Study of overall and local electrochemical responses of oxide films grown on CoCr alloy under biological environments

The interaction of the physiological medium and living tissues with the implant surfaces in biological environments is regulated by biopotentials that induce changes in the chemical composition, structure and thickness of the oxide film. In this work, oxide films grown on CoCr alloys at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl have been characterized through overall and localized electrochemical techniques in a phosphate buffer solution and 0.3% hyaluronic acid. Nanopores of 10–50 nm diameter are homogeneously distributed along the surface in the oxide film formed at 0.7 V vs Ag/AgCl. The distribution of the Constant Phase Element studied by local electrochemical impedance spectroscopy showed a three-dimensional (3D) model on the oxide films grown at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl. This behaviour is especially noticeable in oxide films grown at 0.7 V vs Ag/AgCl, probably due to surface inhomogeneities, and resistive properties generated by the potentiostatic growth of the oxide film.This work was supported by the Spanish National government [MINECO-MAT2011-29152-C02-01].Peer reviewe

Chemical conversion treatments to protect biodegradable magnesium in applications as temporary implants for bone repair

7 páginas, 7 figuras, 1 tabla.[ES] El presente estudio se desarrolló para mejorar la resistencia a la corrosión del magnesio puro, modificando su superficie mediante recubrimientos de conversión química. Se generaron capas de carbonato y fluoruro por inmersión en soluciones de NaHCO3 al 9 % y de HF al 48 %, respectivamente. La resistencia a la corrosión de las muestras con recubrimiento se evaluó en comparación con la del sustrato desnudo mediante técnicas electroquímicas en una solución fisiológica (PBS). Los resultados obtenidos han mostrado que el recubrimiento de carbonato no es capaz de proteger de la degradación al sustrato de magnesio. Por el contrario, el recubrimiento de fluoruro ha demostrado aumentar, significativamente, la resistencia a la corrosión del magnesio en medio fisiológico. La alta compacidad y adherencia al sustrato metálico de la capa de MgF2 generada mediante este sencillo tratamiento de conversión química confieren al recubrimiento buenas propiedades protectoras.[EN] The present study was developed to improve the corrosion resistance of pure magnesium by applying chemical conversion coatings. Carbonate and fluoride layers were generated by immersion in solutions of NaHCO3 of concentration 9 wt.%and HF of concentration 48 wt.%, respectively. Corrosion resistance of the coated samples was evaluated in comparison with that of the uncoated substrate by electrochemical techniques in a physiological solution (PBS). Results have shown that the carbonate coating is not viable to be used for protecting magnesium against corrosion.On the contrary, the fluoridemagnesiumcoating significantly increases the corrosion resistance ofmagnesium in physiological medium. The high compactness and adherence to the base metal of theMgF2 layer produced by this simple chemical conversion treatment confer the protective properties to the coating.Los autores agradecen al MEC la financiación del proyecto con referencia MAT 2008-06719-C03-01. M. Carboneras agradece al CSIC la concesión de un contrato JAE-Doc.Peer reviewe

Corrosión in vitro e in vivo de las prótesis mixtas acero inoxidable-cerámica

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Sección de Químicas. Fecha de lectura: 1-05-198

Corrosion behaviour of FeAl-type intermetallic compounds

In this study, the corrosion behaviour of two different iron aluminides based on FeAl, with two different microstructures, in a chloride-containing solution (pH = 7.4), has been investigated using electrochemical techniques. Both materials were studied in as-received condition and also after heat-treatment at 1100°C for two hours. This thermal process was performed to generate an alumina layer on the intermetallic surface with the purpose of improving its corrosion resistance. The polarization resistance method and the electrochemical impedance spectroscopy reveal similar corrosion resistance values for all samples although the corrosion attack produced is different. This result indicates that for these intermetallic alloys the alumina layer generated after two hours heat treatment is a low protecting layer due to the presence of additional oxides. Visual and optical microscopic observation of the sample surfaces reveal the formation of surface corrosion attack after the fourth day of immersion in the electrolyte for almost all samples. For samples without initial pits the anodic polarization curves showed a low pitting corrosion resistance. © 1997 Elsevier Science Ltd.This work has been supported by the project MAT95-0249-C03-01 of the Spanish Comisión Interministerial de Ciencia y Technologı́a (CICYT) and the CEASI programme on Fe aluminides.Peer Reviewe

Corrosion of reinforcing steel in mortar of cement with CaF2 as a minor component

This paper reports on the corrosion behaviour of steel embedded in mortar of cement manufactured using CaF2 as a mineraliser and flux agent. Corrosion rates of steel in this new cement measured with electrochemical techniques are compared with the corrosion rates of steel in contact with a traditional cement of similar characteristics in the same conditions. It was confirmed that the new cement does not lead to pitting corrosion and corrosion rates of steel are similar to traditional cement even in presence of corrosive agents such as chlorides or carbonation of cement. © 1995 Elsevier Science Ltd All rights reserved.Peer Reviewe

