Capacitors are also common electronic components in our circuits. There are thousands of capacitors in a car. A capacitor is an
electronic component consisting of two conductors sandwiched between an insulator. As one of the three basic components,
the capacitor's main function is energy storage and filtering. It also has functions such as DC blocking, bypass, coupling, rectification,
tuning, and energy conversion. Among capacitors, there is a special type of capacitor called an electrolytic capacitor. So what is an electrolytic
capacitor and what are its characteristics?
Electrolytic capacitor is a type of capacitor. The metal foil is the positive electrode (aluminum or tantalum). The oxide film (aluminum oxide or tantalum pentoxide)
close to the positive electrode is the dielectric. The cathode is made of conductive material and electrolyte (the electrolyte can be liquid or Solid) and other materials.
Because the electrolyte is the main part of the cathode, the electrolytic capacitor gets its name. At the same time, the positive and negative electrolytic capacitors cannot
be connected incorrectly.
Electrolytic capacitors are divided into aluminum electrolytic capacitors and tantalum electrolytic capacitors based on their positive electrodes. The negative electrode
of aluminum electrolytic capacitors is composed of tissue paper/film or electrolyte polymer soaked in electrolyte solution (liquid electrolyte); the negative electrode of tantalum
electrolytic capacitors usually uses manganese dioxide.
Aluminum electrolytic capacitors are polar capacitors. The positive plate is made of aluminum foil, which is immersed in the electrolyte for anodizing treatment.
A layer of aluminum oxide film is formed on the surface of the aluminum foil. Its thickness is generally 0.02 - 0.03μm. . This oxide film is the insulating medium
etween the positive and negative plates. The negative electrode of the capacitor is composed of electrolyte. The electrolyte is generally composed of boric acid,
ammonia, ethylene glycol, etc. In order to facilitate the manufacture of capacitors, Lorida Company usually impregnates the electrolyte solution on special paper,
and then uses a strip of raw aluminum plastic and the paper soaked in the electrolyte solution to fit together. This can be more conveniently led out on the raw
aluminum foil strip. negative electrode.
as the picture shows. The above-mentioned positive and negative electrodes are wound around their central axis to form the core of the aluminum electrolytic capacitor,
and then the core is placed in an aluminum shell and packaged to form the aluminum electrolytic capacitor. In order to prevent the electrolyte solution from leaking or drying up,
the mouth of the aluminum housing of the electrolytic capacitor is sealed with a rubber plug. In order to obtain a larger capacitance and a smaller volume, a chemical etching
method is used to form an uneven surface on one side of the positive electrode aluminum foil, which increases the surface area of the electrode and thereby increases the capacitance.
The reason why aluminum electrolytic capacitors have polarity is because the aluminum oxide film on the positive plate has one-way conductivity. Only when the positive electrode
of the capacitor is connected to the positive electrode of the power supply and the negative electrode is connected to the negative electrode of the power supply, the aluminum oxide
film can act as an insulating medium. effect. If the polarity of the aluminum electrolytic capacitor is reversed, the aluminum oxide film will become a conductor. Not only will the electrolytic
capacitor not be able to function, but a large current will pass through, causing overheating and damage to the capacitor. In order to prevent accidental explosions of aluminum electrolytic
capacitors during use, grooved mechanical weak links are usually pressed on the end face of the aluminum shell package. Once the internal pressure of the electrolytic capacitor is too high,
the grooves in the weak links will crack and release the pressure. Explosion proof.
The working medium of tantalum electrolytic capacitor is an extremely thin layer of tantalum pentoxide film (Ta2O5) formed on the surface of tantalum metal. Tantalum powder is pressed
into shape and sintered into an anode body in a high-temperature furnace. The dielectric is to put the anode body into acid to energize it to form a porous amorphous Ta2O5 dielectric film.
The working electrolyte is a manganese nitrate solution that is decomposed at high temperature to form MnO2 , used as a lead-out connection through the graphite layer. Similar to aluminum
electrolytic capacitors, tantalum capacitors also have unidirectional conductivity, so they have positive and negative electrodes.
