Chemistry of minerals from amphibole-chlorite veins of ODP Site 209-1270

We examined small-scale shear zones in drillcore samples of abyssal peridotites from the Mid-Atlantic Ridge. These shear zones are associated with veins consisting of chlorite + actinolite/tremolite assemblages, with accessory phases zircon and apatite, and they are interpreted as altered plagiogranite melt impregnations, which originate from hydrous partial melting of gabbroic intrusion in an oceanic detachment fault. Ti-in-zircon thermometry yields temperatures around 820��C for the crystallization of the evolved melt. Reaction path modeling indicates that the alteration assemblage includes serpentine of the adjacent altered peridotites. Based on the model results, we propose that formation of chlorite occurred at higher temperatures than serpentinization, thus leading to strain localization around former plagiogranites during alteration. The detachment fault represents a major pathway for fluids through the oceanic crust, as evidenced by extremely low d18O of altered plagiogranite veins (+3.0-4.2 per mil) and adjacent serpentinites (+ 2.6-3.7 per mil). The uniform oxygen isotope data indicate that fluid flow in the detachment fault system affected veins and adjacent host serpentinites likewise.

Chemistry on manganese nodules from the Pacific Ocean

Three manganese nodules from the Pacific Ocean have been analysed for 35 elements by using mainly spectrophotometric and spectrographic methods. Cu, Co, Ni, Zn, and Pb were found in amounts approaching 1 %, which far exceeds their average concentrations in igneous rocks. On the other hand, elements having readily hydrolysable ions, such as Ga, Sc, Zr, Y, La and Ti, are present only in amounts comparable with their concentrations in igneous rocks. Sb, Bit Be, and Cr were not detected. The hydrochloric acid-insoluble fraction of nodules is practically free of the heavy metals that are characteristic of the acid-soluble fraction; it consists principally of clay minerals, together with lesser amounts of quartz, apatite, biotite and sodium and potassium felspars.

Geochemistry and age determination of zircons in Cretaceous to Quaternary sediments

In central Antarctica, drainage today and earlier back to the Paleozoic radiates from the Gamburtsev Subglacial Mountains (GSM). Proximal to the GSM past the Permian-Triassic fluvial sandstones in the Prince Charles Mountains (PCM) are Cretaceous, Eocene, and Pleistocene sediment in Prydz Bay (ODP741, 1166, and 1167) and pre-Holocene sediment in AM04 beneath the Amery Ice Shelf. We analysed detrital zircons for U-Pb ages, Hf-isotope compositions, and trace elements to determine the age, rock type, source of the host magma, and "crustal" model age (T(C)DM). These samples, together with others downslope from the GSM and the Vostok Subglacial Highlands (VSH), define major clusters of detrital zircons interpreted as coming from (1) 700 to 460 Ma mafic granitoids and alkaline rock, epsilon-Hf 9 to -28, signifying derivation 2.5 to 1.3 Ga from fertile and recycled crust, and (2) 1200-900 Ma mafic granitoids and alkaline rock, epsilon-Hf 11 to -28, signifying derivation 1.8 to 1.3 Ga from fertile and recycled crust. Minor clusters extend to 3350 Ma. Similar detrital zircons in Permian-Triassic, Ordovician, Cambrian, and Neoproterozoic sandstones located along the PaleoPacific margin of East Antarctica and southeast Australia further downslope from central Antarctica reflect the upslope GSM-VSH nucleus of the central Antarctic provenance as a complex of 1200-900 Ma (Grenville) mafic granitoids and alkaline rocks and older rocks embedded in 700-460 Ma (Pan-Gondwanaland) fold belts. The wider central Antarctic provenance (CAP) is tentatively divided into a central sector with negative ?Hf in its 1200-900 Ma rocks bounded on either side by positive epsilon-Hf. The high ground of the GSM-VSH in the Permian and later to the present day is attributed to crustal shortening by far-field stress during the 320 Ma mid-Carboniferous collision of Gondwanaland and Laurussia. Earlier uplifts in the ~500 Ma Cambrian possibly followed the 700-500 Ma assembly of Gondwanaland, and in the Neoproterozoic the 1000-900 Ma collisional events in the Eastern Ghats-Rayner Province at the end of the 1300-1000 Ma assembly of Rodinia.

Geochemistry of samples from Valtournenche, Western Italian Alps

Slices of polycyclic metasediments (marbles and meta-cherts) are tectonically amalgamated with the polydeformed basement of the Dent Blanche tectonic system along a major Alpine shear zone in the Western Alps (Becca di Sal�� area, Valtournenche Valley). A combination of techniques (structural analysis at various scales, metamorphic petrology, geochronology and trace element geochemistry) was applied to determine the age and composition of accessory phases (titanite, allanite and zircon) and their relation to major minerals. The results are used to reconstruct the polyphase structural and metamorphic history, comprising both pre-Alpine and Alpine cycles. The pre-Alpine evolution is associated with low-pressure high-temperature metamorphism related to Permo-Triassic lithospheric thinning. In meta-cherts, microtextural relations indicate coeval growth of allanite and garnet during this stage, at ~ 300 Ma. Textures of zircon also indicate crystallization at HT conditions; ages scatter from 263-294 Ma, with a major cluster of data at ~ 276 Ma. In impure marble, U-Pb analyses of titanite domains (with variable Al and F contents) yield apparent 206Pb/238U dates range from Permian to Jurassic. Chemical and isotopic data suggest that titanite formed at Permian times and was then affected by (extension-related?) fluid circulation during the Triassic and Jurassic, which redistributed major elements (Al and F) and partially opened the U-Pb system. The Alpine cycle lead to early blueschist facies assemblages, which were partly overprinted under greenschist facies conditions. The strong Alpine compressional overprint disrupted the pre-Alpine structural imprint and/or reactivated earlier structures. The pre-Alpine metamorphic record, preserved in these slices of metasediments, reflects the onset of the Permo-Triassic lithospheric extension to Jurassic rifting.

Superplastic deformation of directionally solidified nanofibrillar Al2O3-Y3Al5O12-ZrO2 eutectics

Nanofibrillar Al2O3���Y3Al5O12���ZrO2 eutectic rods were manufactured by directional solidification from the melt at high growth rates in an inert atmosphere using the laser-heated floating zone method. Under conditions of cooperative growth, the ternary eutectic presented a homogeneous microstructure, formed by bundles of single-crystal c-oriented Al2O3 and Y3Al5O12 (YAG) whiskers of ���100 nm in width with smaller Y2O3-doped ZrO2 (YSZ) whiskers between them. Owing to the anisotropic fibrillar microstructure, Al2O3���YAG���YSZ ternary eutectics present high strength and toughness at ambient temperature while they exhibit superplastic behavior at 1600 K and above. Careful examination of the deformed samples by transmission electron microscopy did not show any evidence of dislocation activity and superplastic deformation was attributed to mass-transport by diffusion within the nanometric domains. This combination of high strength and toughness at ambient temperature together with the ability to support large deformations without failure above 1600 K is unique and shows a large potential to develop new structural materials for very high temperature structural applications.

