; Flores-Holguin, N; Pérez-Hernández, A ; Pinon-Miramontes, M; Glossman-Mitnik, D.
J Mol Model. F. I. 1.871. 17, 979-985. (2011)
In this work, we make use of a model chemistry within density functional theory (DFT) recently presented, which is called M05-2X, to calculate the molecular structure of the flavonoid Morin and its Pt(II), Pd(II) and Zn(II) complexes, as well to predict their IR and UV-Vis spectra, the dipole moment and polarizability, the free energy of solvation in different solvents as an indication of solubility, the HOMO and LUMO orbitals, and the chemical reactivity parameters that arise from Conceptual DFT. The calculated values are compared with the available experimental data for these molecules.
Electronic structure study using density functional theory in organic dendrimers
Gutierrez-Pérez, RM; Flores-Holguin, N; Glossmann-Mitnik; Rodriguez-Valdez, LM.
J Mol Model. F. I. 1.871. 17, 1963-1972. (2011)
The electronic and structural properties of pyrrolic ring derivatives were studied using density functional theory (DFT) in terms of their application as organic semiconductor materials in photovoltaic devices. The B3LYP hybrid functional in combination with Pople type 6-31G(d) basis set with a polarization function was used in order to determine the optimized geometries and the electronic properties of the ground state, while transition energies and excited state properties were obtained from time-dependent (TD)-DFT with B3LYP/6-31G(d) calculation. The investigation of pyrrolic derivatives formed by the arrangement of several monomeric units revealed that three-dimensional (3D) conjugated architectures in which the combination of a triphenylamine (TPA) core with pi-conjugated rings attached to the core, present the best geometric and electronic characteristics for use as an organic semiconductor material. The highest occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) energy gap was decreased in 3D-structures that extend the absorption spectrum toward longer wavelengths, revealing a feasible intramolecular charge transfer process in these systems. All calculations in this work were performed using the Gaussian 03 W software package.
Enhancement of photoluminescence due to erbium-doped in CdS thin Films
O. Zelaya-Angel, S.A. Tomás, P.rodríguez, J.G.Mendoza-Álvarez, R. Lozada-Morales, O.Portillo-Moreno y J. González-Hernández.
J Materi Sci. F. I. 1.859. 47, 479-485. (2011)
Cadmium sulfide (CdS) thin films were synthesized by chemical bath deposition on glass substrates at 80 C. The CdS thin films were doped with erbium (Er3?) during the growth process by adding aqueous solutions of Er(NO3)3 3H2O to the CdS chemical bath. The relative volume (Vr) of the doping-solution was varied to obtain ten different doping levels. X-ray diffraction patterns displayed the zincblende crystalline structure for all the CdS:Er samples, with a remarked preferred orientation along the (111) direction. The (111) interplanar distance (ID) first decreased, reaching a minimum value at Vr = 3%, after which point it increased up to saturation for largest values of Vr. The dependence of the band-gap energy (Eg) on Vr
followed an opposite behavior to that described by the ID. The photoluminescence (PL) spectra showed essentially two main bands: the green emission (GE) band of CdS and a red emission (RE) band. The increasing of the PL signal, for Vr B 4% has been associated with the presence of Er3? into the CdS lattice. For Vr[4%, Er degrades the lattice.
Growth of Aligned ZnO Nanorods on Transparent Electrodes by Hybrid Methods
M.F. Meléndrez, K. Hanks, Francis Leonard-Deepak, F. Solis-Pomar, E. Pérez-Tijerina, E. Martinez, and M. José-Yacaman.
J Mater Sci. F. I. 1.859. 47, 2025-2032. (2011)
The fabrication of ZnO (80 nm) thin film was achieved by hybrid atomic layer deposition (ALD) to prevent the reaction between the reactants and conductive layer of the substrates. ZnO nanorods (ZnO-NRs) growth over the substrates was performed by wet chemical procedure in which Zn(NO3)2 and hexamethylenetetramine were used as the precursors. HR-TEM, SAED, FE-SEM, X-ray diffraction (XRD), and UV–Vis spectroscopy were employed to characterize the ZnO-NRs samples on the substrates. XRD and HR-TEM analyses confirmed that the ZnO nanorod structure is hexagonal wurtzite type with growth in the  direction. Length and thickness of the ZnO-NRs ranged between 45 and 90 nm and 480 and 600 nm, respectively. It was observed that the growth rate of NRs in  direction is 10 times higher than in  direction. The growth mechanism and resulted dimensions of nanorods are function of the synthesis parameters (in hybrid ALD process) such as reaction time, temperature, precursor molar ratio, and thickness of ZnO film.
