Thermal and Mechanical Properties of Magnetic Materials for Carnot Magnetic Refrigeration on Hydrogen Liquefaction

摘要

Magnetic refrigeration makes use of the magneto-caloric effect (MCE) of magnetic materials,and it can operate high efficient Carnot magnetic cooling cycles. In this paper, we propose theCarnot magnetic refrigeration for the production of liquid hydrogen, where the gaseoushydrogen is condensed directly by using the cooling surface of the magnetic material. In thismethod, the magnetic materials must be inactive for hydrogen, therefore, rare-earth oxidemagnetic materials such as Gd3Ga5O12, Dy3Al5O12 and (GdxDy1-x) 3Al5O12 (x=0.1, 0.2) havebeen chosen to avoid the hydrogenation, while metallic compounds are used for conventionalmagnetic refrigeration materials.Poly crystal (GdxDy1-x)3Al5O12 (x=0, 0.1 and 0.2) samples have been fabricated to investigatetheir entropy characteristics. Heat capacity measurements show that increasing theconcentration'decreases the peak temperature of the heat capacity curve from 2.54 K (x=0)to 1.58 K (x=0.2). The saturation magnetic entropy around 4 K increases with the x, becauseGd provides higher magnetic moment of J=7/2 than that of J=1/2 in Dy for the temperaturerange below 20 K. Such increased saturation entropy contributes to provide large entropychanges in (GdxDy1-x) 3Al5O12. It is found that the Gd0.2Dy0.8 3Al5O12 sample is able toenhance the MCE up to 60% larger than that of Gd3Ga5O12 by applying the magnetic field of6T at 20 K.