Crystal structures and distribution of chemically reactive areas have been studied about the electrodeposited nickel having (211), (210) and (110) orientations by means of electron microscopy. In case of nickel electrodeposited on the mechanically polished substrate, characteristic preferred orientations occur in the specimens having the thickness of more than a few μ. A special procedure of the transmission electron microscopy is devised in order to observe directly the structure of thin top layer of the thick deposits having the preferred orientation.
The surface of the nickel deposits with the (211) orientation is covered by many hillocks twinned on a (111) plane perpendicular to the (211) orientation plane. Twin and grain boundaries in these deposits are chemically reactive and dissolved preferentially in a corrosive solution. In the electrodeposited nickel with the (210) orientation, in which the density of twin boundaries and stacking faults is low, these crystal defects are dissolved during immersion in the corrosive solution. In the deposits having the (110) orientation, twinning is seldom observed, and these deposits do not show particularly chemically reactive areas except grain boundaries. When prepared by the present electrodepositing conditions, the nickel deposits with the (211) orientation appear to be chemically more reactive than the deposits having other orientations, because of high density of chemically reactive crystal defects.

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The electrochemical studies have been made in order to know the corrosion resistance of nickel-chromium (Ni-Cr) electroplates. It was found that chromium plate tends to become passive at less noble potentials than the nickel in acid sulfate solution, and the rate of dissolution of the former is very small compared with the nickel electroplate.
The nickel corrodes somewhat more rapidly than it would in the absence of chromium, because of the galvanic cell created by chromium covering to nickel. In the initial stage of the corrosion reaction, the rate of attack of the nickel was found to be affected by the numbers of the defects of chromium coatings and also by the nature of nickel coating.
The microscopic examination of the cross section of Ni-Cr electroplate which have been subjected to the electrochemical measurement showed that corrosion pits in the nickel layer were distributed rather uniformly in the case of microcracked chromium, but randomly in the conventional chromium plate.
The corrosion resistance of the double-layer nickel can be explained by the fact that the sulfur-containing nickel plated on the sulfur-free nickel will undergo preferential attack and is effective in the retardation of the rate of penetration into the double-layer nickel coatings.

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An investigation was carried out about the effect of interstitial elements and iron on corrosion resistance of commercially pure titanium in hydrochloric acid and sulfuric acid at room temperature and their boiling temperatures.
The results obtained in this study were summarized as follows.
(1) Oxygen, nitrogen or carbon, up to 0.5%, improved the corrosion resistance of commercially pure titanium in hydrochloric acid and sulfuric acid.
(2) Addition of iron to the specimens containing oxygen, nitrogen or carbon, showed a tendency to decrease corrosion resistance.
(3) The specimen containing semi-transformed structure was inferior to equiaxed α structure as for corrosion resistance.
(4) Anodic polarization was measured in the hydrochloric acid by Gerischer type potentiostat. And the above mentioned results were confirmed from the standpoint of anodic polarization.

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