Structural, microstructural and Mössbauer study of BiFeO3 synthesized at low temperature by a microwave-hydrothermal method
J. Prado-Gonjal, D. Ávila, M.E. Villafuerte-Castrejón, F. González García, L. Fuentes, R.W. Gómez, J.L. Pérez-Mazariego, V. Marquina, E. Morán.
Solid State Sci. F. I. 1.828. 13, 2030-2036. (2011)
Multiferroic BiFeO3 has been rapidly synthesized by a microwave – hydrothermal method using nitrates as the metallic source. Structural characterization was performed by thermal analysis, X-ray diffraction and transmission electron microscopy. Generally accepted trigonal space group R3c, as well as recently suggested monoclinic symmetries, were assayed in the search for the best fit. Due to the ambiguity of the Rietveld refinement to distinguish between crystal systems, a micro-diffraction and HRTEM study has been performed. The best solution was obtained with the trigonal model. The room-temperature Mössbauer spectra reveal the presence of a small fraction (2%) of iron in low spin configuration.
SnO2 thin films grown by pulsed Nd:YAG laser deposition
E. Chan y Díaz, A. Duarte Moller and F. Román.
Appl Phys A-Mater. F. I. 1.765. 105, DOI 10.1007/s00339-011-6630-7. (2011)
SnO2 thin films have been deposited on glass substrates by pulsed Nd:YAG laser at different oxygen pressures, and the effects of oxygen pressure on the physical properties of SnO2 films have been investigated. The films were deposited at substrate temperature of 500°C in oxygen partial pressure between 5.0 and 125 mTorr. The thin films deposited between 5.0 to 50 mTorr showed evidence of diffraction peaks, but increasing the oxygen pressure up to 100 mTorr, three diffraction peaks (110), (101) and (211) were observed containing the SnO2 tetragonal structure. The electrical resistivity was very sensitive to the oxygen pressure. At 100 mTorr the films showed electrical resistivity of 4 × 10−2 _cm, free carrier density of 1.03 × 1019 cm−3, mobility of 10.26 cm2 V−1 s−1 with average visible transmittance of ∼ 87%, and optical band gap of 3.6 eV.
Instrument-related geometrical factors affecting the intensity in XPS and ARXPS experiments
F.S. Aguirre-Tostadob,P.G. Mani-Gonzaleza, M. Vázquez-Lepea,A. Sánchez-Martineza, O. Ceballos-Sáncheza,R.M. Wallacec,
G. Contid,Y. Uritskyd.
J Electron Spectosc. F. I. 1.75. 184, 487-500. (2011)
The angular dependence of the X-ray photoelectron spectroscopy (XPS) signal is influenced not only by the electron take-off angle, but also by instrument-relatedgeometricalfactors. The XPS signal is, in fact, integrated over the overlap between the X-ray beam, the spectrometer analysis volume, and the sample surface. This overlap depends on the size and shape of the spectrometer analysis volume and X-ray beam, as well as on their relative orientation. In this paper it is described the models and protocols for the characterization of the parameters defining the geometry of an XPSinstrument. The protocols include practical methods for assessing the spectrometer analysis area and the X-ray beam spot dimension. Simple systems consisting of flat and “thick” gold films on silicon wafers were employed. The parameters found with those samples are transferable to other more complex systems since they are geometrical in nature. The method allows for the prediction of the actual intensity of XPS peaks, hence removing the need of normalizing the peak areas to the area of a determined substrate peak. The associated reduction of the uncertainty in half is of special importance since the quantitative analysis of angle-resolved XPS data could be very sensitive to noise. Two rotating and one non-rotating XPSinstruments are described. Some examples of the applications of the method are also provided.
