The refractoriness of magnesia Refractory Brick is more than 2000 ℃, and the softening temperature under load varies greatly with the melting point of the binding phase and the liquid phase produced at high temperature. The starting temperature of load softening of ordinary magnesia bricks is 1520~1600 ℃, while that of high-purity magnesia bricks can reach 1800 ℃. The difference between the load softening start temperature and the collapse temperature of magnesia bricks is small, which is quite different from that of silica bricks. This is because the main phase composition of magnesia Refractory Brick is periclase, but periclase crystals in magnesia bricks are not crystallized network skeleton, but are cemented by bonds. Therefore, the properties of the binder determine the high temperature structural strength of magnesia bricks. In ordinary magnesia bricks, silicate phases with low melting point, such as forsterite and magnesia rose pyroxene, are generally used as the binding substances. Although the melting point of periclase grains that make up the magnesia bricks is high, there are silicate phases that begin to melt at about 1500 ℃, and the viscosity of the liquid phase is very small at high temperatures. Therefore, it reflects that the difference between the load deformation temperature and the collapse temperature of ordinary magnesia bricks is not large, but it is quite different from the refractoriness. The starting temperature of load softening of high-purity magnesia bricks can reach 1800 ℃, mainly because the bond between periclase grains is forsterite or dicalcium silicate, and the melting temperature of the eutectic formed with MgO is high, the character strength between crystals is high, the plastic deformation under high temperature is small, and the crystal particles are well combined.
The linear expansion rate of magnesia bricks at 1000~1600 ℃ is generally 1.0%~2.0%, which is approximately linear. In refractory products, the thermal conductivity of magnesia brick is only inferior to that of carbon brick. It decreases with the increase of temperature. Under the condition of water cooling at 1100 ℃, the thermal shock frequency of magnesia brick is only 1~2 times. Magnesia bricks have strong resistance to alkaline slag of CaO and iron oxide, but weak resistance to acid slag containing SiO2. Therefore, they cannot directly contact with silica bricks in use, and they are generally separated by neutral bricks. At room temperature, the conductivity of magnesia brick is very low, but at high temperature, its conductivity cannot be ignored. The properties of magnesia bricks are quite different due to different raw materials, production equipment, process measures, etc.
Magnesia bricks are widely used in steel making furnace lining, ferroalloy furnace, mixer furnace, nonferrous metallurgy furnace, lime kiln for building materials, regenerator lattice and heat exchanger for glass industry, high-temperature calcining kiln and tunnel kiln for refractory industry due to their good high-temperature performance and strong alkali slag resistance.
