Effect of electrolyte temperature on the structure and properties of Ta2O5 anodic oxide film
Ta2O5 anodic oxide film was prepared on the surface of high-purity tantalum foil by anodic oxidation in phosphoric acid electrolyte.And the effects of electrolyte temperature were investigated,which could greatly affect the structure,chemical composition,dielectric properties and insulating properties of the Ta2O5 anodic oxide film.The investigation was performed by elliptical polarization spectroscopy,X-ray diffractometry,X-ray photoelectron spectroscopy,and electrochemical tests.The results show that some electrolyte anions are bound in the Ta2O5 anodic oxide film,and the content and depth distribution of the bound anions decrease at higher electrolyte temperature.The dielectric constant and strength of the Ta2O5 anodic oxide film increase at higher electrolyte temperature.However,high temperature promotes crystallization of amorphous Ta2O5 and leads to the deterioration of the oxide film performance.When the electrolyte temperature is increased from 25 ℃ to 85 ℃,the oxide film dielectric constant increases by about 3.5％,and the breakdown voltage increases by about 1％,and the depth of distribution of bound anions in the film decreases from～1/2 to～1/4 of the oxide film thickness.Based on the experimental results,the optimum anodic oxidation temperature of tantalum in phosphoric acid electrolyte is 85 ℃.
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