干渉色による鉄表面の酸化膜厚さ決定法の吟味

抄録

The iron surface prereduced by hydrogen was oxidized to give rise to interference colors, and was observed with a microscope. The interference color of each grain surface is uniform in its boundary, but the colors differ from each other. After a specimen was oxidized at 400°C, it was once reduced and oxidized again to the same extent at 265°C, and the colors of the same part of the surface in these two cases were compared. It was found that a certain pair of grains interchanged the color with each other. These results would suggest that the rate of growth of the oxide film differs with the crystallographic direction of the grain surface, and that one grain of the pair showing a larger rate at 400°C shows a smaller rate at 265°C. The above result shows that not only the activation energy of the reaction differs in each grain surface, but also the frequency factor of the rate constant is also different in each grain surface. Assuming that the growth of the oxide film obeyed the parabolic law at either temperature, the author calculated, as an example, the difference of the activation energies and the ratio of the frequency factors of the reactions on two grains which showed a comparatively marked color difference. They are 4.3 kcal/mol and 39 respectively. The fact that the color differs in each grain has not been taken account of, in previous works, in estimating the thickness of oxide film by means of the interference color. The author examined the method of estimating thickness by comparing (1) the thickness estimated from the overall color, (2) the average thickness obtained from the color of each grain and its area, and (3) the thickness calculated from the amount of absorbed oxygen.