100 Questions on Basic Electroplating Knowledge (Part 8)
Separated Letters Gold Metal Logos
36.What is the role of boric acid in nickel plating solution, if the boric acid is insufficient, what will happen?
Answer: Boric acid is the buffer of nickel-plating solution, buffering the role of the pH value of the plating solution. When the concentration of 31 g / liter or more, there is a significant effect, but not too high, because the solubility of boric acid at room temperature about 40 g / liter or so. Due to the buffering effect of boric acid, so that the cathode area solution pH value does not produce a sharp change, thus allowing the use of higher cathode current density without precipitation of hydroxides on the cathode. It also has the effect of improving cathodic polarization and plating properties. However, excessive levels of it can reduce cathode current efficiency. The buffering effect is very weak when it is lower than 20g/liter, which makes the pH value of the plating solution change intensify and affects the quality of plating layer, and even makes the plating process impossible.
37.nickel plating, the pH of the electrolyte near the anode and the cathode near the pH of the electrolyte that a high, why?
Answer:The pH of the electrolyte near the cathode is higher. This is due to the electrolysis process, the cathode on the precipitation of hydrogen gas and make the pH rise. 2H + + 3 → H2 ↑
Separated Letters Gold Metal Logos
38.After galvanizing the passivation layer, white passivation and color passivation layer that a good corrosion resistance?
Answer:The corrosion resistance of a passivated coating after galvanizing is better with a colored passivation than with a white passivation. This is because the passivation white treatment, is already formed in the color passivation film in the bleaching solution to dissolve off a layer, so that the color passivation film becomes white. Since the white passivation film layer is thinner than the color passivation film layer, the corrosion resistance is reduced. Separated Letters Gold Metal Logos
39.barium carbonate treatment of chromium plating solution in excess of sulfuric acid, a gram of sulfuric acid with how many grams of barium carbonate?
Answer:To remove 1 gram of sulfuric acid, about 2 grams of barium carbonate is theoretically needed.
40.Why can’t the newly prepared pure chromic acid solution be plated with chromium? Why is it necessary to electrolyze or add some old plating solution to produce good quality plating?
Answer: newly prepared pure chromic acid solution, if there is no trivalent chromium and catalytic anion, is not easy to connect in the cathode electrolytic reduction, chromic acid in the hexavalent chromium ions are not reduced to trivalent chromium ions, and not reduced to metallic chromium. The result of electrolysis is equivalent to the decomposition of water, in the cathode to produce hydrogen 2H + + 2e → H2 ↑, in the anode to produce oxygen 4OH – 4e → 2H2O + O2 ↑. So no chromium can be plated. When the solution to add sulfuric acid, it and the solution of trivalent chromium to generate complex positively charged chromium sulfate [Cr4O (SO4) (H2O) 4] 2 +, because of the small radius of the sulfate ion, high charge, so easy to be adsorbed by positively charged chromium sulfate, through the alkaline chromate chromium colloidal mucous membrane, prompting the Cr ions can be discharged in the cathode precipitation of chromium metal. Newly formulated chromium plating solution, due to the absence of trivalent chromium, chromium is not easy to plating, so the need for electrolytic treatment to produce trivalent chromium. The purpose of adding some old plating solution is also to make the plating solution contains a certain amount of trivalent chromium to facilitate the precipitation of metal.
