Abstract
In order to clarify the mechanism that zinc and phosphorus elements entering the micro-arc oxidation (MAO) coatings developed on Ti-6Al-4V alloys, anodic coatings containing different zinc and phosphorus were fabricated using an orthogonal experiment of four factors with three levels in an electrolyte containing EDTA-ZnNa2, KOH, and phytic acid. Surface morphology, element composition, chemical state and phase structure of MAO coatings were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The concentrations of zinc and phosphorus in the electrolyte were analyzed by an inductively coupled plasma optical emission spectrometry (ICP-OES). The results show that zinc and phosphorus elements in MAO coatings exist in the form of Zn3(PO4)2. Phytic acid is the most important factor on both zinc and phosphorus contents of MAO coatings. With the increase of phytic acid concentration or the decrease of KOH concentration, the contents of zinc and phosphorus in MAO coatings present a similarly increasing tendency. Our results indicate that phosphorus takes part in coating formation mainly by diffusion, while zinc enters into MAO coatings with phosphorus from phytic acid.
Highlights
Titanium alloys are widely used as metallic implants due to the combination of their outstanding characteristics such as high strength, low density, high immunity to corrosion, and good biocompatibility [1,2,3]
Surface morphology and chemical composition of the micro-arc oxidation (MAO)-treated titanium alloys were characterized by a field emission scanning electron microscope (SEM, Zeiss, Oberkochen, Germany) and energy dispersive X-ray spectrometer (EDS) attached to SEM
In order to further clarify the underlying mechanism of Zn and P ions into MAO coatings, one MAO solution was simultaneously fetched by three syringes in anode area, the middle area and cathode area during treatment for 40 s and 120 s (Figure 2)
Summary
Titanium alloys are widely used as metallic implants due to the combination of their outstanding characteristics such as high strength, low density, high immunity to corrosion, and good biocompatibility [1,2,3]. The functional coatings can be developed on titanium alloys by adjusting the electrolyte compositions, concentration and the applied electric parameters [3,5]. Inorganic phosphorus-containing electrolytes, for example, H3PO4, anodic coatings on titanium implants can improve cell adhesion and proliferation [6]. Glycerophosphate disodium salt pentahydrate, NaH2PO4, and (NaPO3) are widely used in MAO on inorganic phosphorus-containing electrolytes, for example, H3 PO4 , glycerophosphate disodium salt titanium alloys [5,6,7,8,9]. The influences of EDTA-ZnNa2 , KOH, phytic acid concentrations and treating time on the the contents of Zn and P elements in MAO coatings were systematically investigated. %, and 8.81 wt % Zn were abbreviated as Zn-2.86 wt %, Zn-5.83 wt %, and Zn-8.81 wt %, respectively
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