Process And Mechanism Study Of Electroplating Gold In Choline Chloride Based Ionic Liquids

For the purpose of improving energy conversion efficiency in the InertialConfinement Fusion (ICF) researches, uranium and uranium alloys are appropriatesubstitute for gold as conversion layer. In order to keep stable in numerous severeenvironments, a gold layer is usually used to support and protect the uranium layer.Because of the high reaction activity of uranium in aqueous solution, it is difficult for usto obtain qualified gold layer in traditional aqueous electroplating baths. Therefore, anew non-aqueous and excellent gold plating technique is urgently needed.In this thesis, Reline and Ethaline room temperature ionic liquids were chosen assolvent and the main constituent of the gold plating bath were studied. The effect ofmain constituent and some technological parameters, such as temperature and currentdensity, on the coating were investigated thoroughly.By means of orthogonal experiment in Reline, a basic bath with determinedconditions of Au3+4g/L, DMH45g/L, LiCl15g/L and deposition potential-1.4V(vs. Pt)was obtained. Single-factor experiment proved that the bath temperature and currentdensity strongly affect the Au coating, while the effect of LiCl concentration isinapparent. A uniform, compact and adherent gold layer was obtained from this basicbath under a small current. To improve current density, numerous methods wereinvestigated, including increasing temperature and adding diluent.In Ethaline, a basic bath was also determined, which was Au3+30g/L, DMH156g/L and Na2CO35g/L. From2mA/cm2to10mA/cm2, a golden gold layer wasobtained, and the uniformity of the gold layer was best when current density reached6.5mA/cm2. Skip plant tended to appear when gold layer was nickel based, and no skipplanting was found on gold foil base. Increasing the concentration of main salt and bathtemperature could improve the plating current density significantly, and the higher thetemperature was, the better the coating quality. Due to strong oxidizing property of Au3+,a curious phenomenon happened among anode and cathode process.The crystalline structure were investigated by X-ray diffraction (XRD), whichproved to be face-centred cubic structure in both systems. X-ray photoelectronspectroscopy (XPS)， X-ray fluorescence (XRF) and Energy DispersiveSpectrometer(EDS) proved that no organic impurity was added. Scanning electronmicroscopy (SEM) and atomic force microscope (AFM) were used to investigatesurface morphologies of gold electrodeposits.The reduction mechanism of Au3+and the reversibility of electrode process wereexamined by cyclic voltammetry, which proved that the reduction of Au3+was step by step. The influence of additives, such as saccharin sodium and butynediol, onelectrochemical behavior were investigated by linear sweep voltammetry indicating thatthose two additives have little effect on cathodic polarization. Chronoamperometry wasused to confirm nucleation mechanism on glassy carbon electrode, and continuousnucleation mechanism was found.