Refractories

Refractories are heat-resistant materials designed to withstand high temperatures while retaining mechanical integrity. They form the linings and structures of furnaces, kilns, reactors, and other high-temperature processing equipment. Refractories must resist melting, deformation, chemical attack, and wear under load.

They are categorized by refractoriness and chemical behavior, by form, and by bonding. By temperature rating, they are selected for their ability to remain stable at service temperatures, often described using refractoriness under load (RUL). By form, they exist as shaped products such as bricks, molds, and castable monolithics, or as unshaped materials like gunning mixes, mortars, and plastics. By chemistry, they range from acidic to basic to neutral, and include non-oxide and oxide systems.

Common materials include fireclay and high-alumina bricks, silica bricks, magnesia and dolomite bricks, and more advanced materials such as alumina-silica, silicon carbide, zirconia, and cordierite refractories. Non-oxide refractories like silicon carbide and graphite offer high thermal conductivity and oxidation resistance in specific environments.

Manufacture typically involves preparing a mix of mineral raw materials, sometimes with binders, forming bricks or monolithics, and then firing to develop strength. Monolithic refractories are supplied as castables, plastics, or gunnables and set by curing or chemical reaction.

Applications span the steel industry (linings for basic oxygen furnaces and ladles), cement and lime kilns, glass furnaces, and various petrochemical and energy systems. Refractory performance is affected by thermal shock, chemical attack, hydration, and mechanical wear, and maintenance frequently includes inspection, repair, and replacement. Advances focus on improved resistance to corrosion, reduced thermal conductivity, and longer service life.