直接還元に用いる原料ボーキサイトの熱的性状

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  • Thermal Properties of Bauxites for the Source Materials of Direct Reduction. (Studies on the Production of Crude Aluminium Alloy by the Direct Reduction of Aluminous Ores.)
  • チョクセツ カンゲン ニ モチイル ゲンリョウ ボーキサイト ノ ネツテキ セイジョウ

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The thermal behaviors of bauxites used as the source materials in the direct reduction of aluminium were investigated.<BR>By the microscope observation under cross Nicols, it was found that the texture of Australian bauxite was composed of fine gibbsite crystals and the crystals were finer than the Bintan and Sematan bauxites.<BR>The outer skin of the Australian ore particles and smaller particles had a much higher boehmite content than the central and larger samples.<BR>According to thermobalance, every sample had a small amount of adsorbed water.<BR>The change of gibbsite was mainly due to the formation of χ-Al2O3, and less than 20% of gibbsite was transformed to boehmite, and above 1000°C all the samples changed to α-Al2O3.<BR>From the decrease in intensity of infrared absorption and neuclear magnetic resonance, an indication of decomposition of gibbsite was found in the samples heated for 1 hr at 110°C.<BR>In addition, the free water due to decomposition of the O-H group was detected in 1600 cm−1 of infrared absorption and 1 gauss of neuclear magnetic resonance, and a larger quantity of the free water was found in the samples heated at 310°C, for 1 hr than in those treated at 110°C.<BR>This free water was assumed to be a solvent which takes part in dissolution and precipitation during the transformation of gibbsite to boehmite.<BR>Furthermore, owing to the more developed gibbsite crystal in the Bintan bauxite, a small quantity of water was still found in the sample calcined at 700°C.

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