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Objectives In this study hybrid nanofibers embedded with niobium pentoxide (Nb2O5) were synthesized, incorporated in self-adhesive resin cement, and their influence on physical-properties was evaluated. Methods Poly(D,L-lactide), PDLLA cotton-wool-like nanofibers with and without silica-based sol–gel precursors were formulated and spun into submicron fibers via solution blow spinning, a rapid fiber forming technology. The morphology, chemical composition and thermal properties of the spun fibers were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC), respectively. Produced fibers were combined with a self-adhesive resin cement (RelyX U200, 3 M ESPE) in four formulations: (1) U200 resin cement (control); (2) U200 + 1 wt.% PDLLA fibers; (3) U200 + 1 wt.% Nb2O5-filled PDLLA composite fibers and (4) U200 + 1 wt.% Nb2O5/SiO2-filled PDLLA inorganic–organic hybrid fibers. Physical properties were assessed in flexure by 3-point bending (n = 10), Knoop microhardness (n = 5) and degree of conversion (n = 3). Data were analyzed with One-way ANOVA and Tukey’s HSD (α = 5%). Results Composite fibers formed of PDLLA-Nb2O5 exhibited an average diameter of ∼250 nm, and hybrid PDLLA + Nb2O5/SiO2 fibers were slightly larger, ∼300 nm in diameter. There were significant differences among formulations for hardness and flexural strength (p < 0.05). Degree of conversion of resin cement was not affected for all groups, except for Group 4 (p < 0.05). Significance Hybrid reinforcement nanofibers are promising as fillers for dental materials. The self-adhesive resin cement with PDLLA + Nb2O5 and PDLLA + Nb2O5/SiO2 presented superior mechanical performance than the control group. Keywords Cotton-wool-like nanofibersHybridsMechanical propertiesNiobium pentoxideResin cementSolution blow spinning

Er3+-doped and Er3+/Yb3+-codoped GeO2-Nb2O5-K2O glasses were prepared by conventional melt-quenching method. Thermal and spectroscopic analysis were performed. The niobium insertion into the glass structure has decreased the OH groups resulting in a slight increase in the luminescence efficiency as the niobium content. Glass network structure is modified depending on rare earth doping concentration and niobium content. The number of bridge oxygen bonds and nonbridge oxygen bonds is altered and consequently the crystallization composition. The spectroscopic features were discussed in terms of niobium concentration and its influence on the applications as optical devices. The addition of niobium broadens the emission band in the region of 1.5 µm covering C, S and L-telecommunication bands. The gain coefficient has calculated establishing high potentiality to use the niobium germanate glasses for optical amplification. The codoping by Er3+/Yb3+ intensifies the emission in the NIR and visible (upconversion) region in relation to the doped samples and may be interesting for application as visible and near-infrared emitters. In addition, the codoped samples with variable niobium contents have potential as visible tunable phosphors emitting either green or red light. Accordingly, the niobium germanate glasses are interesting matrices for rare earth ions doping and for the development of optical devices, such as visible and NIR laser and optical amplifiers.

In this article, Nb heterostructure-based (NaNbO3/Na2Nb4O11) and Nb/Clay-based materials were prepared, characterized and evaluated for the Rhodamine B (C28H31ClN2O3) photodegradation under UV radiation (253.7 nm). As far as this research understands, this is the first time that the photocatalytic activity of the Nb heterostructure (NaNbO3/Na2Nb4O11) is reported. Nb heterostructure is composed of sodium niobate and disodium tetraniobium hendecaoxide (NaNbO3/Na2Nb4O11). The material was synthesized by a simple and economic method via basic precipitation of ammoniacal niobium oxalate (NH4 [NbO (C2O4)2·H2O] XH2O) followed by thermal treatment at 500 °C. Nb/Clay-based materials were synthesized from the natural clay suspension (Montmorillonite) precursor. The addition of Nb to the natural clay by the methodology employed in this work modified the band-gap energy and increased the specific surface area of the resultant materials (to almost twice the value of the original specific surface area). Furthermore, this addition also decreased the luminescence and trap centres and potentiated the photocatalytic activity of the Nb/Clay materials. The Nb heterostructure showed higher photocatalytic activity in Rhodamine B photodegradation (recorded up to 95% removal at natural conditions). Similar values were reported to Nb/Clay materials. Despite the natural clay having more luminescence and trap centres than Nb/Clay materials, it recorded very low photocatalytic activity. Nb addition to natural clay increased the photocatalytic activity of the material, which would give other use to clay along with being used as an adsorbent.