Solar Heat Reflective Glass by Nanostructured Sol-Gel Multilayer Coatings
Z. Nagamedianova, R.E. Ramírez-García, S.V. Flores-Arévalo, M. Miki-Yoshida, M. Arroyo-Ortega.
Opt Mater. F. I. 1.679. 33, 1999-2005. (2011)
New 3-layer near-infrared previous termreflectivenext termprevious termglassesnext term were prepared by previous termcoatingnext term clear float soda-lime previous termglassnext term with previous termnanostructurednext term TiO2 and SiO2 films using a dip previous termcoatingnext term technique. previous termReflectivenext term interference filters at NIR region (800–1000 nm) were designed by simulation and prepared onto 4 mm clear previous termglassnext term. Optical, microstructural and mechanical properties were determined for the coated previous termglassesnext term. 3-layer previous termsolnext term–previous termgelnext termprevious termglassesnext term show high visible transmittance >70% combined with high previous termsolarnext term reflectance about 30% (with reflectivity up to 60% at region from 800 to 950 nm) and high UV blockage (transmittance <35%). Due to good abrasion resistance of the filters, application for monolithic windows in automotive and architectural areas is promising.
Microstructural study of ZnO nanostructures by Rietveld analysis
Francisco Pola-Albores, Francisco Paraguay-Delgado, Wilber Antúnez-Flores, Patricia Amézaga-Madrid, Edna Ríos-Valdovinos, Mario Miki-Yoshida.
J Nanomater. F. I. 1.675. *, 643126. (2011)
ZnO nanorods were synthesized by induced seeds by chemical bath deposition using hexamethylenetetramine (HMT) as a precipitant agent and zinc nitrate (ZN) as Zn(2+) source at 90 degrees C. The influence of reactants ratio was studied from 2 to 0.25 ZN/HMT molar. The results obtained by scanning electron microscopy confirm that the diameter of nanorods was affected directly by the concentration of both zinc and OH(-) sources. Nanotubes (hollow nanorods) were obtained with high HMT concentrations and were turning over nanorods as HMT concentration decreased. Microstructural information was obtained by Rietveld refinement of grazing incidence X-ray diffraction data. These results evidence low-textured materials with oriented volumes less than 18% coming from (101) planes in Bragg condition.
Synthesis of carbon black/polystyrene conductive nanocomposite. Pickering emulsion effect characterized by TEM
Zaragoza-Contreras, EA; Hernández-Escobar, CA; Navarrete-Fontes, A; Flores-Gallardo, SG.
Micron. F. I. 1.649. 42, 263-270. (2011)
In this study, carbon black/polystyrene electrically conductive composites were obtained by suspension polymerization technique. The composite was characterized using transmission electron microscopy, which indicated two outstanding features concerning to the carbon black; first, that the carbon particles were adsorbed onto the surface of the polystyrene particles, similarly as in the Pickering emulsion phenomenon and second, that the primary aggregate structure of the carbon black was significantly affected by the dispersion process. On the other hand, the composite resistivity was in the order of 200 Omega cm, which was attributed to the direct contact of primary carbon black particles (percolation) and not to the tunneling effect. The obtained composite was evaluated as the electrically conductive element in SBR matrix.
Effects of sulfur substitutional impurities on (ZnO)(n) clusters (n=4-12) using density functional theory
Flores-Hidalgo, MA; Barraza-Jimenez, D; Glossman-Mitnik, D.
Comput Theor Chem. F. I. 1.599. 965, 154-162. (2011)
In this theoretical work we used Density Functional Theory, B3LYP and LanI2dz basis set to study (ZnO)(n) nanoclusters (n = 4-12) with sulfur as substitutional impurity. We study the effects when one single atom of the substituent is placed at each oxygen location within each (ZnO)(n) nanocluster. We analyze all structures by measuring bond length and angle sizes and discuss the relationship of the structural effects after the substituent addition as well as effects in binding energy and electronic properties on each variant. Relative energies were calculated between the different cluster families and our results were compared with prior works. Binding energy increased in all the structures after the substituent was applied and with a few exceptional cases HOMO-LUMO gap energy decreased when compared to the pristine form results.
Structure and reactivity of Ben cycles (n = 3–12): A DFT study
María Esther Sánchez-Castro; Mario Sánchez-Vázquez.
