The initial sintering of alkaline earth oxides in water vapor and hydrogen gas.
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概要
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The initial sintering (crystallite growth and surface-area diminution) of freely dispersed powders was studied. For MgO in H<SUB>2</SUB>O vapor, the sintering rate at 1073 K was directly proportional to the water-vapor pressure, <I>P</I><SUB>H<SUB>2</SUB>O</SUB>, in the range of 27–2700 Pa, and the apparent activation energy, <I>E</I>, for the sintering was 137 kJ mol<SUP>−1</SUP>. These facts lead to the conclusion that, in this system, the surface migration of O<SUP>2−</SUP> caused by the repetition of the adsorp-tion-desorption cycle of the H<SUB>2</SUB>O molecule is rate-determining step for the sintering. For CaO in H<SUB>2</SUB>O vapor, the rate-determining step appears to be migration on and/or near the surface of a cation vacancy produced by the H<SUB>2</SUB>O adsorption, judging upon the facts that the sintering rate at 873 K was proportional to <I>P</I><SUB>H<SUB>2</SUB>O</SUB><SUP>0.34</SUP> in the range of 11–1600 Pa and that <I>E</I> was 79.4 kJ mol<SUP>−1</SUP>. For MgO in H<SUB>2</SUB> gas, the sintering rate at 1123 K was approximately proportional to the hydrogen pressure in the range of 3.3–66.5 kPa and <I>E</I> was 310 kJ mol<SUP>−1</SUP>, indicating that the sintering in H<SUB>2</SUB> was caused by H<SUB>2</SUB>O vapor formed upon the desorption of the surface hydroxyl groups which had been produced by a heterolytic dissociative adsorption of H<SUB>2</SUB>.
- 公益社団法人 日本化学会の論文
著者
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Ito Tomoyasu
Department Of Electronic Engineering Tamagawa University
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Watanabe Masahiro
Department Of Agricultural Chemistry Faculty Of Agriculture The University Of Tokyo
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Tokuda Taneki
Department of Chemistry, Faculty of Science, Tokyo Metropolitan University
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Fujita Masato
Department of Chemistry, Faculty of Science, Tokyo Metropolitan University
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Ito Tomoyasu
Department of Chemistry, Faculty of Science, Tokyo Metropolitan University
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Watanabe Masahiro
Department of Chemistry, Faculty of Science, Tokyo Metropolitan University
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