One of the most commonly used raw materials for magnesia refractory——Fused magnesia

Magnesia is the main raw material of magnesia refractories. The main chemical component is MgO and the mineral is periclase. Isotope is an equiaxed crystal system with a density of 3.56-3.67g/cm3, a hardness of 5.5, a linear expansion coefficient of 13.5×10-6K-1, and a large modulus of elasticity, which is cubic, octahedral or irregular. It is chemically stable, has a large lattice energy and a melting point of up to 2800 °C.

 

High-quality magnesite or light burnt magnesium powder is melted in an electric arc furnace at a high temperature of 2800 ° C or higher, and the product obtained after crushing is fused magnesia. The strength, corrosion resistance and chemical stability of fused magnesia are both It is better than sintered magnesia, and the purity varies depending on the purity of the raw materials. In magnesia or magnesia carbon refractories, more and more fused magnesia is replacing the sintered magnesia. The raw material is naturally cooled after being melted in an electric arc furnace, and the periclase is crystallized and grown from the melt. After cooling, the under-melt on the bulk is removed and the under-melt can be returned to the arc furnace for high-temperature melting. When fused magnesia is produced from magnesite or magnesite, a large amount of gas is discharged, causing crystallization and density to be affected.

 

The fused magnesia is mainly a brownish-yellow, dark-brown granular block with good uniformity, and the main mineral is periclase. The fused magnesia has a low impurity content, a low silicate content and an island-like distribution. The magnesite crystallizes from the melt, the crystal is coarse, the direct contact between the crystal grains is high, the structure is compact, the high temperature volume and chemical stability are good, and the hydration resistance and slag resistance are better. In an oxidizing atmosphere, the stability can be maintained below 2300 ° C, so that the good properties of the periclase can be fully exerted. It can be obtained by special process smelting to obtain colorless and transparent large-grained periclase. Large grain magnesia has the following excellent properties and uses:

1. large crystalline magnesia has good crystallization, stable lattice constant, high purity and few defects. It can be applied to superconductors, printed boards for films with strong insulating materials, and substrate materials for far infrared inductive receivers.

 

2. The refractory material made of fused large crystal magnesia is used for the special part of the metal melting furnace which is highly corrosive, which improves the service life of the melting furnace.

 

The grain size of the periclase in the sintered magnesia is 60-200 μm, and the grain size of the periclase in the fused magnesia is 200-400 μm, and the large-crystal fused magnesia is 700-1500 μm or even 5000 μm or more.