Diseño y síntesis de materiales nanoestructurados basados en aluminatos de estroncio con propiedades fotoluminiscentes

Durante la última década, se han llevado acabo numeroso estudios sobre la síntesis de materiales fotoluminiscentes sub-micrónicos, en gran medida, al amplio número de aplicaciones que demandan este tipo de materiales. En concreto dentro de los materiales fosforescentes o también 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, señalización de seguridad pública, cerámicas, relojes, textiles y juguetes fosforescentes. Dado al amplio campo de aplicación de los SrAl2O4:Eu, Dy, se han investigado múltiples rutas de síntesis como la ruta sol-gel, la síntesis hidrotermal, la síntesis por combustión, la síntesis láser y la síntesis en estado sólido con el fin de desarrollar un método eficiente y que sea fácilmente escalable. Sin embargo, en la actualidad el método que se emplea para el procesamiento a nivel industrial de los materiales basados en aluminato de estroncio es la síntesis por estado sólido, que requiere de temperaturas de entre 1300 a 1900oC y largos tiempos de procesamiento. Además el material obtenido tiene un tamaño de partícula de 20 a 100 μm; siendo este tamaño 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 específicos: Estudio de los parámetros que gobiernan los procesos de reducción del tamaño de partícula mediante molienda y su relación en la respuesta fotoluminiscente. Estudio de la síntesis por combustión de SrAl2O4:Eu, Dy, evaluando el efecto de la temperatura y la cantidad de combustible (urea) en el proceso para la obtención de partículas cristalinas minimizando la presencia de fases secundarias. Desarrollo de nuevas rutas de síntesis de SrAl2O4:Eu, Dy empleando el método de sales fundidas. Determinación de los mecanismos de reacción en presencia de la sal fundida en función de los parámetros de proceso que comprende la relación de sales y reactivos, la naturaleza de la alúmina y su tamaño, la temperatura y atmósfera de tratamiento. Mejora de la eficiencia de los procesos de síntesis para obtener productos con propiedades finales óptimas en procesos factibles industrialmente para su transferencia tecnológica. Es este trabajo han sido evaluados los efectos de diferentes procesos de molienda para la reducción del tamaño de partícula del material de SrAl2O4:Eu, Dy comercial. En el proceso de molienda en medio húmedo por atrición se observa la alteración de la estructura cristalina del material debido a la reacción de hidrólisis generada incluso empleando como medio líquido etanol absoluto. Con el fin de solventar las desventajas de la molienda en medio húmedo se llevo a cabo un estudio de la molturación en seco del material. La molturación en seco de alta energía reduce significativamente el tamaño medio de partícula. Sin embargo, procesos de molienda superiores a una duración de 10 minutos ocasionan un aumento del estado de aglomeración de las partículas y disminuyen drásticamente la respuesta fotoluminiscente del material. Por tanto, se lleva a cabo un proceso de molienda en seco de baja energía. Mediante este método se consigue reducir el tamaño medio de partícula, d50=2.8 μm, y se mejora la homogeneidad de la distribución del tamaño de partícula evitando la amorfización del material. A partir de los resultados obtenidos mediante difracción de rayos X y microscopia electrónica de barrido se infiere que la disminución de la intensidad de la fotoluminiscencia después de la molienda en seco de alta energía con respecto al material inicial se debe principalmente a la reducción del tamaño de cristalito. Se observan menores variaciones en la intensidad de la fotoluminiscencia cuando se emplea un método de molienda de baja de energía ya que en estos procesos se preserva el dominio cristalino y se reduce la amorfización significativamente. Estos resultados corroboran que la intensidad de la fotoluminiscencia y la persistencia de la luminiscencia de los materiales de SrAl2O4:Eu2+, Dy3+ dependen extrínsecamente de la morfología de las partículas, del tamaño de partícula, el tamaño de grano, los defectos superficiales e intrínsecamente del tamaño de cristalito. Siendo las características intrínsecas las que dominan con respecto a las extrínsecas y por tanto tienen mayor relevancia en la respuesta fotoluminiscente. Mediante síntesis por combustión se obtuvieron láminas nanoestructuradas de SrAl2O4:Eu, Dy de ≤1 μm de espesor. La cantidad de combustible, urea, en la reacción influye significativamente en la formación de determinadas fases cristalinas. Para la síntesis del material de SrAl2O4:Eu, Dy es necesario incluir un contenido de urea mayor que el estequiométrico (siendo m=1 la relación estequiométrica). La incorporación de un exceso de urea (m>1) requiere de la presencia de un agente oxidante interno, HNO3, para que la reacción tenga lugar. El empleo de un mayor contenido de urea como