Electrolytic capacitor materials and processes
Oct 14, 2019|
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Electrolytic capacitor materials and processes
material
The aluminum foil used now is very elegant in composition and structure. High purity is no longer required, for example, for anode foils, which are required to be of high purity. In order to improve the initial corrosion point, mechanical strength and properties of the dielectric oxide film, the foil should contain some impurities. And some use alloy foil. In terms of structure, for low-pressure foils, the proportion of cubic structure is not required to be large, but for high-pressure foils, this structure is required to account for 80% to 90%. For the cathode foil. In order to increase the specific volume thereof, an alloy aluminum foil having a certain amount of impurities having a random orientation of crystal grains is required. The working electrolyte consists of three components. That is, solvents, solutes, and additives, such as electrolytes that have been used for a long period of time, are composed of ethylene glycol, glycerin, boric acid, and aqueous ammonia. Due to the development of aluminum electrolytic capacitors, this electrolyte is far from satisfactory, so many new electrolytes have been produced to reduce the operating temperature range of the capacitor (eg -55 ° C - 125 ° C). The formulation principle of these new electrolytes is: 1 mixed with two solvents. To achieve complementarity. 2 Two weak acids are used to provide the two anionic groups required. 3 add alkali, such as organic amine, to adjust the pH and flash voltage of the electrolyte. Change its resistivity. 4 Additives which improve the characteristics of the electrolyte, such as phosphoric acid or a salt thereof which prevents hydration of the aluminum oxide film, dinitrobenzene which absorbs hydrogen, etc., and an ethylene oxide which raises the flashover voltage of the electrolyte.
Process
In addition to the mechanization and automation of production, the progress of aluminum electrolytic capacitors in the process is mainly two processes of corrosion and energization. The corrosion coefficient of aluminum foil is not only high (low-voltage capacitor foil has reached 100, the high voltage is up to 25), and aluminum foil with different pothole morphology can be etched according to the performance requirements of the capacitor. The etching process is a kind of corrosive liquid type, concentration, temperature, original foil composition, structure, surface state, foil speed during corrosion, and dynamic balance process of power source type, waveform, frequency, voltage, etc. The question is how to get the best dynamic balance and how to determine the best balance according to the requirements. Therefore, it cannot be said that the corrosion process has reached the optimum state.
The current energization process has been able to produce high-quality dielectric oxide films, and different dielectric oxide films can be fabricated according to different requirements. For example, for DC capacitors, γ and γ'-type crystalline aluminum oxide films are fabricated, and the exchange is performed. The capacitor is an amorphous film. The biggest advancement in the energization process is the ability to convert an aluminum hydroxide film into a dielectric aluminum oxide film and form a water-repellent layer on the surface. In addition, defects and cracks in the dielectric film can be eliminated.