Study On The Cathodic Process Of Zinc Electrodeposition In Alkaline Zincate Solution

Steady polarization curve, cyclic voltammetry, electrochemical impedance spectroscopy, chronopotentiometry and chronoamperometry were used to study electrodeposition behaviors of zinc in zincate solution, the cathodic reduction of zinc, electrodeposition kinetics equation, electrochemical nucleation mechanism and the mode of the growth of zinc coating were obtained The function of two additives on the the zinc electroplating, the effect of two additives on the electrodeposition behaviors of zinc and on the electrochemical nucleation mechanism were used to study by making use of polarization curve, cyclic voltammetry, electrochemical impedance spectroscopy, X ray diffraction and SEM. the effect of process parameters on the texture coefficient of zinc coating was studied, and the electrodeposition conditions for the preparation of zinc deposits with fully preferred orientation were investigated in detail, and the corrosion resistance of zinc deposits with fully preferred orientation on was also investigated by polarization curve and electrochemical impedance spectroscopy, the results show that:（1） Zn existed in the solution in the form of Zn（OH）₄^2-, but Zn（OH）2was the species directly discharged on the cathodic surface, the chemical transformation reaction Zn（OH）₄^2- translated into Zn（OH）₂existed in the electrodeposition process, the Zn（OH）₂get two electrons by two steps, the electrochemistry active middle product Zn（OH）ad producted by the first reduce step of Zn（OH）2adsorbed on the cathodic surface, the two steps are all nonreverible reductions, the first electron gaining step is rate determing step The electrocrystallization of zinc belonged to a three-dimensional progressive nucleation mechanism.（2） The two kinds of additives functioned in different ways during zinc electroplating. The additive A make the grain size reduced and additive B have the function of Leveling ability, the nanocrystalline zinc coating which the grain size was about57nm was obtained when the two additives were added. The synergy coefficient was6.37%,0.64%and17.83%when additive A, additive B and two additives was used, Anccordingly, a strong synergistic effect between additive A and additive B, （3） The electrodeposition of zinc was controlled by diffusion step while without additives in solution the electrodeposition of zinc was inhibited while additive A was added, and the rate controlling step was also changed in this case, the electrodeposition of zinc was controlled by electrochemical step the inhibition was not obvious while additive B was added, and the rate controlling step was not changed, the electrodeposition of zinc was controlled by diffusion step the inhibition was maximum while additive A and additive B were added at the same time, the electrodeposition of zinc was controlled by electrochemical step.（4） The instantaneous nucleation followed by three-dimensional growth was found for the electrocrystallization from the electrolytes without additives the mechanism of electrocrystallization of zinc was changed while additive A was added, followed three-dimensional continuous nucleation and crystal growth was inhibited the mechanism of electrocrystallization of zinc was changed while additive B was added, followed three-dimensional instantaneous nucleation, the inhibition was not obvious on the crystal growth the inhibition was maximum on the crystal growth while additive A and additive B at the same time, followed three-dimensional continuous nucleation, Because of the two reasons, the grain size was smallest. Additive A increased the overpotential, proportional relationship existed between crystal density and concentration of additive A, but inverse relationship existed between crystal density and concentration of additive B, becaused additive B adsorbed on the low potential place, the electrochemical active sites able to transform into nucleation were covered.（5） Additive A inhibites zinc electrodeposition, and advantageous to preferred orientation of （110） plane of zinc coating, the inhition of additive B is not obvious, the effect of additive B on the preferred orientation is also not obvious, the inbition is maximum while additive A and additive B are used and resultes in fully preferred orientation of （110） plane because of their strong synergistic effect. The corrosion potential of the zinc coating with fully preferred orientation of （110） plane positive displacement146mV, the impedance value increases7times compare with the zinc coating with random orientation, the structure of zinc coating influence its corrosion resistance.