Permeation of Hydrogen through Tungsten and Molybdenum

摘要

Using ultrahighhyphen;vacuum and masshyphen;spectroscopic techniques, permeation of hydrogen through wroughthyphen;and vaporhyphen;deposited W tubes and through a drawn Mo tube has been measured for pressures between 10minus;6and 200 torr and temperatures between 1050deg; and 2400deg;K. Permeation rates varied with pressure and temperature in a complex manner. Expressions for the permeation rate are derived on the assumptions that (a) the rate determining step of permeation is diffusion of hydrogen in the bulk of the sample, and (b) the rate of desorption of hydrogen atomsDa,the rate of recombinative desorption of hydrogen moleculesDm,and the concentration of dissolved hydrogen atoms are each determined by the concentration of hydrogen atoms adsorbed on the metallic surface. For the hydrogenndash;tungsten system, this analysis agrees with measured rates over the entire range of temperature and pressure, and the experimental data is consistent with Hickmott's values for: the ratesDaandDm;the sticking probability for hydrogen atoms; and the probability that an incident hydrogen molecule adsorbs as two atoms. For the hydrogenndash;molybdenum system, permeation is controlled by phasehyphen;boundary processes at low driving pressures. Measured permeation constants follow the equationPthinsp;equals;thinsp;P0expthinsp;lpar;minus;thinsp;QPthinsp;sol;thinsp;RTrpar;above 1 torr. The resultsP0thinsp;equals;thinsp;lpar;1.5thinsp;plusmn;thinsp;0.5rpar;thinsp;times;thinsp;10minus;3torrmiddot;litercmminus;1middot;secminus;1middot;torrminus;1thinsp;sol;thinsp;2andQPthinsp;equals;thinsp;lpar;31.5thinsp;plusmn;thinsp;1rpar;kcalthinsp;sol;thinsp;moleare found for W. For Mo, the corresponding numbers are (7.1thinsp;plusmn;thinsp;2)thinsp;times;thinsp;10minus;4and (21.5thinsp;plusmn;thinsp;1).