Nitrogen-Doping in ZnO via Combustion Synthesis?

We report the synthesis and characterization of colored ZnO-based powders via solution combustion reaction of urea and zinc nitrate hexahydrate in varying molar ratios between 1:1 and 10:1. Among other techniques, we employ X-ray diffraction, nuclear magnetic resonance, and Raman spectroscopy to characterize the products. Within a narrow range of reactant ratios, we reproducibly find an unidentified, crystalline precursor phase related to isocyanuric acid next to ZnO. Finally, we complement our investigations by performing Prompt Gamma Activation Analysis (PGAA) on selected products in order to directly determine elemental bulk compositions and compare these with X-ray photoelectron spectroscopy (XPS) measurements. Our data show traces of nitrogen mainly on the surface of the particles, and thus we question the solution combustion method as a reliable synthesis toward N-doped ZnO. Furthermore, we exclude nitrogen as being responsible for the appearance of the four controversially discussed Raman bands superimposed onto the spectrum of pure ZnO (at 275, 510, 582, and 643 cm–1) and show that the combination of PGAA and XPS is an excellent and complementary method to obtain information about the distribution of the elements in question.

Co2 capture in power plants-using the oxy-combustion principle

In the C02 capture from power generation, the energy penalties for the capture are one of the main challenges. Nowadays, the post-combustion methods have energy penalties 10wer than the oxy combustion and pre-combustion technologies. One of the main disadvantages of the post combustion method is the fact that the capture ofC02at atmospheric pressure requires quite big equipment for the high flow rates of flue gas, and the 10w partial pressure of the CO2generates an important 10ss of energy. The A1lam cyc1e presented for NETPOWER gives high efficiencies in the power production and 10w energy penalties. A simulation of this cyc1e is made together with a simulation of power plants with pre-combustion and post-combustion capture and without capture for natural gas and forcoa1. The simulations give 10wer efficiencies than the proposed for NETPOWER For natural gas the efficiency is 52% instead of the 59% presented, and 33% instead of51% in the case of using coal as fuel. Are brought to light problems in the CO2compressor due the high flow ofC02that is compressed unti1300 bar to be recyc1ed into the combustor.

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.

Improved electrochemical performance of Sr2Fe1.5Mo0.4Nb0.1O6-δ -Sm0.2Ce0.8O2-δ composite cathodes by a one-pot method for intermediate temperature solid oxide fuel cells

In this paper, Sr₂Fe_1.5Mo_0.4Nb_0.1O_6-δ (SFMNb)-xSm_0.2Ce_0.8O_2-δ (SDC) (x = 0, 20, 30, 40, 50 wt%) composite cathode materials were synthesized by a one-pot combustion method to improve the electrochemical performance of SFMNb cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The fabrication of composite cathodes by adding SDC to SFMNb is conducive to providing extended electrochemical reaction zones for oxygen reduction reactions (ORR). X-ray diffraction (XRD) demonstrates that SFMNb is chemically compatible with SDC electrolytes at temperature up to 1100 °C. Scanning electron microscope (SEM) indicates that the SFMNb-SDC composite cathodes have a porous network nanostructure as well as the single phase SFMNb. The conductivity and thermal expansion coefficient of the composite cathodes decrease with the increased content of SDC, while the electrochemical impedance spectra (EIS) exhibits that SFMNb-40SDC composite cathode has optimal electrochemical performance with low polarization resistance (R_p) on the La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ electrolyte. The R_p of the SFMNb-40SDC composite cathode is about 0.047 Ω cm² at 800 °C in air. A single cell with SFMNb-40SDC cathode also displays favorable discharge performance, whose maximum power density is 1.22 W cm^-2 at 800 °C. All results indicate that SFMNb-40SDC composite material is a promising cathode candidate for IT-SOFCs.