The effect of fluoride on corrosion of reinforcing steel in alkaline solutions

The influence of fluoride content of alkaline solutions on the corrosion of reinforcements has been studied, by means of electrochemical techniques, in saturated solutions of Ca(OH)2 and same pH NaOH solutions with additions of NaF, thus simulating the liquid phase of concrete. Fluoride can be present as a minor component in low-energy cements. The joint presence of chlorides and fluorides in the corrosion process of steel has also been analysed. It has been established that fluoride anions are able to produce pitting of reinforced steel in alkaline media of high pH. In Ca(OH)2 saturated solution, the precipitation of CaF2 lowers F- concentration below the minimum that promotes a pitting corrosion process; if there is not enough Ca(OH)2 to precipitate all F- ions, the presence of fluoride in these media causes an increase in passive film dissolution and corrosion rates. © 1994.Peer Reviewe

Synthesis and Electrochemical Characterisation of Magnetite Coatings on Ti6Al4V-ELI

© 2020 by the authors.Titanium alloys have been widely employed in implant materials owing to their biocompatibility. The primary limitation of these materials is their poor performance in applications involving surfaces in mutual contact and under load or relative motion because of their low wear resistance. The aim of this work is to synthesis magnetite coatings on the Ti6Al4V-ELI alloy surface to increase corrosion resistance and to evaluate its electrochemical behaviour. The coatings were obtained using potentiostatic pulse-assisted coprecipitation (PP-CP) on a Ti6Al4V-ELI substrate. The preliminary X-Ray Diffraction (XRD) results indicate the presence of the magnetite coating with 8–10 nm crystal sizes, determined for the (311) plane. Using X-ray photoelectron spectroscopy (XPS), the presence of the magnetite phase on the titanium alloy was observed. Magnetite coating was homogeneous over the full surface and increased the roughness with respect to the substrate. For the corrosion potential behaviour, the Ti6Al4V-ELI showed a modified Ecorr that was less active from the presence of the magnetite coating, and the impedance values were higher than the reference samples without coating. From the polarization curves, the current density of the sample with magnetite was smaller than of bare titanium.This research was funded by Instituto Politécnico Nacional, Consejo Nacional de Ciencia y Tecnología (CONACyT), Proyecto SIP 20195816, and Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC) Madrid, España supported this project.Peer reviewe

Laser surface treatment and corrosion behaviour of martensitic stainless AISI 420 steel

The effect of laser surface treatment of AISI 420 steel was studied. The operation conditions of the laser treatment were optimized with regard to beam power and displacement rate in order to produce different surface microstructures. The corrosion behaviour was studied as a function of the microstructures developed in the material. Maximum hardness was observed in the non-melted and carbide-free zone which was transformed into martensite. The best corrosion behaviour was observed in completely melted areas; this behaviour is similar to that observed in the starting material which is quenched and homogeneously tempered. Heterogeneous zones exist after laser heat treatment which have to be considered for final applications. © 1992.Peer Reviewe

3D, chemical and electrochemical characterization of blasted TI6Al4V surfaces: Its influence on the corrosion behaviour

The blasting process to increase the roughness of the surface of metallic biomaterials is widely used. As a consequence, one can produce a renewed surface with different topography and chemical composition compared to the original one, which can alter the general corrosion behaviour of the samples. With this idea, the aim of this work is not only the topographical and compositional characterization of blasted surfaces of Ti6Al4V alloy but mainly its influence on the corrosion behaviour of these modified surfaces. The surfaces of Ti6Al4V alloys were blasted with SiO2/ZrO2 and Al2O3 particles of different size in order to obtain different roughnesses. To carry out the microstructural and topographical characterization of the blasted surfaces, the scanning electron microscopy (SEM) coupled with an energy dispersive X-ray (EDX), the contact profilometry method and the 3D characterization by means of stereo-Fe-SEM have been used. By means of stereo-Fe-SEM, the roughness and the real surface area of the rough surfaces have been calculated. The microstructural, topographical and compositional results have been correlated with the corrosion behaviour of the samples immersed in Hank's solution and studied by means of electrochemical impedance spectroscopy (EIS). The blasting process alters topographical and chemically the surface of the samples. These modifications induce to an increase in the capacitance values of the roughened samples due to the prevalence of the effect of electrochemically active areas of Ti6Al4V surface over the effect of the presence of Al2O3 and ZrO2 particles on the blasted surfaces. However, the general corrosion behaviour of the samples is not drastically changed. © 2007 Elsevier Ltd. All rights reserved.Peer Reviewe

In vitro corrosion behaviour of MA 956 superalloy

The need for appropriated metallic materials for long-term implants is nowadays the driving force for the development of alternative materials with improved corrosion resistance in body fluids. In this work the in vitro corrosion behaviour of MA 956 is evaluated by means of electrochemical techniques during long-term tests in simulated human body media. This alloy, after an isothermal treatment at 1100°C, develops on the surface a fine, dense and adherent α-alumina scale which considerably enhances the good corrosion resistance of the non-treated alloy. | The need for appropriated metallic materials for long-term implants is nowadays the driving force for the development of alternative materials with improved corrosion resistance in body fluids. In this work the in vitro corrosion behaviour of MA 956 is evaluated by means of electrochemical techniques during long-term tests in simulated human body media. This alloy, after an isothermal treatment at 1100°C, develops on the surface a fine, dense and adherent α-alumina scale which considerably enhances the good corrosion resistance of the non-treated alloy.Peer Reviewe