Oxidation Kinetics of a Continuous Carbon Phase in a Nonreactive Matrix

Abstract

Analytical solutions of and experimental results on the oxidation kinetics of carbon in a pore are presented. Reaction rate, reaction sequence, oxidant partial pressure, total system pressure, pore/crack dimensions, and temperature are analyzed with respect to the influence of each on an overall linear‐parabolic rate relationship. Direct measurement of carbon recession is performed using two microcomposite model systems oxidized in the temperature range of 700° to 1200°C, and for times to 35 h. Experimental results are evaluated using the derived analytical solutions. Implications on the oxidation resistance of continuous‐fiber‐reinforced ceramic‐matrix composites containing a carbon constituent are discussed.

Degradation of Continuous Fiber Ceramic Matrix Composites under Constant Load Conditions

“…Across the temperature range of 550-1500°C, theoretical calculations show that the diffusion coefficient will change by a factor of three while the reaction rate constant changes by three orders of magnitude. The calculations for the reaction rate are based on a carbon activation energy of 100 kJ/mol and use linear recession rate data from Eckel et al [16] to solve the Arrhenius NASA/TM-2000-209681reaction rate equation. The diffusion coefficients were calculated using Chapman-Enskog kinetic theory.…”

Mechanical and environmental models for ceramic matrix composites

“…In equation (7), the oxidation of carbon phase is thought to be controlled by mixed diffusion of oxygen gas through the matrix microcracks. The recession distance x can be properly developed, related to the exposure time t, as (Eckel et al [6])…”

Oxygen Diffusion and Reaction Kinetics in Continuous Fiber Ceramic Matrix Composites

“…The discussion does not consider Knudsen effects in which molecular-wall collisions are more frequent than intermolecular collisions. Knudsen effects are not a factor until the pore becomes as small as 0.1 u,m [7]. In the material studied, typical cracks in the matrix and seal coating are on the order of 1 u.m.…”

“…Only the relevant equations will be discussed. More thorough discussions and derivations can be found in papers by Eckel et al [7] and dime et al [8].…”

“…When the linear term in equation (1) dominates and carbon dioxide is the evolving oxide, the equation for the recession distance is expressed as [7]:…”