Magnesium bricks are fired at high temperature and are the most important products among alkaline refractory materials. They have high refractoriness, and have good corrosion resistance to iron oxides, alkaline slag and high-calcium fluxes. They are used in metallurgy It is widely used in kilns.

 

Refractories with magnesia as the main component and periclase as the main crystalline phase are collectively referred to as magnesia refractories. At present, the main varieties of magnesia refractories are as follows.

 

(1) Ordinary magnesia bricks are made of sintered magnesia as raw materials, sintered, containing about 91% MgO, magnesia refractory products directly combined with qualitative silicates, which are widely produced and used.

 

(2) Directly bonded magnesia bricks are made by sintering high-purity sintered magnesia. Containing more than 95% MgO, it is a magnesia refractory product directly bonded between periclase crystal grains.

 

(3) Magnesia silica bricks are made by firing high-silicon sintered magnesia, containing SiO25%~11%, CaO/SiO2 molar ratio≦1, which is a magnesia refractory product combined with forsterite.

 

(4) Magnesia chrome bricks are made of sintered magnesia as the main raw material, added with appropriate amount of chromium ore, and sintered, containing 38% to 20% Cr2O. It is a magnesia refractory product combined with magnesia chromium spinel.

 

(5) Forsterite bricks Forsterite refractories are refractories with pig crystal phase. It is made of peridotite and pure peridotite as the main raw materials.

 

(6) Magnesia alumina bricks are made of sintered magnesia as the main raw material and added with appropriate amount of materials rich in Al2O3. They are sintered and contain Al2O35%-10%. They are magnesia refractory products combined with magnesia alumina spinel.

 

Magnesia-calcium bricks are made by firing high-calcium sintered magnesia, containing CaO6%~10%, CaO/Si2O molar ratio ≧2, it is a magnesia refractory product combined with dicalcium silicate

 

Magnesium products are mainly composed of various crystals. In ordinary magnesium products, the main crystalline phase of periclase grains are separated by the crystal and glass phase in the matrix composition, so that the periclase grains cannot directly form a direct bond. The network organization, such structural characteristics, make the nature and use effect of the product depend on the quantity and characteristics of the matrix components.

 

From the perspective of chemical composition, in addition to the main component MgO, there are CaO, Fe2O3, Al2O3 (Cr2O3), SiO2, etc. They are all impurities, so they constitute a five-element system.

 

Most of these oxides themselves have high melting points and chemical stability, but when they coexist, it is possible to form new compounds and form a lower eutectic point with the new compounds, thereby reducing fire resistance and chemical stability. stability.

 

The main component of magnesia refractories is magnesium oxide, and the main crystal phase is periclase. Many magnesia refractory products also contain silicate, spinel or other ingredients. However, the properties of the main crystalline phase periclase and its behavior at high temperatures directly control the performance of magnesia refractories.

 

The periclase is an ionic crystal with high electrostatic attraction between ions. The lattice energy is as high as 3935kJ/mol, so the melting point is very high, reaching 2800℃. However, when the temperature reaches 1800°C or higher, sublimation can occur, and its stability decreases with the increase of temperature; the lower the pressure, the lower the stability.