酸化タングステンのコロイド状粒子および酸化ニッケルの水素還元過程の電子顕微鏡による研究

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  • Electron Microscopic Studies on the Progress of Reduction of Colloidal Particles of Tungsten Trioxide and Nickel Oxide. (Electron Microscopic Studies on the Progress of Reduction of Metal Oxide by Hydrogen. 4th Report)
  • サンカ タングステン ノ コロイドジョウ リュウシ オヨビ サンカ ニッケル ノ スイソ カンゲン カテイ ノ デンシ ケンビキョウ ニ ヨル ケンキュウ

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Colloidal particles of tungsten trioxide having boat-like and rectangular shapes were prepared from aqueous solution of tungstic acid. These crystals were single-crystalline (Photo. 1), and they were mounted on a carbon film placed on a perforated thin gold plate, and were reduced by hydrogen at one atmospheric pressure in the specimen-treating adaptor to the electron microscope, previously devised by the present author, and the morphological and the chemical changes of a certain chosen region of the specimen were followed by taking micrographs and selected-area diffraction patterns (Photo. 2). By reduction at 500°C, the entire uniform surface of the particle becomes finely granular and the patterns of β-W and α-W appeared, but by further reduction at 600°C, β-W was completely transformed into α-W, and the granular surface became coarser and finally at 700°C broke into separate particles, later becoming somewhat rounded. Even at the highest temperature these tungsten particles filled uniformly the unshrunk contours of the original oxide crystals. Above 700°C the tungsten particles reacted with carbon film to form carbide. Nickel oxide particles prepared by heating nickel nitrate hexahydrate were mounted on the sharply pointed end of a tungsten wire, and the progress of reduction was examined. Fine nickel particles produced by reduction grew to larger ones and coalesced together at higher temperatures (Photo. 3). On the contrary, fine nickel particles produced by reduction of the oxide prepared by heating kieselguhr and asbestos fibers impregnated with nickel nitrate solution did not show any sign of coalescence even at high temperatures (Photo. 4, 5). Based on these observations the mechanism of formation of nickel particles and the role of support for catalysts have been discussed.

収録刊行物

  • 日本金属学会誌

    日本金属学会誌 23 (7), 422-426, 1959

    公益社団法人 日本金属学会

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