Alkali Resistant Brick
Alkali resistant bricks usually refers to alkaline refractory bricks which is mainly composed of CaO or MgO. All alkaline refractory bricks have good alkali corrosion resistance, and they are suitable to be used at alkaline working environment. The classification of alkali resistant bricks are as follows.
Magnesia bricks
The main raw material of magnesia brick is magnesite. Magnesia brick contains at least 80% of MgO.
Magnesia chrome brick
The main raw materials of magnesia chrome brick are magnesite and chromite. Magnesia chrome brick contains 55%~80% of MgO.
Chrome magnesia brick
The main raw materials of chrome magnesia brick are chromite and magnesite. Chrome magnesia brick contains 25%~55% of MgO.
Chrome brick
The main raw material of chrome brick is chromite. Chrome brick contains more than 25% of Cr2O3 and less than 25% of MgO.
Forsterite brick
The main mineral composition of forsterite brick is forsterite.
Dolomite brick
The main mineral composition of dolomite brick is dolomite.
The Properties of Alkali Resistant Bricks
Corrosion resistance
Alkali resistant bricks have good corrosion resistance to metallurgical slag, cement clinker, glass batch materials and ash. Different hot media have different influence on alkaline bricks. At strong alkalinity environment, such as cement kiln sintering zone, cement clinker corrosion resistance ability sequence is: Magnesite dolomite brick>magnesia chrome brick> magnesia spinel brick. In converter lining and electric furnace lining, Magnesia bricks with higher CaO/SiO2 ratio have better alkali corrosion resistance than those which have lower CaO/SiO2 ratio. In glass kiln regenerator checkerwork, Magnesia brick with lower CaO/SiO2 ratio has better corrosion resistance than that with higher CaO/SiO2. When producing stainless steel by AOD furnace, the alkalinity of furnace slag is less than 2.2, the slag resistance of magnesia chrome brick is better than mangesite dolomite brick. When slag alkalinity is higher than2.2, magnesite dolomite brick has better slag corrosion resistance than magnesia chrome brick. In heavy metals smelting furnaces, FeO-SiO2 slag corrosion resistance ability of different alkali resistant bricks is: magnesia chrome brick> magnesia brick>magnesia spinel brick> magnesite dolomite brick.
High temperature performance
The refractoriness of alkali resistant bricks are above 2000℃, higher than other firebricks. Refractoriness under load, high temperature modulus of rupture, high temperature volume stability and high temperature compression creep performance are all positively correlated to density, sintering temperature and purity of the raw materials. The RUL temperature of ordinary basic products is about 1550℃~1600℃, while that of high grade alkali resistant bricks(magnesite dolomite brick, magnesia spinel brick, high purity magnesia brick, direct bonded magnesite chrome brick, etc) is above 1700℃, that of semi-rebonded magnesia chrome brick and rebonded magnesia chrome brick can reach to 1750~1800℃.
The high temperature modulus of all kinds of alkaline refractory bricks decreases with the raising of tests temperature. Rebonded magnesia chrome bricks with higher Cr2O3 content have higher high temperature strength. Basic refractory bricks which adopts fused raw materials also have higher high temperature strength.
The thermal expansion rate of alkali resistant bricks is higher than other firebricks. At 1600℃, magnesia bricks have the highest linear expansion rate, about 2.0%. High grade magnesia chrome bricks have the lowest thermal expansion rate, about 1.6%. The thermal expansion rate of other basic bricks is between these two values.
Alkali resistant bricks have higher thermal conductivity than high alumina bricks, chamotte bricks and silica bricks.
The specific heat capacity of alkali resistant bricks is higher than silica bricks and clay bricks, among them, that of magnesia brick is the highest.
The thermal shock resistance of alkali resistant bricks is not so good as clay bricks or high alumina bricks. The thermal shock resistance ability of different kinds of alkaline bricks is: magnesia spinel brick>magnesia chrome brick>magnesia dolomite brick>magnesia brick.
