KJ Ceramics 31

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Detailed Program

Paper Number : ST-O01

Time Frame : 15:30~15:50

Presentation Date : Thurseday, 27, November

Session Name : Structural Ceramics

Session Chair 1# : Hai-Doo Kim

Session Chair 2# : Junich tatami

Fabrication of Si3N4 ceramics by post-reaction sintering using Si-Y2O3-Al2O3 nanocomposite particles prepared by mechanical treatment

Kwangjin JEONG

Yokohama National University

Silicon nitride (Si3N4) ceramics have been attracting attention as advanced materials with excellent mechanical properties and thermal stability at room and high temperatures. The reduction of production cost and the improvement of mechanical reliability are desired to expand an application target of Si3N4 ceramics. Post-reaction sintering technique is one of the solutions to reduce the production cost, in which a powder compact of a powder mixture of inexpensive Si and sintering aids is nitrided, followed by densification at higher temperatures1). However, the control of the nitridation of Si is difficult because of its exothermic reaction. Inhomogeneous nitridation sometimes results in the strength degradation of the Si3N4 ceramics. One of the ideas is to avoid abnormal heating uniform coating of the sintering aids on the surface of the Si particles. In this research, Si3N4 ceramics were fabricated by the post-reaction sintering technique using the Si-Y2O3-Al2O3 nanocomposite particles prepared by mechanical treatment. Specific surface area of the powder mixtures of Si-Y2O3-Al2O3 prepared by mechanical treatment decreased with an increase in the applied power due to an increase in joining area between Si and the additives. The prepared nanocomposite particles were molded by uniaxial pressing, followed bycold isostatic pressing. The green body thus obtained was calcined at 1375°C for 2 h in 0.15 MPa, N2 gas to form Si3N4. For comparison, a powder mixture prepared by conventional wet ball milling was used. Nitridation in the green body produced from the nanocomposite particles prepared by mechanical treatment were more uniform and nitridation ratio was higher than that of ball milling process. Furthermore, nitridation ratio was also increased by mechanical treatment with an increase in the applied power. This means that nitridation was enhanced by using the nanocomposite particles while abnormally exothermic reaction between Si and N2 was inhibited. After densification at 1800°C for 2 h in 0.9 MPa, N2 gas, the Si3N4 ceramics prepared by mechanical treatment had more homogeneous microstructure and higher density than that by ball milling process.

Figure 1 The SEM photographs of the microstructure of RBSN bodies after nitridation
(a) 3kW, (b) 4kW, (c) 5kW and (d) Ball-Mill

References:

[1] S. H. Lee, et al., J. Kor. Ceram. Soc., Vol. 50, No. 3, (2013) 218-225.

Acknowledgements :

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