| EDTA is nontoxic chelating agent with very good complexing performance. At present, our country has not yet seen the report about that EDTA is served as main complexing agent in the copper electroplating process. In this paper, it is discussed that whether good performances of electroplating process can be gained when EDTA is employed main complexing agent with the relevant theories. The performances of the solution and the coating are researched mainly, and five formulations are optimized and selected. Compared citric acid - tartaric acid system to cyanide system, EDTA system has comprehensive performances and is able to meet the production practice. The research conformances the developing trend of the copper plating craft and widens the selection scope of copper plating for "cleanness production".In this paper, the developing history of electroplating industry is summarized at first, and the important status of copper plating is emphasized. After introducing copper plating processes available, it is pointed out that copper plating will keep its current status in electroplating industry all the time and continue its development. However, the advanced copper cyanide plating processes will be washed out for its severe toxicity in the end. To seek a feasible substitute non-cyanide copper plating craft that can be applied in the practical production is inevitable developing trend of copper plating.Based on the background mentioned above, research works are made sure. Firstly, the electroplating theory and relevant principles are introduced simply in the paper, Then, the overvoltage, which is the primary factor in the course of electrodeposition and plays an important role in the practical work, is pointed out. With the theory, the tests are carried on to many kinds of complex compound solutions of the copper. According to this, the feasible analysis to EDTA system is done, and a rough copper plating formulation that employed EDTA as main complexing reagent is presented.In the experiment, the polarization curve and Hull cell experiment have been conducted to the rough formulation, which has been adjusted and optimized gradually, and five feasible formulations labeled 6, 7, 8, 9 and 10 respectively, are presented (Among them, form.6 is without any additive, form.7 contains Rochelle salt, form.8 contains potassium citrate, form.9 contains Rochelle salt and potassium nitrate, form. 10 contains potassium citrate and potassium nitrate). From further testifying the performance of solution with those prescriptions, such as current efficiency of solution, throwing power, microthrowing power, deep hole plating power, stability, it is discovered that the EDTA system copper plating craft has good comprehensive performance. When two supplementary complex compound, Rochelle salt and potassium citrate, are added in form.6, the throwing power and the deep hole plating power of the solution is increased while the polarizing value is enhanced at slight current density and the bright current density range are widened. And, Rochelle salt reduces the microthrowing power of the solution while potassium citrate opposites. In addition, adding conducting salt, potassium nitrate, in form.7 and form.8, the throwing power, the microthrowing power, the deep hole plating power are enhanced properly as the tank voltage is reduced evidently and the bright current density range is morewiden at low temperature, the current efficiency, however, is reduced greatly.Compared citric acid- tartaric acid system to cyanide system, EDTA system has obvious advantages. Although form.6 has better throwing power and its microthrowing power is higher than the citric acid - tartaric acid system notably, the deep hole plating power is relatively low and the bright current density range is thinner at low temperature. Whereas Form.7 has better throwing power, and the deep hole plating power is enhanced properly with the lower microthrowing power. Form.8 has the best microthrowing power in all seven solutions, and the throwing power is better within the good deep hole plating power. Lastly, both form.9 and form.10 share with widener scope of current in the bright areas of the coating and lower current efficiency for potassium nitrate being added. Form.9 owns the best throwing power and worse microthrowing power, while form. 10 owns all better performances except for lower current efficiency in all seven solutions. The stability test is carried on to form.6, 7 and all have good stability. Electrolysed 170 hours at 60~70℃ Celsius, all thosesolutions can be worked normally.Then, the tests of coating performances are carried on to the five formulations. It is discovered that the coating gained from all five solutions have good adhension, which can meet industry requirements, and they all can be applied in the multilayer coating process of copper-nickle-chromium. However, when supplementary complex compound are added into prescription, the porosity of the coating will be increased, in which the potassium tartate sodium has more evident effect. As the result, the adhension of the coating gained from form.7 is lowered. On the contrary, adding potassium nitrate, the porosity of the coating is lower while the adhension is enhanced. The coating gained from all the solutions own lower porosity than citric acid - tartaric acid system except form.7. Among those formulations, the porosity of form. 10 is lower than cyanide system when the coating is thinner. Through testing the adhension quantitatively, it showed that although some performances of EDTA system are inferior to cyanide system, its values are much better than the citric acid - tartaric acid system.In sum, the solutions of the EDTA system copper plating process are nontoxic and in favor of environmental protection. Hence, it is in the developing trend of the copper plating craft. It has good comprehensive performances and is suitable for electroplating directly on steel basis material. As a whole, the performances are superior to citric acid - tartaric acid system and approaching or beyond cyanide system although some performances of the solution and the coating from the single formulation of the EDTA system are inferior to cyanide system. Therefore, the EDTA system copper plating process is able to meet the practical requirements and can be applied to industry. |
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