In the world of mechanical seals, this usually refers to Alumina (also called aluminum oxide, Al2O3). Ceramic is a material that is neither a metal nor a polymer.
Ceramics (CER) often include what we traditionally see as ceramics, earthenware, stoneware and porcelain. But ceramics is actually a collective name for materials such as metal. Steel and aluminum are examples of metals, while alumina, glass, diamond and silicon carbide are examples of ceramics.
In the mechanical seals industry, the word ceramic (abbreviated as CER) is actually used for a technical ceramic consisting of 99.5% pure aluminum oxide. To be precise, this is an ionic ceramic, composed of a metal (aluminum) and a non-metal (oxygen).
Typical properties of this material are a high degree of hardness, thermal stability and corrosion resistance. In addition, the material is inert and does not conduct electricity. The material is brittle and is therefore often used as a tread in combination with a stainless steel seat or housing.