(A) study on kinetics of hydride formation in hafnium and hydrogen permeation through type 304 stainless steel

Abstract

The rate controlling step of hafnium hydride formation governing the overall reaction using powder-type hafnium specimens was investigated from the relation between pressure and reaction rate under the pressure of 200 - 770 torr. For a constant reacted fraction, dependence on pressure of the absorption rate tend to be proportional to the second-power of pressure at the early stage of reaction and gradually to the first-power of pressure at the later stage of reaction. These results indicate the mass transfer of hydrogen molecule to arrive at the surface of hafnium powder specimen is the rate controlling step at the early stage of reaction, and the rate controlling step changed to is chemisorption at the surface of hafnium powder specimen at the later stage of reaction. The mechanism of hydrogen evolution from the hafnium-hydrogen solid solution was studied by the thermal analysis method usisng a gas chromatograph. The diffusion coefficient of hydrogen in disc-type hafnium specimen was determined from the slope of the plot of $Ln (1-Q_t/Q_{oo})$ as the function of time t for a fixed thickness 1. The activation energy for diffusion of hydrogen in