combustible permite una quelación efectiva de los cationes en el sistema y la creación 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 ignición de 600oC tiene un tamaño medio 5-25 μm con un espesor de ≤1 μm. Mediante procesos de molturación en seco de baja energía es posible disminuir el tamaño medio de partícula ≈2 μm y homogenizar la distribución del tamaño de partícula pero hay un deterioro asociado de la respuesta luminiscente. Sin embargo, se puede mejorar la respuesta fotoluminiscente empleando un tratamiento térmico posterior a 900oC N2-H2 durante 1 hora que no supone un aumento del tamaño de partícula pero si permite aumentar el tamaño de cristalito y la reducción 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. Además 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 métodos de síntesis para la obtención de los materiales bajo estudio. Por esta razón, en este trabajo se desarrollo una ruta de síntesis novedosa para sintetizar SrAl2O4:Eu, Dy mediante el método de sales fundidas para la obtención de materiales de gran cristalinidad con tamaños de cristalito del orden nanométrico. Se empleo como sal fundente la mezcla eutéctica de NaCl y KCl, denominada (NaCl-KCl)e. La principal ventaja de la incorporación de la mezcla es el incremento la reactividad del sistema, reduciendo la temperatura de formación del SrAl2O4 y la duración del tratamiento térmico en comparación con la síntesis en estado sólido. La formación del SrAl2O4 es favorecida ya que se aumenta la difusión de los cationes de Sr2+ en el medio líquido. Se emplearon diferentes tipos de Al2O3 para evaluar el papel del tamaño de partícula y su naturaleza en la reacción asistida por sales fundidas y por tanto en la morfología y propiedades del producto final. Se obtuvieron partículas de morfología pseudo-esférica de tamaño ≤0.5 μm al emplear como alúmina precursora partículas sub-micrónicas ( 0.5 μm Al2O3, 0.1 μm Al2 O3 y γ-Al2O3). El mecanismo de reacción que tiene lugar se asocia a procesos de disolución-precipitación que dominan al emplear partículas de alúmina pequeñas y reactivas. Mientras al emplear una alúmina de 6 μm Al2O3 prevalecen los procesos de crecimiento cristalino siguiendo un patrón o plantilla debido a la menor reactividad del sistema. La nucleación y crecimiento de nanocristales de SrAl2O4:Eu, Dy se genera sobre la superficie de la alúmina que actúa como soporte. De esta forma se desarrolla una estructura del tipo coraza-núcleo («core-shell» en inglés) donde la superficie externa está formada por los cristales fosforescentes de SrAl2O4 y el núcleo está formado por alúmina. Las partículas obtenidas tienen una respuesta fotoluminiscente diferente en función de la morfología final obtenida. La optimización de la relación Al2O3/SrO del material de SrAl2O4:Eu, Dy sintetizado a partir de la alúmina de 6 μm permite reducir las fases secundarias y la concentración 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 emisión 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 tamaño medio ≤ 10μm. Por otra parte, es necesario tener en cuenta que el SrAl2O4 tiene dos polimorfos, la fase monoclínica 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 monoclínica presenta propiedades luminiscentes, sin embargo existen discordancias a cerca de las propiedades luminiscentes de la fase hexagonal. Mediante la síntesis por sales fundidas es posible estabilizar la fase hexagonal empleando como alúmina precursora γ-Al2O3 y un exceso de Al2O3 (Al2O3/SrO:2). La estabilización de la fase hexagonal a temperatura ambiente se produce cuando el tamaño de los cristales de SrAl2O4 es ≤20 nm. Además se observó que la fase hexagonal presenta respuesta fotoluminiscente. El diseño de materiales de SrAl2O4:Eu,Dy nanoestructurados permite modular la morfología del material y por tanto la intensidad de la de la fotoluminiscencia y la persistencia de la luminiscencia. La disminución de los materiales precursores, la temperatura y el tiempo de tratamiento significa la reducción de los costes económicos del material. De ahí la viabilidad de los materiales de SrAl2O4:Eu,Dy obtenidos mediante los procesos de síntesis 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 μm 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 μm, 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 μm 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 μm with a thickness ≤1 μm 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 μm 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 μm when a sub-micron Al2O3 ( 0.5 μm Al2O3, 0.1 μm Al2O3 and γ-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 μm 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 6μm 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 μm 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 6μm 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 γ-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.

