Magnesia Bricks Introduction
In the 1880s, Austria first produced magnesia bricks. Later, the United States and Russia also began to produce magnesia bricks in 1895 and 1900, respectively. In the 1960s and 1980s, they began mass production of recombined magnesia bricks and direct-combined magnesia bricks.
The raw material of magnesite bricks is mainly magnesite, whose basic component is MgCO3, which is calcined at high temperature and then crushed to a certain size to become sintered magnesia. Magnesia is widely used as furnace repair material and ramming material. Magnesia with less impurities (ω(CaO)<2.5%, ω(SiO2)<3.5%) is used as the raw material for making magnesia bricks. The reserves and output of magnesium ore in my country rank among the top in the world.
Magnesia bricks are divided into two types: sintered magnesia bricks and chemically bonded magnesia bricks according to their different production processes. 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 chemically bonded magnesia brick 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 chemically bonded magnesia bricks is low, and the performance is not as good as sintered magnesia bricks, but the price is less than half of the price of sintered magnesia bricks. 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. The refractoriness of magnesia brick 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 magnesia bricks at 30~50℃ is also poor, which is an important reason for the damage of magnesia bricks.
In heating furnaces and soaking furnaces, magnesia bricks are mainly used to pave the bottom surface of the furnace and the lower part of the soaking furnace wall. It can resist the corrosion of oxide scale.