In the examination of atmospheric corrosion of steel panels specimens were exposed to an industrial atmosphere (Koto-ku, Tokyo) for one year at inclination angles of 0°, 30°, 60° and 90°, in order to know how the exposure angle affects the corrosion rate.
Results obtained were as follows:
(1) No difference in the corrosion rate was apparent between 30° and 60° specimens;
(2) The corrosion rate was the greatest for 0° and 90° ones;
(3) As for the corrosion rate on the surface and the back side of a specimen, it was found greater on the latter;
Judging from the above-mentioned facts, specimen racks used for the atmospheric corrosion tests in our country should be designed to give specimens inclination angle between 30° and 60°.

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A study has been made of the protective zinc phosphate coating on mild steel in acid solutions saturated with zinc phosphate to find the effect of additional oxydants and of electrochemical polarization on the formation of the phosphate film. In the solution containing no additional oxydant deposition does not occur, even though the hydrogen ion may act as a weak oxydant in corrosion of iron. Oxygen dissolved in solution, however, causes the formation of phosphate deposit at relatively slow rate. Addition of strong oxydants such as KMnO₄ and H₂O₂ gives rise to passivation of iron and hence results in no deposition of the phosphate film. A moderate oxydant of sodium nitrate that has been used in practice seems to be the most suitable for the phosphate coating. The phosphate film is also formed by means of electrochemical polarization of mild steel in the direction either anodic or cathodic even in the solution containing no oxydant. Addition of small amount of iron in the solution containing nitrate accelerates the formation of the phosphate film.
These results are discussed in view of the following reaction scheme:
HPO₃H₂PO^-₄+H⁺
Zn²⁺+2H₂PO^-₄→Zn(H₂PO₄)₂
nZn(H₂PO₄)→{Zn(H₂PO₄)₂}n
{Zn(H₂PO₄)₂}_n→1/3[Zn₃(PO₄)₂]^solid_n+2/3nH₃PO₄
It is suggested that the role of oxydant and electrochemical polarization is to build up the driving force, i. e. the positive affinity of the overall deposition reaction in zinc phosphate-saturated solution by probably taking off the hydrogen ion at the surface of mild steel.

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