Ester Schmidt Rieder

Influence of the Addition of Montmorillonite in an Epoxy Powder Coating Applied on Carbon Steel

Polymer coatings have been used for the corrosion protection of metal surfaces acting as a physical barrier against several corroding media. In spite of the good efficiency of these coatings their resistance is limited due to the presence of localized defects which give place to localized corrosion. Aiming to improve the barrier properties of these coatings this work has proposed the use of nanocomposites as powder coatings based on a standard formulation of a commercial powder varnish. Nanocomposites with 2 and 4 wt% contents of organophilic montmorillonite (OMMT) were obtained in the molten state through of a co-rotating twin-screw extruder. The application of the nanocomposite coatings was performed by electrostatic pulverization on mild steel panels. The coatings were characterized to determine their structure using X-ray diffraction (XRD). The morphologies of the coatings were assessed using transmission electron microscopy (TEM). Gloss and adhesion measurements and the flexibility and impact resistance of the coatings were included in the physical assessment of the coatings. The corrosion performance was evaluated by the salt spray test and by electrochemical impedance spectroscopy (EIS). The coatings with clays presented predominantly exfoliated structures, with good dispersion of OMMT in the epoxy matrix. The addition of OMMT reduced the impact resistance, flexibility and gloss but increased the barrier properties of the coatings. The best corrosion performance in NaCl solution was achieved for 4 wt% OMMT.

Epoxy-Montmorillonite Nanocomposites Applied to Powder Coatings

Abstract The wide range of applications associated with nanocomposites is due to their improved properties when compared to conventional composites. In this study, commercial epoxy-based powder coatings were formulated with 2 and 4% (w/w) of an organically modified montmorillonite (OMMT) by incorporation in the melt state (extrusion). These composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction (XDR). The thermal behavior and stability of the epoxy nanocomposites were studied by TGA and DSC. The nanoparticle structure within the polymer matrix was analyzed by XRD and TEM. A predominantly exfoliated structure was observed by TEM, which was confirmed by XDR analysis. The study demonstrated that the nanoclay increases the glass transition and crosslinking temperatures and also enhances the thermal stability of the coating.

Caracterización de Revestimientos de Niobio formados por Aspersión Térmica a Plasma sobre Acero API 5l X65

The morphology and electrochemical behavior of niobium coating obtained by thermal plasma spray process on a substrate of steel API 5L X65 was evaluated. The coating was obtained, using electrical current of 500 A, 15 g/min of powder and 2.0 L/min of argon gas. The preparation of the substrate surface was performed with preheating and abrasive blasting with alumina. After thermal spraying, the morphology of the coating was analyzed by scanning electron microscopy (SEM), while the surface roughness was evaluated by profilometry, hardness by Vickers microhardness test and adhesion by bending at 180 o. The corrosion resistance of the coating was evaluated from the polarization test in 3.5% NaCl solution. The results show that the coating presented cracking and lack of padding between the plates sprayed, relative high hardness and deficient adhesion to the substrate. However, the values of current density carried by the system compared to uncoated steel were reduced.

Investigação dos principais processos de corrosão em estações de energia elétrica do Estado do RS

This study investigated the main corrosion agents in four electric energy station in the state of Rio Grande do Sul, three on the coast and one in Porto Alegre (capital of Rio Grande do Sul). The objective was to determine the corrosion rates of various metallic materials exposed to the aggressive agents present in the stations atmosphere. Loss mass experiments of the materials exposed in real time in the electric stations, soil potential monitoring, soil resistivity measurement, soil chemical analysis, and micrographic and chemical analysis of the materials after exposure in the study sites were performed. The loss mass experiments were performed using the International Organization of Standardization, ISO, 8407, 8565 e 9223 a 9227. The soil resistivity was determined using the Wenner method and the micrographs and chemical analysis of the corrosion products were obtained using scanning electron microscopy and energy dispersive spectroscopy, respectively. Results showed significant change in the mass of steel and cooper, mainly in the stations located on the coast. Although the corrosive agents are present in the soil, the high corrosion rates on the coast were strongly associated with the marine atmosphere. All station soils presented high resistivity, which implies low aggressiveness to metallic materials. With these conclusions, it is evident that the procedures and precautions related to corrosion of the metallic components exposed to conditions of extreme aggressiveness, such as those in the presence of chloride ions and solid particulates, cannot be the same as the ones used for the atmospheres free of these components.

Effects of Mould Temperature in Squeeze Casting of Zamak 5

Squeeze casting process of Zamac 5 for obtain faucets enables higher productivity associated with better dimensional characteristics. In this process, the die cooling system can influence the solidification of the alloy and its properties. This study evaluates the influence of die temperature on solidification under pressure from Zamac 5. Pieces were removed from the die at several temperatures. Samples were evaluated by neutral salt spray corrosion, optical microscopy and microhardness. The results show that the corrosion is related to the porosity defects, which was most intense in part regions which solidified lastly. These regions also showed different results of microhardness. However, the behavior of the samples was similar in the range of die temperatures studied.

Influence of the pH and Stirring Speed of the Electrodeposition Bath in the Performance of Zinc and Zinc-Nanocomposite Coatings

With the increase of environmental restrictions, chromium and cadmium-based coatings have been replaced by zinc layers. These coatings can be obtained through electrodeposition, whose industrially established pH range is from 5.0 to 5.8, and stirring speed is uncontrolled, which has led to part rejections. In addition, the corrosion resistance of zinc coatings is inferior to cadmium and chromium coatings, which has boosted the research of zinc composite coatings. The proposed work presents the performance of zinc-bentonite composite coatings in regards to corrosion relating to pH variation and stirring speed. The samples were degreased for 5 minutes in a commercial degreasing solution at a temperature of 55 °C, with magnetic stirring and, posteriorly, submitted to a pickling process with a duration of 1 to 2 minutes in a commercial bath, followed by a washing process with deionized water. The electrolyte used for electrodeposition was a zinc bath with a chemical composition of 85 g/l ZnCl2, 210 g/l KCl and 25 g/l H3BO3. For the zinc-bentonite electrodepositions 20 g/l of bentonite nanoparticles was added to the bath. Zinc and zinc-bentonite coatings were characterized by scanning electron microscopy, open circuit potential and potentiodynamic polarization. This work shows that a 5.2 pH is the most recommended for the zinc electrodeposition process. Potentiodynamic polarization tests indicated that pure zinc coatings developed in the stirring speed of 380 rpm and zinc-bentonite produced in the stirring speed of 710 rpm showed the best results.

Catalyst based on Pt, Sn and Ni: Effect of carbon functionalization on ethanol electro-oxidation

Composite nanocatalysts, based on platinum, tin and nickel on carbon, using mono, binary and ternary systems, for the electro-oxidation of ethanol in direct ethanol fuel cells were synthesized in this work. The effect of carbon pre-treatment in HNO3 solution on the electro-oxidation of ethanol was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that the nanoparticles containing only platinum and the ones containing platinum and tin supported on functionalized carbon presented higher electrocatalytic activities for ethanol oxidation, compared to the ones supported on the non-functionalized carbon. The presence of tin and nickel in the platinum system (binary and ternary systems) promoted the catalytic activity in both ends, the oxidation of ethanol and the oxidation of intermediate carbon species.