Study On The Nucleation And Growth Mechanism Of NiW Alloy During Electrodeposition

Nickel tungsten alloy is famous for its high hardness,high melting point,corrosion environment,strong corrosion resistance and high abrasion resistance characteristics and has been widely applied to the wear conditions of components,such as coating on the surface of specific products,bearing,piston cylinder and the oil industry.However,the dendrite segregation of the coating seriously affects the mechanical properties of the alloy,which will also affects the use of the alloy,so it is necessary to explain the influence of the crystallization process on the surface morphology of the coating.For more than a century,the nucleation and growth phenomena have been studied by colloidal synthesis,thin film growth,electrochemical deposition and so on.Although many scholars have studied the mechanism of the crystallization of alloy by Webb nucleation theory,they have not considered the aggregation of nano clusters,so theories are still incomplete.In this article,we have systematically studied the ammonia and deposition substrate of NiW alloy in the early stage of nucleation and growth:(1)Alloy electrocrystallization mechanismOn the basis of the low energy substrate(glassy carbon electrode)deposited on the nickel tungsten alloy,this paper has made some improvements to the theory of Webb nucleation.We proposed a universal alloy electrocrystallization mechanism,which has considered the nanoclusters instead of individual atoms,and discuss the nanocluster surface diffusion,aggregation and coalescence on nucleation and growth mechanism,influence of current time curve.On the one hand,the size of the nanoclusters depends on the substrate material and the deposition potential.On the other hand,the deposition morphology depends on the degree of surface diffusion and aggregation.If the aggregation is in a small degree,or partial recrystallization,it will lead to dendritic structure.And if the aggregation is in a large degree,or complete recrystallization,it will produce a smooth surface.The latter case can be explained by classical nucleation theory,but the former cannot.Therefore,our proposed model,designed to be an important scientific breakthrough,is also aimed at obtaining more effective control of the electrochemical deposition process in order to obtain the desired morphology and enhanced performance.(2)The effect of ammonia on the electrochemical crystallization of the alloyThe effect of ammonia on the crystallization behavior and the morphology of Ni-tungsten alloy on glassy carbon electrode was studied.It was found that the growth of nickel-tungsten alloy on glassy carbon electrode in the citric acid-ammonia bath also follows the three-dimensional nucleation.At the same time,as the deposition potential increases,the nucleation model will change,For continuous nucleation.This is consistent with the results obtained when adding sodium hydroxide.At this point,we can conclude that the addition of aqueous ammonia to the bath does not alter the nucleation mechanism compared to the addition of sodium hydroxide,and the nucleation mechanism still changes with the deposition potential and ultimately affects the plating appearance.(3)Effect of deposition substrate on electrocrystallization of alloyThe similarities and differences between the deposition of nickel tungsten alloy on glassy carbon electrode and gold electrode have been studied.It is found that the growth of Ni and W particles is consistent with the three-dimensional nucleation on the glassy carbon electrode and the gold electrode.But with the increase of deposition potential,the nucleation model will change,the glassy carbon electrode by instantaneous nucleation will gradually be changed to continuous nucleation.Gold electrode will also be changed from instantaneous nucleation to continuous nucleation.But we eventually tend to adopt instantaneous nucleation model.In general,the deposited substrate has an important influence on the crystallization.This is because all kinds of electrode reactions occur at the interface between the electrode and the solution.