| In this work, theoretical and experimental studies are presented regarding the application of Chemical Vapor Deposition (CVD) and Magnetron Sputtering for preparation of different types of inorganic membranes in/on porous supports. In the theoretical part, semi-analytical solutions of mathematical models that describe CVD in porous media are first developed, considering introduction of vapor precursors from either one side or opposite sides of a porous support. These solutions describe the deposition characteristics and pore narrowing kinetics as explicit functions of the various process parameters (precursors concentrations and diffusivities, reaction kinetics) and support properties (pore size, thickness and porosity). The extention of these solutions for the purpose of predicting macroscopic properties of inorganic membranes, of relevance to their application in gas separations, such as permeance, pore size (distribution) and selectivity is also demonstrated.; The feasibility of CVD for preparing novel nanocrystalline ceramic-supported palladium membranes using different precursors and reaction schemes is demonstrated in this work. Thin (0.5-5 {dollar}mu{dollar}m), nanocrystalline (15-50 nm grain size) Pd membranes can be prepared inside pores or on the surface of ultrafiltration ceramic supports, using volatile inorganic or metallorganic palladium salts and hydrogen as precursors, under proper experimental conditions. These membranes exhibit satisfactory permselectivity only when Pd is deposited in the form of a metal layer on the surface of the support.; For the first time, synthesis of submicron-thick, ceramic-supported Pd-based metallic membranes with substantial permselectivity at elevated temperatures is demonstrated in this work, using the magnetron sputtering technique. The effect of synthesis conditions on metallic membrane texture and permeation properties is also systematically investigated. For Pd-based metallic membranes coated to a thickness of 0.1-1.5 {dollar}mu{dollar}m on the surface of ultrafiltration ceramic supports by CVD or sputtering, the H{dollar}sb2{dollar} permeance, H{dollar}sb2{dollar}:He selectivity and activation energy for permeation were in the range 1.0-{dollar}rm 2.0times 10sp{lcub}-7{rcub} molcdot msp{lcub}-2{rcub}cdot ssp{lcub}-1{rcub}cdot Pasp{lcub}-1{rcub}{dollar}, 80-300 (both at 300{dollar}spcirc{dollar}C), and 23-30 kJ/mol, respectively. The thickness and temperature dependence of H{dollar}sb2{dollar} permeation suggest that "surface reaction" rather than "bulk atomic diffusion" is the rate-limiting step for H{dollar}sb2{dollar} transport through these membranes. |
