Characteristics and Characteristics of Direct Bonded Magnesium Chromium Bricks

Magnesium chromium refractory material is a type of refractory material mainly composed of magnesia and supplemented by chromite; After adding magnesia to chromite and being fired at high temperature, there is a significant physical and chemical reaction between magnesia and chromite. The MgO in magnesia and Cr₂O₃ components in chromite diffuse with each other during the sintering process, forming dotted secondary spinel inside periclase and original spinel in chromite; According to the different processes and raw materials used, magnesium chromium bricks form varying degrees of secondary composite spinel and periclase secondary spinel composites during the cooling process, in order to achieve a structure where the various phases are directly combined and the chromite phase is wrapped in magnesium sand.

In the development history of magnesium chromium refractory materials used in the copper smelting industry, silicon bricks were first used to build furnace linings. However, due to the high content of FeO and SiO₂ in the slag composition and the high content of SO₂ acidic gas in the smelting atmosphere, the erosion and damage of silicon bricks are very serious. From the 1950s to the 1960s, alkaline bricks have been used in the copper smelting industry. Today, after several generations of continuous improvement, The production process and application of magnesium chromium refractory materials in the copper smelting industry are becoming increasingly mature. There are several types of magnesium chromium refractory materials commonly used in the copper smelting industry:

(1) Ordinary silicate bonded magnesium chromium bricks

The magnesium chromium brick combined with ordinary silicate is formed by firing lower grade magnesia and lower grade chromium ore at 1550 ℃. The magnesium chromium brick combined with ordinary silicate contains more silicate phase, and the quantity of secondary spinel is relatively small, forming a microstructure of silicic acid phase wrapped periclase phase.

In ordinary silicate bonded magnesia chrome bricks, the low melting point silicate phase separates and wraps the high melting point periclase and chromite, while the high melting point periclase and chromite are directly bonded with silicate without forming a direct bonding structure. The low melting point silicates are interconnected to form a continuous phase; The silicate phase with low melting point is easily softened and dissolved during use, seriously affecting the load-bearing softening temperature, thermal strength, volume stability and other properties of magnesium chromium bricks; In addition, cracks can propagate through the silicate glass phase, and slag is also more prone to penetration and corrosion from the weak silicate glass phase. Therefore, the thermal shock resistance and slag corrosion resistance of silicate bonded magnesium chromium bricks are poor.

(2) Directly bonded magnesium chromium bricks

Directly combined with magnesium chromium bricks, high-grade magnesium sand and chromium concentrate with low impurities such as silicates are fired at a high temperature of around 1700 ℃; In directly bonded magnesia chrome bricks, there is a relatively small amount of silicate phase, which exists in the matrix in the form of isolated islands. The direct bonding between periclase periclase and periclase composite spinel results in good high-temperature resistance, corrosion resistance, and thermal shock resistance of directly bonded magnesia chrome bricks.