Process Research On Low Temperature Synthesis Of Zircon Powder By The Sol-Gel Approach

Zirconium silicate whose chemical formula is ZrSiO4 and which belongs to the teragonal crystal system is of the island structure of silicate minerals. Because ZrSiO4 has so many excellent properties, for example high melting point, low thermal conductivity, low expansion coefficient, wonderful chemical and phase stability and so on, so it is widely used in refractory materials and pigment of zirconium based. Meanwhile sintered zirconium silicate is provided with superb thermal shock resistance, therefore, it becomes an important candidate material for high-temperature structural ceramics. The widespread use of zirconium silicate in ceramic industries is for its features such as nice chemical stability, good resistance to acids and alkali and organic solvents, great mechanical strength, strong ability of antimicrobial resistance and resistant to high temperature. In addition, it is also used in surface protection of metallic materials in corrosive environment. Zirconium silicate existing in the nature includes impurities like alumina, ferric oxide and titanium oxide, etc. which lead to the low purity. So the application of zirconium silicate is limited. It is well known that the synthesis temperature for the high-purity of zirconium silicate reaches up to 1500 degrees. In consequence, it is significant to study process research of zirconium silicate powders in low temperature.In this paper, zirconium silicate powders are prepared by sol-gel method using zirconium oxychloride and tetraethoxysilane as raw materials, deionized water and ethanol as dissolvant, NaF as a mineralizer to promote crystallization of zirconium silicate. The influences of sol-gel synthesis parameters such as the ratio of precursor, calcining temperature, whether or not the mineralizer contained and the content of mineralizer on preparing zircon particles are researched by means of XRD and SEM as well. The results show that the synthesis temperature of zirconium silicate can be greatly reduced and the synthesis rate of zirconium silicate can be greatly increased by improving the ratio of precursor properly and adding moderate content of mineralizer. The original synthesis temperature of zircon is as high as 1250℃ without the introduction of any mineralizers to precursor sols, when the temperature turns to 1500℃, the synthesis rate of zircon powder is not very high, and that after adding sodium fluoride as mineralizer to the sols, the diffraction peak of zircon appears at 550℃, and the zircon powder which is calcined at the temperature of 800 degree not only has high synthesis rate, but also shows good crystallinity. From what I have mentioned above, we can work out that the optimal process parameters is that adding sodium fluoride as a mineralizer, deionized water and ethanol as dissolvant, making the molar ratio of tetraethoxysilane and zirconium oxychloride become 1.2:1 and the molar ratio of sodium fluoride and tetraethoxysilane turn into 0.3:1, the best calcining temperature is 800 degree which indicates the successful synthesis of zircon at low temperature.