Recent trends in the downsizing of electrical appliances such as laptop computers and cellular phones have accelerated the demand for high-performance capacitors. Due to this trend and the fact that tantalum capacitors have the greatest capacity per unit volume and are thermally stable as compared to other capacitors, the production volume of tantalum metal powder has increased dramatically in the last 20 years.
Currently, more than 50% of tantalum resources are used in tantalum capacitors. However, the production volume of tantalum metal powder for capacitors is limited because the tantalum resource in the earth’s crust is scarce and tantalum is one of the valuable metals. In the year 2000, the balance between the demand and supply of tantalum ore collapsed due to a strong demand in the market. The price of the ore increased six-fold and tantalum capacitor manufacturers encountered a material crisis.
Considering this situation, extensive research on the production of niobium powder as a substitute for tantalum in capacitors is being carried out. This is primarily due to the fact that the chemical and physical properties of niobium are very similar to those of tantalum. In recent years, “niobium capacitors” and “niobium oxide capacitors” have been successfully produced on a commercial scale and their potential demand is increasing.
Extractive metallurgy of niobium has attained immense academic interest, mainly due to its application in the emerging niobium and its niobium oxide electrolytic capacitors and also in the superconducting radio frequency cavities for particle accelerators, also used in mint metal. Reductants such as aluminum and calcium are used for the preparation of niobium metal from its oxide. Niobium metal and its alloys such as ferro niobium and nickel niobium alloys are being commercially produced by aluminothermic reduction process. High purity niobium metal is prepared by electron beam melting and refining of the niobium metal which is obtained from the aluminothermic reduction of its oxide.
Carbothermic process can be considered as another process exploited for its commercial production. Requirement of niobium metal powder with stringent purity specifications for its possible use in electrolytic capacitor has necessitated the development of new techniques.
Niobium metal powder is generally prepared by hydriding, crushing of niobium hydride, and dehydriding. It is reported that niobium metal powder is prepared from its oxide by calcium using electron-mediated reduction process. Similar to tantalum, niobium fine powder is also prepared by liquid-liquid reduction with sodium. Niobium metal powders can be also prepared by using magnesiothermic reduction process. Using a cyclone separator assembly, niobium is prepared by the reaction between the magnesium vapor and niobium oxide.
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