Preparation And Property Of Silica-alumina Composite For High Temperature Insulation Tile

ZrB₂ has great application prospects at present for its advantages of excellent chemical stability and high strength. SiC material is added as a second phase in the preparation of ZrB₂-SiC-based ceramic, as it can improve the strength and density and other properties of the material. Though Zr B 2-SiC-based ceramics have high strength after a hot press ing, but its low toughness limited its further application. In recent decades researchers focused on how to use carbon fiber to enhance the toughness of ZrB₂-SiC-based composite materials. Fiber can effectively change the fracture mode of composite materials, and enlarge the critical crack size of the material, which is very favorable for the application of the material. However, there are also many problems about preparation of Carbon fiber reinfoced ZrB₂-SiC-based ceramics, such as the strong interface of carbon fiber and matrix are not conducive to the appearance of fiber pull-out phenomenon when crack propagated. Structural transformation during the high-temperature composite process and reacted with matrix also can cause degradation of performance of carbon fiber. These all limit the carbon fiber exert a good role in the composite material.To solve these problems, this article prepared a pyrolysis carbon coating on the carbon fiber surface to weaken the interface between matrix and fiber. More fiber pull-out phenomenon will happen after this. At the same time, the coating impeded the reaction between carbon fiber and the matrix. And it will ultimately improve the performance of the material. Subsequently, author analyzed the influence of pyrolysis carbon coating on axial tensile strength of monofilament and interfacial shear properties. The pyrolysis carbon coating can effectively improve the interfacial properties of carbon fiber, and toughened composites via weakened interface between carbon fiber and m atrix. But the study found that carbon fiber strength decreases after the pyrolysis carbon coating which was prepared by chemical vapor deposition method, and the strength of the carbon fiber gradually decreases with the increasing of the deposition time（increasing of thickness of the pyrolysis carbon coating）. To explain this phenomenon, this article discovered two main reasons through a variety of test and analysis. On one hand the introduction of the coating brings more defects. On the other hand, during the preparation of the coating process, the microstructure of carbon fiber changed, after high-temperature heat treatment. These both affected the performance of carbon fiber.For the carbon fiber oxidized easily in air at high teperatue, author continued to prepare a SiC protective layer on the carbon fiber surface which has been coated by a pyrolysis carbon layer, eventually it a SiC / C /Cf composite structure was obtained. SiC coating is so dense that it can prevent the diffusion of oxygen in the surface of carbon fiber and enhance the oxidation resistance properties of the material. SiC coating was prepared on the fiber surface using a chemical vapor deposition method and embedding method respectively. It was found that a uniform coating could be fabricated and the thickness of coating could be controlled via chemical vapor deposition method. So this experiment prepared the SiC coating by chemical vapor deposition in the carbon fiber surface which has been coated by a pyrolysis carbon layer.In this study, ZrB₂-SiC-Cf materials was prepared by hot pressing sintering. Then the effect of fiber surface coating on the mechanical properties of the composites was analyzed. The coating was found to change the fracture mode of the material, and the composites is not catastrophic damage when it suffered large loads. So the coating improved the toughening effect of carbon fiber. This article provides a new idea to improve the ultra-high temperature ceramic brittleness.