Abstract
A study has been made of the kinetics and mechanisms of the oxidation resistance of rimming steels to carbon dioxide atmospheres over long periods of testing. The effects of moisture and carbon monoxide additions to the carbon dioxide, gas pressures up to 600 psig and temperatures from 350 to 550° have been investigated.
It is shown that protective oxide films are usually formed at a gas pressure of one atmosphere, but at high pressures and particularly with moisture and carbon monoxide in the gas, the oxide film may locally break down, giving rise to oxide excrescences which can grow in size and number to cover most or all of the surface of the specimen. The formation of excrescences causes the rate law to change from cubic or parabolic to linear over a transitional period. The reaction rate constants are dependent essentially on the temperature whilst moisture, carbon monoxide and gas pressure are mainly effective in promoting the initiation and development of excrescences.
Possible causes for the formation of excrescences, as well as the mechanism of the linear rate law during the post-breakaway period, are discussed.
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