Abstract
To obtain smooth TiO2 coatings for building a new design of Ti-6Al-4V heart valve, the anodic oxidation technique in pre-spark conditions was evaluated. TiO2 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 (Ra ≤ 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 H2SO4 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 H2SO4. An increase in the concentration of H2SO4 decreases the voltage at which the transformation of amorphous to crystalline coatings occurs; i.e., with 4 M H2SO4, the anatase phase appears at 60 V.
Highlights
With the objective of building a new mechanical heart valve design [1], the Ti-6Al-4V alloy coated with titanium dioxide (TiO2 ) has been selected as the building material [2]
Ti-6Al-4V alloy is an α/β Ti alloy widely used in biomedical applications due to its corrosion resistance and high bio- and hemocompatibility [6,7]
The recognized properties of Ti alloys are mainly due to the formation of a natural TiO2 oxide at room temperature, which can reach a thickness of 2–10 nm [6,7]. This native thin film oxide often has a high density of defects, which reduce mechanical properties such as wear resistance or chemical properties such as corrosion resistance [8]
Summary
With the objective of building a new mechanical heart valve design [1], the Ti-6Al-4V alloy coated with titanium dioxide (TiO2 ) has been selected as the building material [2]. Ti-6Al-4V alloy (grade 5 in ASTM B367) is an α/β Ti alloy widely used in biomedical applications due to its corrosion resistance and high bio- and hemocompatibility [6,7]. The recognized properties of Ti alloys are mainly due to the formation of a natural TiO2 oxide at room temperature, which can reach a thickness of 2–10 nm [6,7]. This native thin film oxide often has a high density of defects (mainly cracks), which reduce mechanical properties such as wear resistance or chemical properties such as corrosion resistance [8]. Anodic oxidation is a viable technique due to its low cost, simplicity of application, and control of the coatings’ characteristics
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