The Research On The Mechanism Of The Colored Rhodium Plating

With the rapid development of the jewelry in recent years, the demand for the different color of jewelry is also increasing. Rhodium plating is the material of plating in the field of jewelry gains wide range of use. Colored rhodium plating is reported to be produced, however there are rare reports about the coloring mechanism of rhodium plating. In this paper investigation about the mechanism of color rhodium plating is performed.Sulfamic acid, triethylamine, and benzylamine solution are selected as additives in this paper, different colors such as white, gray and black are obtained based on the general conditions of electroplating process. And the paper also analyzed the mechanism of color plating, color changing in high temperature, and the related properties such as hydrophilic, electric properties, and plating solutions.The results of the research are as follows:1) With the increase in the additive concentration of sulfamic acid, triethylamine, and benzylamine solution, the light intensity value of plating gradually reduced and turned into gray. The color of plating was bright white with 2ml/L concentration of sulfamic acid addition, which means that this concentration of additive can be used as brightening agent for Rhodium-plating. When benzylamine solution was added, the light intensity value of plating dropped to lower than 70.0. When its concentration of solution was 6ml/L, the light intensity value of plating dropped to 28.0 which mean the color of plating turned to be aterrimus, and showed an obvious sub-light phenomenon, Electroplating time has no significant influence on the color of plating;2) All the three additives significantly increased the polarization of plating solution. But the plating with sulfamic acid addition showed an effect of grain refinement, and other plating showed a ball oriented particle. In the preparation of plating which had no additive or added sulfamic acid solution have not showed an obvious existence of carbon type organic matter. The carbon type organic matter were found in the preparation of plating which added triethylamine benzylamine solution, and formed cauliflower-like ball oriented particle. The adsorption of organic additive and the special physical structure that had the absorption capability to the visible light in the plating, which made the plating turn obfuscation or black;3) After heated in the oxygen atmosphere and protective atmosphere of argon, the plating grain size that had no additive or added sulfamic acid solution were fine-tuned, and the light intensity value of plating had no significant change but also showing a certain increase. However, as the cauliflower-like miniature balls formed by the plating that been added organic solvent experienced a high temperature of decomposition and volatilization of organic matter, its miniature balls of plating was destroyed and being smooth, which made the plating lost its original black color;4) The contact angle of plating which added benzylamine solution was greater than 90 degree, which mean the plating showed hydrophobicity, while others showed hydrophilia. Electroplating time has little impact on the contact angle of plating. The contact angle increased with electroplating time. Sulfamic acid and triethylamine solution had no significant effect on plating contact resistance. A rapid increase of contact angle could be found when the plating was added with benzylamine solution because of the large numbers of introduced organic matter in plating and the formed cauliflower-like miniature balls, but it still reflected a better conductivity as a whole.