Magnesia Chrome Brick

Magnesia chrome bricks are widely used in industry and construction because of their high-quality properties such as heat resistance and pressure resistance. There are also several different types of magnesia chrome bricks. According to the requirements of different products, there are mainly three types of magnesia chrome bricks. kind:

1. Fired magnesia chrome bricks: fired magnesia chrome bricks are made of fine ingredients of high-quality magnesia and chrome ore. The content of Cr2O3 is adjusted according to different needs. The product has good thermal stability and high temperature performance. It is widely used in cement kilns and non-ferrous metallurgy. Furnace and so on.

2. Directly combined magnesia-chrome bricks: Directly combined magnesia-chrome bricks use low-impurity chrome ore and high-quality high-purity magnesia as raw materials, after high-pressure molding, and high-temperature firing at a temperature above 1 700 ℃. Good high temperature performance, strong resistance to slag erosion. Resistant to cement clinker erosion. It is widely used in non-ferrous metallurgical furnaces and cement rotary kilns.

3. Semi-recombined magnesia chrome bricks and recombined magnesia chrome bricks: semi-recombined magnesia chrome bricks and recombined magnesia chrome bricks, using part or all of fused sand (fused synthetic sand) as raw materials, fine ingredients, high pressure molding, Ultra-high temperature calcination, good particle bonding, high product strength, good volume stability, widely used in RH, VOD, AOD and other external refining devices, non-ferrous metallurgy furnaces, etc.

4. Magnesia chrome bricks are alkaline refractory products containing 55% to 80% MgO and 8% to 20% Cr2O3, composed of periclase, composite spinel and a small amount of silicate phase. Composite spinel includes MgAl2O4, MgFe2O4, MgCr2O4 and FeAl2O4 spinel solid solutions.

Magnesia chrome bricks have developed rapidly after the 1960s due to the increase in raw material purity and firing temperature. At present, magnesia chrome bricks can be divided into ordinary bricks, direct bonded bricks, co-sintered bricks, recombined bricks and Cast bricks, etc.

(1) Ordinary magnesia chrome brick: This is a traditional product, using chrome ore as coarse particles and magnesia as fine powder. Or the two materials are composed of graded particles, and the firing temperature is generally 1550~1600°C. The microstructure of this brick shows that there is little direct bonding between chromite particles and periclase, mostly silicate (CMS) cementation or fissure isolation; there are few desolvent phases in periclase, and there is little direct contact in the matrix. In combination, this brick has poor mechanical properties and poor slag corrosion resistance.

(2) Directly bonded magnesia-chrome bricks: Directly bonded magnesia-chrome bricks are developed on the basis of ordinary magnesia-chrome bricks. There are two main production characteristics. One is the use of purer raw materials, and the other is the use of higher firing. temperature. The so-called direct bonding means that there is more direct contact between the chrome ore particles in the brick and the periclase, because the raw material contains less SiO2 (controlled below 1% to 25%), and the amount of silicate generated is small. The firing method squeezes the silicate into the corners of the solid particles. Thereby improving the direct bonding of the solid phase.

Directly bonded magnesia-chrome bricks have a high degree of direct bonding, so that the bricks have higher high temperature strength, slag resistance, corrosion resistance, erosion resistance, corrosion resistance, excellent thermal shock stability and volume stability at 1800°C.

(3) Co-sintered magnesia-chrome brick: The production process of this product is characterized by high-temperature furnace firing of a mixture of magnesia and chromium ore fine powder in a certain ratio to achieve the generation of secondary spinel and magnesia-chrome ore Solid-phase reaction for the purpose of direct bonding to prepare a common sintered material, which is used to produce fired products or chemically bonded products.

The direct bonding and microstructure uniformity of co-sintered magnesia-chrome bricks are better than those of direct-bonded bricks. The amount of periclase desolubilization phase and intergranular secondary spinel is more. Co-sintered magnesia-chrome bricks have a series of more direct Combined with the better performance of bricks, it is especially famous for its high temperature strength, rapid temperature resistance and slag resistance. Common sintered bricks can also be divided into two varieties, one is the full common sintered brick, the whole series of common sintered materials of particles and fine powder, whether it is fired or chemically combined, its microstructure is basically similar; the second is partly common For sintered bricks, there is a part of the ingredients, such as the common sintering material for coarse particles, and the fine powder part can be mixed into the brick in a certain proportion with fine chrome ore and magnesia paper powder, so that the fired and chemically combined products will be microscopic The structure is different.

