Calcination

　　1. Crystalline phase formation: Minerals in refractory materials undergo a process of crystalline phase formation at high temperatures. During the calcination process, the compounds and oxides in the original material react chemically, transform into a crystalline phase, and form a uniform and dense grain structure through the crystallization process. These crystalline phases endow refractory materials with desired physical and chemical properties, such as high temperature stability, thermal shock resistance, etc.

　　2. Increased hardness and strength: After the refractory raw materials are calcined, the crystal structure is enhanced, and more bonding points and connections are formed between the grains. This leads to a significant increase in the hardness and strength of the refractory material, allowing it to withstand mechanical and thermal stress in high-temperature environments, preventing cracking and damage.

　　3. Exclude moisture and volatiles: refractory raw materials usually contain a certain proportion of moisture and volatile components. During the calcination process, the high temperature drives away moisture and volatile matter from the raw material, so that the refractory material can obtain lower water content and volatile matter content. This is very important because the presence of moisture or volatile components at high temperatures can cause the refractory to burst or lose stability during service.

　　4. Dimensional stability: The calcination process can change the volume and size of refractory raw materials, and achieve stable shape and size through rearrangement of crystal structure. This is very important for the assembly and application of refractory materials, ensuring its precise fit with other components, providing good sealing performance and structural stability.

　　5. Special performance control: During the calcination process, the special performance of the refractory material can be controlled by adjusting the calcination process parameters (such as temperature, time, etc.). For example, the calcination process can improve the corrosion resistance, thermal conductivity, electrical conductivity, etc. of refractory materials to meet the needs of specific applications【more】

　   1. Structural stability: At high temperatures, refractory materials need to have good structural stability to resist mechanical effects such as thermal expansion, contraction and thermal stress. The calcination process can make the particles in the refractory raw materials more tightly bonded, forming a strong structure, and improving the strength and stability of the refractory material.

　　2. Ensure chemical purity: Some refractory raw materials may contain impurities or volatiles, such as moisture, organic matter, sulfur, etc. Calcination can remove these impurities through high temperature treatment, improving the purity and stability of refractory materials.

　　3. Improve refractory performance: During the calcination process, some components in refractory materials may undergo crystalline phase transition or liquid phase formation, thereby changing the crystal structure and chemical properties of the material. This can improve the corrosion resistance, wear resistance, high temperature resistance and other specific properties of refractories, making them more suitable for applications in high temperature environments.

　　4. Adjusting material properties: By controlling parameters such as temperature, time, and atmosphere during the calcination process, the microstructure, crystal size, and chemical composition of refractory materials can be adjusted to meet specific application requirements. For example, calcination can make certain materials denser and more uniform, or change their thermal conductivity.

　　5. Reduce the water absorption of materials: For some refractory materials, controlling the calcination conditions can make them have lower water absorption, so as to avoid the material from absorbing water to swell or being damaged by moisture in a humid environment【more】

　　The principle of calcination involves the following aspects:

　　1. Crystalline phase transition: During the calcination process, some substances in the refractory may undergo a crystalline phase transition. This crystalline phase transition can change the material's crystal structure and lattice arrangement, thereby affecting its physical and chemical properties.

　　2. Sintering: During calcination, the particles in the refractory gradually come into contact, interact and form a tighter structure. At high temperatures, sintering occurs between the particles, where the surfaces of the particles bond together to form a strong structure. This sintering process increases the strength and compactness of the refractory.

　　3. Liquid Phase Formation: Certain refractories form a liquid phase during calcination. When certain components in the material reach the melting point, the formation of a liquid phase can fill the voids between particles, promote particle bonding and increase the density of the material. The formation of a liquid phase can also promote crystal growth and crystalline phase transition.

　　4. Exclusion of volatile matter: refractory materials may contain some volatile substances, such as moisture, organic matter, etc. During calcination, high temperatures cause these volatiles to evaporate or decompose, thereby being excluded from the material, increasing its stability and durability【more】