| Mullite-corundum multiphase ceramic which possesses many excellent properties such as high melting point, high thermal shock resistance, high creep resistance, oxidation resistance are used as high temperature kiln furniture and ceramic roller, and has been considered one of the most promising high temperature thermal shock resistance ceramics for abundant raw materials and high cost performance. At present, the researches on mullite-corundum multiphase ceramic mainly focused on the macroscopic properties, there existed great differences each other, and thermal shock resistance was relatively poor.In this paper, the present status of thermal shock resistance ceramics and mullite-corundum multiphase ceramics and the methods for improving thermal shock resistance were systematically reviewed. By means of the methods of thermal expansion dismatch and in-situ synthesis of whisker, the mullite-corundum thermal shock resistance multiphase ceramic was prepared at about 1700癈 with composite aggregate (mullite and corundum), matrix (alumina powder and silicon powder), binder (silicon-alumina gel or clay) and additive (aluminum fluoride) as raw materials. With XRD (X-ray Diffraction), SEM((Scanning Electron Microscope), TEM (Transmission Electron Microscope), the characteristics of the binder and additive were analyzed, the mechanical properties and structure properties of the ceramic such as strength, retention of flexural strength, fracture toughness, and apparent porosity, and microscopic structure were measured and analyzed, and the relationships between the properties of the ceramic and grain size gradation, kinds and content of the binders, and milling time of additive were discussed.The research results of the properties of the binders and additive show that the clay and a-A!2O3 can form granular mullite after high temperature heat treatment, and form columnar mullite when aluminum fluoride is added; the silicon-alumina gel can form mullite crystalline phase (the grain size is 100~500nm) after heat -treatment At 1250癈 and form mullite whisker when aluminum fluoride is added, the size of theinwhisker is 28um on length, is 700nm on diameter, and the ratio of length and diameter is 30.The research results of the structure and properties of the multiphase ceramics show: (Dwhen the mass ratio of mullite and corundum is 3, thermal expansion discrepancy of the multiphase ceramics is more suitable, the thermal shock resistance becomes better, and the retention of flexural strength reaches 51.3 %; ￤hen the binder is silicon- alumina gel, the properties of the ceramics are better than those when the binder is the clay, after heat-treatment the silicon-alumina gel forms fine mullite particle, and incorporate into the multiphase ceramics as toughening phase, which enhances thermal shock resistance and improves comprehensive properties; when the content of the silicon- alumina gel is 9%, the retention of flexural strength and fracture toughness are 64.5% and 1.84MPa ?m'/2 respectively; ￤hen the aluminum fluoride additive is added, the mullite whiskers are in situ synthesized in the multiphase ceramics as toughening phase to enhance thermal shock resistance; the toughening effect of the whisker also relates to milling time of additive, when the milling time is 40h, the thermal shock resistance becomes better, and the retention of flexural strength and fracture toughness are 69% and 3.03MPa ?m172 respectively; ?amorphism silicon powder can improve sintering of the ceramics, enhance the mechanical properties, but not for thermal shock resistance.On the basis of above studies, the industrial production of mullite-corundum thermal shock resistance multiphase ceramic kiln furniture was carried out through optimizing proportion and parameters of process, the thermal shock resistance times of the kiln furniture reaches over 45, and the flexural strength and compression strength are 13.95MPa and 75MPa respectively. |
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