Comportamiento mec��nico de nuevas aleaciones de wolframio en funci��n de la temperatura

La presente memoria de tesis tiene como objetivo principal la caracterizaci��n mec��nica en funci��n de la temperatura de nueve aleaciones de wolframio con contenidos diferentes en titanio, vanadio, itria y lantana. Las aleaciones estudiadas son las siguientes: W-0.5%Y2O3, W-2%Ti, W-2% Ti-0.5% Y2O3, W-4% Ti-0.5% Y2O3, W-2%V, W- 2%Vmix, W-4%V, W-1%La2O3 and W-4%V-1%La2O3. Todos ellos, adem��s del wolframio puro se fabrican mediante compresi��n isost��tica en caliente (HIP) y son suministradas por la Universidad Carlos III de Madrid. La investigaci��n se desarrolla a trav��s de un estudio sistem��tico basado en ensayos f��sicos y mec��nicos, as�� como el an��lisis post mortem de las muestras ensayadas. Para realizar dicha caracterizaci��n mec��nica se aplican diferentes ensayos mec��nicos, la mayor��a de ellos realizados en el intervalo de temperatura de 25 a 1000 �� C. Los ensayos de caracterizaci��n que se llevan a cabo son: ��� Densidad ��� Dureza Vicker ��� M��dulo de elasticidad y su evoluci��n con la temperatura ��� L��mite el��stico o resistencia a la flexi��n m��xima, y su evoluci��n con la temperatura ��� Resistencia a la fractura y su comportamiento con la temperatura. ��� An��lisis microestructural ��� An��lisis fractogr��fico ��� An��lisis de la relaci��n microestructura-comportamiento macrosc��pico. El estudio comienza con una introducci��n acerca de los sistemas en los que estos materiales son candidatos para su aplicaci��n, para comprender las condiciones a las que los materiales ser��n expuestos. En este caso, el componente que determina las condiciones es el Divertor del reactor de energ��a de fusi��n por confinamiento magn��tico. Parece obvio que su uso en los componentes del reactor de fusi��n, m��s exactamente como materiales de cara al plasma (Plasma Facing Components o PFC), hace que estas aleaciones trabajen bajo condiciones de irradiaci��n de neutrones. Adem��s, el hecho de que sean materiales nuevos hace necesario un estudio previo de las caracter��sticas b��sicas que garantice los requisitos m��nimos antes de realizar un estudio m��s complejo. Esto constituye la principal motivaci��n de la presente investigaci��n. La actual crisis energ��tica ha llevado a aunar esfuerzos en el desarrollo de nuevos materiales, t��cnicas y dispositivos para la aplicaci��n en la industria de la energ��a nuclear. El desarrollo de las t��cnicas de producci��n de aleaciones de wolframio, con un punto de fusi��n muy alto, requiere el uso de precursores de sinterizado para lograr densificaciones m��s altas y por lo tanto mejores propiedades mec��nicas. Este es el prop��sito de la adici��n de titanio y vanadio en estas aleaciones. Sin embargo, uno de los principales problemas de la utilizaci��n de wolframio como material estructural es su alta temperatura de transici��n d��ctil-fr��gil. Esta temperatura es caracter��stica de materiales met��licos con estructura c��bica centrada en el cuerpo y depende de varios factores metal��rgicos. El proceso de recristalizaci��n aumenta esta temperatura de transici��n. Los PFC tienen temperaturas muy altas de servicio, lo que facilita la recristalizaci��n del metal. Con el fin de retrasar este proceso, se dispersan part��culas insolubles en el material permitiendo temperaturas de servicio m��s altas. Hasta ahora se ha utilizado ��xidos de torio, lantano e itrio como part��culas dispersas. Para entender c��mo los contenidos en algunos elementos y part��culas de ��xido afectan a las propiedades de wolframio se estudian las aleaciones binarias de wolframio en comparaci��n con el wolframio puro. A su vez estas aleaciones binarias se utilizan como material de referencia para entender el comportamiento de las aleaciones ternarias. Dada la estrecha relaci��n entre las propiedades del material, la estructura y proceso de fabricaci��n, el estudio se completa con un an��lisis fractogr��fico y microgr��fico. El an��lisis fractogr��fico puede mostrar los mecanismos que est��n implicados en el proceso de fractura del material. Por otro lado, el estudio microgr��fico ayudar�� a entender este comportamiento a trav��s de la identificaci��n de las posibles fases presentes. La medida del tama��o de grano es una parte de la caracterizaci��n microestructural. En esta investigaci��n, la medida del tama��o de grano se llev�� a cabo por ataque qu��mico selectivo para revelar el l��mite de grano en las muestras preparadas. Posteriormente las micrograf��as fueron sometidas a tratamiento y an��lisis de im��genes. El documento termina con una discusi��n de los resultados y la compilaci��n de las conclusiones m��s importantes que se alcanzan despu��s del estudio. Actualmente, el desarrollo de nuevos materiales para aplicaci��n en los componentes de cara al plasma contin��a. El estudio de estos materiales ayudar�� a completar una base de datos de caracter��sticas que permita hacer una selecci��n de ellos m��s fiable. The main goal of this dissertation is the mechanical characterization as a function of temperature of nine tungsten alloys containing different amounts of titanium, vanadium and yttrium and lanthanum oxide. The alloys under study were the following ones: W-0.5%Y2O3, W-2%Ti, W-2% Ti-0.5% Y2O3, W-4% Ti-0.5% Y2O3, W-2%V, W- 2%Vmix, W-4%V, W-1%La2O3 and W-4%V-1%La2O3. All of them, besides pure tungsten, were manufactured using a Hot Isostatic Pressing (HIP) process and they were supplied by the Universidad Carlos III de Madrid. The research was carried out through a systematic study based on physical and mechanical tests as well as the post mortem analysis of tested samples. Diverse mechanical tests were applied to perform this characterization; most of them were conducted at temperatures in the range 25-1000 ��C. The following characterization tests were performed: ��� Density ��� Vickers hardness ��� Elastic modulus ��� Yield strength or ultimate bending strength, and their evolution with temperature ��� Fracture toughness and its temperature behavior ��� Microstructural analysis ��� Fractographical analysis ��� Microstructure-macroscopic relationship analysis This study begins with an introduction regarding the systems where these materials could be applied, in order to establish and understand their service conditions. In this case, the component that defines the conditions is the Divertor of magnetic-confinement fusion reactors. It seems obvious that their use as fusion reactor components, more exactly as plasma facing components (PFCs), makes these alloys work under conditions of neutron irradiation. In addition to this, the fact that they are novel materials demands a preliminary study of the basic characteristics which will guarantee their minimum requirements prior to a more complex study. This constitutes the motivation of the present research. The current energy crisis has driven to join forces so as to develop new materials, techniques and devices for their application in the nuclear energy industry. The development of production techniques for tungsten-based alloys, with a very high melting point, requires the use of precursors for sintering to achieve higher densifications and, accordingly, better mechanical properties. This is the purpose of the addition of titanium and vanadium to these alloys. Nevertheless, one of the main problems of using tungsten as structural material is its high ductile-brittle transition temperature. This temperature is characteristic of metallic materials with body centered cubic structure and depends on several metallurgical factors. The recrystallization process increases their transition temperature. Since PFCs have a very high service temperature, this facilitates the metal recrystallization. In order to inhibit this process, insoluble particles are dispersed in the material allowing higher service temperatures. So far, oxides of thorium, lanthanum and yttrium have been used as dispersed particles. Tungsten binary alloys are studied in comparison with pure tungsten to understand how the contents of some elements and oxide particles affect tungsten properties. In turn, these binary alloys are used as reference materials to understand the behavior of ternary alloys. Given the close relationship between the material properties, structure and manufacturing process, this research is completed with a fractographical and micrographic analysis. The fractographical analysis is aimed to show the mechanisms that are involved in the process of the material fracture. Besides, the micrographic study will help to understand this behavior through the identification of present phases. The grain size measurement is a crucial part of the microstructural characterization. In this work, the measurement of grain size was carried out by chemical selective etching to reveal the boundary grain on prepared samples. Afterwards, micrographs were subjected to both treatment and image analysis. The dissertation ends with a discussion of results and the compilation of the most important conclusions reached through this work. The development of new materials for plasma facing components application is still under study. The analysis of these materials will help to complete a database of the features that will allow a more reliable materials selection.

