Evaporation of solids by laser pulses. II. Zirconium hydride

Publisher Website
Google Scholar
Abstract
The vaporization of hydrogen from the binary solid compound zirconium hydride induced by pulses from a Q−switch ruby laser was studied using a quadrupole mass spectrometer. The rate of vaporization of H and H2 during the rapid temperature transient was determined from the measured mass spectrometer signals. Application of an equilibrium model to the vaporization process predicts that predominantly H2 (rather than H atoms) should be emitted. The vaporized hydrogen should have a Maxwellian velocity distribution characteristic of the instantaneous surface temperature, and the rates of vaporization should be related to the equilibrium H2 and H pressures by the Langmuir equation. Since the equilibrium pressure is a function of both surface temperature and surface hydrogen concentration, it was necessary to solve simultaneously the time−dependent heat conduction and hydrogen diffusion equations in the heated zirconium hydride in order to predict the vaporization rates. It was found that H atoms and H2 molecules were emitted at thermal equilibrium with the surface. At low laser power density, the magnitude of the H2 signals agreed with the equilibrium model. At high laser power density, the magnitude of the H2 signals was less than predicted, possibly because of a diffusion barrier at the surface. The H atom signals were much larger than predicted, indicating that they were produced by a nonequilibrium surface process which favored direct vaporization of adsorbed hydrogen atoms rather than recombination followed by H2 desorption.

This publication has 3 references indexed in Scilit: