Scielo RSS <![CDATA[Matéria (Rio de Janeiro)]]> vol. 20 num. 3 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[Materiais para um Novo Paradigma da Indústria Química]]> <![CDATA[Nitrogen dopedTiO<sub>2</sub>photoactive in visible light]]> abstractIn this research TiO2 modified with nitrogen has been prepared. The synthesis method used was sol gel from the hydrolysis of titanium tetrabutoxide with urea solution, combined with a low temperature treatment at atmospheric pressure. The theoretical mole ratio N/Ti was equal to 0.5 and the theoretical mole ratio HNO3/TiO2 was equal to 0.5. The solid obtained was calcined at different temperatures in static air with high heating rate and residence time of 1 hour. The samples were characterized by X-ray diffraction, FTIR Raman and diffuse reflectance spectroscopy, thermodifferential and thermogravimetric analysis and specific surface area. All calcined solids exhibit absorption in the visible range. The Raman spectroscopy and X-ray diffraction revealed for all the heat treatments, the presence of crystalline phases corresponding to anatase and brookite polymorphism. The photocatalytic activity of the catalysts was tested in degradation of an artificial dye under visible light, yielding the best results for the sample treated at 250°C. Our results allow to say that this behaviour is due to the absorption of visible light, good efficiency for the adsorption of the dye and presence of two crystalline phases that decreases the recombination of photogenerated electrons and holes. The synthesis technique used allows obtaining solids with textural and attractive photocatalytic properties. <![CDATA[Thermal and mechanical properties of commercial MgO-C bricks]]> abstractMgO-C (magnesia-carbon) refractories are widely used in several steelmaking linings. These refractories are exposed to extreme stress due to high temperatures (T &gt; 1600 °C) required to cause the metallurgical reactions. These working conditions produced refractory wear through various related processes. The different types of degradation that the material suffers can be from thermochemical or thermomechanical origin. In this work, the Young's modulus, the fracture resistance and the thermal expansion coefficient of three commercial magnesia-carbon bricks (A, B, and C) were measured to evaluate their resistance to thermomechanical degradation. These data provided an estimation of the thermomechanical stresses that they can withstand. According to the results, the lowest fracture toughness is developed by brick C. This behavior is associated to a higher porosity and quality of the binder and magnesia used. Furthermore, while the brick B has the highest resistance to crack initiation due to thermal shock, the brick A proves to be the most suitable, taking into account the relationship between resistance to the initiation and propagation of cracks. A greater degree of strain to the level of the fracture stress is also presented in the bricks A and B. This is connected to their higher content of graphite (9-12 %) compared to brick C (~ 4 %). <![CDATA[CoAl<sub>2</sub>O<sub>4</sub> blue nanopigments prepared by liquid-feed flame spray pyrolysis method]]> abstractCoAl2O4 pigments were synthesized through Liquid-Feed Flame Spray Pyrolysis (LF-FSP) method using metallorganic precursors of cobalt propionate and alumatrane. The precursors were dissolved in ethanol and aerosolized into a methane/oxygen flame where it was combusted to result in nanopowders at a single step. The resulting nanopowders were collected in electrostatic precipitators and analyzed by x-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), colorimetry, Field Emission Scanning Electron Microscopy (FE-SEM) and BET (Brunauer-Emmett-Teller) nitrogen adsorption. Results show formation of single phase blue nanopigments, suggesting that LF-FSP is an excellent method to produce nanoparticles with high quality in a continuous process for new industrial applications. The nanoparticles presented spherical morphology with specific surface area of 50 m2/g, corresponding to average particle size of 27 nm. The pigments were calcined at 500, 600, 800, 1000, 1200 and 1300 °C, aiming to find the color stability whereby the colors were measured using the color space CIE L*a*b* under standardized D65 light. The brightest and bluest was obtained at calcination temperature of 1200°C and its application into a glaze was carried out at 1200 °C to evaluate the color performance and stability after a decoration process. Finally, LF-FSP produced pigments were compared with those produced by solid state reaction. Differences in the color due to the average particle size and process conditions were observed. It is possible to obtain new hues for ceramic applications by LF-FSP method. <![CDATA[Passivity in phosphate solution of unidirectionally solidified stainless steels]]> RESUMENLa pasividad de los aceros inoxidables es atribuida a la formación de una película protectora, conformada por óxidos, sobre la superficie del metal. Esta película posee propiedades semiconductoras y está relacionada con múltiples factores que la hacen de importancia para la comprensión de los fenómenos de corrosión. En este trabajo se estudia la película pasiva formada en aceros inoxidables solidificados unidireccionalmente, Fe-18Cr-10Ni-2Mo-0,08C (muestra A), Fe-18Cr-14Ni-8Mo-0,03C (muestra C) y Fe-18Cr-10Ni-8Mo-0,08C (muestra F), para determinar la influencia de la variación de la estructura (equiaxial, columnar y con transición de columnar a equiaxial-TCE) en la resistencia a la corrosión, así como investigar la relación entre la resistencia a la corrosión y el espaciamiento dendrítico secundario del material. Para ello se emplean técnicas potenciodinámicas y galvanostáticas, análisis de MottSchottky y espectroscopía de impedancia electroquímica que se realizaron en solución de Na2HPO40,5 M (pH 9,2).Las curvas potenciodinámicas indican una región pasiva y un máximo de corriente en la región transpasiva. Las medidas galvanostáticas realizadas sobre películas pasivas formadas previamente indican dos amesetamientos de potencial, debido al óxido de Cr y óxido de Fe, del cual surgen dos tiempos de transición. El mayor espesor de óxido de hierro se encuentra en las estructuras equiaxial de la muestra F, que posee el menor espaciamiento dendrítico respecto de los otras dos muestras teniendo en cuenta la misma estructura. El análisis de Mott Schottky muestra que la película pasiva se comporta como un semiconductor tipo n en el rango de potenciales de -0,45 V a 0 V, con una densidad de donores que varía de acuerdo a la composición del acero inoxidable. También se observa que la densidad de donores varía de acuerdo al tipo de estructura para un mismo material.<hr/>ABSTRACTPassivity of the stainless steel is attributed to the development of a protector film, formed by oxides on the metal surface. This film has semiconductor properties, and it is important for the understanding of corrosion phenomena.The objective of this work is to study the passive films formed in stainless steels samples solidified unidirectionally. The composition of the alloying elements in the samples are Fe-18Cr-10Ni-2Mo-0,08C (sample A), Fe-18Cr-14Ni-8Mo-0,03C (sample C) y Fe-18Cr-10Ni-8Mo-0,08C (sample F), and determine the influence of the structure (equiaxed, columnar and columnar-to-equiaxed transition, CET) in the corrosion resistance, as well as investigate the relationship between the corrosion resistance and the size of the secondary dendritic arm spacing. For this are used potentiodynamic and galvanostatic techniques, Mott Schottky analysis and electrochemical impedance spectroscopy.The measurements were performed in Na2HPO40,5 M (pH = 9,2), at room temperature (25ºC).Potentiodynamic measurements indicate a passive region and a maximum current in the transpassive region. The galvanostatic measurements of the passive films indicate two plain of potential, due to chromium oxide and iron oxide, in which two transition times occur. The greater thickness of the iron oxide is in the equiaxed structures of sample F, which has the smallest dendritic spacing with respect to other two samples, given the same structure. Mott Schottky analysis shows that the passive film behaves as an n-type semiconductor in the potential range of -0.45 V to 0 V, with a density of-donor that varies according to the composition of stainless steel. It is also observed that the density-donor varies according to the type of structure for the same material. <![CDATA[Analysis of corrosion resistance in simulated acid rain of Zn-Sn alloys]]> ResumENEl zinc y el estaño, junto con las aleaciones Zn-Sn, son empleados en la industria como recubrimientos del acero frente a la corrosión. Uno de sus usos más frecuentes es el galvanizado para exteriores, el cual es afectado por la corrosión debido a la lluvia ácida. El objetivo del trabajo es evaluar el comportamiento electroquímico que presentan las aleaciones Zn-Sn, con respecto a los metales puros, en una solución acuosa de lluvia ácida simulada compuesta por 31,85 mg/L H2SO4, 15,75 mg/L HNO3, 21,25 mg/L NaNO3, 46,20 mg/L (NH4)2SO4, 31,95 mg/L Na2SO4, 84,85 mg/L NaCl, con un pH entre 3,5 y 4,0, a temperatura ambiente (25ºC). Para ello, se emplearon probetas de aleaciones con diferentes porcentajes en peso de estaño (6, 10 y 50), y de los metales puros, solidificadas horizontalmente. Se tomaron muestras de cada estructura de grano revelada y se las desbastaron con papeles de SiC, de granulometría entre #60 y #1200. Posteriormente, se realizaron medidas de polarización potenciodinámica en una celda electroquímica convencional de tres electrodos y ensayos de inmersión. Cada probeta se examinó mediante microscopia óptica, antes y después de realizar los ensayos. De las curvas potenciodinámicas se observó para los cortes transversales, que a medida que aumenta el contenido de estaño en la aleación, los potenciales tienden a valores más nobles. A partir de los ensayos de inmersión se denotó que la estructura columnar de zinc y las aleaciones presentan una mayor pérdida de masa que las demás estructuras. Además, el zinc y las aleaciones presentaron la velocidad máxima de corrosión al primer día de inmersión, para todas las estructuras de grano. En las micrografías se evidenció que el zinc presentó corrosión generalizada.<hr/>abstractZinc and tin, together with Zn-Sn alloys are used in industrial operations and steel coatings against corrosion. One of its most common uses is the galvanizing process for outdoor structures, which is affected by corrosion caused by acid rain. The aim of the study is to evaluate the electrochemical behavior of Zn-Sn alloys with respect to pure metals, in an aqueous simulated acid rain solution consisting of 31.85 mg/L H2SO4, 15.75 mg/L HNO3, 21.25 mg /L NaNO3, 46.20 mg/L (NH4)2SO4, 31.95 mg/L Na2SO4, 84.85 mg/L NaCl, at a pH between 3,5 and 4,0, at room temperature (25°C). Zn-Sn alloys samples were used with different percentages of tin (6 wt. % Sn, 10 wt. % Sn and 50 wt. % Sn), and pure metals samples. The samples were obtained by horizontal directional solidification. Samples of each of the revealed structures were taken and roughed with papers of SiC, of grain size between # 60 and # 1200. Subsequently, potentiodynamic polarization essays were performed in a conventional three electrode electrochemical cell and immersion tests. Each ones was examined by optical microscopy, before and after performing the tests. For cross sections of samples, in potentiodynamic curves was observed that increasing tin content in the alloy, the potential tend to nobler values. From immersion tests was observed that the columnar structure of zinc and alloys exhibit greater mass loss than other structures. Moreover, zinc and alloys have high corrosion rates on the first day of immersion, for all grain structures. The micrographs showed that zinc presents generalized corrosion. <![CDATA[Síntesis verde y caracterización de sólidos de matriz silícea con cobre y plata obtenidos a partir de dos precursores para su aplicación como aditivos antifúngicos]]> ResumENLa síntesis de nuevos productos con actividad antimicrobiana, amigables con el medio ambiente, aplicados a la formulación de recubrimientos que prevengan la formación de biopelículas es un tema que ha cobrado gran relevancia en los últimos años. Las biopelículas producen cambios indeseables (biodeterioro) en las propiedades de los materiales como consecuencia de la actividad vital de los microorganismos. Por otro lado, afectan la salud humana, al constituirse en el interior de las viviendas y disminuir la calidad del aire por contribuir con la formación de bioaerosoles. El presente trabajo tiene como objetivo la síntesis verde y la caracterización de sólidos de matriz silícea asociados con cobre y plata, como contracationes de un heteropoliácido para su uso como aditivos antimicrobianos en pinturas. Los sólidos se obtienen a partir del método sol-gel mediante diferentes medios ácidos. La actividad antifúngica de los sólidos sintetizados se evaluó frente a dos aislamientos fúngicos, Alternaria alternata y Chaetomium globosum, obtenidos a partir de películas de pinturas biodeterioradas. Se prepararon sílices empleando tetraetilortosilicato y metiltrimetoxisilano como precursores y catalizadores ácidos para la reacción de hidrólisis del alcóxido. Una vez finalizada la etapa de síntesis y caracterización de las sílices propuestas, se evaluó su actividad antifúngica frente a los hongos de interés y se determinó el porcentaje de inhibición en cada caso. De los sólidos ensayados, la mayoría mostraron tener actividad antifúngica por inhibir el crecimiento de ambos hongos con las menores concentraciones en relación a su blanco, aunque los que contenían cobre y plata presentaron un mayor grado de inhibición en todos los casos.<hr/>abstractThe synthesis of new environmentally friendly products with antimicrobial activity, applied to the formulation of coatings that prevent biofilm formation is an issue that has become important in recent years. Biofilms produce undesirable changes (biodeterioration) in material properties due to the vital activity of microorganisms. They reduce indoor air quality by contributing to the formation of bioaerosols and therefore affect human health. This paper aims to greensynthesis and characterization of solid silica matrix associated with copper and silver, as counter cations of a heteropolyacid for use as antimicrobial additives in paints. The solids were obtained from the sol-gel method using different acidic medium. The antifungal activity of the synthesized solids was evaluated against two fungal isolates, Alternaria alternata and Chaetomium globosum, obtained from biodeteriorated paints films. Different silicas were prepared using tetraethyl orthosilicate and methyltrimethoxysilane as precursors and acids as catalysts for the hydrolysis reaction of the alkoxide. Once the synthesis phase and the characterization of the samples were finished, the antifungal activity against the microorganisms selected was evaluated and the inhibition percent was determined in each case. Among the solids tested, most showed antifungal activity, because they inhibited the fungal growth at the lower concentrations compared to the sample without the solids, although the presence of copper and silver increases the inhibition in most cases. <![CDATA[Study of Ni microstructural changes when subjected to high energy milling]]> ResumENLa investigación realizada por este grupo de trabajo tiene como objetivo principal el estudio y fabricación de vidrios metálicos base cobre (Cu-Ni-Zr) mediante aleado mecánico. Se planteó la caracterización de los elementos puros (Cu y Ni), aleaciones binarias Cu-Ni y Cu-Zr y aleaciones ternarias Cu-Ni-Zr en las mismas condiciones de molienda de alta energía. En este trabajo se presenta el cambio microestructural del Níquel al ser sometido a molienda de alta energía. Para este fin se utilizó un molino SPEX 8000D con las siguientes condiciones de molienda: atmósfera de argón, acido esteárico, RBP=10:1, con tiempos desde 1 hasta 60 horas, 1 h de molienda efectiva y seguida de 0,5 h de descanso. Las muestras posteriores a la molienda fueron analizadas mediante difracción de rayos X, microscopía electrónica de transmisión y espectroscopia de absorción atómica, obteniendo el tamaño de cristalita, parámetro de red y contaminación de Fe. Los resultados obtenidos muestran que el níquel al ser sometido a molienda mecánica alcanza un tamaño de cristalita de aproximadamente 10 nm que se hace asintótico a partir de las 5 horas; el parámetro de red incrementa al aumentar el tiempo de molienda, posiblemente debido al incremento del componente interfacial conjuntamente a la incorporación de Fe dentro de la red, producto del alto porcentaje de contaminación a las 60 h.<hr/>abstractResearch by this working group's takes as a principal aim the study and manufacture of bulk metal glass based copper (Cu-Ni-Zr) by mechanical alloying. First, the characterization of the milled pure copper, Cu-Ni and Cu-Zr binary alloys and Cu-Ni-Zr ternary alloys in the same conditions of high energy millings. In this work, the microstructural change of Nickel to be subjected to high energy milling is presented. For this purpose a SPEX 8000D mill with the following conditions of milling: argon, stearic acid, BPR = 10:1, with milling time from 1 to 60 hours, 1 h of effective milling followed by a rest period of 0,5 h. Subsequent to the milling samples were analyzed by ray-X diffraction, transmission electron microscopy and atomic absorption spectroscopy, obtaining the crystallite size, lattice parameters and Fe contamination. The results show that nickel when subjected to mechanical milling reaches a crystallite size of about 10 nm which is asymptotic from 5 h; the lattice parameter increases with increasing milling time, possibly due to increased interfacial component together with the incorporation of Fe, due to the high percentage contamination at 60 h. <![CDATA[Anodization growth of self-organized ZrO2 nanotubes on zircaloy-4. Evaluation of the photocatalytic activity]]> ABSTRACTZrO2nanotube arrays were prepared through anodic oxidation in glycerol organic electrolyte containing ammonium fluoride. The morphology of these nanotube arrays can be controlled by changing the preparation parameters such as applied voltage, fluoride ion concentration and time of anodization. While the oxidation voltage is the main factor that controls the diameter of nanotubes, the length of nanotubes is mainly depending on the oxidation time, and the crystal type is closely related to the annealing temperature. We also studied their photocatalytic performance. The photocatalytic activity of samples was calculated by the degradation of a model dye, under halogen light illumination.<hr/>RESUMENNanotubos de ZrO2 se prepararon a través de oxidación anódica en un electrolito orgánico de glicerina conteniendo fluoruro de amonio. La morfología de estas matrices de nanotubos puede ser controlada cambiando los parámetros de preparación, tales como la tensión aplicada, la concentración de iones fluoruro y el tiempo de anodización. Mientras que la tensión de la oxidación es el factor principal que controla el diámetro de los nanotubos, la longitud de los mismos depende principalmente del tiempo de oxidación, y el tipo de cristal está estrechamente relacionado con la temperatura de recocido. También se estudió el desempeño fotocatalítico. La actividad fotocatalítica de las muestras se calculó por la degradación de un colorante patrón, bajo iluminación de luz halógena. <![CDATA[Characterization of semi-finished titanium alloys processed by extrusion and lamination perforation (Mannesmann process)]]> RESUMENPara la fabricación de tubos y caños sin costura se utilizan como materias primas, semielaborados huecos provenientes de procesos de deformación en caliente tales como extrusión y laminación perforación (proceso Mannesmann). A partir de los cuales y por medio de sucesivas reducciones de área a través de laminación o de trafilación se alcanzan las medidas finales solicitadas. El proceso de laminación perforación, por efecto Mannesmann, contempla la perforación de tochos cilíndricos, a través de una compresión diametral progresiva, que genera una fractura en el núcleo y facilita la perforación junto a la laminación transversal oblicua. En cambio la extrusión es un proceso por compresión en el cual el metal es forzado a fluir a través de una matriz para darle forma a su sección transversal. El presente trabajo de caracterización se realizó sobre semielaborados provenientes de ambos procesos, laminación perforación y extrusión, en aleaciones de titanio (Titanio Gr. 2 (Titanio Comercialmente Puro) y Titanio Gr. 5 (Ti-6Al-4V)). Se realizaron ensayos destructivos (tracción, aplastado y abocardado), no destructivos (inspección visual, videoscopía, dimensionales, rugosidad superficial y determinación de discontinuidades por tintas penetrantes) y macro y micro metalografías. También se evaluó la contaminación química provocada por la atmósfera del horno. Finalmente se analizaron los defectos característicos provenientes de cada proceso de deformación, su causa raíz y sus posibles soluciones.<hr/>ABSTRACTFor the manufacture of seamless pipes and tubes are used, as raw materials, hollow bars from hot deformation processes like extrusion and rotary tube piercing (Mannesmann process). Starting from these semi-elaborated products and by means of successive cross sections reductions through tube drawing or tube rolling (cold pilgering) the requested final dimensions are achieved. The rotary tube piercing process, Mannesmann process, includes drilling cylindrical billet through a progressive diametral compression that generates a crack at the center and facilitates perforation along the oblique transverse rolling. In contrast, the extrusion is a compression process in which the metal is forced to flow through a die to shape cross section. This characterization work was performed on semifinished products from both processes, extrusion and rotary tube piercing in titanium alloys (Titanium Gr. 2 (Titanium Commercially Pure) and Titanium Gr. 5 (Ti-6Al-4V)). Destructive tests (tensile test, flattening test and flaring test) non-destructive tests (visual inspection, boroscopy, dimensional, surface roughness and discontinuity determination by dye penetrant) and metallogra-phy (macro and micro) were performed. Chemical contamination caused by the furnace atmosphere was also assessed. Finally, the characteristic defects from each deformation process, their root cause and possible solutions were discussed. <![CDATA[Influence of Ni and Ti on the response to simulated marine corrosion of weathering steel A242]]> RESUMENExiste un gran interés en la industria siderúrgica por incorporar nuevos productos que superen las propiedades de los ya existentes. Dentro de estas propiedades, la resistencia a la corrosión es de gran importancia para los países que, al igual que Chile, tienen abundante litoral marino. En las zonas costeras los iones cloruro presentes en el aire producen deterioro por corrosión lo que disminuye la vida útil de las estructuras. Por esta razón es que es de vital importancia investigar la influencia de los distintos elementos aleantes y tratamientos que lleven a mejorar la resistencia de los aceros frente a la corrosión marina. Este trabajo apunta al estudio de aceros autopatinables ASTM A242 de baja aleación, específicamente con adición de Níquel a la aleación, y a la adición de Titanio como afinador de la microestructura, y su influencia sobre la resistencia a la corrosión atmosférica utilizando ensayos de corrosión acelerada producida en cámara de niebla salina con ciclos de humectación y secado. En las aleaciones estudiadas se determinó el espesor corroído de las muestras y la velocidad de corrosión. Los diferentes productos de corrosión, óxidos y oxihidróxidos de hierro se identificaron por rayos X. Los resultados muestran claramente que luego de 40 ciclos (960 horas) de tratamiento, en comparación con un acero ASTM A242, la velocidad de corrosión disminuye en forma significativa en el mismo acero con aleación de Níquel, y más aún con adición de Titanio como afinador de grano. Este resultado se ve también reflejado en una disminución del espesor corroído de los cupones, observándose el menor espesor corroído en el acero ASTM A242 con Ni y Ti.<hr/>ABSTRACTThere is a great interest in the steel industry to incorporate new products in the market with better properties of those already in production. Among these properties, corrosion resistance is of great importance for countries with a large marine seacoast, like Chile, where chloride ions from sea spray produce corrosion, leading to irreversible failure of steel structures decreasing their life. For this reason, it is of vital importance to investigate the influence of various alloying elements and treatments for steels with superior corrosion resistance properties in marine environment. This work aims at studying the specific influence of Nickel - as an alloy constituent - and Titanium - as a microstructural tuner - on ASTM A242 low alloy weathering steel. For that, atmospheric corrosion resistance was evaluated through accelerated salt spray corrosion experiments under wet/dry cycles. For each alloy the thickness of corrosion products and corrosion rates were determined. The oxides and oxyhydroxides were identified by X-Ray diffraction technique. The results showed that corrosion rates at 40 cycles (960 hours) were low for Ni alloyed specimens and even lower for the Ti alloyed specimens, in comparison to the ASTM A242 alloy specimens. These results are reflected in a decrease in the thickness of the corroded coupons, with the lowest value observed for the ASTM A242 steel specimens alloyed with Nickel and Titanium. <![CDATA[Mechanical Behavior of a Twip Steel (Twinning Induced Plasticity)]]> ABSTRACTA TWIP steel (0.65%C; 22%Mn; 0.28%Cr; 0.16%Si) was produced in the laboratory by melting, casting, hot forging and hot rolling. The relationship between mechanical twinning fraction and mechanical behavior of this steel was studied through tension tests at the following temperatures: 25, 300, 325, 350, 375 and 400°C. Fracture toughness was measured from J integral evaluation at temperatures where the principal hardening mechanism is mechanical twinning and dislocation glide (325 and 375°C respectively), for which a set of CT samples were pre-cracked by fatigue and then loaded until fracture in accordance to ASTM 1820. The plastic strain energy absorbed by each sample during crack growth was studied, correlating twinning with the mechanical response of the material, determining a decrease of plastic deformation energy around 375ºC, where the main deformation mechanism is strain hardening by dislocation glide and not mechanical twinning. Results obtained by different mechanical tests show that mechanical twinning activates in a range of stacking fault energy in the range 18 to 50 mJ/m2. <![CDATA[Marine atmospheric corrosion behavior of structural ferritic pearlitic and ferritic martensitic weathering Steel]]> RESUMENLa industria del acero se encuentra constantemente enfrentada al desafío del desarrollo de nuevos y mejores aceros para diversas necesidades, tales como la necesidad de aceros estructurales con mayor resistencia a la corrosión marina que los que existen en la actualidad, y que además posean una mayor resistencia mecánica. Por ello y en pos de lo anteriormente expuesto es evidente que, investigar en forma sistemática tanto la influencia de los elementos aleantes, como las variables del proceso de fabricación de aceros estructurales resistentes a la corrosión marina es relevante para el desarrollo del mercado acerero nacional.El presente trabajo tendrá por objetivo, la comparación de comportamiento a la corrosión atmosférica marina (espesor corroído en el tiempo) entre aceros de composición autopatinable (ASTM A242 y ASTM A588) con estructuras ferrítico-perlítica y ferrítico-martensítica. Para lo anterior se realizaron ciclos de humectación salina y secado. La humectación salina se realizó en cámara de niebla salina, de acuerdo a los requerimientos presentados en la norma ASTM B177, y el secado, en una mufla a 40 °C. Tras el retiro de muestras, se realizaron decapados químicos, según lo requerido en ASTM G1, para la determinación de espesor corroído.