Silicon Nitride Rapid Decomposition for Ceramic Nanopowder Manufacturing

Abstract

Rapid decomposition of silicon nitride at high temperatures has been successfully used to manufacture ceramic nanopowders in the Si-C-N and Si-O-N systems. For powder processing, the solid combustion called self-propagating high-temperature synthesis (SHS) was realized and investigated. The well-mixed powdered reactants were placed in porous container; then, the reaction was locally ignited and combustion was propagated in a self-sustaining regime, achieving temperatures of over 2000°C. In all these experiments, combustion propagated with the formation of the transient Si3N4 phase resulted in either SiC or Si2ON2 nanosized grains. To elucidate the role of the decomposition of silicon nitride in the formation of nanosized products, thermodynamic data, temperature profiles, morphology (SEM, TEM), dispersion (BET) and phase composition (XRD) of the products were evaluated. It was found that, in both Si-C-N and Si-O-N systems, silicon nitride forms transiently at early stages of combustion because of thermodynamic and kinetic considerations. Finally, it was demonstrated that the technology of silicon carbide and silicon oxynitride nanopowders achieved by the decomposition of Si3N4 is very efficient compared to other conventional techniques. The powders obtained are well sinterable and, after further processing, can be used in a wide range of applications, such as refractory materials, ceramic armor, elements of chemical equipment, etc.