Currently, ordinary high alumina bricks refer to burned products made from high alumina bauxite, which have been and are still the most widely used refractory materials. The process of manufacturing high alumina refractories with high alumina bauxite basically follows the method used for making clay bricks. The physical-chemical reactions during the firing process mainly involve the decomposition of kaolinite and diaspore, as well as the secondary mullitization process. But why is high alumina brick more prone to deformation than clay brick?
The performance indicators of high alumina lining bricks vary widely depending on the product grade and usage location. Generally, high alumina lining bricks are divided into four types based on their alumina content: 75%, 65%, 55%, and 48%. Currently, there is no specialized national standard for high alumina bricks used in glass kilns, and GB2988-2012 for general high alumina bricks is commonly adopted as the standard. The above indicators are basic performance requirements, and creep resistance and thermal shock resistance should also be considered according to the usage conditions. Chemical resistance depends directly on the Al2O3 content and porosity.
The high creep rate of high alumina lining bricks is their main disadvantage. According to the creep rate formula, microstructure is the main expansion factor, which has no direct relationship with the Al2O3 content. Microstructural analysis shows that high alumina lining bricks usually consist of fine-grained corundum, columnar mullite, and a glass phase distributed among them. The relative content and distribution state of corundum and mullite have a great influence on the creep rate. The glass phase is distributed between the grain-like corundum, and under high-temperature thermal load, the softening of the glass phase causes the corundum to "slide," resulting in deformation.
If a solid matrix composed of columnar mullite crystals is used, the creep resistance can be relatively improved. However, generally speaking, the creep rate of high alumina bricks under conditions of 1400-50h-0.2MPa can reach 10%-20%, and even significant deformation can occur after a constant temperature time of only 50 hours. Therefore, while high alumina refractory brick has higher refractory temperature resistance, its strength in certain application fields is not as good as that of clay bricks.