<hr/>ABSTRACTThe steel industry constantly faces the challenge of developing new and better steels for diverse needs, on of this necessities is the use of structural steels with higher corrosion resistance to marine atmospheres and improved mechanical properties than those that currently exist. Therefore, it is necessary to systematically research both the influence in the corrosion resistant to marine atmospheres of the alloying elements, and others variables such as changes in the manufacturing process of this materials.This work aims to compare the behavior on marine atmospheric corrosion between weathering steels (ASTM A242 and ASTM A588) with ferritic-pearlitic and ferritic-martensitic structures. Wetting and drying cycles were performed. Saline wetting was performed in a salt spray apparatus, according to ASTM B177, while drying was performed in a furnace at 40°C. At the end of each cycles, the corrosion products were removed in accordance to ASTM G1. <![CDATA[Tartrazine degradation by supported TiO<sub>2</sub>on magnetic particles]]> ABSTRACTMagnetic beads were obtained by dropping a solution of sodium alginate containing magnetite particles into a CaCl2 solution. TiO2anatase particles were synthetized by a sol-gel method at low temperature (75 °C), and were supported on magnetic beads to obtain the magnetic photocatalyst, MC. Magnetite particles and magnetic photocatalyst were characterized by nitrogen adsorption (BET, surface area), their morphology observed by scanning electronic microscopy (SEM) and TiO2 phase was analyzed by means of Raman spectroscopy. The photocatalytic activity of MC was evaluated on tartrazine degradation, highly used in food industry, at two different concentrations. Finally, MC stability was evaluated by reusability assays in several subsequent cycles. Results showed a good photocatalytic response for tartrazine degradation, especially at low concentration, easy recuperation and appropriate perform in the reusability of MC.<hr/>RESUMENEn el presente trabajo se han obtenido perlas magnéticas mediante la adición de una solución de alginato de sodio conteniendo partículas de magnetita a una solución de CaCl2, las cuáles fueron utilizadas como soporte de TiO2. Las partículas de TiO2 en fase anatasa, obtenidas por el método sol-gel a baja temperatura (75 °C), fueron soportadas en las perlas magnéticas para obtener el fotocatalizador magnético, CM. La superficie específica BET del núcleo de magnetita y el fotocatalizador magnético fueron obtenidas por adsorción de N2, la morfología de las partículas fueron observadas por microscopía electrónica de barrido (SEM) y la fase TiO2fue analizada mediante espectroscopía Raman. La actividad fotocatalítica de CM fue evaluada en la degradación del colorante tartrazina, muy utilizado en la industria alimenticia, a dos concentraciones diferentes. Finalmente, la estabilidad del catalizador fue evaluada mediante ensayos de la re-usabilidad en varios ciclos posteriores. Los resultados mostraron que la fase anatasa soportada en las partículas magnéticas presentan buena actividad fotocatalítica en la de degradación de tartrazina, principalmente cuando la concentración del colorante es baja, y que pueden ser fácilmente recuperados y re-utilizados en varios ciclos con una moderada pérdida en la eficiencia fotocatalítica. <![CDATA[Optical characterization of surface defects incadmium selenide (CdSe) colloidal quantum dots]]> RESUMENEn el presente estudio se han caracterizado ópticamente defectos superficiales ("non-stoichiometric" y "dangling bonds") en puntos cuánticos (QDs) coloidales de CdSe sintetizados por el método de descomposición térmica. En especial, se estudió la presencia de defectos vinculados con una alta relación área/volumen de los QDs. Los espectros de fotoluminiscencia (PL) de estos QDs presentan dos bandas, atribuibles a la recombinación excitónica y a la recombinación excitónica vía defectos superficiales. Luego de la síntesis las muestras permanecieron durante un tiempo sin ningún tratamiento adicional. Durante este tiempo se observó mediante el monitoreo de la evolución de las bandas de PL, un incremento en la intensidad de la banda atribuible a defectos respecto a la de emisión excitónica. Posteriormente, las muestras se lavaron utilizando abundante etanol y fueron disueltas en 1-octadeceno. Con este tratamiento se ha observado una recuperación gradual de la PL de la banda excitónica. Esto podría atribuirse a la remoción de los residuos de la reacción que pudieron formar defectos y a un reacomodo de los surfactantes, mostrando de esta manera una forma de pasivación de defectos superficiales. Para todas las muestras estudiadas en este trabajo, se observó mayor presencia de defectos superficiales para QDs con mayor relación área/volumen.<hr/>ABSTRACTIn this work, non-stoichiometric defects and dangling bond defects were optically characterized for CdSe colloidal quantum dots (QDs), which were prepared by the thermal decomposition method. Particularly, the presence of defects linked to a high QD surface to volume ratio was studied. The photoluminescence (PL) spectra of the samples show two bands, which could be associated to excitonic recombination and excitonic recombination via surface defects. The samples remained untreated for a period of time after preparation. During this time a gradual deterioration of the QDs was observed by monitoring the evolution of PL spectra. An increase in intensity of the band associated to recombination via defects, with respect to the excitonic emission band, was observed. Subsequently, the samples were washed using abundant ethanol and dissolved in 1-octadecene. After this treatment a gradual recovery of the excitonic PL band was observed. This could be attributed to the removal of reaction residues that could give rise to defects, and to a rearrangement of the surfactants, thus showing a form of surface defects passivation. For all the samples, investigated in this work, a greater presence of surface defects for QDs of higher surface to volume ratio was observed. <![CDATA[Design of new polyurethanes inspired by themacromolecular architecture of spider silk]]> RESUMENEn este trabajo se presentan los resultados de la síntesis en masa y caracterización de copolímeros de poliuretano (PU) formados a partir de 1,6-hexametilen diisocianato (HDI) y N-metil dietanolamina (MDEA) y 1,4-butanodiol (BD) como glicoles de las fases flexibles y rígidas, respectivamente. Se compara las propiedades mecánicas y morfológicas de este tipo de PU con las de un PU convencional formado con un policarbonato de peso molecular intermedio. Los materiales se han caracterizado mediante calorimetría diferencial de barrido, espectroscopia infrarroja de transformada de Fourier y mecánicamente mediante tracción uniaxial. Se ha observado que las unidades de MDEA que, pese a tener la capacidad de asociarse por puentes de hidrógeno, presentan características elástoméricas similares a las de glicoles de mayor peso molecular y separación entre unidades donoras-aceptoras de enlaces de hidrógeno. El comportamiento de esta nueva serie de PU con alta densidad de puentes de hidrógeno puede resultar interesante en el desarrollo de materiales resilientes y tenaces tales como las sedas.