Microeletrodo com cavidade: técnica eletroquímica utilizada para estudo da estabilidade de produtos de corrosão de metais

O presente trabalho tem como objetivo apresentar os aspectos básicos da construção de um microeletrodo com cavidade e demonstrar, através da revisão de literatura e de um exemplo prático, a possibilidade de uso do mesmo no campo da arqueometria para o estudo da estabilidade de produtos de alteração em artefatos metálicos pertencentes ao patrimônio histórico cultural.This work aims to present the basic features of the construction of a cavity microelectrode (CME) and to demonstrate, through a literature survey and also presenting a practical example, the possibility of using CME in the field of archaeometry, to investigate the stability of alteration products in metallic artefacts

In-vitro evaluation of the anti-cariogenic effect of a hybrid coating associated with encapsulated sodium fluoride and stannous chloride in nanoclays on enamel

Objective: The aim of this study is to test, in vitro, the anti-cariogenic effect of experimental hybrid coatings, with nano clays of halloysite or bentonite, loaded with sodium fluoride or with a combination of sodium fluoride and stannous chloride, respectively. Methodology: The varnish Fluor Protector (1,000 ppm of F-) was used as positive control and no treatment was the negative control. Enamel specimens (5 mm × 5 mm) were obtained from bovine teeth. The specimens (n=10) had their surfaces divided into two halves (5 mm × 2.5 mm each), in which one half received one of the treatments (Hybrid; Hybrid + NaF; Hybrid + NaF + SnCl2; Hybrid + NaF Loaded; Hybrid + NaF + SnCl2 Loaded). The specimens were submitted to a cariogenic challenge using a biofilm model (S. mutans UA159, for 5 days). Enamel surfaces both under and adjacent to the treated area were analyzed for mineral loss and lesion depth, by transverse microradiography. The pH of the medium was measured twice a day, and the fluoride release was analyzed. Additional specimens were submitted to confocal analysis. Results: Data were statistically analyzed by two-way ANOVA followed by Tukey test (α=0.05). None of hybrid groups were able to reduce the lesion depth; the Hybrid + NaF group, however, was able to reduce mineral loss differing from the negative control (p=0.008). The groups showed no significant difference in the pH measurement and fluoride release. Confocal analysis confirmed that for all groups the biofilm growth was similar. Conclusion: None of the hybrid groups reduced lesion depth, but the Hybrid + NaF group was able to promote protection against mineral loss

Anti-erosion potential of fluoride solutions associated with aminomethacrylate copolymer: in situ randomized crossover study

The anti-erosion potential of fluoride solutions associated with aminomethacrylate (AMC) was evaluated in the presence of acquired pellicle on enamel and dentin. It is concluded that AMC was able to increase the anti-erosion potential of fluoride solutions in the presence of acquired pellicle

The effect of powdered juice on human dental enamel dissolution

Aim: The aim of this in vitro study was to evaluate the dissolution potential of an artificial powdered juice in human dental enamel. Methods: Three commercially available beverages were tested by first evaluating the pH and the titratable acidity. After this, 40 enamel specimens were individually immersed in the respective solutions for 120 min (n = 8) as follows: C+: distilled water (positive control); TAN: artificial powdered orange juice; DEL: natural orange juice, CC: Coca-Cola and C-: citric acid solution 1% (negative control). At the end, each solution was analyzed for the amount of calcium (Ca) released and the data obtained were analyzed using ANOVA followed by Tukey test (p <0.05). Results: All solutions had low pH values. The C- group had the highest titratable acidity, followed by DEL, TAN and CC. TAN (0,92)a resulted in a lower release of Ca, being statistically similar to C+ group (0,46)a, while CC (6,32)c resulted in the higher release of calcium, followed by C- (4,17)bc and DEL (3,13)b groups. Relevance: The artificial powdered juice tested, although acid and high titratable acidity caused no enamel dissolution

Study of the wettability and the corrosion protection of the hybrid silane (3-aminopropyl) triethoxysilane (APTES) and (3-glycidyloxypropyl) trimethoxysilane (GPTMS) film on galvannealed steel

In this work, the wettability of the galvannealed surface pretreated with the hybrid silane APTES/GPTMS film was measured by sessile drop method. The coatings were applied on the substrate from dip-coating method and dried in an oven. The study followed an experimental factorial design, 3³, with contact angle as response. The corrosion resistance was evaluated by electrochemical techniques and the surface morphology was characterized by scanning electron microscopy. The wettability results showed the best condition for galvannealed steel pretreated with the hybrid silane film for 2:1 APTES:GPTMS ratio, 2% silane concentration and 150 min of hydrolysis time, because the result may be related to a higher rate of hydrolysis of the silanes that is influenced by both the functional group present and by the type and number of hydrolyzed groups, resulting consequently in a higher availability of silanol groups in solution, promoting a greater crosslinking of the film on the metallic substrate. Keywords: hybrid silane, corrosion, galvannealed  steel, pretreatment, wettability

Local electrochemical investigation of copper patina

The patination of copper is known for its complexity and heterogeneous formation. For a deeper investigation, a locally resolved surface analysis was considered. An exact determination of the accessed area and a potentiostatic control in a three-electrode configuration was reached with the use of the electrochemical microcell technique, which enables local electrochemical measurement such as local electrochemical impedance spectroscopy and cyclic voltammetry. Such a technique provides a unique way for performing the investigation of heterogeneities on electrode surfaces. The local electrochemical measurements on the artificially patinated surface have allowed distinguishing areas of different reactivity even when the analysis of the surface revealed a homogenous chemical composition of patina. Local measurements with the electrochemical microcell showed the presence of small defects on the patina layer that can be modelled by considering a hemispherical diffusion process at small active areas surrounded by larger less reactive domains.CAPESSpanish Education Ministr

