β-アルミナ焼結体におけるNa-Kイオン交換速度

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  • 針田 彬
    東京工業大学工業材料研究所 川崎製鉄 (株) 千葉製鉄所
  • 佐多 敏之
    東京工業大学工業材料研究所

書誌事項

タイトル別名
  • Na-K Ion Exchange Rate in Sintered Body of β-alumina in Nitrate Melt
  • ベータ アルミナ ショウケツタイ ニ オケル Na K イオン コウカン ソク

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抄録

Na-β-alumina is important for industrial uses as refractories for grass tank furnace and as solid electrolyte, and is also very interesting material with anisotropic properties caused from its characteristic layer crystal structure. In this report Na-K ion exchange rates of sintered polycrystalline body (12mmφ and 97% density) of β-alumina solid solution (Na2O⋅9.23 Al2O3) in NaNO3-KNO3 melts were measured at 280°-440°C by determining weight changes. The exchange rate obtained in all experiments was proportional to (time) 1/2 indicating a process controlled by counter diffusion of Na or K ion in the body, and its rate constant is proportional to the diffusion constant.<br>For the exchange of Na-β or K-β in the NaNO3-KNO3 melt, the diffusion coefficients decreased with increasing contents of Na or K from 10-6-10-7 to 10-7-10-8cm2/s and its activation energy increased to 10-13kcal/mol from 4-5kcal/mol for single crystals. This situation corresponds to the so called mixed alkali-effect. In the case of exchange of mixed Na-K β-alumina in the NaNO3 or KNO3 melt, the preceding effect was also found indicating the minimum diffusion at intermediate compositions. In the exchange of Na-β in the NaNO3-KNO3 melt with compositions larger than 50 at% of K and also in the exchange of Na-K-β containing less than 50 at% of K in the pure KNO3 melt, the sintered bodies disintegrated because of an expansion effect of diffused K.<br>The concentration profiles of Na or K in the exchanged bodies were measured by EPMA, from which the diffusion coefficients by Matano were obtained for the various compositions of Na-K-β alumina. For example, diffusion layers of 100-1000μm were observed in the exchange of 300°-400°C for 10-13min.

収録刊行物

  • 窯業協會誌

    窯業協會誌 87 (1001), 48-56, 1979

    公益社団法人 日本セラミックス協会

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