The Research Of Cyanide-free Silver Plating Additives

The demand for silver plating is the biggest in the precious metals plating, on-cyanide clean production is the inexorable trend of the development of plating industry, that requires electroplaters speed up the researches in terms of the cyanide-free silver plating, innovative production technology, reduce the pollution, protect the environment.Through orthogonal test, the dissertation offers the optimal technological condition and index of the potassium iodide system cyanide-free silver plating; Additive DS1 and DS2 were prepared, they can improve the combination property of the bath and clad layer. The effect of additives on the surface morphology of the deposit, anti-tarnishing capability, corrosion resistance and grain structure were studied by scanning electronic microscope(SEM), the anti-tarnishing experiments, the comparison of electrochemical performance and X-Ray Diffraction(XRD), the effect of additives on the dispersive power of the bath were studied by Hull cell tests, the effect of additives on the deposition rate and current efficiency were studied by weight method.The results show that DS1 added in electrolyte, shininess of plating can be increased from 82 to 88, deposit rate keep on 26μm/h hold, current efficiency can be increased from 94.5% to 95%, dispersive power can be increased from 64% to 78%, the time of starting to colour can be increased from 30min to 50min. When DS2 added in electrolyte, shininess of plating can be increased to 90, deposit rate drop to 24μm/h, current efficiency can be increased to 96%, dispersive power can be increased to 80%, the time of starting to colour can be increased to 55min, the coating obtained from basal bath have coarse grain, when DS1 was added in electrolyte, crystal grains decreased obviously, DS2was added in electrolyte, crystal grains are smaller than obtained from DS1. The 0.05% hydrogen sulfide, 0.05% sulfur dioxide and 5% Na2S aqueous solution spot test show that anti-tarnishing of silver deposit obtained by DS1 much better than obtained by basal bath, obtained by DS2 is better than obtained by DS1. The studies from electrochemical performance showed that the free corrosion potential of the clad layer obtained from DS2 bath is most positive, obtained from basal bath is most negative. The results of X-Ray Diffraction show that the layer obtained from basal bath is of plane (111) and (200) strongly preferred orientation, when DS1 or DS2 added in electrolyte, the layer is of plane (111) strongly preferred orientation only, but compared with DS2 bath, DS1 bath have more grains orientated along (111) plane.