The Obtaining Two-layer Oxide Films on Titanium Medical Implants by Electrochemical Oxidation in Aqueous-organic Electrolytes

Abstract

The results of a study of the processes of electrochemical formation of oxide films on titanium doped with vanadium and aluminum additives in organic-aqueous electrolytes with a mixed solvent based on ethylene glycol and water and the addition of an activating additive in the form of ammonium fluoride are presented. It is shown that the formation dependences reflecting the dynamics of the formation of oxide films on the alloy under the conditions of anodic polarization of the samples depend on the composition of the electrolyte and the electrical parameters of electrolysis. In electrolytes with a low content of ammonium fluoride, the formation dependences have a form characteristic of a change in the voltage across the cell during the formation of a continuous oxide film. With an increase in the concentration of ammonium fluoride in the electrolyte, a plateau appears on the curves, which corresponds to the formation of a two-layer oxide coating consisting of a thin barrier component and thickened porous parts. It should be noted that an increase in the anode current density causes the plateau to disappear, but this is not a sign that a change in this parameter can lead to a uniform film. The effect is explained by the fact that an increase in the current density leads to the rapid formation of an oxide film due to the intense oxidation of the surface layer of the metal and the plateau does not have time to appear on the curve, although the resulting coating has porosity. In this case, the use of a mixed organic-aqueous solvent has a beneficial effect on the process of film formation. This occurs due to a decrease in the surface tension at the interface, which leads to the formation of a uniform oxide layer over the entire metal surface. In addition, the introduction of ethylene glycol into the electrolyte contributes to a decrease in the aggressiveness of the electrolyte due to a change in the interionic interaction with a change in the dielectric constant of the solution. The data obtained are used to form oxide coatings of titanium implant samples and are a prerequisite for the development of a technological process for the oxidation of medical products.