Anodic oxide film on aluminum is subjected to secondary electrolysis in an electrolytic bath containing Al3+ and/or Ca2+ to allow aluminum and calcium oxides (hydrates) to be deposited in fine pores in the film, thus serving for white coloring of the film. Three electrolytic baths are examined. One contains an aqueous calcium sulfate solution alone and a second one contains additional ammonium aluminum sulfate 12-water (ammonium alum). The third is prepared by adding gluconic acid to the latter mixture solution. As test samples of anodic oxide film, double layered film is prepared by performing anodic oxidation successfully in a sulfuric acid bath and then in a phosphoric acid solution bath. The results show that film most homogeneously colored with the highest whiteness degree is obtained when A. C. electrolytic coloring is carried out in a bath containing calcium sulfate and ammonium alum. Aluminum and small amount of calcium (both appearing to be a hydrate) are found to be deposited in the resultant film. A. C. voltage scanning reveals that the deposition of these substances occurs rapidly arouud 18 V.
The spherical particles of hydrated iron oxide, used as microcapsule shell, were prepared by “Inter-facial Reaction Method”, in which the hydrated iron oxide was formed by the reaction of Fe (NO3) 3 aqueous solution emulsified in benzene with NaHCO3 aqueous solution. The preparation of the spherical particles by using the surfactants of various HLB was examined in order to determine the best HLB range of surfactant for the formation of the spherical particles. The pH value of the reaction mixtures was measured during the reaction time in order to study the mechanism of the formation of the spherical particles. The differential thermal analysis curve, the X-ray diffraction pattern, the particle mean diameter, the specific surface area, and the pore volume distribution were measured to determine the properties of the spherical particles. The spherical particles of hydrated iron oxide were not crystalline and transformed to crystalline α-Fe2O3 particles by heating at 500°C, of which shapes were also spherical. The particle mean diameter was about 0.9-1.0μm, the specific surface area was 400-450 m2/g, and the particle had many pores of 20-40Å in diameter on the surface. The spherical particles were formed in the HLB range of 4-7, by slower reaction (20-30min.) than in other HLB range (1-2min.). These results suggest that, in the HLB range of 4-7, the Fe (NO3) 3 aqueous solution microdrop has the stable protective layer of surfactant-benzene on the surface, and the protective layer maintains the sphere of emulsion and interferes with the reaction of Fe (NO3) 3 and NaHCO3.