The price of bonded magnesia-chrome bricks is the MgO-Cr2O3 refractory product made of high-purity magnesia and chromium concentrate with low impurity content, which is ground and fired at high temperature (above 1700℃). Due to the high direct bonding rate of high-temperature mineral phase, it has high resistance Slag, high temperature strength and excellent thermal shock resistance; combined with magnesia chrome bricks are MgO-Cr2O3 refractory products made of fused magnesia chrome sand as raw materials, high-pressure forming and high-temperature firing at 1800℃. Due to the higher direct bonding rate, low apparent porosity, and high volume density, the high temperature strength and slag corrosion resistance of combined magnesia-chrome bricks are higher than that of directly combined magnesia-chrome bricks. However, the thermal shock resistance of combined magnesia chrome bricks is poor. The main characteristics of the damage of the slag line of the refined steel tank using MgO-Cr2O3 refractory materials: chemical erosion of slag, structural spalling caused by slag penetration, and erosion of high-temperature molten steel slag. The corrosion resistance of MgO-Cr2O3 refractories against -SiO2 slags with low/SiO2 ratio (less than 2), but for -SiO2 slags with high/SiO2 ratio at high temperature, especially when Fe2O3 content is high, it is low The eutectic temperature drops rapidly, and the corrosion resistance is very poor. Converter magnesia carbon brick
Due to the presence of magnesia-iron spinel, iron oxides can promote the sintering of magnesia-chromium refractories to a certain extent, but due to the variable value of iron oxides, and the solid solubility of the two oxides FeO and Fe2O3 in periclase It is slightly different. This reason makes the magnesia-chromium products with high iron oxide content not suitable for copper smelting production with unstable atmosphere and unstable temperature.
If magnesia-chromium refractories with higher iron content are used in copper converters, loose layers may be formed due to the following phenomena: In the case of high temperature reduction, Fe2O3 in the periclase solid solution will be reduced to FeO. Low-iron spinel is formed in the brick body; while the temperature is reduced or the oxidizing atmosphere, the low-iron spinel will be oxidized again to generate MgO·Fe2O3; and in the process, the volume changes, which will cause magnesium chromium The inflation of high-quality refractories and the formation of evacuation layers.
The above-mentioned substances do not have their own influence on the magnesia-chromium refractories during the use of the copper smelting process, and their interaction with iron-silicon slag and SO2 atmosphere is also worth noting. Nowadays, common magnesia-chrome bricks, direct-combined magnesia-chrome bricks, recombined (semi-recombined) magnesia-chrome bricks and unburned magnesia-chrome bricks are widely used in commercial contacts.
1. Ordinary magnesia chrome brick:
Ordinary magnesia chrome bricks are generally produced from sintered magnesia (with a mass fraction of MgO between 89% and 92%) and refractory chrome ore. Due to many impurities, the refractory grains are combined with silicate. The magnesia-chrome bricks commonly referred to in the country generally refer to fired ordinary magnesia-chrome bricks, also known as silicate-bonded magnesia-chrome bricks, or magnesia-chrome bricks for short. The production process of ordinary magnesia-chrome bricks is simple, cheap and widely used. Cement kiln (Cr2O3 mass fraction rarely exceeds 14%), glass kiln regenerator, steelmaking furnace lining, refining steel cladding, non-ferrous metallurgy furnace, lime kiln, mixing furnace and refractory high-temperature furnace lining, etc.
2. Directly combined with magnesia chrome bricks:
The main difference between the production process of direct combined magnesia chrome brick and ordinary magnesia chrome brick is that the former uses raw materials with less impurity content and is fired at a relatively high temperature. For the production of magnesia directly combined with magnesia-chrome bricks, the mass fraction of MgO is generally greater than 95%, preferably greater than 97%, the particle bulk density is about 3.25g/cm3, and the mass fraction of SiO2 in chrome ore is generally limited to less than 3%. In the case of chromium concentrate, the mass fraction of SiO2 can be less than 1.0%. According to different needs and uses, sometimes one or two kinds of magnesia and one or two kinds of chrome ore can be used as ingredients. Directly bonded magnesia-chrome bricks for cement kilns generally use magnesia as fine powder and part of the granular material, while chromium ore is used as granular material, and the mass fraction of Cr2O3 is 3% to 14%; it is used as a direct-bonded magnesium for metallurgical furnace lining. Chrome bricks sometimes require the mass fraction of Cr2O3 to be as high as possible (such as 20%). When relatively pure magnesia and chrome ore are used as the matrix, the products tend to expand when they are fired. Directly bonded magnesia-chrome bricks generally refer to products made from chrome ore with lower impurity content and purer magnesia, fired at temperatures above 1700°C, and refractory grains are mostly in direct contact. In the chemical composition of directly bonded magnesia-chrome bricks, there are few impurity components, and the direct bonding rate between refractory grains is high, so slag resistance and high temperature performance are good.
