Public nuisance in plating industry has increased year after year. In order to cope with these circumstances, severe controls are now brought into effect by local governments for the limits of discharge of poisonous substances, particularly of cyanides and chromic acid.
The object of the present studies was to prevent the above nuisance in the range of commercial practice.
The results obtained were as follows.
(1) The brightness of deposit was nearly proportional to the concentration of crude pentose as an additive, but it reached a constant value at above 20g/l.
(2) The crystals of deposit clearly indicated excellent orientation along a definite face (103) and also showed fine structure.
(3) Very lustrous deposit generally appeared at low pH. At about pH 5.0, the brightness was likely to decrease with the increase of pH value.
(4) Most of the conventional cyanide zinc platings are carried out under low current density. However, the present bath gave good bright deposit even under high current density.

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Bath composition and plating conditions of black chromium plating bath containing hydrogen silicofluoride were given in the previous report (Part 1). The addition of hydrogen silicofluoride to this bath was intended to give higher blackness and evenness in coloration but these effects were not com- plete in the results.
Then, effects of further addition agents to the above bath were studied and found that the addition of nitric and formic ions among acid radicals and barium ion among metallic ions was most effective for color in platings; and no other agents were effective.
Bath composition and plating conditions for giving the most even and black coloration were as follows:
Cr₂O₃……300g/l
H₂SiF₆……1g/l
Addition agents……3-5g/l
Bath temperature……above 10°C
Dk……30-50amp./dm2

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Addition of nitric ions to the black chromium plating bath containing hydrogen silicofluoride was most effective for blackness of platings as described in the previous report (Part 2). Then, platings from the bath containing hydrogen silicofluoride and nitric ions were studied and it was observed that the bath was very stable and gave platings, having extremely good characteristics.
The results obtained were as follows.
(1) Thermal resistance: Resistant at 500°C for 5hr. on nickel plated substrate.
(2) Adhesion: Satisfactory results in tape-test and 180° bending test.
(3) Wear resistance: Lower than that of nickel platings, and much lower than that of chromium platings (equivalent to a few divisions of the latter).
(4) Hardness: Lower than that of nickel platings.
(5) Adhesion of paints: Satisfactory results for some kinds of paints.
(6) Corrosion resistance: No rust was observed in continuous salt-spray test for 64hr.

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This study was undertaken to examine the throwing power in electrodeposition of zinc onto mild steel for several typical baths containing zinc sulfate and cyanide complex by means of hull cell method and fluorescent X-ray analysis.
The results obtained were summarized as follows.
(1) It was confirmed by experiments that the throwing power in cyanide bath was much higher than that in sulfate bath, though the latter was fairly improved by addition of some agents, particularly dextrin.
(2) Much difference was found in polarization characteristics between sulfate and cyanide baths. Namely, a remarkable polarization was observed in the latter and the addition of dextrin promoted the polarization in the former.
(3) The throwing power practically observed agreed well with the calculated values, which had been estimated from Blum's equation on the basis of the slope of polarization curve and specific conductivity in the individual solutions.

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The structures of heat-treated barium titanate coating and intermediate layer produced between the coating and Ni substrate were analyzed in detail by means of X-ray diffractometer and microanalyzer.
Barium titanate coating deposited by flame-spraying on Ni substrate essentially consisted of glassy and crystalline components. The crystalline component comprised crystallites having various axial ratios (c/a), centering around 1.0029. On annealing the coating at 1, 200°C, the glassy component almost disappeared and central axial ratio changed to 1.0066, and to 1.0088 on annealing at 1, 400°C.
Dielectric constant obtained by annealing at 1, 400°C was 3, 000, which was nearly twice as large as that of ceramic barium titanate (ordinarily, about 1, 500). The cause of the large value of dielectric con- stant was found to be the formation of fine crystals due to the inhibition of crystalline growth and it was one of peculiar characteristics of flame-sprayed barium titanate.
The intermediate layer (mainly of Ni) produced by heat treatment at a high temperature between the coating and Ni substrate was thicker with the rise of annealing temperature. However, the content of barium titanate in the layer did not increase as expected. The thickness of the intermediate layer produced by heat treatment, containing a very small amount of barium titanate, was nearly 9μ (by 1, 200°C annealing) or 47μ (by 1, 400°C annealing).

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Phosphorus contents of nickel plating films obtained from electroless nickel plating baths containing various kinds of organic salts were determined.
Corrosion resistances of electroless nickel plating films, having different phosphorus contents from plating baths of the same compositions (but of different pH values), were measured by a few sorts of electrochemical methods and dissolution tests in solutions of IN-H₂SO₄, 5%-NaCl, and IN-NaOH.
As the results, the corrosion resistances of the plating films increased with the increase of phosphorus contents, but passivity effects were not found in each film containing phosphorus.

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