How does alumina content affect the use temperature of fireclay refractories?

In fireclay refractories, the alumina content typically ranges from 25 to 45 percent. The use temperature of these materials is directly related to this composition: as the alumina content increases, the maximum temperature at which the material can be effectively used also rises.1

Fireclays are categorized into grades—low-duty, medium-duty, high-duty, and super-duty—based on their alumina-to-silica ratio and the presence of impurities such as alkalis and iron oxides. These materials are primarily composed of the mineral kaolinite and are commonly manufactured into firebricks for use in industrial environments like blast furnaces and coke ovens.1