K.E. García

K.E. García
University of Antioquia | UdeA · Instituto de Química

PhD chemistry

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37
Publications
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402
Citations
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January 2005 - December 2015
University of Antioquia
Position
  • Professor (Associate)

Publications

Publications (37)
Article
Mössbauer spectroscopy has long been used to calculate the degree of inversion (λ) in ferrites. To perform this calculation in NiFe2O4, it is assumed that the recoilless f-factors ratio of the Fe³⁺ cations at octahedral [B] and tetrahedral (A) sites of the spinel structure, [Formula presented], is equal to 1 at very low temperatures and equal to 0....
Article
Full-text available
We report line broadening in the 77 K 57Fe Mössbauer spectra of some commercially available medicines based on ferrous sulfates and on ferrous fumarates. While introducing only a single ferrous doublet is required to fit the RT spectra of all samples, on the contrary the line shapes of the 77 K spectra are properly described with two ferrous double...
Article
57Fe Mössbauer spectrometry (MS) has long been used to study medicines that contain organic and inorganic iron-based compounds. The technique contributes to identify the type of iron compound, to reveal the presence of impurities, and to determine the coordination polyhedron, valence and spin states of iron in these materials. The possibilities of...
Chapter
This chapter discusses the possibilities of using 57Fe M?ssbauer spectrometry in corrosion research in the case of three accelerated corrosion tests in chloride environments. It describes some models used to fit some of the iron phases in rust layers, such as goethite, akaganeite, and spinel phases. Additional information for other iron phases can...
Article
We propose a new direct method for calculating simultaneously two recoilless f-factors of any iron-bearing compound relative to that of a reference material by collecting only a single-temperature Mössbauer spectrum. This methodology is comparatively much simpler than the usual one which requires taking Mössbauer spectra of the compound at several...
Article
Full-text available
We propose a simple method for simultaneously calculating the two room temperature relative recoilless f-fractions of akaganeite without using the Debye approximation and by taking a single Mössbauer spectrum. The method relays on the correct determination of the two subspectral areas associated to the two akaganeite's iron sites relative to the su...
Article
Full-text available
The structural and hyperfine properties of pure and substituted akaganeites prepared in the presence of Mn, Co and urea are presented and discussed. In all samples, the chloride content increased with the increase in the urea concentration of the parent solution, and a small Mn-for-Fe or Co-for-Fe substitution occurred. In pure akaganeites, the inc...
Article
To calculate the amount of iron corroded from the steels that form part of the adherent rust, α, we propose a procedure that considers mass measurements and the use of spectroscopic techniques to estimate the relative iron phase abundances. We derived an equation to calculate α and evaluate it for carbon steels (CS) and weathering steels (WS) expos...
Article
It is usually assumed that α∗, the amount of iron that is converted into adherent rust (AR), in steels exposed to immersion corrosion is a constant independent of time, pollutant concentration, and steel composition. In order to investigate these ideas, we have performed total immersion tests with varying chloride concentration and immersion time i...
Article
Full-text available
Carbon, CS, and weathering steels, WS, were totally immersed in a NaCl containing solution. The influence of steel composition and the presence/absence of air flux into the solution on the physical properties of spinel and other iron phases were investigated. Large amounts of defective magnetite were formed only on CS, whereas little amounts of sma...
Article
The influences of chloride concentration, immersion time and steel composition on the physical properties of spinel phases formed as corrosion products in totally immersed tests were investigated. The results suggested that the spinel phase formed on carbon steels was magnetite, whereas that formed on weathering steels was maghemite independent upo...
Article
Full-text available
The refinement of the Mössbauer spectra, i.e. the assignation of the correct number of spectral components and their physical origin, has been a long controversy in the case of akaganeite. Most interpretations are based upon the earlier reported tetragonal structure, and very few upon the recently reported monoclinic structure. On the other hand, t...
Article
Products of corrosion were obtained from low alloy steels submitted to total immersion tests in solutions containing sodium chloride at different concentrations, during seven days. In order to properly characterize the adherent (AR) and the non-adherent rusts (NAR), a methodology including room temperature Mössbauer spectrometry, diffuse reflectanc...
Article
Crystallographic, chemical, and physical properties of akaganeite formed in the presence of Al3+, Cr3+, and Cu2+ ions and urea when it is obtained by the hydrolysis of FeCl3 solutions were investigated by different techniques. X-ray diffraction (XRD), RT and 77 K Mössbauer spectrometry, Fourier transformed infrared spectroscopy (FTIR) and thermogra...
Article
During the electrochemical corrosion of iron and steel not all the iron removed from the steel forms later part of the iron phases that remain stick to the surface. Here we report numerical data that demonstrates that the conversion of iron into adherent rust is not always equal to one, at least for steels submitted to chloride ions in dry–wet cycl...
Article
This paper deals with the influence of Al3+ and Ti4+ ions on the formation of akaganeite when prepared by hydrolysis of FeCl3 solutions. The products were characterized by X-ray diffraction (XRD) using Rietveld refinement, Infrared spectroscopy (FTIR) and 300 and 77 K Mössbauer spectrometry (MS). Akaganeite is the only phase being formed independen...
Article
Full-text available
