Deterioration of anodic films and chemical films for aluminum alloy by heating was investigated. Material kinds of specimens were 2S and 24S-T4, and surface treatments used were sulfuric acid anodizing, chromic acid anodizing and chemical film treatment.
Those finished specimens were heated for 8 hours and 100 hours at 80°C, 120°C, 160°C, and 200°C, respectively.
Then, deteriolation of those finishes was examined by salt spray tester, running continuously for 500 hours.
Test results are shown in fig. 1 to 6, and summarized as follows:
(1) The appearance of specimens, of both anodic coating ane chemical films were some what changed at 80-120°C or higher.
(2) After salt spray exposure little or no corrosion attack was found on 2S specimens, but severe one was found on 24S specimens heated to 80°C or higher.
(3) Chemical films were more sensitive to heat than anodic coatings.
(4) Sulfuric acid anodized 2S specimens were crazed by heating, nevertheless their corrosion resistance were not reduced.

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It was shown by the Hull cell test that semi-bright tindeposits could be obtained from stannous sulfate bath in the presence of Pluronics (non-ionic surface active agents), and also the beneficial action of Pluronics was overshadowed by adding a small amount of halogen ions.
Polarization associated with electrodeposition of tin from the stannous sulfate bath (1M H₂SO₄, 0.43M SnSO₄, Pluronics and/or halogen ions) was measured in order to make clear the mechanism of action of Pluronics and halogen ions added to the bath in the concentration ranges of 0.01-0.5% and 0.00003-0.3M respectively.
In the presence of Pluronics, at low current densities the polarization increased very little, then a sudden increase (300-400mV) occurred at a certain current density, and then it increased gradually until hydrogen was evolved.
The current density of the sudden increase point was examined as the function of the Pluronics concentration, the bath temperature and the ratio of the hydrophilic and hydrophobic portion of the pluronic molecule, presence of halogen ions rendered the sudden increase point to higher current densities. Such an activity of halogen ions were remarkable in the following order: I^->Br^->Cl^->F^-.
The result was tried to be explained by the fact that Pluronics tended to accumulate onto the metal-solution interface and adsorption of halogen ions on the interface was stronger than that of Pluronics and the adsorbed halogen ions made the electrode reaction more reversible.

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Voltage-amperage curves for anodizing pure aluminum, 17S, 52S and 61S in sulfuric acid solution with d. c. constant current density can be divided into three types. Electrolytic conditions to get good films of wear resistance are as follows:
1) Initial voltage is high but final voltage low and the rate of film growth also low.
For instance, voltage vs. time curve is parallel to horizontal line (time).
2) Both initial and final voltage are high and the forming voltage increases very fast and the rate of film growth is also high.
For instance, voltage vs. time curve is parallel to vertical line (voltage).

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For the purpose of disposing the industrial waste containing chromic anhydride, the electrolytic reduction of Cr₂O₇^2- into Cr³⁺ in the chromium plating solution diluted 200-fold is preliminarily examined on a small scale.
The reduction is effectively carried out by the use of the iron anode and cathode. On the cathode, the electrochemical reduction takes place mainly, while on the anode, iron dissolves into the solution in the form of Fe²⁺ which reduces Cr₂O₇^2-.
The pH of the solution must be kept less than 2.8 otherwise hydroxide will be formed that makes voltage high and time of electrolysis long.
The optimum range of current density should be from 1 to 2A/dm² from the viewpoint of the terminal voltage and reduction speed.
The current efficiency of the electrochemical reduction on the cathode is less than 52% in the range of current density from 0.5 to 3A/dm², where the current efficiency decreases with an increase of the current density.

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