Estudo da substituição da fluorita por alumina ou sodalita e de cal por resíduo de mármore em escórias sintéticas dessulfurantes.

A siderurgia vem sofrendo transformações que buscam inovação e matérias-primas alternativas. Dentro deste contexto, o uso de resíduos industriais para a formação de escórias sintéticas é tido como alternativa na busca de novos materiais e rotas de reaproveitamento de resíduos. Portanto, este trabalho teve como objetivo estudar o uso de escórias sintéticas na etapa de dessulfuração do ferro-gusa, aço e ferro fundido. Assim como, propor a utilização da sodalita e da alumina em substituição à fluorita e o resíduo de mármore em substituição à cal convencional. Inicialmente, o resíduo foi caracterizado utilizando as seguintes técnicas: análise química, análise granulométrica, área de superfície específica, difração de raios-X, microscopia eletrônica de varredura (MEV) e análise de espectroscopia por energia dispersiva (EDS). Os resultados da caracterização mostraram que aproximadamente 90% das partículas do resíduo de mármore estão abaixo de 100m e sua área superficial foi de 0,24m²/g. Através da difração de raios-X foi observado que o resíduo é composto por CaCO3, MgCO3 e SiO2. Na sequência, foram feitas simulações com o software Thermo-Calc para obter dados termodinâmicos das fases presentes nas misturas e compará-los com os resultados experimentais. Além disso, também foram calculados dados de capacidade de sulfeto (Cs), partição de enxofre (Ls) e basicidade ótica () das misturas iniciais. Posteriormente, foram realizados os ensaios experimentais em escala laboratorial para ferro-gusa, ferro fundido e aço, respectivamente nas temperaturas de 1400°C, 1550°C e 1600°C. Nos ensaios de dessulfuração do aço e do ferro-gusa, utilizou-se um rotor de alumina com o objetivo de favorecer a agitação no metal e aumentar a remoção de enxofre. Na etapa de dessulfuração do ferro-gusa, constatou-se que a fase sólida de CaO é a responsável pela remoção de enxofre e que a presença das fases silicato tricálcio e aluminato tricálcio (3CaO.SiO2 e 3CaO.Al2O3) limitam a reação, sendo maiores suas concentrações nas escórias que utilizaram o resíduo de mármore e sodalita, devido a presença de SiO2 e Al2O3 nestas matérias-primas. Já para o aço e o ferro fundido, que foram estudados com escórias à base de CaO e Al2O3, observou-se que o aumento da fase líquida favoreceu a dessulfuração. Verificou-se que a dessulfuração no ferro fundido foi por escória de topo e no aço por um processo misto, onde a fase líquida e fase sólida participaram da dessulfuração.