Avaliação da resistência à corrosão do filme de silanoviniltrimetoxisilano modificado com íons Ce (III) e Ce (IV) como pré-tratamento do aço carbono

Silanos são compostos organo funcionais utilizados como agentes de acoplamentos entre interfaces orgânicoinorgânicas,com boas propriedades de adesão. Por esta razão, o uso de silanos como pré-tratamento paraaços, vem ganhando espaço já que também são geradores de resíduos de menor toxidade ao meio ambiente eà saúde humana. Para melhorar a barreira de proteção do filme de silano e conferir propriedades deautorreparação, esses filmes podem ser modificados com íons cério. Assim, esse trabalho tem como objetivoavaliar a resistência à corrosão do filme de silanoviniltrimetoxisilano (VTMOS) modificado com íons Ce(III)ou íons Ce(IV) aplicado em aço carbono, utilizando a espectroscopia de impedância eletroquímica (EIE),técnica de varredura por eletrodo vibratório (Scanning Vibrating Electrode Technique - SVET), microscopiaeletrônica de varredura (MEV) e transformada de Fourier de espectroscopia na região do infravermelho(Fourier Transform Infrared Spectroscopy - FTIR). Os resultados mostraram que os filmes com adição deíons Ce(IV) apresentaram uma melhor resistência à corrosão se comparados aos filmes com íons Ce(III), istoporque o filme formado com a adição de íons Ce(IV) mostrou um melhor efeito barreira devido à uma maiorreticulação do filme.Palavras-chave: Silanos, corrosão, EIE, SVET, íons cério

Dodecylamine-loaded halloysite nanocontainers for active anticorrosion coatings

Currently the most promising approach in the corrosion protection by smart coatings is the use of nanoreservoirs loaded with corrosion inhibitors. Nanocontainers are filled with anti-corrosive agents and embedded into a primer coating. Future prospective containers are halloysite nanotubes due to their low price, availability, durability, with high mechanical strength and biocompatibility. The aim of this work is to study the use of halloysite nanotubes as nanocontainers for encapsulated dodecylamine for active corrosion protection of carbon steel. Halloysite clay was characterized by XRD and TGA- thermogravimetric analysis techniques. Halloysite nanotubes were loaded with dodecylamine and embedded into an alkyd primer with a weight ratio of 10 wt.% . The anticorrosive performance of the alkyd primer doped with 10 wt.% of entrapped-dodecylamine halloysite was tested on coated carbon steel by direct exposure of the coated samples with a provoked defect into 0.01 mol/L NaCl corrosive media using electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). EIS and SVET measurements showed the self-healing properties of the doped alkyd coating. Coated samples were also evaluated in a salt spray chamber and the self-healing effect was unequivocally noticed

Coulometric reduction of copper corrosion products obtained in acetic acid and hydrogen sufide environments

RESUMEN: En ambientes contaminados, es normal encontrar cantidades elevadas de compuestos gaseosos tanto orgánicos como inorgánicos. Los compuestos orgánicos de ácidos volátiles (principalmente acético y fórmico) contribuyen significativamente a la agresividad del ambiente. Por su parte, el ácido sulfhídrico es otro poderoso contaminante capaz de producir productos de corrosión en el cobre tanto en ambientes secos como húmedos. El presente estudio muestra los resultados de la caracterización de los productos de corrosión al exponer muestras de cobre en una corriente de aire con diversos contenidos de ácido acético (HAc) y ácido sulfhídrico (H2S) a 80% de humedad relativa y 30 ºC, empleando la técnica de la reducción coulométrica. Particularmente se encontró que los productos de corrosión son cuprita (Cu2O) y tenorita (CuO) en los ambientes no contaminados o contaminados con HAc (hasta 400 ppbv). El espesor de estos compuestos crece con un aumento en el contenido de HAc. En el caso de la mezcla con HAc (200 ppbv) y H2S (400 ppbv) se detectaron, aparte de la cuprita y la tenorita, dos nuevos compuestos: Cu2S y uno denominado X (no identificado). De todas las condiciones evaluadas en el presente estudio, esta combinación resultó ser la más agresiva

Comparative investigation of the adhesion of Ce conversion layers and silane layers to a AA 2024-T3 substrate through mechanical and electrochemical tests

Cerium conversion layers and silane films are among the potential substitutes for the carcinogenic chromate conversion layers used to protect high-strength Al alloys. In the present work the adhesion of a cerium conversion layer and of a silane film to an aluminium alloy (AA) 2024-T3 substrate was investigated using mechanical and electrochemical tests. Scanning electron microscopy (SEM)- X ray energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and X ray photoelectron spectroscopy (XPS) were used to characterize the layers prior and after the mechanical test consisting of ultrasonic rinse in deionized water during 30 minutes. Mechanically tested and untested layers were also submitted to electrochemical impedance spectroscopy (EIS) and anodic polarization measurements in 0.1 M NaCl solution. The results of the characterization tests have pointed to a stronger adhesion of the Ce layer to the substrate in comparison with the silane film, which was confirmed by the electrochemical tests. The adhesion between the silane film and the Ce conversion layer was also tested, to evaluate the possibility of using the system as a protective bi-layer in accordance with the new trends being developed to substitute chromate conversion layers