Mechanical characterisation of tungsten-1wt.% yttrium oxide as a function of temperature and atmosphere

This study evaluates the mechanical behaviour of an Y2O3-dispersed tungsten (W) alloy and compares it to a pure W reference material. Both materials were processed via mechanical alloying (MA) and subsequent hot isostatic pressing (HIP). We performed non-standard three-point bending (TPB) tests in both an oxidising atmosphere and vacuum across a temperature range from 77 K, obtained via immersion in liquid nitrogen, to 1473 K to determine the mechanical strength, yield strength and fracture toughness. This research aims to evaluate how the mechanical behaviour of the alloy is affected by oxides formed within the material at high temperatures, primarily from 873 K, when the materials undergo a massive thermal degradation. The results indicate that the alloy is brittle to a high temperature (1473 K) under both atmospheres and that the mechanical properties degrade significantly above 873 K. We also used Vickers microhardness tests and the dynamic modulus by impulse excitation technique (IET) to determine the elastic modulus at room temperature. Moreover, we performed nanoindentation tests to determine the effect of size on the hardness and elastic modulus; however, no significant differences were found. Additionally, we calculated the relative density of the samples to assess the porosity of the alloy. Finally, we analysed the microstructure and fracture surfaces of the tested materials via field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In this way, the relationship between the macroscopic mechanical properties and micromechanisms of failure could be determined based on the temperature and oxides formed

Microstructural and mechanical characterization of tungsten based materials for fusion reactors

El wolframio (W) y sus aleaciones se consideran los mejores candidatos para la construcci��n del divertor en la nueva generaci��n de reactores de fusi��n nuclear. Este componente va a recibir las cargas t��rmicas m��s elevadas durante el funcionamiento del reactor ya que estar�� en contacto directo con el plasma. En los ��ltimos a��os, despu��s de un profundo an��lisis y siguiendo una estrategia de reducci��n de costes, la Organizaci��n de ITER tom�� la decisi��n de construir el divertor integramente de wolframio desde el principio. Por ello, el wolframio no s��lo actuar�� como material en contacto con el plasma (PFM), sino que tambi��n tendr��a aplicaciones estructurales. El wolframio, debido a sus excelentes propiedades termo-f��sicas, cumple todos los requerimientos para ser utilizado como PFM, sin embargo, su inherente fragilidad pone en peligro su uso estructural. Por tanto, uno de los principales objetivos de esta tesis es encontrar una aleaci��n de wolframio con menor fragilidad. Durante ��ste trabajo, se realiz�� la caracterizaci��n microstructural y mec��nica de diferentes materiales basados en wolframio. Sin embargo, ��sta tarea es un reto debido a la peque��a cantidad de material suministrado, su reducido tama��o de grano y fragilidad. Por ello, para una correcta medida de todas las propiedades f��sicas y mec��nicas se utilizaron diversas t��cnicas experimentales. Algunas de ellas se emplean habitualmente como la nanoindentaci��n o los ensayos de flexi��n en tres puntos (TPB). Sin embargo, otras fueron especificamente desarrolladas e implementadas durante el desarrollo de esta tesis como es el caso de la medida real de la tenacidad de fractura en los materiales masivos, o de las medidas in situ de la tenacidad de fractura en las l��minas delgadas de wolframio. Diversas composiciones de aleaciones de wolframio masivas (W-1% Y2O3, W-2% V-0.5% Y2O3, W-4% V-0.5% Y2O3, W-2% Ti-1% La2O3 y W-4% Ti-1% La2O3) se han estudiado y comparado con un wolframio puro producido en las mismas condiciones. Estas aleaciones, producidas por ruta pulvimetal��rgica de aleado mec��nico (MA) y compactaci��n isost��tica en caliente (HIP), fueron microstructural y mec��nicamente caracterizadas desde 77 hasta 1473 K en aire y en alto vac��o. Entre otras propiedades f��sicas y mec��nicas se midieron la dureza, el m��dulo el��stico, la resistencia a flexi��n y la tenacidad de fractura para todas las aleaciones. Finalmente se analizaron las superficies de fractura despu��s de los ensayos de TPB para relacionar los micromecanismos de fallo con el comportamiento macrosc��pico a rotura. Los resultados obtenidos mostraron un comportamiento mec��nico fr��gil en casi todo el intervalo de temperaturas y para casi todas las aleaciones sin mejor��a de la temperatura de transici��n d��ctil-fr��gil (DBTT). Con el fin de encontrar un material base wolframio con una DBTT m��s baja se realiz�� tambi��n un estudio, a��n preliminar, de l��minas delgadas de wolframio puro y wolframio dopado con 0.005wt.% potasio (K). ��stas l��minas fueron fabricadas industrialmente mediante sinterizado y laminaci��n en caliente y en fr��o y se sometieron posteriormente a un tratamiento t��rmico de recocido desde 1073 hasta 2673 K. Se ha analizado la evoluci��n de su microestructura y las propiedades mec��nicas al aumentar la temperatura de recocido. Los resultados mostraron la estabilizaci��n de los granos de wolframio con el incremento de la temperatura de recocido en las l��minas delgadas de wolframio dopado con potasio. Sin embargo, es necesario realizar estudios adicionales para entender mejor la microstructura y algunas propiedades mec��nicas de estos materiales, como la tenacidad de fractura. Tungsten (W) and tungsten-based alloys are considered to be the best candidate materials for fabricating the divertor in the next-generation nuclear fusion reactors. This component will experience the highest thermal loads during the operation of a reactor since it directly faces the plasma. In recent years, after thorough analysis that followed a strategy of cost reduction, the ITER Organization decided to built a full-tunsgten divertor before the first nuclear campaigns. Therefore, tungsten will be used not only as a plasma-facing material (PFM) but also in structural applications. Tungsten, due to its the excellent thermo-physical properties fulfils the requirements of a PFM, however, its use in structural applications is compromised due to its inherent brittleness. One of the objectives of this phD thesis is therefore, to find a material with improved brittleness behaviour. The microstructural and mechanical characterisation of different tunsgten-based materials was performed. However, this is a challenging task because of the reduced laboratory-scale size of the specimens provided, their _ne microstructure and their brittleness. Consequently, many techniques are required to ensure an accurate measurement of all the mechanical and physical properties. Some of the applied methods have been widely used such as nanoindentation or three-point bending (TPB) tests. However, other methods were specifically developed and implemented during this work such as the measurement of the real fracture toughness of bulk-tunsgten alloys or the in situ fracture toughness measurements of very thin tungsten foils. Bulk-tunsgten materials with different compositions (W-1% Y2O3, W-2% V- 0.5% Y2O3, W-4% V-0.5% Y2O3, W-2% Ti-1% La2O3 and W-4% Ti-1% La2O3) were studied and compared with pure tungsten processed under the same conditions. These alloys, produced by a powder metallurgical route of mechanical alloying (MA) and hot isostatic pressing (HIP), were microstructural and mechanically characterised from 77 to 1473 K in air and under high vacuum conditions. Hardness, elastic modulus, flexural strength and fracture toughness for all of the alloys were measured in addition to other physical and mechanical properties. Finally, the fracture surfaces after the TPB tests were analysed to correlate the micromechanisms of failure with the macroscopic behaviour. The results reveal brittle mechanical behaviour in almost the entire temperature range for the alloys and micromechanisms of failure with no improvement in the ductile-brittle transition temperature (DBTT). To continue the search of a tungsten material with lowered DBTT, a preliminary study of pure tunsgten and 0.005 wt.% potassium (K)-doped tungsten foils was also performed. These foils were industrially produced by sintering and hot and cold rolling. After that, they were annealed from 1073 to 2673 K to analyse the evolution of the microstructural and mechanical properties with increasing annealing temperature. The results revealed the stabilisation of the tungsten grains with increasing annealing temperature in the potassium-doped tungsten foil. However, additional studies need to be performed to gain a better understanding of the microstructure and mechanical properties of these materials such as fracture toughness.

