Magnesia alumina brick is superior to magnesia brick in thermal shock resistance due to its main crystal phase of periclase and matrix of magnesia-alumina spinel. In order to improve the thermal shock resistance of magnesia brick, alumina or bauxite clinker fine powder is introduced into the ingredients to form magnesia alumina spinel matrix, thus making it. That are characterized by good thermal shock resistance, high load softening temperature, load softening temperature above 1580 °, and good glass corrosion resistance. With the increase of the content, the apparent porosity of the brick increases. However, when the content is less than 10%, the brick is still dense, and the apparent porosity can reach 14%, generally 15%~18%. The plastic flow of it starts at 1000~1200 ° and accelerates at 1300 °. Similar to magnesia-chrome brick, but different from magnesia brick, the rapid flow temperature of magnesia brick is 100~200 ° higher. When the amount of alumina added is less than 15%, the will not expand when reacting with iron oxide; When the addition amount reaches 15%, it will expand slightly; 20%; 28% had severe swelling.
Compared with magnesia brick,it has the following characteristics: 1. it has good thermal shock stability and can withstand 20~25 times or even higher water cooling. It has good thermal shock stability because both magnesia-alumina spinel and periclase belong to cubic crystal system, and the thermal expansion along each crystal axis is the same, so the expansion and contraction are uniform when the temperature fluctuates, and the thermal stress is small. 2. The main performance of it is slightly stronger than that of magnesia brick. Due to the high melting point of magnesia-alumina spinel, the load softening temperature of it is better than that of magnesia brick, reaching 1620~1690 °. Magnesia-alumina spinel can better protect periclase particles from slag erosion than montmorillonite, so magnesia alumina brick has stronger resistance to alkaline slag and iron oxide slag than magnesia brick. Magnesia alumina brick has the above excellent properties, so it is widely used as the masonry material for the top of high temperature smelting furnaces such as steel making open hearth furnace and copper reverberatory furnace in China, and has achieved the effect of prolonging furnace life. There are about 300 large open hearth furnaces and more than 1000 medium and small open hearth furnaces.
The production process of it is roughly the same as that of fired magnesia brick, except that a certain proportion of industrial alumina or special bauxite clinker is added to the ingredients. The impurity content of industrial alumina is lower than that of high-alumina clinker. Adding natural bauxite clinker can improve the plasticity of clay. Under the same conditions, the bulk density of brick is higher. The addition amount of industrial alumina is generally 5%~10%. It is usually added in the form of fine powder after grinding with magnesite in a certain proportion, which is conducive to the formation of new crystal phase of magnesia-alumina spinel with uniform distribution in the product matrix. The firing temperature of it depends on the purity of raw materials, generally 30~50 ° higher than that of it, and the firing temperature of high-purity it reaches 1750~1800 °.