<hr/>ABSTRACTThis works presents results on the synthesis and characterization of a novel bio-inspired polyurethane (PU) elastomer with high density of hydrogen bonding. The PU were formed by the condensation of 1,6 hexamethylen-diisocyanate with N-methyl diethanolamine (MDEA) and 1,4-butanediol (BD) as components of the elastic and rigid phases, respectively. The mechanical performance and morphology of this PU are compared with those of a common PU elastomer formed with a medium molecular weight polycarbonate. The materials have been tested by means of Fourier-transformed infrared spectroscopy, differential calorimetry and by uniaxial tensile testing. It has been observed that units composed of MDEA segments present elastomeric behavior despite being highly hydrogen bonded with denser packaging between donor and acceptor of hydrogen bridges than in the case of an intermediate molecular weight polyol. The properties exhibited by these new type of PUs with high density of hydrogen bonding can be considered interesting for the development of resilient and tough materials such as silks. <![CDATA[Hacia una reducción del contenido decobre en pinturas antiincrustantes]]> RESUMENEl biofouling conduce al deterioro de las estructuras emplazadas en el mar acarreando graves pérdidas económicas. La aplicación de pinturas a base de óxido cuproso es el método más difundido para el control de las incrustaciones aún siendo nocivas para los ecosistemas marinos. Ante la necesidad de desarrollar formulaciones más inocuas se propone el uso de productos de origen natural que puedan reemplazar parte del cobre disminuyendo su aporte al medio ambiente.El timol se aísla de los aceites esenciales de numerosas plantas (tomillo, orégano, albahaca) y ha sido ampliamente estudiado por sus propiedades antimicrobianas. La hipótesis que se plantea es que inhibiría el proceso inicial del asentamiento de organismos incrustantes.El objetivo de este trabajo es reducir el contenido de cobre en las pinturas antifouling empleando al timol como aditivo.Se prepararon dos pinturas antifouling, una conteniendo 16% v/v de cobre y otra con 1,6% de cobre + 2% de timol. Las pinturas se aplicaron sobre paneles de acrílico y se sumergieron en el puerto de Mar del Plata. Luego de 6 meses los paneles se retiraron y observaron en el laboratorio bajo lupa binocular y microscopio óptico. La estimación de la fijación para cada especie sobre los paneles se evaluó con una grilla de 25 puntos al azar. Se trabajó por triplicado, con controles y se aplicaron test estadísticos.Las pinturas con cobre+timol presentaron una muy buena performance dado que disminuyeron el asentamiento del biofouling. No se registraron diferencias significativas en los porcentajes de cobertura entre las formulaciones con cobre y la pintura con cobre+timol (p&gt;0,05). El timol empleado como aditivo en la formulación antiincrustante permitió reducir 90% el contenido de cobre manteniendo la efectividad en servicio.<hr/>ABSTRACTBiofouling leads to deterioration of any submerged material. The most widespread method for control is the application of cuprous oxide antifouling paints which are toxic. For this reason non-toxic natural products could be combined with small amounts of copper to diminish its contribution to the environment.Thymol is isolated from essential oils of several plants (thyme, oregano, basil) and it is well known for its antimicrobial properties. The hypothesis proposed in this study is this compound would inhibit initial steps in fouling sequence and consequently would also inhibit settlement of later species.The aim of this work was to reduce the amount of copper in antifouling paints employing thymol as an additive. Two antifouling paints were prepared, one containing 16% v/v copper and another with 1.6% copper + 2% thymol. Paints were applied on acrylic panels and were submerged in Mar del Plata harbor.After 6 months of immersion in Mar del Plata harbor fouling cover percentage on panels was estimated under stereomicroscope and optic microscope. Estimation of fouling cover by species was carried out using a 25 random point grid. Also, control paints and unpainted acrylic tiles were simultaneously submerged. All tests were performed in triplicate.Paints containing 1.6% copper + thymol and 16% copper were effective. No significance differences were registered in cover percentage between copper-based paints and copper+thymol based paints (p&gt;0.05). Although these formulations showed a similar performance, copper+thymol based paint contains 90% lesser copper than a traditional copper based formulation. Then, the aim of this work was reached. <![CDATA[Evaluation of thymol to antifungiccontrol on paint films]]> RESUMENLa colonización microbiana en el interior de los edificios preocupa en forma creciente no solo por el deterioro estético que puede ocasionar en los revestimientos sino por los problemas de salud que causan los microorganismos en personas con bajas defensas o con problemas respiratorios. En este sentido, la limpieza es fundamental para mantener las condiciones de higiene, por esto es que existen algunos productos comerciales que ayudan a la prevención y eliminación de los mohos en los revestimientos.El timol (2-isopropil-5-metilfenol) es un monoterpeno que se encuentra como compuesto principal de varios aceites esenciales, como el de orégano y tomillo. Hay numerosos estudios que muestran el buen desempeño "in vitro" de este compuesto como antimicrobiano y desinfectante. El objetivo de esta investigación fue estudiar el desempeño del timol sobre las películas de pintura como potencial compuesto a utilizar en líquidos fungicidas para controlar la incidencia y propagación de los mohos. Para los ensayos se utilizaron paneles pintados que se colocaron sobre papel de filtro humedecido en placas de Petri. Se inocularon con una solución de esporas del hongo Alternaria alternata. Por último, se roció un grupo de paneles con una solución de timol y otro con un fungicida comercial. Como controles se utilizaron paneles rociados con el solvente del timol (etanol) y paneles sin rociar. Se incubaron a 28ºC por 2 meses. Se observó que el spray de timol inhibió el crecimiento del hongo sobre el panel pintado mientras que el producto comercial y los controles no lo inhibieron. Por lo tanto, el uso de timol resulta una alternativa natural para la formulación de productos destinados a la prevención del desarrollo de los mohos sobre las superficies pintadas.<hr/>ABSTRACTThe microbial colonization is an issue of increasing concern inside buildings not only because of causing aesthetic damages in coatings but also for developing diseases in persons with low-defense systems or respiratory problems. In this sense, cleaning is fundamental to maintain the hygienic conditions and some commercial products that help to prevent and eliminate moulds in coatings have been developed.The aim of this research was to study the performance of thymol onto paint films as a potential compound to be used in fungicide liquids to control the incidence and spread of moulds. Thymol (2-isopropyl-5-methylphenol) is a monoterpene found as the main compound in various essential oils, such as thyme and oregano. Numerous "in vitro" studies have shown the good performance of this compound as an antimicrobial and disinfectant. Painted panels were placed on moistened filter paper in Petri and, a spore solution of Alternaria alternata, an environmental fungus was inoculated onto the paint. Finally, a set of panels was sprayed with a solution of thymol and another set with a commercial product. Sprayed panels with the thymol solvent (ethanol) and not sprayed panels were used as controls. Petri dishes were incubated at 28°C for 2 months. It was observed that the thymol spray inhibited the fungus growth onto painted panels, while the commercial product and the controls did not show inhibition. Therefore, thymol is a natural alternative to formulate products that help to prevent the development of moulds on painted surfaces. <![CDATA[Production of copper-based metallic glasses: evolution of the phases during mechanical alloying]]> RESUMENEn este estudio se fabricaron diferentes materiales (base cobre) bajo las mismas condiciones de molienda: molino empleado fue un SPEX 8000D, atmósfera de argón, acido esteárico, RBP=10:1, con tiempos variables desde 1 hasta 120 horas, con el objetivo de comparar los cambios microestructurales durante el proceso de: Cobre puro, Aleaciones Cu-Ni, Aleaciones Cu-Zr y aleaciones Cu-Ni-Zr. Las muestras, tras la molienda, fueron analizadas mediante difracción de rayos X, microscopía electrónica de transmisión y calorimetría diferencial de barrido. De acuerdo a los resultados, el cobre al ser sometido al proceso alcanza un tamaño de cristalita que se hace asintótico a partir de las 5 horas, mientras que en el sistema Cu-Ni, en vez de apreciarse un refinamiento microestructural a ese mismo periodo, se advierte una total solubilización del níquel en cobre (40-60 y 50-50) y de cobre en níquel (60-40). Por su parte, en el sistema binario Cu-Zr, se encontró, también para 5 horas, que el sistema estaba prácticamente amorfizado (60-40 y 50-50) al igual que en el caso de las aleaciones ternarias Cu-Ni-Zr (60-10-30 y 50-10-40).