(4) Recombination of magnesia-chromium bricks: the magnesia-chromium mixed powder is melted by the electric melting method, and the melt is crystallized to form a fairly uniform microstructure, with magnesia-chromium spinel and periclase mixed crystals as the main phase composition The fused magnesia-chromium material is crushed into a certain particle size, mixed and molded, and then fired to prepare recombined bricks, or directly used as chemical cemented bricks.

The microstructure of the combined brick is characterized by a high degree of direct bonding and a large amount of spinel desolvent phase: the base crystal containing a large amount of desolvent phase essentially changes the physical and chemical properties of periclase, such as reducing the thermal expansion coefficient. , Improve thermal shock resistance, improve resistance to acid-alkaline slag erosion. Combined bricks have similar properties to those of fused-cast bricks, but have better resistance to rapid temperature changes and a more uniform microstructure than fused-cast bricks.

Combined with the magnesia chrome brick, it is a fine-grained matrix with uniform pore distribution and microcracks, and its sensitivity to sudden changes in temperature is better than that of melting and casting. The high-temperature performance of the product is between the fused-cast brick and the direct-bonded brick.

(5) Fused and cast magnesia chrome bricks: Place the mixture of magnesia and chrome ore in an electric arc furnace to completely melt, and then pour the melt into a refractory mold for casting. During the solidification process, stable periclase and spinel crystal phases are formed, and a fine crystal structure is formed at the same time, so the cast magnesia chrome brick has excellent high temperature strength and slag corrosion resistance.

Magnesium chrome bricks are mainly used in the metallurgical industry, such as the construction of open hearth furnace tops, electric furnace tops, out-of-furnace refining furnaces and various non-ferrous metal smelting furnaces. The high-temperature part of the wall of the ultra-high power electric furnace is made of fused-cast magnesia-chrome bricks, the high-erosion area of ​​the refining furnace outside the furnace is made of synthetic materials, and the high-erosion area of ​​the non-ferrous metal flash smelting furnace is made of fused-cast magnesia-chrome bricks and synthetic materials. Made of magnesia chrome bricks. In addition, magnesia-chrome bricks are also used in the burning zone of cement rotary kilns and regenerators of glass kilns.

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Magnesia Chrome Brick

Magnesia chrome bricks are widely used in industry and construction because of their high-quality properties such as heat resistance and pressure resistance. There are also several different types of magnesia chrome bricks. According to the requirements of different products, there are mainly three types of magnesia chrome bricks. kind:

1. Fired magnesia chrome bricks: fired magnesia chrome bricks are made of fine ingredients of high-quality magnesia and chrome ore. The content of Cr2O3 is adjusted according to different needs. The product has good thermal stability and high temperature performance. It is widely used in cement kilns and non-ferrous metallurgy. Furnace and so on.

2. Directly combined magnesia-chrome bricks: Directly combined magnesia-chrome bricks use low-impurity chrome ore and high-quality high-purity magnesia as raw materials, after high-pressure molding, and high-temperature firing at a temperature above 1 700 ℃. Good high temperature performance, strong resistance to slag erosion. Resistant to cement clinker erosion. It is widely used in non-ferrous metallurgical furnaces and cement rotary kilns.

3. Semi-recombined magnesia chrome bricks and recombined magnesia chrome bricks: semi-recombined magnesia chrome bricks and recombined magnesia chrome bricks, using part or all of fused sand (fused synthetic sand) as raw materials, fine ingredients, high pressure molding, Ultra-high temperature calcination, good particle bonding, high product strength, good volume stability, widely used in RH, VOD, AOD and other external refining devices, non-ferrous metallurgy furnaces, etc.

4. Magnesia chrome bricks are alkaline refractory products containing 55% to 80% MgO and 8% to 20% Cr2O3, composed of periclase, composite spinel and a small amount of silicate phase. Composite spinel includes MgAl2O4, MgFe2O4, MgCr2O4 and FeAl2O4 spinel solid solutions.

Magnesia chrome bricks have developed rapidly after the 1960s due to the increase in raw material purity and firing temperature. At present, magnesia chrome bricks can be divided into ordinary bricks, direct bonded bricks, co-sintered bricks, recombined bricks and Cast bricks, etc.

