Attenuation of water-soluble polychlorinated biphenyls by earth materials /

Mode of access: Internet.

Hydric behavior of earth materials and the effects of their stabilization with cement or lime: study on repair mortars for historical rammed earth structures

Earthen building materials bear interesting environmental advantages and are the most appropriate to conserve historical earth constructions. To improve mechanical properties, these materials are often stabilized with cement or lime, but the impact of the stabilizers on the water transport properties, which are also critical, has been very rarely evaluated. We have tested four earth-based repair mortars applied on three distinct and representative rammed earth surfaces. Three mortars are based on earth collected from rammed earth buildings in south of Portugal and the fourth mortar is based on a commercial clayish earth. The main objective of the work was over the commercial earth mortar, applied stabilized and not stabilized on the three rammed earth surfaces to repair, to assess the influence of the stabilizers. The other three earth mortars (not stabilized) were applied on each type of rammed earth, representing the repair only made with local materials. The four unstabilized earth materials depicted nonlinear dependence on t1/2 during capillary suction. This behaviour was probably due to clay swelling. Stabilization with any of the four tested binders enabled the linear dependence of t1/2 expected from Washburn's equation, probably because the swelling did not take place in this case. However, the stabilizers also increased significantly the capillary suction and the capillary porosity of the materials. This means that, in addition to increasing the carbon footprint, stabilizers like cement and lime have functional disadvantages that discourage its use in repair mortars for raw earth construction.

Application of rare earths in thermal barrier coating materials

Rare earths are a series of minerals with special properties that make them essential for applications including miniaturized electronics, computer hard disks, display panels, missile guidance, pollution controlling catalysts, H-2-storage and other advanced materials. The use of thermal barrier coatings (TBCs) has the potential to extend the working temperature and the life of a gas turbine by providing a layer of thermal insulation between the metallic substrate and the hot gas. Yttria (Y2O3), as one of the most important rare earth oxides, has already been used in the typical TBC material YSZ (yttria stabilized zirconia). In the development of the TBC materials, especially in the latest ten years, rare earths have been found to be more and more important. All the new candidates of TBC materials contain a large quantity of rare earths, such as R2Zr2O7 (R=La, Ce, Nd, Gd), CeO2-YSZ, RMeAl11O19 (R=La, Nd; Me=Mg, Ca, Sr) and LaPO4. The concept of double-ceramic-layer coatings based on the rare earth materials and YSZ is effective for the improvement of the thermal shock life of TBCs at high temperature.

Luminescence properties of LB films based on heteropolytungstate of rare earth

In this work, the LB films based on heteropolytungstate of Dy and Sm have been prepared. The X-ray diffraction shows the LB films have a highly ordered lamella structure. The luminescence characteristics of the LB films were studied. The charge transfer bands of LB films are in higher energies than those of the corresponding solids. It is noticed that the yellow to blue intensity ratio (Y:B) of Dy3+ in the LB films is different from that of the solid. The differences in the spectra show that the Dy3+ site symmetry in LB film was changed due to the interaction between the surfactant and the polyanions. The differences could also be found in the luminescence spectra of the LB films of Sm complex.

Molecular dynamics studies of nanoparticle impacts

This thesis concerns the dynamics of nanoparticle impacts on solid surfaces. These impacts occur, for instance, in space, where micro- and nanometeoroids hit surfaces of planets, moons, and spacecraft. On Earth, materials are bombarded with nanoparticles in cluster ion beam devices, in order to clean or smooth their surfaces, or to analyse their elemental composition. In both cases, the result depends on the combined effects of countless single impacts. However, the dynamics of single impacts must be understood before the overall effects of nanoparticle radiation can be modelled. In addition to applications, nanoparticle impacts are also important to basic research in the nanoscience field, because the impacts provide an excellent case to test the applicability of atomic-level interaction models to very dynamic conditions. In this thesis, the stopping of nanoparticles in matter is explored using classical molecular dynamics computer simulations. The materials investigated are gold, silicon, and silica. Impacts on silicon through a native oxide layer and formation of complex craters are also simulated. Nanoparticles up to a diameter of 20 nm (315000 atoms) were used as projectiles. The molecular dynamics method and interatomic potentials for silicon and gold are examined in this thesis. It is shown that the displacement cascade expansionmechanism and crater crown formation are very sensitive to the choice of atomic interaction model. However, the best of the current interatomic models can be utilized in nanoparticle impact simulation, if caution is exercised. The stopping of monatomic ions in matter is understood very well nowadays. However, interactions become very complex when several atoms impact on a surface simultaneously and within a short distance, as happens in a nanoparticle impact. A high energy density is deposited in a relatively small volume, which induces ejection of material and formation of a crater. Very high yields of excavated material are observed experimentally. In addition, the yields scale nonlinearly with the cluster size and impact energy at small cluster sizes, whereas in macroscopic hypervelocity impacts, the scaling 2 is linear. The aim of this thesis is to explore the atomistic mechanisms behind the nonlinear scaling at small cluster sizes. It is shown here that the nonlinear scaling of ejected material yield disappears at large impactor sizes because the stopping mechanism of nanoparticles gradually changes to the same mechanism as in macroscopic hypervelocity impacts. The high yields at small impactor size are due to the early escape of energetic atoms from the hot region. In addition, the sputtering yield is shown to depend very much on the spatial initial energy and momentum distributions that the nanoparticle induces in the material in the first phase of the impact. At the later phases, the ejection of material occurs by several mechanisms. The most important mechanism at high energies or at large cluster sizes is atomic cluster ejection from the transient liquid crown that surrounds the crater. The cluster impact dynamics detected in the simulations are in agreement with several recent experimental results. In addition, it is shown that relatively weak impacts can induce modifications on the surface of an amorphous target over a larger area than was previously expected. This is a probable explanation for the formation of the complex crater shapes observed on these surfaces with atomic force microscopy. Clusters that consist of hundreds of thousands of atoms induce long-range modifications in crystalline gold.

