Zhenkun Zheng1, Jianhua Tong1, Vadim V. Guliants2, and Scott Misture3. (1) Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221, (2) Department of Chemical Engineering, University of Cincinnati, Cincinnati, OH 45221-0171, (3) New York State College of Ceramics at Alfred University, 2 Pine St., Alfred,, New York, NY 14802
The sodalite (SOD) zeolite membranes are highly promising for hydrogen separation from larger gas molecules due to the presence of small ~2.8Å pores formed by the six-membered rings of the sodalite cages. Novel pure-silica sodalite membranes (PSSMs) were synthesized in the presence of organic template on alpha-alumina supports by in-situ crystallization and seeded secondary growth methods. Continuous and defect-free pure-silica sodalite layers < 5μm thick were grown under solvothermal synthesis conditions. Various synthesis parameters, such as the synthesis composition, temperature, time and support orientation, were investigated. The XRD, high temperature XRD and SEM techniques were used to investigate the phase composition, thermal stability, and microstructure of PSSMs. Pure-silica sodalite phase was stable up to 800ºC and progressively re-crystallized into the dense cristobalite phase at higher temperatures. Pure silica sodalite framework slightly expanded up to 400ºC and slightly contracted above this temperature. This change in the sodalite unit cell volume with temperature may be explained by the partial release of gaseous decomposition products of the organic template occluded inside the sodalite cages during synthesis. Pure-silica sodalite powders (PSSPs) were also synthesized by the same solvothermal method and characterized by XRD, high temperature XRD, TGA-MS and SEM techniques.