firebrick

Firebrick, or refractory brick, is a brick designed to withstand high temperatures without softening or breaking, making it suitable for lining furnaces, kilns, fireplaces, and ovens. Most firebricks are made from refractory clays such as fireclay and other silica-alumina formulations, and are fired to a ceramic bond that provides resistance to heat, chemical attack, and thermal cycling.

Two broad classes are used in industry: dense firebrick and insulating firebrick. Dense bricks are high-density, low-porosity linings that provide structural strength and tend to tolerate higher mechanical loads and temperatures around 1,000–1,400°C. Insulating bricks are lightweight and highly porous, with much lower thermal conductivity, used to reduce heat loss but not typically for load-bearing applications. Variants include high-alumina and silica bricks with higher refractoriness or slag resistance.

Performance depends on composition, porosity, and thermal shock resistance. Refractoriness ratings, such as refractoriness under load (RUL) or use temperature, guide suitability for a given furnace temperature. Fireclay bricks commonly tolerate about 1,000–1,200°C, while high-alumina varieties can exceed 1,400°C. Chemical resistance varies with slag exposure and mineral content.

Manufacture involves shaping refractory clay or grog, drying or preheating, and firing in a kiln to a vitrified ceramic state. Bricks are then used with fireproof mortar to form linings in appropriate geometries.

Common applications include fireplaces, wood-burning stoves, pizza ovens, metalworking and glass furnaces, and ceramic kilns.

Color is usually red to brown, influenced by iron oxide content.