Performance and characteristics of six types of magnesia chrome bricks

According to the raw materials and process characteristics of the products, it can be divided into fused cast magnesia chrome bricks, direct bonded magnesia chrome bricks, silicate bonded magnesia chrome bricks, recombined magnesia chrome bricks, semi-recombined magnesia chrome bricks, pre-reacted magnesia chrome bricks and non-reactive magnesia chrome bricks. Burnt magnesia chrome bricks.

①Fused cast magnesia chrome brick

Fused-cast magnesia chrome brick is a refractory product made of magnesia and chrome ore by electric melting and casting. The production process of fused cast magnesia chrome bricks is shown in Figure 1. It is characterized by large pores and isolated existence, compact products, high strength, corrosion resistance, and sensitivity to temperature changes. The chemical properties of magnesia-chrome bricks are alkaline. Compared with magnesia bricks and chrome bricks, they have good thermal shock resistance, stable volume at high temperatures, and high softening temperature under load.

② Directly combined with magnesia chrome brick

Directly bonded magnesia-chrome bricks are made by combining sintered magnesia and chromite. It is required that the raw material has a low SiO2 content and is fired at a high temperature above 1700°C to form a direct bond between the periclase and chromite particles. The typical physical and chemical properties of directly bonded magnesia-chrome bricks are: MgO: 82.61%, Cr2O3: 8.72%, SiO2: 2.02%, apparent porosity 15%, and bulk density 3.08g/cm3. Compressive strength 59.8MPa, load softening temperature 1765℃, thermal shock resistance (1100℃ water cooling) 14 times, flexural strength 8.33MPa.

③Silicate combined magnesia chrome brick

Silicate-bonded magnesia-chrome bricks are made by sintering magnesia and chrome ore as raw materials, mixing in appropriate proportions, and firing at high temperatures. The mineral composition of the product is periclase, spinel and a small amount of silicate. The production of silicate bonded magnesia chrome bricks uses brick magnesia and general refractory chrome ore as raw materials. SiO2<4% in magnesia, MgO>90%, and Cr2O3 in chrome ore: 32%~45%. After kneading and molding with sulfite as a binder, it is fired at about 1600°C. In order to prevent abnormal expansion of products during firing, a weak oxidizing atmosphere must be maintained in the kiln. The chemical composition of the product: SiO2: 2.98%~4.50%, MgO: 61.75%~72.69%, Cr2O3: 10.04%~14.90%. Physical properties: apparent porosity 18%-21%, normal temperature compressive strength 36.1-50.0MPa, load softening temperature 1600-1640°C.

④Recombined magnesia chrome bricks and semi-recombined magnesia chrome bricks

Combined magnesia chrome bricks are made by re-sintering fused magnesia chrome sand as raw materials. Fused magnesia chrome sand has poor sinterability, and the product is a fine-grained matrix with uniform pore distribution, and has small cracks, and its sensitivity to rapid temperature changes is better than that of fused-cast bricks. The high-temperature performance of the product is between the fused-cast brick and the direct-bonded brick. The typical physical and chemical properties of combined magnesia chrome bricks are: MgO: 68%, Cr2O3: 15%, SiO2: 3%, apparent porosity 14%, bulk density 3.20g/cm3, compressive strength 52.8MPa, load softening temperature 1740℃ , Flexural strength 7.86MPa.

Semi-recombined magnesia chrome bricks are made of fused magnesia chrome sand and magnesia, chromite or pre-reacted magnesia chrome sand. The product has some characteristics of recombined magnesia chrome brick and directly combined magnesia chrome brick or pre-reacted magnesia chrome brick. The typical physical and chemical properties of semi-recombined magnesia chrome bricks are: MgO: 71.58%, Cr2O3: 16.45%, SiO2: 2.75%, apparent porosity 13%, compressive strength 46.7MPa, load softening temperature 1760℃, flexural strength 9.09MPa .

⑤Pre-reacted magnesia chrome brick

Pre-reacted magnesia chrome bricks are made of all or part of pre-reacted magnesia chrome sand. The production cost is lower than that of recombined magnesia chrome bricks. Part of the reaction between magnesia and chromite is completed when the clinker is calcined, so the porosity of the product is lower than that of directly bonded bricks of equivalent composition, and the high temperature strength is higher. The typical composition of pre-reacted magnesia chrome brick is MgO: 62.8%, Cr2O3: 15.3%, SiO2: 3.25%, apparent porosity 17%, compressive strength 51.3MPa, and load softening temperature 1650℃.

⑥Unburned magnesia chrome brick

Unburned magnesia chrome bricks are made of sintered magnesia and chromite as raw materials, adding a small amount of chemical bonding agent, and heat treating at a lower temperature to harden the product. Some products can be hardened at room temperature, and some need to be heated to an appropriate temperature to make the products have a certain strength. When the product is used at high temperature, it forms a ceramic bond or high temperature resistant phase. The typical composition of unburned magnesia chrome bricks is: MgO: 52.73%, Cr2O3: 18.08%, SiO2: 5.0%, apparent porosity 10.9%, compressive strength 58MPa, and load softening temperature 1520-1530°C.