过烧功能瓷中气孔形成机理的探讨

瓷件在过高的烧成温度下易形成大量气孔,使瓷件的致密性降低,性能变劣。过烧的原因,一般认为是到了烧结的最高温度时保温时间过长,或烧成温度偏高。作者认为过烧气孔的形成原因,除了晶界的快速运动把气态杂质陷入晶体内部形成气孔外,还由于存在着肖特基缺陷而在晶体内缔聚形成气孔。

On the Mechanism of Gas Cavity Formation in Overfired Functional Ceramics

Large quantities of gas cavities will be formed in a ceramic piece if overfired. It is pointed out that, apart from the gas voids formed by the gas on the grain boundary trapped into the interior of crystal owing to too rapid growth of crystal, there are gas cavities formed by the accumulation of lattice vacancies due to Schotty thermal defects, etc. occurring at high temperatures. In general, the Schotty defect is the dominant one among the thermal defects in an oxide crystal. As the temperature increases, the diffusion coefficient goes up and the time required for lattice vacancy to reach the equilibrium state decreases. In fact, the density of lattice vacancy increases exponentially with the temperature. With the increase of the density of lattice vacancy in the body, there is greater probability for the lattice vacancy to meet with each other. When two or more vacancies meet, they will probably accumulate to form (VMVX)n. In a semifinished product, all cavities, surfaces and cracks can be the lattice vacancy source for Schotty thermal defect. At high temperatures, the density of the lattice vacancy in the body is high and as the temperatnre decreases, the lattice vacancy will probably accumulate further to form small but uniformly distributed gas cavities.