窒化ケイ素の泥しょう鋳込成形と焼結体の機械的特性(第4報) : 焼結助剤組成と焼結条件

概要

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The effects of Cmpositions of Al_2O_3-Y_2O_3 sintering additives and sintering conditions on the mechanical properties were studied to determine the fabrication conditions of silicon nitride via slip casting. Slurries containing 67 wt% solids (92 wt%Si_3N_4 and 8 wt% Al_2O_3-Y_2O_3), 33wt% distilled water and 0.01 wt% deflocculant (polyacrylic ammonium) were prepared. After the forming by vacuum filtration using a porous polymer resin mold, samples were adequately dried and sintered in the temperature range from 1775 to 1825℃ at 0.9 MPa of N_2 pressure. High-density sintered bodies (3.16-3.25 g/cm^3) were obtained. The density tended to increase with raising temperature for a short sintering period (4 h), while, decrease with raising temperature for a long sintering period (10 h) . Under the present preparation conditions, flexural strength maxima were observed at 3 wt%Al_2O_3-5 wt%Y_2O_3. A sample sintered at 1775℃ for 10 h showed an average flexural strength of 1138 MPa and a Weibull modulus, of 17.3. A composition of 3 wt%Al_2O_3-5 wt%Y_2O_3, that ratio corresponds to the liquid phase compositions at the lowest temperature in the system Al_2O_3-Y_2O_3-SiO_2, was favorable to obtain silicon nitride ceramics with high-strength at room temperature.
1993-08-01