This study specifically investigated reduction of the white smoke originating from flux during the hot-dip zinc galvanizing process. White smoke is generated by ammonium chloride in the flux treatment solution. To replace the ammonium chloride solution, we developed a new flux treatment solution, prepared using some halogen compounds, with sodium chloride, potassium chloride, and/or sodium fluoride added to zinc chloride. The new flux solutions decreased white smoke. It was contained hydrogen chloride and hydrogen fluoride in the exhaust port, but it was not clear that the exhaust gas concentration influenced worker health conditions. The plating thickness and surface obtained when using these new solutions exhibited the same level as hot-dip zinc galvanizing with the ammonium chloride solution. In addition, these retained the same corrosion resistance from the salt spray test. Results show that characteristics of drying and moisture adsorption, and the addition of sodium chloride, potassium chloride, and sodium fluoride inhibited the moisture adsorption of zinc chloride.
Polystyrene particle composite nickel coatings were prepared using polystyrene particles of three types having methyl, sulfo, and amino functional groups on the particle surface. The polystyrene particle composite nickel coatings were produced in a Watts bath containing cetyl trimethyl ammonium bromide (CTAB). The maximum co-deposition ratios of the polystyrene particles having methyl, sulfo, and amino functional groups in the nickel film were about 25, 20, and 10%, respectively, at 30 mA cm－2. The order of maximum co-deposition ratio was independent of that of zeta potential of the polystyrene particles measured in the CTAB-containing Watts bath. Results show that the CTAB adsorption form and stability on the functional group-modified polystyrene surfaces are important for improvement of the co-deposition ratio.
Formation behavior, structure, and corrosion resistance of chemical conversion coatings containing alkaline earth metals of various kinds formed on the AZ91D Mg alloy were investigated. The pH near the AZ91D surface was measured using a Sb microelectrode probe, which revealed that the pH increased from 3.0 to 10.5 during the chemical conversion reaction. The XRD results indicated that the precipitates obtained from the chemical conversion baths adjusted to pH 10.5 containing Ca, Sr, Ba, and Mg ions respectively corresponded to apatite, apatite-Sr, Ba3(PO4)2, and amorphous. Surface and cross-sectional SEM observations indicated that the chemical conversion coating containing Mg was the thickest among all the coatings, and showed many penetrative cracks reaching the substrate. In contrast, the coatings respectively containing Ca, Sr, and Ba were less defective and showed only small cracks. The salt spray test showed that the coatings respectively containing Ca, Sr, and Ba showed excellent corrosion resistance.