Scalable synthetic method for IT-SOFCs compounds

Póster presentado en: 12th EUROPEAN SOFC & SOE FORUM 2016. 5–8 July 2016, KKL Lucerne/Switzerland

Local atomic structure in tetragonal pure ZrO(2) nanopowders

The local atomic structures around the Zr atom of pure (undoped) ZrO(2) nanopowders with different average crystallite sizes, ranging from 7 to 40 nm, have been investigated. The nanopowders were synthesized by different wet-chemical routes, but all exhibit the high-temperature tetragonal phase stabilized at room temperature, as established by synchrotron radiation X-ray diffraction. The extended X-ray absorption fine structure (EXAFS) technique was applied to analyze the local structure around the Zr atoms. Several authors have studied this system using the EXAFS technique without obtaining a good agreement between crystallographic and EXAFS data. In this work, it is shown that the local structure of ZrO(2) nanopowders can be described by a model consisting of two oxygen subshells (4 + 4 atoms) with different Zr-O distances, in agreement with those independently determined by X-ray diffraction. However, the EXAFS study shows that the second oxygen subshell exhibits a Debye-Waller (DW) parameter much higher than that of the first oxygen subshell, a result that cannot be explained by the crystallographic model accepted for the tetragonal phase of zirconia-based materials. However, as proposed by other authors, the difference in the DW parameters between the two oxygen subshells around the Zr atoms can be explained by the existence of oxygen displacements perpendicular to the z direction; these mainly affect the second oxygen subshell because of the directional character of the EXAFS DW parameter, in contradiction to the crystallographic value. It is also established that this model is similar to another model having three oxygen subshells, with a 4 + 2 + 2 distribution of atoms, with only one DW parameter for all oxygen subshells. Both models are in good agreement with the crystal structure determined by X-ray diffraction experiments.

Crystallite size-dependent phases in nanocrystalline ZrO(2)-Sc(2)O(3)

ZrO(2)-10, 12 and 14 mol% Sc(2)O(3) nanopowders were prepared by using a nitrate-lysine gel-combustion synthesis. These materials were studied by synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy after calcination at different temperatures from 650 to 1200 degrees C, which led to samples with different average crystallite sizes, up to about 100 nm. The results from SXPD and Raman analyses indicate that, depending on Sc(2)O(3) content, the metastable t ''-form of the tetragonal phase or the cubic phase are fully retained at room temperature in nanocrystalline powders, provided an average crystallite sizes lower than similar to 30 nm. By contrast, powders with larger average crystallite sizes exhibit the stable rhombohedral, beta and gamma, phases and do not retain or very partially retain the metastable t '' and cubic ones.

Synchrotron X-ray powder diffraction and extended X-ray absorption fine structure spectroscopy studies on nanocrystalline ZrO(2)-CaO solid solutions

The crystal structure and the local atomic order of a series of nanocrystalline ZrO(2)-CaO solid solutions with varying CaO content were studied by synchrotron radiation X-ray powder diffraction and extended X-ray absorption fine structure (EXAFS) spectroscopy. These samples were synthesized by a pH-controlled nitrate-glycine gel-combustion process. For CaO contents up to 8 mol%, the t' form of the tetragonal phase (c/a > 1) was identified, whereas for 10 and 12 mol% CaO, the t '' form (c/a=1; oxygen anions displaced from their ideal positions in the cubic phase) was detected. Finally, the cubic phase was observed for solid solutions with CaO content of 14 mol% CaO or higher. The t'/t '' and t ''/cubic compositional boundaries were determined to be at 9 (1) and 13 (1) mol% CaO, respectively. The EXAFS study demonstrated that this transition is related to a tetragonal-to-cubic symmetry change of the first oxygen coordination shell around the Zr atoms.

High-temperature X-ray powder diffraction study of the tetragonal-cubic phase transition in nanocrystalline, compositionally homogeneous ZrO2-CeO2 solid solutions

Crystal structure of compositionally homogeneous, nanocrystalline ZrO2-CeO2 solutions was investigated by X-ray powder diffraction as a function of temperature for compositions between 50 and 65 mol % CeO2 center dot ZrO2-50 and 60 mol % CeO2 solid solutions, which exhibit the t'-form of the tetragonal phase at room temperature, transform into the cubic phase in two steps: t'-to-t '' followed by t ''-to-cubic. But the ZrO2-65 mol % CeO2, which exhibits the t ''-form, transforms directly to the cubic phase. The results suggest that t'-to-t '' transition is of first order, but t ''-to-cubic seems to be of second order. (C) 2008 International Centre for Diffraction Data.

