oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 66 )

2019 ( 371 )

2018 ( 406 )

2017 ( 401 )

Custom range...

Search Results: 1 - 10 of 291217 matches for " C. I. Elsner "
All listed articles are free for downloading (OA Articles)
Page 1 /291217
Display every page Item
Synthetic and natural Iron oxide characterization through microparticle voltammetry
Rico, Y;Bidegain, J. C.;Elsner, C. I.;
Geofísica internacional , 2009,
Abstract: we are hereby presenting the results obtained from a study on using microparticle voltammetry (mpv) for identifying iron oxides and oxy-hydroxides. this technique allowed us to distinguish different mineral species, such as hematite, goethite, magnetite and maghemite, in both synthetic and natural samples. by measuring synthetic pigments at different temperatures, evidence was found of an electrochemical behavioral pattern which allowed differenciating them. the current peak location (potential value) proved to vary according to the mineral species, grain size and chrystallinity degree. the area varies in terms of electroactive concentration of the species given. width varies according to particle size distribution. in high iron oxide and oxy-hydroxide concentration samples, peaks were defined at current values of ma (milliampers) and in paleosol samples having an overall iron content lower than 6%, peaks were recorded at currents of μa (microampers). therefore, a possibility arises of applying this technique to environmental and palaeo-environmental studies of these minerals. mpvs main advantages compared to conventional methods are speed and simplicity as well as the fact that it allows processing a few sample grains, in spite of its chrystallinity degree. unlike magnetic methods - strongly influenced by the presence of magnetite- mpv is highly sensitive for detecting weakly magnetic species.
Synthetic and natural Iron oxide characterization through microparticle voltammetry
Y. Rico,J. C. Bidegain,C. I. Elsner
Geofísica internacional , 2009,
Abstract: We are hereby presenting the results obtained from a study on using Microparticle Voltammetry (MPV) for identifying Iron oxides and oxy-hydroxides. This technique allowed us to distinguish different mineral species, such as hematite, goethite, magnetite and maghemite, in both synthetic and natural samples. By measuring synthetic pigments at different temperatures, evidence was found of an electrochemical behavioral pattern which allowed differenciating them. The current peak location (potential value) proved to vary according to the mineral species, grain size and chrystallinity degree. The area varies in terms of electroactive concentration of the species given. Width varies according to particle size distribution. In high iron oxide and oxy-hydroxide concentration samples, peaks were defined at current values of mA (milliampers) and in paleosol samples having an overall iron content lower than 6%, peaks were recorded at currents of μA (microampers). Therefore, a possibility arises of applying this technique to environmental and palaeo-environmental studies of these minerals. MPV s main advantages compared to conventional methods are speed and simplicity as well as the fact that it allows processing a few sample grains, in spite of its chrystallinity degree. Unlike magnetic methods - strongly influenced by the presence of magnetite- MPV is highly sensitive for detecting weakly magnetic species.
