The Source of Oxygen in the Anodization of Vanadium

Abstract

Single crystals of vanadium have been anodized by the method of Keil and Salomon for water soluble oxides. Oxygen-18 enriched water or acetic acid was used in order to trace the oxygen ~rom the acetic acid based solution to the oxide film. The oxygen isotope in the oxide film was determined by the method of nuclear microanalysis utilizing the i60(d,p) and isO(p,~) reactions. The results were compared to those for zirconium anodized in an isO enriched water-based solution. The results showed that, while the zirconium oxide was iso rich, the vanadium oxides were 160 rich. This implies that the anodization mechanism is not the conventional one assumed by Keil and Salomon. Another possible anodization mechanism which could explain the data is discussed.When vanadium is anodized in an aqueous solution, the vanadium oxide film tends to dissolve in the solution as vanadyl ions. Therefore, because of the high solubility of vanadium oxides in water, nonaqueous solutions are necessary to form uniform oxide films on vanadium by anodization. Glacial acetic acid containing small additions of water and sodium tetraborate has been found most suitable for the anodization of vanadium (1-5).Keil and Salomon (1, 2) found that anodization in an acetic acid solution 2.0M in water and 0.02M in NaeB40~ leads to films which are reproducible and characteristic of the formation voltage. The total amount of Na2B407 present in the solution was not considered to be critical; however, the film growth was observed to be sensitive to the water-borate ratio. Breakdown of the oxide film was observed at applied potentials above about 25V.Later studies found that lesser amounts of water in the acetic acid solution would still yield good oxide films. Ellis et al. (4) used an acetic acid solution containing only enough water to dissolve all the sodium tetraborate. Arora and Kelly (5) used a solution 0.02M in sodium tetraborate and 1.0M in water. Therefore, the water-borate ratio may not be as important as previously thought. When the water content was reduced, formation voltages of up to 80 or 90V yielded reproducible films.The oxide film which is formed on vanadium is amorphous (5), and the oxidation state of vanadium in the film is 4.0 [Ref. (2)]. The amorphous structure is retained until the film is heated to about 370~ Keil and Salomon (2) have suggested that the oxygen in the oxide film is provided by the water in the anodizing solution. This was based upon the fact that no oxide film could be formed on the vanadium if water were not present regardless of the voltage or current density applied to the anode. However, the amount of water seems not to be very critical as long as a quantity sufficient to dissolve the sodium tetraborate is present. Other sources of the oxygen may be from the acetic acid itself or from the sodium tetraborate. The source of the oxygen in the film is important in determining the mechanism of formation oI the film. This paper demonstrates a method of determining the source of oxygen in the anodization process. Experiment...

Anodic oxidation of vanadium and properties of vanadium oxide films

“…Therefore, AOFs on transition metals can consist of different oxide phases [7,10]. In particular, the phase composition of anodic oxides on vanadium has been identified by different authors as either V 2 O 5 [4,10,11] or VO 2 [9,12,13], or as a mixture of V 2 O 5 and lower oxides [10,[14][15][16]. Also, passive films composed of barium vanadate [14] or vanadophosphate [17] can be obtained by anodization of V in aqueous solutions in some cases.…”

“…When vanadium is anodized in an aqueous solution, the vanadium oxide film tends to dissolve in the solution as vanadyl ions [12,14,18]. Therefore, because of the solubility of vanadium oxides in water, non-aqueous solutions are necessary for obtaining uniform oxide films on vanadium by anodization.…”

An Optical Study of Hydrogen Insertion in the Anodic Oxide of Vanadium

“…Keil and Salomon (3,4) grew the first anodic oxide films on vanadium using an acetic acid electrolyte containing a small quantity of water and saturated with sodium tetraborate, and concluded that the films were composed of V204. The same electrolyte was used by Mackintosh and Plattner (5) in a transport number study which identified the oxide as V205, and by Lewis and Perkins (6) who concluded that the tetraborate, not the water, acted as the source of oxygen for the film. Pelleg (7) found an acetone-based electrolyte (again containing sodium tetraborate) in which anodic oxide films could be grown,.but his interest was in microsectioning vanadium, not in growing oxide.…”

Mesoporous vanadium nitride as anion storage electrode for reverse dual-ion hybrid supercapacitor

“…Owning to vanadium oxide film tends to dissolve as vanadyl ions in the aqueous solution during anodizing process ( Yang et al., 2011 ). To induce the porous structure, the Na 2 B 4 O 7 as extra oxygen source is introduced in the solution ( Lewis and Perkins, 1979 ). The nanoporous (NPs) V 2 O 5 electrodes were prepared by anodizing process.…”