Dise��o y s��ntesis de materiales nanoestructurados basados en aluminatos de estroncio con propiedades fotoluminiscentes

Durante la ��ltima d��cada, se han llevado acabo numeroso estudios sobre la s��ntesis de materiales fotoluminiscentes sub-micr��nicos, en gran medida, al amplio n��mero de aplicaciones que demandan este tipo de materiales. En concreto dentro de los materiales fosforescentes o tambi��n denominados materiales con una prolongada persistencia de la luminiscencia, los estudios se han enfocado en la matriz de SrAl2O4 dopada con Europio (Eu2+) y Disprosio (Dy3+) dado que tiene mayor estabilidad y persistencia de la fosforescencia con respecto a otras matrices. Estos materiales se emplean mayoritariamente en pinturas luminiscentes, tintas, se��alizaci��n de seguridad p��blica, cer��micas, relojes, textiles y juguetes fosforescentes. Dado al amplio campo de aplicaci��n de los SrAl2O4:Eu, Dy, se han investigado m��ltiples rutas de s��ntesis como la ruta sol-gel, la s��ntesis hidrotermal, la s��ntesis por combusti��n, la s��ntesis l��ser y la s��ntesis en estado s��lido con el fin de desarrollar un m��todo eficiente y que sea f��cilmente escalable. Sin embargo, en la actualidad el m��todo que se emplea para el procesamiento a nivel industrial de los materiales basados en aluminato de estroncio es la s��ntesis por estado s��lido, que requiere de temperaturas de entre 1300 a 1900oC y largos tiempos de procesamiento. Adem��s el material obtenido tiene un tama��o de part��cula de 20 a 100 ��m; siendo este tama��o restrictivo para el empleo de este tipo de material en determinadas aplicaciones. Por tanto, el objetivo de este trabajo es el desarrollo de nuevas estrategias que solventen las actuales limitaciones. Dentro de este marco se plantean una serie de objetivos espec��ficos: Estudio de los par��metros que gobiernan los procesos de reducci��n del tama��o de part��cula mediante molienda y su relaci��n en la respuesta fotoluminiscente. Estudio de la s��ntesis por combusti��n de SrAl2O4:Eu, Dy, evaluando el efecto de la temperatura y la cantidad de combustible (urea) en el proceso para la obtenci��n de part��culas cristalinas minimizando la presencia de fases secundarias. Desarrollo de nuevas rutas de s��ntesis de SrAl2O4:Eu, Dy empleando el m��todo de sales fundidas. Determinaci��n de los mecanismos de reacci��n en presencia de la sal fundida en funci��n de los par��metros de proceso que comprende la relaci��n de sales y reactivos, la naturaleza de la al��mina y su tama��o, la temperatura y atm��sfera de tratamiento. Mejora de la eficiencia de los procesos de s��ntesis para obtener productos con propiedades finales ��ptimas en procesos factibles industrialmente para su transferencia tecnol��gica. Es este trabajo han sido evaluados los efectos de diferentes procesos de molienda para la reducci��n del tama��o de part��cula del material de SrAl2O4:Eu, Dy comercial. En el proceso de molienda en medio h��medo por atrici��n se observa la alteraci��n de la estructura cristalina del material debido a la reacci��n de hidr��lisis generada incluso empleando como medio l��quido etanol absoluto. Con el fin de solventar las desventajas de la molienda en medio h��medo se llevo a cabo un estudio de la molturaci��n en seco del material. La molturaci��n en seco de alta energ��a reduce significativamente el tama��o medio de part��cula. Sin embargo, procesos de molienda superiores a una duraci��n de 10 minutos ocasionan un aumento del estado de aglomeraci��n de las part��culas y disminuyen dr��sticamente la respuesta fotoluminiscente del material. Por tanto, se lleva a cabo un proceso de molienda en seco de baja energ��a. Mediante este m��todo se consigue reducir el tama��o medio de part��cula, d50=2.8 ��m, y se mejora la homogeneidad de la distribuci��n del tama��o de part��cula evitando la amorfizaci��n del material. A partir de los resultados obtenidos mediante difracci��n de rayos X y microscopia electr��nica de barrido se infiere que la disminuci��n de la intensidad de la fotoluminiscencia despu��s de la molienda en seco de alta energ��a con respecto al material inicial se debe principalmente a la reducci��n del tama��o de cristalito. Se observan menores variaciones en la intensidad de la fotoluminiscencia cuando se emplea un m��todo de molienda de baja de energ��a ya que en estos procesos se preserva el dominio cristalino y se reduce la amorfizaci��n significativamente. Estos resultados corroboran que la intensidad de la fotoluminiscencia y la persistencia de la luminiscencia de los materiales de SrAl2O4:Eu2+, Dy3+ dependen extr��nsecamente de la morfolog��a de las part��culas, del tama��o de part��cula, el tama��o de grano, los defectos superficiales e intr��nsecamente del tama��o de cristalito. Siendo las caracter��sticas intr��nsecas las que dominan con respecto a las extr��nsecas y por tanto tienen mayor relevancia en la respuesta fotoluminiscente. Mediante s��ntesis por combusti��n se obtuvieron l��minas nanoestructuradas de SrAl2O4:Eu, Dy de ���1 ��m de espesor. La cantidad de combustible, urea, en la reacci��n influye significativamente en la formaci��n de determinadas fases cristalinas. Para la s��ntesis del material de SrAl2O4:Eu, Dy es necesario incluir un contenido de urea mayor que el estequiom��trico (siendo m=1 la relaci��n estequiom��trica). La incorporaci��n de un exceso de urea (m>1) requiere de la presencia de un agente oxidante interno, HNO3, para que la reacci��n tenga lugar. El empleo de un mayor contenido de urea como combustible permite una quelaci��n efectiva de los cationes en el sistema y la creaci��n de las condiciones reductoras para obtener un material de mayor cristalinidad y con mejores propiedades fotoluminiscentes. El material de SrAl2O4:Eu, Dy sintetizado a una temperatura de ignici��n de 600oC tiene un tama��o medio 5-25 ��m con un espesor de ���1 ��m. Mediante procesos de molturaci��n en seco de baja energ��a es posible disminuir el tama��o medio de part��cula ���2 ��m y homogenizar la distribuci��n del tama��o de part��cula pero hay un deterioro asociado de la respuesta luminiscente. Sin embargo, se puede mejorar la respuesta fotoluminiscente empleando un tratamiento t��rmico posterior a 900oC N2-H2 durante 1 hora que no supone un aumento del tama��o de part��cula pero si permite aumentar el tama��o de cristalito y la reducci��n del Eu3+ a Eu2+. Con respecto a la respuesta fotoluminiscente, se obtiene valores de la intensidad de la fotoluminiscencia entre un 35%-21% con respecto a la intensidad de un material comercial de referencia. Adem��s la intensidad inicial del decaimiento de la fosforescencia es un 20% de la intensidad del