Accurate control of fH2 in cold-seal pressure vessels with the Shaw membrane technique
Schmidt, Burkhard C.; Scaillet, Bruno; Holtz, Francois
European Journal of Mineralogy Volume 7 Number 4 (1995), p. 893 - 904
published: Aug 1, 1995
manuscript accepted: Feb 23, 1995
manuscript received: Aug 29, 1994
ArtNo. ESP147050704016, Price: 29.00 €
Abstract An experimental setup is described to use the Shaw membrane technique in cold-seal pressure vessels (CSPV), allowing constant partial pressures of hydrogen (PH2) and hence hydrogen and oxygen fugacities (ƒH2,ƒΟ2) to be maintained in experimental charges for long durations (up to several weeks). The experimental setup permits the accurate determination of ƒH2 prevailing in gas pressurized vessels. In contrast to previous designs (CSPV and internally heated pressure vessels), osmotic equilibrium with this setup can be attained by diffusion of H2 from the membrane toward the pressure vessel (without adding H2 to the pressure medium before the heating up). PH2 and thus/H2 can be fixed at any desired value with a minimum precision of± 1 bar. Osmotic equilibrium is reached within less than 2 or less than 20 hours, with membranes made of Ag23Pd77 and Ag70Pd30 alloys, respectively (at 770°C, 1 kbar total pressure and PH2 up to 50 bars). The technique described here has been successfully used to calibrate the/o2 imposed by the Co-CoO solid buffer assemblage at 735°C and 780°C at 1 kbar.