| More and more researchers have paid attention to research alumina hollow sphere, because of its unique characteristics, such as low density, high specific surface area, low thermal conductivity, good mobility and other characteristic. In this paper, novel micron-sized alumina hollow spheres are used as raw materials to fabricate alumina hollow sphere ceramics by dry pressing process, processing parameters of dry pressing and the mechanical properties of alumina hollow sphere ceramics was investigated. Sintering additives were used to coat hollow spheres, in order to enhance the interface bonding strength of between hollow spheres and improve the mechanical properties of hollow sphere ceramics. The main findings are as follows:Alumina hollow sphere ceramics were first fabricated by dry pressing process. The effect of processing parameters (such as dry pressure and holding time), presinter temperature, addition the amount and the diameter size of alumina hollow sphere on the properties of alumina hollow sphere ceramics was investigated. The results show that:6MPa pressure and1min holding time is the optimal processing parameters of dry pressing. With the increase of the addition amount of alumina hollow spheres, the bending strength, fracture toughness and shrinkage of alumina hollow sphere ceramics is decreased; the porosity of alumina hollow sphere ceramics is increasing. With the increase of the presinter temperature and diameter size of alumina hollow sphere, the bending strength and shrinkage of alumina hollow sphere ceramics is decreased, the porosity of alumina hollow sphere ceramics is increasing. The bending strength and fracture toughness of alumina hollow sphere is54MPa and1.29MPa·m1/2by dry pressing using the optimization processing parameters, respectively.Alumina hollow spheres were coated by slurry impregnation. The effect of MgO-Al2O3-SiO2sintering additives on the mechanical properties of alumina hollow spheres ceramics was investigated. The results show that:the sintering temperature is1500℃, with the increase coating content of kaolin and talcum, the bending strength and fracture toughness of alumina hollow sphere ceramics firstly increase and then decrease. When kaolin and talcum coating content is11.5wt.%, and the bending strength (177MPa) and fracture toughness (3.08MPa·m1/2) of alumina hollow sphere ceramics reach the maximum, respectively. The bending strength of coated alumina hollow sphere ceramics increased two times, comparing with uncoated alumina hollow sphere ceramics; the sintering temperature is1550℃, with the increase coating content of kaolin and talcum, the bending strength of alumina hollow sphere ceramics is increasing and the fracture toughness of alumina hollow sphere ceramics firstly increase and then decrease. When kaolin and talcum coating content is11.5wt.%, the bending strength of alumina hollow sphere ceramics is168MPa, the fracture toughness (3.33MPa·m1/2) of alumina hollow sphere ceramics reach the maximum.Alumina hollow spheres were coated by chemical co-precipitation. The effect of CaO-SiO2sintering additives on the mechanical properties of alumina hollow spheres ceramics was investigated. The results show that:with the increase of sintering additives coating content, the bending strength and fracture toughness of alumina hollow sphere ceramics is increasing. When sintering additives coating content is9.8wt.%, the bending strength and fracture toughness of alumina hollow sphere ceramics reach to191.09MPa and3.97MPa·m1/2, respectively. The bending strength of coated alumina hollow sphere ceramics increased two times, comparing with uncoated alumina hollow sphere ceramics. Coated alumina hollow spheres with sintering additives can significantly improve the bonding strength between alumina hollow spheres and increase the bending strength and fracture toughness of alumina hollow sphere ceramics.Alumina hollow sphere coated by sintering additives which effectively improve the interfacial bond strength between the hollow spheres and greatly improve the mechanical properties of ceramic hollow spheres ceramics, compared with other method. Preparation of porous ceramic with ceramic hollow spheres is a new method for preparing high flexural strength and good fracture toughness of porous ceramics. |
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