material de referencia. Por tanto, teniendo en cuenta estos resultados, es necesario explorar otros m��todos de s��ntesis para la obtenci��n de los materiales bajo estudio. Por esta raz��n, en este trabajo se desarrollo una ruta de s��ntesis novedosa para sintetizar SrAl2O4:Eu, Dy mediante el m��todo de sales fundidas para la obtenci��n de materiales de gran cristalinidad con tama��os de cristalito del orden nanom��trico. Se empleo como sal fundente la mezcla eut��ctica de NaCl y KCl, denominada (NaCl-KCl)e. La principal ventaja de la incorporaci��n de la mezcla es el incremento la reactividad del sistema, reduciendo la temperatura de formaci��n del SrAl2O4 y la duraci��n del tratamiento t��rmico en comparaci��n con la s��ntesis en estado s��lido. La formaci��n del SrAl2O4 es favorecida ya que se aumenta la difusi��n de los cationes de Sr2+ en el medio l��quido. Se emplearon diferentes tipos de Al2O3 para evaluar el papel del tama��o de part��cula y su naturaleza en la reacci��n asistida por sales fundidas y por tanto en la morfolog��a y propiedades del producto final. Se obtuvieron part��culas de morfolog��a pseudo-esf��rica de tama��o ���0.5 ��m al emplear como al��mina precursora part��culas sub-micr��nicas ( 0.5 ��m Al2O3, 0.1 ��m Al2 O3 y ��-Al2O3). El mecanismo de reacci��n que tiene lugar se asocia a procesos de disoluci��n-precipitaci��n que dominan al emplear part��culas de al��mina peque��as y reactivas. Mientras al emplear una al��mina de 6 ��m Al2O3 prevalecen los procesos de crecimiento cristalino siguiendo un patr��n o plantilla debido a la menor reactividad del sistema. La nucleaci��n y crecimiento de nanocristales de SrAl2O4:Eu, Dy se genera sobre la superficie de la al��mina que act��a como soporte. De esta forma se desarrolla una estructura del tipo coraza-n��cleo (��core-shell�� en ingl��s) donde la superficie externa est�� formada por los cristales fosforescentes de SrAl2O4 y el n��cleo est�� formado por al��mina. Las part��culas obtenidas tienen una respuesta fotoluminiscente diferente en funci��n de la morfolog��a final obtenida. La optimizaci��n de la relaci��n Al2O3/SrO del material de SrAl2O4:Eu, Dy sintetizado a partir de la al��mina de 6 ��m permite reducir las fases secundarias y la concentraci��n de dopantes manteniendo la respuesta fotoluminiscente. Comparativamente con un material comercial de SrAl2O4:Eu, Dy de referencia, se han alcanzado valores de la intensidad de la emisi��n de hasta el 90% y de la intensidad inicial de las curvas de decaimiento de la luminiscencia de un 60% para el material sintetizado por sales fundidas que tiene un tama��o medio ��� 10��m. Por otra parte, es necesario tener en cuenta que el SrAl2O4 tiene dos polimorfos, la fase monocl��nica que es estable a temperaturas inferiores a 650oC y la fase hexagonal, fase de alta temperatura, estable a temperaturas superiores de 650oC. Se ha determinado que fase monocl��nica presenta propiedades luminiscentes, sin embargo existen discordancias a cerca de las propiedades luminiscentes de la fase hexagonal. Mediante la s��ntesis por sales fundidas es posible estabilizar la fase hexagonal empleando como al��mina precursora ��-Al2O3 y un exceso de Al2O3 (Al2O3/SrO:2). La estabilizaci��n de la fase hexagonal a temperatura ambiente se produce cuando el tama��o de los cristales de SrAl2O4 es ���20 nm. Adem��s se observ�� que la fase hexagonal presenta respuesta fotoluminiscente. El dise��o de materiales de SrAl2O4:Eu,Dy nanoestructurados permite modular la morfolog��a del material y por tanto la intensidad de la de la fotoluminiscencia y la persistencia de la luminiscencia. La disminuci��n de los materiales precursores, la temperatura y el tiempo de tratamiento significa la reducci��n de los costes econ��micos del material. De ah�� la viabilidad de los materiales de SrAl2O4:Eu,Dy obtenidos mediante los procesos de s��ntesis propuestos en esta memoria de tesis para su posterior escalado industrial. ABSTRACT The synthesis of sub-micron photoluminescent particles has been widely studied during the past decade because of the promising industrial applications of these materials. A large number of matrices has been developed, being SrAl2O4 host doped with europium (Eu2+) and dysprosium (Dy3+) the most extensively studied, because of its better stability and long-lasting luminescence. These functional inorganic materials have a wide field of application in persistent luminous paints, inks and ceramics. Large attention has been paid to the development of an efficient method of preparation of SrAl2O4 powders, including solgel method, hydrothermal synthesis, laser synthesis, combustion synthesis and solid state reaction. Many of these techniques are not compatible with large-scale production and with the principles of sustainability. Moreover, industrial processing of highly crystalline powders usually requires high synthesis temperatures, typically between 1300 a 1900oC, with long processing times, especially for solid state reaction. As a result, the average particle size is typically within the 20-100 ��m range. This large particle size is limiting for current applications that demand sub-micron particles. Therefore, the objective of this work is to develop new approaches to overcome these limitations. Within this frame, it is necessary to undertake the following purposes: To study the parameters that govern the particle size reduction by milling and their relation with the photoluminescence properties. To obtain SrAl2O4:Eu, Dy by combustion synthesis, assessing the effect of the temperature and the amount of fuel (urea) to synthesize highly crystalline particles minimizing the presence of secondary phases. To develop new synthesis methods to obtain SrAl2O4:Eu, Dy powders. The molten salt synthesis has been proposed. As the method is a novel route, the reaction mechanism should be determine as a function of the salt mixture, the ratio of the salt, the kind of Al2O3 and their particle size and the temperature and the atmosphere of the thermal treatment. To improve the efficiency of the synthesis process to obtain SrAl2O4:Eu, Dy powders with optimal final properties and easily scalable. On the basis of decreasing the particle size by using commercial product SrAl2O4:Eu2+, Dy3+ as raw material, the effects of different milling methods have been evaluated. Wet milling can significantly alter the structure of the material through hydrolysis reaction even in ethanol media. For overcoming the drawbacks of wet milling, a dry milling-based processes are studied. High energy dry milling process allows a great reduction of the particle size, however milling times above 10 min produce