Research On Electrolytic Tin Powder Based On Choline Chloride-ethylene Glycol Eutectic Solvent

Tin powders are widely used in the manufacture of solder paste,carbon products,friction materials,oil-bearing bearings and battery materials due to its stable chemical properties,strong corrosion resistance,good electrical conductivity,and non-toxicity at room temperature.The electrolytes used for electrodepositing tin powder in an aqueous solution are mainly acidic solution,and serious hydrogen evolution reactions together with environmental pollution are inevitably existed.Deep eutectic solvent?DES?is a new type of green solvent.Compared with aqueous solution,the electrodeposition of tin powders in DES has many advantages,such as low energy consumption,environmental protection,and wide electrochemical window.It is promising to reduce side reactions when used in electrodeposited tin powders.Occurrence,avoid environmental pollution,and has broad industrial application prospects.In this paper,choline chloride-ethylene glycol?Ch Cl-EG?eutectic solvent?DES?was synthesized and a certain amount of Sn Cl was dissolved therein.The existence form of tin ions was studied by means of infrared visible spectrum,ultraviolet visible l spectrum,and electrospray mass spectrometry.The effects of temperature and Sn Cl₂concentration on the viscosity and conductivity of Sn Cl₂-Ch Cl-EG DES were studied;The electrochemical behavior of Sn?II?ions in Ch Cl-EG was characterized by cyclic voltammetry,cathodic polarization,and chronoamperometry;The dissolution behavior of tin anode was studied by Tafel;By variation the conditions of electrodeposition experiments,Sn Cl₂-Ch Cl-EG DES was used as the electrolyte to investigate the effects of electrolytic parameters such as current density,Sn Cl₂ concentration,temperature,and interelectrode distance on current efficiency,energy consumption,product morphology,phase composition,and preferred orientation;Besides,the corresponding relationship between electrodeposition parameters and products,and control mechanisms was determined;The SEM and AFM were employed to characterized the morphology of tin anode before and after dissolution.The main research results are as follows:?1?Electrospray mass spectrometry showed that the existence form of Sn?II?in Sn Cl₂-Ch Cl-EG DES was[Sn Cl₃]^-.Temperature and Sn Cl₂ concentration have effects on the viscosity and conductivity of Ch Cl-EG DES:as the temperature increases,the solution viscosity gradually decreases and the conductivity gradually increases;With the Sn Cl₂ concentration increasing,the solution viscosity decreases first and then increases,while the conductivity decreases first and then increases.?2?Cyclic voltammetry tests show that Sn?II?can be reduced to metallic tin in Ch Cl-EG DES.The good linear relationship between the cathode peak current ipc and the square root?^1/2of the sweep speed indicates that the reduction process of Sn?II?on the nickel electrode is a quasi-reversible one-step two-electron transfer controlled by diffusion.Increasing temperature will make the diffusion coefficient of Sn?II?reduction increase,which is beneficial to the electrodeposition reduction of tin.As the Sn Cl₂concentration increases,the reduction potential of metal tinwill move positively.?3?The cathodic polarization curve shows that compared with other electrodes,the reduction potential of Sn?II?is more correct on the nickel electrode,and it is easier to form tin powders;As the temperature is appropriately reduced,the smaller the particle size,the easier it is to obtain metal tin powder.In Ch Cl-EG DES,the electrodeposition of metal tin on nickel electrodes has undergone the process of nucleation and growth.It is found from the nucleation curve in the range of potential change that tin grows in three-dimensional transient nucleation.The Tafel test shows that the apparent activation energy of the tin anode dissolution process is low(25.536k J·mol^-1),which indicates that the tin anode dissolution process is a diffusion-controlled process.The SEM and AFM indicate the tin anode before and after dissolution,tin can be electrochemically polished in Ch Cl-EG DES without any by-products.The result indicates that its roughness is significantly reduced after electrochemical polishing.?4?In the range of current density at 10?30 m A·cm^-2,Sn Cl₂concentration at 30?70 m M,temperature of 313?353 K,and interelectrode distance at 1?3 cm,the current efficiency first increases with the increase of the current density,Sn Cl₂ concentration,and temperature.It decreases after increasing,and decreases with the increase of the pole spacing;the energy consumption increases with the increase of the current density and the pole spacing,and decreases with the increase of the Sn Cl₂ concentration and temperature.Compared to current density and Sn Cl₂ concentration,electrode distance and temperature have a greater impact on current efficiency and energy consumption.?5?The SEM test of tin powders shows that in Ch Cl-EG DES electrolytic tin powder with dendritic,needle and pyramidal structure can be obtained by adjusting the deposition parameters.When the current density is increased,the particle size of the tin powder becomes smaller and the branches are finer;when the concentration and temperature of Sn Cl₂ are increased,the grain size of the tin powder becomes larger;when the pole spacing is increased,the grain size of the tin powder is almost unchanged.XRD showes that the tin powder has a body-centered tetragonal crystal structure.With the increase of current density and interelectrode distance,the preferred crystal plane changes from?200?to?101?;As the Sn Cl₂ concentration increases,the preferred crystal plane changes from?211?to?200?;Temperaturee affectes less on thevariation of crystal plane.