A new method of crystallizing the thick-hexagonal-plate-crystals of aluminum sulfate from a hot saturated solution of aluminum sulfate acidified with sulfuric acid is mentioned. This crystallization method is to reform crystal habit and to purify the thick-hexagonal-plate-crystals by the unique temperature control. The process consists of four steps. In the first step, a hot saturated solution of aluminum sulfate acidified with sulfuric acid is cooled to crystallize aluminum sulfate; then, in the second step, the resulting slurry containing the crystallized aluminum sulfate is heated up to the temperature at which only a part of the aluminum sulfate crystals dissolve in the solution, and this condition is kept at least one hour; in the third step, the slurry is then cooled at a rate not exceeding 10°C per hour to allow the aluminum sulfate crystals to grow; in the final step, the crystals are separated from the slurry. We have applied this techniques to the treatment of the waste sulfuric acid of anodizing aluminum, and succeeded in recovery and re-use of sulfuric acid and aluminum sulfate by the perfect-closed-system. The product of the thick-hexagonal-plate aluminum sulfate crystals in highly pure, and used for coagulant whereas recovered sulfuric acid can be re-used to anodizing aluminum after the step of mixture control.

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Mechanisms of high-speed electroless copper deposition from EDTA bath were investigated by means of analytical method, X-ray diffraction and electrochemical method. From the analysis of bath components and the reaction products such as copper and hydrogen gas during the electroless copper deposition at 70°C, it was confirmed that the following reactions were occurring in the bath.
Cu deposition reaction: Cu(II)-EDTA+2HCHO+4OH^-→Cu+2HCOO^-+H₂+2H₂O+EDTA…(1)
Cannizzaro reaction: 2HCHO+OH^-→CH₃OH+HCOO^- …(2)
The reaction (2) was remarkably promoted by the increase of bath temperature above 60°C and pH higher than 12.5. X-ray diffraction data of the powdery deposits which have been obtained by 1 hour mixing of CuO and Cu₂O powders with the Cu-EDTA bath at 60°C showed that the reducing power of the solution containing both formaldehyde and EDTA was higher than that of the solution containing each component separately. In the former case, the added Cu₂O was completely reduced to metallic copper. This fact suggests that the spontaneous decomposition of the EDTA bath does not occur through the formation of Cu₂O contrary to the case of Rochelle salt bath, but spontaneous decomposition starts in the bath either by copper particles removed from the surface or by the reduction of metallic copper when the reducing power of the solution increases. The mixed potential theory of the reaction (1) was also studied by potential sweep method.

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Four kinds of anodic oxide films were formed on aluminum, that is, barrier type films formed in an ammonium borate bath, barrier layer films (porous layers thicknesses are negligible) formed in a sulfuric acid bath, porous oxide films whose thicknesses of barrier layers are constant but thicknesses of porous layers are different, and porous oxide films whose thicknesses of porous layers are constant but thicknesses of barrier layers are different. These films were cathodically polarized in a nickel sulfateboric acid mixture solution. Different polarization curves were obtained for the four kinds of anodic oxide films. The thickness of barrier layers and that of porous layers influenced cathodic polarization behavior. And complex effects of the barrier layers and porous layers on the cathodic polarization were observed.

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Dyeing affinity, CR value and properties of the anodized films on aluminum produced in alkaline solutions (0.1M-NaF, 0.1M-NaOH, 0.1M-Na₂CO₃, 0.1M-Na₃PO₄ and NH₄OH-NH₄F baths) at low temperature (0°C) have been investigated and compared with those produced at room temperature (20°C). Anodized films produced at low temperature showed a higher corrosin resistance, scratch hardness and better wear resistance than the films produced in room temperature baths except for dyeing affinity. A thick film and high CR value were obtained in NH₄OH-NH₄F bath at low temperaure, and the CR value was about double of the anodized film produced in room temperature bath. In the case of dyeing affinity, anodized films produced in low temperature baths were inferior to the films produced at room temperature. The films produced in NH₄OH-NH₄F bath or NH₄F bath had very high hardness and better wear resistance compared with films produced in other alkaline baths. The film formed in Na₃PO₄ had very high corrosion resistance. It was considered from these results that the high corrosion resistance was caused by precipitation of aluminum fluoride or phosphate on the surface and in pores.

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The electrode potential and the rate of the electroless copper plating were measured in an iminodiacetate bath. The effect of the concentration of copper complex ion and formaldehyde, and the pH of the bath on the electrode potential and plating rate have been discussed based on the mixed potential theory. Experiments were made at various copper concentration (0.002M-0.1M), formaldehyde concentration (0.1M-2.0M), and pH (9.0-12.5). The rate of copper deposition increased with increasing either copper concentration or formaldehyde concentration with an asymptotic behavior. Corresponding to the change in the deposition rate, the mixed potential was shifted to the noble potentials with increasing copper concentration and moved to less noble potentials with increasing formaldehyde concentration. The average rate of copper deposition seems to increase remarkably above pH 11.0 but the initial deposition rate increased proportional to [OH^-] concentration. The changes in the potential and the rate of electroless copper deposition in the iminodiacetate bath, were fully explained by the mixed potential theory.

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