Sedimentologic and magnetic data of sediment cores on the western slope of the Mid-Atlantic Ridge

The relative paleointensity (RPI) method assumes that the intensity of post depositional remanent magnetization (PDRM) depends exclusively on the magnetic field strength and the concentration of the magnetic carriers. Sedimentary remanence is regarded as an equilibrium state between aligning geomagnetic and randomizing interparticle forces. Just how strong these mechanical and electrostatic forces are, depends on many petrophysical factors related to mineralogy, particle size and shape of the matrix constituents. We therefore test the hypothesis that variations in sediment lithology modulate RPI records. For 90 selected Late Quaternary sediment samples from the subtropical and subantarctic South Atlantic Ocean a combined paleomagnetic and sedimentological dataset was established. Misleading alterations of the magnetic mineral fraction were detected by a routine Fe/kappa test (Funk, J., von Dobeneck, T., Reitz, A., 2004. Integrated rock magnetic and geochemical quantification of redoxomorphic iron mineral diagenesis in Late Quaternary sediments from the Equatorial Atlantic. In: Wefer, G., Mulitza, S., Ratmeyer, V. (Eds.), The South Atlantic in the Late Quaternary: reconstruction of material budgets and current systems. Springer-Verlag, Berlin/Heidelberg/New York/Tokyo, pp. 239-262). Samples with any indication of suboxic magnetite dissolution were excluded from the dataset. The parameters under study include carbonate, opal and terrigenous content, grain size distribution and clay mineral composition. Their bi- and multivariate correlations with the RPI signal were statistically investigated using standard techniques and criteria. While several of the parameters did not yield significant results, clay grain size and chlorite correlate weakly and opal, illite and kaolinite correlate moderately to the NRM/ARM signal used here as a RPI measure. The most influential single sedimentological factor is the kaolinite/illite ratio with a Pearson's coefficient of 0.51 and 99.9% significance. A three-member regression model suggests that matrix effects can make up over 50% of the observed RPI dynamics.

Chitosan-based spray-dried respirable powders for sustained delivery of terbutaline sulfate

In this study, we describe the preparation of highly dispersible dry powders for pulmonary drug delivery that display sustained drug release characteristics. Powders were prepared by spray-drying 30% v/v aqueous ethanol formulations containing terbutaline sulfate as a model drug, chitosan as a drug release modifier and leucine as an aerosolisation enhancer. The influence of chitosan molecular weight on the drug release profile was investigated by using low, medium and high molecular weight chitosan or combinations thereof. Following spray-drying, resultant powders were characterised using scanning electron microscopy, laser diffraction, tapped density analysis, differential scanning calorimetry and thermogravitational analysis. The in vitro aerosolisation performance and drug release profile were investigated using Multi-Stage Liquid Impinger analysis and modified USP II dissolution apparatus, respectively. The powders generated were of a suitable aerodynamic size for inhalation, had low moisture content and were amorphous in nature. The powders were highly dispersible, with emitted doses of over 90% and fine particle fractions of up to 82% of the total loaded dose, and mass median aerodynamic diameters of less than 2.5microm. A sustained drug release profile was observed during dissolution testing; increasing the molecular weight of the chitosan in the formulation increased the duration of drug release. (c)2007 Elsevier B.V. All rights reserved.

The use of absorption enhancers to enhance the despersibility of spray-dried powders for pulmonary gene therapy

Background: Pulmonary gene therapy requires aerosolisation of the gene vectors to the target region of the lower respiratory tract. Pulmonary absorption enhancers have been shown to improve the penetration of pharmaceutically active ingredients in the airway. In this study, we investigate whether certain absorption enhancers may also enhance the aerosolisation properties of spray-dried powders containing non-viral gene vectors. Methods: Spray-drying was used to prepare potentially respirable trehalose-based dry powders containing lipid-polycation-pDNA (LPD) vectors and absorption enhancers. Powder morphology and particle size were characterised using scanning electron microscopy and laser diffraction, respectively, with gel electrophoresis used to assess the structural integrity of the pDNA. The biological functionality of the powders was quantified using in vitro cell (A549) transfection. Aerosolisation from a Spinhaler® dry powder inhaler into a multistage liquid impinger (MSLI) was used to assess the in vitro dispersibility and deposition of the powders. Results: Spray-dried powder containing dimethyl-β-cyclodextrin (DMC) demonstrated substantially altered particle morphology and an optimal particle size distribution for pulmonary delivery. The inclusion of DMC did not adversely affect the structural integrity of the LPD complex and the powder displayed significantly greater transfection efficiency as compared to unmodified powder. All absorption enhancers proffered enhanced powder deposition characteristics, with the DMC-modified powder facilitating high deposition in the lower stages of the MSLI. Conclusions: Incorporation of absorption enhancers into non-viral gene therapy formulations prior to spray-drying can significantly enhance the aerosolisation properties of the resultant powder and increase biological functionality at the site of deposition in an in vitro model. Copyright © 2005 John Wiley & Sons, Ltd.