agglomeration and accelerates the decrease of the photoluminescence feature. To solve these issues the low energy dry milling process proposed effectively reduces the particle size to d50=2.8 ��m, and improves the homogeneity avoiding the amorphization in comparison with previous methods. The X-ray diffraction and scanning electron microscope characterization allow to infer that the large variations in PL (Photoluminescence) values by high energy milling process are a consequence mainly of the crystallite size reduction. The lesser variation in PL values by low energy milling proces is related to the coherent crystalline domain preservation and the unnoticeable amorphization. These results corroborate that the photoluminescence intensity and the persistent luminescence of the SrAl2O4:Eu2+, Dy3+ powders depend extrinsically on the morphology of the particles such as particle size, grain size, surface damage and intrinsically on the crystallinity (crystallite size); being the intrinsically effects the ones that have a significant influence on the photoluminescent response. By combustion method, nanostructured SrAl2O4:Eu2+, Dy3+ sheets with a thickness ���1 ��m have been obtained. The amount of fuel (urea) in the reaction has an important influence on the phase composition; urea contents larger than the stoichiometric one require the presence of an oxidant agent such as HNO3 to complete the reaction. A higher amount of urea (excess of urea: denoted m>1, being m=1 the stoichiometric composition) including an oxidizing agent produces SrAl2O4:Eu2+,Dy3+ particles with persistent luminescence due to the effective chelation of the cations and the creation of suitable atmospheric conditions to reduce the Eu3+ to Eu2+. Therefore, optimizing the synthesis parameters in combustion synthesis by using a higher amount of urea and an internal oxidizing agent allows to complete the reaction. The amount of secondary phases can be significantly reduced and the photoluminescence response can be enhanced. This situation is attributed to a higher energy that improves the crystallinity of the powders. The powders obtained have a particle size c.a. 5-25 ��m with a thickness ���1 ��m and require relatively low ignition temperatures (600oC). It is possible to reduce the particle size by a low energy dry milling but this process implies the decrease of the photoluminescent response. However, a post-thermal treatment in a reducing atmosphere allows the improvement of the properties due to the increment of crystallinity and the reduction of Eu3+ to Eu2+. Compared with the powder resulted from solid state method (commercial reference: average particle size, 20 ��m and heterogeneous particle size distribution) the emission intensity of the powder prepared by combustion method achieve the values between 35% to 21% of the reference powder intensity. Moreover, the initial intensity of the decay curve is 20% of the intensity of the reference powder. Taking in account these results, it is necessary to explore other methods to synthesize the powders For that reason, an original synthetic route has been developed in this study: the molten salt assisted process to obtain highly crystalline SrAl2O4 powders with nanometric sized crystallites. The molten salt was composed of a mixture of NaCl and KCl using a 0.5:0.5 molar ratio (eutectic mixture hereafter abbreviated as (NaCl-KCl)e). The main advantages of salt addition is the increase of the reaction rate, the significant reduction of the synthesis temperature and the duration of the thermal treatment in comparison with classic solid state method. The SrAl2O4 formation is promoted due to the high mobility of the Sr2+ cations in the liquid medium. Different kinds of Al2O3 have been employed to evaluate the role of the size and the nature of this precursor on the kinetics of reaction, on the morphology and the final properties of the product. The SrAl2O4:Eu2+, Dy3+ powders have pseudo-spherical morphology and particle size ���0.5 ��m when a sub-micron Al2O3 ( 0.5 ��m Al2O3, 0.1 ��m Al2O3 and ��-Al2O3) has been used. This can be attributed to a higher reactivity in the system and the dominance of dissolution-precipitation mechanism. However, the use of larger alumina (6 ��m Al2O3) modifies the reaction pathway leading to a different reaction evolution. More specifically, the growth of SrAl2O4 sub-micron particles on the surface of hexagonal platelets of 6��m Al2O3 is promoted. The particles retain the shape of the original Al2O3 and this formation process can be attributed to a ��core-shell�� mechanism. The particles obtained exhibit different photoluminescent response as a function of the final morphology of the powder. Therefore, through this study, it has been elucidated the reaction mechanisms of SrAl2O4 formation assisted by (NaCl-KCl)e that are governed by the diffusion of SrCO3 and the reactivity of the alumina particles. Optimizing the Al2O3/SrO ratio of the SrAl2O4:Eu, Dy powders synthesized with 6 ��m Al2O3 as a precursor, the secondary phases and the concentration of dopant needed can be reduced keeping the photoluminescent response of the synthesized powder. Compared with the commercial reference powder, up to 90% of the emission intensity of the reference powder has been achieved for the powder prepared by molten salt method using 6��m Al2O3 as alumina precursor. Concerning the initial intensity of the decay curve, 60% of the initial intensity of the reference powder has been obtained. Additionally, it is necessary to take into account that SrAl2O4 has two polymorphs: monoclinic symmetry that is stable at temperatures below 650oC and hexagonal symmetry that is stable above this temperature. Monoclinic phase shows luminescent properties. However, there is no clear agreement on the emission of the hexagonal structure. By molten salt, it is possible to stabilize the hexagonal phase of SrAl2O4 employing an excess of Al2O3 (Al2O3/SrO: 2) and ��-Al2O3 as a precursor. The existence of nanometric crystalline domains with lower size (���20 nm) allows the stabilization of the hexagonal phase. Moreover, it has been evidenced that the hexagonal polymorph exhibits photoluminescent response. To sum up, the design of nanostructured SrAl2O4:Eu2+, Dy3+ materials allows to obtain different morphologies and as consequence different photoluminescent responses. The reduction of temperature, duration of the thermal treatment and the precursors materials needed imply the decrease of the economic cost of the material. Therefore, the viability, suitability and scalability of the synthesis strategy developed in this work to process SrAl2O4:Eu2+, Dy3+ are demonstrated.

