A Study On The Eoneerning Fundamentals And Cathodic Processes Of Zinc-cobalt Alloy Coatings Deposited In Alkaline Zincate Solution

Zinc alloy electroplating technique has come into wide use in industries such as automobile、electrical home appliances、machines hardware for based on the traditional techniques,a small amount of different metals is added and accordingly the ornamental and anticorrosive ability of the coating call be enhanced.Based on current research,tries to study the electroplating process of alkaline zincate based Zn-Co and the fundamentals.The Process of alkaline zineate Zn-Co alloy eleetroplating has been studied, through the investigation of the alloy eleetroplating solution ingredients, the process variables and their relationship with the Co coontent in the alloy coating, the optimum proeess has been obtained: Total concentration of zinc and cobalt ions 0.3mol/L, Zinc cobalt ions mole ratio 9:1, Na OH 150g/L,additive A 15ml/L, additive B 1ml/L,Current density 3A/dm2, operating temperature 25~40℃. Under the optimum conditions, the Zn-Co alloy coating with 2.0%~2.2% Co has been obtained. It has been found that Zn-Co alloy eleetrodeposition belongs to anomalouse codeposition; Within certain range, the optieal brightness and corrosion resistance of the coating raise with the inereasing of Co content in the coating, and when the parameters which could effect the optical brightness change, accordingly Co content in the coating would change.The nanocrystalline Zn-Co coating which the grain size was about 41.6nm was obtained when the two additives were added. The effect of additive A on co deposition was obvious, and the inhibition was not obvious while additive B was added, tthe inhibition was maximum while additive A and additive B were added at the same time. Based on the growth mechanism of the three dimensional continuous nucleation of zinc and cobalt in the basic bath, the growth mechanism of the after the additive A was carried out according to the growth mechanism of the three-dimensional instantaneous nucleation.The electrochemical behavior of the Zn-Co electroplating solution has been studied respectively by linear sweep voltammetry and cyclic voltammetry.The reasons why Co content in the Zn-Co coating is influenced by the ingredients of the electroplating solution and by temperature as well areexamined.The codeposition and electrocrystallization of Zn-Co alloy in Alkaline Zincate Solution were studied by linear sweep voltammetry(LSV),cyclic voltammetry(cv),and chronoamperometry.The Scharifker-Hil I(SH) theory model and Heerman-Tarallo(HT) theory model were applied to analyze the chronoamperometry data.The results show that the Zn-Co alloy codeposition on Glassy carbon electrode, fo Ilowing instantaneous nucleation with three-dimensiona I(3D) growth under diflusion control.The kinetic parameters were obtained using the HT model.As the step potential shifted from-2.00 to-2.10 V, the nucleation rate constant(A) increased from 0.85 s-1 to 10.20s-1,the density of active nucleation sites(N0) increased.The under-potential deposition of zinc in Zn-Co solution has been investigated by using cyclic voltammetry.The dissertation points out that the anomalous codeposition of Zn-Co alloy results from the under-potential deposition of Zn.