Sandra Raquel Kunst

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 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.

The effects of curing temperature on bilayer and monolayer hybrid films: mechanical and electrochemical properties

Thermal curing contributes to the formation and performance of hybrid films (HFs), because it enhances barrier properties by reticular densification, which originates from a less porous layer, and improves corrosion protection and mechanical properties. Increasing the number of deposited layers further enhances these properties. In this work, a HF formed by an alkoxide precursor solution of 3-(trimethoxysilylpropyl) methacrylate and tetraethoxysilane with cerium nitrate and polyethylene glycol was applied to the galvanized steel. The films were obtained by either monolayer or bilayer dip coating, and they were cured at different temperatures (60 and 90xa0°C) for 20xa0min. The results indicate that both the temperature and the number of layers interfere on the ability of HFs to act as effective barriers against corrosion. The bilayer system cured at 60xa0°C showed the best electrochemical impedance results; however, the monolayer HF cured at 90xa0°C presented higher wear resistance.

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.

Hybrid films with (trimethoxysilylpropyl) methacrylate (TMSM), poly (methyl methacrylate) PMMA and tetraethoxysilane (TEOS) applied on tinplate

The tetraethoxysilane (TEOS) influences morphological and electrochemical properties of hybrid films by function of concentration. Moreover, the use of acetic acid as a catalyst in the sol enables a more complete hydrolysis of the silane precursors due to the fact that the acetic acid goes through a more complete ionization when in aqueous solution. The aim of this paper is to study the effect of the concentration of tetraethoxysilane (TEOS) on the protective properties of the film on tinplate substrate. The tinplate was coated with a hybrid film obtained from a sol-gel method constituted of the following alkoxide precursors: 3 - (trimetoxisililpropil) methacrylate (TMSM) and poly(methyl methacrylate) PMMA. The effect of tetraethoxysilane (TEOS) concentration has also been evaluated. The films hydrolysis was performed at a pH value of 3.0 using acetic acid as a catalyst. The films were obtained by dip-coating process, cured for 3 hours at 160 °C. The film morphology was evaluated by SEM and profilometry. The electrochemical behavior of the films was evaluated by open circuit potential monitoring, potentiodynamic polarization and electrochemical impedance spectroscopy. The film hydrophobicity was determined by contact angle measurements. The studied films have shown good performance as to corrosion resistance on tinplate. The hybrid film which was obtained through the addition of an excessive amount of TEOS (T3A3) showed increased thickness. Nevertheless, due to an intense densification of the film, promoted by the addition of TEOS, a formation of cracks was registered, thereby compromising the corrosion resistance.

Niobium and niobium-iron coatings on API 5LX 70 steel applied with HVOF

The present study aimed to create and characterize niobium and niobium-iron 60% coatings applied to steel API 5L X70 using the hypersonic thermal spray process (HVOF). The morphologies of the coatings were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and profilometry, while the coatings hardnesses was evaluated using the Vickers hardness test. The coatings corrosion resistance was evaluated by monitoring their open circuit potential and potentiodynamic polarization and performing electrochemical impedance spectroscopy in a 0. 05 M NaCl solution. The results showed that the niobium-iron coating contained minor porosity regions, while such defects occurred over large regions of the niobium coating. In terms of corrosion resistance, the coatings obtained in this work promoted a reduction in the substrates corrosion rate, but the presence of discontinuities such as porosity compromised the barrier effects of these coatings.

Influence of anion chain length of protic ionic liquids on the corrosion resistance of API X70 steel

The objective of this paper is to evaluate the corrosion resistance of API X70 steel in three different protic ionic liquids (PILs). Protic ionic liquids cation was 2-hydroxiethylammonium, and their anion was a carboxylate where the carbon chain length was varied. The synthetised PILs were characterised by nuclear magnetic resonance. The corrosion resistance of API X70 steel was evaluated on the hand of the monitoring of the open circuit potential and electrochemical impedance spectroscopy. Results showed that PIL adsorption on the substrate surface occurs to form a film that enhances corrosion inhibition effects. However, the adsorbed film can break due to desorption that exposes the substrate surface and promotes corrosion of the substrate. In addition, it was observed that corrosion inhibition effects improve with the increase in the anion carbon chain length, since the longer is the anion the larger is the substrate coverage.

Elaboration and Characterization of Siloxane-PMMA Hybrid Films on Tinplate Substrates

The characteristics of siloxane-PMMA hybrid films permit the obtaining of coatings with thickness of few microns without cracking. Besides, the methacrylate groups (MMA) can be easily polymerizated by UV irradiation or thermal treatments. These hybrids can also be applied in anti-corrosive coatings for metals and alloys, replacing chromates which exhibit high toxicity. In this context, the aim of this work is to study the behavior of tinplate coated with a siloxane-PMMA hybrid film by dip-coating process and cured by thermal cure process. The systems were characterized by electrochemical, morphological and physicochemical analysis. Preliminary results showed that the systems studied presented a regular and adherent siloxane-PMMA hybrid film, which increased the corrosion resistance of tinplate substrates.

Obtención y Caracterización de Revestimientos Protectores a Base de Silanos para la Protección de Aceros Galvanizados

Resumen Se presenta un estudio del comportamiento de peliculas de silanos Gamma-Aminopropyl tirethoxysilano y del N-(Beta-Aminoethyl)-Gamma-Aminopropyl trimethoxysilano aplicados por el proceso de revestimiento por inmersion (dip-coating) sobre el acero galvanizado. Se usan los mecanismos de curado termico y curado por irradiacion ultravioleta. Los substratos y revestimientos a base de zinc reciben normalmente un tratamiento de superficie para mejorar la resistencia a la corrosion, pero usan cromo hexavalente que presenta un elevado grado de toxicidad. Las peliculas polimericas conteniendo silanos organofuncionales surgen como alternativa para la pasivacion de substratos a base de zinc. Los revestimientos de silano obtenidos fueron evaluados a partir de ensayos electroquimicos y angulos de mojabilidad y la morfologia fue caracterizada por microscopia electronica de barrido. Los resultados muestran que las peliculas elaboradas presentan una cobertura homogenea y que el tipo de silano empleado tiene influencia en la formulacion y en los parametros de curado.

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.