Abstract
The effects of admixtures of H <sub>2</sub> O and H <sub>2</sub> S with H <sup>2</sup> gas on hydrogen diffusion and permeation in both austenitic and ferritic stainless steels were studied using a gas-phase permeation technique at T = 100-360°C. The effective hydrogen diffusivity and permeability from atmospheres of H <sub>2</sub> , H <sub>2</sub> O and H <sub>2</sub> S in Pd-coated, deformed AISI 304 at 320°C were in the order of H <sub>2</sub> ≈ H <sub>2</sub> S > H <sub>2</sub> O. In uncoated AISI 302, both transport parameters from H <sub>2</sub> O were consistently less than those from H <sub>2</sub> . Additions of H <sub>2</sub> O and H <sub>2</sub> S to H <sub>2</sub> gas were shown to reduce both hydrogen diffusion and permeation. The extent of reduction in a ferritic alloy was greater than in an austentic alloy. Pd-coating was effective in protecting the metal matrix from reaction with H <sub>2</sub> O, however, H <sub>2</sub> ,S interacted strongly with the Pd-coating. The oxidized surface could be completely recovered by heating in pure H <sub>2</sub> , gas at 320°C, but the sulfidized surface could not. © 1988.