2004 Volume 53 Issue 12 Pages 576-582
An attempt has been made as a fundamental study on monitoring of high temperature oxidation of carbon steel with an AC impedance method. A typical environment of hot air at 873K was preferred for acceleration tests of oxide film growth. Two specimens of carbon steel were faced with each other with a narrow gap, which was placed by thin mica sheets at 873K. Then impedance measurements were carried out in a frequency range from 60Hz to 1MHz. It was recognized that both electric resistance and capacitance not only of hot air within the narrow gap but also of the oxide films formed on the surfaces gradually changed with the oxide film growth. During the film growth, the dielectric constant of the hot air was nearly constant. On the other hand, the changes in the dielectric constant of the oxide films were observed, which suggested a time dependence of the oxide film growth. The impedance measurements also detected the film delamination caused by thermal stress. These results suggested a good feasibility of monitoring of high temperature oxidation by the AC impedance method.