Influence of β‐Si₃N₄ whiskers on sintering and crystallization of fused silica ceramics

Abstract

Fused silica ceramics are widely applied for radome materials, crucibles, and vanes, but the mechanical properties were deteriorated due to the cristobalite crystallization. The fused silica ceramics added with by β-Si 3 N 4 whiskers were prepared by a slip-casting method to retard the cristobalite crystallization. The influences of the sintering environments and the β-Si 3 N 4 whiskers on the microstructure and phase structure were investigated. The silanol (Si-(OH) n ) and oxygen vacancies (V O ) in the fused silica in formed in different conditions were studied by Fourier Transform Infra-Red (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the results indicated that the ball-milled produced a large amount of the silanol groups onto the surface of the fused silica particles. The fused silica heated in the vacuum created the maximum oxygen vacancies (24.2%) on the surfaces. Silanol groups reacted with the β-Si 3 N 4 whiskers, and the O atoms in the silanol groups were fixed into the bulk materials. And the crystallization kinetics and the activation energy of Si 3 N 4w /SiO 2 ceramics at the temperature ranging from 1200 to 1400 • C were calculated based on the JMA(Johnson-Mehl-Avrami) model. The activation energy of the fused silica ceramics with the addition of the β-Si 3 N 4 is 506.2 kJ/mol, increased by 23.6% than that of the pure fused silica ceramic.