The Chemistry of Gaseous Hydrogen Embrittlement
The chemical reactions of gaseous hydrogen on nonsurfaces have been determined by volumetric and magnetization adsorption experiments. It has been found that the process involves the formation of a chemisorbed molecular hydrogen ion (H2 +) prior to the formation of the atomic embrittling ion (H-). At low temperatures (77K), the kinetics and equilibrium isotherm clearly show the equilibrium between the two adsorbed species is dominated by the molecular ion. As the temperature is increased the concentration of the embrittling ion increases and reaches a maximum at approximately room temperature. Above room temperature the desorption of the molecular ion and hence the decrease in concentration of the embrittling ion becomes the dominant process. The temperature dependence of slow crack growth measurements in gaseous hydrogen is explained on the basis of the above chemistry.
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