Hydrogen absorption-desorption characteritics, kinetics of hydrogen absorption and thermodynamics of dissolved hydrogen in Zr_(0.1)Tb_(0.9)Fe_(1.5)Co_(1.5)

摘要

The hydrogen absorption and desorption pressure-composition isotherms of the PuNi_3 type rhombohedralZr_(0.1)Tb_(0.9)Fe_(1.5)Co_(1.5) are investigated by using asieverts' type apparatus based on pressure reduction method in theranges 75≤T(deg C) ≤ 150 and 0.01≤P(bar)≤30. The hydrogensolubility properties are compared with those ofZr_(0.1)Tb_(0.9)Fe_3 to study the effect of Co substitution at theFe site. The P-C isotherms show the #alpha#->(#alpha#+#beta#)transition at an average hydrogen concentration (y=n_H_(fu)) of0.2 and (#alpha#+#beta#)->#beta# transition at an average valueof y=2.5. Further, the plateau pressure ofZr_(0.1)Tb_(0.9)Fe_(1.5)Co_(1.5)-H at any given temperatureincreases when compared to that of Zr_(0.1)Tb_(0.9)Fe_3-H. It isfound that hysteresis is quite small in the temperature regionsinvestigated. At a hydrogen concentration of 3.1 hydrogen atomsperformula unit, the host lattice is accompanied by an expansion ofabout 16% without any change in crystal structure as evidenced bypowder X-ray diffraction studies ofZr_(0.1)Tb_(0.9)Fe_(1.5)Co_(1.5)H_(3.1). The thermodynamicalparameters viz., the relative partial molar enthalpy (#DELTA#H_H)and the relative partial molar entropy (#DELTA#S_H) ofdissolved hydrogen are found to be in the ranges –(17-23)kJ(molH)~(-1) for desorption. From the dependence of #DELTA#H_Hon y, the different phases [#alpha#, (#alpha#+#beta#), #beta#] andphase boundaries [#alpha#->(#alpha#+#beta#)],[(#alpha#+#beta#)->#beta#] of the alloy-hydrogen system areidentified. The different phases identified by the thermodynamicstudiesagree well with those seen in the hydrogen absorptionisotherms of the respective alloy. These phases are furtherconfirmed through powder X-ray diffraction studies. The kineticstudies show that the rate of hydrogen absorption is relatively slowwhen compared with Zr_(0.1)Tb_(0.9)Fe_3-H.