1.pressureless sintered silicon carbide(abbreviated ssic) is better in performance than reaction bonded silicon carbide(abbreviated sic),but both of them can be made into mechanical seal faces and seal rings 

2.Another two kinds of silicon carbide are pressureless sintered silicon carbide/ssic with carbon grains dispersing and silicon carbide/sic with carbon grains dispersing too and the ssic and sic seal face and seal ring have carbon grains on faces.

3.The fifth:QSSic with carbon grain mean ssic matrix has plenty of micropores with carbon grains dispersing.

 Seal faces and seal rings in Sic with carbon,ssic with carbon and QSSic with carbon are often used as dry gas mechanical seal rings and seal faces which will work in a dry way because a good self-lubrication belong to carbon with small friction when the other materials run against them