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.
Magnesia bricks are divided into fired magnesia bricks unfired magnesia bricks. Fired magnesia bricks are divided into silicate bonded magnesia bricks, direct bonded magnesia bricks recombined magnesia bricks. Magnesia-calcium sand unburned magnesia bricks are divided into chemically bonded magnesia bricks asphalt bonded magnesia bricks.
In the 1880s, Austria first produced magnesia bricks. Later, the United States Russia also began to produce magnesia bricks in 1895 1900, respectively. In the 1960s 1980s, they began mass production of recombined magnesia bricks direct-combined magnesia bricks.
The raw material of magnesite bricks is mainly magnesite, whose basic component is MgCO3, which becomes sintered magnesia after being calcined at high temperature crushed to a certain size. Magnesia is widely used as furnace repair material 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 output of magnesium ore in my country rank among the top in the world.
Magnesia bricks are divided into two types, sintered magnesia bricks chemically bonded magnesia bricks, according to their different production processes. Sintered magnesia bricks are made of dead-burned magnesia with proper particle size ratio, adding brine (MgCl2 aqueous solution) sulfite pulp waste liquid as binders, pressurized molding, sintered at a high temperature of 1550-1650°C. The chemically bonded magnesia brick does go through the firing process. After the sintered magnesia is prepared according to the particle size ratio, an appropriate amount of mineralizer binding agent are added, pressed into shape, dried to become the finished product. The strength of chemically bonded magnesia bricks is lower the performance is 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 soaking furnaces.
Magnesium 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 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 softening to 40% deformation is very small, the thermal stability of magnesia bricks at 30~50℃ is also poor, which is an important reason for the damage of magnesia bricks.