<hr/>ABSTRACTIn this study, different, copper-based materials were fabricated under equal milling conditions (SPEX 8000D, argon atmosphere, stearic acid, BPR=10:1) and variable amounts of time, from 1 to 120 hours, in order to compare the microstructural changes during the process. The materials were: Pure copper; Cu-Ni alloys; Cu-Zr alloys; and Cu-Ni-Zr alloys. Subsequent to milling, the samples were measured with X-Ray Diffraction, Electron Transmission Microscopy, and Differential Scanning Calorimetry. According to the results, copper, upon being subjected to the process, reaches a crystallite size that tends towards an asymptote starting at 5 hours. In the Cu-Ni system, instead of observing a microstructural refinement during this same period, there was rather a total solubilization of the nickel into the copper (40-60 and50-50), and of the copper into the nickel (60-40). As for the Cu-Zr binary system, it was found that, for five hours as well, the system was practically amorphous (60-40 and 50-50), a condition also present in the Cu-Ni-Zr ternary alloys (60-10-30 and 50-10-40). <![CDATA[Evolution of texture and microstructure during thermo-mechanical processingin ultrathin low carbon steels]]> ABSTRACT In this research paper an analysis concerning the evolution of crystallographic texture during hot rolling processing of low carbon steel is presented. The study was performed on a steel sheet with an initial thickness of 1.9 mm used in the process of cold rolling. In order to assess the differences between tensile and compressive deformation, a 90˚ cold bending was carried out in this specimen. Texture evolution analysis greatly helps to assess the effect of some mechanical properties, particularly formability. The material was annealed under different conditions of time and temperature using an inert atmosphere. The chemical composition was determined by optical emission spectrometry. The study of crystallographic texture present in this steel was performed using the electron backscatter diffraction (EBSD) technique by means of OIM (Orientation Imaging Microscopy) mapping, inverse pole figures and orientation distribution functions (ODFs). Electron diffraction Backscattered (EBSD) is a technique that allows to detect and analyze information crystallographic on the surface of a sample which is observed by scanning electron microscope (SEM). An analysis of the effect of processing parameters and differences between tensile and compressive deformation on the microstructure and crystallographic texture changes in these materials is presented. The results are discussed in terms of both the resulting anisotropy after the annealing treatment and the primary fibers founded by this technique. <![CDATA[Influence of the porosity on the magnetic properties of Ni nanowires arrays]]> RESUMENSe estudiaron las propiedades de histéresis magnética de arreglos ordenados de nanohilos de Ni, electrodepositados éstos en una membrana de alúmina con un arreglo hexagonal de poros cilíndricos. Se analizó el efecto de la geometría de los nanohilos individuales (diámetro y longitud) y del ordenamiento y porosidad del arreglo sobre la coercitividad y la remanencia del conjunto. Las membranas de alúmina auto-ensambladas se sintetizaron por anodizado en dos pasos, usando una celda electroquímica y potencial eléctrico constante. Se variaron los diámetros de poro entre 20 nm y 40 nm (no así la distancia media entre ellos) sumergiendo las membranas en ácido fosfórico al 5% durante distintos tiempos. Estas membranas se caracterizaron por microscopía de barrido (SEM). Los nanohilos de Ni se obtuvieron por electrodeposición AC, a 20 V, 200 Hz y temperatura ambiente. Una vez sintetizados, los arreglos de nanohilos se caracterizaron estructuralmente por SEM y magnéticamente usando un SQUID. Se observa que las propiedades magnéticas de los arreglos son fuertemente dependientes de la relación largo/diámetro de los nanohilos, la que regula el valor de su anisotropía de forma, y también de la porosidad, que determina la magnitud del campo de interacción dipolar que percibe cada nanohilo por la presencia de sus vecinos en el arreglo. En particular, se encontró que la coercitividad decrece con la porosidad y que el parámetro ε, que regula la intensidad de las barreras de energía del sistema, debe ser variable y depender de la porosidad del arreglo para ajustar bien los datos experimentales.<hr/>ABSTRACTThe hysteresis properties of ordered arrays of Ni nanowires, electrodeposited into cylindrical nanoporous alumina membranes were investigated. The effect of the nanowire geometry (diameter and length), the array order and the nanowires' volume fraction on the array coercivity and remanence were analyzed. Porous alumina membranes were produced by a two-step anodization process in a potentiostatic electrochemical cell. The pores' diameters were varied from 20 nm to 40 nm by immersing the membranes in a 5% phosphoric acid solution for different times. The membranes were characterized using a scanning electron microscope (SEM) and both the pore size distribution as well as their separation were determined. These membranes were used as templates for the AC electrodeposition of Ni nanowires, using a voltage of 20 V and a frequency of 200 Hz, at room temperature. The Ni nanowire arrays were structurally and magnetically characterized by SEM and with a SQUID magnetometer, respectively, at room temperature. It was found that the magnetic properties of the array strongly depend on the nanowires aspect ratio -length/diameter ratio- which regulates the wire shape anisotropy and also on the porosity, which determines the magnitude of the dipolar interaction field acting on the array. Particulary, it was found that coercitivity decreases with porosity and that the parameter ε, which is related to the energy barriers of the system, must depend on the porosity of the ensemble in order to accurately describe the experimental data. <![CDATA[Controlled coverage of glass substrateswith metallic nanorods]]> RESUMENSe realizó la síntesis de nanobastones de oro monodispersos con una eficiencia superior al 80% sobre el total de nanopartículas, caracterizado por una resonancia plasmónica longitudinal cercana a los 800 nm. Se modificaron superficialmente sustratos de vidrio y se los recubrió con los nanobastones sintetizados, con control de la densidad superficial. Se monitoreó la dinámica del recubrimiento a través de espectros de extinción, y se observó una densidad máxima de saturación dada por repulsión electrostática y un tiempo característico del proceso. Luego de alcanzada la saturación de nanobastones por unidad de área se observa un ensanchamiento de las resonancias hacia el infrarrojo, debido a interacciones entre los nanobastones por producirse agregaciones sobre la superficie. Estos resultados tienen aplicación inmediata en el diseño y fabricación de dispositivos plasmónicos, por ejemplo en el sensado molecular.<hr/>ABSTRACTMonodispersed gold nanorods were synthesized with efficiency above 80% of all nanoparticles, characterized by longitudinal plasmon resonance around 800 nm. Glass substrates were surface modified and covered with the synthesized nanorods with control of surface density. Coverage dynamics was monitored through extinction spectra, and a saturation maximum density was observed, given by electrostatic repulsion, and a characteristic time of the process. A widening of the resonance towards the infrared is observed after reaching the saturation of nanorods per unit area, due to interactions between nanorods on account of surface aggregation. These results have immediate application in the design and manufacture of plasmonic devices, for example in molecular sensing. <![CDATA[Production of porous ceramic materialusing different sources of alumina and calcia]]> ABSTRACTNumerous papers and publications report the use of microporous calcium hexaluminate (CaO.6Al2O3; CA6) as a key raw material for high temperature insulating materials. This material has unique properties with respect to chemical purity and mineral composition. Another important property of CA6 is its structure, which consists of platelet-shaped crystals that interlock. The free distance between the crystals defines the microporous structure. The low density in combination with the micropores hampers heat transfer by radiation at temperatures exceeding 1000 oC and results in a low thermal conductivity. Given the advantages presented by this material, it is necessary to understand the formation mechanism of CA6 grains in order to better develop the potential applications of this material. CA6 can be fabricated using organic binders to consolidate the Al2O3-CaCO3 powder mixture and to provide green strength so that a green body can be formed and retains the desired shape before heating. However, these organic binders must be completely thermally decomposed so that they do not remain in the sintered body as carbon or ash. Moreover, the use of organic binders releases large volumes of gases such as carbon dioxide from the green body during heating. Therefore, an eco-friendly ceramic fabrication process has been developed that employs an inorganic binder (hydraulic alumina). The aim of the present work was to study the synthesis of porous calcium-hexaluminate ceramics using calcined alumina or hydraulic alumina combined with different sources of calcia (CaCO3 and Ca(OH)2) at different temperatures. The materials produced were characterized by X-ray diffraction, scanning electron microscopy, apparent porosity and mercury intrusion porosimetry. The materials produced by hydraulic alumina presented higher porosity and larger pores compared to those produced from calcined alumina <![CDATA[Optical absorption enhancement in sensitized ZnO nanorods for solar cells]]> ABSTRACTThe Optical Properties of ZnO Nanorods (NR) sensitized with different semiconductors in Core-Shell nanostructures were studied, comparing them with those of bare ZnO NR. Experimental measurements of Transmittance and Diffuse Reflectance show an increased light absorption at the solar spectrum and the appearances of new absorption edges (AE). The measurements are compared with numerical simulations based on Bruggeman Effective Medium Approximation. An increased absorption with the sensitizer content is observed. For similar changes in filling fractions, CdTe presents higher changes in absorption than CdS. Shifts in the AE are observed experimentally (e.g. between 2.34 eV and 2.66 eV for CdS). These shifts cannot be assigned to sensitizer content or confinement effects. A similar behaviour is observed for CdTe in which the AE measured by transmittance is between 1.31 eV and 1.36 eV, while the one obtained from Kubelka-Munk analysis of reflectance is, for the same samples, 1.57 eV and 1.49 eV, respectively. Moreover, the split-off AE is also observed at 2.55 eV and 2.28 eV. The observed large red-shifts could be associated with an enhancement of the subbandgap absorption due to an increase in the light free path at the core-shell nanostructure.