ELECTROCHEMICAL SYNTHESIS OF POROUS CRYSTALLINE TANTAL OXIDE

Abstract

Self-organization of nanoscale structures during electrochemical processing is most pronounced during the formation of porous anodic metal oxides (aluminum, titanium, tungsten, niobium, tantalum). These oxides contain arrays oriented perpendicular to the pore substrate. A distinctive feature of these films is a high degree of orderliness in the arrangement of pores and the possibility of controlled variation of the pore diameter in a wide range (from 10 to 150 nm). In this work, the features of the electrochemical formation of nanoporous oxide coatings on tantalum in acid-fluoride and organic electrolytes are investigated. Tantalum foil with a thickness of 0.1 mm and a purity of 99.99 % was used as a working electrode. For the formation of tantalum oxides, 1 M H2SO4 solutions with the addition of HF (0.1 M; 0.25 M; 0.5 M; 1 M) and an organic electrolyte were used: EG + 5.5 М H2O + 0.05 М H3PO4 + 0.8 М NH4F, EG + 5.5 М H2O + 0.05 М H3PO4 + 0.8 М NaF. Polarization studies were carried out on a P-45X potentiostat. in potentiodynamic mode. The reference electrode is saturated silver chloride. The magnitudes of the potentials are given relative to the normal hydrogen electrode. The morphology of the obtained coatings was studied using scanning electron microscopy using a JSM-7001F microscope. It is shown that the use of fluoride ion activator and electrolytes of different nature allows at the initial stage of anodizing to provide conditions for the formation of a crystalline anodic oxide film with different surface morphology. By varying the anodizing regime on tantalum, it is possible to synthesize porous films of amorphous or crystalline types. To obtain a crystalline porous oxide of tantalum with a developed surface, it is advisable to use an organic aprotic electrolyte composition: EG + 5.5 М H2O + 0.05 М H3PO4 + 0.8 М NH4F.