Soot measurements in steady and pulsed ethylene/air diffusion flames using Laser-Induced Incandescence

Combustion-generated carbon black nano particles, or soot, have both positive and negative effects depending on the application. From a positive point of view, it is used as a reinforcing agent in tires, black pigment in inks, and surface coatings. From a negative point of view, it affects performance and durability of many combustion systems, it is a major contributor of global warming, and it is linked to respiratory illness and cancer. Laser-Induced Incandescence (LII) was used in this study to measure soot volume fractions in four steady and twenty-eight pulsed ethylene diffusion flames burning at atmospheric pressure. A laminar coflow diffusion burner combined with a very-high-speed solenoid valve and control circuit provided unsteady flows by forcing the fuel flow with frequencies between 10 Hz and 200 Hz. Periodic flame oscillations were captured by two-dimensional phase-locked LII images and broadband luminosity images for eight phases (0° – 360°) covering each period. A comparison between the steady and pulsed flames and the effect of the pulsation frequency on soot volume fraction in the flame region and the post flame region are presented. The most significant effect of pulsing frequency was observed at 10 Hz. At this frequency, the flame with the lowest mean flow rate had 1.77 times enhancement in peak soot volume fraction and 1.2 times enhancement in total soot volume fraction; whereas the flame with the highest mean flow rate had no significant change in the peak soot volume fraction and 1.4 times reduction in the total soot volume fraction. A correlation (fvRe-1 = a + b·Str) for the total soot volume fraction in the flame region for the unsteady laminar ethylene flames was obtained for the pulsation frequency between 10 Hz and 200 Hz, and the Reynolds number between 37 and 55. The soot primary particle size in steady and unsteady flames was measured using the Time-Resolved Laser-Induced Incandescence (TIRE-LII) and the double-exponential fit method. At maximum frequency (200 Hz), the soot particles were smaller in size by 15% compared to the steady case in the flame with the highest mean flow rate.

Soot Measurements in Steady and Pulsed Ethylene/Air Diffusion Flames Using Laser-Induced Incandescence

Combustion-generated carbon black nano particles, or soot, have both positive and negative effects depending on the application. From a positive point of view, it is used as a reinforcing agent in tires, black pigment in inks, and surface coatings. From a negative point of view, it affects performance and durability of many combustion systems, it is a major contributor of global warming, and it is linked to respiratory illness and cancer. Laser-Induced Incandescence (LII) was used in this study to measure soot volume fractions in four steady and twenty-eight pulsed ethylene diffusion flames burning at atmospheric pressure. A laminar coflow diffusion burner combined with a very-high-speed solenoid valve and control circuit provided unsteady flows by forcing the fuel flow with frequencies between 10 Hz and 200 Hz. Periodic flame oscillations were captured by two-dimensional phase-locked LII images and broadband luminosity images for eight phases (0°- 360°) covering each period. A comparison between the steady and pulsed flames and the effect of the pulsation frequency on soot volume fraction in the flame region and the post flame region are presented. The most significant effect of pulsing frequency was observed at 10 Hz. At this frequency, the flame with the lowest mean flow rate had 1.77 times enhancement in peak soot volume fraction and 1.2 times enhancement in total soot volume fraction; whereas the flame with the highest mean flow rate had no significant change in the peak soot volume fraction and 1.4 times reduction in the total soot volume fraction. A correlation (ƒv Reˉ1 = a+b· Str) for the total soot volume fraction in the flame region for the unsteady laminar ethylene flames was obtained for the pulsation frequency between 10 Hz and 200 Hz, and the Reynolds number between 37 and 55. The soot primary particle size in steady and unsteady flames was measured using the Time-Resolved Laser-Induced Incandescence (TIRE-LII) and the double-exponential fit method. At maximum frequency (200 Hz), the soot particles were smaller in size by 15% compared to the steady case in the flame with the highest mean flow rate.

