The production of niobium powder and electric properties of niobium capacitors

Abstract

In order to evaluate the electrical and frequency properties of niobium powder manufactured by the metallothermic reduction method for use as a capacitor, the present study measured capacitor performance evaluation factors such as leakage current, permittivity loss (tanδ) and capacitance, etc. The niobium powder used in this experiment was processed using the external continuous supply method and had large coarse globular particles of 0.5 μm to 1.0 μm, but the granularity distribution was very irregular. Capacitance decreased significantly from 150 μF in electrolyte (wet cap) to 130 μF after carbon (C)/silver (Ag) solution coating, and to around 115 μF after aging, falling within the capacity tolerance of tantalum capacitors. Converted to CV/g, capacitance was around 81,000 CV/g. Permittivity loss (tanδ) decreased significantly from 13.0 % after C/Ag coating to 7.5 % after aging, satisfying the general standard level of 10 % or less. Leakage current was 2.5 μA after C/Ag coating and 3.0 μA after aging, both less than the standard level of 6.3 μA. On the whole, the niobium capacitor showed somewhat more unstable characteristics than commercial tantalum capacitors but is nonetheless considered applicable as a future substitute for tantalum capacitors.