The relationship between the corrosion resistance and the surface film structure of titanium coated with palladium oxide and titanium oxide mixture (PdO/TiO₂ coated titanium) was investigated. PdO/TiO₂ coated titanium specimens were prepared by applying the mixed alcoholic solution of PdCl₂ and TiCl₃ on the surface of titanium substrate followed by drying and oxidizing this surface in air atmosphere.
The corrosion resistance and electrochemical characteristics of PdO/TiO₂ coated titanium were evaluated by immersion tests and polarization measurements in HCl, H₂SO₄ and H₃PO₄ solutions, respectively. Furthermore, the structure of PdO/TiO₂ film was analyzed by X-ray diffraction and ESCA method. The results obtained are as follows.
(1) PdO/TiO₂ coated titanium which prepared by oxidizing at 500°C×30min has the most excellent corrosion resistance in HCl, H₂SO₄ and especially H₃PO₄ solutions in which uncoated was subjected to active corrosion.
(2) PdO/TiO₂ coated titanium has the excellent corrosion resistance even in small amount of coating weight.
(3) At least a part of PdO and TiO₂ in the surface film are in the states of mutual combination.
(4) Because the overvoltage of cathodic reaction on the PdO/TiO₂ film is very small, titanium substrate is polarized to noble side and its surface is covered with the passive film. Therefore, PdO/TiO₂ coated titanium has the excellent corrosion resistance.

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The corrosion potential variation with time was measured to clarify the corrosion behavior of Fe-Cr alloys in saturated monocarboxylic acid solution and the corrosion behavior of Fe-Cr alloys was investigated comprehensively by the addition of the results of polarization and immersion tests. The effect of heat treatment of a 24%Cr-Fe alloy on the corrosion behavior was studied.
In formic acid solution at 25°C, the corrosion potential of alloys containing less than 13%Cr was less noble than that of pure iron, whereas the corrosion potential of alloys containing more than 18%Cr was more noble than that of pure iron. At solution temperatures between 50°C and 75°C, the corrosion potential of a 18%Cr-Fe alloy was less noble than that of pure iron. The corrosion potential of a 13%Cr-Fe alloy became more noble than that of pure iron in propionic solution.
The polarization test was conducted in solutions of various degree of deoxidation. The Fe-Cr alloys containing 5-18%Cr had the maximum corrosion rate in formic and acetic acid solutions due to dissolved oxygen.
The effect of heat treatment on the corrosion behavior was examined with a 24Cr-Fe alloy. The corrosion resistance of the vacuum melted alloy decreased by aging at 490°C due probably to miscibility gap. On the other hand, the corrosion resistance of the alloy melted in air was improved by the same aging treatment.

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The measurements of the cathodic polarization curve by the potentiodynamic method were made with the observation of the rust width by the naked-eyes in order to classify types of corrosion at the deffective parts of coated steel plate. It was found from the measurements for a variety of coated steels that the cathodic curve for the defective parts showing non-pitting corrosion had a characteristic peak, while one showing pitting corrosion was normal without any peak. Moreover, it was shown that this new estimation method for the judgment of corrosion type could be applied to almost all coated steel panels.

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The effect of precipitate films on metal corrosion has been reviewed on the basis of the selective mass transport through the films.

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