Effects of composition and thermal treatment on infrared transmission of Dy-α-sialon

By spark plasma sintering (SPS) and post-sintering thermal treatment at 1700 °C for 7 and 17 h, respectively, the infrared transmissions of Dy-α-sialon with three compositions, Dy0.33Si9.3Al2.7O1.7N14.3, Dy0.4Si10.2Al1.8O0.6N15.4 and Dy0.67Si9Al3O1N15, (abbreviated as Dy1017, Dy1206 and Dy2010, respectively), in 1500–4000 cm−1 wave number (6.6–2.5 μ) regions were investigated. The results showed that the second crystallized phase, the sizes of α-sialon grains, the distribution of cations in the grains and the existence of holes on the surface of ceramics were main factors that affected the infrared transmittance of Dy-α-sialon. Among the three SPS-ed specimens, Dy2010 (0.5 mm in thickness) possessed the highest infrared transmission 65%, while those are 58 and 44% for Dy1206 and Dy1017, respectively. Through thermal treatment at 1700 °C for 7 h, the infrared transmittance of Dy2010 and Dy1206 decreased greatly, while that of Dy1017 nearly kept invariable. When thermal treatment time was prolonged from 7 to 17 h, the corresponding infrared transmittance of Dy1206 increased from 37 to 65%. Based on XRD analysis and microstructure observation, the influence of second phase and concentration distribution of cations in the grains on the transmissions of Dy–α-sialon ceramics were discussed.