Research on Sintering Acceleration with Structural Disorder-order Transformation

Recent interest focused on the preparation of dense bulk nanostructured silicon carbide has been motivated by expected improvement in properties resulting from grain size reduction. Grain size refinement, for example, offers the potential for superplastic behavior for SiC. However, consolidating nanostructured SiC while maintaining its fine crystallite size has been only achieved through the use of additives or the application of extremely high pressures during sintering. Consolidation of nanopowders to produce dense bodies for further property characterization has been attempted through the use of several techniques including sintering, hot pressing, and spark plasma (or pulsed electric current) sintering (SPS). In all of these approaches, the focus is on avoiding or minimizing grain growth. In view of the nonequilibrium state of the nanomaterials and the fact that consolidation steps take place at high temperatures and require a relatively long holding time, grain growth (Ostwald ripening) is anticipated and in fact takes place. To achieve high densities and avoid exaggerated grain growth, consolidation of nanostructured SiC has been made through liquid phase sintering (where oxide additives are required) or through solid state sintering (where very high pressures and additives such as boron and carbon have been also used). In this research we investigated a new process by which the sintering of nanostructured and stacking-disordered SiC formed through a mechanochemical process is achieved. Dense nanostructured β-SiC is formed without the use of additives or the deployment of very high pressures. Furthermore, evidence is provided demonstrating the role of a stacking disorder-order transformation in the densification process.