Permeation Velocities at High Pressures

Wiistner s (75) studies upon the hydrogen permeability of silica glass (Chap. Ill) showed that even up to 800 atm. the permeation rate-pressure isotherm was linear  

A few comparable studies have been made upon the per-meabihties of metals to oxygen and hydrogen. Smithells and Ransley(76) observed that at pressures of 112 atm. the permeation rate-pressure isotherm obeyed accurately the Richardson equation  

Their data are shown in Fig. 59. A similar result was obtained by Lombard and Eichner(09) at pressures of 26kg./cm.2 for 

Among the possible phase-boundary processes one might include the following An adsorbed gas molecule or atom is driven into the solid by molecular bombardment by an activated gas molecule. Smithells and Ransley tested this possibility by introducing argon at 100 atm. into a diffusion system Hg-Ni where the hydrogen pressure on the ingoing side 

Their own experiments were conducted at current densities of up to 0 043amp./cm.2 By carrying out these experiments at large current densities, it should be possible to reach a current density at which the surface layers of metal were completely saturated. The permeation velocity should then no longer increase as the current density increases. This point has been tested (53), and has important implications in the discussion on mechanisms of diffusion in the next section. It was found that only in very active palladium tubes could a limiting permeation velocity be reached (see Fig. 62). 

---