Formation of silver chloride nanocrystals as a corrosion product of silver in H2SO4 solution

The purpose of this study is to characterize the corrosion product on the surface of silver, employing H2SO4 (0.5M) as electrolyte. The electrochemical parameters, Ecor, Icor, V cor and Rp were obtained after analyzing the potentiodynamic polarization curve in which two peaks were observed. The smallest (passive region) is attributed to the Cl- traces from the reference electrode, with micro-cracks. The second peak (in the transpassivation region) corresponds to the polarization curve of silver in H2SO 4 without contaminants. SEM images and EDS analysis reveal images of a surface layer on silver, consisting of structures containing sulfur, oxygen, silver and chloride, as the corrosion product. On this layer silver sulfate crystals were observed, which occurs during the formation of silver chloride nanocrystals with different morphologies, when chloride ions were added to the electrolyte medium. ©The Electrochemical Society.

Hydrogen oxidation on ordered intermetallic phases of platinum and tin - A combined experimental and theoretical study

Hydrogen oxidation on the surfaces of the intermetallic compounds Pt 3Sn, PtSn and PtSn2 has been studied by the rotating disc electrode technique. Pt3Sn and PtSn were found to be good catalysts, about as good as Pt, while PtSn2 was inactive over the investigated range of potentials. Underpotential deposition of hydrogen is observed only on Pt3Sn. These results are explained by theoretical calculations based on a theory developed within our own group, and by density functional theory. © 2012 Elsevier B.V.

Low tungsten content of nanostructured material supported on carbon for the degradation of phenol

A comparative study using different mass proportions of WO3/C (1%, 5%, 10% and 15%) for H2O2 electrogeneration and subsequent phenol degradation was performed. To include the influence of the carbon substrate and the preparation methods, all synthesis parameters were evaluated. The WO3/C materials were prepared by a modified polymeric precursor method (PPM) and the sol-gel method (SGM) on Vulcan XC 72R and Printex L6 carbon supports, verifying the most efficient metal/carbon proportion. The materials were physically characterized by X-ray diffraction (XRD) and by X-ray photoelectron spectroscopy (XPS) techniques. The XRD and the XPS techniques identified just one phase containing WO3 and elevated oxygen concentration on carbon with the presence of WO3. The oxygen reduction reaction (ORR), studied by the rotating ring-disk electrode technique, showed that WO3/C material with the lowest tungsten content (1% WO3/C), supported on Vulcan XC 72R and prepared by SGM, was the most promising electrocatalyst for H2O2 electrogeneration. This material was then analyzed using a gas diffusion electrode (GDE) and 585mgL-1 of H2O2 was produced in acid media. This GDE was employed as a working electrode in an electrochemical cell to promote phenol degradation by an advanced oxidative process. The most efficient method applied was the photo-electro-Fenton; this method allowed for 65% degradation and 11% mineralization of phenol during a 2-h period. Following 12h of exhaustive electrolysis using the photo-electro-Fenton method, the total degradation of phenol was observed after 4h and the mineralization of phenol approached 75% after 12h. © 2013 Elsevier B.V.

Estudos não-isotérmicos da cinética de nucleação e cristalização de vidros 20Li2O80TeO2

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento e estudo de nanocatalisadores bimetálicos para catodos de células a combustível

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparação e teste de nanocatalisadores 'PTFENI'/'C' e 'PTFECO'/'C' para redução de oxigênio

Pós-graduação em Química - IQ

Desenvolvimento de metodologia para determinação de álcoois superiores em álcool combustível, utilizando a técnica de cromatografia líquida de alta eficiência com detecção eletroquímica

Pós-graduação em Química - IQ

Desenvolvimento de método para determinação de acetaldeído em álcool etílico hidratado combustível por cromatografia líquida de alta eficiência com detecção eletroquímica

Pós-graduação em Química - IQ

Concentração de flúor nas refeições e saúde bucal de crianças matriculadas em creches públicas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de métodos analíticos para a determinação da concentração de fosfito em fertilizantes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de métodos eletroanalíticos para determinação de compostos nitrogenados em combustíveis derivados do petróleo

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Estudo de composições vítreas no sistema ternário Ga-Ge-Te para o armazenamento de dados

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cell membrane integrity of candida albicans after different protocols of microwave irradiation