Estudo de duas pseudoligas de Nb-Cu obtidas pela rota da metalurgia do pó

The Nb-Cu pseudoalloys present themselves as potential substitutes for the alloys from a well known system and already commercially applied, as the W-Cu alloys, used in applications such as heat sinks, electrical contacts and coils for the generation of high magnetic fields. Because it is an immiscible system, where there is mutual insolubility and low wettability of the liquid Cu on the Nb surface, the processing route used in this work was the Powder Metallurgy. Two Nb alloys were used, with additions of 10% and 20% in weight of Cu, and times of 20, 30 and 40 hours for the high energy milling of the starting powders. The milling evolution of the powders is presented through the characterization techniques, such as the LASER diffraction for particle size, XRD, SEM, EDS, DSC, dilatometry, TEM and chemical analysis. After the milling, portions of the loads were submitted to the annealing heat treatment. The process used for the samples consolidation was the hot pressing, which has been applied both on some milled powders samples, as on the annealed powders. Subsequent heat treatments were performed in the samples at temperatures of 1000ºC (solid phase) and 1100ºC (in the Cu liquid phase). All sets of consolidated samples, and also the two sets of the heat treated, were analyzed by XRD, SEM, EDS, density and Vickers microhardness. Moreover, other Nb powder samples with 10% and 20% in weight of Cu obtained by simple mechanical mixing, were consolidated, thermally treated and characterized with the same techniques applied to the others, and the results were compared among themselves. Despite the difficulty of consolidation and densification of the two pseudoalloys of the Nb-Cu system of this study, on the route that passes through the HEM, samples were obtained with densities around 90% of the theoretical density. And, on the processing route of which were only mixed, the values reached up to 97%. Therefore, in this work are also emphasized the processes that made possible these results.

Efeito da adição de WC e Co na sinterização e propriedades mecânicas da alumina

Composites based on alumina (Al2O3), tungsten carbide (WC) and cobalt (Co) exhibit specific properties such as low density, high oxidation resistance, high melting point and high chemical inertia. That composite shows to be a promising material for application in various fields of engineering. In this work, the mechanical properties of the composite (Al2O3 – WC – Co), particularly density and hardness, were evaluated according to the effects of the variables of powder processing parameters, green compact and sintered. Powder composites with the composition of 80 wt% Al2O3, 18 wt% WC and 2 wt% Co were processed by high energy ball milling in a planetary mill for 50 hours as well as mixed by manual mixing in a glass vessel with the same proportion. Samples were collected (2, 10, 20, 30, 40 and 50 hours) during the milling process. Then, the powders were compacted in a cylindrical die with 5 mm in diameter in a uniaxial press with pressures of 200 and 400 MPa. The sintering was in two stages: first, the solid phase sintering was performed at 1126 and 1300 °C for 1 hour with a heating rate of 10 °C/min in a resistive furnace under argon atmosphere for green samples compacted in 200 and 400 MPa; the second sintering was performed on dilatometer in solid phase at 1300 °C for green sample compacted in 200 MPa, another sintering also was performed on dilatometer, this time in liquid phase at 1550 °C for green samples compacted in 200 and 400 MPa, with the same parameters used in resistive furnace. The raw materials were characterized by X – ray diffraction (XRD), X – ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and laser particlemeter. The sintered samples were subjected to microhardness testing. The results showed that high energy milling achieved to the objectives regarding the particle size and the dispersion of composite phases. However, the hardness did not achieve to significant results, this is an indication that the composite has low fracture toughness.

