Stress of the chromium deposit obtained from various baths, at different temperature and current density, was measured with Brenner and Senderoff's contractometer, to study the relation between the stress and other properties, such as brightness, hardness, cracks and corrosion resistance.
Result:
(1) In chromium plating at a certain current density, the luster of the deposit changes gradually in the order from “mat” to “frosted, ” then to “bright, ” and finally to “milky, ” depending on the change of temperature. Stress of the thin deposit is very small with “mat, ” rapidly increases with “frosted, ” then becomes maximum with “bright” and decreases again with “milky.” It is supposed that the smaller the grainsize of the deposite is, the brighter is the luster.
Stress of the thicker deposite becomes smaller, depending on brightness, and finally compressive at “bright.” This phenomenon can be explained by the exceptionally good micro-throwing power of chromium plating in the cracks of the deposited. Many theories have been so far discussed upon the brightness of chromium plating, but the good micro-throwing power is supposed to be one of the reasons for brightness as in the case of nickel plating.
(2) The facts that its iso-hardness curve resembles its iso-stress curve and that the brighter the deposit is, the higher is the stress, suggest that the hardness of chromium deposit should have much to do with its stress.
(3) Cracks produced in the cromium deposit are supposed to be caused by its initial big stress. this means that the stress is greater than the tensile strength. In fact, when the initial stress is small, few or not cracks occur. Such deposits can be obtained from the bath of concentrated CrO₃, high ratio of CrO₃/H₂SO₄, and higher temperature, which can also be considered as right plating conditions to get a deposit of good corrosion resistance.
(4) Initial stress of the chromium deposit from the bath of SiF₆ and CR-110 is comparatively greater than that from Sargent bath. Stress of the thicker deposit is smaller, which usually has fine cracks and brighter luster.
(5) The deposit from the bath with selenic acid has smaller stress and fewer cracks, but its brightness becomes poor.

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Improved corrosion protection of recently developed duplex nickel-chromium coating is generally attributed to the galvanic effect of semibright nickel and bright nickel contact corrosion cell. From the same viewpoint, copper and bright nickel couple is expected to have similar effect in copper-nickel-chromium coating, which, however, is not empirically evaluated as high as duplex nickel-chromium system.
A series of electrochemical experiments was, therefore, carried out to compare galvanic effect of the above two couples in different corrosive solutions. Conclusions are as fallows:
i) From static electrode potential-time curves of various types of nickel, copper and chromium electrodeposits, it is found that bright nickel acts as anode except copper and bright nickel couple in CASS test solution, the open circuit cell voltage of which is very small, and semibright nickel and bright nickel couple in sulfurous acid solution, between which there is not significant potential difference.
ii) From the weight loss due to corrosion, chromium was found to be in passive state in most corrosion test solutions. Therefore, galvanic effects of the above two couples are presumed to be independent of chromium top layer.

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Aluminum metal reacts with various organic halides to give aluminum halides at a very slow rate initially. Then the aluminum halide in this reaction system autocatalytically accelerates the reaction itself. So that, it needs an induction period to give the aluminum halide actually. When aluminum or aluminum alloy was washed by various chlorinated hydrocarbon to remove the oily dirt from its surface, much trouble caused from corrosive degradation of aluminum surface or explosive reaction owing to the autocatalytic reaction has been reported.
The present study has been made to prevent this trouble and also to clarify the mechanism of the reaction.
First, several methods of measuring the induction period were examined, from which a new simplified method to measure it rapidly and accurately was proposed.
Then, many experiments were carried out to ascertain the factor which controls the induction period.
As a result, it was suggested that the rate of the halogen radical formation from organic halide by heating was one of the most important factors which had much to do with the induction period.

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