Surface layers preparation high-temperature treatment

The excellent separation properties of silica membranes prepared at temperatures as high as 825°C enables their use for high temperature applications, such as the dehydrogenation of H2S (chapter 8). Unfortunately no hydrothermal stability of the prepared layers could be tested because the mesoporous intermediate layer was not hydrothermally stable, but an indication of the hydrothermal stability of the unsupported material could be obtained from the specific surface area and XRD measurements. These measurements did not show any structural change in the material during SASRA treatment, which is a very hopeful result for the operation of real, supported, membranes at high temperatures and high pressures. 

Petrii and Entin [54, 57, 78, 150, 180, 243] investigated the adsorption and electrochemical characteristics of platinum and ruthenium alloys in detail. The optimum alloy compositions for oxidation of methanol at various temperatures were determined, the anodic oxidation reactions of various compounds of the alloys were investigated, the stability of the alloys after prolonged use was investigated, and the characteristics of platinum— ruthenium alloys prepared by various methods (skeletal electrodes, electro-lytically mixed deposits on a platinum and titanium carbide bases, powders deposited by sodium borohydride, smooth alloys) were compared. It was found that heat treatment of platinum - ruthenium alloys at 800 C in an atmosphere of inert gas led to loss of their high catalytic properties and formation of catalysts which behave similarly to platinum. This phenomenon is explained by diffusion of ruthenium atoms from the surface layer into the volume. 

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