Synchrotron X-ray powder diffraction study of the tetragonal-cubic phase transition in nanostructured ZrO2-Sc2O3 solid solutions

The transition between tetragonal and cubic phases in nanostructured ZrO2-Sc2O3 solid solutions by high-temperature X-ray powder diffraction using synchrotron radiation is presented. ZrO2-8 and 11 mol% Sc2O3 nanopowders that exhibit the t'- and t ''-forms of the tetragonal phase, respectively, were synthesized by a stoichiometric nitrate-lysine gel-combustion route. The average crystallite size treated at 900 degrees C was about 25 nm for both compositions. Our results showed that t'-t '' and t ''-cubic transitions take place for the 8 and 11 mol% Sc2O3 samples, respectively. (C) 2008 International Centre for Diffraction Data.

Cerium-based phosphors: blue luminescent properties for applications in optical displays

In this paper, we describe the blue photoluminescence (PL) observed in the multi-component oxosalt phosphor GdVO(4)center dot Ce(3+). Different doping concentrations (0.25-1 mol%) and heat treatment (900-1100 degrees C) were used to evaluate which conditions would lead to the most suitable blue phosphor for optimal display performance. The cerium doping concentration influences the profile of the emission spectrum (broad peak at 412 nm under UV excitation at 330 nm), as reflected on the values of chromaticity coordinates. On the basis of luminescent properties, we can conclude that, among the phosphors prepared in this work the most adequate for a blue display is the one obtained via the combustion method using glycine as fuel, a 0.50 mol% cerium doping concentration, and heat treatment at 1000 degrees C.

Comparison of different methods for the determination of total organic carbon and humic substances in Brazilian soils

ABSTRACTAiming to compare three different methods for the determination of organic carbon (OC) in the soil and fractions of humic substances, seventeen Brazilian soil samples of different classes and textures were evaluated. Amounts of OC in the soil samples and the humic fractions were measured by the dichromate-oxidation method, with and without external heating in a digestion block at 130 °C for 30 min; by the loss-on-ignition method at 450 °C during 5 h and at 600 °C during 6 h; and by the dry combustion method. Dry combustion was used as reference in order to measure the efficiency of the other methods. Soil OC measured by the dichromate-oxidation method with external heating had the highest efficiency and the best results comparing to the reference method. When external heating was not used, the mean recovery efficiency dropped to 71%. The amount of OC was overestimated by the loss-on-ignition methods. Regression equations obtained between total OC contents of the reference method and those of the other methods showed relatively good adjustment, but all intercepts were different from zero (p < 0.01), which suggests that more accuracy can be obtained using not one single correction factor, but considering also the intercept. The Walkley-Black method underestimated the OC contents of the humic fractions, which was associated with the partial oxidation of the humin fraction. Better results were obtained when external heating was used. For the organic matter fractions, the OC in the humic and fulvic acid fractions can be determined without external heating if the reference method is not available, but the humin fraction requires the external heating.

Genetic relationships of Corynebacterium diphtheriae strains isolated from a diphtheria case and carriers by restriction fragment length polymorphism of rRNA genes

In the present study we report the results of an analysis, based on ribotyping of Corynebacterium diphtheriae intermedius strains isolated from a 9 years old child with clinical diphtheria and his 5 contacts. Quantitative analysis of RFLPs of rRNA was used to determine relatedness of these 7 C.diphtheriae strains providing support data in the diphtheria epidemiology. We have also tested those strains for toxigenicity in vitro by using the Elek's gel diffusion method and in vivo by using cell culture method on cultured monkey kidney cell (VERO cells). The hybridization results revealed that the 5 C.diphtheriae strains isolated from contacts and one isolated from the clinical case (nose case strain) had identical RFLP patterns with all 4 restriction endonucleases used, ribotype B. The genetic distance from this ribotype and ribotype A (throat case strain), that we initially assumed to be responsible for the illness of the patient, was of 0.450 showing poor genetic correlation among these two ribotypes. We found no significant differences concerned to the toxin production by using the cell culture method. In conclusion, the use of RFLPs of rRNA gene was successful in detecting minor differences in closely related toxigenic C.diphtheriae intermedius strains and providing information about genetic relationships among them.