Comput Theor Chem. F. I. 1.599. 967, 136-139. (2011)
In this paper, we present the electronic and structural study of Be3–Be12 cycles. In addition, a reactivity study of the Be3–Be8 structures toward Li+ was carried out, this cation receive electronic density from each cycle. We also evaluated the Be6 cycle as acceptor of electron density by placing one and two molecules of benzene. The natural bond orbital (NBO) analysis performed shows a clear evidence of those interactions in the six-membered beryllium cycle toward benzene molecules.
Theoretical study of beryllium structures analogous to crown ethers
Sánchez-Castro, M; Sánchez-Vázquez, M. .
Comput Theor Chem. F. I. 1.599. 966, 127-132. (2011)
In this paper we present the electronic and structural study of beryllium molecules analogous to crown ethers, where the -CH(2)- groups have been exchanged for beryllium atoms. The resulting structures are completely planar, unlike crown ethers, that the latter are bi-dimensional and flexible. In addition, the coordination of lithium atoms (as Li(+)), which are arranged directionally to each oxygen atom, are able to accommodate in its coordination sphere from three to four hydrogen molecules. We also evaluated the binding energy between lithium complexes and hydrogen molecules in each structure with the same method.
B(12)-induced formation of stishovite in sol-gel produced amorphous SiO(2) matrices
Espericueta, E; Martinez, JR; Guerrero-Serrano, AL; Ortega-Zarzosa, G; Gonzalez-Hernández, J.
J Sol-Gel Sci Techn. F. I. 1.525. 59, 215-221. (2011)
Composites containing vitamin B(12) (cyanocobalamin) dispersed in amorphous silica xerogel were studied structurally as a function of annealing temperature. Silica xerogel samples were prepared by the sol-gel method using an ethanol:H(2)O:TEOS molar ratio of 4:11.6:1 and loaded with cyanocobalamin. We found that the structure of the cobalamin is unaltered, although decoordination of the benzimidazole nucleobase of B(12), whereas the amorphous quartz structure of the matrix is maintained under heat-treatment without low-cristobalite phase transformation, typically of this kind of materials. We found in our samples partial crystallization of the glass matrix in form of stishovite obtained at very lower pressure than those specified by the phase diagram, and temperatures about 400 A degrees C due to the presence of vitamin B(12).
Preparation, characterization and photocatalytic properties of TiO(2) nanostructured spheres synthesized by the Sol-Gel method modified with ethylene glycol
Del Angel-Sánchez, K; Vázquez-Cuchillo, O; Salazar-Villanueva, M; Sánchez-Ramírez, JF; Cruz-Lopez, A; Aguilar-Elguezabal, A.
J Sol-Gel Sci Techn. F. I. 1.525. 58, 360-365. (2011)
Monodispersed nanostructured TiO(2) spheres were obtained by the Sol-Gel method modified with ethylene glycol. The sample morphology and surface textural properties were characterized by X-ray diffraction (XRD), N(2)-physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and diffuse reflectance spectroscopy (DRS). The SEM image showed spheres with sizes ranging from 600 to 700 nm. In addition, HRTEM micrographs reveal hexagonal grains slightly elongated (20 nm). The powders present a BET surface area of 116 m(2) g(-1). Samples without thermal treatment and those treated at 400 A degrees C both showed characteristic reflections of the anatase phase. The photocatalytic activity of the prepared TiO(2) spheres was determined by degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. Kinetics parameters have displayed than the nanostructured material present a reaction half-life time of 30 min and it was two times faster than commercial TiO(2) (P25).
Evaluation of corrosion inhibitors performance using real time monitoring methods
Villamizar-Suarez, W; Malo, JM; Martinez-Villafane, A; Chacón-Nava, JG.
J Appl Electrochem. F. I. 1.496. 41, 1269-1277. (2011)
The implementation of real-time corrosion-monitoring techniques can provide a reliable mechanism for detecting the overall effectiveness of chemical treatment programs and contribute to the selection and implementation of an adequate corrosion inhibitor system. Inadequate corrosion monitoring can result in an increase of both uniform and localized (pitting) corrosion activities which can lead to premature material failures. The present research was undertaken to ascertain whether linear polarization resistance (LPR), harmonic analysis (HA), and electrochemical noise (EN) in combination are suitable for the study of performance of corrosion inhibitors under a wide variety of conditions; for example, in the absence and the presence of hydrocarbons with or without the addition of corrosion inhibitors. The findings showed questionable results regarding the usefulness of the pitting factor derived from EN and HA data. In addition, statistical parameters were obtained, such as skew and kurtosis, and these results were compared with the pitting factor.