Objective: In this work, niobium carbide (NbC) coatings were deposited on substrates of the tool steels AISI H13 and AISI D2 using thermoreactive deposition/diffusion (TRD) in order to analyze their behavior against corrosion in a saline environment. Materials and methods: The niobium carbides were obtained using salt baths composed of borax pentahydrate, aluminum and ferroniobium. This mixture was heated at 1050 °C for 4 hours. The chemical composition was determined by X-ray fluorescence (XRF). The coatings were morphologically characterized using scanning electron microscopy (SEM), the crystal structure was analyzed using X-ray diffraction (XRD), and the electrochemical behavior was studied using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Results and discussion: The XRF analysis indicated that the coatings contained 87.476 wt% Nb and 51.943 wt% Nb for the D2-substrate and the H13- substrate, respectively. The SEM images revealed that the morphology of the surface of the coatings was homogeneous. The XRD analysis established that the coatings were polycrystalline, and the electrochemical tests established that the corrosion resistance increased slightly in the covered substrates with respect to the uncoated steels, with the best results being obtained in the layers of niobium carbide deposited on AISI D2 steel. Conclusions: The analysis of corrosion resistance revealed that the coatings prepared on D2 steel have a higher corrosion resistance because they have fewer surface imperfections, which causes the coating to exhibit a dielectric behavior. Resumen Objetivo: En el presente trabajo se depositaron recubrimientos de carburo de niobio (CNb) sobre aceros para herramientas AISI H13 y AISI D2 mediante deposición/difusión termoreactiva (TRD), con el fin de analizar su comportamiento frente a la corrosión en un ambiente salino. Materiales y métodos: Los carburos de niobio se obtuvieron empleando baños de sal, compuestos por borax pentahidratado, aluminio y ferroniobio; Esta mezcla se calentó a 1050°C durante 4 horas. La composición química de las capas obtenidas se determinó por fluorescencia de rayos X (FRX). Los recubrimientos se caracterizaron morfológicamente mediante microscopía electrónica de barrido (MEB), se analizó la estructura cristalina mediante difracción de rayos X (DRX) y se estudió el comportamiento electroquímico por medio de curvas de polarización potenciodinámica y espectroscopia de impedancia electroquímica. Resultados y discusión: El análisis FRX indicó que los recubrimientos contenían 87,476% en peso de Nb y 51,943% en peso de Nb, para los sustratos D2 y H13 respectivamente. Las imágenes MEB revelaron que la morfología de la superficie de los recubrimientos era homogénea. El análisis DRX estableció que los recubrimientos eran policristalinos y las pruebas electroquímicas establecieron que la resistencia a la corrosión aumentaba ligeramente en los sustratos recubiertos respecto a los aceros sin recubrimiento, obteniendo los mejores resultados en las capas de carburo de niobio depositadas sobre acero AISI D2. Conclusiones: El análisis de la resistencia a la corrosión reveló que los recubrimientos preparados sobre el acero D2 tienen una mayor resistencia a la corrosión porque presentan menos imperfecciones en la superficie, lo que hace que el recubrimiento exhiba un comportamiento dieléctrico.

Henry Enfield Roscoe (1833–1915), together with Robert Bunsen, his mentor, carried on fundamental research in photochemistry, determining its laws and quantitative effects. His most important studies were on the chemistry of vanadium, uranium, tungsten, and molybdenum, their oxides and oxychlorides, carrying on, for the first time, their synthesis and separation. He also did important studies on public heath. His academic activities transformed Owens College (Victoria University) into the leading chemistry school in Britain.

Resumo A hidroxiapatita sintética (Ca10(PO4)6(OH)2; HA) devido à propriedade de biocompatibilidade com o tecido ósseo tornou-se um material cerâmico amplamente utilizado na reconstrução óssea. A biocompatibilidade assim como outras propriedades físico-químicas da hidroxiapatita podem ser modificadas por meio da adição de diferentes íons na sua estrutura. O íon nióbio (V) não tem sido empregado comumente na síntese de hidroxiapatitas. O objetivo deste trabalho foi verificar o emprego da rota hidrotérmica na síntese de hidroxiapatita dopada com íon nióbio (V). A rota empregada utiliza o complexo di-hidrogeno tris(oxalato) oxiniobato (V) de amônio trihidratado (NH4H2[NbO(C2O4)3].3H2O), como precursor de íon nióbio (V). A adição de ácido cítrico e ureia na rota hidrotérmica é usada para o controle do pH da síntese e da taxa de precipitação. Amostras pura e aditivada com 5,3 ppm de íon nióbio (V) foram obtidas. A coexistência de outras fases além da hidroxiapatita não foi observada em ambas amostras por meio dos empregos das técnicas de difração de raios X e espectroscopia no infravermelho. Por meio da técnica de FTIR observou-se a presença de grupos funcionais característicos da hidroxiapatita. Na análise por microscopia eletrônica de varredura, verificou-se a formação de aglomerados compostos por partículas arredondadas confirmadas pela técnica de microscopia eletrônica de transmissão. A análise espectroscópica de fluorescência de raios X detectou a presença de nióbio na amostra aditivada obtida. Os resultados apontam que podem ser sintetizadas hidroxiapatitas aditivadas com íon nióbio (V) por meio da rota hidrotérmica, podendo ser considerado como enorme o potencial para a aplicação em biocerâmicas.

