Abstract
Coatings with developed surface stereometry, being based on a porous system, may be obtained by plasma electrolytic oxidation, PEO (micro arc oxidation, MAO). In this paper, we present novel porous coatings, which may be used, e.g., in micromachine’s biocompatible sensors’ housing, obtained in electrolytes containing magnesium nitrate hexahydrate Mg(NO3)2·6H2O and/or zinc nitrate hexahydrate Zn(NO3)2·6H2O in concentrated phosphoric acid H3PO4 (85% w/w). Complementary techniques are used for coatings’ surface characterization, such as scanning electron microscopy (SEM), for surface imaging as well as for chemical semi-quantitative analysis via energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES), and X-ray powder diffraction (XRD). The results have shown that increasing contents of salts (here, 250 g/L Mg(NO3)2·6H2O and 250 g/L Zn(NO3)2·6H2O) in electrolyte result in increasing of Mg/P and Zn/P ratios, as well as coating thickness. It was also found that by increasing the PEO voltage, the Zn/P and Mg/P ratios increase as well. In addition, the analysis of XPS spectra revealed the existence in 10 nm top of coating magnesium (Mg2+), zinc (Zn2+), titanium (Ti4+), and phosphorus compounds (PO43−, or HPO42−, or H2PO4−, or P2O74−).
Highlights
In the literature, the terms plasma electrolytic oxidation (PEO) or micro arc oxidation (MAO) refer to the electrochemical method of surface treatment of lightweight metals and their alloys, which leads to the spontaneous development of an oxide layer on their surfaces
These alloys usually consist of elements/metals, which may be found in the fourth and fifth B groups of the periodic table, i.e., titanium [1], zirconium [2,3], hafnium [4,5], niobium [6,7], tantalum [8,9], though the first works related to PEO (MAO) technique were carried out on aluminum, magnesium, and their alloys [10,11,12,13,14]
It should be noted that the use of the PEO (MAO) treatment creates coatings enriched with selected chemical elements in micro scale, while the nanolayers may be fabricated with the use of standard electropolishing [16], magnetoelectropolishing [17], or high current electropolishing [18]
Summary
The terms plasma electrolytic oxidation (PEO) or micro arc oxidation (MAO) refer to the electrochemical method of surface treatment of lightweight metals and their alloys, which leads to the spontaneous development of an oxide layer on their surfaces These alloys usually consist of elements/metals, which may be found in the fourth and fifth B groups of the periodic table, i.e., titanium [1], zirconium [2,3], hafnium [4,5], niobium [6,7], tantalum [8,9], though the first works related to PEO (MAO) technique were carried out on aluminum, magnesium, and their alloys [10,11,12,13,14]. Such results could lead to establishing a novel knowledge to be used in any micromachines’ applications
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