Structural and electrical properties of Germanium-doped Sb(70)Te(30) eutectic thin films
Prokhorov, E; Gonzalez-Hernández, J; Mendoza-Galvan, A; Trapaga, G; Luna-Barcenas, G.
J Non-Cryst Solids. F. I. 1.492. 357, 1610-1614. (2011)
Ge-doped Sb(70)Te(30) eutectic films show high potential for high transfer rate recording and non-volatile memory applications. Their potential applications are based on the difference in optical and electrical properties between the crystalline and amorphous phases. However, the structure and crystallization mechanism of such films is not yet well understood. The aim of this work is to study the amorphous-to-crystalline phase transformation mechanism in eutectic thin films of pure Sb(70)Te(30) and doped with 2, 5 and 10 at% of Ge. Results of isokinetics and isothermal annealing were carried out using various techniques: four-probe electrical, optical reflectance and X-ray measurements. The results of optical and electrical measurements of Ge doped Sb(70)Te(30) eutectic films showed that the addition of Ge increases both, the crystallization temperature and the effective activation energy of crystallization and that the mechanism of crystallization does not depend on Ge contents. In amorphous films, Ge acts as impurity center and does not affect the optical band gap value, but decreases the pre-exponential factor in the thermally activated conductivity. In crystalline films, Ge is probably incorporated into the Sb(70)Te(30) structure and Ge vacancy are responsible for p-type metallic conduction, which increases with increasing the Ge content.
Compressive strength, hardness and fracture toughness of Al(2)O(3) whiskers reinforced ZTA and ATZ nanocomposites: Weibull analysis
Nevarez-Rascon, A; Aguilar-Elguezabal, A; Orrantia, E; Bocanegra-Bernal, MH.
Int J Refract Met H. F. I. 1.41. 29, 333-340. (2011)
The aim of this investigation was to study the variability in compressive strength, fracture toughness and microhardness applying the well-known Weibull statistics and to be able to provide a wide spectrum of mechanical properties in Al(2)O(3) whisker reinforced alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) nanocomposites for possible dental applications. Uniaxial compression tests at room temperature of samples 6.35 +/- 0.03 mm in diameter and 12.50 +/- 0.63 mm in length and Vickers hardness measurements on polished surfaces were carried out. The indentation fracture toughness (K(IC)) was derived from the average crack length. Weibull analysis was performed on the data. The ATZ2 (18.0 wt.% Al(2)O(3) + 2.0 wt.%((w)) + 80.0 wt.% ZrO(2) (TZ-3Y)) nanocomposite reported the highest average compressive load of 1200 MPa, the highest value of characteristic strength, sigma(o) of 1340 MPa with Weibull modulus of 3.25 and relatively high fracture toughness (4.7 +/- 0.7 MPa m(1/2)), suggesting that with the wide range of mechanical properties obtained in our work, different dental applications could be offered without lead to premature failure.
Experimental and numerical investigation of shear strain along an elasto-plastic bonded lap joint
Chataigner, S; Caron, JF; Van, AD; Diaz, AD.
Constr Build Mater. F. I. 1.366. 25, 432-441. (2011)
This study investigates the use of an elasto-plastic adhesive in a bonded double lap joint to increase its ultimate capacity. The first section describes the experimental work we performed to characterize the materials and measure the shear strain along the joint. A comparison between an elastic adhesive and a highly plastic adhesive is made and the effect of the type of behaviour on both the capacity and the characteristic anchorage length is studied. The second section then compares the experimental results with a classical 3D finite element model. Good correlation was found between numerical expectations and experimental measurements, and the modelling allowed us to highlight typical phenomena linked to the use of an elasto-plastic adhesive. In addition, a parameter based on a microscopic measurement has been defined which allows us to describe the onset of plasticity and predict maximum capacity.
Comparative Theoretical Study of the Electron Affinities of the Alkaline-Earth Clusters: Be(n), Mg(n), and Ca(n) (n=2, 3)
Diaz-Torrejon, CC; Espinosa-Magana, F; Kaplan, IG.
