if the rust layer becomes more compact with time, then the diffusion coefficient decreases, and n-value will be lower than 0.5. On the contrary, if the diffusion process is accelerated by removing the rust layer, the exponent n will be higher than 0.5, attaining the limiting value of 1.0. Therefore the value of n depends both on the metal nature, the local atmosphere, the maximum exposure time, and the exposure condition (out-door, in-door, position of samples…). On the other hand, the parameter A provides the criterion for gauging short-term atmospheric corrosion susceptibility. It provides a measure of the inherent reactivity of a metal surface to produce a corrosion product layer in a short-term atmospheric exposure.