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After selecting and experimenting,in this article we made our decision on Citric Acid—Tartrate Copper Plating Technology in which the citric acid works as the main complexing agent,tartaric acid salt as a supporting agent,and cupric carbonate basic as the major salt.The testing result of the coating performance showed that,being evenly coated,the copper layer obtained from this process was generally able to reach the brightness level of grade two or even grade one,and it had very low porosity.And the plating solutions,according to the results,also had a desirable performance in stability, throwing power and covering power,among which the throwing power could achieve a level of 84.41%,while the covering power reaching 4.3.On this basis,we applied orthogonal test to optimize the formulations of non-cyanide Copper Plating Technology and selected the best technical formulation and process conditions as follows:cupric carbonate of 55 g/L,citric acid of 260 g/L, potassium sodium tartrate of 32 g/L,sodium bicarbonate of 1.5 g/L,glossenhancer of 0.02 g/L,pH of 9.0,temperature of 35℃,current density of 1.5 A/dm~2,athode to anode area ratio of 1:2 and plating time of 8 minutes.The testing results of the performance of the coating and the solutions showed the bath enjoyed very good stability,with the throwing power reaching 84.52%and covering power reaching 4.5.And the brightness of the coating obtained could reach the level of grade one,and the coating had very low porosity,good bonding ability with the matrix and it was coated evenly.This copper plating layer can be used as a decorative bottom or middle coating.And then,after plating copper by the best non-cyanide copper plating formulation, we performed non-cyanide silver plating continuously.Subsequent testing results of plating performance indicated a neat surface of silver plating,good bonding ability between copper and silver plating and the middle copper plating also improved brightness of the silver plating.When we plated non-cyanide imitation gold on top of copper plating,the outlook of imitation gold plating appeared golden brown,meticulous and evenly coated,which complied with standard of brightness level of grade two.The coating had a neat surface and nice outloook.After thermal shock test,the coating showed no sign of frothing or separation,which indicated good bonding ability between the coating and matrix.The non-cyanide imitation gold plating obtained by our techniques had a bright colour, exceptional performance and it was suitable to be used as decorative coating.
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