Nanostructured thin palladium-silver membranes: effects of grain size on gas permeation properties

• Published in: Journal of materials science Vol. 36; no. 13; pp. 3221 - 3227
• Main Authors: MCCOOL, B. A, LIN, Y. S
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Heidelberg Springer 01.07.2001; Springer Nature B.V
• Subjects: Activation energy; Aluminum oxide; Carbonation; Chemistry; Colloidal state and disperse state; Crystallites; Exact sciences and technology; Gas permeation; General and physical chemistry; Grain boundaries; Grain growth; Grain size; Helium; Hydrogen; Hydrogen permeation; Materials science; Membranes; Palladium; Partial pressure; Penetration; Reluctance; Selectivity; Silver base alloys; Transitional aluminas; Gaseous permeation; Silver Alloys; Scanning electron microscopy; Transition metal Alloys; Platinoid Alloys; Hydrogen; Palladium Alloys; Membrane; Helium; Alumina; X ray diffraction; Nanocrystal
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1023/A:1017938403725

Submicron-thick Pd-Ag alloy membranes, prepared on 4 nm pore γ-alumina support by magnetron sputter deposition, are nanocrystalline with a grain (crystallite) size of about 20 nm. The membranes show good selectivity for hydrogen over helium (about 4000 at 300°C). Hydrogen permeation is dominated by the surface reaction steps in 100–200°C with an activation energy of about 30 kJ/mol. Bulk diffusion resistance becomes important at higher temperatures (>200 °C). Grain size is the most critical parameter affecting the hydrogen permeance of the thin nanostructued Pd-Ag membranes. Increase in Pd-Ag grain size from about 20 to 60 nm results in a substantial improvement in hydrogen permeance with a higher apparent activation energy in 100–300°C. Grain growth appears to increase the hydrogen permeability in the bulk phase of the Pd-Ag membranes. Helium permeance through the grain boundary decreases with increasing temperature or hydrogen partial pressure due to grain expansion. Carbonation and the accompanied grain expansion have detrimental effects on the perm-selectivity of the Pd-Ag membranes.