Evaluation of kinetics by utilizing the normalized pressure dependence method for the alloy Ti0.95Zr0.05Mn1.48V0.43Fe0.08Al0.01

A recently suggested normalized pressure dependence method, NPDM, was utili zed in this study. For the decomposition process the NPDM includes a pressu re dependence function F(P) = (P-eq - P)/P-eq which changes in the limits o f 0 < F(P) less than or equal to 1. F(P) is inserted into an integrated rat e equation as follows, R-i(alpha) = ktF(P), where i refers to a particular mechanism or process order. A best fit line of experimental values of R-i(a lpha)/F(P) vs. t yields a temperature only dependent kinetic constant, k. I sothermal measurements were carried out in a closed volumetric system for d ifferent system volumes, V-s, and different initial pressures, P-o, and int erpreted according to the NPDM. Hydride decomposition/formation kinetics of the alloy Ti0.95Zr0.05Mn1.48V0.43Fe0.08Al0.01, labeled C5, were studied in the temperature range of -20 to 20 degrees C. The kinetics were found to c orrespond to a first order process for which the preexponential factor and the activation energy were k(o) = 6.0 X 10(6) s(-1) and E-a = 40 kJ/mol, re spectively. For the decomposition of the LaNi5 hydride in the temperature r ange of -6 to 60 degrees C, the results were found to correspond to a first order process with the kinetic parameters k(o) = 3.1 x 10(7) s(-1) and E-a = 52.8 kJ/mol. The hydride decomposition/formation thermodynamic equilibri um parameters Delta H and Delta S for both considered alloys were derived. (C) 1999 Elsevier Science S.A. All rights reserved.