Matias de Angelis Korb

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.

Formation of Spinel from Fe-Ni Coating Electrodeposited on AISI 430 Ferritic Stainless Steel

Ferritic stainless steels exhibit properties, such as good electrical conductivity, good corrosion resistance and low cost, that are beneficial for their application as interconnects in intermediate temperature solid oxide fuel cells (ITSOFC) that function at temperatures between 600°C and 800°C. However, the stainless steel corrosion resistance is attributed to the amount of Cr, which is an element that forms a chromium oxide (Cr2O3) layer, acts as an oxidation protective barrier at high temperatures, and reduces the interconnector performance due to its low electrical conductivity. In this context, the objective of this work was to obtain spinel coatings from the Fe and Ni metallic alloy thermal conversion on AISI stainless steel 430 substrate produced by electrodeposition. The morphology and microstructure of the spinel films deposited on stainless steel were characterized by SEM, EDS, XRD and adherence analysis. The results obtained showed that the films were adherent, dense and continuous along the AISI stainless steel 430 substrate surface. In addition, the heat treatment procedure effectively produced crystalline spinels ((NiFe)3O4).

Elaboração e caracterização de compósitos magnéticos

In the induction heating treatment process, the material is heated by a magnetic field generated by a high frequency alternating current that passes through an inductor. To improve the efficiency of the process, a flux concentrator, which is constituted by soft magnetic materials, is used. This flux concentrator consists of ferromagnetic components and a dielectric binder. In some industrial processes, the dimensional adjustment of this tool can cause loss of raw material and produce waste. The aim of this work was the elaboration and characterization of a magnetic composite of polymeric matrix from the waste generated by the dimensional adjustment. To prepare the magnetic composite, the waste was comminuted and mixed with two different types of phenolic resin at a concentration of 3%wt. The magnetic composites obtained were characterized according to morphology, mechanical, magnetic and electrical properties and environmental characterization. The results showed that the composites presented a reduction of magnetic and mechanical properties compared to the original material. However, reduction of magnetic losses was observed for the composite obtained, highlighting the potential of this composite for use as a magnetic flux concentrator.

Heat Treatment as an Alternative to Brass Warping

This paper proposes the reduction of warping after the machining of alloys of brass with lead. For this purpose the brass alloys were submitted to heat treatment and analyzed before and after the machining process. Elongation and dimensional variation, microstructure and chemical microanalysis of the samples were assessed. It was found that warping may be related to the chemical composition of the alloy, added to the rolling process used to obtain the material to be machined. The results showed that heat treatment before the machining process eliminates the warping seen in the workpieces.

La, Sr and Co Based Coatings Obtained on Ferritic Stainless Steel by Dip-Coating Technique

The ferritic stainless steels have been used in applications where suitable properties are required at high temperatures. These metallic materials are applied, for example, as interconnects in ITSOFC fuel cells (600-800 °C).The aim of this work is to produce a La, Sr and Co based coatings using the dip-coating and spray pyrolysis techniques, on an AISI 430 ferritic stainless steel. These coatings are known for acting as barriers, increasing the oxidation resistance when applied on stainless steel at high temperatures. The obtained coatings were heat treated at 800 °C for 120 min, seeking the formation of La0,6Sr0,4Co,and, then characterized regarding their morphology and microstructure using scanning electron microscopy (SEM) and X-ray diffraction. The results showed that the coatings obtained by spray pyrolysis covered regularly the surface while the ones obtained by dip-coating exhibited some crack formation.

Phases Obtained from Heat Treatment of Mn-Co-Based Coatings Deposited by Dip Coating

Studies have been performed to improve the oxidation resistance of ferritic stainless steels at high temperatures because these materials have been proposed for the manufacture of interconnectors for solid oxide fuel cell (SOFCs) and solid oxide electrolysis cells (SOECs) operating at intermediate temperatures (IT-SOFCs). Among the coatings employed, ceramic spinel-type oxides have been the most frequently applied. In this context, Mn-Co-based coatings were deposited on ferritic stainless steel (AISI 430) in this study using a dip-coating technique. The obtained coatings were characterized with respect to their morphology by SEM, their elementary composition by EDS and their structure by XRD. It was possible to produce continuous and adherent Mn-Co-based coatings on the surface of the metallic substrates.

