Sintering is the last process of forming zirconia ceramics. Before sintering, the ceramic green body is composed of many single solid particles. In fact, the degreasing process is very important in the previous process. So what factors affect the firing quality of zirconia ceramics?
Simply put, organic matter is separated from the ceramic body by heating or other methods. Debinding is a very important stage in the entire manufacturing process and has a great influence on subsequent sintering. If it is not well controlled, it will cause a series of problems, such as pores or microcracks. Therefore, zirconia ceramics have very high requirements for degreasing during the firing process.
The quality of the original powder
Generally speaking, the higher the degree of dispersion of the material, the higher its surface energy, which is beneficial to sintering. At the same time, in the process of full pulverization, fine particles can increase the driving force for sintering, shorten the distance of atom diffusion, and increase the solubility of particles in the liquid phase, thereby effectively increasing the sintering rate.
The quality of additives
Under normal circumstances, the addition of additives will inhibit the growth of grains; however, in some cases, the result is just the opposite. For example, in solid phase sintering, adding a small amount of additives can change the properties of the liquid phase (such as viscosity, composition, etc.), so as to promote sintering.
Sintering temperature and holding time
Ambient temperature and high temperature retention time are important external factors for the complete sintering of the green body. The greater the lattice energy in the crystal, the stronger the ion bonding, the more difficult the ion diffusion, and the higher the sintering temperature. Different types of crystals have different bonding conditions, so the sintering temperature varies greatly. Even for the same crystal, the sintering temperature is not a fixed value.
During the sintering process, if the migration direction of particles or vacancy defects is appropriate, the greater the speed and efficiency, the better the sintering. This effect can improve the diffusion efficiency of particle or vacancy migration, which is called migration driving force, including surface energy, environmental pressure and grain boundary free energy. The energy consumption for completing the sintering process is reduced, the density of the sintered body is increased, and the green body that cannot be sintered at normal temperature can be fired. Generally speaking, the higher the molding pressure, the closer the contact between the particles, which is beneficial to sintering.
Different sintering atmospheres have different effects on the sintering process of ceramics, either promoting sintering or hindering sintering.
Each of the above factors will affect the firing of zirconia ceramics, as well as several main factors affecting the firing of zirconia ceramics: degreasing stage, raw powder, additives, sintering temperature and time, pressure and sintering atmosphere.