Relationship between residual stresses and mechanical behavior in ceramic composites

En este trabajo, materiales de tipo al��mina/Y-TZP (ZrO2 tetragonal, estabilizada con 3 mol. % Y2O3), como sistema cer��mico popular por sus mejoradas propiedades mec��nicas en comparaci��n con las cer��micas de al��mina puras, han sido estudiados en t��rminos de propiedades mec��nicas y tensiones residuales. El novedoso m��todo de colado en cinta, consistente en el apilamiento de cintas de cer��mica verde a temperatura ambiente y el uso de bajas presiones, se ha escogido para la presente investigaci��n con el fin de poder aprovechar al m��ximo el futuro desarrollo de materiales laminados de al��mina-��xido de circonio. Se han determinado las propiedades de los materiales obtenidos por este nuevo m��todo de procesamiento compar��ndolas con las de los materiales obtenidos por ���slip casting���, con el fin de analizar si el m��todo propuesto afecta a la microestructura y, por tanto, a las propiedades mec��nicas y tensiones residuales propias de estos materiales. Para analizar la idoneidad del proceso de fabricaci��n, utilizado para evitar la presencia de discontinuidades en las intercaras entre las l��minas as�� como otros fen��menos que puedan interferir con las propiedades mec��nicas, se estudiaron materiales cer��micos con la misma composici��n en cintas. Por otra parte tambi��n se analiz�� el efecto de la adici��n de ��xido de circonio sobre la aparici��n de tensi��nes residuales en cer��micas Al2O3/Y-TZP, teniendo en cuenta su notable influencia sobre las propiedades microestructurales y mec��nicas de los materiales, as�� como el requisito de co-sinterizaci��n de capas con diferentes materiales compuestos en materiales laminados. La caracterizaci��n del material incluye la determinaci��n de la densidad, el an��lisis de la microestructura, la obtenci��n de las propiedades mec��nicas (m��dulo de elasticidad, dureza, resistencia a la flexi��n y tenacidad de fractura) as�� como de las tensiones residuales. En combinaci��n con otros m��todos de medida tradicionales, la nanoindentaci��n tambi��n se emple�� como una t��cnica adicional para la medida del m��dulo de elasticidad y de la dureza. Por otro lado, diferentes t��cnicas de difracci��n con neutrones, tanto las basadas en longitud de onda constante (CW) como en tiempo de vuelo (TOF), han sido empleadas para la medici��n fiable de la deformaci��n residual a trav��s del grosor en muestras a granel. Las tensiones residuales fueron determinadas con elevada precisi��n, aplicando adem��s m��todos de an��lisis apropiados, como por ejemplo el refinamiento de Rietveld. Las diferentes fases en cer��micas sinterizadas, especialmente las de zirconia, se examinaron con detalle mediante el an��lisis de Rietveld, teniendo en cuenta el complicado polimorfismo del ��xido de Zirconio (ZrO2) as�� como las posibles transformaciones de fase durante el proceso de fabricaci��n. Los efectos del contenido de Y-TZP en combinaci��n con el nuevo m��todo de procesamiento sobre la microestructura, el rendimiento mec��nico y las tensiones residuales de los materiales estudiados (Al2O3/Y-TZP) se resumen en el presente trabajo. Finalmente, los mecanismos de endurecimiento, especialmente los relacionados con las tensiones residuales, son igualmente discutidos. In present work, Alumina/Y-TZP (tetragonal ZrO2 stabilized with 3 mol% Y2O3) materials, as an popular ceramic system with improved mechanical properties compared with the pure alumina ceramics, have been studied in terms of mechanical properties and residual stresses. The novel tape casting method, which involved the stacking of green ceramics tapes at room temperature and using low pressures, is selected for manufacturing and investigation, in order to take full advantage of the future development of alumina-zirconia laminated materials. Features of materials obtained by the new processing method are determined and compared with those of materials obtained by conventional slip casting in a plaster mold, in order to study whether the proposed method of processing affects microstructure and thereby the mechanical properties and residual stresses characteristics of materials. To analyse the adequacy of the manufacturing process used to avoid the presence of discontinuities at the interfaces between the sheets and other phenomena that interfere with the mechanical properties, ceramic materials with the same composition in tapes were investigated. Moreover, the effect of addition of zirconia on residual stress development of Al2O3/Y-TZP ceramics were taken into investigations, considering its significantly influence on the microstructure and mechanical properties of materials as well as the requirement of co-sintering of layers with different composites in laminated materials. The characterization includes density, microstructure, mechanical properties (elastic modulus, hardness, flexure strength and fracture toughness) and residual stresses. Except of the traditional measurement methods, nanoindentation technique was also used as an additional measurement of the elastic modulus and hardness. Neutron diffraction, both the constant-wavelength (CW) and time-of-flight (TOF) neutron diffraction techniques, has been used for reliable through-thickness residual strain measurement in bulk samples. Residual stresses were precisely determined combined with appropriate analysis methods, e.g. the Rietveld refinement. The phase compositions in sintered ceramics especially the ones of zirconia were accurately examined by Rietveld analysis, considering the complex polymorph of ZrO2 and the possible phase transformation during manufacturing process. Effects of Y-TZP content and the new processing method on the microstructure, mechanical performance and residual stresses were finally summarized in present studied Al2O3/Y-TZP materials. The toughening mechanisms, especially the residual stresses related toughening, were theoretically discussed.

