![]() If the oxide film initially produced is porous the oxygen is able to pass through and continue to react at the oxide–metal interface. Oxides are therefore usually composed of an aggregate of individual grains or crystals, and exhibit phenomena such as recrystallization, grain growth, creep involving lattice defects, just as in a metal. Each nucleated region grows, impinging on one another until the oxide film forms over the whole surface. After the build-up of a few adsorbed layers the oxide is nucleated epitaxially on the grains of the base metal at favourable sites, such as dislocations and impurity atoms. This process, involving dissociation and ionization, is known as chemisorption. During oxidation the first oxygen molecules to be absorbed on the metal surface dissociate into their component atoms before bonding chemically to the surface atoms of the metal. Bishop PhD, CEng, MIM, in Modern Physical Metallurgy and Materials Engineering (Sixth Edition), 1999 12.2.1.2 Kinetics of oxidationįree energy changes indicate the probable stable reaction product but make no prediction of the rate at which this product is formed. ![]()
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