Examinando por Autor "López, Antonio Julio"

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Influence of roughness and grinding direction on the thickness and adhesion of sol-gel coatings deposited by dip-coating on AZ31 magnesium substrates. A Landau–Levich equation revision
(Elsevier, 2021-01-02) Fernández-Hernán, Juan Pablo; López, Antonio Julio; Torres, Belén; Rams, Joaquín
AZ31 magnesium alloys with four different roughness values and two different grinding directions were coated with sol-gel silica coatings to assess the influence of the initial surface conditions of the substrates on the final coating thickness. Sol-gels were prepared from two silicon alkoxide precursors and deposited on the surface of the magnesium substrates by the dip-coating method. Roughness tester and scanning electron microscopy (SEM) were used to assess the thickness of the silica coatings and the presence of defects in the coatings. Shear stress tests were developed to study the adhesion of the coatings. An analysis of variance was carried out to determine the implication of the substrate roughness and the direction of the grinding lines in the final sol-gel coating thickness and its adhesion on the substrate. The results show that the roughness has a significant influence both on the thickness and on the adhesion of the coatings. Thus, thicker coatings were obtained on substrates with higher roughness values, going from 2.18 μm to 1.42 μm for substrate roughness values of 1.47 μm and 0.27 μm respectively, in the case of horizontal grinding lines, and from 2.01 μm to 1.37 μm for substrate roughness values of 1.47 μm and 0.27 μm respectively, in the case of vertical grinding lines. However, the grinding direction has no significant influence on the thickness nor the adhesion, but it has a clear influence on the formation of defects in the coatings. Finally, the inclusion of the r parameter in the Landau-Levich equation is proposed to adjust it, taking into account the roughness of the substrates intended to be coated and the evaporation of solvent and water from the coating during the dip-coating.
Silicon oxide multilayer coatings doped with carbon nanotubes and graphene nanoplatelets for corrosion protection of AZ31B magnesium alloy
(Elsevier, 2020-06-20) Fernández-Hernán, Juan Pablo; López, Antonio Julio; Torres, Belén; Rams, Joaquín
Magnesium (Mg) AZ31B alloy substrates were coated by the dip-coating method to obtain four different coating configurations. Three different sol-gels were synthesized to create different monolayer and multilayer coating configurations from two silicon alkoxides, tetraethyl orthosilicate (TEOS) and methyl-triethoxysilane (MTES). Two of these sol-gel solutions were doped with nanocharges. The final concentration of nanocharges in the coatings was 0.045 wt% and 0.046 wt% for multiwall carbon nanotubes (MWCNTs) and functionalized graphene nanoplatelets (COOH-GNPs), respectively. The anti-corrosion behaviour of these coatings was assessed by electrochemical and hydrogen evolution tests in 3.5 wt% NaCl solution. All of the coating configurations significantly improved the behaviour against corrosion compared with the bare substrate, especially the SG + SG/GNP (sol-gel + sol-gel doped with 0.046 wt% COOH-GNPs) multilayer coating system. The sol-gel synthesis combined with the dip-coating method was demonstrated to be an effective way to generate compact and homogeneous coatings for corrosion protection.
Sol-gel coatings doped with graphene nanoplatelets for improving the degradation rate and the cytocompatibility of AZ31 alloy for biomedical applications
(Elsevier, 2021-09-23) Fernández-Hernán, Juan Pablo; Torres, Belén; López, Antonio Julio; Rams, Joaquín; Martínez-Campos, Enrique
SiO2 coatings doped with four different functionalized graphene nanoplatelets (COOH-GNPs) concentrations (from 0.005 to 1 wt%) were deposited on AZ31 magnesium substrates to control the corrosion rate and to increase the cytocompatibility of this alloy for MC3T3 pre-osteoblastic cells, to develop biodegradable implants for bone fracture and orthopedic applications. The results show that the highest nanoplatelets concentration promoted the generation of nanoparticle aggregates acting as crack-nucleation points embedded in the coating, decreasing the protective behavior of these coatings. Nanoplatelets concentrations of 0.005 wt% and 0.05 wt% led to obtaining crack-free coatings that provided an improved barrier effect. Cytocompatibility tests show that all the conditions, even the bare AZ31, led to cell proliferation. However, low cell adhesion was found in the bare substrate, contrary to the coated substrates. The coatings with the highest nanoplates concentrations augmented the metabolic activity of cell cultures. The sol-gel coating doped with 0.05 wt% COOH-GNPs presented the best corrosion rate control behavior and improved cytocompatibility, with the generation of a confluent preosteoblastic monolayer on its surface after one week of cell culture.
The Role of the Sol-Gel Synthesis Process in the Biomedical Field and Its use to Enhance the Performance of Bioabsorbable Magnesium Implants
(MDPI, 2022-07-07) Fernández-Hernán, Juan Pablo; Torres, Belén; López, Antonio Julio; Rams, Joaquín
In the present day, the increment in life expectancy has led to the necessity of developing new biomaterials for the restoration or substitution of damaged organs that have lost their functionalities. Among all the research about biomaterials, this review paper aimed to expose the main possibilities that the sol-gel synthesis method can provide for the fabrication of materials with interest in the biomedical field, more specifically, when this synthesis method is used to improve the biological properties of different magnesium alloys used as biomaterials. The sol-gel method has been widely studied and used to generate ceramic materials for a wide range of purposes during the last fifty years. Focused on biomedical research, the sol-gel synthesis method allows the generation of different kinds of biomaterials with diverse morphologies and a high potential for the biocompatibility improvement of a wide range of materials commonly used in the biomedical field such as metallic implants, as well as for the generation of drug delivery systems or interesting biomaterials for new tissue engineering therapies.