Alumina magnesia castables are currently the most widely used cutting-edge lining products in ladles. Refractory workers at home and abroad have done a lot of work on aluminum-magnesium castables, mainly from aggregates, magnesia, corundum fine powder and micro powder, and silica. Micropowder and other aspects introduce the influencing factors on the performance of aluminum-magnesium castables.
1. Selection of aggregates
The alumina aggregates used in Alumina magnesia castables mainly include fused alumina, sintered alumina and natural alumina clinker. The castable made of fused high alumina corundum as aggregate has the best fluidity, while the castable made of alumina spinel has the worst thermal shock stability. The brown corundum aggregate sample has the best fluidity. In terms of thermal shock stability, white corundum aggregate is the best, followed by brown corundum aggregate, and bauxite clinker aggregate is the worst.
2. Selection of corundum fine powder
The Al2O3 in the corundum fine powder can react with the CaO in the slag to form CA2 and CA6 with high melting points. At the same time, due to the presence of cation defects in the aluminum-rich spinel, it can capture FeO and MnO in the slag to form (Mg, Fe, Mn )O·Al2O3, the SiO2 content in the slag increases, and the viscosity of the slag increases, which can improve the slag corrosion resistance and slag penetration resistance of the sample. Compared with pure calcium aluminate cement-bound castables, the matrix of ρ-Al2O3-bound castables is purer, extending the service life of Alumina magnesia castables .
3. Spinel ratio
The chemical formula of magnesia-aluminum spinel is MgO·Al2O3, and its theoretical content is MgO28.3% and Al2O371.7%. Magnesium-rich spinel is often used as kiln lining for large cement kilns. Aluminum-rich spinel is often combined with Al2O3 raw materials to mainly manufacture large and medium-sized ladle castables or prefabricated parts and special parts such as ladle breathable bricks and seat bricks. Alumina-based spinel castables synthesized from natural raw materials are mainly used for small ladle castables.
4. Magnesia content
Magnesium oxide, as the main raw material for in-situ spinel generation in Alumina magnesia castables, has a significant impact on the strength, volume stability, slag resistance and thermal shock stability of the sample. As the addition amount of magnesia increases, the slag erosion resistance of the sample decreases and the slag penetration resistance increases. However, when too much magnesia is added, the material structure becomes loose, resulting in a decrease in slag resistance.
5. Silica powder
Silica powder has an important impact on the performance of alumina magnesia castables, which is mainly reflected in the following: using silica powder in Aluminia magnesia refractory castables can significantly reduce the amount of water added, inhibit magnesia hydration, increase fluidity, and improve construction. Performance: On the one hand, adding silica powder will form a low-melting phase (anorthite, anorthite, forsterite and rhodonite) with MgO, CaO, and Fe2O3 in the sample, which is detrimental to the high-temperature performance of the sample, but On the other hand, this can be used to adjust the volume expansion accompanying the spinel reaction and accelerate the spinel formation reaction.
