Abstract
Translucent Si3N4 ceramics are expected to use for a special optical application in high temperature and corrosive environment owing to its high mechanical strength and thermal and chemical stability. To achieve the translucency of Si3N4 ceramics, fine-grained microstructure with an appropriate sintering aid is important to reduce light scattering. The Si3N4 ceramics were fabricated by spark-plasma sintering (SPS) with AlN – MgO additive. Fine α – Si3N4 powder with high purity was useful to obtain translucent Si3N4 sintered body. When the additive content was large, α – SiAlON formed, whereas β – Si3N4 formed at a small additive content, revealing the high translucency of both phases in visible light region. The AlN/MgO ratio should be on the SiAlON forming line (AlN/MgO = 3/1) in Si3N4 – AlN – MgO phase diagram. The short-time sintering at high temperature (1850 ˚C, 5 min) by SPS was effective to obtain the dense and fine-grained microstructure, and the transmittance of 22～28 % at the wavelength of 900 nm was achieved under the optimal conditions.
