Chromium coatings of 2.5 to 20μm film thicknesses were prepared by an ion-plating method. Properties of the films were examined and compared with those of conventional electroplated chromium films on the same kind of steel. Film thickness measurement was made by optical microscopy. The structure and surface morphology of the films were observed by scanning electron microscopy. Wear resistance of ion-plated chromium was studied by the use of Ogoshi rapid wear testing machine in dry air. Heat and corrosion resistances were also determined with these specimens. In the sliding distance range from 66.1 to 400m under constant sliding speed and load, the wear loss of ion-plated films of 10μm or more thickness was less than that of electro-plated films. Specific wear was measured as a function of sliding speed from 0.61 to 3.5m/sec under constant sliding distance and load; the specific wear of the ion-plated films of more than 10μm thickness was less than that of electro-plated films, especially in the high range of sliding. speed. The heat resistance of ion-plated films was determined by evaluating the weight gain of the oxidized specimen at 800 and 900°C in air as a function of heating time. In this test, any notable differences were not found between the ion-plated films and electro-plated ones. Salt spray tests and anodic polarization measurements in a nitric acid aqueous solution revealed that the ion-plated films were more resistant to corrosion than electro-plated films.

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Experiments were carried out to find the optimum bath composition and plating conditions for obtaining a bright chromium plating from CrCl₃·6H₂O-CH₃OH baths. It was found that the appearance of the bright chromium deposits is influenced by plating time and current density. The cathodic current efficiency was ca 50% with the bath containing CrCl₃·6H₂O 300g/l (current density: 250mA/cm², plating time: 3-5sec, 30°C). The addition of a small amount of lithium hydride to the bath gave rise to smooth and silver-white deposits. X-ray diffraction patterns showed that the Cr deposits obtained had no preferred orientation of crystal. The mean lattice constant and grain size of the deposits were found to be 4.56-4.58Å and 85-390Å respectively.

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Several equations to calculate throwing power index have been proposed to compare the throwing power for various plating solutions. In Watson's method (Hull Cell method), Field's equation is mostly preferred. Throwing power index, T(%), calculated from the equation does not necessarily indicate an essential strength of throwing power because any value can be obtained for a certain secondary current distribution, if measuring points on a Hull Cell panel are intentionally selected. Field's equation contains the terms of primary and secondary current density ratio (L and M) which are determined from the thicknesses at two points on the panel. If the measuring points are adjacent to each other and are on a high current density edge of the panel, L and M values gradually reach unity and T value zero. In order to improve this defect in Field's equation a new equation has been formulated on the basis of the slope of a secondary current distribution curve determined from the thicknesses measured at two points on the Hull Cell panel and from plating time.

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In a practical double nickel plating process, nickel concentration tends to increase in the bright bath, but to decrease in the semi-bright bath. For this process, the following recycle was studied; the first brightener containing sulfur was removed from a Watts type bright bath by an adsorption process through a column packed with polymeric adsorbents, and the bright bath treated with the adsorbents was utilized as a part of the semi-bright bath. In this work, sodium p, p′-ditoluensulfonimide (DTI) was used as the first brightener and Amberlite XAD-7 (XAD-7) as the polymeric adsorbent. The concentration of DTI was measured by optical absorption. As a result of treating the bright bath by means of the column method, it was found that DTI is removed by adsorption on XAD-7, and DTI adsorbed on XAD-7 is desorbed by water. In the range of 0.8 to 6.7g/l of DTI, the adsorption amount was 25g/l-XAD-7 until DTI leakage became 20mg/l. Besides, the adsorption capacity of XAD-7 is not decreased by the repeated cycles of adsorption and desorption of DTI. The adsorption of DTI on XAD-7 mainly results from the salt-out effect of nickel salt in the bath.

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A study of the burning phenomena of Al surfaces during anodic oxidation has been made in the forced laminar flow of oxalic acid under galvanostatic conditions. The experiment showed that the bath voltage at the start of the burning was not affected by applied current densities, bath temperature and flow rate of the electrolyte, and that decreased with increasing specimen's surface temperature. The thickness of the oxide film at the start of the burning decreased with increasing current densities. These results suggest that the mass transfer of ion through the porous oxide film affects the burning phenomena and that the deplation and non-uniformity of ion concentrations near the barrier layer lead to the burning. A theoretical equation for the relation between the thickness of the oxide film at the start of the burning and the current density was derived: The equation indicates that the thickness is inversly propotional to the current density. The calculated values of the thickness are in good agreement with the experimental results.