In this work, we investigated the role of solid-state dealumination by (NH4)2SiF6 (25% Al removal and 13% Si insertion), the impregnation of niobium (10, 18, and 25 wt. %) on dealuminated *BEA (DB) zeolite and their catalytic properties in ethanol and xylose transformations. Among all the studied catalysts, 18%Nb-DB showed increased mesoporosity and external areas. A leveling effect in the number and strength of the proposed two sites (Br&oslash, nsted and Lewis) present in the catalyst (n1 = 0.24 mmol g&minus, 1, &minus, &Delta, H1 = 49 kJ mol&minus, 1, and n2 = 0.20 mmol g&minus, 1, &ndash, H2 = 42 kJ mol&minus, 1) in the catalyst 18%Nb-DB, might be responsible for its good activity. This catalyst presented the highest selectivity for diethyl ether, DEE (97%) with 61% conversion after 50 ethanol pulses at 230 &deg, C (turnover number, TON DEE = 1.15). These features allowed catalytically fruitful bonding of the ethanol molecules to the neighboring sites on the channels, facilitating bimolecular ether formation through a possible SN2 mechanism. The same catalyst was active and selective for transformation of xylose at 180 &deg, C, showing 64% conversion and 51% selectivity for furfural (TON Furfural = 24.7) using water as a green solvent.