La voltamperometría de micropartículas en la diferenciación de óxidos y oxihidróxidos de hierro Voltammetry of microparticles in the differentiation of iron oxides and oxihydroxides
Y. Rico,C.I. Elsner,J.C. Bidegain
Revista de la Asociación Geológica Argentina , 2007,
Abstract: Con el propósito de implementar el uso de la técnica de voltamperometría de micropartículas en la caracterización de óxidos y oxihidróxidos de hierro de origen natural, en una primera etapa, se realizaron numerosas experiencias con muestras sintéticas de magnetita (Fe3O4), hematita (aFe2O3) y goethita (aFeO.OH), según la metodología propuesta por Grygar (1995). Luego se efectuaron ensayos sobre muestras de minerales naturales y sedimentitas con alto contenido en óxidos y oxihidróxidos de hierro. Los análisis se realizaron sobre la muestra original y luego de tratarla a distintas temperaturas, esto último, a los fines de estimar la potencialidad del método en la detección de cambios de fase. Técnicas complementarias, tales como microscopía óptica, difractometría de rayos x y susceptibilidad magnética a bajas temperaturas, fueron utilizadas para evaluar la confiabilidad del método. En la presente contribución, se confirma que la técnica de voltamperometría de micropartículas es altamente sensible a la detección de especies débilmente magnéticas, como la hematita y la goethita (antiferromagnéticas) y en menor medida a las fuertemente magnéticas, como la magnetita (ferrimagnética). En virtud de esto, se considera que esta técnica es apropiada para estudios ambientales y puede ser relacionada con otras técnicas de magnetismo ambiental. In order to develop capacities which would make pos sible the voltammetry of microparticles to be applied in the characterization of natural iron oxides and oxihydroxides, a serie of measurements were performed on synthetic magnetite (Fe3O4), hematite (aFe2O3) and goethita (aFeO.OH). To test the capability of the methodology known natural iron minerals and sedimentary rocks containing unknown iron minerals have also been included in the present contribution. The electrochemical analyses were carried out at RT and after heating in order to estimate the potential of the method for detection of phase changes. The reliability of the method was checked by applying complementary technologies as optic microscopy, Rx diffractometry and magnetic susceptibility at low temperature. The results obtained indicate that the method and technical recourses applied are suitable ones for making a differentiation of iron oxides and oxihydroxides. The sensibility of the voltammetry of microparticles is higher for differentiation of less magnetic compounds such as hematite and goethite than for ferrimagnetic minerals such as magnetite. This technique is an appropriated method for environmental studies and can be related with other techniques applie
Atmospheric Corrosion of Painted Galvanized and 55%Al-Zn Steel Sheets: Results of 12 Years of Exposure
C. I. Elsner,P. R. Seré,A. R. Di Sarli
International Journal of Corrosion , 2012, DOI: 10.1155/2012/419640
Abstract: Zinc or 55%Al-Zn alloy-coated steel sheets, either bare or covered by different painting systems, have been exposed for 12 years to the action of the urban atmosphere at the CIDEPINT station located in La Plata (34° 50′ South, 57° 53′, West), province of Buenos Aires, Argentina. The samples exposed surface was evaluated through periodical visual inspections, standardized adhesion tests, and electrochemical impedance measurements. The ambient variables monitored were average annual rains and temperatures, time of wetness, sulphur and chloride concentration, relative humidity, and speed and direction of the winds. It was found that in this atmosphere, the corrosion resistance of the bare 55% Al-Zn/steel sheets was higher than of the galvanized steel, and the polyurethane painting system was more protective than the alkyd and epoxy ones, which degraded after 6-7 years of exposure. 1. Introduction Exposed to specific aggressive media, metal or alloy stability depends upon the protective properties of the surface film formed, because its chemical composition, conductivity, adherence, solubility, hygroscopicity, and morphological characteristics determine the film capacity to work as a controlling barrier [1]. In such a sense, steel galvanic protection by means of zinc or zinc alloys is a common example, owing not only to the fact that the zinc, being electrochemically more active than the steel, corrodes preferentially, but also to the barrier effect of the corrosion products precipitated on the metallic surface. In particular, the coatings based on zinc are widely used to protect steel structures against atmospheric corrosion [2], because of the protective properties afforded by an insoluble film of basic carbonate. However, if the exposure conditions are such that there is changes of the ambient variables like atmospheric conditions, UV radiation intensity, type and level of pollutants, wet-dry cycles, depletion of air but high humidity, or a medium containing strongly aggressive species like chloride or sulphate ions, the zinc could dissolve forming soluble, less dense, and scarcely protective corrosion products, which sometimes lead to localized corrosion [2–5]. This condition can be reached during the storage and transportation of galvanized steel sheets or when they are exposed to marine and/or industrial environments [6]. Aluminium coatings have overcome these two factors. Nevertheless, as they cannot provide cathodic protection to exposed steel in most environments, early rusting occurs at coating defects and cut edges; besides, these coatings are
Behavior of Electrogalvanized Steel Pre-Treated with Cr(III)-Based Baths and Exposed to 0.5 M Na2SO4 Solution
C.R. Tomachuk,C.I. Elsner,A.R. Di Sarli
Portugaliae Electrochimica Acta , 2012,
Abstract: As Cr (VI) compounds used to formulate conversion layers provide enhanced anticorrosive protection to zinc coatings, but they are produced using hazardous chemicals, the development of ''green'' technologies is a paramount purpose. Consequently, the corrosion behavior of zinc coatings subjected to a Cr3+ based passivating treatment, with and without sealing, was studied through EIS measurements in 0.5 M Na2SO4 solution. The analyses of the experimental data allowed inferring that the Cr3+-based conversion treatment with an adequate sealer provides good corrosion resistance and, coupled to an adequate painting system, could be a suitable alternative to traditional chromate coatings.
