Properties of Diphyl
General chemical and physical properties
Diphyl is a
clear, pale yellow liquid with a low viscosity. It is an eutectic mixture
consisting of approx. 73.5% by weight diphenyl oxide and approx. 26.5 % by
weight diphenyl. There is no significant rise in viscosity before the fluid solidifies at approx. 12.3°C.
In contrast to
water there is a reduction in volume when Diphyl changes from the
fluid to the solid state which means that there is no risk of plant or pipelines
damaged if Diphyl solidifies.
Diphyl has an application range from +13°C
to +400°C and a high boiling point
of approx.257 °C at a pressure of 1.013 bar, thus permitting the pressureless
operation of standard heat transfer systems at temperatures up to 250 °C. At a maximum application temperature of 400°C, the pressure amounts to only 10.7 bar. This means that simple plant designs can be used, even in high
temperature regions. The plant should be designed so that the temperature at the heating
is limited to 410 °C.
content of Diphyl is in equilibrium with the atmospheric humidity and
amounts to a maximum of 0.02% by weight on delivery. Diphyl is not hygroscopic
and is virtually immiscible with water. Even at 30°C and 100% relative humidity, a maximum of only 0.07 % by weight water dissolves in Diphyl. As with all
combustible fluids, there is also the possibility of Diphyl forming an explosive mixture with air. However the explosive range between 1.0 and 3.5 % by volume
for the Diphyl vapour is very small.
Diphyl will not
ignite spontaneously before reaching an autoignition temperature
above 615°C. Diphyl thus belongs to Temperature Class T1.
inherent odour of Diphyl enables leaks to be identified quickly.
The level of production‑related impurities, such as chlorine and sulphur compounds,
is so low in Diphyl that corrosive damage caused by the heat transfer fluid coming
into contact with the materials of the plant can be ruled out.
Detailed references in:
Diphyl - specification and characteristic data
Specification Test method
Diphenyl oxide content (GC) Internal 2011-0270101 91 % 72 - 75
Biphenyl Content (GC) Internal 2011-0270101 91 % 25 - 28
Chlorine content Internal 2011-0380801 93 mg/kg max. 10
Solidification point Internal 65073/161/1 °C min. 12.2
ASTM D 1493/67
Water Internal 2011-0332301 92 mg/kg max. 200
ASTM D 1744-83
Compliance with the Specification is subject to constant monitoring.
Density (20°C) DIN 51757 kg/m3 approx. 1062
ASTM D 4052-91
Kinematic viscosity (20°C) DIN 51561 mm2/s approx.. 4.12
ASTM D 445/446
Neutralization number (acidic) DIN 51558 mg KOH/g approx. 0.01
ASTM D 974-64
Boiling temperature (1.013 bar) ISO 918 °C approx. 257
OECD-Test Spec. 103
Flash point EN 22719 °C approx. 115
ASTM D 93-75
Autoignition temperature DIN 51794 °C approx. 615
ASTM D 286-58T
Lower explosion limit (108,5 °C) - % by vol. approx. 1.01
Upper explosion limit (138,5°C) - % by vol. approx. 3.47
Solubility in water (20°C)
Diphenyl oxide Quentin method mg/l 11.3
Biphenyl mg/l 3.9
Surface tension (20°C) OECD-ring method N/m approx. 0.04
Thermal conductivity (20°C) - W/m . K approx. 0.138
Mean specific heat (20°C) - kJ/kg .K approx. 1.55
Max. film temperature - °C approx. 410
Gross calorific value, H0 - MJ/kg approx. 37.6
Net calorific value, HU - MJ/kg ca. 36.3
Temperature class VDE 0171 - T1
Hazard class - - None
Coefficient of thermal expansion (20 - 300°C) - K-1 10,6 . 10 -4
Characteristic data provide further information of the product.
and are not subject to constant monitoring.