(1) Ordinary magnesia chrome brick: This is a traditional product, using chrome ore as coarse particles and magnesia as fine powder. Or the two materials are composed of graded particles, and the firing temperature is generally 1550~1600°C. The microstructure of this brick shows that there is little direct bonding between chromite particles and periclase, mostly silicate (CMS) cementation or fissure isolation; there are few desolvent phases in periclase, and there is little direct contact in the matrix. In combination, this brick has poor mechanical properties and poor slag corrosion resistance.

(2) Directly bonded magnesia-chrome bricks: Directly bonded magnesia-chrome bricks are developed on the basis of ordinary magnesia-chrome bricks. There are two main production characteristics. One is the use of purer raw materials, and the other is the use of higher firing. temperature. The so-called direct bonding means that there is more direct contact between the chrome ore particles in the brick and the periclase, because the raw material contains less SiO2 (controlled below 1% to 25%), and the amount of silicate generated is small. The firing method squeezes the silicate into the corners of the solid particles. Thereby improving the direct bonding of the solid phase.

Directly bonded magnesia-chrome bricks have a high degree of direct bonding, so that the bricks have higher high temperature strength, slag resistance, corrosion resistance, erosion resistance, corrosion resistance, excellent thermal shock stability and volume stability at 1800°C.

(3) Co-sintered magnesia-chrome brick: The production process of this product is characterized by high-temperature furnace firing of a mixture of magnesia and chromium ore fine powder in a certain ratio to achieve the generation of secondary spinel and magnesia-chrome ore Solid-phase reaction for the purpose of direct bonding to prepare a common sintered material, which is used to produce fired products or chemically bonded products.

The direct bonding and microstructure uniformity of co-sintered magnesia-chrome bricks are better than those of direct-bonded bricks. The amount of periclase desolubilization phase and intergranular secondary spinel is more. Co-sintered magnesia-chrome bricks have a series of more direct Combined with the better performance of bricks, it is especially famous for its high temperature strength, rapid temperature resistance and slag resistance. Common sintered bricks can also be divided into two varieties, one is the full common sintered brick, the whole series of common sintered materials of particles and fine powder, whether it is fired or chemically combined, its microstructure is basically similar; the second is partly common For sintered bricks, there is a part of the ingredients, such as the common sintering material for coarse particles, and the fine powder part can be mixed into the brick in a certain proportion with fine chrome ore and magnesia paper powder, so that the fired and chemically combined products will be microscopic The structure is different.

(4) Recombination of magnesia-chromium bricks: the magnesia-chromium mixed powder is melted by the electric melting method, and the melt is crystallized to form a fairly uniform microstructure, with magnesia-chromium spinel and periclase mixed crystals as the main phase composition The fused magnesia-chromium material is crushed into a certain particle size, mixed and molded, and then fired to prepare recombined bricks, or directly used as chemical cemented bricks.

The microstructure of the combined brick is characterized by a high degree of direct bonding and a large amount of spinel desolvent phase: the base crystal containing a large amount of desolvent phase essentially changes the physical and chemical properties of periclase, such as reducing the thermal expansion coefficient. , Improve thermal shock resistance, improve resistance to acid-alkaline slag erosion. Combined bricks have similar properties to those of fused-cast bricks, but have better resistance to rapid temperature changes and a more uniform microstructure than fused-cast bricks.

Combined with the magnesia chrome brick, it is a fine-grained matrix with uniform pore distribution and microcracks, and its sensitivity to sudden changes in temperature is better than that of melting and casting. The high-temperature performance of the product is between the fused-cast brick and the direct-bonded brick.

(5) Fused and cast magnesia chrome bricks: Place the mixture of magnesia and chrome ore in an electric arc furnace to completely melt, and then pour the melt into a refractory mold for casting. During the solidification process, stable periclase and spinel crystal phases are formed, and a fine crystal structure is formed at the same time, so the cast magnesia chrome brick has excellent high temperature strength and slag corrosion resistance.

Magnesium chrome bricks are mainly used in the metallurgical industry, such as the construction of open hearth furnace tops, electric furnace tops, out-of-furnace refining furnaces and various non-ferrous metal smelting furnaces. The high-temperature part of the wall of the ultra-high power electric furnace is made of fused-cast magnesia-chrome bricks, the high-erosion area of ​​the refining furnace outside the furnace is made of synthetic materials, and the high-erosion area of ​​the non-ferrous metal flash smelting furnace is made of fused-cast magnesia-chrome bricks and synthetic materials. Made of magnesia chrome bricks. In addition, magnesia-chrome bricks are also used in the burning zone of cement rotary kilns and regenerators of glass kilns.

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