Corrosion Performance of Conversion Treatments for Electrogalvanised Steel Sheet  [PDF]
A. R. Di Sarli, C. I. Elsner, L. E. M. Palomino, C. R. Tomachuk
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2019, DOI: 10.4236/jmmce.2019.75022
Abstract: Chromate conversion treatments have been widely used due to their excellent corrosion resistance properties; however, their use is increasingly restricted because of the highly toxic chromic acid solutions required, with consequent effluent disposal and ecological problems. The removal of these toxic chemicals is considered a priority within most of the developed countries. In this work, the corrosion resistance of different alternative pretreatments applied on electrogalvanised steel sheet: 1) Cr(III) and Zr complexes layer, 2) Ce(III) layer, 3) Ce(III)/Ce(IV) double layer, 4) Cr(VI) chromating was investigated, and its results compared with those from the tests performed using bare electrogalvanized steel sheets as a substrate. These samples were exposed to aerated 0.05 mol/L NaCl or 0.1 mol/L Na2SO4 solutions. The electrochemical behavior of samples was studied by electrochemical techniques. For three days of immersion in the solution test, the experimental results have shown that, compared with the Cr(VI) protective properties, the Cr(III) + Zr complex layer presented similar performance. Even though the initial corrosion resistance was offered by the Ce(III) and Ce(VI)/Ce(III) conversion coatings was relatively good, it quickly decreased as a function of the exposure time.
Factores que afectan a la estructura de los recubrimientos de cinc obtenidos por inmersión
Seré, P. R.,Culcasi, J. D.,Elsner, C. I.,Di Sarli, A. R.
Revista de Metalurgia , 1997,
Abstract: Coating solidification during hot-dip galvanizing is a very complex process due to Al-Fe, Al-Fe-Zn and Fe-Zn intermetallic compounds development. Fe-Zn intermetallic are brittle and detrimental for the coating ductility, while the diffusion towards the surface of a segregated insoluble alloying such as antimonium causes the sheet darkness. Steel sheets of different roughness were hot-dip galvanized under different operation conditions using a laboratory scale simulator. The effect of steel roughness and process parameters upon coating characteristics were analyzed. Experimental results showed that the steel roughness affects the coating thickness, zinc grain size and texture as well as the out-bursts development, while the process parameters affects the Fe2Al5 morphology and antimonium segregation. En el proceso de galvanizado por inmersión, la solidificación del recubrimiento constituye una etapa compleja en la que, además de formarse compuestos intermetálicos de Al-Fe, Al-Fe-Zn y Fe-Zn, tiene lugar la segregación de elementos aleantes insolubles como el antimonio. Ambos fenómenos son, al menos parcialmente, indeseables ya que la fragilidad de los intermetálicos de Fe-Zn afecta a la ductilidad del recubrimiento y la difusión del antimonio hacia la superficie causa su ennegrecimiento. Con un simulador dise ado a escala de laboratorio se galvanizaron chapas de diferente rugosidad sujetas a condiciones operativas también diferentes, analizándose el efecto de la rugosidad del acero y de los parámetros del proceso sobre las características del recubrimiento. Los resultados obtenidos demostraron que la rugosidad afecta tanto al espesor del recubrimiento, tama o de grano y textura del cinc como a la formación de out-bursts, mientras que los parámetros del proceso lo hacen sobre la morfología del intermetálico Fe2Al5 y la segregación de antimonio.
