The Study Of Electroplating With Thrivalent Chromium In Sulfate System

Chromium plating is one of the most broad technologies used in electroplating industry.The traditional chromium plating has carried through according to the technology of Sargent.The technology of Sargent has some problems,such as:low cathode current efficiency, bad throwing power and ability of covering,which brings harms to workers and circumstance pollution.So the chromium plating in trivalent chromium solution has been developed recently.The sulfate solution we studied has covercome above metioned problems.The solution has a good throwing power and ability of covering and high current efficiency.The coating electrodeposited by the new solution also has high brighting level.Fuethermore,the technology has the advantage of lower plating cost and broader width of the current density and temperature.The main work of this thesis consists of the following four parts:l.The study of technology about chromium plating for trivalent chromiumElectroplating with trivalent chromium in sulfate system is decided by orthographical test,which is studied in the Hull Cell and small bath e-xperiments.The effects of all sorts of compositions and electroplating condition on the coating are discussed.It is also put forward the best technology conditions and the resolvents of frequently questions. The fittest process condition is also decided.In addition,the effects of impurities and the ways to remove are discussed.2.The effect of the additives on the electro-crystal behavior of plating in the solution of the trivalent chromiumThe effect of additives on the electro-crystal behavior of plating with the trivalent chromium in sulfate solution are studied by the means of steady-state polarization,potentiosatically step,cyclic voltammograms.scan electronic microscope(SEM) and spectrophotometer.When the content of sexivalent chromium attains to ten milligrams in one litre,the solutioncan't work ,even have no coating.The stabilizer has the quality of deoxid-ization,so it can remove oxidants in the solution and restrain trivalent chromium becoming to sexivalent chromium.So it can keep the solution steady.The brightener can increase cathode polarization,so it can gain bright coating in broader width of the current density.It is found that the mechanism of the trivalent chromium electroposition is not changed by the addition of the additives to the fundermental solution.It still keeps to instantaneous nucleation.3.The experiments of some kinds of properties of the solution and the coating of electroplating with trivalent chromium from the sulfate solutionSome kinds of properties of the coating and solution of electroplating with trivalent chromium from the sulfate solution have been tested by some professional standard means. It is found that the some character of the coating and solution can attain to requirement of manufacture.Furthermore the results of experiment indicate that the capability of trivalent chromium are better than the sexivalent chromium's.4.The study of anode for the electroplating with trivalent chromiumGraphite,Stainless Steel and Ru-Ti anode are tested by Hull Cell and small bath experiments.Among these,it is emphasized on the Ru-Ti anode. It can received by the three steps,such as spreading,drying,hot oxidating. The electrochemical characteristics and service life of the Ru-Ti anode are measured.It is found that the Ru-Ti anode has long service life,good ability of evolution of oxygen and also can restrain trivalent chromium becoming to sexivalent chromium.So the Ru-Ti anode can satisfy ectroplating with trivalent chromium.