100 Questions on Basic Electroplating Knowledge (Part 7)
31.Why is pig iron castings more difficult to plating than other steel parts?
Answer: Cast pig iron parts, the surface is often uneven and porous, in such a surface will only get rough and porous plating. In addition, in the pig iron surface, there are free graphite, it not only affects the plating and the combination of base metal, at the same time, there are pores in the plating of the case, it will become the cathode of the corrosion battery, so that the plating of the metal is quickly destroyed, the graphite in the pig iron, and sometimes have to reduce the role of the hydrogen super-voltage, resulting in the hydrogen is easy to precipitate in the place, impeding the deposition of metal, so the casting of the pig iron parts more than other Iron and steel parts are difficult to plating.
32.. In the cyanide copper plating, free cyanide is insufficient, what should be added? Can I add cuprous cyanide?
Answer:When free cyanide is insufficient in copper cyanide plating, sodium (or potassium) cyanide should be added. If you add cuprous cyanide, the free cyanide is further reduced, and the copper coating becomes coarse and rough.
CuCN+2NaCN=Na2Cu(CN)3
33.When preparing a cyanide copper plating solution, is it correct to dissolve the powdered cuprous cyanide in warm water and then add it to the plating bath?
Answer:No. Because cuprous cyanide is insoluble in water. Copper cyanide should be dissolved in a solution of sodium (or potassium) cyanide, and the amount of sodium cyanide is 1.15 times that of copper cyanide.
34.In the cyanide copper plating solution, the use of air stirring is appropriate?
Answer:It is not suitable to use air stirring in cyanide copper plating solution. Because the carbon dioxide in the air will react with the alkali in the solution to form carbonate. Excess carbonate will have a negative effect on the copper coating.CO2+2NaOH=Na2CO3+H2O
35.sulfuric acid in copper sulfate plating solution, what does it do? What is the effect of the level of content on the coating?
Answer: sulfuric acid in copper sulfate solution has the following roles: (1) to prevent the hydrolysis of copper and the formation of cuprous oxide or other alkali salt precipitates. (2) Reduce the effective concentration of copper ions, so that the crystallization of copper plating layer fine. (3) Reduce the resistance of the solution, improve the conductivity of the solution and reduce the consumption of electrical energy. (4) Prevent rough or dendritic plating layer under high current density. Sulfuric acid content in the plating solution is generally 60 ~ 80 g / liter, the content is too high or too low are not suitable, too much it can make the plating layer brittle, and reduce the solubility of copper sulfate. Too little can cause rough plating, anode passivation and solution dispersion ability to reduce the failure.
