Improving the method of “colorimetric determination of NL-I of H-V W-M Co.”, a volumetric chemical analysis of naphthalene sulphonats in nickel plating baths was devised. As naphthalene sulphonate is quantitatively oxidised in hot solution of K2Cr2O7-H2SO4, when heated for 2.5 minutes after the white fume of H2SO4 begins to be generated, chloride ion and second class brighters in nickel baths are also oxidized by K2Cr2O7, so that it is found that there is no trouble in heating naphthalene sulphonates in acidic solution with H2SO4 until the appearence of white fume of H2SO4. Thus the chroride ion and second brighters are eliminated before adding K2Cr2O7. The both results of “Colorimeter determination of NL-I visual composition method” and this method coincide farely well. Reproducing of this action is pretty good, and the equivalent of 8 Mol K2Cr2O7 seems to correspond to 1Mol naphthalene sulphonate, regardless of the number of sulphonate radicals.
To investigate the mechanism of adhesion in plating metals to anodized aluminum, various experiments are carried out. By these experiments, it is found that there are several essential factors controling the adhesive property. i) Surface roughness: It is obvious that the surface roughness of base metals affects the adhesiveness, and the microscopic roughness is more important than the macroscopic roughness. The surface treated by anodized coating using phosphoric acid has microscopic surface structure and is very homogenious. The microscopic structure becomes the nuclei for the plating and gives very good adhesive. The surfaces treated by anodized coating using sulphuric acid and oxalic acid do not show such a homogenious microscopic structure. ii) Cell structure: There are many pores in the surfaces treated by anodized coating. The mean diamater of those pores differs for the different bath. Among the three kinds of bath, the above meutioned phosphoric acid gives the largest and the sulphuric acid the smallest size of pores. Therefore, the number of those pores becomes just reversed in the order above meutioned. This means that the volume of the pores per unit area of the surface treated by phosphoric acid is larger than that treated by other two acids. That is, the oxide film treated by phosphoric acid has the smallest electric-resistance. This cell structure has also much to do with the surface roughness. iii) Active layer of anodized film: The anodized films treated by phosphoric acid are the most active for reduction. However, if rested in the air or the plating bath for a short time, the high activity gradually decreases. The higher the activity of the anodized film, the better the adhesive can be obtained. iv) Purity of base metals; The adhesiveness of anodized coating depends also on the purity of the base metals. Impure aluminum shorws better adhesion than pure aluminum. The former has higher electrode-potential than the latter, so that there are more defects in the anodized film resulting in the better adhesiveness.
Usually the covering power value of the chromium plating bath deviates markedly when measured by Hull cell test. Experiments were carried out in order to investigate the cause of the deviation, and to find the better pre-treating method of the cathode which gives better reproducibility in the test result. Results are as follows: (1) Cyanide bath dipping and chemical polishing of the cathode (copper), especially the latter, increase covering power value remarkably. (2) In chemical polishing the brighter the surface of cathode, the less was the deviation. (3) The least deviation was obtained by using the cathode uniformly electro-plated about 10 microns thick.
By measureing the current efficiencies and by the Hull cell test, the unfavorable effect and the permissible amount of anionic impurities such as Cl-, NO3-, and PO43- were studied on the Sargent bath (CrO3 250 and H2SO4 2.5g/l) and the bath contining sodium fluorosilicate (CrO3 250, H2SO4 1.5, and Na2SiF6 5.0g/l). Each impurity decreases the current efficiency and brightness range. The permissible amount of each impurity is as follows: Cl- is 1g/l (as NaCl) for the both baths, NO3- 1g/l (as NaNO3) for the Sargent bath and 2g/l for the sodium fluorosilicate bath, and PO43- 4g/l (as Na2HPO4⋅12H2O) for the both baths. At the range of so low current density as not to deposit Cr, the base metal of copper, nickel, or iron dissolves into the both baths containing Cl-.