Preparation And Research Of Electro Fused Zirconia Powders

With the progress in the research of zirconia materials, its application area is expanding rapidly. Zirconia powders produced by chemical method are characterized by the advantage of high purity, excellent crystallinity and high activity of the powder surface. Compared with the production process of chemically prepared zirconia, the production process of fused zirconia is more efficient, environmentally friendly, and with lower cost. But in practical applications, zirconia produced by chemical method performs better than fused zirconia. More study are needed in order to improve the performance of fused zirconia powder.Partially stabilized zirconia powders with different CaO content were prepared by electric melting and blowing process, then the powders were heated under different temperatures, and the impact of heat treatment process on the phase transition behavior of zirconia were studied.During the production process of fused zirconia, high temperature melt were so quickly cooled and solidified that growth process of zirconia grain is inhibited, and the grain size of obtained powders were about 10nm, which smaller than the critical size of phase transformation. Thus the stable phase zirconia was composed by two parts:stabilized zirconia doped by calcium ions, and metastable tetragonal zirconia without any doping.When heated under high temperature, the particle size of zirconia will gradually grow up, and finally surpass the critical size of phase transformation, and occurred the phase transformation from tetragonal to monoclinic, accompanied by volume expansion effect, which contributed to the cracking of samples prepared with the powder during sintering process.Yttrium oxide can significantly improve the densification process during the sintering of the fused zirconia products. Yttrium ions segregated on the surface of zirconium oxide particles. The reaction between yttrium and zirconia formed Y2O3-ZrO2 binary system, which act as the mass transfer channel to promote the grain boundary diffusion process. By adding 1mol% Y2O3, the best sintered sample was achieved, with the density reaching 5.61g/cm3, grain size of sample was small, the combination between grains was dense, and no residual pores were observed. Besides, the segregation of yttrium ions on the surface of zirconia grains inhibited the migration and integration of grain boundaries, resulting to the refining of grains. When yttrium oxide and magnesium oxide were added into fused zirconia powder at the same time. MgO-Y2O3-ZrO2 ternary system were formed, promoting the grain boundary mass transfer process. And because radius is smaller than Zr4+ Mg2+ tend to dissolve into the zirconia lattice, forming large amount of lattice defects, thus contributing to the volumetric mass transfer process. When lmol% yttrium oxide and 8mol% magnesium oxide were added, the best sintered sample was obtained, which density was of 5.58g/cm3. However, excessive additives would lead to the decline of sintered density and flexural strength of samples, and the increase of residual pores and disappears grain boundaries.