Lilian Vanessa Rossa Beltrami

Characterization of Siloxane-poly(methyl methacrylate) Hybrid Films Obtained on a Tinplate Substrate Modified by the Addition of Organic and Inorganic Acids

Tinplate is used to food packaging and other types of packages. The corrosion resistance of the tinplate has been study due the necessity of an alternative to high environmental impact of chromatization process. Therefore protective coatings as hybrid films base elaborations with different acids are studied to improve the barrier effect against corrosion. The objective of this work is characterize hybrid films deposited on a tinplate from a sol made up of the alkoxide precursors 3-(trimethoxysilylpropyl)methacrylate (TMSM), tetraethoxysilane (TEOS) and poly(methyl methacrylate) (PMMA) together with one of three acids (acetic, hydrochloric or nitric acid) and to verify their action against the corrosion of the substrate. The films were obtained by a dip-coating process and cured for 3 hours at 160 °C. The film hydrophobicity was determined by contact angle measurements, and the morphology was evaluated by SEM. FTIR measurements were performed to characterize the chemical structures of the films. The electrochemical behavior of the coatings was evaluated by techniques open circuit potential monitoring (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results demonstrate that the siloxane-PMMA films improve the protective properties of the tinplate, with the films obtained by acetic acid addition exhibiting the greatest improvement.

Effect of Tetraethoxy-silane (TEOS) Amounts on the Corrosion Prevention Properties of Siloxane-PMMA Hybrid Coatings on Galvanized Steel Substrates

Siloxane-poly(methyl methacrylate) (PMMA) organic-inorganic hybrid coatings were deposited on galvanized steel by the dip-coating sol-gel technique. Anticorrosion properties, as well as the morphological, surface and structural features were studied. Hybrid coatings were synthesized from tetraethoxy-silane (TEOS) and methyl methacrylate (MMA) as inorganic and organic phases, respectively, linked by 3-metacriloxypropyl-trimethoxysilane (TMSM) as a coupling agent. The MMA/TMSM ratio was kept constant, whereas the four TEOS/TMSM ratios were varied. The characterization of coatings was assessed using several techniques such as Scanning Electronic Microscopy (SEM), Contact Angle, Fourier Transform Infrared (FT-IR), Open Circuit Polarization (OCP), Atomic Force Microscopy (AFM) and Electrochemical Impedance Spectroscopy measurements (EIS). The EIS results, which were obtained for the hybrid coatings, were discussed based on an electrical equivalent circuit used to adjust the experimental data. The results showed that the increasing the TEOS content caused increase in coating thickness, increased in the surface roughness and increased in the surface hydrophobicity. The film with the highest TEOS content presented the best electrochemical performance, more effective in protecting against corrosion.

Effect of curing temperature and architectural (monolayer and bilayer) of hybrid films modified with polyethylene glycol for the corrosion protection on tinplate

Hybrid films obtained by a sol-gel process are based on two important reactions: hydrolysis and condensation. The condensation reaction is influenced by the curing temperature, since it induces the development of the intrinsic properties of the gel. The aim of this work is to coat tinplate, a substrate widely used in the packaging industry, with monolayered and bilayered hybrid films modified with polyethylene glycol and obtained through dip-coating. The results showed that the bilayered hybrid film obtained at 60oC had a higher layer thickness, and the best performance in the electrochemical assays, as well as the most hydrophobic character, in relation to the other samples. For the monolayered systems, the 90oC-cured system showed a lower layer thickness; however, this system showed a more compact, uniform and less porous layer, and presented better electrochemical impedance results, in comparison with the 60oC-cured samples.

New Sol-gel Formulations to Increase the Barrier Effect of a Protective Coating Against the Corrosion and Wear of Galvanized Steel

This study proposes a new pretreatment method that uses alkoxide precursors with a plasticizing agent; the purpose of this study is to improve the electrochemical and mechanical properties of a galvanized steel surface. Galvanized steel was covered with a hybrid film obtained from a sol that consisted of two alkoxide precursors, 3 - (trimethoxysilylpropyl) methacrylate (TMSM) and tetraethoxysilane (TEOS), with nitrate cerium in a concentration of 0.01 M and a polyethylene glycol (PEG) plasticizer. The hybrid coatings were obtained by dip-coating method with various concentrations of plasticizer (0, 20, 40 and 60 g.L-1). The hybrid films were analyzed by scanning electron microscopy (SEM), profilometry, contact angle measurements, a tribometer with the type-setting ball on the plate and electrochemical tests. The addition of the plasticizer into the hybrid films improves the corrosion resistance behavior compared to the sample without the plasticizer. The addition of 20 g.L-1 of plasticizer showed the best performance in the electrochemical tests. The mechanical behavior results indicated that higher PEG concentrations resulted in films with enhanced durability.

