Influence of the Electrolyte Concentration on the Smooth TiO2 Anodic Coatings on Ti-6Al-4V

Abstract

Abstract:To obtain smooth TiO 2 coatings for building a new design of Ti-6Al-4V heart valve, the anodic oxidation technique in pre-spark conditions was evaluated. TiO 2 coating is necessary for its recognized biocompatibility and corrosion resistance. A required feature on surfaces in contact with blood is a low level of roughness (R a ≤ 50 nm) that does not favor the formation of blood clots. The present paper compares the coatings obtained by anodic oxidation of the Ti-6Al-4V alloy using H 2 SO 4 at different concentrations (0.1-4 M) as electrolyte and applying different voltages (from 20 to 70 V). Color and morphological analysis of coatings are performed using optical and scanning microscopy. The crystalline phases were analyzed by glancing X-ray diffraction. By varying the applied voltage, different interference colors coatings were obtained. The differences in morphologies of the coatings caused by changes in acid concentration are more evident at high voltages, limiting the oxidation conditions for the desired application. Anatase phase was detected from 70 V for 1 M H 2 SO 4 . An increase in the concentration of H 2 SO 4 decreases the voltage at which the transformation of amorphous to crystalline coatings occurs; i.e., with 4 M H 2 SO 4 , the anatase phase appears at 60 V.

Surface Activation and Pretreatments for Biocompatible Metals and Alloys Used in Biomedical Applications

“…Using different electrolyte solutions, electrolyte pH, anodization time, and applied potential will affect the crystallinity and morphology of the oxide film. Titanium oxide naturally grown has a thickness of 2-6 nm; in order to increase the thickness of this oxide layer, anodic oxidation is a good choice due to its low costs, simplicity of the experiment, and control of the coating's thickness [34]. For titanium, the electrolyte may consist of a variety of acids, neutral salts, and alkaline solutions; but, acidic electrolytes are generally favored due to higher affinity for oxide formation compared to other electrolytes [35].…”

“…Anodic oxidation of a titanium surface was also studied using sulfuric acid (H 2 SO 4 ) by Vera et al, the electrolyte concentration varied from 0.1 to 4 M, and the applied voltages varied from 20 to 70 V [34]. After the oxidation process, samples were rinsed with DI water and dried under hot air.…”

“…At 20 V, the samples went from dark blue/orange to yellow/green for different concentrations; at 40 V, the samples went from light orange to yellow; at 60 V, the samples went from dark orange to red; at 70 V, the samples went from yellow to purple and pink. The color changes were due to the higher concentration and conductivity of the electrolyte affecting the growth rate or changing the orientation of the phases on the substrate [34]. However, the morphology of the surface significantly changed from amorphous to crystalline, with an increase in applied voltage but not with an increase in acid concentration.…”

Non-Contact Roughness Measurement in Sub-Micron Range by Considering Depolarization Effects

“…In general, this improved technique can be used in the field of coatings [22] with numerous industrial applications. For instance, this method may be viable for determining the roughness of the surface finish of optical components based on silicon and germanium (IR optics), optical glasses in lens manufacturing [23], or in polymer components (CR-39, PMMA) used as substrates for depositing coatings [24], indium tin oxide (ITO) films [25], coatings for tribological performances [26], and some TiO 2 layers for medical applications [27], among others.…”

High-Temperature Oxidation Resistance of NiAl Intermetallic Formed In Situ by Thermal Spraying

“…Titanium and titanium alloys are widely used as structural materials in fields such as the aerospace industry or automobile industry, due to their high melting point, low density, and their superior high-temperature mechanical properties [1][2][3][4][5]. However, the maximum temperature at which the alloys can be used is 873 K, above which the mechanical properties will be reduced and the life of the alloys seriously affected.…”