When selecting and purchasing refractory materials, we often find ourselves overwhelmed by their diverse performance metrics, operating temperatures, and application ranges.
However, understanding the raw materials used in various refractories enables quick identification of suitable options.
Therefore, today we introduce the 8 most common raw materials for refractories used in the high-temperature kiln industry. This will help you gain a deeper understanding of refractories, enabling you to recognize, differentiate, and select them with confidence and clarity!
The primary raw materials in modern high-efficiency refractory products now extensively utilize high-purity materials, homogeneous materials, electrically fused materials, and synthetic materials, significantly enhancing the performance of refractory products. So, what are the common raw materials used in refractory materials for the cement industry?
1. Mullite
Mullite is a refractory material with the primary crystalline phase 3Al₂O₃·2SiO₂. Natural mullite is extremely rare and is typically synthesized artificially through sintering or electric melting methods.
Characteristics: Uniform expansion, excellent thermal shock stability, high load-bearing softening point, low high-temperature creep value, high hardness, and good resistance to chemical corrosion.
2. Magnesium-Aluminum Spinel
Magnesium aluminum spinel is synthesized through high-temperature sintering or electric melting using industrial alumina and light-burned magnesium oxide as raw materials. Its chemical formula is MgO·Al₂O₃, with MgO content at 28.2% and Al₂O₃ content at 71.8%.
Characteristics: High-temperature resistance, wear resistance, corrosion resistance, high melting point, low thermal expansion, low thermal stress, excellent thermal shock stability, strong resistance to alkali slag erosion, and good electrical insulation properties.
3. Silicite, Spinel, Kyanite
It is commonly referred to as tri-stone, with the chemical formula Al₂O₃ – SiO₂. Its theoretical composition consists of 63.1% Al₂O₃ and 36.9% SiO₂.
Characteristics: Upon heating, it irreversibly transforms into mullite and quartz. It exhibits excellent slag resistance, thermal shock stability, and a high load-bearing softening point.
Kyanite group minerals serve as premium raw materials for amorphous refractories. Due to their minimal volume change during heating, sillimanite and andalusite can be directly used for brick manufacturing or as refractory aggregates.
4.High-Alumina Bauxite
China’s high-alumina bauxite resources are primarily distributed in Shanxi, Henan, Guangxi, and Guizhou provinces. Calcined high-alumina bauxite clinker, produced through high-temperature calcination, is mainly used in high-alumina refractories and can also be employed to manufacture fused brown corundum and sub-white corundum.
Characteristics: Low absorption rate and stable performance (in recent years, China has exclusively produced bauxite clinker).
5.Magnesite
Magnesite is a natural alkaline mineral raw material primarily composed of magnesium carbonate (MgCO₃). It is mainly used in the production of sintered magnesia, fused magnesia, and alkaline refractory materials.
China possesses abundant magnesite resources of high quality and large reserves, primarily distributed in Liaoning Province.
6.Sintered magnesia
Sintered magnesia is produced by fully sintering magnesite ore at temperatures between 1600 and 1900°C, with the primary mineral being periclase. It serves as one of the main raw materials for manufacturing basic refractories.
Characteristics: High-quality magnesia typically contains over 95% MgO, with a bulk density of no less than 3.30 g/cm³. It exhibits excellent resistance to alkali slag erosion.
7. Electro-fused magnesia
Electrofused magnesia is produced by melting carefully selected magnesite or sintered magnesia in an electric arc furnace at temperatures exceeding 2500°C.
Characteristics: Compared to sintered magnesia, it features coarse grains of the primary crystalline phase, periclase, which are in direct contact. It exhibits high purity, a dense structure, strong resistance to alkaline slags, and excellent thermal shock stability.
8.Silicon carbide
Silicon carbide is typically produced by high-temperature smelting in an electric furnace using a mixture of coke and silica sand as primary raw materials. At temperatures between 1400-1800°C, β-SiC (cubic crystal structure) forms, while temperatures exceeding 1800°C yield α-SiC (hexagonal crystal structure).
Characteristics: High hardness, high thermal conductivity, low thermal expansion coefficient, and excellent resistance to neutral and acidic slags.
More details about refractory material
What are the most refractory materials?
The oxides of aluminium (alumina), silicon (silica) and magnesium (magnesia) are the most important materials used in the manufacturing of refractories. Another oxide usually found in refractories is the oxide of calcium (lime). Fire clays are also widely used in the manufacture of refractories.
What are examples of highly refractory materials?
Refractory raw materials, such as alumina, magnesia, silica, zirconia, and carbon, form the foundation of all high-temperature industrial processes. Alumina and magnesia are the two most widely used oxides, valued for their high melting points, corrosion resistance, and mechanical strength.
What exactly is refractory material?
Refractory materials are inorganic (not from living material), non-metal substances that can withstand extremely high temperatures without any loss of strength or shape. They are used in devices, such as furnaces, that heat substances and in tanks and other storage devices that hold hot materials.
Can refractory materials be repaired?
Begin by cleaning the surface of the refractory of any loose material with the goal of “V”ing out the crack. Once complete, you can apply the appropriate refractory repair compound to the crack. This often requires the crack be at least 5 mm in size. Work the compound into the crack and finally smooth it out.