In this work adherent (AR) and non-adherent (NAR) rust, formed on low carbon steel coupons exposed to total immersion corrosion processes in a 0.6 M NaCl solution, were obtained. The immersion was realized for 7 days. The Mössbauer spectra (MS) of the AR show the presence of lepidocrocite (?- FeOOH), goethite (a-FeOOH) and/or akaganeite (ß-FeOOH) p...
Chapter
The rust products formed on weathering and carbon steels exposed to dry-wet cyclical processes in different chloride-rich solutions are carefully examined by means of different techniques. Special emphasis is given to the methodology of analysis of the data using 300 K and 77 K Mössbauer spectrometry and X-ray diffraction. The rust that is loosely...
Article
Adherent (AR), differentiated as scraped and hit, and non-adherent (NAR) rusts formed on carbon and weathering steels exposed to chloride solutions in total immersion tests were examined by means of different techniques. The NAR for both steels is composed of lepidocrocite, the most abundant, akaganeite, and goethite, whereas the AR in both steels...
Article
The Mössbauer spectra of akaganeite have always been interpreted considering both the tetragonal structure and the chlorine content. However, very recently it has been suggested that the crystallographic structure is not tetragonal but monoclinic, thus another interpretation for the Mössbauer spectra is required. For this purpose, we have prepared...
Article
Full-text available
En este trabajo se examina un concepto de análisis del daño de superficies de corrosión usando procesamiento digital de imágenes. El fenómeno de corrosión es analizado usando un valor digital para el daño de la superficie morfológica, en lugar de característica electromecánicas. Una imagen es categorizadas por color y textura. Para calcular el colo...
Article
Full-text available
We have derived the Melchers¿ mathematical model of the oxygen diffusion across the rust layer formed on the surface of the steels submitted to total immersion, by a most fundamental principle: the Planck-Nersnt law. To achieve it, we have neglected the convection and migration of the oxygen molecules, and we have assumed both that this problem is...
Article
Full-text available
This paper deals with the influence of Al, Cr, and Cu ions on the formation of akaganeite. Powder samples were prepared by thermal hydrolysis of several mixtures of iron and the other cations so-lutions at 70°C during 48 hours. X-ray diffraction and Mössbauer spectrometry at 77 K and 300 K demonstrate that akaganeite is the only iron phase being fo...
Article
Full-text available
En este trabajo se evalúa la acción de tres convertidores, basados en ácidos tánico, fosfórico y su mezcla, sobre la magnetita (Fe3O4), maghemita (g-Fe2O3) y hematita (a-Fe2O3). A las muestras de oxido puras y a las obtenidas después de aplicar el convertidor se les realizó una caracterización por espectroscopía de infrarrojo por transformada de Fo...
Article
Full-text available
Se presenta un estudio de la acción de los ácidos tánico, fosfórico y su mezcla sobre la lepidocroci-ta, akaganeita, goethita magnética y goethita superparamagnética. A 500 mg de cada óxihidroxido se le adicionaron 20 mL de cada uno de los ácidos y se dejaron reaccionar espontáneamente durante un día y un mes. Las muestras sintetizadas y los produc...
Article
Preliminary assignments of the low-temperature Mössbauer signals obtained by taking into account a monoclinic structure for the akaganeite are presented. A powder sample was prepared by thermal hydrolysis of 0.1M FeCl3 solutions at 70°C during 48h according to the literature. X-ray diffraction demonstrates the purity of the synthetic sample. The X-...
Article
Full-text available
We have performed drying-humectation cyclical processes (CEBELCOR) on eight A36 low carbon steel coupons in NaCl solutions containing 1×10−2 M and 1×10−1 M concentrations. The main purpose of these experiments is to contribute to the understanding of the conditions for akaganeite formation. Additionally, and with the idea to perform a complete char...
Chapter
The actions of tannic acid, phosphoric acid and their mixture on lepidocrocite, goethite, superparamagnetic goethite, akaganeite, magnetite, hematite and maghemite for 1day and 1month were explored. It was found that these acids form iron tannates and phosphates. Lepidocrocite and magnetite were the iron phases more easily transformed with the mixt...
Article
This paper deals with the influence of Al, Cr, and Cu ions on the formation of akaganeite. Powder samples were prepared by thermal hydrolysis of several mixtures of iron and the other cations so- lutions at 70ºC during 48 hours. X-ray diffraction and Mössbauer spectrometry at 77 K and 300 K demonstrate that akaganeite is the only iron phase being f...
Article
Full-text available
Recibido 22 de Oct. 2007; Aceptado 3 de Mar. 2008; Publicado en línea 15 de Abr. 2008 Resumen Se investigó la influencia del tipo de acero y el tiempo de inmersión sobre la formación de magnetita en procesos de corro-sión. Con este propósito, se sometieron aceros autoprotectores (WS) y al carbono (CS) a pruebas de inmersión total en una solución 0....
Article
Full-text available
Resumen: Se presenta un estudio de los productos de la descomposición térmica de la akaganeita y magnetita. La akaganeita fue tratada en aire en un rango de temperaturas variando entre 150ºC y 500ºC a distintos tiempos entre una y cinco horas. La magnetita se trató en aire durante cinco horas a 500ºC. Los productos antes y después del tratamiento f...
Article
Normalmente los espectros Mössbauer de la akaganeita se interpretan en términos de su estructura tetragonal. Sin embargo recientemente algunos autores arguyen que la estructura cristalina no es tetragonal sino monoclínica. En este trabajo se propone una interpretación alternativa de los espectros Mössbauer de la akagenita en términos de esta última...

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Projects (2)
Project
I am currently study how defects (interfaces, surfaces, oxygen vacancies, cation inversion) influence in magnetic and transport properties of complex oxides (Zn, Ti, Mg, ferrites). I use light synchrotron techniques such as x-ray absorption spectroscopy (@ LNLS, Campinas, Brazil), as well as magnetization techniques in order to study the structure and magnetism of the materials. On the other hand, I employ Mossbauer spectroscopy as a fundamental tool to characterize Fe doped materials. I complement the experimental results with theoretical models through the collaboration with other research groups.