Leonardo Marasca Antonini

The Electrochemical Behavior of the NiTi Alloy; in Different Simulated Body Fluids

In order to improve the NiTi alloy biocompatibility, surface treatments become very important. Nevertheless, researchers use different solutions to simulate the body fluids in electrochemical assays, and the correlation between the obtained results is difficult and might not even be possible. The present paper evaluated the electrochemical behavior of polished NiTi surfaces exposed to different simulated body fluid solutions: Hanks solution, Hanks’ balanced salt (HBSS) solution, saline body fluid (SBF) solution, and Ringer solution. The electrochemical behavior of NiTi was evaluated by open circuit potential (OCP) and cyclic voltammetry tests. The surfaces of the samples were also characterized by scanning electron microscopy, which was performed after the electrochemical tests. The results demonstrated that the NiTi alloy shows the same corrosion mechanism (pitting) in all simulated body fluids that were studied. However, the corrosion potential changes for each electrolyte, being HBSS, SBF and Ringer the most corrosive solutions. Furthermore, the Hanks and HBSS solutions demonstrated good reproducibility of the electochemical results. Considering that the HBSS represents an extreme environment, this solution seems to be the most indicated to study the corrosion behavior of NiTi treated surfaces.

Oxide Formation on NiTi Surface: Influence of the Heat Treatment Time to Achieve the Shape Memory

Several studies regarding superficial treatments of Nitinol (NiTi) shape-memory have been developed aiming to the improve corrosion resistance and to block the Ni release to adjacent tissues. The necessary heat treatment to achieve the shape memory effect normally occurs at temperatures between 500 and 600 °C. However, titanium oxide (TiO2) is formed on the NiTi surface during the shape memory process heat treatment. In this work the effects of the heat treatment time on the surface characteristics of the formed NiTi oxide, at temperatures that promote the shape-memory (530 and 570 °C), were evaluated. The TiO2 layers which were obtained were evaluated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscope (SEM), thermogravimetric analysis (TGA), wettability and roughness. The results show that by increasing the exposure time at the temperature of 570 °C the formation of a thicker oxide is promoted, with less superficial roughness and of a hydrophobic nature. According to the literature, these characteristics indicate that the obtained oxide layer has properties that accelerat the osseointegration process.

Effect of Application of the Shot Peening Process in the Corrosion Resistance of the AISI 430 Ferritic Stainless Steel

Stainless steels are materials used in specific applications where a good corrosion resistance property combined with high material mechanical resistance are required. The shot peening process has been used in order to improve the mechanical properties of metallic surfaces. Besides, it might has influence on the material electrochemical behavior, depending of the used parameters in the operational process. The purpose of this study is to evaluate the effect of the shot peening process in the corrosion resistance of AISI 430 ferritic stainless steel. Wettability test, atomic force microscopy (AFM), open circuit potential (OCP) and potentiodynamic polarization curves have been used in order to evaluate the behavior of AISI 430 ferritic stainless steel after the shot peening process. The aim of this study was to demonstrate the influence of shot peening on the surface properties of ferritic stainless steel AISI 430 and correlate them with the reactivity of the surface. The results showed that the shot peening process, contributes to avoid the localized corrosion resistance of the AISI 430 ferritic stainless steel.

Nanostructured Titanium Surface Obtained by Electrochemical Treatment

Research on titanium and its alloys as biomaterials have been attracted the interest because of its clinical success, but they have been facing problems due to failures caused by tissue cohesion loss, fracture. Studies involving the influence of surface roughness of titanium implants on the osseointegration rate and biomechanical fixation have been develop. However, it is neessary to understand the effect of surface morphology on the osseointegration process. This paper aims to examine the effect of current density on the electropolishing process of Ti in order to obtain nanostructured surfaces. Ti samples were mechanically abraded and then subjected to electropolishing in acidic solution. After the electropolishing process, the samples were characterized by atomic force microscopy, profilometry and wettability tests. Preliminary results show that the increase on current density contributed to the decrease in nanoroughness of substrate yet it did not affect the surface wettability, which presented an hydrophilic behaviour.

The Influence of the Operating Parameters of Titanium Electropolishing to Obtain Nanostructured Titanium Surfaces

Titanium and Ti alloys have been widely used as biomaterial due to their mechanical properties and high in vitro and in vivo cytocompatibility. Studies have showed that the acceleration of the osseointegration process is associated to the modification of the surface morphology. The aim of this work is to study the influence of the operating parameters of titanium electropolishing to obtain nanostructured titanium surfaces. The titanium electropolishing was carried out with different temperatures (7°C, 18°C and 25°C), current density of 0.19 A/cm2 and electropolishing time of 8 minutes. After the electropolishing process the titanium samples were characterized by Atomic Force Microscopy, profilometry (mechanical profilometer) and contact angle measurements. Preliminary results showed that the Ti nanostructured surfaces formation, strongly depends on the control of operating parameters.

GALVANIZED STEEL PRE-TREATED WITH HYBRID FILM CURED BY UV: INFLUENCE OF PHOTOINITIATOR CONCENTRATION ON THE CORROSION RESISTANCE

Several coatings have been proposed as an alternative to replacement processes based on hexavalent chromium. Among them stand out the hybrid films. Some hybrids films, with modified composition by the addition of photoinitiators, can be cured by ultraviolet system (UV). The UV cure is the instantaneous conversion of a reactive liquid in a solid induced by radiation, starting from the polymerization and cross-linking reactions of the chemical species. In order that reaction takes place through the action of UV radiation, it is necessary to add, in the composition of the hybrid film, a substance sensitive to this radiation called photoinitiator. The aim of this work is the preparation and characterization of hybrid films, cured by UV, from TEOS and TMSPMA alkoxide precursors, with addition of photoinitiators with different concentrations (1 and 2%) and without photoinitiator on galvanized steel. The films were characterized concerning the morphology, physicochemical properties and electrochemical behavior. The presence and the increase of photoinitiator concentration on hybrid films improved corrosion resistance of the system.

Superficies Nanoestructuradas de la Aleación Ti6Al4V: Influencia del Tiempo de Electropulido

The aim of the present research was to study the influence of operational parameters in the electropolishing process of titanium alloys, involving nanostructured surfaces. The electropolishing operational parameters influence the formation of nanostructured materials, promoting the obtainment of specific properties. In this work, a variation time was studied to produce nanostructured surfaces by the electropolishing process. The surfaces obtained were evaluated by atomic force microscopy and surface hydrophobicity was determined by the measurement of the contact angle. Preliminary results showed that the control on the size and depth of nanostructures on these surfaces is possible by electropolishing time variation.