State of Small Amount of Elements in Silicon Nitride Fabricated by Post-Sintering Process Using Low-Grade Silicon Powder as Raw Materials

The state of small amount of elements containing impurity in silicon nitride produced by the post sintering method from low-grade silicon powder was investigated. Iron reacted with other components in the raw materials in the sintering process to form iron silicide particles which were subsequently distributed. Most particles were as large as 2 μm in diameter. Linear voids that were considered to originate in the difference of thermal expansion coefficients were observed in their perimeter. Ta2O5 also reacted with other elements and it was observed in the form of tantalum silicide particles. The size was few hundreds nanometer. Calcium was detected from multigrain pockets. However, not a particular particle segregation could be observed. For this reason, it is presumed that Calcium was solved into the grain-boundary phase.