<hr/>RESUMENSe estudiaron las Propiedades Ópticas (PO) de Nanovarillas (NV) de ZnO sensibilizadas con diferentes semiconductores en nanoestructuras núcleo-corteza, comparándolas con las PO de NV de ZnO. Las medidas experimentales de Transmitancia y Reflectancia Difusa muestran un incremento en la absorción de luz en el espectro solar y la aparición de nuevos bordes de absorción (BA). Las medidas se compararon con simulaciones numéricas basadas en Aproximación de Medio Efectivo (Bruggeman). Las simulaciones corresponden con las medidas reproduciendo la dependencia con el contenido de sensibilizante. Para CdTe se observa un aumento de la absorción con la cantidad del sensibilizante, siendo los cambios mayores para iguales cambios en las fracciones de llenado respecto al CdS. Las mediciones experimentales muestran corrimientos en las posiciones de los BA entre 2.34 eV y 2.66 eV para CdS. Estos corrimientos no pueden explicarse sólo por cambios en el contenido de sensibilizante o por los efectos de confinamiento en las nanoestructuras. Similar es el comportamiento del BA de muestras sensibilizadas con CdTe que se ubica entre 1.31 eV y 1.36 eV, analizadas por Transmitancia, mientras que para las mismas muestras este BA se encuentra en 1.57 eV y 1.49 eV, respectivamente, según el método de Kubelka-Munk de la Reflectancia. Además se observa el BA de la banda split-off en 2.55 eV y 2.28 eV. Estos corrimientos pueden asociarse a un incremento de la absorción sub-bandgap debido al aumento del recorrido libre medio de la luz en la estructura. <![CDATA[Surface and textural characterization of TiO<sub>2</sub> pillared organoclays]]> ABSTRACTTiO2 organoclays are potential adsorbents for aqueous pollutants and subsequently they could favour the photocatalysis of them. For this reason, the study of their surface and textural characteristics is important for the improvement of those processes. In this work TiO2 pillared organoclays were studied. The surfactant (hexadecyltrimethilammonium bromide) was introduced post-pillaring or during the pillaring process. The effect of the use of different acids of hydrolysis and different surfactants ratios was investigated. The clays were characterized by thermogravimetric analysis, infrared spectroscopy and nitrogen sorptometry. It was found that the highest adsorption capacity post-pillaring of the surfactant is near to 0.5 times the CEC of the original pillared clay, independently of the amount of surfactant offered. An increment in the amount of the surfactant introduced only increased the ratio adsorbed as ionic pair. In these samples the CEC measured after the adsorption was between 0.26 and 0.47 times the original CEC. It was observed a decrease in the total pore volume and the BET surface for every sample. The surface hydrophobicity of the samples with post-pillaring adsorption was higher than in those with co-adsorption. In conclusion, it was demonstrated that the incorporation of surfactant modifies the surface and textural properties of the material in different extent in accordance with the incorporation stage and the amount of surfactant used. <![CDATA[Study of cis- and trans-stilbene structures by atomic force microscopy]]> RESUMENLa nanotecnología es un área multidisciplinaria que ha tenido un gran auge en los últimos años, principalmente debido al desarrollo de instrumental que permite "ver", estudiar y manipular la materia a nivel atómico y molecular. El estilbeno y algunos de sus derivados son moléculas orgánicas de origen natural, que presentan una estructura química de interés en la fabricación de nanoestructuras y bloques constituyentes de máquinas moleculares (potencialmente aplicables en tecnología de nanosensores, almacenamiento de datos, liberación controlada de fármacos, entre otros). Sin embargo todavía no han sido ampliamente exploradas como nanomateriales. El interés en este tipo de sistemas reside en sus aplicaciones en medicina, farmacia y biotecnología.Este trabajo presenta los primeros resultados obtenidos al estudiar formas isoméricas de estilbeno: cis- y trans-estilbeno, líquido y sólido a temperatura ambiente, respectivamente, con el objetivo de explorar sus propiedades, al estar las mismas en contacto con superficies policristalinas de oro (Au/mica) y grafito (HOPG).Se encontró que la inmovilización de trans-estilbeno sobre una superficie puede modificar el proceso de cristalización de estas moléculas orgánicas, cuya morfología depende del sustrato. Mientras que el trans-estilbeno forma "clusters" que originan cristales de forma pseudo-romboide sobre HOPG, sobre la superficie de Au/mica forma estructuras dendríticas con ramificaciones en ángulos a 90 º.Por otra parte, se observó que el cis-estilbeno a escala nanométrica forma también "clusters" sobre HOPG, comportándose de manera similar al trans-estilbeno. Un paulatino incremento en la cantidad de cis-estilbeno conlleva al crecimiento de dichos "clusters" y a su coalescencia en una fase amorfa. Por el contrario, la interacción molécula-sustrato de cis-estilbeno sobre Au/mica es más lábil que sobre HOPG y ya no resulta posible observar centros de nucleación o nanoestructuras estables. Un aumento en la cantidad de cis-estilbeno sobre Au/mica resulta en una especie de película delgada líquida.<hr/>ABSTRACTNanotechnology is a multidisciplinary field that emerged in recent years due to the development of tools to "see", study and manipulate matter at atomic and molecular levels. Stilbene and some of its derivatives are organic molecules found in nature, which have chemical structures of interest in nano-fabrication of molecular machine building blocks (with prospective applications in nano-sensors, data storage and drug controlled release, among others). However, they have not been extensively explored as nanomaterials. This kind of systems is of interest in medicine, pharmacy and biotechnology.This work presents the first results obtained by studying stilbene isomers: cis- and trans-stilbene, liquid and solid at room temperature, respectively, to explore their properties on polycrystalline substrates of gold (Au/mica) and graphite (HOPG).We found that immobilization of trans-stilbene on a substrate can modify the crystallization process of the organic molecules, and the crystal morphology depends on the substrate. While trans-stilbene forms clusters that lead to pseudo-rhomboidal crystals on HOPG, dendritic structures with 90 º proyected branches are formed on equally prepared samples of Au/mica.Additionally, we found at nanometer scale that cis-stilbene forms clusters on HOPG as well, similarly to trans-stilbene. A gradual increase in the amount of cis-stilbene enlarges the clusters until they coalesce in an amorphous phase. In contrast, the molecule-substrate interactions of cis-stilbene on Au/mica are weaker than on HOPG and do not form crystal nuclei centers or stable nanostructures. Instead, increasing cis-stilbene molecular concentration on Au/mica leads to a sort of liquid film. <![CDATA[Nanostructured films of hyperbranched polymeras template to metalic structures]]> RESUMENLa molécula Boltorn H30 es un polímero hiperramificado polihidroxilado de tercera generación de origen comercial con forma aproximadamente globular de diámetro promedio de 3,3 nm y tiene una cavidad endoreceptora que puede ser aprovechada para la incorporación de iones u otras moléculas pequeñas. En este caso, se analiza la adsorción espontánea de Boltorn H30 sobre sustratos de carbono para generar superficies nanoestructuradas capaces de captar o retener cationes cobre (II) en su interior. Posteriormente, las películas formadas se llevan a una celda electroquímica con el fin de reducir electroquímicamente el catión y generar estructuras metálicas usando el polímero hiperramificado como plantilla o molde. Estas plataformas desarrolladas con cobre electrodepositado han mostrado ser útiles para la electrocatálisis de peróxido de hidrógeno. Las superficies estudiadas en este trabajo han sido caracterizadas mediante diferentes técnicas espectroscópicas, microscópicas y electroquímicas.