Silicon nitride ceramics' properties

What is silicon nitride ceramics?

Silicon nitride (Si3N4) is a kind of ceramic material with high melting point and high hardness and chemical inertness. Hot-pressed silicon nitride, in particular, is one of the hardest substances in the world.  

Silicon nitride ceramics have low thermal expansion coefficient and high thermal conductivity, so they have excellent thermal shock resistance. Silicon nitride has high strength and impact resistance at moderate temperatures.  However, when used above 1200℃, damage will appear with the growth of use time, which reduces its strength.  

Silicon nitride chemical formula:

The molecular weight of silicon nitride is 140.28, the chemical formula is Si3N4, and it dissolves at 1900℃ under pressure.  After high temperature sintering, the color is usually gray or black.  

Common silicon boron nitride molding process

Pneumatic silicon nitride ceramics

Air pressure sintering of silicon nitride ceramics is the most popular method for producing silicon nitride components with high strength and complex geometry. The pneumatic sintering method uses silicon nitride powder that has been mixed with a sintering agent to promote liquid phase sintering (usually yttrium oxide, magnesium oxide and/or alumina) and a binder to improve the mechanical strength of the green ceramic body. The powder is pressed into the desired shape and then processed in green. The blocks are then placed in an oven with a pressurized nitrogen atmosphere to aid densification and prevent evaporation and decomposition of silicon, nitrogen and additives.

Hot-pressed silicium nitride ceramics

Hot pressing sintered si3n4 ceramics are produced by uniaxial pressing si3n4 powder and sintering additive heating simultaneously.  This process requires special types of presses and molds. It produces silicon nitride with excellent mechanical properties.  However, this molding method can only produce simple shapes, such as plates or rods. By hot-pressing si3N4, almost zero porosity can be achieved.  This results in excellent mechanical properties and corrosion resistance even in high-temperature applications.