Electrolytic Dielectrics and Their Capacitors

Electrolytic dielectrics include metal oxides, aqueous-based liquid electrolytes, and non-aqueous-based liquid electrolytes. The most commonly used metal oxides are aluminum oxide, tantalum pentoxide, and niobium oxide. A typical aqueous-based liquid electrolyte contains boric acid or sodium borate in aqueous solution with various sugars or ethylene glycol to retard evaporation. Eor example, there are three major types of water-based electrolytes for aluminum electrolytic capacitors standard water-based (with 40% to 70% water), those containing ethylene glycol (with less than 25% water), and dipropyl ketone (with less than 25% water). 

In practice, the two major types of electrolytic capacitors are (1) aluminum electrolytic capacitors and (2) tantalum electrolytic capacitors. Aluminum electrolytic capacitors are fabricated from two conducting aluminum foils, one of which is coated with an insulating oxide layer and a paper spacer soaked in electrolyte. The foil insulated by the oxide layer is the anode while the liquid electrolyte and the second foil act as the cathode. Tantalum electrolytic capacitors are subdivided into wet and dry types based on whether their counter electrodes are served by sulfuric acid or a manganese dioxide film. Dry tantalum electrolytic capacitors possess a greater capacitance-to-volume ratio relative to aluminum counterparts and are utilized in computer and 

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