The advanced ceramics of the type MexNy (Me=Al, Si, V, Ti,Е) possess a great relevance for modern engineering. They are characterized by high hardness in combination with high thermal stability. We studied the synthesis of gamma-Si3N4(spinel structure, space group Fd-3m) in the shock-wave lab of the Freiberg High-Pressure Research Centre.Our experiments show the present impossibility to synthesize oxygen-free cubic silicon-nitride phases.
The dynamic shock wave synthesis with high explosives permits the preparation of 0.25 to 1.0 g of Si3N4in the pressure range from 30 to 72 GPa. The synthesized powder has a grain size of 20-40 nm.
These large samples allow the application of standard analytical and spectroscopic methods, e.g. IR- and NMR-spectroscopy, XRD-analysis, HR-TEM-analysis as well as thermal chemical analysis. The lattice parameters show a clear dependence on the oxygen content of the Si3N4.
We applied different precursors standard commercial alpha- and beta Si3N4, as well as special designed Si-N bearing compositions prepared at the Institute for Inorganic Chemistry of the TU Bergakademie Freiberg. The aspired goal of our experiments is the synthesis of nearly oxygen free gamma- Si3N4.