The longer stacking sequence results in the α-phase having higher hardness than the β-phase. However, the α-phase is chemically unstable compared with the β-phase. When a liquid phase is present at high temperatures, the α-phase always transforms into the β-phase. Therefore, β-Si3N4 is the major form used in Si3N4 ceramics. Abnormal grain growth may occur in doped β-Si3N4, whereby abnormally large elongated grains form in a matrix of finer equiaxed grains and can serve as a technique to enhance fracture toughness in this material by crack bridging. Abnormal grain growth in doped silicon nitride arises due to additive-enhanced diffusion, resulting in composite microstructures, which can also be considered "in-situ composites" or "self-reinforced materials. Specifically, polycarbosilane can be readily converted to an amorphous form of silicon carbonitride-based material upon pyrolysis, with valuable implications in the processing of silicon nitride materials through processing techniques more commonly used for polymers. One of the major applications of sintered silicon nitride is in the automobile industry as a material for engine parts. Those include in diesel engines, glowplugs for faster start-up; precombustion chambers (swirl chambers) for lower emissions, faster start-up, and lower noise; turbochargers for reduced engine lag and emissions. In spark-ignition engines, silicon nitride is used for rocker arm pads for lower wear, turbocharger turbines for lower inertia and less engine lag, and exhaust gas control valves for increased acceleration. As examples of production levels, an estimated more than 300,000 sintered silicon nitride turbochargers are made annually. If you are looking for high quality, high purity, and cost-effective Silicon nitride, or if you require the latest price, please email contact mis-asia.