Effect of the Shot Peening Process on the Corrosion and Oxidation Resistance of AISI430 Stainless Steel

Ferritic stainless steels are used in specific applications where corrosion resistance, oxidation resistance and a high mechanical resistance are required. Shot peening is a process applied to add residual compression stresses in metallic surfaces with the intent of improving the material when exposed to corrosion due to stress and fatigue. Some studies about the effect of the shot peening process on the fatigue resistance, bending fatigue behavior, and residual surface stress in the ferritic stainless steels have been performed. However, the effect of the shot peening process on the corrosion and oxidation resistance of the stainless steel is not well known. In this context, the purpose of this study is to evaluate the effect of the shot peening process on these superficial properties of ferritic AISI430 stainless steel. The obtained results showed that the ferritic AISI430 stainless steel samples treated with shot peening presented a significant modification on the surface morphology and an important decrease of oxidation and corrosion resistance, evidencing that the shot peening process compromises the chemical and physical properties of the surface.

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.

Development and Characterization of PLA/Buriti Fibre Composites – Influence of Fibre and Coupling Agent Contents

The use of biodegradable polymers has aroused academic and technological interest directed to the replacement of conventional polymers aiming at reducing the environmental impact caused by these materials. Vegetable fibres as reinforcement elements provide gains in mechanical, thermal and degradation properties to polymer composites. The buriti fibre (Mauritia flexuosa) is an abundant crop of easy cultivation in tropical countries and its use in composites with poly(lactic acid) (PLA), can provide the development of a material with specific features, combining good mechanical properties and excellent degradation potential to the obtained composites. In this research, PLA and buriti fibre composites were developed with the use of triacetin as coupling agent. For a 30% content by mass of fibre, the results showed that the mechanical properties of the composites were similar to those of neat PLA. This was attributed to the fibre/matrix interaction observed by the SEM analysis and to an increase in crystallinity assessed by thermal properties.

Anticorrosive performance of commercial nanoceramic coatings on AISI 1010 steel

The aim of this work was to study the corrosion behavior of three commercial nanoceramic coatings in comparison to zinc phosphate coatings applied on mild steel (SAE 1010). The coatings were evaluated by scanning electron microscopy (SEM), profilometry and hydrophobicity. The electrochemical behavior was evaluated by dynamic polarization. The results showed that the samples coated with nanoceramics presented contact angles greater than 100o, achieving hydrophobic behavior. Evaluating the electrochemical behavior under dynamic polarization revealed that the nanoceramic coating containing chromium (CHT) exhibited a higher corrosion potential and lower current than the other nanoceramic coatings tested, although its performance in a dilute sodium chloride solution was below that of the zinc phosphate-based coating. Although the nanoceramic coatings exhibited poor electrochemical behavior compared to the zinc-based coatings, they had a higher corrosion resistance when associated with an organic coating.

OBTAINING NIOBIUM OXIDES IN ACETIC ACID WITH ADDITION OF HF

During anodizing, the chemical attack of hydrofluoric acid (HF) electrolytes on niobium can promote the formation of oxides with porous structures. However, this chemical attack can also cause an intense dissolution of the oxide during its formation. This effect can be minimized by varying the HF concentration of the anodizing electrolyte, thereby controlling the growth of the porous oxide. Studies have alternative electrolytes that do not use HF to obtain porous oxides. Thus, organic electrolytes, such as acetic acid, may be a viable alternative. In this context, the objective of this study is to obtain and evaluate the anodization of niobium in acetic acid at different current densities (10, 20 and 50 mA/cm2) and to study the influence of the addition of HF to the electrolyte. The results showed that the anodized anodic in acetic acid, under conditions of 100 V and 10 mA/cm2, presented porous oxide with less defects. Therefore, this result indicates that it is possible to produce porous niobium oxides by anodizing in HF-free electrolyte.

Development of Alkoxide Precursors-Based Hybrid Coatings on Ti-6Al-4V Alloy for Biomedical Applications: Influence of pH of Sol

The Ti-6Al-4V alloy, widely used in biomedical applications, is associated with cytotoxic effects due to the release of aluminum and vanadium ions in the human body. One of the most effective ways to control the release of cytotoxic ions is through anti-corrosive coatings. Among them, the alkoxysilanes stand out for their good barrier properties and the absence of toxicity. Aiming to improve the clinical success rate of metallic implants, this study sets out to evaluate the influence of the pH of the sol on the physico-chemical, morphological, mechanical and electrochemical characteristics of hybrid films based on 3-(trimethoxysilylpropyl)methacrylate (MAP) and tetraethoxysilane (TEOS) applied to Ti-6Al-4V. The film was prepared by using the sol–gel method for pH values of 3, 4, and 5. The results indicated that maintaining the pH of the sol at 4 favors the hydrolysis rate of alkoxide precursors, which results in a uniform, dense and adherent film with excellent anti-corrosion performance.