fireclays

Fireclays are a class of refractory clays used for high-temperature service. They are natural clay materials with relatively high alumina (Al2O3) content and low iron oxide, and their mineral assemblage commonly includes kaolinite, illite, and trace mica. The refractoriness of fireclays generally exceeds 1,600°C and can approach 1,800°C for higher-alumina varieties. They are distinguished from ordinary brick clays by greater resistance to deformation, slag attack, and thermal stress at elevated temperatures.

Geologically, fireclays occur in sedimentary basins as clayey layers within coal measures and other silica-rich sequences. They are mined for refractory use and selected for high refractoriness, low impurity content, and suitable plasticity to enable shaping before firing.

The primary use of fireclays is in refractory brick and shaped products such as furnace linings, kiln linings, crucibles, and ladles. Grade differentiation in the industry typically centers on alumina content, plasticity, firing behavior, and resistance to slag. Common terms include common fireclay, high-alumina fireclay, and dead-burned fireclay, reflecting variations in processing and in-service performance. After mining, the material is processed through crushing, milling, drying, and sometimes calcination to tailor properties for specific applications.

Processing and performance depend on mineralogy and particle size, which influence bonding, porosity, and thermal shock resistance. When properly produced, fireclay bricks and shapes offer reliable protection for equipment operating at high temperatures, with good slag resistance and mechanical integrity over time.