Kinetic Model
Mathematical descriptions of film growth track how the thickness of a protective layer increases over time in a reactive environment. The parabolic oxidation rate applies when the process is limited by the diffusion of ions through the existing oxide scale. As the film gets thicker, the path for oxygen to reach the metal substrate becomes longer and slower.
Measurement Parameter
Thermogravimetric analysis records the mass gain of a sample to calculate the speed of the reaction. Engineers use the parabolic oxidation rate to predict the service life of high temperature sensors. A constant value is derived by plotting the square of the mass gain against the duration of the exposure.
Environmental Factor
Temperature and pressure influence the speed at which atoms move through the oxide lattice. A higher temperature increases the parabolic oxidation rate by providing more thermal energy for ion migration. If the oxide layer cracks, the reaction may switch from a parabolic to a linear behavior as the protective barrier fails.
Material Qualification
Alloy selection for turbine blades and sensor probes depends on achieving a low and stable growth speed. Materials that follow a parabolic oxidation rate are preferred because the self limiting nature of the process protects the bulk metal from rapid destruction. During the qualification phase, samples are held at peak operating temperatures for thousands of hours to verify that the diffusion mechanism remains dominant.
If the rate constant deviates from the expected value, it indicates that the chemical composition of the alloy is not providing a sufficiently dense barrier.
