The firing of refractory materials is a very complex high-temperature process. In this process, a series of physical and chemical changes occur in the batch, such as decomposition, dehydration, phase change, melting, solid-phase reaction and sintering, which can be roughly divided into the following stages:
1. Water discharge stage of green body. 10 ℃ - 200 ℃, mainly discharging the residual free water and adsorbed water in the brick blank
2. Decomposition and oxidation stage. 200 ℃ - 1000 ℃, discharge of chemically bound water and physical and chemical changes, decomposition of compounds, oxidation and combustion of organic matters, and crystal transformation or formation of a small amount of liquid phase. At this time, the quality of the brick is reduced, the porosity is increased, and the strength is changed
3. Liquid phase formation and new phase formation stage. Above 1000 ℃, the decomposition of this stage continues. With the increase of temperature, the amount of liquid phase increases and some new mineral phases begin to form
4. Sintering stage. The sintering temperature of the brick is generally 0.3-0.9 times of the melting temperature of the material. The green body shrinks with the extension of time and the increase of temperature to form dense polycrystalline, and the strength and hardness increase. After the sintering, the green body forms a certain mineral phase microstructure, which makes the refractory material have specific properties
5. Cooling stage. At this stage, the crystallization of refractory phase, the transformation of some crystal forms, the solidification of glass phase, etc. occur, and the strength, density and volume of brick have corresponding changes