La valorización de biomasa lignocelulósica y de sus derivados supone una alternativa sostenible frente a la utilización de fuentes fósiles para la producción de combustibles y productos químicos. En este contexto, el aprovechamiento de compuestos oxigenados presentes en efluentes acuosos derivados de tratamientos primarios de la biomasa (vía pirólisis rápida), tras un proceso de separación de fases, es fundamental en el esquema actual de bio-refinería. La estrategia consiste en transformar estos compuestos orgánicos en mezclas de hidrocarburos y compuestos aromáticos de utilidad como componentes y/o aditivos en combustibles líquidos. Los materiales catalíticos comúnmente estudiados para este tipo de procesos deben su actividad a sus propiedades multifuncionales. Sin embargo, su actividad en mezclas acuosas complejas y su estabilidad bajo condiciones de reacción más próximas a la realidad industrial continúan siendo un desafío en vistas a su futura aplicación. La presente Tesis Doctoral se centra en el diseño de nuevos catalizadores heterogéneos que sean activos y resistentes en reacciones de condensación consecutivas en fase acuosa de mezclas de compuestos oxigenados ligeros (C1-C4) bajo condiciones de reacción moderadas. En este sentido, este trabajo difiere de los estudios habituales que emplean compuestos modelo de manera individual y en ausencia de agua. En primer lugar, óxidos mixtos (incluyendo CexZr1-xO e hidrotalcitas), que han sido ampliamente utilizados en reacciones de condensación y cetonización, muestran buenos resultados catalíticos en la condensación en fase acuosa, pero graves problemas de estabilidad debido principalmente al leaching de la fase activa de estos materiales. Esto demuestra la necesidad de desarrollar nuevos catalizadores ácidos capaces de operar en sistemas complejos en presencia de agua y ácidos orgánicos, bajo condiciones de reacción moderadas. En este sentido, la adición de HF durante la síntesis de catalizadores basados en TiO2, permite obtener materiales donde se expone mayoritariamente el plano {001}, que es catalíticamente más activo. Además, los sitios ácidos de Lewis presentes en estos materiales de TiO2 facetados, presentan una gran estabilidad en reacciones de condensación, especialmente en presencia de ácidos y grandes cantidades de agua. Esta estrategia permite desarrollar materiales con mejor actividad catalítica y estabilidad que otros catalizadores comerciales basados en TiO2. Por otra parte, la síntesis hidrotermal de óxidos metálicos basados en Nb y W-Nb permite obtener materiales cuya estructura cristalina, propiedades texturales y propiedades ácidas pueden ser modificadas controlando la composición y las condiciones de calcinación aplicadas. Esto permite obtener catalizadores optimizados respecto a los empleados en literatura, que muestran gran actividad y elevada estabilidad en reacciones de condensación de compuestos oxigenados en fase acuosa. Por último, se han desarrollado nuevos materiales basados en óxidos mixtos de estaño, titanio y/o niobio (SnxTiyNbzO) preparados por co-precipitación que presentan mayoritariamente la estructura tipo rutilo del SnO2, la cual posee características hidrófobas. El control de la composición y las condiciones de calcinación permite obtener óxidos con estructuras cristalinas uniformes, altas áreas superficiales y mayor densidad de sitios ácidos de Lewis respecto a los respectivos óxidos comerciales. Estos materiales son catalizadores activos y muy resistentes en la valorización de compuestos oxigenados presentes en efluentes acuosos derivados de distintos tratamientos de la biomasa., The valorisation of lignocellulosic biomass and its derivatives has become a sustainable alternative to the use of fossil sources for the production of fuels and chemicals. In this context, the conversion of light oxygenated compounds present in aqueous effluents derived from primary treatments of biomass (i.e. fast pyrolysis), after a phase separation process via water addition is a key step in the actual bio-refinery scheme processes. The strategy is based on the transformation of these low-value water-soluble oxygenated compounds into a mixture of hydrocarbons and aromatics useful for blending with automotive fuels. In general, the activity of the catalysts employed in these processes is based on their bifunctional character. Nonetheless, their activity in complex aqueous mixtures and their stability under faithful operating conditions close to industrial scenarios are critical challenges to be further applied. This thesis comprises a detailed work in the design of new solid catalysts with high activity and stability in consecutive aqueous-phase condensation reactions of light oxygenated compounds (C1-C4) mixtures under moderated process conditions. In this sense, this work differs from usual probe molecules studies performed even in the absence of water. Firstly, mixed oxides (including CexZr1-xO and hydrotalcite-derived materials) were employed as they have been widely studied in condensation and ketonization reactions. These materials show good catalytic results in the liquid-phase condensation of light oxygenates, but strong catalysts deactivation was observed due to the active phase partial leaching. Therefore, new heterogeneous acid catalysts must be developed in order to meet these new process requirements: complex aqueous environments with high contents of organic acids and moderated reaction conditions. In this sense, the addition of aqueous HF during TiO2 catalysts synthesis is essential to selectively control the preferential growth of catalytic more reactive {001} TiO2 facets. Moreover, Lewis acid sites on faceted TiO2 materials have great stability in condensation reactions, especially in the presence of organic acids and high water contents. Thus, this strategy allows obtaining materials that show better catalytic results and stability than other commercial titanium oxides. Moreover, hydrothermal synthesized Nb- and WNb-mixed oxides have shown the advantage of having crystalline structure, area and acid properties modified by tailoring their composition and post-synthesis heat-treatments conditions. Optimized NbOx and WNbO materials show higher activity and stability in the aqueous-phase condensation of oxygenated compounds than other commercial samples, commonly employed in literature Finally, new acid catalysts prepared via co-precipitation based on tin, titanium and niobium (SnxTiyNbzO) mixed oxides have been developed. These materials mainly present SnO2 rutile-phase crystalline structure, which has been claimed to have interesting hydrophobic characteristics. Tailoring of composition and calcination conditions allows obtaining mixed oxides with uniform crystalline structures, enhanced surface areas and a higher concentration of Lewis acid sites compared to analogous commercial catalysts. These materials show high activity and stability in the valorisation of oxygenated compounds present in aqueous effluents derived from different biomass processes., La valorització de biomassa lignocel·lulòsica i dels seus derivats suposa una alternativa sostenible enfront de la utilització de fonts fòssils per a la producció de combustibles i productes químics. En aquest context, l'aprofitament de compostos oxigenats presents en efluents aquosos derivats de tractaments primaris de la biomassa (via piròlisi ràpida), després d'un procés de separació de fases, és fonamental en l'esquema actual de bio-refineria. L'estratègia consisteix a transformar aquests compostos orgànics en mescles d'hidrocarburs i compostos aromàtics d'utilitat com a components o additius en combustibles líquids. Els materials catalítics comunament estudiats per a aquest tipus de processos deuen l'activitat a les seues propietats multifuncionals; no obstant això, la seua activitat en mescles aquoses complexes i la seua estabilitat sota condicions de reacció més pròximes a la realitat industrial continuen sent un desafiament amb vista a la seua futura aplicació. La present tesi doctoral se centra en el disseny de nous catalitzadors heterogenis que siguen actius i resistents en reaccions de condensació consecutives en fase aquosa de mescles de compostos oxigenats lleugers (C1-C4) sota condicions de reacció moderades. En aquest sentit, aquest treball difereix dels estudis habituals, que empren compostos model de forma individual i en absència d'aigua. En primer lloc, òxids mixts (inclosos CexZr1-xO i hidrotalcites), que han sigut àmpliament utilitzats en reaccions de condensació i cetonització, mostren bons resultats catalítics en la condensació en fase aquosa, però greus problemes d'estabilitat a causa principalment de la lixiviació de la fase activa d'aquests materials. Això demostra la necessitat de desenvolupar nous catalitzadors àcids capaços d'operar en sistemes complexos en presència d'aigua i àcids orgànics, sota condicions de reacció moderades. En aquest sentit, l'addició d'HF durant la síntesi de catalitzadors basats en TiO2, permet obtenir materials on s'exposa majoritàriament el plànol {001}, que és catalíticament més actiu. A més, els llocs àcids de Lewis presents en aquests materials de TiO2 facetats, presenten una gran estabilitat en reaccions de condensació, especialment en presència d'àcids i grans quantitats d'aigua. Aquesta estratègia permet desenvolupar materials amb millor activitat catalítica i estabilitat que altres catalitzadors comercials basats en TiO2. D'altra banda, la síntesi hidrotermal d'òxids metàl·lics basats en Nb i W-Nb permet obtenir materials l'estructura cristal·lina, les propietats texturals i les propietats àcides dels quals poden ser modificats controlant la composició i les condicions de calcinació aplicades. Això permet obtenir catalitzadors optimats respecte als emprats en la literatura, que mostren gran activitat i elevada estabilitat en reaccions de condensació de compostos oxigenats en fase aquosa. Finalment, s'han desenvolupat nous materials basats en òxids mixts d'estany, titani o niobi (SnxTiyNbzO) preparats per coprecipitació, que presenten majoritàriament l'estructura tipus rútil del SnO2, la qual té característiques hidròfobes. El control de la composició i les condicions de calcinació permeten obtenir òxids amb estructures cristal·lines uniformes, altes àrees superficials i major densitat de llocs àcids de Lewis respecte als respectius òxids comercials. Aquests materials són catalitzadors actius i molt resistents en la valorització de compostos oxigenats presents en efluents aquosos derivats de diferents tractaments de la biomassa.

