What are the types of ceramics that can be used as sealing rings of mechanical seals and its characteristics

Ceramics have good chemical stability and high wear resistance, and the price is relatively low. Because it is very sensitive to shock, vibration and temperature changes, and has low thermal conductivity, it can only be used in corrosive media with low pv values.Commonly used ceramics are alumina (AI₂O₃), silicon nitride (Si8N4), boron carbide (B4C), titanium carbide (TiC) and silicon carbide (SiC). Some mechanical seal parts adopt integral ceramic rings, and some are sprayed with a layer of ceramics on the surface of the sealing ring of the mechanical seals.

Alumina ceramics have good corrosion resistance and can withstand the corrosion of various acids, alkalis, salts, various organic solvents and strong oxidants.Their performances are related to the content of alumina, high alumina content means good performance and good wear resistance.The hardness of alumina is second only to diamond and boron carbide, RC85~86, the mechanical strength is similar to that of ordinary cast iron, and the source of raw materials is extensive, and the manufacturing process is simple. Due to its brittleness and poor thermal conductivity, it is often used as a spraying material. It should be pointed out that the rotary faces and stationary seats of mechanical seals cannot be made of alumina, because of the danger of static electricity.

Silicon nitride is a newly developed sealing ring material in making of mechanical seals. In addition to its excellent corrosion resistance, due to its small linear expansion coefficient (2.5x10¯6~2.8×10¯6 1/°C), its thermal resistance & shock resistance properties are better than that of oxidation Aluminum. In the air, from room temperature to 1000 °C, it can withstand dozens to hundreds of rapid cooling and rapid heating cycles without cracking. Silicon nitride has good wear resistance and a low coefficient of friction. According to the different manufacturing methods of silicon nitride, there are reaction sintered silicon nitride and hot-pressed silicon nitride. Hot-pressed silicon nitride has high strength and is used for parts that do not require machining. Reaction-sintered silicon nitride is widely used due to the characteristics of the manufacturing process. 

The physical and mechanical properties of these ceramics are shown in the table below.