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7100 Calibration Bath
User's Guide
8.1.10.4
8.1.10.5
8.1.10.6
30
approximately 95% methanol and 5% water by volume or approximately 93%
methanol and 7% water by weight. The viscosity is quite acceptable from
–80°C up. A mixture of 50/50 methanol and water provides a non-flammable
solution capable of attaining –40°C. Because methanol has an infinite capabil-
ity to absorb water, there is no ice formation below 0 °C. This is convenient for
long term use. The mixture has poor electrical resistivity and so may not be
suitable for some applications.
The primary disadvantage with methanol is its toxicity. It is also quite flamma-
ble. Some labs may not permit its use. Refer to the MSDS sheets for more in-
formation. Use methanol only in a well ventilated area and use a hood that
draws the vapors away from the user at temperatures above 0°C.
Halocarbon 0.8
Halocarbon 0.8 is a low temperature fluid with a wide temperature range. It
may be used as low as –90 to –100 °C before viscosity becomes too great. It
may be used as high as 70°C before evaporation becomes excessive.
Halocarbon 0.8 does not absorb water and will therefore form ice at tempera-
tures below 0 °C. Ice crystals turn the fluid into a slush which effectively in-
creases the viscosity and reduces temperature stability. Pumping systems may
be rendered ineffective due to ice blockage. The ice (water) can be removed oc-
casionally by heating the fluid up to 100 °C for brief periods of time. Use
halocarbon 0.8 under a fume hood at higher temperatures to remove vapors.
Toxicity is low but caution is always recommended. Halocarbon 0.8 has excel-
lent electrical resistivity. This fluid is fairly expensive.
Mineral Oil
Mineral oil or paraffin oil is often used at moderate temperatures above the
range of water. Mineral oil is relatively inexpensive. At lower temperatures
mineral oil is quite viscous and control may be poor. At higher temperatures
vapor emission becomes significant. The vapors may be dangerous and a fume
hood should be used. As with most oils mineral oil expands as temperature in-
creases so be careful not to fill the bath too full that it overflows when heated.
The viscosity and thermal characteristics of mineral oil is poorer than water so
temperature stability will not be as good. Mineral oil has very high electrical
resistivity. Use caution with mineral oil since it is flammable and may also
cause serious injury if inhaled or ingested.
Silicone oil
Silicone oils are available which offer a much wider operating temperature
range than mineral oil. Like most oils, silicone oils have temperature control
characteristics which are somewhat poorer than water. The viscosity changes
significantly with temperature and thermal expansion also occurs. These oils
have very high electrical resistivity. Silicone oils are fairly safe and non-toxic.
These oils are relatively expensive.
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