The Refining Effect And Mechanism Of Rare Earth Elements On Electrodeposited Coatings Of Nickel In Industrial Electrolytes

In industry,nickel plates of different specifications and properties are obtained through electrodeposited coatings of nickel,which are used in the subsequent short-process rolling to produce nickel foil and high-purity nickel strips,which are used as raw materials for precision instruments such as batteries,cameras,instruments and meters.At present,these raw materials are mainly obtained through smelting and plastic processing of nickel plates obtained by nickel electrodeposition.Although the purity of the currently produced electrodeposited coatings of nickel is as high as 99.96%,and some of the grain size can reach the nanometer level,there are still problems such as electrolytic nickel slag,high electroplating nickel residue rate,nickel separation,and uneven electrolysis.Therefore,it is particularly important to control the morphology and performance of the microstructure during the nickel electrodeposition process.This requires a in-depth study of the nucleation and growth mechanism of nickel electrodeposition,and continuous improvement of the process of industrial production of electrodeposited nickel.A higher degree of refinement of the nickel deposit is obtained.The traditional process often deposits nickel plates that meet the standards in industrial electrolytes,performs smelting processing,and improves its mechanical properties by adding rare earth refiners.This subject explores a new short-process research method.By adding rare earths directly into industrial electrolytes as additives,the refining effect of rare earth elements on nickel deposits is studied,thereby shortening the process flow and improving the microstructure and uniformity of the nickel plate.To achieve the improvement of industrial production efficiency.This topic uses nickel sulfide soluble anode/sulfate industrial electrolyte system,and selects Ce、La、Pr、Nd from 17 rare earths based on atomic theory such as charge-to-mass ratio,ion radius and polarization degree and existing literature.element.Use SEM,AFM and other analytical methods to study the surface grain refinement of the electrodeposited coatings of nickel to determine the best type and content of rare earth elements.The polarization curve,cyclic voltammetry curve,and chronocurrent curve are used to analyze the mechanism of the rare earth effect on the nickel deposition process.The surface and cross-sectional microstructures of the deposited layer are observed and analyzed by SEM,AFM and EBSD to further confirm the fineness of the rare earth on the nickel deposit.Since rare earths are used as catalysts to participate in grain nucleation/doping in the deposited layer to affect grain growth in the process of electrocrystallization refinement,qualitative analysis of whether rare earths are incorporated into the deposited layer was carried out by EDS and XPS.The study found that the rare earth Ce compound is most suitable as a rare earth additive in industrial electrolyte systems.Both SEM and AFM found that the average grain size of the nickel deposited layer after the addition of rare earth was reduced by more than 100 nanometers than before,indicating that the addition of an appropriate amount of rare earth improved the degree of refinement and uniform organization of the deposited layer.Since the sulfate industrial electrolyte system is dominated by sulfate ions,cerium sulfate was selected as an additive for research.By studying the nucleation mechanism of nickel ions in the electrolyte,it is obtained from the polarization curve that the corrosion current of the nickel deposit after the addition of cerium sulfate becomes smaller,and the corrosion potential moves forward.When the addition amount is 0.6 g/L,the best resistance is shown.Corrosion performance,more than this concentration will reduce the corrosion resistance.The analysis of the cyclic voltammetry curve shows that the addition of rare earths can positively shift the deposition potential,increase the electro-deposition power,generate more fine grains,and increase the fine density of the deposited layer.The analysis of the chronoamperometric curve shows that the nucleation relaxation time is the shortest and the nucleation rate is the fastest when the rare earth addition is 0.6 g/L;when t<t_m,the arbitrary step potential curve is close to the instantaneous nucleation theoretical curve,at t>t_m.Sometimes it deviates from the theoretical curve and tends to be stable,which is related to the complexity of the industrial electrolyte used in the experiment.SEM observation of the surface morphology of the deposited layer showed that the addition of cerium sulfate gradually increased from 0 g/L to 0.6 g/L,the grains became smaller and the grain boundaries increased,and the needle-like grains became wider if the concentration exceeded this concentration.The average particle size of the surface detected by AFM can be reduced from 0.48μm to 0.45μm.The surface of the deposited layer is smooth,the structure is uniform,and the degree of refinement is high.It is confirmed that the optimal concentration of cerium sulfate additive is 0.6g/L.By EBSD,when no rare earth compound is incorporated into the electrolyte,the average size of the cross-sectional crystal grains is 0.9887μm,the orientation is mostly<001>,and there is a strong plate texture{100}<111>,{110}<100>and silk texture<110>//Y0,which indicates that there is a preferential orientation in the growth of grains during the nickel deposition process;when the addition of cerium sulfate is 0.6 g/L,the average grain size is reduced to 0.66319μm,and the small-angle grain boundaries are more.The cross-sectional orientation of the nickel deposition layer is still dominated by<001>,but there are more<111>,<101>,<212>,<112>orientations,and plate texture{211}<100>and<110>,{100}<410>,{110}<100>.At the same time,the symmetry of the pole figure is not as obvious as the cross section without rare earth addition,and the distribution of the pole density points is disordered,indicating that the addition of rare earth will change the growth mode of the crystal grains.The hardness test shows that the hardness of the electrodeposited coatings of nickel before and after the addition of rare earth increases by 20.39,and the bonding force between the deposited layer and the substrate becomes better.In order to further determine the role of rare earth in the process of nickel electrocrystallization,a short peak with extremely weak Ce intensity was obtained by EDS and XPS.The peak area ratio was used to find the two electronic orbitals and chemical states that appeared after nickel ion deposition.The amount of nickel itself deposited varies with The increase of rare earth addition has a slight increasing trend,indicating that the deposition efficiency of nickel ions after adding rare earth is improved.Due to the limitations of the solubility of rare earths and testing methods,it is difficult to find obvious co-deposition phenomena in the deposited layer.In the future,the kinetic system of the nickel ion deposition process of the rare earth in the electrolyte should be deeply studied.