MicroRNA-146a Regulates Human Foetal Femur Derived Skeletal Stem Cell Differentiation by Down-Regulating SMAD2 and SMAD3
Kelvin S. C. Cheung, Nunzia Sposito, Patrick S. Stumpf, David I. Wilson, Tilman Sanchez-Elsner, Richard O. C. Oreffo
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0098063
Abstract: MicroRNAs (miRs) play a pivotal role in a variety of biological processes including stem cell differentiation and function. Human foetal femur derived skeletal stem cells (SSCs) display enhanced proliferation and multipotential capacity indicating excellent potential as candidates for tissue engineering applications. This study has examined the expression and role of miRs in human foetal femur derived SSC differentiation along chondrogenic and osteogenic lineages. Cells isolated from the epiphyseal region of the foetal femur expressed higher levels of genes associated with chondrogenesis while cells from the foetal femur diaphyseal region expressed higher levels of genes associated with osteogenic differentiation. In addition to the difference in osteogenic and chondrogenic gene expression, epiphyseal and diaphyseal cells displayed distinct miRs expression profiles. miR-146a was found to be expressed by human foetal femur diaphyseal cells at a significantly enhanced level compared to epiphyseal populations and was predicted to target various components of the TGF-β pathway. Examination of miR-146a function in foetal femur cells confirmed regulation of protein translation of SMAD2 and SMAD3, important TGF-β and activin ligands signal transducers following transient overexpression in epiphyseal cells. The down-regulation of SMAD2 and SMAD3 following overexpression of miR-146a resulted in an up-regulation of the osteogenesis related gene RUNX2 and down-regulation of the chondrogenesis related gene SOX9. The current findings indicate miR-146a plays an important role in skeletogenesis through attenuation of SMAD2 and SMAD3 function and provide further insight into the role of miRs in human skeletal stem cell differentiation modulation with implications therein for bone reparation.
Evaluation of the protective performance of several duplex systems exposed to industrial atmosphere
Sacco,E.A.; Culcasi,J.D.; Elsner,C.I.; Di Sarli,A.R.;
Latin American applied research , 2002,
Abstract: the atmospheric corrosion behaviour of galvanised steel sheets and steel/55%al-zn system with or without different paint schemes was analysed. the samples were exposed to the atmosphere in the experimental station of cidepint. periodically, all specimens were visually inspected and sampling was made to evaluate the general behaviour of the protective system. normalised physicochemical and eis tests were performed on each specimen. the corrosion products were characterised by sem. the data included in the present work concern to the first step of exposure (800 days). the foreseen whole period of testing is 7 years. from the present results may be concluded that: 1) on the analysed industrial environment, the bare sheets of steel/55%al-zn system have suffered less damage than the bare galvanised ones, 2) chloride and sulphide are present in the corrosion products denoting the aggressiveness of environment, and 3) in general, all duplex systems have shown a fairly good protective behaviour.
Evaluation of the protective performance of several duplex systems exposed to industrial atmosphere
E.A. Sacco,J.D. Culcasi,C.I. Elsner,A.R. Di Sarli
Latin American applied research , 2002,
Abstract: The atmospheric corrosion behaviour of galvanised steel sheets and steel/55%Al-Zn system with or without different paint schemes was analysed. The samples were exposed to the atmosphere in the experimental station of CIDEPINT. Periodically, all specimens were visually inspected and sampling was made to evaluate the general behaviour of the protective system. Normalised physicochemical and EIS tests were performed on each specimen. The corrosion products were characterised by SEM. The data included in the present work concern to the first step of exposure (800 days). The foreseen whole period of testing is 7 years. From the present results may be concluded that: 1) on the analysed industrial environment, the bare sheets of steel/55%Al-Zn system have suffered less damage than the bare galvanised ones, 2) chloride and sulphide are present in the corrosion products denoting the aggressiveness of environment, and 3) in general, all duplex systems have shown a fairly good protective behaviour.
Page 1 /291217
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.