水熱条件下におけるMgO添加Si<sub>3</sub>N<sub>4</sub>常圧焼結体の溶出挙動

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  • Leaching Behavior of Pressureless-Sintered Si<sub>3</sub>N<sub>4</sub> Containing MgO under Hydrothermal Conditions
  • スイネツ ジョウケンカ ニ オケル MgO テンカ Si3N4 ジョウアツ シ

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Leaching behavior of pressureless-sintered Si3N4 containing MgO was studied under hydrothermal conditions using an autoclave. Si3N4 specimens were prepared from two kinds of commercial grade Si3N4 powders, by the imide-decomposition (specimen M-1) and silicon-nitridation methods (specimen M-2). They were doped with 10wt% MgO. No differences in microstructure were observed in the sintered specimens from these starting powders. Leaching test was carried out under the hydrothermal conditions at 300°C and 8.6MPa for 1-10 d. Specific weight loss (mg/cm2) in leaching test for these specimens was more than that for the Si3N4-Y2O3/Al2O3 specimens in the previous work. The weight loss increased linearly with time with the same steep slope for both M-1 and M-2 in the early stage (up to 3 d) and leveled off in the later stage (4-10d); M-1 showed a larger saturated weight loss than M-2. The result in the early stage indicates that the leaching behavior depends on the grain morphology of sintered body as found in the Si3N4-Y2O3/Al2O3. Chemical analysis of a leaching solution showed that Si was the main leached element and Mg was leached little. EPMA and SEM observations revealed that the leached layer was composed of thin hydrated silica and magnesium silicate hydrate layers. Based on the experimental results, it is suggested that the leaching behavior of pressureless-sintered Si3N4 under hydrothermal conditions depends on the leaching characteristics of constituting ions in MgO and Y2O3-Al2O3 doped as sintering aid.

収録刊行物

  • 窯業協會誌

    窯業協會誌 95 (1103), 730-735, 1987

    公益社団法人 日本セラミックス協会

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