The main crystal phase of magnesia brick is periclase, which has the typical characteristics of general alkaline refractory products, but its thermal shock resistance is poor.
It can be fired and not fired. The fired magnesia bricks are divided into silicate bonding, direct bonding and recombining magnesia bricks. The unburned ones are divided into chemical bonding and asphalt bonding magnesia bricks.
It was first produced in Austria in the 1880s. Later, the United States and Russia also started production in 1895 and 1900, respectively. In the 1960s and 1980s, they began mass production of recombination and direct bonding magnesia bricks, respectively.
Its raw material is mainly magnesite, and its basic component is MgCO3, which is calcined at high temperature and then crushed to a certain size to become sintered magnesia. Magnesium sand is widely used as furnace repair material and ramming material. Magnesium sand with less impurities (ω(CaO)<2.5%, ω(SiO2)<3.5%). The reserves and output of magnesium ore in my country rank among the top in the world.
According to different production processes, it can be divided into sintering and chemical combination. The sintered magnesia brick is made of magnesia that has been burnt and has a proper particle size ratio, added with brine (MgCl2 aqueous solution) and sulfite pulp waste liquid as a binding agent, pressurized and molded, and fired at a high temperature of 1550-1650°C. The chemical combination does not go through the sintering process. After the sintered magnesia is prepared according to the particle size ratio, an appropriate amount of mineralizer and binding agent are added, pressed into shape, and dried to become the finished product. The strength of chemical bonding is low, and the performance is not as good as sintered, but the price is cheaper, less than half of the sintered price. It is used in parts with low performance requirements, such as furnace bottoms and soaking furnaces.
Magnesia brick is an alkaline refractory material, which has strong resistance to alkaline slag, but cannot resist the erosion of acid slag. It can react with silica bricks, clay bricks and even high alumina bricks at a high temperature of 1600°C. Its refractoriness is above 2000℃, but its softening point under load is only 1500~1550℃. Moreover, the temperature interval from softening to 40% deformation is very small, and the thermal stability of only 30~50℃ is also poor, which is an important reason for its damage.
In heating furnaces and soaking furnaces, it is mainly used to pave the bottom surface layer and the lower part of the soaking furnace wall. It can resist the corrosion of oxide scale.
