Taking representative points on a zinc phosphate conversion coating is suggested as a method of preteatment in auto body painting. Conversion treatment for the dip process has been applied to improve anti-corrosion performance over the whole of the body work, and it is noted that zinc phosphate crystal converted by such treatment theoretically has an excellent quality reaction.
That is, when the dip method conversion treatment is applied a coating consisting mainly of phosphophyllite (Zn₂Fe(PO₄)₂⋅4H₂O) is found on cold-rolled steel, while on zinc coated steel, a hopeite coating (Zn₃(PO₄)₂⋅4H₂O) is found.
With a view to improve water proof ness and adhesion to zinc-coated steel, metal ions such as Mn²⁺ or Ni²⁺ were added to the treatment bath to alter the quality of the hopeite crystal. All these conversion coatings by the dip method were found to have stable properties under the paint coating, and to play an extremely important role in corrosion proofing the auto body.
It is also pointed out that the surface condition of the steel is key to phosphatability.

View full abstract

Aluminum was anodized for different durations in a 13M H₂SO₄ solution (20°C) at constant voltages of 30, 35, 40 and 45V.
It was possible to deposit nickel uniformly into the pores of the oxide films formed without any pretreatment. Electrodeposition did not take place with films formed in dilute H₂SO₄ solutions. The behavior and mechanism of the electrodeposition in relation to film structure were examined and the results are summarized as follows:
Film structure: Reanodizing behavior of the specimens in a neutral borate solution suggests that the 13M H₂SO₄ films have numerous micro-voids in the barrier layer. The formation of the microvoids, which probably penetrate through the oxide to the substrate metal, is caused by incorporation of SO₄^2- ions in the oxide and their partial removal when the film is washed with water.
Deposition behavior: Electrodeposition was carried out in two steps in a solution of 70g·dm^-3 NiSO₄⋅7H₂O-30g·dm^-3 H₃BO₃ (20°C) by applying a small cathodic current of 0.05A·dm^-2 for 15min, followed by a current of 1.45A·dm-2 for 45min.
The first step with the small current is essential to form nickel nuclei in the micro-voids, and a uniform deposit was obtained only by the two step procedure. The maximum thickness of the uniform deposit increased with the voltage at which films formed. The distribution of nickel in the pores and the surface of films was observed by XMA.

View full abstract

Pb-Te and Pb-Ag alloys were tested as anodes for chromium electroplating, and were compared with the Pb, Pb-Sn and Pb-Sb alloys that are used as anodes in commercial chromium electroplating. The Pb-Ag alloys did not dissolve in H₂SO₄ during the electrolysis test period.
The amount of PbCrO₄ produced on the anode surface in the electrolytes was very small for Pb-Ag alloys, while electrocatalytic activity during anodic oxidation of Cr³⁺ to Cr₂O₇^2- was lower than for the other Pb alloys. Pb-Te alloys were found to be the most suitable anodes for chromium electroplating because their anodic dissolution was relatively small and their electrocatalytic activity for this reaction was high.
The relationship between electrocatalytic activity and the rate of production of PbCrO₄ was also discussed.

View full abstract

Lead (II) ion coexisting in a plating bath as an impurity, of which source is chemical agents and/or dissolution of electrode, adversely affects the plating finish. We attempted the removal of trace amounts of lead (II) ion using inorganic adsorbents. Adsorption test for 5mg dm^-3 of lead (II) ion in an iron-zinc alloy plating bath [FeSO₄⋅7H₂O 300gdm^-3, ZnSO₄⋅7H₂O 150gdm^-3, (NH₄)₂SO₄ 30g dm^-3, and citric acid 10g dm^-3] with various inorganic substances was carried out by means of batchwise operation. Of these substances, hydrous antimony (V) oxide exhibited the outstanding ability, but the fact that antimony (V) ion tended to leach out to the bath was undesirable. However, it was found that silica-titania mixed-oxide gel was favorable for the adsorption of the antimony (V) ion.
After the flow of 6dm³ of the plating bath containing 5mg dm^-3 lead (II) ion through two columns of 10mm inner diameter connected in series (the first packed with 3g of hydrous antimony (V) oxide and the second with 3g of silica-titania gel) at a rate of 1cm³min^-1, the concentration of lead (II) ion in the effluent was still kept below 0.17mg dm^-3, which corresponded to a removal rate of 97%.

