The Use of Niobium as an Anode Material in Liquid Filled Electrolytic CapacitorsReport as inadecuate

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ElectroComponent Science and Technology - Volume 1 1974, Issue 1, Pages 27-37

Allen Clark Research Centre, Caswell, Towcester, Northants, UK

Received 17 October 1973; Accepted 21 January 1974

Copyright © 1974 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Field crystallisation during the anodisation of niobium can be reduced to a minimum by employing a phosphoricacid electrolyte at low temperature. For certain other electrolyte systems, reduced crystalline growth rates areobtained by increasing the solute concentration or by adding either phosphate or ethylene glycol.

Porous anodes were prepared from niobium powders of nominal particle size 8μm or 10μm using sinteringtemperatures of 1400–1800℃. The capacitance of these bodies was in the range 4,600–10,000μF Vgm

. afteranodising at 20℃. Shelf tests on experimental capacitors filled with a concentrated sulphuric acid electrolyteindicated a maximum working temperature of 85℃. Although chemical compatibility between the dielectric oxideand the sulphuric acid was maintained up to 125℃, thermal effects on the oxide at this temperature resulted inunacceptably large increases in capacitance and leakage current. Endurance tests at 85℃ of capacitors rated at35V-200μF or 63V-60μF showed good stability of capacitance and dissipation factor over a period of 3000 hours.Final leakage currents were in the region of 10



at 85℃ and crystalline growth was greatly restricted.

Author: N. F. Jackson and J. C. Hendy



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