Refractory Ceramics

Refractory ceramics are structural ceramics that withstand high temperatures. They constitute a subset of refractory materials.

Refractories are used in the "fire industry", notably in all the linings used in industrial furnaces. They are present at the hot heart of most material transformation, energy production and heat containment processes involving temperatures ranging from 600°C to over 2,000°C.

Without these widely available materials, our daily lives would undoubtedly be much less pleasant. We wouldn't have steel, cast iron, metal alloys, glass, ceramics, cement or petroleum cracking... at a reasonable price.

There are several main families of refractories:

• electrofused refractories. By melting the raw materials, electrofused refractory blocks or parts are produced after solidification;

• refractories obtained by particle agglomeration. In this case, particle cohesion is achieved by sintering or chemical reaction. A distinction is made between :

• refractory ceramics, sintered by high-temperature firing before a possible finishing step,

• carbon refractories or carbon-oxide composites with carbon binders. Cohesion is achieved by polymerization of resins, or by polycondensation and crosslinking in the case of pitches and tars,

• mineral-bonded refractories. Mineral bonds act cold by forming gels, then at medium temperature by chemical reaction with the product's fine particles,

• hydraulically bonded refractories. The bond provided by the hydration of an aluminous refractory cement is used in refractory concretes.

This article deals only with refractory ceramics. Other refractory materials will not be discussed.

The performance of refractory ceramics owes much to past know-how, particularly in the ceramic arts (earthenware and porcelain in particular), then in the construction industry (building bricks, terracotta, sanitaryware, etc.) and the steel industry, which pushed the limits of refractory ceramics beyond 1,500°C. In 1897, the arc furnace reached 2,000°C. In the 21st century, the ITER (International Thermonuclear Experimental Reactor) will simultaneously use several heating techniques to raise the plasma in the machine's core to 150 million degrees Celsius.

In addition to the high temperature level and hence infusibility of these materials, which is the main characteristic of all refractories, refractory ceramics must possess a number of additional properties in order to withstand the stresses to which they are subjected in use. Since their behavior is governed mainly...