View full abstract

Electroless Ni-P-SiC composite coatings were studied to determine the factors affecting SiC particle content in deposits. The quantity of particles codeposited into the nickel matrix was found to vary with the impingement number, the holding time of particles on the substrate and the deposition rate. It was found that the impingement number of the particles was affected by SiC concentration in the bath and air volume for agitation of the bath solution, and that the holding time on the substrate was affected by SiC particle size, the setting angle of the specimen, and the volume of air used in agitation of the solution.

View full abstract

Molibdenum coatings having a thickness of 5-30μm were chemically deposited on 10×13×0.5mm substrates of nickel, iron, copper and 18-8 stainless steel for 60 minutes, using the following CVD reaction;
2MoCl₅(g)+5H₂(g)→2Mo(s)+10HCl(g)……(1)
The molybdenum coatings on nickel substrates were obtained at 550-750°C and resisted peeling even under a thermal shock of 600-700°C. A diffusion layer 3-10μm thick was observed at the interface between the molybdenum and the nickel substrate. Examination using a micro X-ray diffraction meter showed that the compound MoNi₄ formed in the diffusion layer.
Molybdenum coatings were also deposited on iron substrates at 750-800°C, on copper at 550-650°C, and on 18-8 stainless steel at 550-750°C. The molybdenum coatings on iron and copper were thicker than those on nickl. A diffusion layer was observed between molybdenum and each of the substrates.
The use of nickel-plated iron substrates made it possible to obtain molybdenum coatings on iron substrates at temperatures as low as 550°C.

View full abstract

The film properties of electroless Ni-Mo-P alloy films after complete formation of the final compounds and phases were investigated in relation to Mo content. Films may be classified into two groups on the basis of their structure -amorphous and crystallized- in the as-plated condition and two groups differ in Mo-dependence. Residual Mo content, calculated from substituting the amount of Ni₃P compound, emphasized the differences between the groups: in amorphous films, the estimated Mo content calculated from the interplanar spacing of Ni-Mo alloy is almost equal to the residual Mo content, whereas in crystallized films, residual Mo content is higher than the estimated value. Finally, the resistivity of the Ni-Mo-P alloy films after heat-treatment at 900°C is closely related to estimated Mo content, and the large difference in the crystallized films is due to the Mo-rich zone, which makes the resistivity higher than that of bulk Ni-Mo alloy.

View full abstract

The influence of magnetic fields on the structure of electrodeposits from complex, and on the mechanism of cathodic and anodic reactions with the electrodeposits were examined. Magnetic fluxdensity was 0.3T on the working electrode. It became clear that the action of Lorentz force accounted for the major part of magnetic field effect. The pH 12 electrolytic baths used were composed of 0.05-0.5mol·dm^-3 CuSO₄+0.1-1.0mol·dm^-3 EDTA solutions including 0.2mol·dm^-3 sodium sulfite. Anodic reactions were independent of magnetic field, but cathodic reactions were affected. The most important of these influences were as follows: The stability constant of the Cu(II)-EDTA complex became larger. Limiting current density increased. The (111) face of the deposits increased. The grain of the deposits was fine. Exchange current density decreased. Charge transfer resistance decreased. The temperature in the vicinity of the cathode dropped and that in vicinity of the anode rose. This was attributed to decrease in the thickness of the diffusion layer due to Lorentz force.

View full abstract

Electrodeposition behavior of Zn-Mn alloys was studied by measuring the polarization curves in sulfate baths containing sodium citrate. Zn began to be electrodeposited at about -1.1V (vs. Ag/AgCl) and the codeposition of Mn was recognized at potentials less noble than -1.4V. This points out a feature of normal codeposition in which the more noble Zn is electrodeposited preferentially to Mn.
The effect of the addition of sodium citrate on the partial polarization curves of Zn and Mn was also investigated. It not only lowered the limiting current densities of both Zn and Mn, but also shifted their deposition potentials to the less noble direction. Therefore, both Zn- and Mn-citrate complexes seemed to be formed in the Zn-Mn alloy plating baths.
Lowering the pH of the baths increased the current efficiency for alloy deposition, although white precipitates were formed in the baths during the electrodeposition of the alloys.