Efeito da adição de WC e Co na sinterização e propriedades mecânicas da alumina

Composites based on alumina (Al2O3), tungsten carbide (WC) and cobalt (Co) exhibit specific properties such as low density, high oxidation resistance, high melting point and high chemical inertia. That composite shows to be a promising material for application in various fields of engineering. In this work, the mechanical properties of the composite (Al2O3 – WC – Co), particularly density and hardness, were evaluated according to the effects of the variables of powder processing parameters, green compact and sintered. Powder composites with the composition of 80 wt% Al2O3, 18 wt% WC and 2 wt% Co were processed by high energy ball milling in a planetary mill for 50 hours as well as mixed by manual mixing in a glass vessel with the same proportion. Samples were collected (2, 10, 20, 30, 40 and 50 hours) during the milling process. Then, the powders were compacted in a cylindrical die with 5 mm in diameter in a uniaxial press with pressures of 200 and 400 MPa. The sintering was in two stages: first, the solid phase sintering was performed at 1126 and 1300 °C for 1 hour with a heating rate of 10 °C/min in a resistive furnace under argon atmosphere for green samples compacted in 200 and 400 MPa; the second sintering was performed on dilatometer in solid phase at 1300 °C for green sample compacted in 200 MPa, another sintering also was performed on dilatometer, this time in liquid phase at 1550 °C for green samples compacted in 200 and 400 MPa, with the same parameters used in resistive furnace. The raw materials were characterized by X – ray diffraction (XRD), X – ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and laser particlemeter. The sintered samples were subjected to microhardness testing. The results showed that high energy milling achieved to the objectives regarding the particle size and the dispersion of composite phases. However, the hardness did not achieve to significant results, this is an indication that the composite has low fracture toughness.

Design of experiments to study the impact of process parameters on droplet size and development of non-invasive imaging techniques in tablet coating

Atomisation of an aqueous solution for tablet film coating is a complex process with multiple factors determining droplet formation and properties. The importance of droplet size for an efficient process and a high quality final product has been noted in the literature, with smaller droplets reported to produce smoother, more homogenous coatings whilst simultaneously avoiding the risk of damage through over-wetting of the tablet core. In this work the effect of droplet size on tablet film coat characteristics was investigated using X-ray microcomputed tomography (XμCT) and confocal laser scanning microscopy (CLSM). A quality by design approach utilising design of experiments (DOE) was used to optimise the conditions necessary for production of droplets at a small (20 μm) and large (70 μm) droplet size. Droplet size distribution was measured using real-time laser diffraction and the volume median diameter taken as a response. DOE yielded information on the relationship three critical process parameters: pump rate, atomisation pressure and coating-polymer concentration, had upon droplet size. The model generated was robust, scoring highly for model fit (R2 = 0.977), predictability (Q2 = 0.837), validity and reproducibility. Modelling confirmed that all parameters had either a linear or quadratic effect on droplet size and revealed an interaction between pump rate and atomisation pressure. Fluidised bed coating of tablet cores was performed with either small or large droplets followed by CLSM and XμCT imaging. Addition of commonly used contrast materials to the coating solution improved visualisation of the coating by XμCT, showing the coat as a discrete section of the overall tablet. Imaging provided qualitative and quantitative evidence revealing that smaller droplets formed thinner, more uniform and less porous film coats.

Towards optical polarization control of laser-driven proton acceleration in foils undergoing relativistic transparency

Control of the collective response of plasma particles to intense laser light is intrinsic to relativistic optics, the development of compact laser-driven particle and radiation sources, as well as investigations of some laboratory astrophysics phenomena. We recently demonstrated that a relativistic plasma aperture produced in an ultra-thin foil at the focus of intense laser radiation can induce diffraction, enabling polarization-based control of the collective motion of plasma electrons. Here we show that under these conditions the electron dynamics are mapped into the beam of protons accelerated via strong charge-separation-induced electrostatic fields. It is demonstrated experimentally and numerically via 3D particle-in-cell simulations that the degree of ellipticity of the laser polarization strongly influences the spatial-intensity distribution of the beam of multi-MeV protons. The influence on both sheath-accelerated and radiation pressure-accelerated protons is investigated. This approach opens up a potential new route to control laser-driven ion sources.

