What is liquid phase sintering?
Liquid phase sintering is the process of introducing certain additives during the sintering process to form the glass phase and other liquid phases. Due to the rearrangement of particles in the liquid phase and the viscous flow, a dense product can be obtained and the sintering temperature can be reduced. It can not only reduce the sintering temperature and increase the density of the sintered body. And sometimes the glass phase is an important ceramic material component.
Several physical effects that occur during the sintering process
The presence of a liquid phase tends to intensify the sintering process. Sintering with the participation of the liquid phase generally has three stages. First, the formation, movement, and filling of the pores of the porcelain blank by the liquid phase. That is the particle rearrangement process. Second, the solid particle dissolution-precipitation process proceeds, and the resulting significant densification of the porcelain is damaged. Third, the connection and growth of solid particles are often accompanied by the formation of pores wrapped inside the solid particles.
- Lubrication effect. When the liquid phase appears, the liquid phase lubricates the powder particles. The friction between the powder particles is reduced. Which facilitates the relative movement of the powder particles and reduces the internal stress left during molding.
- Capillary pressure and the initial rearrangement of the powder particles. When the liquid phase can wet the solid phase well, most of the pores between the powder particles will be filled with the liquid phase to form a capillary liquid film. The existence of this liquid film generates huge capillary pressure between adjacent powders. Coupled with the lubrication of the liquid phase, the powder particles in the formed body are rearranged. A tighter space stacking can be achieved.
- Capillary pressure and smooth contact. The gap between the protruding parts of adjacent powder particles or the contact of spherical powder particles is small, and the capillary pressure is the largest. Compressive stress helps the dissolution of solids in liquids.
- Dissolution-precipitation process.
- Ripening adaptation process
- Formation of solid veins.
The liquid phase participates in several stages of sintering
Only when the amount of liquid phase is sufficient to fill the pores of the ceramic body. The first stage of sintering can ensure that the ceramic body is fully densified. The second stage of sintering is usually the stage of intense densification of the porcelain material. Experimental data show that when the liquid phase appears, in the green body formed with less liquid phase, the ceramic particles will no longer maintain a spherical shape. And gradually become the shape required for the closest packing.
Three prerequisites exist for liquid phase sintering: First, the system must have a certain liquid phase content. Second, the liquid phase must be able to wet the solid phase well. Third, the solid phase must have a significant solubility in the liquid phase. The following physical effects may occur during the sintering process.
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