Effect Of Chemical Zinc Plating On Anodic Aluminum Foil For Aluminum Electrolytic Capacitor And Its Mechanism

With the rapid development of electronic industry,the requirements for high capacity,small size and low cost of electrolytic capacitors are becoming more and more urgent.Direct current erosion method of external DC power supply has high corrosion efficiency and is one of the electrochemical corrosion expansion methods widely used at present.However,the quality stability of the foil surface,the opening rate of tunnel holes and the uniformity of hole distribution still can not meet the requirements of high-performance aluminum electrolytic capacitors.Therefore,it is necessary to discuss in depth in order to prepare high quality corroded aluminium foil which can meet the needs of miniaturization and integration.External power supply consumes a lot of energy and costs in the process of corrosion expansion.It is urgent to develop corrosion technology without external power supply so as to save production costs and enhance the competitiveness of enterprises.At present,it has not been seen that specific metal elements are deposited on the surface of aluminium foil by electroless plating to form micro-batteries to promote the corrosion expansion of aluminium foil.In this paper,firstly,the anodic aluminum foil was pretreated with acid and alkali before corrosion to improve the surface state of aluminum foil,adjust the thickness and structure of oxide film,and increase the surface activity of aluminum foil.Then,the trace Zn elements with higher potential than the standard electrode were deposited uniformly on the surface of the aluminum foil.Finally,the method of direct current erosion with external direct current power supply and the method of corrosion battery without external power supply are adopted to treat the corrosion holes of aluminum foil.The corrosion of aluminium foil was characterized by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),section metallography(OM),thinning rate,weight loss rate and polarization curve.The acid and alkali pretreatment,chemical galvanized with high purity aluminum foil dc erosion corrosion and corrosion cell method influence of the expansion were studied,to explore the pretreatment,electrolytic liquid system and the way of corrosion time and temperature,corrosion and corrosion of aluminum foil covering the relationshipbetween the analysis of these factors under the action of the corrosion process and mechanism of aluminum foil for corrosion tunnel hole formation and development of law,in order to obtain better aluminum foil corrosion process conditions and parameters,for industrial preparation high hematocrit corrosion on aluminum foil to lay the theoretical foundation and provide technical support.The main research contents and results are as follows:(1)Study on dc erosion process and mechanism of high purity anodic aluminum foil(1)When the concentration of sodium hydroxide solution at 40 °C is 0.5mol/L,the effect of tunnel pore density and length after DC corrosion on 60 sC is the best.When the concentration of hydrochloric acid solution at 70 °C is 1.0mol/L,the density and length of tunnel holes after DC erosion are the best for pretreated 180 s.(2)Electroless galvanizing deposits a trace amount of zinc on the surface of aluminum foil and forms a Zn-Al microbattery with aluminum foil to improve and promote the corrosion of aluminum foil.When the pH of the plating solution is 4-5,the plating temperature is 80 °C,and the plating time is 20 s.The preferred process conditions for galvanizing,under these conditions,the specific surface area and specific capacitance of the galvanized aluminum foil after DC etching are better.(3)In a mixed electrolyte solution of 3.0 mol/L sulfuric acid and 1.0 mol/L hydrochloric acid,the pore-forming temperature is 80 ° C and the pore-forming time is 6 min,which is a preferred process condition for the corrosion of the galvanized aluminum foil after acid-base pretreatment.Under the condition,the corrosion of the aluminum foil surface is uniform,the corrosion surface expansion effect is better,the tunnel hole density is larger,the length is longer,and the specific capacitance is larger.(4)The zinc element deposited on the surface of the aluminum foil and the aluminum constitute a large number of micro battery cells,which generate a galvanic effect,increase the current density in the circuit to some extent,and improve the corrosion efficiency of the aluminum foil in the mixed acid system;in addition,the existence of the micro battery unit can be increased Aluminum foil corrodes the uniformity of the hair holes.(2)Study on corrosion process and mechanism of high purity anode aluminum foil by corrosive battery method(1)When the concentration of sodium hydroxide solution at 40 °C is 0.7mol/L,the aluminum foil pretreated for 60 s has the best tunnel hole density and length after etching by corrosive cell method;when the concentration of hydrochloric acid solution at 70 °C is 1.0mol/L,the aluminum foil pretreated for 180 s has the best tunnel hole density and length after corrosion by corrosive cell method.Compared with the direct current etching method,the optimum NaOH concentration for alkali-treated aluminum foil corrosion cell expansion is slightly higher.(2)When the pH of plating solution is 4-5,the plating temperature is 80 °C and the plating time is 20 s,which is the best process condition for electroless zinc plating.Under this condition,the specific surface area and specific capacitance of the galvanized aluminum foil after etching by the etching method are larger.Compared with the direct current etching method,the aluminum foil corrosion cell method has a slightly lower expansion effect under the same plating time and plating temperature,but has an energy saving advantage.(3)In a mixed electrolyte solution with a concentration of 3.0mol/L sulfuric acid,1.0mol/L hydrochloric acid and 0.3mol/L sodium nitrate,the pore temperature is80°C and the pore time is 6.5min,which is the corrosion of the galvanized aluminum foil corrosion cell method.Preferred process conditions.Compared with the direct current etching method,the galvanized aluminum foil requires a longer opening time when the surface is expanded by the etching method.(4)Electroless galvanizing deposits a trace amount of zinc on the surface of aluminum foil to form a Zn-Al microbattery with a potential difference of 0.9V.In the corrosion system,cathode graphite and anode aluminum foil form a C-Al corrosion cell with a potential difference of 1.794V;Zn-Al microbattery and The C-Al corrosion cell produces a superposition effect,promotes the initiation of pitting on the surface of the aluminum foil,increases the tunnel hole density,and increases the specific surface area and specific capacitance of the corroded aluminum foil.