Desenvolvimento de materiais nanoestruturados �� base de SiO2-Nb2O5 preparados por uma nova rota sol-gel com aplica����es em fot��nica

Este trabalho concentra-se na prepara����o e caracteriza����es estrutural e espectrosc��pica de materiais nanoestruturados �� base de SiO2-Nb2O5 dopados e codopados com ��ons Er3+, Yb3+ e Eu3+ na forma de p��s e guias de onda planares. Os nanocomp��sitos foram preparados atrav��s de uma nova rota sol-gel utilizando ��xido de ni��bio como precursor em substitui����o ao alc��xido de ni��bio. A correla����o estrutura propriedades luminescentes foi estudada por difra����o de raios X, microscopia eletr��nica de transmiss��o, espectroscopia vibracional de absor����o no infravermelho, espectroscopia vibracional de espalhamento Raman, an��lise t��rmica, reflect��ncia difusa e especular, espectroscopia de fotoluminesc��ncia e acoplamento M-line. Inicialmente foi avaliado a influ��ncia da concentra����o de ni��bio nas propriedades estruturais e luminescentes de nanocomp��sitos (100-x)Si-xNb dopados e codopados com ��ons Er3+, Yb3+ e Eu3+ tratados termicamente a 900 ��C por 3h. A cristaliza����o do Nb2O5 foi dependente da concentra����o de Nb na matriz, com a distribui����o dos ��ons lantan��deos preferencialmente no Nb2O5, afetando as propriedades luminescentes. Para os nanocomp��sitos codopados com ��ons Er3+ e Yb3+ foram obtidos valores de largura de banda a meia altura (FWHM) da ordem de 70 nm na regi��o de 1550 nm e tempos de vida de at�� 5,2 ms. A emiss��o na regi��o do vis��vel, decorrente de processos de convers��o ascendente, revelou-se dependente da concentra����o de ni��bio. Foi verificada emiss��o preferencial na regi��o do verde para menores concentra����es de Nb. Enquanto que, para as maiores concentra����es, processos de relaxa����o cruzada levaram a um aumento relativo na intensidade de emiss��o na regi��o do vermelho. A efici��ncia qu��ntica de emiss��o dos nanocomp��sitos (100-x)Si-xNb dopados com Eu3+ variou com o comprimento de onda de excita����o, refletindo os diferentes s��tios de simetria ocupados por este ��ons nesta estrutura complexa. A influ��ncia da temperatura de tratamento t��rmico no processo de cristaliza����o do Nb2O5 em nanocomp��sitos 70Si:30Nb codopados com ��ons Er3+ e Yb3+ foi avaliada. Material amorfo foi obtido a 700 ��C enquanto que a 900 e 1100 ��C foram identificas as fases ortorr��mbica (fase T) e monocl��nica (fase M) do Nb2O5. Intensa emiss��o na regi��o de 1550 nm com valores de FWHM de 52 e 67 nm e tempos de vida de 5,6 e 5,4 ms foram verificados a 700 e 900 ��C sob excita����o em 977 nm, respectivamente. Por fim, foram obtidos guias de onda planares com excelentes propriedades ��pticas e com grande potencial de aplica����o em dispositivos de amplifica����o ��ptica. Especificamente, materiais fot��nicos com banda larga de emiss��o na regi��o do infravermelho foram preparados, indicando fortemente a potencialidade para a aplica����o em telecomunica����es envolvendo n��o somente a banda C como tamb��m as bandas L e S em materiais contendo somente ��ons Er3+ como centros emissores.

Enhanced glass-forming ability of a Zr-based bulk metallic glass with yttrium doping

A significant enhancement in glass formation in a newly developed Zr51Cu20.7Ni12Al16.3 alloy has been achieved by yttrium doping. With just 0.5 at.% yttrium doping, the critical diameter of the as-cast alloys for glass formation has been increased from 3 mm to at least 10 mm. In the undoped, large-sized alloys, massive oxygen stabilized crystalline phases are observed but disappear in yttrium doped alloys. Very small amounts of stable alpha-Y2O3 phases found in the yttrium doped alloys, and their negligible effect on the metallic glasses' properties, provide a superior solution to achieve metallic glasses with a high glass formability. (c) 2006 Elsevier B.V. All rights reserved.

Structure and thermal properties of yttrium alumino-phosphate glasses

The structure and thermal properties of yttrium alumino-phosphate glasses, of nominal composition (Y2O3)(0.31-z)(Al2O3)(z)(P2O5)(0.69) with 0 less than or similar to z less than or similar to 0.31, were studied by using a combination of neutron diffraction, Al-27 and P-31 magic angle spinning nuclear magnetic resonance, differential scanning calorimetry and thermal gravimetric analysis methods. The Vickers hardness of the glasses was also measured. The data are compared to those obtained for pseudo-binary Al2O3-P2O5 glasses and the structure of all these materials is rationalized in terms of a generic model for vitreous phosphate materials in which Y3+ and Al3+ act as modifying cations that bind only to the terminal (non-bridging) oxygen atoms of PO4 tetrahedra. The results are used to help elucidate the phenomenon of rare-earth clustering in phosphate glasses which can be reduced by substituting Al3+ ions for rare-earth R3+ ions at fixed modifier content.

Luminescence of delafossite-type CuAlO2 fibers with Eu substitution for Al cations

CuAlO2 has been examined as a potential luminescent material by substituting Eu for Al cations in the delafossite structure. CuAlO2:Eu3+ nanofibers have been prepared via electrospinning for the ease of mitigating synthesis requirements and for future optoelectronics and emerging applications. Single-phase CuAlO2 fibers could be obtained at a temperature of 1100 ��C in air. The Eu was successfully doped in the delafossite structure and two strong emission bands at ~405 and 610 nm were observed in the photoluminescence spectra. These bands are due to the intrinsic near-band-edge transition of CuAlO2 and the f-f transition of the Eu3+ activator, respectively. Further electrical characterization indicated that these fibers exhibit semiconducting behavior and the introduction of Eu could act as band-edge modifiers, thus changing the thermal activation energies. In light of this study, CuAlO2:Eu3+ fibers with both strong photoluminescence and p-type conductivity could be produced by tailoring the rare earth doping concentrations.

Development of Zirconia based phosphors for application in lighting and as luminescent bioprobes

The strong progress evidenced in photonic and optoelectronic areas, accompanied by an exponential development in the nanoscience and nanotechnology, gave rise to an increasing demand for efficient luminescent materials with more and more exigent characteristics. In this field, wide band gap hosts doped with lanthanide ions represent a class of luminescent materials with a strong technological importance. Within wide band gap material, zirconia owns a combination of physical and chemical properties that potentiate it as an excellent host for the aforementioned ions, envisaging its use in different areas, including in lighting and optical sensors applications, such as pressure sensors and biosensors. Following the demand for outstanding luminescent materials, there is also a request for fast, economic and an easy scale-up process for their production. Regarding these demands, laser floating zone, solution combustion synthesis and pulsed laser ablation in liquid techniques are explored in this thesis for the production of single crystals, nanopowders and nanoparticles of lanthanides doped zirconia based hosts. Simultaneously, a detailed study of the morphological, structural and optical properties of the produced materials is made. The luminescent characteristics of zirconia and yttria stabilized zirconia (YSZ) doped with different lanthanide ions (Ce3+ (4f1), Pr3+ (4f2), Sm3+ (4f5), Eu3+ (4f6), Tb3+ (4f8), Dy3+ (4f9), Er3+ (4f11), Tm3+ (4f12), Yb3+ (4f13)) and co-doped with Er3+,Yb3+ and Tm3+,Yb3+ are analysed. Besides the Stokes luminescence, the anti- Stokes emission upon infrared excitation (upconversion and black body radiation) is also analysed and discussed. The comparison of the luminescence characteristics in materials with different dimensions allowed to analyse the effect of size in the luminescent properties of the dopant lanthanide ions. The potentialities of application of the produced luminescent materials in solid state light, biosensors and pressure sensors are explored taking into account their studied characteristics.