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In the previous paper, it was reported that Cr₇C₃ layer can be easily formed on cemented carbides immersed in a borax bath containing pure chromium metal powder, and the oxidation and corrosion resistances of the cemented carbides, thus treated, can be remarkably improved. The present study was undertaken to investigate the possibilities of VC, NbC and TaC coatings on cemented carbides. Both NbCl₅ and electrolytically dissolved Nb in the borax bath were effective in providing NbC layer on cemented carbide. VC layer was obtained in the bath containing VCl₃, and TaC layer was obtained in the borax bath containing electrolytically dissolved Ta. These layers can be thought to be formed by the reactions between atomic V, Nb or Ta in the bath and either C in Co binder phase or, to some extent, carbon in WC carbide. The parabolic law can be applied to the relation between the thickness of the NbC layer and the treating time. The corrosion resistance of cemented carbides against 10%HNO₃ and 10%H₂SO₄ aqueous solutions was remarkably improved by NbC and TaC coating.

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Effects of S- and N-compounds such as sodium thiosulfate, nicotinic acid, thiourea, glycin, etc. on the codeposition of molybdenum in the electrodeposition of Ni-Mo alloys were studied by measuring the partial cathode current efficiencies of nickel and molybdenum. The bath used contained 0.22M of nickel sulfate, 0.05M of acid molybdate, 0.27M of potassium sodium tartrate, and ammonium hydroxide (for adjusting the pH of the solution to 10.5). S- and N-compounds used in this work (except urea and glycin) prevented the codeposition of molybdenum with nickel. Further, polarographic behavior of nickel ion in the presence of S- and N-compounds was studied, and it was indicated that the additive compounds which prevented molybdenum codeposition facilitated discharge of nickel and hydrogen ions on mercury. Double layer capacity decreased when 40mM of nicotinic acid was added to the bath. This indicated that the adsorption of nicotinic acid occurred at nickel cathode during the electrodeposition of nickel. The adsorbed species appeared to electrocatalyse the deposition of nickel and hydrogen by the same mechanism proposed by Mark et al. on mercury electrode. Adsorbed S- and N-compound species also appeared to occupy the sites of hydrogen to bring about the reduction of intermediate molybdenum lower oxides formed on the cathode.

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A patented method of chromium plating from trivalent chromium bath, developed by Albright & Wilson Ltd. (Japan Kokai Pat. Sho 50-92237), has been examined by Hull Cell Test. A satisfactorily decorative chromium coating was obtained without evolution of chlorine at anode from an aged bath under the following conditions; chromium (III)≅0.4mol/l, formate>0.8mol/l, chloride>1mol/l, ammonium>1mol/l, boric acid>0.5mol/l and bromide ≅0.1mol/l, pH2.5-3.0, bath temperature <30°C, current density 1-200A/dm². The formate formed a complex with chromium (III) such as [Cr₃ (OH)₂(HCOO)₆]⁺, while the bromide suppressed evolution of chlorine in the presence of formate, ammonium and boric acid. When chromium (III) chloride was used as chromium (III)-salt, however, green insoluble compounds were formed after a few days. The amount increased on standing and consequently, chromium coating could not be obtained after about a month. Ammonium chromium (III) sulfate, chromium (III) sulfate and chromium (III) fluoride baths produced soluble compounds which were less green than those from the chromium (III) chloride bath, and thus chromium plating were obtained even after considerably long standing. On the other hand, chromium deposits could not be obtained, from the bath containing chromium (III) nitrate, chromium (III) acetate, chromium (III) perchlorate or chromium (III) sulfamate as chromium (III)-salt. No organic carboxylate except formate gave good results. Permissible impurities were copper<0.02g/l, zinc<0.02g/l, iron (II)<2g/l, nickel<1g/l, cobalt<0.1g/l, chromium (VI)<0.7g/l and nitrate<0.05g/l for this bath.

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