For most special ceramics, it’s hard to get densified product by only solid phase diffusion, so some certain additive will be added to generate glass phase or liquid phase. Due to rearrangement of particles and viscous flow in liquid phase, densified product can be obtained, meanwhile decrease sintering temperature. If liquid phase exists in the whole process of sintering, then it’s called liquid phase sintering, if liquid phase only exists at beginning stage of sintering and disappears later on, then it’s called transient liquid phase sintering.

Liquid phase sintering can decrease sintering temperature and increase density, furthermore, glass phase is an important part of some ceramic materials. For instance, in ZnO pressure-sensitive ceramic, continuous glass interphase between ZnO particles has high electrical resistivity, and forms high energy barrier, only with the interphase and main crystal ZnO, pressure-sensitive resistor can be constituted.

But for high temperature structural ceramics, existence of glass phase between crystals has negative effective to mechanical property under high temperature.