Ceramic sintering capacity
Ceramic sintering is a general term for the densification process and phenomena of raw ceramic blank at high temperature.With the increase of temperature and the extension of time, the solid particles bond with each other, the grains grow up, the interstitial (stoma) and grain boundaries gradually decrease, and through the transfer of materials, the overall volume shrinks, the density increases, and finally becomes a hard polycrystalline sinter with a certain microstructure.
This phenomenon is called sintering.Sintering is a process of reducing the pores in the molding body, enhancing the bonding between particles and improving the mechanical strength.During the sintering process, with the increase of temperature and the extension of heat treatment time, the pores are continuously reduced, and the bonding force between particles is continuously increased. When a certain temperature and a certain heat treatment time are reached, the bonding force between particles presents a maximum value.When the maximum value is exceeded, the pore will slightly increase, and the grain size increases and the mechanical strength decreases.Before the sintering of ceramic products, they should be lined up before sintering.
Proper increase of sintering temperature is beneficial to diffusion and sintering, speed of sintering and densification.Control of zirconia ceramics sintering temperature is important, usually under 600 ℃ should be slow to phase in 1000 ~ 1500 ℃ temperature strictly controlled and slower, as far as possible at above 1500 ℃ heating speed can be accelerated, to prevent coarse grain.Pressure also causes the gap between powder grains to decrease and the diffusion distance to decrease.
Selection of sintering method is the key to make zirconia ceramics have ideal structure and predetermined properties.Proper sintering method can effectively reduce sintering temperature.Atmospheric pressure sintering Al2O3 ceramics at above 1800 ℃, hot pressing (20 mpa) sintered at 1500 ℃ can get close to the theoretical density of the products, and hot isostatic pressing sintering (400 mpa) has reached the densification at about 1000 ℃.
Zirconia ceramic additive
Since the slurry of zirconia ceramics has a high melting point and is difficult to be sintered, some additives promoting sintering can be added to improve the sintering performance.The influence of forming method is based on the need of selecting the appropriate forming method, which can obtain the blank body with uniform microstructure and uniform distribution of each phase. By controlling and eliminating the defects in the forming process, the sintering temperature and shrinkage rate of the blank body can be effectively reduced, the densification process can be accelerated, and the machining quantity of sintered products can be reduced.
The atmosphere has great influence on the sintering of zirconia ceramics.Generally, the lower the oxygen ion partial pressure in the atmosphere, the better the zirconia sintering.In the case of sintering in hydrogen atmosphere, a sintered body close to theoretical density can be obtained because of the small radius of hydrogen atoms and the easy diffusion of hydrogen atoms.The co-h2 atmosphere can make the oxygen ions in the zirconia lattice easier to lose, form vacancy and accelerate the diffusion of cations, thus effectively promoting sintering and obtaining a good density, which is easier to be sintered than the hydrogen atmosphere.