Simplified Paralinear Oxidation Analyses

Abstract

Paralinear oxidative behavior, i.e., concurrent parabolic scale growth (k p ) and linear scale volatility (k l or k v ), was analyzed by an alternative to the Tedmon equation. A convenient COSP for Windows cyclic oxidation program analyzed published data for Cr, NiCr, Pb, SiC, Si 3 N 4 , and BN, all exhibiting scale volatility due to CrO 3 , CrO(OH) 2 , PbCl 2 , Si(OH) 4 , and HBO 2 . The 'cyclic' model used an iterative constant outer layer loss formalism, whereby a normalized spall constant, Q 0 /Δt, de nes the scale volatility rate, k l (or k v ). Optimized trial inputs ( tting maximum mass gain (ΔW max , t max ) and time to cross zero) generated accurate k p and k l and replicated ideal paralinear form. Initial approximations for k p and k l can now be obtained directly as ~ 4.1 (ΔW max 2 / t max ) and ~ 1.2 (ΔW max / t max ), respectively. However, high or low k l extremes, (e.g., burner rig tests of SiC and Ti 2 AlC), may elude classic paralinear behavior.Inconsistencies between Tedmon's stated model parameters and actual data are also discussed.