In this Doctorate research, niobia compounds were evaluated as solid acid catalysts in the continuous esterification reaction. Oleic acid was assumed as model component to represent the free fatty acids (FFA) and ethanol was selected as esterifying agent because is less toxic for humans, renewable, derived from agricultural products and widely available in Brazil. Samples of niobic acid and niobium phosphate were calcined at different temperatures (from 300 to 600 °C), characterized by nitrogen adsorption, thermogravimetric analysis (TGA-DSC), X-ray diffraction (XRD) and temperature-programmed desorption of ammonia (NH3-TPD) and, then, submitted to catalytic tests. For the samples which showed the highest catalytic activity, the experimental conditions of temperature, mass of catalyst and ethanol:oleic acid molar ratio were optimized using design of experiments (DOE) and canonical analysis. Results showed that calcination temperature affected the textural properties, structure and acidity of the materials. An increase on the calcination temperature promoted a decrease on the BET surface area, total acidity and, consequently, on the catalytic performance for the esterification reaction, for both catalysts. However, compared to niobic acid, niobium phosphate showed higher thermal stability, avoiding a more significant decline in the conversions obtained. This fact occurs because niobic acid changes from amorphous to crystalline when calcined at 500 °C and niobium phosphate changed its structure only at calcination temperatures up to 700°C. Besides that, all the parameters significantly affected the yield of esters. Yield of esters up to 70% could be obtained at optimized conditions, for niobic acid and niobium phosphate. In other step of this project, a plant of biodiesel production through hydroesterification process was simulated, using UniSim software and a preliminary economic analysis was performed. Conversions data obtained in laboratory for hydrolysis and esterification reactions were used as input data of the simulated reactors. The hydroesterification process simulated showed to be technologically feasible, producing biodiesel in a flowrate of 770 kg/h (6736 ton/year) with high purity (97%), however, based on the cash flow rate obtained, it was not economically reasonable. No presente trabalho de doutorado, materiais a base de nióbio foram avaliados como catalisadores ácidos sólidos na reação de esterificação contínua. O ácido oleico foi utilizado como componente modelo para representar os ácidos graxos livres (AGL) e o etanol foi selecionado como agente esterificante, uma vez que não é tóxico, renovável, obtido a partir de produtos agrícolas e muito disponível no Brasil. Amostras de ácido nióbico e fosfato de nióbio foram calcinadas a diferentes temperaturas (de 300 a 600 °C), caracterizadas pelas técnicas de adsorção de nitrogênio, análise termogravimétrica (ATG), difração de raios X (DRX) e dessorção de amônia a temperatura programada (DTP-NH3) e, então, submetidas a testes catalíticos. Para as amostras que apresentaram melhores atividades catalíticas, as condições experimentais de temperatura, massa de catalisador e razão molar etanol:ácido oleico foram otimizadas, utilizando a técnica de planejamento de experimentos e análise canônica. Os resultados mostraram que a temperatura de calcinação afetou as propriedades texturais, a estrutura e a acidez dos materiais. O aumento na temperatura de calcinação provocou decréscimos na área superficial, na acidez total e, consequentemente, no desempenho catalítico para a reação de esterificação, em ambos os catalisadores. No entanto, se comparado ao ácido nióbico, o fosfato de nióbio apresentou maior estabilidade térmica, com diminuições não tão significativas nas conversões obtidas. Esse fato ocorreu, pois o ácido nióbico muda sua estrutura de amorfa para cristalina quando calcinado a 500 °C e o fosfato de nióbio somente sofre alterações em sua estrutura quando submetido a temperaturas de calcinação maiores que 700 °C. Todos os parâmetros afetaram significativamente o rendimento em ésteres. Rendimentos em ésteres de até 70% foram obtidos em condições operacionais otimizadas, para ácido nióbico e fosfato de nióbio. Em outra etapa deste projeto, o processo de hidroesterificação para a produção de biodiesel foi simulada, utilizando o software UniSim, e uma análise econômica preliminar foi realizada. Os dados de conversão obtidos em laboratório para as reações de hidrólise e esterificação foram utilizados como dados de entrada para os reatores simulados. O processo de hidroesterificação mostrou-se tecnicamente viável, produzindo biodiesel em uma vazão mássica de 770 kg/h (6736 toneladas/ano) com alta pureza (97%), no entanto, baseado no diagrama de fluxo de caixa obtido, o processo não se mostrou economicamente viável. Tese (Doutorado)

