Corrosion of ceramics

Corrosion is the alteration of a material caused by physico-chemical interactions with its environment. This results in a deterioration of its properties of use, leading eventually to its replacement. Corrosion is distinct from wear and tear, which is the result of mechanical stress, and from aging, which is the spontaneous evolution of materials in the absence of external factors, i.e. under the effect of time alone: cross-linking of polymers, crystallization of glass...

Corrosion is considered the main cause of damage to equipment and installations. Its economic cost is considerable. It has been estimated at over 2% of world product, or more than 1,000 billion euros a year. In fact, most of these losses are due to aqueous corrosion of metals and alloys, which has been the subject of a number of Technical Engineering dossiers [K 830][COR 15] : in particular, it concerns reactions that occur at ambient temperature under the combined effects of oxygen (from the air) and water, possibly charged with salts (marine environments in particular).

Most ceramics are not very sensitive to aqueous corrosion, but, like metals placed at high service temperatures, heated ceramics are subject to chemical degradation caused by their environment, which can be significant, if not rapidly catastrophic. As far as metals are concerned, high-temperature corrosion caused by hot gases (also known as "dry corrosion") has been the subject of two Technical Engineering dossiers [M 4 220][M 4 228] . Similarly, the aim of the present dossier is to summarize what we know about the behavior of ceramics when exposed to high temperatures in hostile environments liable to degrade them. By "hostile environments" we mean, on the one hand, certain hot gases (very often oxygen in the air) and, on the other, liquids: molten metals, salts or oxides. The mode of degradation differs considerably in these...