One component metal sintering additive for β-SiC based on thermodynamic calculation and experimental observations

Various types of metals were examined as sintering additives for β-SiC by considering the standard Gibbs formation free energy and vapor pressure under hot pressing conditions (1973–2123 K), particularly for applications in nuclear reactors. Metallic elements having the low long-term activation under neutron irradiation condition, such as Cr, Fe, Ta, Ti, V and W, as well as widely used elements, Al, Mg and B, were considered. The conclusions drawn from thermodynamic considerations were compared with the experimental observations. Al and Mg were found to be effective sintering additives, whereas the others were not due to the formation of metal carbides or silicides from the decomposition of SiC under hot pressing conditions.

. Standard Gibbs formation free energies vs. temperature for various metal carbides. The heavy line represents the standard Gibbs free energy for β-SiC. The hatched area denotes the typical liquid phase hot pressing temperature of β-SiC (1973–2123 K).Figure optionsDownload as PowerPoint slideHighlights
► Various metal elements were examined as a sintering additive for β-SiC.
► Al and Mg enhanced the density significantly without decomposing β-SiC, as predicted by thermodynamic simulation.
► Cr, Fe, Ta, Ti, V and W additives formed metal carbide and/or silicide compounds by decomposing β-SiC.
► This approach would be useful for selecting effective sintering additive for high temperature ceramics.