Reactions of Silicon‐Based Ceramics in Mixed Oxidation Chlorination Environments

Abstract

The reaction of silicon‐based ceramics with 2% Cl2/Ar and 1% Cl2/1% to 20% O2/Ar at 950 °C was studied with thermogravimetric analysis and high‐pressure mass spectrometry. Pure Si, SiO2, several types of SiC, and Si3N4 were examined. The primary corrosion products were SiCl4(g) and SiO2(s) with smaller amounts of volatile silicon oxychlorides. The reactions appear to occur by chlorine penetration of the SiO2 layer, and gas‐phase diffusion of the silicon chlorides away from the sample appears to be rate limiting. Pure SiO2 shows very little reaction with Cl2. SiC with excess Si is more reactive than the other materials with Cl2, whereas SiC with excess carbon is more reactive than the other materials with Cl2/O2. Si3N4 shows very little reaction with Cl2. These diferences are explained on the basis of thermodynamic and microstructural factors.

Hydrogen Chloride Effects on the CVD of Silicon Carbide from Methyltrichlorosilane

“…It was found that the substrate was attacked by hydrogen chloride at a rate that increased with temperature, but was by more than three orders of magnitude lower than the deposition rates seen in a HCl-free feed stream at the same temperature. [35] These results are in agreement with the findings of Marra et al, [37] who reported that 2 % HCl in Ar did not etch SiC at 1 atm and 950°C. The increase in the etching rate with the temperature agrees with the results of Allendorf and Outka, [38] in experiments carried out under high vacuum, which indicated that when SiC is exposed to HCl, chlorine bonds to Si atoms, leading to desorption of SiCl 4 around 1300 K. Several experimental studies, [37,39,40] covering a wide range of pressure, have reported that etching of silicon carbide by Cl 2 -containing gas mixtures can take place at rates dependent on the composition of the film (increasing as the silicon content of the material increases) and the composition of the corrosive mixture.…”

“…[35] These results are in agreement with the findings of Marra et al, [37] who reported that 2 % HCl in Ar did not etch SiC at 1 atm and 950°C. The increase in the etching rate with the temperature agrees with the results of Allendorf and Outka, [38] in experiments carried out under high vacuum, which indicated that when SiC is exposed to HCl, chlorine bonds to Si atoms, leading to desorption of SiCl 4 around 1300 K. Several experimental studies, [37,39,40] covering a wide range of pressure, have reported that etching of silicon carbide by Cl 2 -containing gas mixtures can take place at rates dependent on the composition of the film (increasing as the silicon content of the material increases) and the composition of the corrosive mixture. The effects of HCl on the composition of the deposited film are in agreement with the well-documented etching of Si, [41,42] the resistance of SiC to chlorine containing mixtures, the preferential bonding of chlorine to silicon atoms, [43] and the occurrence of residual carbon in SiC samples exposed to chlorine.…”

“…The effects of HCl on the composition of the deposited film are in agreement with the well-documented etching of Si, [41,42] the resistance of SiC to chlorine containing mixtures, the preferential bonding of chlorine to silicon atoms, [43] and the occurrence of residual carbon in SiC samples exposed to chlorine. [37,39,40] From the thermodynamics of the various overall deposition reactions that are likely to occur in the Si/C/H/Cl system and yield SiC, Si, or C, one finds that Si-generating reactions, such as that shown in Equation 1 below, which according to Ohshita et al [44] is a major silicon generation route, have much smaller activitybased equilibrium constants, in relative terms, than the equivalent reaction steps that lead to deposition of SiC, such as that shown in Equation 2.…”

Hot Gas Corrosion of Structural Ceramics

“…By mass spectrometric investigations in CI 2 /Ar and CI 2 /0 2 /Ar at 950°C the formation of the volatile compounds SiCl 4 , SiCI 3 , Si 2 0CI 6 , and Si 3 0CI g was observed [19]. Therefore, silicon carbide ceramics are not suitable for use in Cl 2 -containing atmospheres at high temperatures.…”

Corrosion of Ceramic Materials

“…Corrosion in halogenides and SO 2 /SO 3 is not treated (see Jacobson, 1993;Marra, Kreidler, Jacobson, & Fox, 1988;Nickel & Gogotsi, 2000;Nickel et al, 2010;Presser, Heon, & Gogotsi, 2011;Readey, 1998;Van der Biest, Barnes, Corish, & Norton, 1987). Presser and co-workers (Presser et al, 2011) provide an overview of the reaction of different carbides with Cl 2 .…”