The anodic oxidation of vanadium in acetic acid‐sodium tetraborate solutions containing small amounts of water has been studied over a potential range of 100V using the open‐circuit transient analysis technique. An anodic layer which showed bright uniform interference colors was found to grow on the metal surface. Results of these experiments indicate that the dependence of the oxidation current density, i , on the formation potential, V , is expressible in the form i=io exp false(V/Vofalse) , where io and Vo are parameters determined from the data analysis. The parameter io is found to depend on the applied current density, while the parameter Vo varies directly with the formation potential during galvanostatic oxidation. A result in this form implies that the electric field in the oxide is a function of the applied current density. These results show similarities to results previously obtained by others for the anodic oxidation of bismuth, tantalum, and iron.

The anodic oxide film formed on vanadium in an electrolyte of acetic acid, sodium borate, and a small quantity of water has been studied using ellipsometric and electrical measurements. These studies indicate that when a cathodic current is applied to a vanadium electrode upon which an anodic oxide film has been grown conversion of the anodic oxide occurs, and a new species or complex is formed on the electrode surface. Re‐application of an anodic current converts the film back to its original state. Both the refractive index and the solubility of the cathodically converted film differ from the anodic film. In particular, the cathodically converted film is much less soluble in water than is the anodic film. Ellipsometric data are consistent with a model in which the conversion of the film begins at the oxide/electrolyte interface and proceeds toward the metal. Other possible models are given for comparison purposes.

The galvanostatic oxidation of bismuth in sodium borate‐boric acid and sodium carbonate solutions has been studied over a potential range of 90V by analysis of openhyphen;circuit transients. An anodic layer which shows bright interference colors is found to grow on the metal surface. Experimental results indicate that the dependence of the oxidation current density, i, on the overpotential, V, is expressable in the form normali=i0expfalse(V/Vofalse) , where i 0 and Vo are parameters determined from the data analysis. The parameter Vo is found to vary linearly with the overpotential during galvanostatic oxidation, while the parameter i 0 depends on the applied current density. These results are related to a high field conduction model.

Ellipsometry is used to study the electrochromic processes which occur when anodically grown films of vanadium oxide are electrochemically reduced and subsequently reoxidized. Films up to 200 nm in thickness are grown by anodizing vanadium in acetic acid and acetone electrolytes. When the current is made cathodic, the outer surface of the V205 film is reduced to H4V2Os, and as coloring proceeds a phase boundary sweeps inward across the film toward the vanadium substrate. An optical inflection is observed when the phase boundary reaches the substrate, and no additional hydrogen is electrochemically bonded into the structure past this point. A field equal to 20% of the anodizing field is required to move hydrogen through the colored phase, and hydrogen transport is the rate-determining step for the coloring process. When the current is made anodic again, the film undergoes a three-stage bleaching process before oxide film growth continues. The first and third stages are brief but affect the entire film. The first stage culminates in the re-establishment of an oxide film at the electrolyte interface. The second stage proceeds by inward motion of a phase boundary, this time with a bleached layer of V205 on the outside and the colored layer on the inside. A field approximately equal to the anodizing field is required to move hydrogen through the bleached layer, and hydrogen transport is the rate-determining step. Oxygen will be mobile at the anodizing field unless its transport number is zero and is likely to be incorporated in the film in OH2 groups. The third stage of the bleaching process begins when vanadium ions start to enter the film from the substrate and ends when the oxygen-to-vanadium ratio returns to its stoichiometric value.The anodic oxides of vanadium and molybdenum are similar to the anodic oxide of tungsten in many respects, but not in their electrochromic behavior. Electrochemically-bonded hydrogen builds up to a relatively low concentration in tungsten oxide where hydrogen appears to move freely through the film, but it builds up to a high concentration in molybdenum and vanadium oxide even though a high field is required to make the hydrogen mobile. Our objective in this paper is to study the insertion and removal of hydrogen in vanadium oxide using ellipsometric and electrochemical techniques similar to those used in our recent studies of tungsten oxide (1) and molybdenum oxide (2). Studies of hydrogen insertion aimed at the development of electrochromic devices usually involve structures which have been modified to enhance ionic transport." Here we use electrochromic cycles to probe high-field ionic transport through a compact oxide.The solubility of vanadium oxide in water makes it impossible to grow an anodic oxide film on vanadium in an aqueous electrolyte. 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 ...

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