A silica membrane prepared by a counterdiffusion CVD method using tetramethyl orthosilicate and O 2 was applied to a steam reforming reaction of methane. This silica membrane showed hydrothermal stability for more than 80 h at 773 K under H 2 O/N 2 ) 3. The H 2 /H 2 O permeance ratio was about 290 after the hydrothermal stability test. Rh or Ni catalyst was dipped on a porous alumina substrate before chemical vapor deposition (CVD). As a result, a composite catalytic membrane of a hydrogen permselective silica layer and a catalyst layer was obtained. This catalyst composite membrane reactor was applied to steam reforming reaction to extract hydrogen. Rh catalyst showed better stability than that for Ni catalyst. Methane conversion was increased to 64.5% from the equilibrium value (31.4%) at 773 K under S/C ) 2 by the Rh-dipped membrane reactor. High conversion of methane was due to high selectivity of H 2 /H 2 O that was confirmed by the simulation evaluation.
When the residual water content of currently used C104-electropolishing solution is reduced to less than 0.1 g/l, the anodic dissolution of beryllium follows Faraday's law with a valence of one over an extended range of anodic potentials. This result is interpreted in terms of a dissolution mechanism occurring in a succession of two individual steps, each involving a simple electron, thus Be ~ Be + § e-(electrochemical step) Be + -k oxidant ~ Be + + (chemical step occurring away from the electrode) Support for the transitory existence of the monovalent ions is derived from thermodynamic considerations allied with the structure of the anodic layer. Microscopic examination of the state of the anode surface during and after the dissolution shows clearly that a mechanical disintegration of the metal lattice by the action of the current cannot be the origin of the anomalous valence observed. On the contrary, it is shown that disintegration of this type contributes only at low anodic potentials. This phenomenon, known as the "chunk effect," is clearly observable by scanning electron microscopy and accounts for faradaic "efficiencies" of greater than 200% in certain electrolytic conditions.Since 1955 it has been known that the application of Faraday's law to the anodic dissolution of beryllium could lead to calculated anode weight losses which were lower than measured values (1-7).Although, for more than a century now, a number of investigations has been devoted to the study of analogous effects on other metals, the origin of these anomalous dissolution valences remains very controversial. For some investigators, it consists of nothing more than a more or less incidental intervention of a side effect (difference effect, chunk effect 1) (7-12). On the other hand, there are those who consider these discrepancies to be evidence, on a macroscopic scale, of a fundamental reaction process. This process, potentially applicable to all dissolution processes leading to multivalent ions, concerns the mechanism of the charge transfer at the metal/electrolyte interface and is proposed as a series of individual single electron steps (13-21). With this latter view, the systematic study of these "deviations" from Faraday's law provides an approach to a better understanding of the electrolytic dissolution of a metal, and thus, as pointed out specifically by Uhlig (22), also to the essential processes in metallic corrosion.A metal such as beryllium has favorable characteristics for studying anodic dissolution in terms of these two different concepts of the anomalous valences. First, one can use it in the form of the usual industrial polycrystalline material, a form in which it ought to be more sensitive to the occurrence of dif-# Electrochemical Society Active Member. Key words: dissolution anomalous valences, cation solvation, anodic dissolution efficiency, electrolytic polishing, microscope scanning electron.The "'chunk effect" consists of the disintegration of the metallic lattice under the action of the electrolysis current; a hetero...
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