Introduction of Alkaline Refractory Castables

2023-06-08 10:56:36

Alkaline refractory castables are castable refractory materials mainly composed of magnesium oxide, which is divided into basic castable materials such as magnesium, aluminum magnesium, spinel, magnesium, magnesium silicon, and magnesium carbon.

Magnesia (periclase) refractory castable is made of fused magnesia or sintered magnesia aggregate and fine powder. The magnesia refractory castable combined with high magnesium cement has high purity, and a small line change rate after burning, It has the advantage of high softening temperature under load, but with the increase of heat treatment temperature, especially between 400~1200°C, the cementation will be lost due to the dehydration of magnesium hydroxide generated by the hydration of magnesia, and the combination of refractory aggregate and powder Very loose, and the solid phase reaction is very weak, resulting in a sharp drop in the strength of the refractory castable, prone to loosening and peeling. Magnesium refractory castables combined with water glass have the advantages of high strength, strong corrosion resistance of alkali and sodium salt melts, etc.

However, due to the use of water glass as a binder, a large amount of sodium oxide or potassium oxide and silicon dioxide are brought in, which greatly reduces the refractoriness and load softening temperature of magnesia refractory castables, thus limiting the water glass bonded castables. high operating temperature. Magnesium refractory castables combined with polyphosphate have the advantages of high strength after firing, a small decrease in strength with the increase of heat treatment temperature, high softening temperature, and good thermal shock resistance. However, at high temperatures (above 1400°C ), due to a large amount of volatilization of phosphorus pentoxide, the strength of magnesium castables is reduced. In general, magnesium castables use more sodium polyphosphate as a binder, commonly used are sodium tripolyphosphate, sodium hexametaphosphate, etc. In addition, in order to improve the high-temperature strength of magnesia refractory castables, an appropriate amount of calcium-containing materials (such as calcium carbonate, etc.) is added to form Na2O·2CaO·P2O5 phases with high bonding strength and stable existence at high temperatures. However, no matter what kind of binder is used, it is difficult to overcome the problem of easy hydration, and cracks are likely to occur during the drying process. Adding an appropriate amount of silica ultrafine powder can overcome the hydration problem.

Aluminum-magnesium refractory castables are made of fused magnesia, sintered magnesia, fused or sintered magnesia-alumina spinel, fused corundum, alumina powder, high-alumina powder, etc. The binders include water glass, silicon oxide And alumina superfine powder, calcium aluminate cement, phosphate, etc. Due to the existence of aluminum-magnesium spinel or the formation of magnesium-aluminum spinel during the heating process, the aluminum-magnesium refractory castable expands and micro-cracks, which buffers the thermal stress inside the material, so it has good thermal shock resistance. There is a large amount of aluminum-magnesium spinel in the material, so it has a strong effect on the slag.

Magnesia-silicon refractory castables include castables made of forsterite and castables made of magnesia and silica powder. The castable made of magnesium oxide and silica superfine powder has the advantages of good construction performance and less water consumption. When 12% silicon powder is added to the castable, a castable with minimal residual shrinkage can be obtained. With the increase in the amount of silicon dioxide added, the degree of erosion of the castable by slag tends to increase, while the slag tends to decrease.

Magnesia-chromium refractory castable is made of fused magnesia-chrome sand or waste magnesia-chrome brick sand and its fine powder or is made of magnesia, chromite, or chromium oxide, and its binder is mainly phosphate, aluminum Calcium acid cement, cement, and clay, magnesium sulfate, potassium dichromate, superfine oxide powder, etc., but polyphosphate is better used. Using a binder composed of sodium polyphosphate and calcium-containing materials, the effect is better due to the formation of stable Na2O·2CaO·P2O5 with high bonding strength at low temperature to high temperature. When the ratio of CaO/P2O5 is between 1.6 and 1.9, the thermal bonding strength is high. Since SiO2 has a pyrolysis effect on Na2O·2CaO·P2O5, the content of SiO2 should be strictly controlled in magnesium-chromium castables. Magnesium-chromium castables have the advantages of high service temperature, good volume stability at high temperatures, and strong slag corrosion resistance.

Magnesia-carbon refractory castables are made of fused or sintered magnesia, graphite, pitch, and liquid phenolic resin. In order to improve its strength, it is necessary to add an appropriate amount of metal powder (such as aluminum powder, silicon powder, magnesium powder, silicon calcium powder, etc.); in order to control the curing time, it is necessary to add acid as a curing agent. Magnesia-carbon castables can be cured at room temperature without heating. Once cured, it will not soften or deform when heated and has stable strength, but compared with other castables, its curing time is more difficult to control.

Magnesia-aluminum spinel-based refractory castables are made of various corundum, magnesia, high-alumina bauxite, and synthetic magnesium-alumina spinel aggregates and powders. The binder is pure calcium aluminate cement, silica superfine powder, alumina superfine powder or polyphosphate, etc. Since the magnesium-aluminum spinel synthesized by Tianfu has the advantages of high-temperature resistance, small thermal expansion coefficient, and corrosion resistance to molten steel and steel slag, it has a better use effect than the aluminum-magnesium castable magnesium-aluminum spinel produced in use.

Application: Alkaline refractory castables can be widely used in ladle lining, RH, DH vacuum suction nozzle lining, heating furnace bottom, converter lining, cement rotary kiln lining, incinerator lining, non-ferrous metal smelting, glass, and other industries Furnace lining.

Henan Xinhongji Refractory Material Co., Ltd. is committed to the research, development, and manufacture of refractory materials. It is a comprehensive enterprise integrating science, industry, and trade. The company’s main products are high alumina bricks, clay bricks, lightweight insulation bricks, wear-resistant castables, corundum castables, low-cement high-strength castables, anti-seepage materials, self-flowing materials, wear-resistant plastics, fire-resistant balls and various grades The refractory cement and other shaped and unshaped refractory materials are widely used in metallurgy, nonferrous metals, building materials, electric power, petrochemical, and other industries. The products are sold in more than 60 countries around the world and have won wide acclaim from customers.

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