
Electrolytic capacitors use a chemical feature of some special metals, earlier called "valve metals". Applying a positive voltage to the anode material in an electrolytic bath forms an insulating oxide layer with a thickness corresponding to the applied voltage. This oxide layer acts as the dielectric in an electrolytic capacitor. The properties of this aluminum oxide layer compared with tantalum pentoxide dielectric layer are given in the following table: [pdf]
The basic material of the anode for aluminum electrolytic capacitors is a foil with a thickness of ~ 20–100 μm made of aluminum with a high purity of at least 99.99%. This is etched (roughened) in an electrochemical process to increase the effective electrode surface.
Aluminum electrolytic capacitors, often called electrolytic capacitors, are usually selected because they offer a relatively large capacitance for a relatively small physical size. Aluminum electrolytic capacitors tend to be readily available, and with high voltage values (on the order of 700 V).
Electrolytic capacitors are normally made from one of three different materials: aluminum, tantalum, and niobium. Aluminum is one of three metals manufacturers use for electrolytic capacitors for several reasons:
Aluminum electrolytic capacitors are generally divided into two basic reliability categories: capaci-tors for high-reliability applications and capacitors for general-purpose applications. This differen-tiation has also been adopted in the relevant IEC standards.
Aluminum electrolytic capacitors for general applications are called "General-Purpose Grade" (GP) in IEC publications. The international standard for aluminum electrolytic capacitors is IEC 60384-4.
Aluminum electrolytic capacitors with non-solid electrolyte are the best known and most widely used electrolytic capacitors. These components can be found on almost all boards of electronic equipment. They are characterized by particularly inexpensive and easy to process base materials.
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