are generally prepared by means of zirconia powder through the process of molding and presintering to obtain zirconia porcelain pieces, and then the secondary sintering is carried out to improve its density and mechanical strength.
Goes on in the process of sintering molding contained in the body of the composition such as volatile organic solvent, adhesive and decomposition of atoms in the ceramic particles have enough energy to migrate, ceramic powder particles can mutual bond formation of sintering neck, so as to make the grain growth, grain boundary, lower porosity, shrinkage and density increase, eventually forming dense, hard all porcelain dental zirconia ceramic structure.
(1) initial stage of sintering
At this stage, the zirconia ceramic particles began to bond, and the contact points between the particles gradually formed the sintered neck through the processes of nucleation and grain growth, but the shape of the particles and internal grains did not change significantly.At this time, the linear shrinkage rate of ceramics is generally about 2 ~ 3%, and there is no obvious densification process.
(2) intermediate stage of sintering
When the powder particles are in the middle stage of sintering, with the growing of sintering neck, the atoms in them accelerate to migrate to the joint surface between particles, which makes the distance between particles shrink continuously and finally forms the continuous pore network.
During the whole process, the grain size increases continuously, the density and strength of the particles are improved, and the linear shrinkage rate of the whole molding body is over 10%.
(3) later stage of sintering
When the sintering behavior reaches the later stage, the pores between the particles are continuously spheroidized and shrunk, and most of the pores are separated into closed pores, and the substances on the grain boundary continue to migrate to pores, causing the grains to continue to grow.
At this stage, the porosity decreases, the shrinkage rate further decreases, and the density of ceramics is very high.