Abstract
Paralinear oxidative behavior, i.e., concurrent parabolic scale growth (kp) and linear scale volatility (kl or kv), 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, Si3N4, and BN. All of these exhibit scale volatility due to CrO3, CrO2(OH)2, PbCl2, Si(OH)4, or HBO2. The ‘cyclic’ model used an iterative constant outer layer loss formalism, whereby a normalized spall constant, Q0 /Δt, defined the scale volatility rate, kl (or kv). Optimized trial inputs (fitting maximum mass gain (ΔWmax at tmax) and time to reach ΔW = 0) generated accurate kp and kl values. COSP models replicated ideal paralinear form. Simple approximations for kp and kl are also found as ~ 4.1 (ΔWmax2/ tmax) and ~ 1.2 (ΔWmax/tmax), respectively, for most scales. Alternatively, ΔWmax and tmax can be predicted by kp and kl. High or low volatility extremes (e.g., burner tests, short times, or Al2O3 scales) may mask classic paralinear weight change features.
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