Int J Quantum Chem. F. I. 1.302. 111, 103-110. (2011)
If in atoms only one type of the electron affinity (EA) can be defined, in molecules there are three types of EAs: the vertical electron affinity (VEA), adiabatic electron affinity (AEA), and vertical electron detachment energy (VEDE). These three types of EAs for beryllium, magnesium, and calcium dimers and trimers are calculated at the all-electron MP4(SDTQ) level employing the Dunning-type basis sets. All obtained EAs satisfy the following inequality VEDE > AEA > VEA and are quite large to be observed in experiment, especially in the trimer case: VEDE (Be(3)(-)) = 1.63 eV, VEDE (Mg(3)(-)) = 0.72 eV, and VEDE (Ca(3)(-)) = 0.95 eV. The decomposition of VEDE into physical components (Koopmans, relaxation, and correlation) and the atomic orbital population analysis (at the NBO level) are used to elucidate the nature of the outer electron binding in studied anions.
Processing and Rheological Behavior of ABS/Montmorillonite Nanocomposites Via Single Screw Capillary Extrusion
Sánchez, SE; Ibarra, R.
Polym Eng Sci. F. I. 1.296. 51, 1875-1882 . (2011)
Evidence for intercalated and exfoliated clay nanostructures was found in Acrylonitrile-butadiene-styrene/montmorillonite (MMT) compounds. Formulations with MMT from 0.5 to 9 vol. % have been processed by single screw capillary extrusion. Melt rheology showed that the onset of shear thinning shifts to lower shear rates until one order in magnitude in shear rate ((gamma) over dot), as modified clay increases. On the other hand, the viscosity at zero shear (eta(0)) augments in the order of 650% in the highest concentration sample. Furthermore, viscosity curves from capillary rheometry showed a strong shear thinning behavior as clay content is increased. From X-ray diffraction, it is inferred a nanoclay d-spacing increase independent from the clay content in capillary extrusion samples. Transmission Electron Microscopy shows intercalated/exfoliated clay structures from capillary extrusion. Proper processing conditions in conventional equipment for plastics transformation, may lead to obtain intercalated and exfoliated nanocomposites without complex tooling configuration. POLYM. ENG. SCI., 51:1875-1882, 2011.
Arsenic in freshwater fish in the Chihuahua County water reservoirs (México)
Nevarez, M; Moreno, MV; Sosa, M; Bundschuh, J.
J Environ Sci Heal A. F. I. 1.107. 46, 1283-1287. (2011)
Water reservoirs in Chihuahua County, México, are affected by some punctual and non-punctual geogenic and anthropogenic pollution sources; fish are located at the top of the food chain and are good indicators for the ecosystems pollution. The study goal was to: (i) determine arsenic concentration in fish collected from the Chuviscar, Chihuahua, San Marcos and El Rejon water reservoirs; (ii) to assess if the fishes are suitable for human consumption and (iii) link the arsenic contents in fish with those in sediment and water reported in studies made the same year for these water reservoirs. Sampling was done in summer, fall and winter. The highest arsenic concentration in the species varied through the sampling periods: Channel catfish (Ictalurus punctatus) with 0.22 +/- 0.15 mg/kg dw in winter and Green sunfish (Lepomis cyanellus) with 2.00 +/- 0.15 mg/kg dw in summer in El Rejon water reservoir. A positive correlation of arsenic contents was found through all sampling seasons in fish samples and the samples of sediment and water. The contribution of the weekly intake of inorganic arsenic, based on the consumption of 0.245 kg fish muscles/body weight/week was found lower than the acceptable weekly intake of 0.015 mg/kg/body weight for inorganic arsenic suggested by FAO/WHO.
Corrosion inhibition of 70Cu-30Ni alloy in LiBr plus ethylene glycol + H(2)O mixtures by inorganic compounds
Ramírez-Arteaga, MA; Gonzalez-Rodriguez, JG; Rosales, I; Domínguez-Patino, G; Martinez-Villafane, A; Neri-Flores, MA.
