Key influence of chromite composition on magnesia chrome brick

Chromite is the main raw material for producing magnesia chrome bricks, magnesia bricks and chrome magnesia bricks. Its mineral composition is also one of the important factors affecting the properties of magnesia chrome bricks.

The influence of SiO2 content on the high temperature properties of magnesia chrome refractories is very significant. The direct bonding degree of magnesia chrome bricks with low SiO2 content is obviously improved (see Figure 1), and the softening point under high temperature load is also higher than that of magnesia chrome bricks with high SiO2 content (see Table 1). This is because SiO2 and Fe2O3 in chromite form iron olivine (Fe2SiO4) with a very low melting point; The content of SiO2 is low, and the silicate phase formed at the firing temperature is less. The silicate layer in the brick structure is replaced by the direct combination of high refractory phase crystals.

High SiO2 content is also unfavorable to the corrosion resistance of refractories, even for high-grade chromite with high Cr2O3 content. When studying the reaction of SiO2 in high-grade chromite with fused magnesia, it was found that SiO2 and MgO formed silicate liquid phase. The content of SiO2 was high, and the amount of liquid phase was also high, just as slag eroded fused MgO sample, the liquid phase invaded into fused MgO. The performance index of unburned magnesia chrome brick, which is made of sintered magnesia and chromite as raw materials, added with a small amount of chemical binder, and heat treated at a lower temperature to harden the products. Some products can be hardened under normal temperature, while others need to be heated to appropriate temperature to make products have certain strength. When the product is used at high temperature, ceramic bonding or high temperature resistant phase is formed. The forming process is often covered with iron shell, which is called iron sheet unburned brick.