The fire resistance of magnesium brick is as high as more than 2000 ℃, and the softening temperature under load varies with the melting point of the binding phase and the liquid phase produced at high temperature without major changes. Generally, the starting temperature of softening of magnesium brick under load is 1520 ～ 1600 ℃, while the starting temperature of heavy softening of high purity magnesium can reach 1800 ℃.The load softening start temperature and collapse temperature of magnesia bricks are not much different. This is quite different from silica bricks, because the main phase composition of magnesia bricks is periclase, but periclase crystals are not in the magnesia bricks. The crystalline network skeleton is cemented by the conjugate. Therefore, the properties of the combination determine the high-temperature structural strength of the magnesium brick.
In ordinary magnesia bricks, the silicate phase, such as forsterite and magnesite, is generally used as a combination. Although the melting point of the periclase grains constituting the magnesia brick is relatively high, it melts at about 1500 ° C. The silicate phase exists, and its liquid phase has a low viscosity at high temperatures, so it reflects that the load deformation temperature and collapse temperature of ordinary magnesium bricks are not much different, but it is quite different from the fire resistance.
The starting temperature of softening of high-purity magnesia bricks can reach 1800 ° C, which is mainly due to the combination of forsterite or dicalcium silicate and the high melting temperature of the eutectic formed with MgO. , The lattice strength between crystals is large and the plastic deformation at high temperature is small, and the crystal particles are well combined.
The linear expansion coefficient of magnesium brick at 1000 ～ 1600 ℃ is generally 1.0% ～ 2.0%, and it is approximately or linear. Among refractory products, the thermal conductivity of magnesium is second only to carbon bricks. reduce. Under water-cooled conditions at 1100 ° C, the number of thermal shocks of magnesium bricks is only one or two. Magnesium bricks have strong resistance to CaO and ferrite basic slag, but weak resistance to acidic slag containing SiO2. Therefore, they cannot be in direct contact with silicon bricks during use, and are generally separated by neutral bricks. At room temperature, the conductivity of magnesium bricks is very low, but at high temperatures, its conductivity cannot be ignored. The performance of magnesia bricks varies greatly depending on the raw materials, production equipment, and technological measures used.
Magnesium bricks are widely used in steelmaking furnace linings, ferroalloy furnaces, mixed iron furnaces, non-ferrous metallurgical industrial furnaces, lime kilns for building materials, and glass industrial heat storage cell grids due to their high temperature performance and strong resistance to alkaline slag. Heat exchanger, refractory industry, high temperature calcining kiln and tunnel kiln, etc.
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