Study of hydrogenabsorption by ZrMnFe1-xCox (x = 0.2, 0.4, 0.5 and0.6) alloys

Abstract

Hydrogen absorption isotherms have been obtained for the C14-type hexagonal-structured alloys ZrMnFe1-xCox (x = 0.2, 0.4, 0.5 and 0.6) in the temperature and pressure ranges30⩽T/ °C⩽100 and 0.1⩽P/bar⩽40 using a high-pressure unit based on the pressurereduction method. The powder x-ray diffractograms show that the lattice constants and the unit-cell volume for ZrMnFe1-xCox (x = 0.2, 0.4, 0.5 and 0.6) alloys decrease withincrease of xCo. The hydrogen absorption isothermsshow the presence of a single plateau region (α + β)in the temperature and pressure ranges studied and it is foundthat the plateau pressure and plateau slope at any given temperature increase with increase of the xCo-content,except in the case of ZrMnFe0.5Co0.5 wherein thehydrogen absorption plateau slope is found to be smaller due tothe ordering of the alloy. The dependence of the thermodynamics of the dissolved hydrogen in ZrMnFe1-xCox-H (x = 0.2, 0.4, 0.5 and 0.6) systems in thetemperature range 30-50 °C on the hydrogenconcentration shows the different phase regions (α,α + β, β) seen in the hydrogen absorptionisotherms. The powder x-ray diffractograms of the hydrides of ZrMnFe0.8Co0.2 show that the formation of different phasesis manifested in the isotherms without there being any structural change and theinclusion of hydrogen in the interstitial sites expands theunit-cell volume by about 21.Comparison of the hydrogenabsorption kinetics of ZrMnFe1-xCox with that of the corresponding Ni alloys in similar experimental conditions showsthat the kinetics is slow in the ZrMnFe1-xCoxalloys.