The dry sliding wear behaviour of different Ti-Nb and Ti-Mo surfaces was investigated in order to evaluate the role of Nb and Mo beta-stabilizing elements in titanium wear resistance to consider them for biomedical applications. Dry sliding wear tests were performed under =lubricated conditions using a ball-on-plate tribometer (UMT) with reciprocating lineal movement of 1 Hz frequency at different loads (2 and 5 N) and against two counterface materials (alumina and stainless steel) to assess the effect of these parameters on wear. The results indicated an improvement in wear resistance for all the modified Ti surfaces. Metal-on-metal surfaces exhibited higher wear rate than ceramic-on-metal, and higher wear was observed for the more severe conditions. Wear rate values on modified surfaces were between 53% and 96% lower compared to pure Ti tested at 2 N, and up to 79% lower than Ti at 5 N. In both cases the highest wear reduction was observed for Ti-Mo-NH4Cl surface. The authors would like to thank the funding provided for this research by the Regional Government of Madrid (program MULTIMAT-CHALLENGE-CM, ref. S2013/MIT-2862), and by the Institute of Alvaro Alonso Barba (IAAB) of the University Carlos III of Madrid.

This Doctoral Thesis presents a study on the synthesis and characterization of materials based on tungsten bronze partially substituted with transition metals and / or alkaline metals, with hexagonal bronze structure (HTB), to be used as catalysts in the aerobic transformation of methanol to dimethyl ether and/or formaldehyde. Active and selective binary W-X-O catalysts (X = Ti, V or Mo) for methanol transformation, are obtained by hydrothermal synthesis and subsequent thermal treatment in nitrogen at temperatures between 400 and 600 °C. The nature of the active sites (acids and / or redox, depending on the composition of the catalyst) determines the distribution of products (dimethyl ether and/or formaldehyde, respectively). Subsequently, the synthesis and characterization of ternary W-V-M catalysts (M = Mo, Nb or alkali metal) have been studied in order to improve the selectivity to formaldehyde and dimethyl ether. The three types of ternary catalysts studied improve the formation of formaldehyde, although following different strategies: i) increasing the amount of redox sites (W-V-Mo); Ii) decreasing the strength of the acid sites (W-V-Nb) or iii) decreasing the density of acid sites (W-V-alkaline). A second aspect is related to the nature of the vanadium sites, since the presence of a second promoter limits both the amount of vanadium in the material and the oxidation state of vanadium species, which would explain the better selectivity to partial oxidation products obtained by the ternary catalysts. Finally, a comparative study has been carried out between aerobic and anaerobic conditions using some of the most representative catalysts. A study by infrared spectroscopy of adsorbed methanol (in the presence or absence of oxygen) can explain the reaction mechanism (acid and/or redox) of these materials, as well as the factors that influence the deactivation of the catalyst when working under anaerobic conditions., Resumen La presente tesis doctoral presenta un estudio sobre la síntesis y caracterización de materiales basados en bronces de wolframio parcialmente sustituidos con metales de transición y/o metales alcalinos, con estructura de bronce hexagonal (HTB), para ser empleados como catalizadores en la transformación aeróbica de metanol a dimetiléter y/o formaldehído. Mediante síntesis hidrotermal y posterior tratamiento térmico en nitrógeno a temperaturas entre 400 y 600 °C se obtienen catalizadores binarios W-X-O (X = Ti, V o Mo), activos y selectivos para la transformación de metanol. La naturaleza de los centros activos (ácidos y/o redox, dependiendo de la composición del catalizador) determina la distribución de productos (dimetiléter y/o formaldehido, respectivamente). Posteriormente, se ha estudiado la síntesis y caracterización de sistemas ternarios W-V-M (M = Mo, Nb o metal alcalino) con el fin de mejorar la relación de selectividades a formaldehido y dimetiléter. Los tres tipos de catalizadores mejoran la formación de formaldehido, aunque siguiendo estrategias diferentes: i) aumentando los centros redox (W-V-Mo); ii) disminuyendo la fortaleza de los centros ácidos (W-V-Nb); o iii) eliminando la densidad de centros ácidos (W-V-alcalino). Un segundo aspecto está relacionado con la naturaleza de los centros de vanadio, dado que la presencia de un segundo promotor limita tanto la cantidad de vanadio en el material como el estado de oxidación de las especies vanadio, lo que explicaría la mejor selectividad a productos de oxidación parcial de los catalizadores ternarios. Finalmente, se ha llevado a cabo un estudio comparativo entre condiciones aeróbicas y anaeróbicas usando algunos de los catalizadores más representativos. Un estudio por espectroscopia infrarroja de metanol adsorbido (en presencia y ausencia de oxígeno) permiten explicar el mecanismo de reacción (ácido y/o redox) de estos materiales, así como los factores que influyen en la desactivación del catalizador cuando se trabaja en condiciones anaeróbicas., Resum La present tesi doctoral presenta un estudi sobre la síntesi i caracterització de materials basats en bronzes de wolframi parcialment substituït amb metalls de transició i/o metalls alcalins, amb estructura de bronze hexagonal (HTB), per a ser utilitzats com a catalitzadors en la transformació aeròbica de metanol a dimetilèter i/o formaldehid. Se han sintetitzat catalitzadors binaris W-X-O (X = Ti, V o Mo), actius i selectius en la transformació de metanol, mitjançant síntesi hidrotermal i posterior tractament tèrmic en nitrogen a temperatures entre 400 i 600 °C. La naturalesa dels centres actius (àcids i/o redox, depenent de la composició del catalitzador) determina la distribució de productes (dimetilèter i/o formaldehid, respectivament). Posteriorment, s'ha estudiat la síntesi i caracterització de sistemes ternaris W-V-M (M = Mo, Nb o metall alcalí) per tal de millorar la relació de selectivitats a formaldehid i dimetilèter. Els tres tipus de catalitzadors ternaris milloren la formació de formaldehid, encara que seguint estratègies diferents: i) augmentant la quantitat de centres redox (W-V-Mo); ii) disminuint la fortalesa dels centres àcids (W-V-Nb); o iii) disminuint la densitat de centres àcids (W-V-alcalí). Un segon aspecte està relacionat amb la naturalesa dels centres de vanadi, atès que la presència d'un segon promotor limita tant la quantitat de vanadi en el material com l'estat d'oxidació de les espècies vanadi, la qual cosa explicaria la millor selectivitat a productes de oxidació parcial dels catalitzadors ternaris. Finalment, s'ha dut a terme un estudi comparatiu entre condicions aeròbiques i anaeròbiques usant alguns dels catalitzadors més representatius. Un estudi per espectroscòpia infraroja de metanol adsorbit (en presència i absència d'oxigen) permeten explicar el mecanisme de reacció (àcid i / o redox) d'aquests materials, així com els factors que influeixen en la desactivació del catalitzador quan es treballa en condicions anaeròbiques.