To evaluate the ability of low time microwaveexposureto inactivate and damage cell membrane integrity of C. albicans. Materials and Methods: Two 200ml C. albicans suspensions were obtained. Sterile dentures were placed in a beaker containing Experimental (ES) or Control suspensions (CS). ES was microwaved at 650 W for 1, 2, 3, 4 or 5 min. Suspensions were optically counted using Methylene blue dye as indicative of membrane-damaged cells; spread on Agar Sabouraud dextrose (ASD) for viability assay; or spectrophotometrically measured at 550nm. Cell-free solutions were submitted to content analyses of protein (Bradford and Pyrogallol red methods); Ca++ (Cresolphthalein Complexone method); DNA (spectrophotometer measurements at 260nm) and K+ (selective electrode technique). Data were analyzed by Student-t test and linear regression (α=0.05). In addition, flowcytometry analysis of Candida cells in suspensionwas performed using propidium iodide. Results: All ES cells demonstrated cell membrane damage at 3, 4 and 5 min,viable cells were nonexistent at 3, 4 and 5 min ES ASD plates and optical density of ES and CS was not significantly differentfor all exposition times. ES cells released highcontents of protein, K+ , Ca++ and DNA after 2 min exposition when compared to that of the CSs. Similar results were observed with flow cytometry analysiswith regard to the periodsof microwave exposure. Conclusions: Microwave irradiation inactivated C. albicansafter 3min and damaged cell membrane integrity after 2 min exposition.

Corrosion resistance of Ni-Cr alloys in different mouthwashes

Several alloys have been used for prosthodontics restorations in the last years. These alloys have a number of metals that include gold, palladium, silver, nickel, cobalt, chromium and titanium and they are used in oral cavity undergo several corrosion. Corrosion can lead to poor esthetics, compromise of physical properties, or increased biological irritation. The objective of this study was evaluated corrosion resistance of two alloys Ni-Cr and Ni-Cr-Ti in three types of mouthwashes with different active ingredients: 0.5g/l cetylpyridinium chloride + 0.05% sodium fluoride, 0.05% sodium fluoride + 0.03% triclosan (with fluor) and 0.12% chlorohexidine digluconate. The potentiodynamic curves were performed by means of an EG&G PAR 283 potentiostat/galvanostat. The counter electrode was a platinum wire and reference electrode was an Ag/AgCl, KCl saturated. Before each experiment, working electrodes were mechanically polished with 600 and 1200 grade papers, rinsed with distilled water and dried in air. All experiments were carried out at 37.0oC in conventional three-compartment double wall glass cell containing mouthwashes. The microstructures of two alloys were observed in optical microscopy. Analysis of curves showed that Ni-Cr alloy was less reactive in the presence of 0.12% chlorohexidine digluconate while Ni-Cr-Ti alloy was more sensitive for others two types of mouthwashes (0.5g/l cetylpyridinium chloride + 0.05% sodium fluoride  and 0.05% sodium fluoride + 0.03% triclosan). This occurred probably due presence of titanium in this alloy. Microstructural analysis reveals the presence of dendritic and eutectic microstructures for NiCr and Ni-Cr-Ti, respectively.

Photoelectrochemical properties of FTO/m-BiVO4 electrode in different electrolytes solutions under visible light irradiation

Photoelectrochemical properties of FTO/BiVO4 electrode were investigated in different electrolytic solutions, potassium chloride (KCl) and sodium sulphate (Na2SO4), and under visible light irradiation condition. In order to accomplish that, an FTO/BiVO4 electrode was built by combining the solution combustion synthesis technique with the dip-coating deposition process. The morphology and structure of the BiVO4 electrode were investigated through X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. Photoelectrochemical properties were analyzed through chronoamperometry measurements. Results have shown that the FTO/BiVO4 electrode presents higher electroactivity in the electrolyte Na2SO4, leading to better current stabilization, response time, and photoinduced current density, when compared to KCl electrolyte. Besides, this electrode shows excellent performance for methylene blue degradation under visible light irradiation condition. In Na2SO4, the electrode has shown higher degradation rate, 51 %, in contrast to 44 % in KCl, plus higher rate constant, 174 × 10-4 min-1 compared to 150 × 10-4 min-1 in KCl. Results presented in this communication leads to the indication of BiVO4 thin films as alternate materials to use in heterogeneous photoelectrocatalysis, more specifically in decontamination of surface water. © 2013 Springer-Verlag Berlin Heidelberg.