Aproveitamento de resíduos minerais na formulação de argamassas para a construção civil

Current environmental concerns include the excessive consumption and inefficient use of non-renewable natural resources. The construction industry is considered one of the largest consumers of natural raw materials, significantly contributing to the environmental degradation of the planet. The use of calcareous quarry (RPPC) and porcelain tile polishing residues (RPP) as partial replacements of the cement in mortars is an interesting alternative to minimize the exploration of considerably large amounts of natural resources. The present study aimed at investigating the properties of fresh and hardened mortars produced using residues to replace cement. The residues used were fully characterized to determine their specific mass, unitary mass, particle size distribution and morphology, and composition. The performance of the mortars was compared to that of reference compositions, prepared without residues. A total of 18 compositions were prepared, 16 using residues and 2 reference ones. The mortars were prepared using Portland CP II F 32 cement, CH I hydrated lime, river sand and tap water. The compositions of the mortars were 1:1:6 and 1:0.5:4.5 (vol%), and water to cement ratios of 1.87 and 1.45 were used, respectively. The mortars in the fresh state were evaluated by consistency index, water retention, density of mass and incorporated air content tests. In their hardened state, the mortars were evaluated by apparent mass density, modulus of elasticity, flexural tensile strength, compressive strength and water absorption by capillarity. The mortars were also analyzed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and fluorescence. Finally, they were classified according to NBR 13281 standards. The mortars prepared using residues partially replacing the cement exhibited lower modulus of elasticity compared to the reference compositions, thus improving the performance in their intended use. On the downside, the water absorption by capillarity was affected by the presence of residues and both the tensile and compressive strength were reduced. However, from the overall standpoint, the replacement of cement by calcareous quarry or porcelain tile polishing residues did not result in significant changes in the properties of the mortars. Therefore, compositions containing these residues can be used in the construction industry

Caracterização de compósitos Nb-20%cu obtidos por moagem de alta energia e sinterizados por fase líquida

In this work, was studied the formation of a composite of the refractory metal niobium with copper, through the process of high-energy milling and liquid phase sintering. The HEM can be used to synthesize composite powders with high homogeneity and fine size particle distribution. It may also produce the solid solubility in immiscible systems such as Nb-Cu, or extend the solubility of systems with limited solubility. Therefore, in the immiscible system Cu-Nb, the high-energy milling was successfully used to obtain the composite powder particles. Initially, the formation of composite particles during the HEM and the effect of preparation technique on the microstructure of the material was evaluated. Four loads of Nb and Cu powders containing 20%wt Cu were synthesized by MAE in a planetary type ball mill under different periods of grinding. The influence of grinding time on the metal particles is evaluated during the process by the withdrawal of samples at intermediate times of milling. After compaction under different forces, the samples were sintered in a vacuum furnace. The liquid phase sintering of these samples prepared by HEM produced a homogeneous and fine grained. The composite particles forming the sintered samples are the addition of a hard phase (Nb) with a high melting point, and a ductile phase (Cu) with low melting point and high thermal and electrical conductivities. Based on these properties, the Nb-Cu system is a potential material for many applications, such as electrical contacts, welding electrodes, coils for generating high magnetic fields, heat sinks and microwave absorbers, which are coupled to electronic devices. The characterization techniques used in this study, were laser granulometry, used to evaluate the homogeneity and particle size, and the X-ray diffraction, in the phase identification and to analyze the crystalline structure of the powders during milling. The morphology and dispersion of the phases in the composite powder particles, as well the microstructures of the sintered samples, were observed by scanning electron microscopy (SEM). Subsequently, the sintered samples are evaluated for density and densification. And finally, they were characterized by techniques of measuring the electrical conductivity and microhardness, whose properties are analyzed as a function of the parameters for obtaining the composite