Silica-coated Y2O3 : Eu nanoparticles and their luminescence properties

Crystalline Y2O3:Eu is of paramount significance in rare earth materials and research on luminescence spectra. In this work, the nanocrystalline Y2O3:Eu was coated with silica by a facile solid state reaction method at room temperature. The transmission electron microscope (TEM) photographs showed that the prepared Y2O3:Eu particle is polycrystalline with the size of 20 nm, the size of silica-coated particle is about 25 nm. The XPS spectra indicated that the silica layer is likely to interact with Y2O3:Eu by a Si-O-Y chemical bond. The luminescence spectra showed that the intensity of ground samples is lower than that of unground ones, the intensity of silica-coated phosphors is higher than that of the ground samples, while almost the same as that of the unground ones. Therefore, the silica coating decreases the surface defects of nanoparticles of the nanocrystalline Y2O3:Eu, thus increasing their luminescent intensity.

Durabilidad de los bloques de tierra comprimida : Evaluación y recomendaciones para la normalización de los ensayos de erosión y absorción

La presente tesis continúa una línea de investigación iniciada en el 2006, centrada en el estudio de nuevas soluciones constructivas que toman la tierra cruda como base. Se pretende la difusión de los resultados obtenidos con el fin de fomentar estas técnicas constructivas, como por ejemplo, los sistemas de eco-construcción. El empleo de tierra cruda como sistema constructivo presenta grandes ventajas; entre ellas, un bajo impacto medioambiental, la capacidad de integración en el paisaje y un menor consumo energético. Con el fin de superar los inconvenientes que presenta el empleo de la tierra como elemento constructivo y afianzar su valor como posible material para la edificación, se estudian las propiedades de durabilidad de la misma y se dan pautas para una posible normativa futura. Se ha llevado a cabo un análisis exhaustivo de las normativas internacionales, estudiando los ensayos propuestos por los diferentes Organismos Internacionales de Normalización para caracterizar la durabilidad de los materiales de tierra. Ante la gran diversidad y heterogeneidad de las especificaciones encontradas en los ensayos que se aplican para un mismo fin, se han desarrollado dispositivos lo suficientemente versátiles para la ejecución de los ensayos propuestos. El conjunto de ensayos desarrollados en esta tesis, ha permitido elaborar una guía de recomendaciones para ensayos aplicados a materiales de tierra cruda. Además, se han estudiado las diferencias de comportamiento de los bloques de tierra comprimidos (BTC) fabricados en España, evaluando su viabilidad como material de construcción. Esta tesis ayuda a consolidar el papel de la tierra cruda en el panorama de edificación actual, solventando las dudas de los técnicos en cuanto a la durabilidad frente al agua y ausencia de normativa. Por tanto, las conclusiones sobre ensayos de durabilidad en materiales de tierra y las mejoras propuestas en algunos ensayos, sirven de referencia para la determinación de la durabilidad en los materiales basados en tierra cruda. De igual manera, es también un objetivo de la tesis que los resultados obtenidos aporten una visión general del estado normativo de los materiales a base de tierra cruda e información útil a aportar para la elaboración de documentos reconocidos sobre tierra en nuestro país, concretamente, apoyando la labor de normalización llevada a cabo en el subcomité de AENOR. This thesis continues a research line begun in 2006, focused on the study of new building solutions based on unbaked earth. With the aim to promote these construction techniques, it seeks the diffusion of the result obtained, for example eco-building systems. The use of unbaked earth as building system has great advantages such as low environmental impact, integrate ability into the landscape and lower energy consumption. In order to overcome the disadvantages of the use of earth as a building element and consolidate its value as possible building material, it is studied the properties of its durability and it is given guidelines for possible future standard. It has carried out an exhaustive analysis of international standards, studying the tests proposed by several International Organizations of Standards in order to characterize the durability of earth materials. Because of the great diversity and heterogeneity of the specifications found in the tests that are applied for the same purpose, we have developed devices versatile enough for the implementation of the proposed tests. The set of developed tests in this thesis has allowed developing a recommendation guideline for tests applied to unbaked earth materials. In addition, we have studied the differences of behavior of compressed earth blocks (CEB) manufactured in Spain, evaluating its viability as building material. This thesis helps to consolidate the role of unbaked earth in the scene of current building, solving the doubts of technicians about durability against rain and lack of standard. Therefore, the conclusions of durability tests in earth materials and the proposed improvements in some tests, serve as a reference for determining the durability of the materials based on raw earth. In the same way, it is also an objective of the thesis that the obtained results provide an overview of standards status of materials based on unbaked earth and useful information for the development documents recognized on earth in our country, supporting the standardization that is taking place at the subcommittee AENOR.

