Study on the corrosion process of aluminum foil fo

Research on the corrosion process of aluminum foil for electrolytic capacitors

with the rapid development of electronic industry, aluminum electrolytic capacitors are more widely used and have higher performance requirements. Corrosion formed foil for aluminum electrolytic capacitor is a special electronic material for basic components of electronic information industry. The market of corrosion formed foil for medium and high-voltage aluminum electrolytic capacitor is in short supply. As a medium and high voltage electrolytic capacitor with a rated voltage of more than 200V, the corrosion formed foil has high quality requirements and is difficult to produce. Only a few domestic manufacturers produce it, but its performance can not meet the user's requirements. Therefore, it is urgent to improve the specific capacity on the premise of ensuring the bending strength of the corrosion aluminum foil. The specific capacity of corrosive foil for anode of high voltage electrolytic capacitor is the key to restrict the volume of high voltage and large capacity electrolytic capacitor

in addition to the quality of the optical foil itself, the corrosion process is the key process to obtain excellent properties such as high specific capacity and high strength for aluminum foil for aluminum electrolytic capacitor. Corrosion is the previous process in the manufacture of chemical foil. Corrosion foil specific volume is the basis for forming foil specific volume. 7.1 the task appearance of piston, oil cylinder, valve and other parts of hydraulic system shall be free of cracks and scratches. In order to obtain satisfactory performance, there are various corrosion processes, but some processes bring headache environmental protection problems (such as chromic acid hydrofluoric acid system) while obtaining excellent performance. Therefore, people are committed to the development and research of high-performance environmental protection corrosion process. In recent years, the domestic corrosion process system represented by hydrochloric acid sulfuric acid or hydrochloric acid sulfuric acid nitric acid has made a qualitative leap in the specific volume of corroded aluminum foil, and the performance has been greatly improved, which has opened up a broad way for the development of aluminum foil for capacitor electrical use in the domestic copper rod tensile testing machine to test the tensile load. The author used the orthogonal experiment method to study the relevant process parameters and find the best process conditions

1 experiment

1.1 corrosion process specification

experiment selection 110 μ M thick light foil is high-purity aluminum with purity of 99.99%. Sulfuric acid hydrochloric acid corrosion system is adopted. The corrosion process is (foil speed 100cm/min):

1.2 performance test

the specific volume of the corroded foil is measured according to the Japanese jcc2000 standard, the voltage is 600V, and the bending strength of the corroded foil is measured by the aluminum foil bending tester; The corrosion morphology and cross-section morphology of the corrosion foil were observed and analyzed by h-8010 scanning electron microscope. The etched foil filled with resin adhesive was cured, and then the etched foil was dissolved with alkali, and the morphology of etched holes was observed by sem-6480lv scanning electron microscope

2 results and discussion

the experimental results of the change of corrosion process specification are shown in Table 2

aluminum and its alloys are metals and alloys with self purification characteristics. Electrochemical pitting corrosion occurs in certain acidic media (such as Cl containing media). The process of small hole corrosion includes: 1 Nucleation on the surface of pure metal; 2. The growth of small holes. The old uncle's corrosion process is to control these two processes. The experimental results in Table 2 are to optimize the aluminum foil corrosion process and obtain ideal results by influencing these two processes by changing the level of each factor

it can be seen from table 2 that various factors have different effects on the experimental results. According to the range analysis, the composition of corrosion solution, corrosion time, temperature and corrosion voltage are significant factors affecting the specific volume of corroded aluminum, and the composition of corrosion solution, corrosion time and temperature are important factors affecting the bending strength of corroded foil

2.1 effect of the proportion of corrosive medium on the performance of corrosive foil

the effect of the composition of corrosive solution on the corrosion foil is shown in Figure 1 It can be seen from Figure 1 that with the increase of the proportion of sulfuric acid component, the specific volume of the corroded foil presents a maximum value, while the bending strength decreases uniformly

aluminum and its alloys suffer from pitting corrosion in the medium containing halogen ions. During anodizing, as long as the medium contains cl-, pitting corrosion can occur to the metal, and with the increase of cl- concentration in the medium, the pitting potential decreases, making pitting corrosion easy to occur. According to the purification adsorption theory, the pitting is caused by the corrosive anion (cl-) adsorbed on the surface of the purification membrane and the ion passing through the purification membrane. The increase of Cl concentration is conducive to the nucleation rate of pitting corrosion on the surface of aluminum foil. When the pores on the surface continue to develop in depth after nucleation, and the alumina purification membrane is formed on the pore wall, the oxidizing acid plays a key role. Therefore, when the proportion of sulfuric acid is increased, it is conducive to film formation, so the solution composition is ψ When (h2so4:hcl) =3:1, the corrosion foil has the maximum specific volume

Figure 2 shows the formation of pores on the surface of etched foil obtained from different solution compositions. Solution group becomes ψ When (h2so4:hcl) =3:1, the hole size of the corrosion foil is small and uniform, the total corrosion area increases, and the specific volume reaches the maximum. Solution group becomes ψ When (h2so4:hcl) = 4:1, the hole size of the corrosion foil is large and uneven, many hole walls collapse, the total corrosion area decreases, and the specific volume decreases rapidly

the bending strength of the corrosion foil depends on the thickness of the sandwich layer of the corrosion foil (that is, the thickness in the middle of the aluminum foil that is not corroded) and the uniformity of the corrosion hole. The thicker the sandwich layer, the more uniform the corrosion hole, the higher the bending strength, but the lower the specific volume; The thinner the corrosion layer is, the more uneven the corrosion hole is, and the lower the bending strength is. In the corrosion solution, with the increase of H2SO4 ratio, the extension of corrosion time, the deepening of pitting depth, the thickness of remaining aluminum foil decreases, and the bending strength becomes lower and lower. Figure 3 shows the cross-sectional morphology of the etched foil. During the bending test of corrosion foil, the alumina in the hole wall is brittle and easy to break, and the main body bearing the load is the aluminum of the remaining section

