D.C. etching anode aluminum foil to form branch tunnels by electroless depositing Cu

Abstract

Purpose The purpose of this study is to explore the mechanism of branch pits and tunnels formation and increase the specific surface area and capacitance of anode Al foil for high voltage electrolytic capacitor by D.C. etching in acidic solution and neutral. Design/methodology/approach Al foil was first D.C. etched in HCl-H2SO4 mixed acidic solution to form main tunnels perpendicular to the Al surface, and then D.C. etched in neutral NaCl solution including 0.5 per cent C6H8O7 and Cu(NO3)2 with different concentration to form branch tunnels normal to Al surface. Between two etching, Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells. The effects of electroless deposited Cu nuclei on cross-section etching morphologies and electrochemical behavior of Al foil was investigated with SEM, polarization curve and electrochemical impedance spectroscopy (EIS). Findings The results show that sub branch tunnels can form along the main tunnels owing to the formation of Cu-Al micro-batteries, in which Cu is cathode and Al is anode. With increase in Cu(NO3)2 concentration, more Cu nuclei can be electroless deposited and serve as the favorable sites for branch tunnel initiation along the whole length of main tunnels, leading to enhancement in specific capacitance of anode Al foil. Originality/value Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells, which can serve as the favorable sites for branch tunnel initiation along the main tunnels to enhance specific capacitance of anode Al foil.

Microstructure and Recrystallization Behavior of Heating Rate-Controlled Electrolytic Capacitor Aluminum Foil under Cold Forming and Annealing

“…The purpose of this is to investigate how to increase its electric storage capacity and facilitate better design for The microstructure morphology and recrystallization behavior are significantly influenced by various factors such as the degree of cold rolling deformation, annealing temperature, and annealing heating rate. These factors play a crucial role in determining the difference between the initial recrystallization driving force and the secondary grain growth driving force [17,20]. The latter is primarily attributed to the consumption and retention of deformation stored energy.…”

“…Summarizing previous studies, the purpose of Liu et al [20]'s research is to investigate how branch pits and tunnels form and increase the specific surface area and capacitance of anode aluminum foil for high-voltage electrolytic capacitors through D.C. etching in both acidic and neutral solutions. The capacitance and equivalent series resistance of these components have significant effects on the performance and reliability of power electronic systems.…”

Effects of the solution flow rate on the growth of aluminum etch tunnels

“…In addition to this method, scholars have prepared branch tunnels for capacity enhancement by depositing impurity elements. 3,4 The capacity is also increased by preparing composite oxide films to increase the dielectric constant. [5][6][7] However, the impurity elements used to prepare the branch tunnel can degrade the electrical properties of the capacitor.…”

“…8 Fortunately, we developed a polishing method enables counting the tunnel length. Many scholars have studied the effects of bath temperature, 8-10 current density, [10][11][12] and bath chemistry 3,[13][14][15][16][17] on tunnel growth. These factors have a clear impact on tunnel growth and have guided industrial production.…”

“… 2 The average length of tunnels determines the capacity of the anodic electrode. In addition to this method, scholars have prepared branch tunnels for capacity enhancement by depositing impurity elements 3,4 . The capacity is also increased by preparing composite oxide films to increase the dielectric constant 5–7 .…”