View full abstract

An investigation of amorphous iron-molybdenum alloy films formed by electrodeposition was undertaken to determine the influence of various factors, and the corrosion behavior of the films was also examined. The amount of Fe²⁺ in the baths influenced whether the iron-molybdenum alloy films were amorphous or crystalline. The amorphous structure was formed by electrodeposition from a bath containing less than about 10wt% Fe²⁺ when the molybdenum content was 12.5g/L. The presence of Fe³⁺, however, had a detrimental effect on the electrodeposition of iron-molybdenum alloys. The amorphous structure was formed at a molybdenum content of more than about 20wt% in the electrodeposited films. The relation between the current efficiency and the pH value was observed at a current density of 0.8A/dm² in a bath containing 12.5g/L of molybdenum and 6.5g/L of iron at 30°C. It was found that film structure changed from crystalline to amorphous with increasing pH value, with a limiting value of 3.7. Electrochemical corrosion tests were curried out in 0.1N H₂SO₄, 0.1N HCl, 3% NaCl, and 0.5% NaOH aqueous solutions which were air saturated at 25°C. The results indicate that amorphous iron-molybdenum alloy films have higher passivating ability than their crystalline counterparts in all of the solutions studied except NaOH.

View full abstract

Amorphous Co-Ti alloys have been produced by both DC and pulse current plating from an acid sulfate bath, and their electrochemical properties in a sulfuric acid solution have been studied by means of electrochemical polarization measurements. X-ray intensities diffracted from the deposits were progressively lowered with increasing concentration of titanyl ion and faded away for DC-plated deposits containing 17.8mol% Ti. The pulse-plated Co-Ti alloys exhibited an amorphous phase with a high degree of homogeneity as well as high titanium content compared with DC-plated alloys. It is probable that the induced codeposition of amorphous Co-Ti alloys proceeds via the formation of a complex hydroxide, such as [Co⋅Ti_n(OH)_2n+1]_ad, as an adsorbed intermediate. The exchange current for catholic hydrogen evolution on the amorphous alloys was two orders of magnitude larger than that on pure cobalt deposits, whereas there were no differences in their corrosion resistance. This high activity for hydrogen evolution is ascribed to an increase in surface roughness caused by a selective dissolution of titanium from the amorphous alloy electrodes.

View full abstract

Experiments were carried out in accordance with a design of experiment and the following results were obtained.
(1) For rolled structural steel for welding of low (58-73kgf/mm²) and midium (41-52kgf/mm²) strength, yield point and elongation were not affected by the galvanizing conditions.
Tensile strength was affected by the cooling method, but the tensile strength of both galvanized steels were higher than that of the non-galvanized steel, and no adverse effects occured.
All tensile properties of the galvanized steels indicated higher or equivalent values in comparison with the non-galvanized steel.
(2) For high strength low alloy structural steel with a grade of 80kgf/mm², yield point and tensile strength were not affected by the galvanizing conditions.
Elongation was affected by pretreatment conditions. The elongation of steel galvanized after blasting was less than that of steel galvanized after acid pickling, but no significant effect was attributable to whether a galvanized coating was applied or not.

View full abstract

The anodic coatings on aluminum in 5wt% oxalic acid solution were investigated by pulse current with a negative current component, including the effects of such variables as temperature, voltage and negative current density.
It was found that thick coatings could not be obtained under conditions of increasing negative current, thick coatings could only be obtained by controling negative current. The hardness of the coatings increased with decreasing temperature and anodizing time, and with increasing current density. Coatings with a hardness of more than Hv 600 were obtained when anodizing conditions were of 10°C, 4A/dm² were maintained for 30min. In coatings formed by pulse current with a negative current component, cell size was uniform, and the pores were divided into branches.

View full abstract