<hr/>ABSTRACTBoltorn H30 molecule is the third generation of a commercial polyhydroxylated hyperbranched polymer with an almost globular shape of 3,3 nm average diameter, which has an endo-receptor cavity that can be used for ions or some other small molecules inclusion. In this work, we analyze the spontaneous adsorption of Boltorn H30 on carbon substrates with the aim of generating nanostructured surfaces with the ability to capture or retain copper cations (II) inside. Afterwards, the formed films were taken to an electrochemical cell to reduce the cation and generate metallic structures using the hyperbranched polymer as a template. The platforms developed with electrodeposited copper are useful for the electrocatalysis of hydrogen peroxide. Along this work, the studied surfaces were characterized by means of different spectroscopical, microscopical and electrochemical techniques. <![CDATA[Combustion synthesis of Co-Cu-Mn oxides deploying different fuels]]> ABSTRACTTernary spinel-like oxides such as CuFeMnO4, CoCuMnOxand CuCr2O4 are attractive materials due to their absorbent properties when used as pigments for selective surfaces thus improving solar heaters efficiency. These materials are obtained through sol-gel and sol-gel-combustion methods. This work proposes the synthesis of mixed oxides of Co, Cu and Mn by means of original one-step stoichiometric combustion methods starting from Mn(NO3)2,Co(NO3)26H2O, Cu(NO3)23H2O and Aspartic acid (Asp) or Lysine( Lys) as fuels. The resulting ashes after the combustion were calcined at 500 °C. The obtained ashes and the calcined powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and by Brunauer-Emmett-Teller method (BET), and TG-DTA analysis. In calcined powders obtained with Lys (CoCuMnOx-Lys), the phase corresponding to CoCuMnOx and others segregated phases were identified. However, in calcined powders obtained with Asp (CoCuMnOx-Asp) only the phase corresponding to CoCuMnOxwas identified. The sample CoCuMnOx-Lys presented an average crystallite size of 44 nm and a specific surface area of 23 m2/g while in CoCuMnOx-Asp, 54 nm and 13 m2/g values were obtained throughout FT-IR vibrational modes associated with spinel metallic oxides for both calcined powders (Asp and Lys) were observed. Additionally, by means of TEM, polyhedral particles with an average size of 20 to 100 nm were observed. In particular, it was determined in CoCuMnOx-Lys an average size of 44nm. According to the different fuels used (Asp and Lys), an evident variation in the obtained phases was observed. However, it was not obtained any difference in crystallite size and specific area surface values. It is of considerable importance the study of further syntheses processes to verify this trend. <![CDATA[Copper-supported catalysts for the selective reduction of glycerol]]> RESUMENLa industria del biodiesel ha traído aparejada una oferta creciente de glicerol, el cual es el subproducto del proceso, generando una caída de su precio. La transformación del glicerol en compuestos con valor agregado interesa pues mejoraría la ecuación económica global de la producción del biocombustible permitiendo un desarrollo ambiental sustentable al utilizar materia prima renovable. En Argentina, la provincia de Santa Fe tiene una capacidad instalada de 2,5 millones de toneladas/año de biodiesel, con las consiguientes 250.000 tn/año de glicerol, por lo que la temática es de sumo interés para el medio socio-productivo regional. Una ruta para valorizar el glicerol es a través de la reacción catalítica de hidrogenólisis, mejor llamada reducción selectiva, para obtener propanodioles. Catalizadores del tipo metal soportado fueron reportados como activos para conducir la hidrogenólisis en fase líquida, encontrando escasa información para la reacción en fase gas. Por este motivo, se prepararon catalizadores del tipo Metal/Soporte por impregnación por humedad incipiente, siendo evaluados en fase líquida en un sistema con reactor de acero inoxidable y operación semicontinua y en fase gas en un sistema continuo con reactor de lecho fijo y flujo descendente. La reacción se siguió por cromatografía de gases, siendo en línea para la fase no condensada. El rango de condiciones de operación evaluado fue 170-240°C y presiones 1-30 kg cm-2. Para fase líquida, los niveles de actividad y selectividad a 1,2-propanodiol alcanzados fueron similares a los reportados, mejorando la conversión con el incremento de temperatura y presión. Para fase gas, conversión y selectividad fueron fuertemente influenciadas por las condiciones de reacción, siendo el principal co-producto el acetol, indicado como intermediario de la reacción. Los materiales que presentaron mejor comportamiento fueron caracterizados por RTP, DRX y FTIR para determinar sus características, relacionar la actividad catalítica y optimizar la preparación.<hr/>ABSTRACTThe biodiesel industry has brought with it an oversupply of glycerol, which is the byproduct of the process, generating a fall in its price. The transformation of glycerol into value-added compounds interest as it would improve the overall economic balance of biofuel production enabling environmentally sustainable development by using renewable raw material. In Argentina, the province of Santa Fe has an installed capacity of 2.5 million TM/year of biodiesel, with consequent 250,000 TM/year of glycerol, so the topic is of great interest to the regional socio-productive means. One route to valorize glycerol is the catalytic hydrogenolysis reaction, better called selective reduction, to obtain propanediols. Metal supported catalysts were reported as assets to drive the liquid phase hydrogenolysis, finding little information for the gas phase reaction. For this reason, Metal/Support type catalysts were prepared by impregnation following the incipient wetness technique, being evaluated in liquid phase in a system with a stainless steel reactor and semi-continuous operation and in gas phase in a continuous system with a fixed bed down-flow reactor. The reaction was followed by gas chromatography, being on line to the non-condensed phase. The range of operating conditions evaluated was 170-240°C and 1-30 kg cm-2 pressures. For liquid phase, activity and selectivity to 1,2-propanediol were similar to those previously reported, improving conversion by increasing temperature and pressure. For gas phase, conversion and selectivity were strongly influenced by reaction conditions, being acetol the main co-product, which is indicated as the reaction intermediate. Materials displaying better behavior were characterized by TPR, XRD, and FTIR to determine their characteristics, relating catalytic activity, and optimizing preparation. <![CDATA[Mechanical and thermal behavior of polyvinyl alcohol reinforced with aligned carbon nanotubes]]> ABSTRACTIn recent years, due to their high specific mechanical properties, the polymer matrix composites have been widely used. In particular, carbon nanotubes (CNTs) have been used as reinforcement due to its exceptional mechanical and electrical properties. In this work the mechanical behavior of polyvinyl alcohol (PVA) reinforced with different percentages of mechanically oriented CNTs was studied. The composite material was made starting with a solution of PVA+ distilled water, and then the CNTs were added to the solution and dispersed by magnetic stirring and ultrasonic agitation. During this step, a surfactant was added to help with the CNTs dispersion. This mixture was poured into a container and dried using a heat source to accelerate its polymerization and curing. The layers obtained were subjected to mechanical stretching at controlled temperature to align the CNTs in the loading direction. The mechanical properties were measured by tensile testing and nanoindentation. The results show a large increase in modulus and hardness compared with non-reinforced polymeric material, it was also found a significant increase in the tensile strength. The composite with the best properties was subjected to thermal stabilization by ethanol, obtaining an increase in the degradation temperature of about 100°C approximately, although in this case the mechanical stiffness and hardness were decreased compared to unstabilized material, the usefulness of this material is enhanced. <![CDATA[ERRATA]]> ABSTRACTIn recent years, due to their high specific mechanical properties, the polymer matrix composites have been widely used. In particular, carbon nanotubes (CNTs) have been used as reinforcement due to its exceptional mechanical and electrical properties. In this work the mechanical behavior of polyvinyl alcohol (PVA) reinforced with different percentages of mechanically oriented CNTs was studied. The composite material was made starting with a solution of PVA+ distilled water, and then the CNTs were added to the solution and dispersed by magnetic stirring and ultrasonic agitation. During this step, a surfactant was added to help with the CNTs dispersion. This mixture was poured into a container and dried using a heat source to accelerate its polymerization and curing. The layers obtained were subjected to mechanical stretching at controlled temperature to align the CNTs in the loading direction. The mechanical properties were measured by tensile testing and nanoindentation. The results show a large increase in modulus and hardness compared with non-reinforced polymeric material, it was also found a significant increase in the tensile strength. The composite with the best properties was subjected to thermal stabilization by ethanol, obtaining an increase in the degradation temperature of about 100°C approximately, although in this case the mechanical stiffness and hardness were decreased compared to unstabilized material, the usefulness of this material is enhanced.