Si_3N_4の高温強さに及ぼすガラス相の粘度特性

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Tests were performed on Al_2O_3-Y_2O_3 based compounds, which are the most widely used sintering additive for Si_3N_4, with the objectives of evaluating the high-temperature viscosity characteristics of Al-Y-Si-O based glass and clarifying the relationship between high-temperature viscosity and the high-temperature strength of Si_3N_4. The viscosity of the glass at 1600℃ was found to be about 8-50P, while the activation energy for high-temperature viscosity was about 9-37 kJ/mol. Properties of glass such as viscosity are governed by the composition of the glass; for compositions within the glass forming region, it is thought that the network structure, hardens and viscosity becomes high in compositions having a substantial amount of SiO_2, or in compositions where the ratio of Y_2O_3/Al_2O_3 (close to the eutectic composition) is 1.0. For compositions outside the glass forming region, the influence of the precipitation of the crystal phase is considered to become more prominent. The room temperature strength of Si_3N_4 is not governed by the properties of the glass phase, but by micro structural factors such as the residual amount of pores. However, the properties of the glass phase in the sintering process are considered to determine structural factors such as the density of sintered bodies and the morphology of Si_3N_4 grains. The high-temperature strength of Si_3N_4 is dependent on the high temperature viscosity characteristics of the glass phase, and this was seen to impart high high-temperature strength to Si_3N_4 for which glass with high high-temperature viscosity would exist at the grain boundaries. For Si_3N_4 with similar viscosity characteristics at high temperatures, high-temperature strength is dependent on the size of the Si_3N_4 grains, seen to result in superior high-temperature strength for Si_3N_4 with large Si_3N_4 grains. Correlation between the rate of change in 1300℃ strength and the activation energy of viscosity for Si_3N_4 was observed when evaluated in high temperature strength tests conducted at slow cross-head speeds of 0.1mm/min to 0.5 mm/min, and it was found that the rate of change in the 1300℃ strength tended to become smaller for Si_3N_4 compositions with lower activation energy.
社団法人日本セラミックス協会の論文
2005-02-01

Si_3N_4の高温強さに及ぼすガラス相の粘度特性

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