Half-value breadth of X-ray diffraction line profile from the as-plated chromium deposit was found to be about 5.30°, but the same specimens annealed at 600°C gave the half-value breadth of 1.75°. Hard chromium coatings which had wide half-value breadth were characterized by high hardness. Close correlation was also observed between the Micro Vickers hardness and the half-value breadth of X-ray diffraction line. It was found that the hardness of electrodeposited chromium was related to the half-value breadth by the following simple equation, Hv=115B+325. Here, Hv is the value of the Micro Vickers hardness estimated from half-value breadth and B is half-value breadth of X-ray diffraction line. By using this equation, hardness of the chromium coatings can be determined by X-ray diffraction method with deviations of ±4% as compared to the Micro Vickers hardness measurement.

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Aluminium specimens anodized to form porous oxide films in an oxalic acid solution were reanodized in a neutral boric acid-borate solution (pH=7.4, 20°C) at a constant c.d. of 0.5mA/cm² and changes in the anodizing voltage and geometrical structure of the film were examined. An automatic apparatus was used for the current-controlled electrolysis and an ultra-thin sectioning technique was utilized in electron-microscopy. It was found that the oxide formation occurs both at the barrier oxide/solution and oxide/metal interphases. The former which leads to pore-filling is due to the transport of Al³⁺ ions through the barrier oxide whereas the latter is caused by the O^2- ion transportation. The voltagetime relationship is represented by two successive straight lines of different slopes and the pore-filling was found to be completed at the time when the slope changes. Apparent transport numbers for Al³⁺ and O^2- ions were determined respectively to be 0.40 and 0.60 and they were almost independent of the applied c.d. It is shown that the porosity and thickness of the film could be estimated by an analysis of the voltage-time relationship using the above transport numbers.

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Al-Mg-Si alloys aged under various conditions were anodized at 15V in sulfuric acid solution, followed by anodizing at 4V in the same solution, and the anodic oxide films of grey to black in color were obtained. From the micro-structures and the electrical conductivities of aluminum alloys, it was found that the degree of color increases with an increase in the amount of Mg₂Si precipitates, which depends upon the ageing conditions of the alloy. The roughening at metal-oxide interface of colored films suggests that the coloring may chiefly be caused by the formation of branched-pore structure due to the local-attack of the current to Mg₂Si precipitates and resulting uneven dissolution of the barrier layer.

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