I am a ME grad student currently working on the design of a detector array / focal plate of a scientific space instrument operating at a temperature of about -80…-100°C. Although this is not in the cryogenic temperature range, I would like to address two questions to you as the experts in the field.
1. It is extremely difficult to find material property data for polycrystalline / sintered ceramics at low temperatures (esp. thermal expansion & conductivity). I am especially interested in AlN, SiC, C/SiC, Al2O3 (and if possible, Shapal-M, a machineable AlN ceramic) mainly due to the good expansion match with Silicon and high thermal conductivity. I understand that impurities, a variety of additives and different processes cause properties to scatter a lot, however I was not even successful in obtaining data from companies in the field on the low temperature behavior of their particular products. Moreover, while Invar alloys have been characterized in the 60s/70s and are also listed on the NIST cryogenic material property page / old NBS references, I can not find any information on Kovar. Kovar is a ternary iron alloy (Fe53 Ni29 Co17) and appears to be widely used in low temperature electronic packaging / assemblies, which surprises me, as I can find absolutely no reference on measurements with this alloy.
Is it safe to assume it behaves similar to a Fe Ni29 alloy (where I was able to find data)?
2. Does anyone know a helpful reference for designing / dimensioning flexure mounts (as f.e. bipods) which are widely used in the low temperature regime to mount two parts at different temperature levels?
1 Comment
Adam Woodcraft
June 3, 2011> – It is extremely difficult to find material property data for
> polycrystalline / sintered ceramics at low temperatures (esp. thermal
> expansion & conductivity).
This is certainly true, and as you say the companies selling the stuff aren’t usually of much help.
> I am especially interested in AlN, SiC, C/SiC, Al2O3 (and if possible,
> Shapal-M, a machineable AlN ceramic) mainly due to the good expansion
> match with Silicon and high thermal conductivity. I understand that
> impurities, a variety of additives and different processes cause
> properties to scatter a lot
Also grain size, though that is more of an issue at lower temperatures than you are interested in.
For SiC and alumina, there certainly seems to be considerable variation in conductivity.
Conductivity data on SiC can be found in Nemoto et al, Cryogenics 25, 531 (1985)
For alumina, you could look at:
– Nemoto et al (same as above)
– Berman, Proc. Phys. Soc. A65, 1029 (1952)
I am aware of very little information the properties of C/SiC below room temperature; what I do know is in an internal report which you can access from http://teops.lowtemp.org/documents.html (click on “Some notes on C/Sic” near the bottom)
> while Invar alloys have been characterized in the 60s/70s and are also
> listed on the NIST cryogenic material property page / old NBS
> references, I can not find any information on Kovar. Kovar is a
> ternary iron alloy (Fe53 Ni29 Co17) and appears to be widely used in
> low temperature electronic packaging / assemblies, which surprises me,
> as I can find absolutely no reference on measurements with this alloy.
> Is it safe to assume it behaves similar to a Fe Ni29 alloy (where I
> was able to find data)?
I can’t help with Kovar, but I would be very wary of assuming that it is similar to Fe71 Ni29.