Túnel de Viento para el Estudio de la Erosión Eólica

Túnel de viento para el estudio de la erosión eólica, caracterizado por ser ligero y plegable, donde un ventilador genera una corriente de aire, que entra en una estructura "tubular" desplegable. La estructura es telescópica. Se divide en 3 módulos y se han colocado unas bisagras, que permiten transformarlo en un cubo completamente plegado de reducidas dimensiones. Para completar el conjunto telescópico, se ha diseñado un sistema que permite a las paredes adaptarse a ésta estructura, utilizando patines que deslizan sobre un raíl. La recogida y análisis de las muestras, se realiza con 2 sensores: 1. Un láser-scan, que permite la generación de mapas tridimensionales del suelo, antes y después de ser erosionado. 2. Una cámara de visión industrial, que capta imágenes de las partículas fijadas en una serie de placas con adhesivos, colocadas al final del dispositivo.

África Austral: Los minerales como recurso estratégico para los intereses de Estados Unidos y China, período 2000-2010

La región de África Austral emerge como un nuevo escenario geopolítico complejo, en el que la lucha por la adquisición de los derechos de exploración, extracción y distribución de minerales estratégicos ha intensificado la presencia del número de actores estratégicos en esta zona. En este sentido, es interesante analizar el juego de poder que se desarrolla entre Estados Unidos y China con el fin de neutralizar la debilidad estratégica que representa la carencia de estos recursos naturales, esenciales para el desarrollo de sus industrias, así como también la oportunidad que representan como mecanismo para ampliar las esferas de influencia extra continental. Así pues, la presente investigación analiza a partir de la explotación de los minerales como recursos estratégicos, los efectos de la geoestrategia reciente de estos dos jugadores activos del sistema internacional contemporáneo en la relación con los Estados que conforman la región meridional del continente africano, durante el periodo 2000-2010.

Earth-abundant materials for solar hydrogen generation

A critical challenge for the 21st century is shifting from the predominant use of fossil fuels to renewables for energy. Among many options, sunlight is the only single renewable resource with sufficient abundance to replace most or all of our current fossil energy use. However, existing photovoltaic and solar thermal technologies cannot be scaled infinitely due to the temporal and geographic intermittency of sunlight. Therefore efficient and inexpensive methods for storage of solar energy in a dense medium are needed in order to greatly increase utilization of the sun as a primary resource. For this purpose we have proposed an artificial photosynthetic system consisting of semiconductors, electrocatalysts, and polymer membranes to carry out photoelectrochemical water splitting as a method for solar fuel generation.

This dissertation describes efforts over the last five years to develop critical semiconductor and catalyst components for efficient and scalable photoelectrochemical hydrogen evolution, one of the half reactions for water splitting. We identified and developed Ni–Mo alloy and Ni₂P nanoparticles as promising earth-abundant electrocatalysts for hydrogen evolution. We thoroughly characterized Ni–Mo alloys alongside Ni and Pt catalysts deposited onto planar and structured Si light absorbers for solar hydrogen generation. We sought to address several key challenges that emerged in the use of non-noble catalysts for solar fuels generation, resulting in the synthesis and characterization of Ni–Mo nanopowder for use in a new photocathode device architecture. To address the mismatch in stability between non-noble metal alloys and Si absorbers, we also synthesized and characterized p-type WSe₂ as a candidate light absorber alternative to Si that is stable under acidic and alkaline conditions.