The fluoride use for anodizing electrolytes has been primarily responsible for the formation of nanoporous oxides at valve metals, except aluminum, since it causes a dissolution process. This study presents the formation of an oxide model according to the following anodizing parameters: 100 V, 12.73 mA/cm2, room temperature and the niobium samples anodized in niobium oxalate and oxalic acid electrolytes without and with the addition of HF for 5, 30 and 60 min. The anodized samples were analyzed morphologically by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and the hydrophobicity of the samples was assessed by the sessile drop method. The presence of fluor in the niobium oxalate electrolyte formed oxides with lower a dissolution and a low hydrophobicity compared to the one formed in oxalic acid was attributed to the incorporation of niobium and oxalate ions. Thereby, the model proposed in this paper showed that during anodization the migration of the fluoride ion into the oxide occurs at high speed, which results in the formation of microcones, leading to the formation of discrete layers of porous oxide.

The present study aimed to create and characterize niobium and niobium-iron 60% coatings applied to steel API 5L X70 using the hypersonic thermal spray process (HVOF). The morphologies of the coatings were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and profilometry, while the coatings' hardnesses was evaluated using the Vickers hardness test. The coatings' corrosion resistance was evaluated by monitoring their open circuit potential and potentiodynamic polarization and performing electrochemical impedance spectroscopy in a 0. 05 M NaCl solution. The results showed that the niobium-iron coating contained minor porosity regions, while such defects occurred over large regions of the niobium coating. In terms of corrosion resistance, the coatings obtained in this work promoted a reduction in the substrate's corrosion rate, but the presence of discontinuities such as porosity compromised the barrier effects of these coatings.

