Page 51 - Magnesium-based supports for stem cell therapy of vascular disease - Mónica Echeverry Rendón

NOVEL COATINGS FOR COMMERCIAL PURE MAGNESIUM OBTAINED BY PLASMA ELECTROLYTIC OXIDATION THROUGH THE ADDITION OF ORGANIC ADDITIVES
Finally for the MAN electrolyte treated under potentiostatic mode (Fig.2.right), all the curves showed a similar be- havior, only some difference was observed for MAN¬P2, where after the sudden reduction in the current density, a lot more oscillations were registered even until the end of the process. Additionally, sample MAN¬P1 reached a slightly lower final current density. According with these results it is expected that MAN¬P1 present the higher electrical resistance of the three samples despite of being the thinnest coating, according to the potentials employed in each case.
Fig.2 Anodization of c.p Mg under potentiostatic mode with NAF, HMT and MAN
In Fig. 3 pictures of surface and cross-section of samples treated with NAF at galvanostatic mode are shown. It was observed that in this case, thin coatings were obtained with an increment in thickness with the voltage. The surface images of the three samples revealed big defects located randomly and with size of 4.7±2.1μm; the density of them decreased with the increment of current applied. In addition to this defects, higher magnification images showed that sample NAF-G1 presented an almost compact structure whilst in samples NAF-G2 and NAF-G3 a typical porous formation for the PEO technique was observed. The surface of NAF-G1 showed a fine texture. The pore size for NAF- G2 and NAF-G3 ranges from 0.4 to 0.5 μm. The cross section images of samples NAF¬G1 and NAF¬G3 show that the coating is formed by individual layers superposed one on the other. This was not appreciated in NAF¬G2, however the defects observed on the surface suggested a similar structure. Barrier layer were in the order of 0.5μm for all the samples.
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Fig. 3 Top-view SEM image of the surface (1000X and 5000X) and cross-section of samples anodized with NAF solution under galvanostatic control.
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