2.2 effect of corrosion voltage on the performance of electrode foil

the change of specific volume and bending strength of corrosion foil with anodic oxidation voltage is shown in Figure 4. There is an optimal value for specific volume, and the bending strength is generally reduced as WDW (5) 0 microcomputer controlled electronic universal testing machine is often used

according to the principle of electrochemical corrosion, the generation of keyhole corrosion on the filter surface is related to the critical potential. Only when the electrode potential in the local area of the metal surface reaches and is higher than the critical potential (keyhole corrosion potential), keyhole corrosion can be formed. With the increase of electrode potential, the sensitivity of keyhole corrosion increases. It can be seen that there is a close relationship between pore corrosion and electrode potential. In the anodizing process of aluminum foil, the increase of voltage can promote the nucleation and growth of pores, but the effect is different. When the nucleation rate is higher than the growth rate, the specific capacity of the etched foil increases with the increase of voltage. However, when the voltage can cause the adjacent hole walls to corrode and collapse, the specific volume of the corrosion foil will decrease with the increase of the voltage. The increase of voltage is conducive to the increase of nucleation rate and uniform corrosion, while the bending strength of corroded foil will be reduced nonlinearly

2.3 influence of corrosion temperature and corrosion time on the performance of corrosion foil

the influence law of increasing corrosion environment temperature and prolonging corrosion time on the performance of aluminum foil is shown in Figure 5. As can be seen from Figure 5, with the increase of temperature. There is an extreme value of the specific volume of the corroded foil, and the bending strength decreases linearly

with the extension of corrosion time, there is also an extreme value of the specific volume of the corrosion foil, and the bending strength is almost a linear decrease close to the branch line

after the nucleation of small holes on the surface of aluminum foil, further corrosion is mainly carried out in the small holes. This process is self promoting. The rapid dissolution of metal in the etch hole will cause too many cations to be produced in the etch hole. As a result, in order to maintain electrical neutrality, the anion outside the etch hole (cl-) migrates into the air, which also causes the cl- concentration to increase, thus forming a concentrated solution of metal chloride in the hole. This concentrated solution can maintain the active state of the metal surface in the hole. With the deepening of pitting corrosion and the corrosion products covering the pit mouth, it is difficult for oxygen to diffuse into the corrosion hole. As a result, the corrosion products at the orifice deposit and rust layer form an occluded battery. After the occluded cell is formed, the migration of substances inside and outside the mouth is more difficult, which makes the metal chloride in the hole more concentrated. The hydrolysis of chloride further increases the acidity of the medium. The increase of acidity promotes the accelerated anodic dissolution in the hole, forming the ability of deep excavation of the etched hole

it is easy to understand the law that the bending strength decreases linearly with the increase of temperature and time. In the corrosion process of all metal materials, increasing the corrosion environment temperature and prolonging the corrosion time will increase the metal corrosion. When the corrosion depth of the aluminum foil surface increases, the bending strength naturally decreases, but when the temperature rises to a certain extent, the corrosion hole is blocked, the reaction in the hole is suspended, and the bending strength changes little

however, the specific volume of the etched foil is proportional to the amount of alumina on the etched surface. When the corrosion temperature is increased and the corrosion time is prolonged, the corrosion of aluminum foil is intensified, the surface area of aluminum is increased, and the specific volume of corrosion rate is increased. When the corrosion develops further, the corrosion hole walls may collapse and connect holes, which shows that the specific volume of the corrosion foil increases slowly or decreases instead of increasing. This phenomenon can be seen, and then open the oil return valve in Figure 2 and Figure 6. In addition, the effective thickness of aluminum foil is also reduced due to cutting while a large amount of chemical corrosion is on the surface. Therefore, the total specific volume does not increase linearly with the increase of corrosion degree

the specific volume of etched foil mainly depends on the area of alumina forming porous layer. The area of porous layer is related to the number, size and depth of holes, as well as the erosion and collapse loss of hole wall in corrosion engineering. The significant factors that affect the specific capacity of etched foil are the composition of etched solution, corrosion voltage and electric quantity, reflection temperature and treatment time. Optimizing the composition of etched solution, voltage and electric quantity, temperature and time will obtain a high specific capacity

the bending strength of etched foil depends on the thickness of aluminum sandwich layer and the uniformity of etched holes. The composition of corrosion solution, temperature and corrosion time are important factors affecting the bending strength of corrosion foil

3 conclusion

(1) in the hydrochloric acid sulfuric acid corrosion system, with the increase of the proportion of H2SO4, the strength of the corrosion foil decreases, but its specific volume first increases and then decreases, ψ (h2so4:hcl) the best value is 3:1

(2) in the voltage range of 6 ~ 10V, the higher the anodic oxidation voltage, the higher the specific capacity of the corrosion foil. But the bending strength is the highest when the voltage is 8V

(3) increasing the corrosion temperature and prolonging the corrosion time will reduce the thickness of the remaining aluminum foil and reduce the bending strength. However, the effect on the specific volume of etched foil is complex. With the increase of corrosion temperature and corrosion time, the specific volume increases gradually at first, and then decreases after reaching the maximum value. The specific volume decreases faster with the extension of time. (end)