| Electroplating becomes an important surface engineering technology due to its special decorative and functional role. With the development of economy and time passing, the coating quality set higher requirements. The compositions of plating solution are the key to ensure the quality of the coating, hence, research on influence mechanism of compositons in the plating solution on the coatings is of great significance.Nickel plating is an important technology with a long history, concentration of metallic impurities in the plating solution increases as the plating time goes. When the impurities reach a certain concentration, a lot of problems occur in the coatings, such as: the radiance misses, pinhole, pit and so on. Methanesulfonic acid tin plating has become a research hotspot both at home and abroad due to its advantages of high stability and environmental friendliness. Surfactants, as one of additives, play an important role in electroplating process. So research on surfactant is of great significance in the industrial production. This thesis has prompted a series of studies on the influence mechanism of metallic impurities on nickel plating and the influences of surfactants on methanesulfonic acid tin plating. Contributions of this research are listed as follows:1. 2g/L of Co2+, Cr3+, Mn2+, Fe2+, Cd2+, Zn2+ were respectively introduced into the nickel plating solution to get coatings with different quality. The obtained coatings with different quality are characterized by X-ray diffractometry(XRD) and scanning electron microscopy(SEM). The results show that the presence of metallic impurities can reduce the quality of coatings. Regularity of electrochemical behavior of electroplating solution with different metallic impurities was investigated by cathodic II polarization, chronopotentiometry and electrochemical impedance spectroscopy. Last, through the concentration gradient experiments, corrosion experiment, heat cycle and high temperature experiments, the critical concentrations of metallic impurities was guaranteed to obtain high quality Ni coatings for different use. Co2+ ≤ 60mg/L, Cr3+ ≤ 10mg/L, Mn2+ ≤ 100mg/L, Fe2+ ≤ 40mg/L, Cd2+ ≤ 20mg/L, Zn2+ ≤ 120mg/L are guaranteed to obtain Ni coatings with high corrosion resistance. Co2+ ≤ 60mg/L, Cr3+ ≤ 5mg/L, Mn2+ ≤ 90mg/L, Fe2+ ≤ 30mg/L, Cd2+ ≤ 20mg/L, Zn2+ ≤ 110mg/L are guaranteed to obtain Ni coatings with high thermal stability; Co2+ ≤ 60mg/L, Cr3+ ≤ 5mg/L, Mn2+ ≤ 90mg/L, Fe2+ ≤ 20mg/L, Cd2+ ≤ 15mg/L, Zn2+ ≤ 110mg/L are guaranteed to obtain Ni coatings with high temperature performance. Dense, smooth, shiny Ni coatings can be obtained in the obove concentration range, which can resist different conditions of corrosion, thermal cycle and high temperaturecircumistance. The concentration range is the requirements of nickel electroplating.2. The tin coatings are electrodeposited from four kinds of plating solution which were prepared by adding three kinds of surfactants into the basedstannous methanesulfonate solution respectively with a blank sample. The obtained coatings were characterized by X-ray diffraction(XRD) and scanning electron microscope(SEM), we found that the surfactants not only improve dispersion ability, but also the quality of coatings. The structure of the surfactants, such as degree of polymerization, type and position of functional group, has obvious influence on polarization of tin plating and quality of coatings. Polyoxyethylene ether surfactants can improve the quality of coatings better, and polyoxyethylene ether surfactant with low degree of polymerization had the greatest effect on the improvement of tin coating quality. Through electrochemical test on four plating solution, such as cyclic voltammetry, liner sweep, AC impedance, chronopotentionmetry, results indicate the existence of three kinds of surfactants has great influence on polarization and electrochemical reaction rate on tin deposition, thereby the reason of appearance of different quality deposit can be explained. Finally, we study the plating solution adding with NO.3, and the optimum condition of tin electroplating process were obtained through comparing the deposition morphology obtained from condition of different concentration of stannous methanesulfonate, different current densities, different concentration of NO.3 and different temperature by XRD and SEM. |
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