The minimum cost for the recovery process by concentrating has been found to be determined by the concentration of plating solutions, the way of combination of recovery and rinse tanks, and the concentration ratio. The cost depends also upon the drag-out volume of plating solutions. On the other hand, dripping recovery was unfavorable for this case, because it is necessary to recover almost all the drag-out solution in order to maintain the concentration of the rinse tanks as low as that in the concentration recovery process.

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Chromium (VI) is usually disposed by a coagulation-precipitation method after having been reduced to chromium (III) compound, but the disposal method of the sludges has not been wholly established yet. For the study of the incineration treatment of the sludges containing chromium (III) compounds, a pyrogenetic reaction between co-existing metal hydroxides (Fe, Ni, Cu, Zn) and chromium (III) hydroxide has been investigated. When the sludges were incinerated in air, only CaCrO₄ was found as Cr (VI) compound and other metal hydroxides did not seem to react with Cr(OH)₃ to form chromium (III) compounds even at 800°C for 1hr. Under CO atmosphere, on the other hand, it was confirmed that metal, metal oxide and carbide were formed in the incinerated sludges, and CaCrO₄ was completely reduced to Ca₃Cr₁₀O₁₈ regardless of the co-existing metal hydroxides.

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The stability of electrolyte containing cadmium-ethylenediamine (en) chelate in various pH ranges has been investigated to determine the optimum condition for electrodeposition of cadmium. Cathodic polarization measurement was made in the above bath, and the cadmium deposits obtained under various conditions were examined by X-ray diffraction. The results obtained were as follows: 1) Cadmium (II) ions seemed to react with en to form a stable complex, and bright and smooth cadmium deposits on copper plates were obtained over the range of pH 9-12. 2) Complex ions were greatly affected by anion. Cadmium was not deposited from acidic baths containing a small amount of chloride ions and various precipitates such as Cd(en)_mCl₂(m=1-3), but was deposited from neutral and weak acidic baths. Cadmium-en complex was not formed, when pH-value was in acidic or strong alkaline ranges. In this case, en seemed to act merely as an addition agent upon electrolysis. 3) By the addition of gelatine in to the cadmium-en bath, adherent cadmium deposits having a fine grain (270-290Å) structure were obtained. It was shown by X-ray diffraction analysis that the orientation of the cadmium deposits was strong in (101), but weak in (102) and (103). 4) The optimum composition and operation condition of the bath were found to be Cd (CH₃COO)₂⋅2H₂O: 0.3-0.5mol/l, en: 1.2-2.0mol/l, gelatine: 0.5-1.0g/l, pH: 9-11, temperature: 20-50°C, current density: 1.0-2.5A/dm²; current efficiency was above 90%.

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Various methods for pretreating Mg-alloy plates have been evaluated. Chemically treated plates were more adhesive to enamels than anodically oxidized. Neither of these treatments, however, could prevent the samples from growing black in firing of frit. A new pretreatment called water glass method has been proposed, which provides better substrates for the abhesion of lead enamel and also for preventing growing-black. Several pretreatments for Mg-alloy plates: no-treatment (except pickling with 10% HNO₃ at room temperature), Dow 15 method, De Long method and water glass method were applied to find out the cause for growing-black of enamel and also to examine the adhesion of some low melting frits on the Mg-alloy plates. Lead enamel treated by water glass method showed a high adhesive strength in the bending test and the finish of enamelled surface was glossy and transparent. Lead enamels treated by Dow 15 and De Long methods, however, showed poorer adhesion than that by water glass method, and the finish of enamelled surface was black. Phosphate and antimonate enamels, on the other hand, were of the lowest strength of adhesion for all these pretreatments. The best adhesion for the lead enamel was obtained when drying of the slip was done at 50°C for 50min and firing at 540°C for 10sec. Growing-black of enamels was attributed to the deposition of metallic lead in the boundary surface between frit and Mg substrate, that is caused by the reduction of lead oxide in the frit by metallic magnesium in the plates. The metallic lead deposition was found to reduce the adhesive strength of enamels.

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Anodizing of 99.99% aluminum sheets was carried out in various mono-, di- and oxy-carboxylic acids at a current density of 10mA/cm², and the surface states of the films and of the substrata stripped from the oxide were observed by SEM. In mono-carboxylic acids, in general, anodic corrosion easily took place on the barrier films formed at the initial stage of anodizing, while in formic, acetic, and sometimes butyric acids, aluminum compounds such as oxides and hydroxides were formed on the pits. In butyric and gluconic acids, features of the pits were influenced by the orientation of the substrata. In glycolic acid as a mono-oxy mono-carboxylic acid, porous films with some pittings were formed. In di-carboxylic acids, barrier or porous films were produced, and cell diameters of the porous films as observed on the substrata had a linear relationship with the final bath voltage. In maleic acid, the porous film structure was observed clearly only inside the pits. These results obtained from the observation of structures of the film surfaces and substrata have made it possible to elucidate the anodic oxidation processes.

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The effect of alloying elements on the hardness of anodized films on aluminum has been investigated, in the hope that some new high tensile strength alloys having hard oxide films might be developed. Al-binary alloys were anodized in three typical electrolytes and micro Vickers hardness of the films were measured. With respect to the relationship between the hardness of the films and the alloying elements, three different types were observed: (1) Si, Cr, Cu and Mg cause the decrease in the film hardness with increasing contents of the alloying elements. (2) Be, Zn and Mn initially decrease the hardness but finally constant values are obtained. (3) The hardness of Al-Zr alloy film is larger than that of pure aluminum.

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