Niobium powder synthesized by calciothermic reduction of niobium hydroxide for use in capacitors

• Niobium oxide and hydroxide were reduced by calcium dissolved in CaCl2 melt.
• Sub-micrometer spherical metallic particles with coral-like morphology were obtained.
• High capacitance (CV) because of small shrinkage during sintering.

Metallic niobium powder was produced for applications in electric capacitors via calciothermic reduction of niobium hydroxide in molten CaCl2. Sub-micrometer spherical metallic particles with coral-like morphologies reflected the particle size of the starting oxide powder. A fine powder was obtained from the mixtures of niobium hydroxide and CaO or Ca(OH)2, respectively.Sintered pellets of the metallic powder showed a higher capacitance (CV) than those of the simply reduced powder without pre-treatment, because the shrinkage during sintering was smaller. The CV was as large as that of commercially sintered pellets for tantalum capacitors. Therefore, this niobium powder would act as a higher-voltage capacitor by applying chemical anodic treatment at higher voltages, and lower oxygen content in the reduced power could realize a lower leak current.

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