Spinel compound brick composite layer pollution layer does not affect the use of theoretical basis for it
The chemical composition of magnesia spinel brick has an important effect on the performance of. The suitable chemical compositions of spinel are 8%~20%, cao0.5%~1.0%, fe2o30.2%~8%, sio2<0.4%, B2O3 and alkali. The impurity content is less than 0.3%, and the rest is mgo. When the Al2O3 content is less than 8%, less content of spinel crystals, intergranular directly binding to periclase and periclase magnesia brick, showing the shortcomings, namely spalling resistance difference. When the content of Al2O3 is more than 20%, the corrosion resistance of brick decreases. When cao<0.5%, fe2o3<0.2%, spinel mineral crystal is less than 5mm or more hours, almost as crystal direct binding between periclase and periclase, which shows the disadvantages of magnesia brick. With the increase of the content of Cao and Fe2O3, the liquid phase formed by the low melting point of cao-al2o3-fe2o3 system is formed, which makes the spinel crystal grow up and the anti flaking property produced by the spinel crystal can be exploited. But when cao>1%, fe2o3>0.8%, cao-al2o3-fe2o3 system low melting point liquid phase increased spinel crystal size is more than 20mm, because cao-al2o3-fe2o3 system low melting material increased the thermal strength decreased. When the content of SiO2 is more than 0.4% and the content of impurities such as B2O3 and base is more than 0.3%, more low melting substance is produced, and the thermal strength of the brick decreases. The content of Al2O3 in the range of 8%~20%, the microstructure can be observed on spinel mineral evenly distributed in the periclase spinel mineral, the crystal size is about 5~20mm, the better comprehensive performance of brick.
One is the development of the manufacturing process of the magnesia magnesia purity can be improved, with low content of magnesia silicate phase has good resistance to spalling, does not require the addition of alumina can also produce good thermal shock stability is of high quality magnesia brick; two foreign chromite resources is abundant, magnesia chrome refractories production has thermal stability good and anti erosion ability.
The study of mg Al spinel synthesized with MgO raw materials and Al2O3 raw materials (calcined alumina or alumina) has begun as early as 1930s. Magnesia alumina spinel was synthesized from industrial alumina and activated alumina in 1939 and used for making bricks. In 40s, people found that the addition of alumina powder in magnesia could improve its thermal stability, this is actually a spinel bonded brick. When the magnesia brick is mainly used in cement kiln, but in addition to the production of white cement kiln, it was replaced by magnesia chrome refractories.
