I'm looking for a material with a solid-solid phase change in the range -40 and 20 C, for calibrating the temperature in a diffraction experiment. I can't use a melting point as the material is under gas flow. All the standard materials I can find are too high (KNO3) or too low (Rochelle salt, etc). Any suggestions?
Hi Peter.
Ga (metall) has melting point 29.8 C.
Also You can use Fusible alloys (Wikipedia)
These links might prove useful...
http://www.xrayforum.co.uk/viewtopic.php?f=22&t=849&hilit=calibration
http://bl831.als.lbl.gov/~jamesh/pickup/Snell_SG_change_table.pdf
Why not try NH4NO3. There are two solid/solid phase changes in the temperature range you specified. I've only used the changes at 32.3, 84.2 and 125.2C - these changes are very rapid so make excellent temperature calibration points.
I have a feeling that there is another phase change at an even lower temperature but I can't recall where I saw it.
tetragonal < -16.8 C
tetragonal --> beta-orthorhombic -16.8
beta-orthorhombic --> alpha-orthorhombic 32.3
alpha-orthorhombic --> tetragonal 84.2
tetragonal --> cubic 125.2
melting 169.6 C
DO NOT exceed the melting point of 169.6° C.
NH4NO3 decomposes explosively at about 175° C (Don't ask me how I know this!)
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