Research On Using Low-grade Raw Material To Produce Self-strengthening Porcelain

In recent years, porcelain industry has been developed greatly in China, and it has been the largest producer around world, but it is not powerful country in porcelain. The main challenges are the high sintered temperature, low toughness and high-grade raw material decrease fast. In conventional porcelain material, the body is composed of cristobalite, mullite crystal phase and feldspathic glass, the thermal expansion of the cristobalite is 11×10-6/℃, the mullite is 5.7×10-6/℃ and silicate glass is 5.3~5.8×10-6/℃. It is obviously that the thermal expansion among these three phases are quite different, this would make the body be cracked easily during the cooling process, and the toughness strength of porcelain is decreased obviously. The Al is low and Fe, Ti are high in the low-grade raw material, so it is hard to be used in the porcelain industry.In order to improve strength of the porcelain, and the low-grade raw material be used in porcelain industry. The Ca3(PO4)2-Si O2-Al2O3 phase diagram is used in this study, the Ca3(PO4)2 is added in low-grade raw material, and anorthite(the thermal expansion is 4.82×10-6/℃) would generate in the body, the cristobalite would be decreased, the feldspathic glass would be transferred into silicate and phosphate composite glass(the thermal expansion is 5.6~6.2×10-6/℃). So in this study, Firstly the Ca3(PO4)2 is added in different Kaolins, and composition of the crystal phase and glass, microstructure of the porcelain body, whiteness of the sample etc are studied. After studying the sintered kaolins and the calculation based on thermodynamic, the formation of anorthite is earlier than mullite in the system of Ca3(PO4)2-Si O2-Al2O3, when the temperature is high, a part of anorthite will milt into glass, the other will be reaction of mullite. The structure of mullite is mainly acicular. The content of quatz will be decreased, the sintered temperature will be reduced. And the whiteness of body will be improved when the content of Fe is high.Secondly the Ca3(PO4)2 is added in the low-grade porcelain raw body to prepare self-strengthening procelain, the appearance, water absorption, bulk density, bending strength are studied of the porcelain body. The result shows that. when the content of Ca3(PO4)2 is 5% and the sintered temperature is 1220 ℃, the appearance of self-strengthening porcelain is fine and the bending strength reaches maximum 108.2MPa, 19 MPa higher than the raw body sintered at optimum sintered temperature 1320 ℃, the crystal structure is mainly composed of small quartz granules, interconnected nano acicular mullite rodlike and anorthite. In order to improve the microstructure further, increase the amount of mullite, 3% modified kaolins and 3% of firing additives are added in the existing formula respectively. The result shows that. when the sintered temperature is 1220 ℃, the appearance of self-strengthening procelains are fine and the bending strength reach maximum 115.5MPa and 114.9MPa respectively.