Influência do processo de cura das películas híbridas no desempenho de revestimentos obtidos por pintura epoxídica

Pre-treatment with hybrid films obtained by the sol-gel from specific alkoxide precursors has been an environmentally friendly alternative, proposed for the corrosion protection of metallic substrates, including galvanized steel. In hybrid films, inorganic compounds contribute to the increase of corrosion resistance and adhesion to the metallic substrate, while organic compounds increase the density, flexibility and functional compatibility with organic systems, such as painting. The addition of corrosion inhibitors or other compounds, to the hybrid films can modify the properties of the barrier layer, improving corrosion resistance. In this study, galvanized steel was pre-treated with a hybrid film obtained from a sol consisting of alkoxide precursors: 3 - (trimetoxisililpropil) methacrylate (TMSPMA) and tetraethoxysilane (TEOS) with the cerium nitrate addition (0.01M). The hybrid films were submitted to different curing processes: air-drying, thermal curing and ultraviolet curing. The obtained systems were characterized according to adhesion, morphology and electrochemical behavior. Besides, the degree of hydrophobicity of the systems was measured by contact angle measurements. For the accelerated corrosion tests in salt spray, the galvanized steel, pre-treated with a hybrid film, was coated with epoxidic painting. The results showed that the system using galvanized steel/hybtrid film/paint, with hybrid films cured by air -drying and ultraviolet radiation, presented the best results for corrosion resistance.

Nanostructured YSZ Thin Film for Application as Electrolyte in an Electrode Supported SOFC

The development of solid oxide fuel cell with thin film concepts for an electrode supported design based on the yttria-stabilized zirconia has demonstrated favourable results due to its high chemistry stability in oxidization and environment reduction. The spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on different substrates. The precursor solution was obtained by zirconium and yttrium salt dissolutions in a mixture of water and glycerine in several ratios to study the solvent influence. The substrate was initially heated at 600 °C and during the deposition it ranged from 260-350°C, finishing at a fast increase in temperature of 600°C. The heat treatment was carried out in four different temperatures: 700 °C, 750 °C, 800 °C, and 900 °. The precursors were characterized by thermal analysis. The microstructures of the films were studied using scanning electron microscopy and X-ray diffraction. The results obtained showed that the films obtained were crystalline before the heat treatment process and have shown ionic conductivity above 800°C.

Ceramic Coating Based on La, Sr and Co on Ferritic Stainless Steel for ITSOFC Interconnects

Ferritic stainless steels have been used to produce interconnects for intermediate temperature solid oxide fuel cells (ITSOFC) due to their appropriate properties. Ferritic stainless steel presents mechanical stability, much higher thermal and electronic conductivities; significantly lower cost, and mechanical resistance than austenitic steels. Besides, it presents a thermal expansion coefficient compatible with the other materials of the cell components. However, in the range of this device operating temperature (600 °C 800 °C) it can occur the formation of poorly conducting oxide (Cr2O3) reducing the fuel cell performance. The aim of this work was to obtain oxide coatings starting with La, Sr and Co nitrates applied by spray-pyrolysis technique on a stainless steel AISI 430 substrate. The coatings obtained were characterized by X-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy. The oxidation resistance of the ferritic stainless steel, coated with a perovskite (La0,6Sr0,4CoO3) film, was investigated by isothermal oxidation. The results showed that the coating obtained promoted the increase of the ferritic stainless steel oxidation resistance. However, after the oxidation test, it was observed a Cr enrichment and a very pronounced Sr enrichment, near to the alloy/coating interface, which can be associate to the decomposition of La0,6Sr0,4CoO3 film.