We've had a number of customers contacting us to find out which Apiezon grease to use for their particular application in Cryogenics and condensed matter research so we've put together this quick grease selection guide to help them out.
For many years Apiezon N type grease has been one of the mainstays in any cryogenics lab due to its wide working temperature range and a significant amount of low temperature characterisation data being available (see, for example Pobell's 'Matter and Methods at Low Temperatures').
Apiezon N is often used for providing a simple, reversible mounting for encapsulated thermometers - drill an oversize hole in a copper block, fill with grease and push the thermometer home. It's fine for temperatures down to 30K and in liquid, but if you're trying to measure at millikelvin temperatures, or in vacuum, you should probably think again - and instead use GE-Varnish for heatsinking both thermometer and lead wires, as it has a thermal conductivity some 30 times higher than Apiezon N at 1 Kelvin.
Another application where Apiezon N can be useful is for the greasing of pressed metal-metal contacts - here data from NASA (Salerno et. al., Cryogenics 1994, Vol 34, No 8) shows that for low pressure pressed metal-metal contacts a thin layer of Apiezon N grease can improve the conductivity across the interface. It is worth remembering that this is only for relatively low pressure joints, perhaps where you've only got small size screws tapped into a soft copper block. If you're looking for very high thermal conductance then you should try and increase the clamping force to the point at which an Indium foil can flow when clamped and use that instead (see chapter 2.6 in Ekin's 'Experimental Techniques for Low Temperature Measurements' to find out whether 'To Grease, or not to Grease'.)
Turning to the other end of the thermal spectrum - and going above room temperature (don't worry we do appreciate that some of you want to do this) Apiezon H has the unusual property that it does not melt making it suitable for use all the way from room temperature to 240 degrees C - the highest in the Apiezon range. The vapour pressure of Apiezon H is not outstanding at around 10-8 mbar at room temperature, and obviously increasing the higher you go (please contact us for the full vapour pressure curve) but then if you're using grease at temperatures as high as 240 deg C probably vapour pressure is not your prime concern.
| Apiezon® Grease | N | H | L |
|---|---|---|---|
| Useful Temperature Range (deg C) | -273 (0K) to 30 | -10 to 240 | 10 to 30 |
| Vapour pressure at RT (mbar) | ≈10-9 | ≈10-8 | <10-10 |
| Comments | Cryogenic heatsinking, pressed metal contacts | High Temp seals | Lowest outgassing |
If you are working close to room temperature and vapour pressure IS your primary concern then Apiezon L is the best grease to use, as it has a vapour pressure better than 10-10 mbar at this point. Unlike type N grease, Apiezon L is also resistant to radiation so is an ideal choice for mounting of delicate samples on beamlines or diffractometers. Apiezon L, like all the Apiezon greases, are made from hydrocarbons so can easily be removed with organic solvents such as Trichlorethylene, Hexane or Toluene.
Should you require more information or have applications that are not touched upon by the description above, then please contact us.
