Hydrogen Absorption and Desorption of Alloys Under the Influence of Magnetic Fields

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The equilibrium hydrogen pressure was observed as a function of the magnetic field for three systems including ferromagnetic hydrides, LaCo_5-H, GdCo_5-H and Y_2Co_7-H systems. The change in magnetization per reacted hydrogen (DELTAMs) determines the shift of change in the chemical equilibrium and then the change in pressure. The results can be explained using a magnetic data.LaCo_5Hx (X=4.2, the beta+gamma twoーphase region) : The equilibrium hydrogen pressure was measured as a function of the magnetic fields up to 26T at 293K. The pressure was increased with increasing fields : 1.2X10^4Pa in zero fields and 1.8X10^4Pa in 26T. This corresponds to 67% decrease in the equilibrium constant. The logarithmic pressure change, LPC, was not proportional to the field. This behavoir is explained by the magnetization observed in pulsed magnetic fields up to 28T. DELTAMs was increased with increasing magnetic field.GdCo_5Hx (X=1.34, 1.35, 2.52 and 2.53, alpha+beta region) : The equilibrium hydrogen pressure was measured in the magnetic fields up to 14T at 288K. The hydrogen was absorbed with the fields because of a negative value of DELTAMs.Y_2Co_7Hx (X=2-3, the beta single phase) : This system is investigated in the single region but not in the twoーphase region. The equilibrium hydrogen pressure vs. fields was measured at several initial hydrogen pressures, Pi, at 348K. The results were classified into two groups. (1)For Pi more than 86kPa, the LPC scarcely depends on the magnetic field because the magnetization is independent of the pressure in this region. (2)For Pi less than 24kPa, the LPC is decreased with increasing fields until 6T but becomes saturated in higher fields. This saturation was attributed to the metamagnetism occurring in 5.6T in the lower composition hydride of the beta phase.