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A niobium electrolytic capacitor is a polarized capacitor whose anode electrode (+) is made of passivated niobium metal or niobium monoxide on which an insulating niobium pentoxide layer acts as the dielectric of the niobium capacitor. A solid electrolyte on the surface of the oxide layer serves as the second electrode (cathode) (-) of the capacitor. Niobium electrolytic capacitors are passive electronic components and members of the family of electrolytic capacitors. Niobium capacitors are available as SMD chip capacitors and compete with tantalum chip capacitors in certain voltage and capacitance ratings. They are available with a solid manganese dioxide as well as a solid conductive polymer electrolyte. Niobium capacitors are polarized components by manufacturing principle and may only be operated with DC voltage in correct polarity. Reverse voltage or ripple current higher than specified can destroy the dielectric and thus the capacitor. The destruction of the dielectric may have catastrophic consequences. Manufacturers specify special circuit design rules for the safe operation of niobium capacitors. Niobium capacitors were developed in the Soviet Union in the 1960s. Since 2002 they have been commercially available in the West to take advantage of the lower cost and better availability of niobium compared with tantalum. ==Basic information== Niobium is a sister metal to tantalum. Niobium has a similar melting point (2744 °C) to tantalum and exhibits similar chemical properties. The materials and processes used to produce niobium-dielectric capacitors are essentially the same as for existing tantalum-dielectric capacitors. However, niobium as a raw material is much more abundant in nature than tantalum and is less expensive. The characteristics of niobium electrolytic capacitors and tantalum electrolytic capacitors are roughly comparable. Niobium electrolytic capacitors can be made with high purity niobium as the anode but the diffusion of oxygen from the dielectric (Nb2O5) into the niobium anode metal is very high, resulting in leakage current instability or even capacitor failures. There are two possible ways to reduce oxygen diffusion and improve leakage current stability – either by doping metallic niobium powders with nitride into passivated niobium nitride or using niobium oxide (NbO) as anode material. Niobium oxide is a hard ceramic material characterized by high metallic conductivity. Niobium oxide powder can be prepared in a similar structure to that of tantalum powder and can be processed in a similar way to produce capacitors. It also can be oxidized by anodic oxidation (anodizing, forming) to generate the insulating dielectric layer. Thus two types of niobium electrolytic capacitors are marketed, those using a passivated niobium anode and those using a niobium oxide anode. Both types use niobium pentoxide (Nb2O5) as the dielectric layer. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Niobium capacitor」の詳細全文を読む スポンサード リンク
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