Mater Corros. F. I. 1.077. 62, 41-46. (2011)
The corrosion inhibition of a 70 wt% Cu-30Ni alloy in a 55 wt% lithium bromide (LiBr) + ethylene glycol + H(2)O by inorganic inhibitors has been evaluated at different temperatures by using electrochemical techniques. Inhibitors used included lithium chromate (Li(2)CrO(4)), lithium molybdate (LiMoO(4)), and lithium nitrate (LiNO(3)), in a concentration of 5 ppm at 25, 50, and 80 degrees C. Employed techniques included potenthiodynamic polarization curves, linear polarization resistance, and potentiostatic measurements. Results have shown that the alloy had an active-passive behavior at 25 and 50 degrees C, and the passive film properties were improved with the addition of inhibitors, whereas at 80 degrees C the inhibitors did not have any effect. Similarly, in general terms, the best corrosion performance at 25, 50, and 80 degrees C was obtained by adding Li(2)CrO(4), LiNO(3), and LiMoO(4), respectively. However, the alloy was not susceptible to pitting corrosion in presence of inhibitors but it was highly susceptible towards pitting type of corrosion in absence of inhibitors.
Use of Ozone for Gold Extraction from a Highly Refractory Concentrate
Gonzalez-Anaya, JA ; Nava-Alonso, F ; Pecina-Trevino, ET.
Ozone-Sci Eng. F. I. 1.032. 33, 42-49. (2011)
Precious metals are generally recovered from their ores by cyanide leaching. When the gold or silver are locked up in the mineral matrix, they remain unrecovered and the ore is classified as refractory to cyanidation. Ozonization in acidic media of an arsenopyritic-pyritic highly refractory gold concentrate (110 g Au/t) as a treatment prior to cyanidation was evaluated. While the conventional cyanidation of this concentrate recovers only 9% of the gold, a pretreatment with ozone before the cyanidation increases the gold recovery to 23%. The rest of the gold is in solid solution with the matrix. Even if this increase in gold extraction is not large enough to economically process this specific concentrate, it demonstrates that the gold locked up in pyrite or arsenopyrite could be recovered by ozonating the ore before cyanidation.
Effect of Barium on the Properties of Lead Hexaferrite
A.L. Guerrero-Serrano · T.J. Pérez-Juache · M. Mirabal-García · J.A. Matutes-Aquino S.A. Palomares-Sánchez.
J Supercond Nov Magn. F. I. 1.014. 24, 2307-2312 . (2011)
An analysis of the properties of a family based on lead-barium substitution in the M-type hexaferrite is presented. The samples were prepared by the ceramic method according to the general formula Pb (x) Ba(1-x) Fe(12)O(19). The barium content was varied with x=0.1, 0.3, 0.5, 0.7, and 0.9; no secondary phases were detected in any composition. Rietveld refinement analysis was done in order to determinate crystallographic parameters, content of phases and degree of substitution. The effects of the barium on the morphological and magnetic properties were studied. Iron Mossbauer spectroscopy was used for determining the hyperfine parameters of the iron nucleus and their environment; also, the cationic occupancy was evaluated and the results were checked with X-ray refinement results.
Study of Microstructure and Magnetic Properties of SrM Hexaferrites with Neodymium Oxide
Pérez-Juache, TJ; Betancourt, I; Palomares-Sánchez, SA; García, MM; Matutes-Aquino, JA; Guerrero-Serrano, AL.
J Supercond Nov Magn. F. I. 1.014. 24, 2325-2329. (2011)
In this work, we report a systematic study on the microstructure and magnetic properties of isotropic M-type SrNd (x) Fe(12-x) O(19) hexaferrites (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) obtained by conventional ceramic process. According to DRX analysis, a solid solution is formed for Nd contents up to x=0.1, while a composite Sr(NdFe)(12)O(19)/SrFeO(3) microstructure results for x > 0.1. Interesting combinations of hard magnetic properties were obtained for the whole compositional series including increasing coercivity values (up to 329 kA/m for x=0.5) with increasing Nd concentration, together with high Curie temperatures (around 731 K). Results are interpreted in terms of the Nd incorporation into the unit cell as well as within the frame of the nucleation controlled mechanism as the coercivity source for this kind of materials.
Agave lechuguilla Torrey Fiber as Reinforcement of Polyester Resin
Velasquez-Martinez, A ; Diaz-Diaz, A ; Hernández-Escobar, CA ; Zaragoza-Contreras, EA.
