窒化珪素-アルミナ系焼結体

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Sintering by hot-pressing of the system, Si_3N_4-Al_2O_3, was investigated. The purities of the raw materials were about 98.5% for Si_3N_4 and 99.99% for Al_2O_3. Their grain sizes were, both, about 1μ in diameter. Temperature, time and pressure in the hot-pressing were 1650°〜1850℃, 6〜60 min and 250 kg/cm^2, respectively. The following results were obtained. The quantity of Al_2O_3 necessary for full densification of the mixture Si_3N_4-Al_2O_3 was more than 20 mol%, which agreed with that given by Deeley et al. Grain-growth in the sintered body was observed to be remarkable when Al_2O_3-concentration exceeds 40 mol%. The activation energies for sintering under the pressure of 250 kg/cm^2 were determined to be 100 kcal/mol for 80 mol% Si_3N_4-20 mol% Al_2O_3 and 67 kcal/mol for 60 mol% Si_3N_4-40 mol% Al_2O_3. Oxidation resistance of sintered Si_3N_4-Al_2O_3, evaluated by the weight gain, increased with Al_2O_3-concentration, reaching the maximum at 65 mol% of Al_2O_3, followed by decreasing when Al_2O_3-concentration exceeds 65 mol%. At the Al_2O_3-concentration of 65 mol%, the oxidation resistance was more than 10 times as high as that of the system, Si_3N_4-MgO. Abrasive resistance of the sintered body, evaluated by the weight-loss during a abrasive test with abrasive powder, SiC #800, increased with Al_2O_3-concentration, reaching the maximum at the Al_2O_3-concentration of 50 mol%, followed by decreasing when Al_2O_3 concentration exceeds 50 mol%. The maximum abrasive resistance was about 4 times as high as that of sintered 85 mol% Si_3N_4-15 mol% MgO, which is in practical use. By hot-pressing, the solid solution of Si_3N_4 and Al_2O_3, Si_3N_4ss, was found to be formed, which was already pointed out by the present authors. The solubility limit of Al_2O_3 in Si_3N_4s.s. was estimated to be about 67 mol% at 1750℃ and 78 mol% at 1850℃. From the observation of specific gravity of Si_3N_4ss, the solid solution is thought to be of a substitutional type. A new compound was also found, whose composition was estimated to be 2Si_3N_4・3Al_2O_3. The new compound was stable under slightly oxidizing atmosphere and unstable under neutral or slightly reducing atmosphere. The eutectic point in the system was estimated to be 1870°±30℃. An approximate phase diagram was given for Si_3N_4-Al_2O_3.
社団法人日本セラミックス協会の論文
2000-06-01

窒化珪素-アルミナ系焼結体

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