A Review of SiC Fiber Oxidation with a New Study of Hi‐Nicalon SiC Fiber Oxidation

Abstract

The linear and parabolic oxidation rate constants and activation energies for SiC fibers available in the literature are reviewed for the first time. Oxidation experiments are also conducted with Hi-Nicalon SiC fibers over 700-1 300 C in dry O 2 with thermogravimetric analysis. Linear oxidation kinetics are observed from 700 to 800 C and parabolic kinetics are observed from 900 to 1 300 C. The linear and parabolic oxidation rate constant activation energies are determined to be 83 and 108 kJ mol À1 , respectively. These kinetic results are compared with the literature values. Differences in oxidation behavior are assessed as a function of fiber composition.

Boria Effects on the High Temperature Oxidation of Silicon Carbide

“…The Hi-Nicalon™ fiber oxidation observed in the study by Wilson and Opila was governed by linear kinetics at temperatures below 900˚C that then transitioned to parabolic kinetics at higher temperatures, as shown in Figure 4 30 . The temperature dependence of the oxidation rate constants in Wilson and Opila's study 30 were found to be in good agreement with the rate constants reported by others on the oxidation of CVD-SiC in dry O2 17,21 . …”

“…Sylramic fibers exhibited linear TGA weight change at ≤1000˚C exposures, from which oxide growth at these exposures was assumed to be governed by linear oxidation kinetics based on TGA results. The linear rate constants, kl, were calculated from these measured oxide thicknesses per unit time, 30 reported as µm/ h in Table 5. Parabolic oxide growth was assumed from parabolic TGA weight change at ≥ 1100˚C.…”

“…Parabolic oxide growth was assumed from parabolic TGA weight change at ≥ 1100˚C. The Sylramic fiber parabolic oxidation rate constants were calculated from the squared oxide thicknesses per unit time, 30 reported as µm 2 / h in Table 5. Literature results from the dry oxidation of CVD-SiC coupons were compared 17,21 .…”

“…The paralinear oxidation kinetics are characteristics of a non-protective oxide 11 creep resistance provided when the grain microstructure is fine, the Si: C ratio is stoichiometric, and the oxygen content is low 29 . A recent study by Wilson and Opila showed that commercially available Hi-Nicalon™ SiC fibers demonstrated Deal and Grove oxidation kinetics when exposed to dry oxygen environments 30 . The Hi-Nicalon™ fiber oxidation observed in the study by Wilson and Opila was governed by linear kinetics at temperatures below 900˚C that then transitioned to parabolic kinetics at higher temperatures, as shown in Figure 4 30 .…”

“…Parabolic oxidation kinetics were assumed based on the parabolic weight change behavior given by the TGA weight change profiles shown earlier in Figure 47. The oxide thicknesses were squared, then divided by the total exposure time, to calculate the rate of parabolic oxide growth 30 . The kp for Si and SiC are linearly proportional with pressure 24,26 .…”