Alexandre Ferreira Galio

Corrosion Behaviour and Biocompatibility of Titanium Screws Produced by Powder Injection Moulding (PIM) for Temporary Applications

Production of small and geometrically complex parts is a typical application of powder injection molding (PIM) process. The production of parts by PIM can produce a final texture with high roughness. The roughness is an important factor of the adhesion of the human cell on the implant. This intrinsic factor can facilitate high bone - implant fixation, but it reduces the corrosion resistance of implants. A design of a temporary screw probe adapted to peculiarities of this production process was proposed to use in implants as well as in electrochemical essays. This study aims at studying the effect of surface roughness on bone attachment of titanium implants and their corrosion resistance in a saline environment. Temporary implants were produced by PIM to characterize the influence of the temperature of sintering on the self-release process of the samples. The samples were classified into three groups according to sintering temperature (1250, 1270 and 1300oC). Screws were inserted in tibiae of New Zealand white rabbits (Oryctolagus cuniculus). After 4, 8 and 12 weeks the fixation in the bone was evaluated by histomorphometry (all threads along the implant and the three best consecutive threads were analyzed). An average surface recovery of 65 % after 12 weeks of implantation was obtained. Accelerated corrosion tests point to possible susceptibility to crevice corrosion of the sintered implants. Here, we compared some of the recent patents related to corrosion behavior and biocompatibility of titanium screws produced by PIM.

Active Coatings: Examples and Applications

Currently, electrochemical plating, conversion coatings, anodizing, deposition of thin films (organic, inorganic or hybrid), laser surface alloying, cladding and organic coatings are employed to improve surface properties such as hardness or corrosion resistance. For example, the development of new “smart” coating systems implies not only mechanical covering of the protected surface with a dense barrier coating but also provides active properties which can allow continued physical or chemical protection, even after partial mechanical damage of the coating, by self-healing effects. In other cases, the active properties imply biological effects, by releasing of chemicals from “drug delivery” systems, or photoelectric effects due to doping the surface with adequate elements. These “smart” properties can be achieved by inclusion of specific additives into the coating system and can stimulate the superficial reactions after some damage. The sol-gel coating process is one of the most promising methods to create protecting coatings producing sensitive inorganic surfaces in general. In this environmentally friendly process, inorganic or inorganic-organic hybrid polymers are obtained by controlled hydrolysis and condensation reactions of molecular precursors. This article compares examples of the recent patents of active coatings and some of their important industrial utilizations.

Evaluation of Corrosion Protection of Sol-Gel Coatings on AZ31B Magnesium Alloy

Magnesium is one of the lightest metals and magnesium alloys have good strength to weight ratio making them very attractive for many particular applications [1]. The main drawback of magnesium alloys is their high corrosion susceptibility. Improving the corrosion protection by deposition of thin hybrid films can expand the areas of applications of relatively cheap magnesium alloys. This work aims at investigation of new anticorrosion coating systems for magnesium alloy AZ31B using hybrid sol-gel films. The sol-gels were prepared by copolymerization of 3- glycidoxypropyltrimethoxysilane (GPTMS), titanium alcoxides and special additives which provide corrosion protection of magnesium alloy. Different compositions of sol-gel systems show enhanced long-term corrosion protection of magnesium alloy. The sol-gel coatings exhibit excellent adhesion to the substrate and protect against the corrosion attack. Corrosion behavior of AZ31B substrates pre-treated with sol–gel derived hybrid coatings was tested by Electrochemical Impedance Spectroscopy (EIS). The morphology and the structure of sol-gel films under study were characterized with SEM/EDS techniques.

Evaluation of Green Corrosion Inhibitors for Applying in Food Packaging

In this study, the inhibitor effect of Solidago chilensis extract as green corrosion inhibitor for anodized aluminum alloy samples was evaluated in NaCl 3%wt solution. This study was carried out for application on cans for pack of foods. The procedure of the surface treatment of the samples was done by anodizing followed by sealing in a solution containing the inhibitor. Essays of potentiostatic polarization and electrochemical impedance spectroscopy were done to evaluate the inhibitor effect. The mechanical analyses were performed on anodized samples to evaluate the influence of the thickness of anodization on the mechanical resistance of the samples. The potentiostatic essays indicated that a cathodic inhibitor effect occurs only in non-anodized samples and that the anodic effect of the inhibitor not appears on the anodized samples. The calculated efficiency of the inhibitor was 96 %. The EIS results indicated that the higher values of polarization resistance (16 kΩ) occur on anodized samples containing inhibitor after 72 hours of immersion in NaCl 3%wt. The mechanical essays indicated a non – significant difference between anodized and non – anodized samples.