Views: 7 Author: Site Editor Publish Time: 2018-11-25 Origin: Site
Sintering is a process in which heat is used to transform a green body into a dense piezoelectric ceramics body having a certain microstructure. They are sintexring theory points and sintering process, consciously perform the sintering process, here briefly introduce the main points of sintering theory and solid phase sintering process.
According to the thermodynamics and kinetics of sintering, the theoretical points are:
(1) Sintering is a process with phased nature; sintering is generally divided into two categories: solid phase sintering and liquid phase sintering.
(2) The sintering process has its developmental causes (thermodynamic driving force).
External cause is externally given thermal energy; internal cause is reduction of total interface energy of porcelain.
(3) There is material transfer during sintering. The mass transfer model and mechanism of soft material piezoelectric ceramic are mainly aspects. 1 flow; 2 diffusion; 3 steaming hair and agglomeration; 4 dissolution and precipitation.
(4) The speed of the specific sintering process or stage depends on the densification rate (growth kinetic equation.
Grain growth is the result of grain boundary movement in the green body. The curved grain boundary always moves toward the center of curvature, and the smaller is the radius of curvature, the faster the movement. Grains with more sides than six sides tend to grow larger, and grains smaller than six sides are easily swallowed, and hexagonal (grain cross-section) grains with a grain boundary angle of 120°are most stable. At this stage, the line shrinkage and bulk density increased significantly, the apparent porosity of pzt ceramic disc decreased greatly, and the pores became isolated from continuous penetration. Under the obstruction of the second phase inclusion (impurities, pores, etc. in the grain boundaries), the grains gradually slow down.
The grain slowing habit is corrected and grown until a desired degree of sintering is achieved. At the same time, most of the pores are discharged from the grain boundary, and the remaining pores are reduced in volume, and finally become closed pores that are isolated from each other and not connected to each other. Such pores are generally at the junction of a plurality of crystal grains, and the internal pressure is high, further eliminating difficulties. After the optimum sintering temperature is reached, the temperature of piezoelectric discs piezoelectric ceramics is increased, the grain boundary motion is intensified, the secondary grain length is a large number, the closed pores are expanded, cracked, and the density is lowered, which is called over-burning. The performance of porcelain after burning is low and should be controlled.
