Regarding the method known as the Adiabatic Demagnetization of Paramagnetic Salts: What metallic salts are normally used to produce the ultra-low temperatures used for near-absolute-zero cryogenic research? Which salts are the most efficient? Which make the best cooling agents? And which are used most commonly by physicists? I am looking for the exact chemical formulae. I have scoured the web and can’t seem to find more than a general description of the process. Can you help me?
1 Comment
Dr. Randall F. Barron
August 1, 2008Presently, magnetic refrigerators utilize either:
Gadolilium sulfate salt
Gd2 (SO4)3 . 8 H2O
or
Gadolinium gallium garnet (GGG)
Gd3 Ga5 o12
Of the two materials, GGG has shown superior thermal properties. [A.F. Lacaze, R. Beranger, G. Bon Mardion, G. Claudet, and A.A. Lacaze, “Double Acting Reciprocating Magnetic Refrigerator: Recent Developments,” in Advances in Cryogenic Engineering, vol. 29, Plenum Press, New York, (1984), pp. 573-579. See also: C. Delpuech, R. Beranger, G. Bon Mardion, G Claudet, and A.A. Lacaze, Cryogenics, vol. 21, (1981), pg. 579]
Other materials that have been used in magnetic refrigerators include:
Iron ammonium alum (Daunt-Heer-Barnes refrigerator)
Fe2 (SO4)3 (NH4)2 SO4.24 H2O
Chrome potassium alum
Cr2 (SO4)3 K2 SO4 . 24 H20
Further information on magnetic cooling and magnetic refrigerators may be found in:
[1] Steven W. Van Sciver: HELIUM CRYOGENICS, Plenum Press, New York, (1986), pp. 362-376.
[2] R.P. Hudson:PRINCIPLES AND APPLICATION OF MAGNETIC COOLING, North Holland Publishing, Amsterdam, (1972).
[3] J.A. Barclay and W.A. Steyert: MATERIALS FOR MAGNEIC REFRIGERATION, Los Alamos Scientific Laboratory Report LA-8746-MS (May 1981).
[4] Mark W. Zemansky: HEAT AND THERMODYNAMICS, 5th ed., McGraw-Hill Book Co., New York, (1968), pp. 442-479.
[5] J.G. Weisand: HANDBOOK OF CRYOGENIC ENGINEERING, Taylor and Francis Publishers, Philadelphia, PA, (1998), pp. 112-118 (“Magnetic Materials for Cryogenic Refrigerators”)
[6] Graham Walker: CRYOCOOLERS, Part 2: Applications, Plenum Press, New York, (1983), pp. 216-251.