The Research Of The Preparation At Low Temperature Of Transparent Alpha-Sialon Ceramics

In this paper, Si3N4, AlN, Y2O3, A12O3 as raw materials, under the Y-Si-Al-O-N phase diagram and the a-sialon formula Rem/3Si12-(m+n)Al(m+n)OnN16-n for component design, obtained m = 1.2, n = 1.1 for the component points. The powders, after planetary ball milling for 24 hours, then drying, granulation, were sintered by hot sintering in nitrogen environments, under the pressure of 25 MPa. Ball milling speeds, sintering temperatures, heating rates and holding times on the phase composition of sialon ceramics, microstructure and optical properties were studied, by X-ray diffraction (XRD), scanning electron microscopy (SEM) and LabTeach UV/visible spectrophotom-eter.The results showed that the average particle size of powder after ball milling reduced from the 0.603μm to 0.207μm. The powers were sintered as the same method. The ceramic phase of the samples were a-sialon. The grain size of the sample, which was prepared with the powders mixed by the speed 250 r/min, was smaller than it when the speed was 210 r/min. The powders mixed by 250 r/min milling after sintered were dark green, the phenomenon consistent with sialon ceramics under too high sintering temperature sintering.To 250 r/min mixed with the powder out of this study, sintering process showed that at a heating rate of 30℃/min,30 min holding time, the ceramic phases were a-sialon, when the sintering temperature increased from 1650℃to 1900℃. The density and the grain size increased with sintering temperature increasing. When the sintering temperature was 1650℃, the transmission was the lowest. When the sintering temperature was 1700℃, the transmission of sialon ceramic was the highest-34.43%. As the sintering temperature further increased, until 1900℃, ceramics' transmission decreased. When the sintering temperature was 1700℃, holding time 30 min, heating rate from the 30℃/min up to 38.5℃/min process, with the increase of heating rate, material density decreased, grain size decreased, the max transmission reduced. When the sintering temperature was 1700℃, heating rate 30℃/min, the holding time from 30 min down to 15 min, the ceramics' density decreased, grain size decreased, transmittance decreased.To the powders mixed when the milling speed was 250 r/min, the Y-α-sialon ceramic' transmittance was the highest when the sintering temperature was 1700℃, the heating rate was 30℃/min, and the holding time was 30 min.When the wavelength was 1100 nm, it's transmittance was 34.43%, and it's Vickers hardness was 19.10 GPa. Compared with the ceramic's, when the milling speed is 210 r/min, the transmittance increased 1.64%, while the sintering temperature is decreased 200℃.