Fomblin VAC 3 Grease, 100gm
Fomblin® VAC™ 3 is a perfluoropolymer based vacuum grease thickened with a PTFE thickener. It is an inert, homogeneous, and white grease particularly suitable for use as a lubricant for mechanical parts or seals operating at high vacuum and in contact with aggressive chemicals or oxygen. VAC 3 is used in lubricated "for life" applications; its lubricating properties make it suitable for parts requiring boundary (extreme pressure) lubrication in a temperature range from -20°C to 250°C. VAC 3 is designed to meet MIL-G-27617 Type III specifications and test method ASTM E-595-77 as tested by NASA/GSFC (extremely low outgassing in a vacuum environment). Before making any decision about your vacuum grease requirements, be sure to be aware of some of the other information and specifications concerning VAC 3 high vacuum grease.
For the electron microscope laboratory application, Vac 3 is widely used because although the liquid component of the grease does eventually evaporate, when it does, the vapors will not. But unlike hydrocarbon based greases, the fluorocarbon nature of the molecular species that will evaporate, will not be polymerized by the ionizing radiation present in the microscope column. Hence, the user of an electron microscope using non-hydrocarbon greases will find in general a cleaner environment and less contamination of samples. For the hydrocarbon greases, when they do evaporate, they are polymerized, and they end up forming a varnish(e.g. contamination) on both microscope parts, apertures, and sampler.
Temperature use range: One can expect the grease to retain its properties pretty much between -20° C to +250° C. Actually, one can use the grease at lower temperatures, but there will be some diminution of at least some of the properties. Clearly, for the electron microscope application, this temperature range will be more than adequate.
For those requiring or desiring a grease of ultimate smoothness, that is, one where any agglomerates of the PTFE particles in its formulation have been removed by screen pack filter, one might consider the Braycote Micronic 803 Vacuum Grease. However, for most users, this higher level filtration is probably not necessary and therefore the Vac 3, and its lower price would be an acceptable alternative.
We are often asked about how VAC 3 compares with Braycote Micronic 803 in terms of vacuum characteristics. VAC 3 differs from Braycote Micronic 803 in several respects, including the base oil viscosity, consistency, and the type of PTFE used for the thickener.
The viscosity of the base oil used in VAC 3 is about 1400 cSt at 20° C whereas the oil used in the formulation of Braycote Micronic 803 is about 250 cSt. VAC 3 has a NLGI of 3 vs. for Braycote Micronic 803, an NLGI of 2. VAC 3 is slightly stiffer than the Braycote product. From a chemical composition standpoint, the base oil used for VAC 3 is a branched perfluorinated polyether, where as the oil used in the Braycote product is linear. The vapor pressure of VAC 3 is about 10-13 torr at 20° C. Both greases can be used in vacuum, however the torque requirements for VAC 3 would be higher.
Probably the product most equivalent to VAC 3 is Microcote® LVP, which is based on a Krytox® base oil having a viscosity of about 2000 cSt.
For use at low temperatures, for example in conjunction with a cryo stage in an SEM, we would expect that Apiezon N Cryogenic Vacuum Grease should be considered. We believe that the lower temperature properties of the Apiezon N product outweigh any considerations with regard to hydrocarbon off-gassing into the column.
Our intent is to present some of the trade offs between these different fine grease products. We believe this information to be correct to the best of our knowledge. We can not guarantee that any prospective vacuum grease solution for a particular problem that is derived from this information will definitely work, so we would urge caution in the final selection and initial use to confirm that any particular grease or grease combination will indeed work for you.
Removal of unwanted grease from grease applied surfaces:
The composition of this product is a mixture of small PTFE particles (which won't dissolve in anything) and a perfluorinated polyether liquid. We have found that Castrol® Fluoroclean™ HE or Perfluorosolv® PFS-2 is an effective solvent for the liquid component of the formulated composition and aids in the removal of the grease from places where it is no longer needed or wanted.