Screening of Amazonian plants from the Adolpho Ducke forest reserve, Manaus, state of Amazonas, Brazil, for antimicrobial activity

Tropical forests are species-rich reserves for the discovery and development of antimicrobial drugs. The aim of this work is to investigate the in vitro antimicrobial potential of Amazon plants found within the National Institute on Amazon Research's Adolpho Ducke forest reserve, located in Manaus, state of Amazonas, Brazil. 75 methanol, chloroform and water extracts representing 12 plant species were tested for antimicrobial activity towards strains of Mycobacterium smegmatis, Escherichia coli, Streptococcus sanguis, Streptococcus oralis, Staphylococcus aureus and Candida albicans using the gel-diffusion method. Active extracts were further evaluated to establish minimum inhibitory concentrations (MIC) and antimicrobial profiles using bioautography on normal-phase thin-layer chromatography plates. Diclinanona calycina presented extracts with good antimicrobial activity and S. oralis and M. smegmatis were the most sensitive bacteria. D. calycina and Lacmellea gracilis presented extracts with the lowest MIC (48.8 µg/ml). D. calycina methanol and chloroform leaf extracts presented the best overall antimicrobial activity. All test organisms were sensitive to D. calycina branch chloroform extract in the bioautography assay. This is the first evaluation of the biological activity of these plant species and significant in vitro antimicrobial activity was detected in extracts and components from two species, D. calycina and L. gracilis.

Anti-tumour effect of monoclonal antibodies against selected antigens expressed by B-cells in Chronic Lymphocytic Leukaemia : strategies to enhance the efficacy of immunotherapy

