Abstract
To fabricate porous copper coatings on titanium, we used the process of plasma electrolytic oxidation (PEO) with voltage control. For all experiments, the three-phase step-up transformer with six-diode Graetz bridge was used. The voltage and the amount of salt used in the electrolyte were determined so as to obtain porous coatings. Within the framework of this study, the PEO process was carried out at a voltage of 450 VRMS in four electrolytes containing the salt as copper(II) nitrate(V) trihydrate. Moreover, we showed that the content of salt in the electrolyte needed to obtain a porous PEO coating was in the range 300–600 g/dm3. After exceeding this amount of salts in the electrolyte, some inclusions on the sample surface were observed. It is worth noting that this limitation of the amount of salts in the electrolyte was not connected with the maximum solubility of copper(II) nitrate(V) trihydrate in the concentrated (85%) orthophosphoric acid. To characterize the obtained coatings, numerous techniques were used. In this work, we used scanning electron microscopy (SEM) coupled with electron-dispersive X-ray spectroscopy (EDS), conducted surface analysis using confocal laser scanning microscopy (CLSM), and studied the surface layer chemical composition of the obtained coatings by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), glow discharge of optical emission spectroscopy (GDOES), and biological tests. It was found that the higher the concentration of Cu(NO3)2∙3H2O in the electrolyte, the higher the roughness of the coatings, which may be described by 3D roughness parameters, such as Sa (1.17–1.90 μm) and Sp (7.62–13.91 μm). The thicknesses of PEO coatings obtained in the electrolyte with 300–600 g/dm3 Cu(NO3) 2∙3H2O were in the range 7.8 to 10 μm. The Cu/P ratio of the whole volume of coating measured by EDS was in the range 0.05–0.12, while the range for the top layer (measured using XPS) was 0.17–0.24. The atomic concentration of copper (0.54–0.72 at%) resulted in antibacterial and fungicidal properties in the fabricated coatings, which can be dedicated to biocompatible applications.
Highlights
In recent years, apart from the development of the plasma electrolytic oxidation (PEO) process, many other techniques allowing surface functioning for biomedical purposes have been elaborated.Fabrications of porous coatings on titanium or its alloys by means of the plasma electrolytic oxidation (PEO) method are mostly performed in aqueous electrolytes, with the addition of different salts that results in the formation mainly of titanium (IV) oxides enriched with elements from the electrolyte
The 3D roughness parameters were selected in consideration of what might be valid for porosity determination of the outer PEO coating, such as Sa and Sp, which were in the range 1.17–1.90 μm and 7.62–13.91 μm, respectively
It is possible to fabricate porous coatings enriched in copper with the use of an average voltage equaling 450 VRMS, under a PEO process, in electrolytes based on concentrated orthophosphoric acid with the addition of copper(II) nitrate(V) trihydrate
Summary
Apart from the development of the plasma electrolytic oxidation (PEO) process, many other techniques allowing surface functioning for biomedical purposes have been elaborated.Fabrications of porous coatings on titanium or its alloys by means of the plasma electrolytic oxidation (PEO) method are mostly performed in aqueous electrolytes, with the addition of different salts that results in the formation mainly of titanium (IV) oxides (anatase and/or rutile) enriched with elements from the electrolyte. Coatings enriched with copper, coming from copper compounds or nanoparticles located in the electrolyte, exhibit antibacterial properties. Such coatings may be obtained, among other methods, by a four-minute PEO process (16.5 A/dm , 800 Hz, 10%) in the electrolyte based on an aqueous solution containing Ca(CH3 COO)2 ·H2 O, C3 H7 Na2 O6 P·5H2 O, and Cu(CH3 COO). The resulting layers, containing TiO2 (anatase, rutile) and Cu2+ ions, were characterized by a porous structure of craters with diameters of 3 to 5 μm, and the presence of copper in the coating had no significant effect on the change of surface topography and the phase composition of coatings. Studies have shown that the coatings are characterized by antibacterial properties and are non-toxic for living organisms and, in addition, adhesion and osteoblastic growth occur here faster than on coatings that do not contain copper(II) ions [5]
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