Effects of Carbon as a Sintering Aid in Silicon Carbide

Abstract

Self-diffusion data are collected from tlhe literature in an attempt to better understand the strong effects of carbon as a sintering aid in SIC. These data indicate that the presence of excess carbon, in addition to reduciing the native S O 2 layer of the Sic, probably enhances the ralte-controlling bulk self-diffusion rate of Sic by a factor of about 100. [

Microstructure development in hot-pressed silicon carbide: effects of aluminum, boron, and carbon additives

“…Carbon additions can strengthen the boron effect by preventing the reaction between boron and SiO 2 oxidation layers. In addition, Rijswijk et al reported that carbon reduces the loss of boron in the SiC lattice [46]. Therefore, the boron and carbon appear to have similar promotional effects on the β-to-α phase transformations as observed in the present study as well as discussed in other publications [46,47], but the effect of boron is more pronounced.…”

“…Carbon additions increase the overall self-diffusion rate of SiC by a factor of 100 according to Rijswijk et al [46]. A similar effect was found for boron by Friedrich et al [48].…”

“…This assumption was confirmed by other groups in the following years. It has been recognized that at 1200-1600 o C, boron and carbon react with SiO 2 surface layers on SiC powders, reducing the grain boundary energy, and in turn increasing grain boundary diffusion [2,46,49,50]. This reaction could also prevent reaction between SiC and the surface SiO 2 at sintering temperature [50,51].…”

Densification of silicon carbide using oxy-nitride additives for space-based telescope mirror applications

“…The reaction between SiC and SiO 2 (Ref. 7), which is prevalent in the temperature regime of 1500 to 1650 o C is utilized to overcome the effect of the oxide layer as per the following chemical reaction.…”

Stoichiometric silicon carbide from borate‐catalyzed polymethylsilane–polyvinylsilane formulations

“…46,47 It must be pointed out that the presence of boron is also related to an increase in the free carbon content, and carbon, like boron, is known to promote densification and crystallization of SiC. [48][49][50] Oxidation stability of the ceramics Oxidation of silicon carbide is a spontaneous exothermic reaction with an enthalpy of À840 kJ mol À1 at room temperature. The stability of silicon carbide toward air oxidation is the result of a silica barrier at the surface of the SiC particles, which limits the diffusion of oxygen toward SiC.…”