Kinetics of Formation of Magnesium Hydride from Magnesium and Hydrogen

— a)112 = kt, where oc is the fraction of reaction completed after t minutes, takes place, k is directly proportional to the hydrogen pressure and increases with temperature at 3 MPa according to k = 1.75 X 108 exp (— 96500/KT), where R is in JK"1 mole-1 and 465 < < 576 . After the metal surface has been covered, the reaction becomes diffusion controlled with diffusion coefficient De = 3650 exp (— 95500/-R21) cm2 s-i for 465 < < 576 at 3 MPa. De is proportional to pHV0-27 which indicates that diffusion of magnesium interstitials is the rate-determining step. De is independent of oc for oc < 0.5, but above this value it decreases rapidly and at oc > 0.75 is so small that the reaction virtually stops at the experimental pressures and temperatures used.