Polym Composite. F. I. 0.998. 32, 1601-1606. (2011)
This study was aimed to evaluate the application of lechuguilla fiber (Agave lechuguilla Torrey), with no treatment, as reinforcement of polyester resin. Mechanical assays and pull-out tests were performed on specimens of one fiber and strands of 10 fibers and on lechuguilla fiber/polyester composites and polyester matrix alone. The results indicated that there was no important improvement in composite rigidity, as the Young's modulus in both the fiber and the polyester resin were similar; however, an important improvement in composite resistance, in respect to the matrix alone, attributed to a good interfacial adherence fiber-matrix, was observed. POLYM. COMPOS., 32:1601-1606, 2011.
Cotton fabric dyeing with cochineal extract: influence of mordant concentration
Arroyo-Figueroa, G; Ruiz-Aguilar, GML; Cuevas-Rodriguez, G; Gonzalez-Sánchez, G.
Color Technol. F. I. 0.97. 127, 39-46. (2011)
Dyeing with cochineal extract has been carried out in México since pre-Hispanic times as a handcraft process. However, this has limited its application on fabrics other than wool. An experiment was designed to study the influence of mordant concentration on colour behaviour in cotton fabric dyed with cochineal extract at the laboratory. At the same time, colour fastness was determined by applying six fastness tests to define the quality of the dyed fabric. It was concluded that, when there was a larger concentration of metallic ions in the mordant, colour fixation in the fabric was better, as there was less lightness in the red hue of the fabric. In addition, the more hydrogen ions present because of acids, the more intense the red hue. A decreasing trend in the colour fastness tests was observed: dry rubbing > artificial light > acids > alkalis > domestic washing > hot water.
Nixtamalization in two steps with different calcium salts and the relationship with chemical, texture and thermal properties in masa and tortilla
M. G. Ruiz Gutiérrez, A. Quintero Ramos, C. O. Meléndez Pizarro, R. Talamás Abbud, J. Barnard, R. Márquez Meléndez and D. Lardizábal-Gutiérrez.
J food Process Eng. F. I. 0.875. 1, DOI: 10.1111/j.1745-4530.2010.00627.x. (2011)
The present investigation evaluated the chemical and thermal properties using lime and alternative calcium salts, and their effect on the characteristics of masa and tortilla obtained in a two-step nixtamalization process. White dent corn was cooked in calcium hydroxide solution (1.2% [w/v]; 1:3 maize : water ratio) at 80C (30 min), and the calcium hydroxide was replaced either by calcium chloride or lactate at calcium equilibrated concentration (30 min), and steeped in a cooking solution for 2,400 min. Grains were analyzed for water and calcium absorption, and apparent diffusion coefficients were calculated. Thermal properties of flour made from these grains were also determined. Additionally, the masa and tortilla made with nixtamalized corn flours were analyzed for texture and color, and an acceptability test was performed on the tortilla. Water absorption showed a notable increase during cooking, approaching an asymptotic maximum absorption after 8 h of steeping for all treatments. The maximum calcium absorption was obtained in stepwise nixtamalization with solutes of CaCl2 and C6H10O6Ca. The water apparent diffusion coefficients were adequately described by Fick's model and it was found that C6H10O6Ca showed the highest value (5.5901 × 10−10 m2/s), while that for calcium diffusion the model gave low fits. The thermal analysis showed that gelatinization temperatures were affected significantly (P < 0.05) by the cooking and steeping times, while the gelatinization range and enthalpy were affected significantly (P < 0.05) by salt type. The masas and tortillas obtained from all treatments presented good texture and color characteristics in comparison with the commercial flour. Sensory analysis showed that the tortilla nixtamalized with C6H10O6Ca was the most acceptable to consumers.
Impact of the Kind of Ultraviolet Light on the Photocatalytic Degradation Kinetics of the TiO(2)/UV Process
Cortes, JA; Alarcon-Herrera, MT; Villicana-Mendez, M; Gonzalez-Hernández, J ; Pérez-Robles, JF.
The analysis of the possible causes affecting the degradation speed was performed by superposing the emission bands of the used UV light with the absorption bands of the dye and catalyst. It is concluded that the interaction zone between the type of UV light and the catalyst notoriously impacts the degradation kinetics.
Environ Prog Sustain. F. I. 0.86. 30, 318-325. (2011)