Rare earth doped beta-diketone complexes as promising high-density optical recording materials for blue optoelectronics

Some kinds of rare earth beta-diketone complexes with blue-violet light absorption edge were synthesized using the ligands of thenoyltrifluoroacctone (HTTA), 2, 2'-dipyridyl (BIPY) and different metal ions (Gd3+, Sm3+ and La3+). Their contents, structures and optoelectronic parameters were monitored by elemental analysis, MS, IR and UV spectra. The solubility of rare earth beta-diketone complexes in 2, 2, 3, 3-tetrafluoro-1-propanol (TFP) and absorption properties of their films in the region 300-800 nm were measured. The influence on the difference of absorption maximum from rare earth beta-diketone complexes to beta-diketone ligand by different metal ions was studied. In addition, the thermal stability of rare earth beta-diketone complexes was also reported. (C) 2005 Elsevier B.V. All rights reserved.

Rare earth dibenzoylmethane complexes for potential application as high-density recordable optical recording materials

Three kinds of rare earth complexes derived from dibenzoylmethane (DBM) ligand were synthesized by reacting free ligand and different rare earth ions(La (3+), Sm3+ and Gd3+). Their contents and structures were postulated based on elemental analysis, LDI-TOF-MS, FT-IR spectra and UV-Vis spectra. Smooth films on K9 glass substrates were prepared using the spin-coating method. Their solubility in organic solvents, absorption and reflection properties of thin film and thermal stability of these complexes were evaluated. These complexes would be a promising recording material for high-density digital versatile disc-recordable (HD-DVD-R) system. (c) 2007 Elsevier B.V. All rights reserved.

Fiber laser processing of amorphous rare earth NeFeB magnetic materials

Since the exchange coupling theory was proposed by Kneller and Hawig in 1991 there has been a significant effort within the magnetic materials community to enhance the performance of rare earth magnets by utilising nano-composite meta-materials. Inclusions of magnetically soft iron smaller than approximately 10 nm in diameter are exchange coupled to a surrounding magnetically hard Nd2Fe14B matrix and provide an enhanced saturisation magnetisation without reducing coercivity. For such a fine nanostructure to be produced, close control over the thermal history of the material is needed. A processing route which provides this is laser annealing from an amorphous alloy precursor. In the current work, relationships between laser parameters, thermal histories of laser processed amorphous stoichiometric NdFeB ribbons and the magnetic properties of the resulting nanocrystalline products have been determined with a view to applying the process to thick film nanocomposite magnet production.

Preparation, characterization and luminescent properties of MCM-41 type materials impregnated with rare earth complex

Hybrid materials incorporating Eu-(TTA)(3). 2H(2)O (7hereafter designated as Eu-TTA, with TTA: thenoyltrifluoroacetone) in unmodified or modified MCM-41 by 3-aminopropyl-triethoxysilane (APTES) were prepared by impregnation method. The obtained materials were characterized using X-ray diffraction (XRD), IR and diffuse reflectance spectroscopy and luminescence spectra. All the hybrid samples exhibited the characteristic emission bands of EU3+ under UV light excitation at room temperature, and the excitation spectra showed significant blue-shifts compared to the pure rare-earth complex. Although the red emission intensity in the modified hybrid was almost the half of the red emission intensity in the pure Eu-TTA complex at room temperature, the hybrid showed a much higher thermal stability due to the shielding character of the MCM-41 host.

Rare-earth complexes of ferrocene-containing ligands: Visible-light excitable luminescent materials

The ferrocene-derivatives bis(ferrocenyl-ethynyl)-1,10-phenanthroline (Fc(2)phen) and ferrocenoyltrifluoroacetone (Hfta) have been used to synthesize ferrocene-containing rare-earth beta-diketonate complexes. The complexes [Ln(tta)(3)(Fc(2)phen)] and [Ln(fta)(3)(phen)] (where Ln = La, Nd, Eu, Yb) show structural similarities to the tris(2-thenoyltrifluoroacetonate)(1,10-phenanthroline)lanthanide(III) complexes, [Ln(tta)(3)(phen)]. The coordination number of the lanthanide ion is 8, and the coordination sphere can be described as a distorted dodecahedron. However, the presence of the ferrocene moieties shifts the ligand absorption bands of the rare-earth complexes to longer wavelengths so that the complexes can be excited not only by ultraviolet radiation but also by visible light of wavelengths up to 420 nm. Red photoluminescence is observed for the europium(III) complexes and near-infrared photoluminescence for the neodymium(III) and ytterbium(III) complexes. The presence of the ferrocene groups makes the rare-earth complexes hydrophobic and well-soluble in apolar organic solvents.