Résumé : Les anticorps monoclonaux ont une place de plus en plus prépondérante dans le traitement des lymphomes et leucémies. Dans cette étude, trois anticorps monoclonaux murins, dirigés contre les antigènes CDS, CD71 et HLA-DR exprimés à la surface des cellules de leucémies lymphoïdes chroniques (LLC), ont été évalués. In vitro, les anticorps radiomarqués ont montrés des bonnes liaisons spécifiques sur les différentes cellules cibles. L'anti-CD71 inhibait la prolifération de la plupart des lignées cellulaires testées avec une accumulation des cellules en phase S précoce du cycle cellulaire. L'anti-HLA-DR inhibait aussi la prolifération des lignées leucémique JOK1-5.3 et lymphoïde Daudi. Cette inhibition était associée à une agrégation des cellules. Aucune induction d'apoptose n'a pu être clairement observée avec ces anticorps. L'anti-CD5 n'a montré aucun effet d'inhibition de croissance in vitro. In vivo, l'injection des anticorps individuellement augmentait significativement la survie médiane de souris SCID greffées avec des cellules JOK1-5.3 en i.p. De plus, l'anticorps antiCD5 combiné à l'anti-HLA-DR ou l'anti-CD71, sous certaines conditions, inhibait complètement le développement tumoral dans la quasi totalité des souris traitées avec une augmentation significative de l'efficacité comparée aux anticorps seuls. L'augmentation de l'efficacité thérapeutique des anticorps monoclonaux par les cytokines, dont l'IL-2, a déjà été montrée dans la littérature. Au regard du meilleur comportement de l'IL-2 sous la forme complexée à un anticorps anti-IL-2, nous avons évalué l'efficacité de l'IL-2/anti-IL-2 seul ou combinés au rituximab chez différents modèles tumoraux s.c. (BL60.2, Daudi, Ramos) ou i.p. (JOK15.3) de souris SCID. Le complexe IL-2/anti-IL-2 a montré un effet anti-tumoral dans les souris greffées avec BL60.2 et Daudi. Le traitement IL-2/anti-IL-2 combiné au rituximab a montré une efficacité accrue chez des souris avec BL60.2 par rapport au rituximab seul. En revanche, nous n'avons pas observé de différence avec IL-2/anti-IL-2 seul.Aussi, nous avons évalué l'utilisation de l'agent couplant tri-fonctionnel TMEA pour produire des anticorps bispecifiques. Les expériences préliminaires avec les anticorps rituximab et herceptine, ont mis en évidence sur gel SDS-Page la formation de dimers (~100kDa) et de trimers (~150kDa). Les anticorps bispecifiques sont composés d'un fragment Fab' d'une spécificité et de un ou deux fragments Fab' de l'autre spécificité permettant de moduler la capacité de liaison. Nous avons enfin montré qu'une construction anti-CD5/anti-CD20 était capable de se lier indépendamment ou simultanément à ses antigènes cibles. En conclusion, ce travail a montré l'efficacité thérapeutique des trois anticorps monoclonaux étudiés dans un model de LLC in vivo, et plus particulièrement l'intérêt de certaines combinaisons. D'autre part, nous avons montré l'efficacité anti-tumorale du complexe IL-2/anti-IL-2 in vivo. Des études futures devront permettre de définir un régime favorable pour augmenter l'efficacité de la thérapie avec les anticorps monoclonaux. Enfin, nous avons montré la faisabilité d'utiliser l'agent couplant TMEA pour produire des anticorps bispécifiques fonctionnels.Abstract : Monoclonal antibody (mAb) therapy has become an integral part in different treatments of lymphomas and leukaemias. In this study, we describe three murine mAbs directed against the CD5, CD71 and HLA-DR antigens expressed on chronic lymphocytic leukaemia cells (CLL). In vitro, radiolabeled purified mAbs showed good specific binding on live target cells. Anti-CD71 mAb inhibited proliferation of most cell lines with an accumulation of responding cells in early S-phase of the cell cycle, but without induction of apoptosis. Anti-HLA-DR mAb showed proliferation inhibition of leukaemia JOK1-5.3 and lymphoid Daudi cells, associated with cell aggregation, but again no specific sign of apoptosis was observed. Anti-CD5 mAb did not show any growth inhibitory effect in vitro. In vivo, in a model of SCID mice grafted i.p. with JOK1-5.3 cells, injection of individual mAbs induced significant prolongation of median survival, up to complete inhibition of tumour growth in some mice. Antibody combination of anti-CD5 with anti-HLA-DR or anti-CD71, evaluated in an early treatment, completely inhibited tumour growth in most mice, with a significant efficacy enhancement as compared to mAb used as single agents. Previous reports described the improved efficacy of mAb therapy when combined with cytokines such as IL-2. Relying further on the improved efficacy of IL-2 when administered as an immune complex with anti-IL-2 mAb, we evaluated the anti-tumour effect of the IL-2/anti-IL-2 complex alone or combined with rituximab in subcutaneous (BL60.2, Daudi, Ramos) or i.p. (JOK1-5.3) tumour models in SCID mice. The IL-2/anti-IL-2 complex demonstrated an anti-tumour effect in BL60.2 and Daudi grafted SCID mice. Combination of IL-2/anti-IL-2 treatment with rituximab showed increased efficacy as compared to rituximab alone in BL60.2 grafted mice. However, no difference was observed with IL-2/anti-IL-2 complex alone in these experiments. Finally, we evaluated the feasibility of producing bispecific antibodies (bsAbs) using a trifunctional coupling agent, called TMEA. In preliminary experiments coupling rituximab with herceptine Fab' fragments we obtained the formation of dimers (~100kDa) and trimers (~150kDa) as observed on SDS-Page gel. This method allowed us to produce bsAb with one Fab' fragments of one specificity and one or two Fab' fragments of the second specificity. An anti-CD5/anti-CD20 bsAb was shown to bind targeted antigen either independently or simultaneously. In conclusion, these data show that the three mAbs were all able to induce significant growth inhibition of the JOK1-5.3 cell line in vivo, and efficacy was enhanced when used in combination. IL2/anti-IL-2 complex displayed anti-tumour efficacy in vivo. Further evaluation is necessary to define the most favourable combination to improve mAb therapy. BsAb were produced using the tri-functional agent allowing antibody fragments with relatively good binding. The poor yield obtained with such chemical couplings limited the use of these constructs in preclinical experiments.