Effect of magnesia quality on the performance of magnesia carbon bricks

Magnesia carbon bricks are unburned carbon composite refractory materials made with a carbon binder. They are primarily used for the linings of converters, AC and DC electric arc furnaces, and in ladle slag lines. As a composite refractory material, magnesia carbon bricks effectively utilize the strong slag erosion resistance of magnesia and the high thermal conductivity and low expansion of carbon, compensating for magnesia's primary drawback, which is poor spalling resistance. Their main features include: 1. Excellent high-temperature resistance 2. Strong slag resistance 3. Good thermal shock resistance 4. Low high-temperature creep

The Impact of Magnesia Quality on Magnesia Carbon Brick Performance

Magnesia is the primary raw material for magnesia carbon brick production. Magnesia quality has a crucial impact on its performance, and proper selection is crucial to its production. Magnesia includes fused magnesia and sintered magnesia, each with distinct characteristics. Fused magnesia features large grains, low impurities, relatively low silicate content, high grain bonding, and a reduced number of grain boundaries.

Sintered magnesia: Fine grains, high concentrations of impurities and silicate phases, and poor direct bonding.

In addition to chemical composition, magnesia raw materials also require high density and large crystals in terms of microstructure. Therefore, the following quality indicators for magnesia raw materials used in magnesia-carbon brick production should be considered: 1. Magnesium oxide content (purity). 2. Impurity types, especially C/S and B2O3 content. 3. Magnesia density, pore diameter, pore morphology, etc. (sinterability).

Magnesia purity significantly impacts the slag resistance of magnesia-carbon bricks. A higher magnesium oxide content results in fewer impurities, reduced silicate phase segmentation, increased direct bonding of periclase, and improved resistance to slag penetration and slag melt loss. Impurities in magnesia primarily include calcium oxide, silicon dioxide, and iron oxide. High impurity levels, particularly those of boron oxide compounds, can adversely affect the magnesia's refractoriness and high-temperature performance.

Impurities in magnesia have the following negative effects:

1. Reduces the direct bonding of periclase.

2. Forms low-melting products with magnesia at high temperatures.

3. Impurities such as iron oxide and silicon dioxide react with carbon before magnesia at temperatures between 1500-1800°C, leaving pores and impurities that reduce the slag resistance of the finished product.

For magnesia raw materials, in addition to the total amount of impurities, the type and relative content of impurities also have a significant impact on magnesia performance. The CaO/SiO2 ratio and B2O3 content have the most significant impacts. Magnesia refractories generally require a CaO/SiO2 ratio of ≥2 to improve the high-temperature stability of magnesia-carbon bricks.

Magnesia Carbon Bricks