Platinum Metals Rev., 1987, 31, (2), 71
Hydrogen Permeability at Elevated Temperatures
The study of the reactivity of minerals in fluid media under conditions of high temperature and pressure has important implications for their industrial utilisation. In such hydrothermal experiments the precious metals are commonly used as containment materials; platinum and silver-palladium being employed as semi-permeable membranes for hydrogen while gold and silver serve as hydrogen barriers. To date the lack of reliable data on the permeation rates of hydrogen has caused difficulties in the selection of materials and experimental conditions.
Now, however, a study by I-Ming Chou of the U.S. Geological Survey has remedied this deficiency (Am. J. Sci., 1986, 286, 638–658). Using an oxygen-buffered, double capsule technique, Chou has measured the permeation of hydrogen through platinum, two silver-palladium alloys, gold, and silver at a pressure of 2 kilobar (29,000 psi, 200 MN/m2) in the temperature range 450 to 812°C. He showed that the permeabilities lie in the order:
The activation energies increase in this order.
This study shows that the addition of palladium to silver increases its hydrogen permeability exponentially, and extends the data on the silver-palladium system, where the palladium-rich alloys are used commercially as diffusion membranes for the purification of hydrogen.