Study On The Phase-control And Properties Of O'-Sialon Multiphase Ceramics

O'-Sialon multiphase ceramics have been fabricated by in situ synthesis technology. It was designed to explore the changes in phase after sintering and search the relationship between phase and properties by adjusting the formula and optimizing sintering process, so as to find a phase-controlled materials preparation process. The crystalline phase and microstructure were investigated by XRD and SEM, respectively. The relationship among phase composition, microstructure and properties were investgated.O'-Sialon ceramics with a porosity of 28.98⁴4.02 % were prepared at 1420°C using Si3N4,SiO₂ andα-Al₂O₃ as raw materials. The range of bending strength of the ceramics was about 93.5 MPa¹64.14 MPa and the dielectric constant of which was between 3.3986 and 4.6034. The thin slat-like O'-Sialon (Si2-xA1x O1+x N2-x; 0<x≤0.3) grains could be observed in samples as the designed x value was 0.1, but thick slat-like grains were found when it became 0.3. The actual substitution content ofα-Al₂O₃ was estimated via lattice correction and nonlinear fitting of calculation. The effect ofα-Al₂O₃ could be concluded as follows: (1)α-Al₂O₃ was used as sintering aid to form liquid phase with other additives, which could promote the transformation fromα-Si3N4 toβ-Si3N4 and the formation of Si2N2O. (2) The slat-like O'-sialon phase would be achieved through the reaction of residualα-Al₂O₃ and Si2N2O. (3) The reaction maybe also occurred byα-Al₂O₃ and Si3N4 to form crystalline phases. It was also found that formation of nearly single-phase O'-sialon was obtained in the sample containing 10.42 wt. %α-Al₂O₃. Increasing the sintering temperature could also improve the content and grains growth of O'-Sialon. When the sintering temperature was 1460°C, the O'-Sialon phase content reached 98.85 %, and almost single-phase O '-Sialon was also achieved.O'-Sialon andβ-Sialon multiphase ceramics were prepared at 1420°C through adjusting the amount of SiO₂. A considerable content of O'andβwas achieved with 5.59 % SiO₂ in the sample. Its bulk density and bending strength were 2.3516 g·cm-3, 215.69 MPa, respectively. The bulk density of samples gradually increased as the amount of SiO₂ decreased. The effect of increasing sintering temperature on densities and properties was in line with the general laws, but improving sintering temperature simply could not promote the generation of Sialon phase and optimize the phase composition of samples.O'-Sialon /β-Sialon multiphase ceramics were also synthesized with introducing Al₂O₃-Si in raw materials by sol-gel method. Only two-phases, O'-Sialon andβ-Sialon, were eixsted in samples. In this way, Al₂O₃ had a small size effect and surface effect. Therefore, a large number of interface system provided a short-range atomic diffusion paths, resulting in a higher diffusion rate and accelerating materials reactions. Besides, Si powder with high activity also had a great positive effect on the solution reaction. In addition, It was benefit for the generation ofβ-Sialon via raising sintering temperature.