Page 53 - 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
more uniform distribution of the porous features with a size slightly augmented of 1.4 ±0.3μm. In sample HMT G3 big craters of around 7μm were observed surrounded of small pores of 2.1±0.5μm, indicating that larger discharges were produced in those points causing the melting of the material. Cross-section for all the coatings showed the presence of large pores through the layer connecting the inner layer with the outer part of the coating. On the surface of HMT-G3 some particulate material can be observed which can be related with the materials liberated from the coating when the sparks occurred.
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Fig. 5 Top-view SEM image of the surface (1000X and 5000X) and cross-section pictures of samples of c.p Mg treated with HMT at galvanostatic mode.
On the other side, the coatings obtained under potentiostaic mode in HMT (Fig. 6), showed more homogeneous po- rous surfaces in comparison with the described for galvanostatic mode. In HMT☆P1 an early stage of the production of the coating was observed, where pores presented diameters of around ~0.4μm±0.1. In HMT P2 the dimension of those pores increased, reaching around 1.4±0.2μm. Similar characteristic were found in the sample treated with HMT-P3, where the average porous size was of 1.8μm ± 0.2. The thickness of the coatings increased with the incre- ment in the voltage applied. The coating consisted of a porous outer layer and a thin compact inner barrier layer. The pores of the coating appear to be interconnected.
For the samples treated with MAN solution in galvanostatic mode, the most uniform and well distributed porous surface was MAN G1 (Fig. 7). In MAN-G2 and MAN-G3 some big defects were observed, indicating that big discharges took place which are not evident in the voltage-time curve. With respect of the thickness of the coating, the dimen- sions of these coatings were around twice in comparison with NAF-G and HMT-G. The internal morphology of the coatings showed interconnected porous in the outer layer and presence of a barrier inner layer. Size of the porous for MAN G1, MAN G2 and MAN G3 were of 2.1μm ± 0.4, 1.1μm ± 0.3 and 1.5 ± 0.3μm, respectively. Cross sections for these samples showed a non-homogeneous distribution of the pores among the outer layer, oppositely the inner layer was dense and compact. Large pores were observed in all the samples, the number and size of those increased with the increment of the current density applied. Passing through pores can be observed in the coatings, particu- larly for samples MAN-G2 and MAN-G3. Features observed at the substrate/coating interface are considered related with artifacts formed during preparation of the cross-section.
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