Síntese de filme de Nb2O5 por oxidação eletrolítica assistida a plasma (PEO) com regime oscilatório

Abstract

The present work aims to investigate the amplitude, the period, the temperature of five cycles of the oscillatory phenomenon in three current densities and how this behavior can affect the characteristics of the anodic film. During the synthesis of Nb2O5 anodic films in the plasma-assisted electrolytic oxidation process, or Plasma Electrolytic Oxidation (PEO), under specific conditions, an unusual oscillatory phenomenon was observed when analyzing the voltage vs. time curves. A system composed of a C2H2O4 electrolyte with a concentration of 0.1 mol.L-1, an initial temperature of 15°C, and a polished niobium substrate with an area of 100 mm2 was prepared. Given these conditions, three of them were used at different current densities: 5, 10, and 20 mA.cm-1, where the voltage vs. time curves were analyzed. The produced films were characterized for morphological and microstructure properties formed under an oscillatory regime. Studies have shown that the amplitude and the average period of oscillations tend to increase with increasing current densities, the average temperature exhibiting the same behavior. Based on the literature, the mechanism of oscillatory behavior is related to the detachment and reconstruction of the film, forming several layers. The difficult reproducibility of the oscillatory phenomenon was also observed since different replicates of the sample of 10 mA.cm-1 originate different curve shapes, a result of the sensitivity of the process with variations in temperature and simultaneous dissipation parameters. The characterizations of anodic films showed a predominant presence of niobium and oxygen and an orthorhombic structure of Nb2O5. The film has porous characteristics and has several cracks, with an increase in the density of pores on the surface related to an increase in current density. The bandgap values of the oxide coatings formed were lower than those found in the literature for Nb2O5. Studying the oscillatory phenomenon in the synthesis of Nb2O5 under the specified conditions contributes to understanding how the oscillatory behavior is influenced by the current density and can modify the synthesized anodic film.