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Refractory sintering

  • Time:Aug 26, 2023
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Refractory sintering refers to the process of heating refractory raw materials at high temperature to combine particles to form solid block materials with certain strength and stability. During this process, the binder and part of the moisture in the raw material will undergo chemical reactions and physical changes, which will promote the bonding between the particles and form a dense structure.Sintering of refractory materials usually needs to be carried out in a high temperature furnace. During the heating process, the surface of the refractory particles begins to soften, and the binder and other additives act as a bond to make the particles bond to each other. As the temperature increases, the bonds between the particles become stronger, forming a strong structure.

【1】 Sintering method of refractory materials

  1. Hot pressing sintering: This is a common refractory sintering method. During hot-press sintering, raw powders are heated to a temperature close to their melting point, and high pressure is applied to bond the particles. Hot-press sintering typically achieves densification and bonding of materials at relatively low temperatures.

  2. Self-firing sintering (or chemical reaction sintering): Some refractory materials have spontaneous combustion properties, and internal chemical reactions will occur under heating conditions to form a solid structure. This sintering method does not require external pressure, but the combination of materials is achieved by controlling the reaction conditions.

  3. Vacuum sintering: Sintering in a vacuum environment can prevent the oxidation reaction and the existence of impurities, thereby improving the purity and compactness of the refractory material. Vacuum sintering typically requires higher temperatures and longer processing times to ensure adequate bonding of the materials.

  4. Atmosphere sintering: Sintering in a specific atmosphere can control the chemical reaction and structure formation of the material. Common atmospheres include hydrogen, nitrogen, and inert gases. By adjusting the gas composition and pressure in the atmosphere, the sintering process and final properties of the material can be influenced.

  5. Microwave sintering: microwave sintering is a relatively new refractory sintering technology. Under the action of the microwave field, the energy is directly transferred to the interior of the material particles, causing them to heat up rapidly. This sintering method has the characteristics of rapid and uniform heating, which can achieve higher sintering efficiency and better quality control.

Sintering method of refractory materials

【2】 Why should refractories be sintered

  1. Improve compactness: During the sintering process of refractory materials, through the diffusion and rearrangement at high temperature, the particles are combined, thereby improving the compactness of the material. This helps to reduce porosity, increase the compactness of the material, and improve the slag erosion resistance and temperature difference resistance of the refractory.

  2. Improve refractoriness: Sintering can promote chemical reactions in refractory materials to form more stable compounds and crystal structures. These newly formed compounds have higher melting points and better refractory properties at high temperatures, improving the high temperature resistance of refractory materials.

  3. Improve mechanical strength: During the sintering process, the combination of particles at high temperature makes the structure of the refractory material more compact and strong, and increases the bonding force between particles. This results in increased mechanical strength of the refractory, providing better compressive and tensile strength.

  4. Promote crystal growth: During the sintering process of refractory materials, crystal particles gradually grow and crystallize. This helps to increase the material's grain size and crystallinity, improving the material's thermal conductivity and shock resistance.

  5. Improve chemical stability: some original forms of refractory components will undergo chemical reactions during sintering to form more stable and durable compounds. These compounds have good corrosion resistance and can resist acid and alkali corrosion and other chemical media.

Why should refractories be sintered

【3】 How to judge sintering of refractories

  1. Visual observation: Preliminarily judge the sintering degree by visually observing the appearance and color change of the refractory surface. Typically, unsintered or incompletely sintered refractory surfaces will exhibit a rougher, uneven texture and may be lighter in color. The surface of the fully sintered refractory material will be smoother and more uniform, and the color may be darker.

  2. Hardness test: Use a hardness tester, such as a Rockwell hardness tester or a Vickers hardness tester, to perform a hardness test on the surface of the refractory material. The higher the degree of sintering, the hardness of the material generally increases. By comparing with standard samples of known sintering degree, the sintering degree of the refractory material can be roughly judged.

  3. Sound test: tap the surface of the refractory with your fingers and listen to the sound, and you can preliminarily judge the degree of sintering. Generally speaking, fully sintered refractory materials will produce crisp sounds, while unsintered or incompletely sintered materials will produce dull sounds.

  4. Physical property test: By conducting physical property tests, such as density measurement, compressive strength test, etc., the sintering degree of refractory materials can be further evaluated. Fully sintered materials generally have a higher density and higher compressive strength.

How to judge sintering of refractories

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