Magnesia Alumina Bricks
Magnesia alumina brick is an alkaline refractory product with periclase as the main crystal phase and magnesia alumina spinel as the matrix. Its alumina content is 5%-10%, which has good thermal shock resistance. According to Rongsheng Refractory Bricks Manufacturer, In order to improve the thermal shock resistance of magnesia bricks, alumina or special-grade high alumina bauxite is added to the ingredients to form magnesia alumina spinel, thereby making magnesia alumina bricks. The successful trial of magnesia-alumina bricks on the open-hearth roof made them widely promoted and applied in the future.
The Performance of Magnesia Alumina Bricks
Magnesia alumina brick refers to the use of magnesia and industrial lead oxide or alumina as raw materials. It is an alkaline refractory material that is crushed, shaped and fired at about 1600°C. The refractoriness is greater than 2000 ℃, and the resistance to rapid cooling and heating is better than that of magnesia bricks, and it can resist the erosion of alkaline slag.
Magnesia alumina bricks have good thermal shock resistance and high load softening temperature. As the amount of alumina added increases, the apparent porosity of the brick increases. But when the alumina content is less than 10%, it is still dense, and the apparent porosity can reach 14%, generally 15% to 18%.
When the alumina content is within 20%, the elastic modulus of the magnesia alumina brick decreases with the increase of the alumina content in the brick. When the added amount is 4%-10%, it is generally 0.42MPa, which is only one-third of that of magnesia brick (1.20MPa).
The linear expansion coefficient of magnesia-aluminum bricks has a similar pattern of elastic modulus. When the amount of alumina added is 4%-10%, it is generally 10.6×10-6 (20～1000℃), which is about 20% lower than that of magnesia brick (13.0×10-6).
The starting temperature of magnesia-aluminum bricks under load is not only related to the impurity content in the bricks but also increases with the increase of alumina content. When the alumina addition amount is 3%-10%, there is a higher value; when the addition amount exceeds 10%, it starts to decrease. High-purity magnesia-alumina bricks with magnesia and alumina content above 97.5% can have a load softening starting temperature (load 0.2MPa) of more than 1750°C, generally 1600°C.
Before 1000℃, the modulus of elasticity of magnesia alumina bricks increases with the increase of temperature, it is about 5.5×10-4MPa at 1000℃ and drops sharply above 1000℃. Magnesia-alumina bricks begin to exhibit plastic flow at 1000°C and become more pronounced at 1200°C, and the flow accelerates at 1300°C. These are similar to magnesia chrome bricks but different from magnesia refractory bricks. And it is 100-200℃ higher than the rapid flow temperature of magnesia brick.
When the alumina content is less than 15%, the magnesia alumina brick and iron oxide will not cause an explosion. When the added amount reaches 15%, it will show slight expansion, when it is 20%, it will be more obvious, and when it is 28%, the expansion will be serious. The slag resistance (open-hearth slag) increases with the addition of alumina.
The Production Process of Magnesia Alumina Brick
The production process of magnesia alumina brick is roughly the same as that of fired magnesia brick. Just add a certain proportion of industrial alumina or special grade bauxite clinker to the ingredients. The impurity content of industrial alumina is lower than that of high bauxite clinker. Adding natural bauxite clinker to the ingredients can also improve the plasticity of the mud. Under the same conditions, the bricks have a higher bulk density. The amount of industrial alumina added is generally 5% to 10%. It is usually added in the form of fine powder after being finely ground with magnesia in a certain proportion, which is conducive to the formation of a uniformly distributed new magnesia-aluminum spinel crystal phase in the product matrix. There is also a production method that uses pre-synthesized magnesia-aluminum spinel and then batches to make bricks. The critical particle size is large during the batching, which is beneficial to improve the thermal shock resistance of the product but is not conducive to the density and strength of the product. Generally, 3mm is used. The particle size is generally 3～1mm and 1～0.088mm. And the ratio of 3~2mm coarse particles to fine powder less than 0.088mm should be controlled to improve the thermal shock resistance of the product.
The firing temperature of magnesia alumina bricks should be determined according to the purity of the raw materials. Generally, it is 30-50℃ higher than the firing temperature of the magnesia brick. The firing temperature of high-purity magnesia-aluminum bricks is 1750～1800℃.
The Characteristics of Magnesia Alumina Brick
Compared with magnesia bricks, magnesia alumina bricks have the following characteristics:
- ① Magnesia alumina bricks have good thermal shock stability and can withstand water cooling for 20-25 times, or even higher. This is its most prominent advantage, much better than ordinary magnesia bricks. It is believed that the thermal shock stability of magnesia alumina bricks is good because magnesia alumina spinel and periclase belong to the cubic crystal system, and the thermal expansion along each crystal axis direction is the same. Therefore, the expansion and contraction are relatively uniform when the temperature fluctuates, and the thermal stress generated is small.
- ②The main performance of magnesia alumina bricks is also slightly stronger than that of magnesia bricks. Due to the higher melting point of the magnesia-aluminum spinel itself, the load softening temperature of the magnesia-aluminum brick is better than that of the magnesia brick, reaching 1620～1690℃.
The ability of magnesia spinel to protect periclase particles from slag erosion is stronger than that of forsterite. Therefore, the ability of magnesia alumina bricks to resist alkaline slag and iron oxide slag is stronger than that of magnesia bricks.
Magnesia-aluminum bricks have the above-mentioned excellent properties, so they have been widely used as masonry materials for the roof of high-temperature smelting furnaces such as steel-making open-hearth furnaces and copper-making reverberatory furnaces, and have achieved the effect of extending furnace life. The large open hearth can reach about 300 furnaces, and the medium and small open hearth has more than 1000 furnaces.
Rongsheng Refractory Brick Manufacturer
Rongsheng is an experienced refractory brick manufacturer. Rongsheng’s refractory materials have been sold to more than 60 countries and regions all over the world. Whether it is product quality or customer service, it is satisfactory to customers. Quick response to customers, reasonable magnesia alumina bricks prices. For more information about magnesia alumina bricks, please leave your specific needs on our page.