Key Effects of Chromite Composition on Magnesium Chromium Bricks

Chromite is the main raw material for producing magnesium chromium bricks, magnesium bricks, and chromium magnesium bricks, and its mineral composition is also one of the important factors affecting the performance of magnesium chromium bricks.

The effect of SiO₂ content on the high-temperature performance of magnesium chromium refractory materials is very significant. The direct bonding degree of magnesium chromium bricks with low SiO₂ content is significantly improved, and the high-temperature load softening point is also higher than that of magnesium chromium bricks with high SiO₂ content (see Table 1). This is because SiO₂ forms iron olivine (Fe₂ SiO₄) with Fe₂ O₃ in chromite, which has an extremely low melting point; The content of SiO₂ is low, and there is less silicate phase formed at the firing temperature. The silicate layer in the brick structure is replaced by direct bonding between high refractory phase crystals.

High SiO₂ content is also detrimental to the corrosion resistance of refractory materials, even for high-grade chromite with high Cr₂O₃ content. When studying the reaction between SiO₂ in high-grade chromite and fused magnesia, it was found that SiO₂ and MgO form a silicate liquid phase, with a high content of SiO₂ and a high amount of liquid phase formation. Just like slag erosion of fused MgO, the liquid phase invades the interior of fused MgO. The performance indicators of unburned magnesium chromium bricks are made by using sintered magnesia and chromite as raw materials, adding a small amount of chemical binder, and heat treating at lower temperatures to harden the products. Some can harden the product at room temperature, while others need to be heated to an appropriate temperature to give the product a certain strength. When the product is used at high temperatures, it forms a ceramic bond or high-temperature resistant phase. The forming process is often wrapped in an iron shell, which is called iron sheet without burning bricks.