A diversidade do emprego do aço corrobora a sua grande importância para a sociedade. Devido à sua versatilidade e o seu amplo campo de atuação, o aço pode ser utilizado submerso no solo na construção de extensas tubulações, minerodutos e tanques para o transporte de combustíveis. O constante contato entre a tubulação de aço e o solo, com o passar do tempo, torna-o exposto à ação corrosiva. Em decorrência, são envolvidos custos diretos elevados com inspeção, manutenção e a substituição de peças, e custos indiretos devido a problemas de saúde oriundos de contaminação, exaurimento de recursos minerais, perfurações com perdas de materiais, além de danos ambientais. O estudo dos processos corrosivos tem crescido bastante e o conhecimento tanto dos princípios da corrosão quanto da proteção anticorrosiva é fundamental na busca de soluções para mitigar os efeitos advindos da corrosão, prevenir sua ocorrência e desenvolver materiais com maior resistência. Os aços API 5L X70 são utilizados em malhas dutoviárias que transportam gases, petróleo e seus derivados onde se exige elevada resistência mecânica e à corrosão. Desta forma, estes aços são suscetíveis ao processo corrosivo, pois ficam em contato direto com diversos solos e ambientes brasileiros. No presente trabalho, avaliou-se o comportamento do aço API 5L X70 com e sem revestimento de nióbio em solo quimicamente tratado com soluções ácidas (simulando a chuva ácida) e básicas (simulando a calagem do solo). Foram empregadas técnicas como a aspersão térmica (para revestimento das amostras), ensaios experimentais de corrosão e microscopia eletrônica de varredura, com a finalidade de identificar os produtos de corrosão. Ao final, classificou-se as formas e tipos de corrosão obtidas nos corpos de prova, calculou-se a taxa de corrosão e foi avaliada a eficiência e a viabilidade técnica do revestimento com nióbio além de suas propriedades anticorrosivas. Como resultado, as amostras com revestimento em meio ácido apresentaram corrosão elevada, e as que estavam em meio básico, revelaram uma boa resitência ao processo corrosivo. Para as amostras sem revestimento, uma corrosão moderada foi evidenciada com a adição de ácido sulfúrico, enquanto que, com a adição de hidróxido de cálcio, a corrosividade foi alta.

Austenite-martensite transformation influence on the dimensional stability of a new experimental tool steel alloyed with niobium (0.08% wt.) and vanadium (0.12% wt.) has been studied. The dimensional stability of this new steel was compared with the dimensional stability of commercial steel, after and before two thermal treatments, T1 (860 °C) and T2 (900 °C). The thermal treatments consisted on heating and cooling, at 1 atmosphere of pressure, in N2 atmosphere furnace, fol lowing by heating in a conventional furnace at 180 °C during 1 hour. Initially, the experimental steel composition and Ac1 and Ac3 transformation temperatures were determined by glow-discharge luminescence (GDL) and dilatometric tests, respectively, in order to select the austenization temperatures of T1 and T2 treatments. After hardness measurement, the microstructure of both steels was characterized by X-Ray Diffraction (XRD) and optical metallography, before and after of T1 and T2 thermal treatments. Finally, longitudinal and angular dimensional stability analyses were realized for both commercial and experimental steels. After a contrastive hypothesis analysis, the results showed that the longitudinal relative variation of the experimental steel calculated was around 0.2% and the angular relative variation was not significantSe ha estudiado la influencia de la transformación de austenita a martensita en la estabilidad dimensional de un acero experimental para herramientas aleado con niobio (0,08% en peso) y vanadio (0,12% en peso). La estabilidad dimensional del acero experimental fue comparada con la de un acero comercial antes y después de ser sometidos, ambos aceros, a dos tratamientos térmicos diferentes. Los tratamientos térmicos consistieron en un calentamiento y mantenimiento durante una hora a temperaturas de 860 °C (T1) y 900 °C (T2) y un enfriamiento final en horno con nitrógeno (N2) a 1 atmósfera de presión. Inicialmente, se determinaron las composiciones del acero experimental y comercial, mediante técnica de luminiscencia (GDL), y las temperaturas de transformación Ac1 y Ac3 del acero experimental, mediante ensayos dilatométricos, para seleccionar las temperaturas de austenización de los tratamientos T1 y T2. Posteriormente, tras medir la dureza de ambos aceros, se caracterizó la microestructura de los dos aceros mediante técnicas de Difracción de Rayos X (XRD) y metalografía óptica, antes y después de los tratamientos térmicos T1 y T2. Por último, se realizaron los análisis de estabilidad dimensional longitudinal y angular por medio de las medidas de las probetas anulares de los aceros comercial y experimental. Los resultados obtenidos tras haber realizado un contraste de hipótesis mostraron que la variación relativa longitudinal máxima calculada para el acero experimental fue del 0,2% y su variación relativa angular no fue significativa.

Presentado al: 8º Congreso Nacional de Ciencia y Tecnología Metalúrgicas. Madrid 27 a 29 de mayo de 1998 Los carburos de tantalio y de niobio se caracterizan por su extremada dureza y resistencia al ataque químico. Ambos carburos, pero principalmente el de tantalio, se utilizan en la fabricación de metal duro (carburos cementados), junto con otros carburos, para herramientas de corte, matricería y para operaciones especiales de mecanizado que requieran resistencia al desgaste y resistencia al choque mecánico y a alta temperatura. También se está investigando su uso como refuerzo de aceros rápidos para el desarrollo de materiales resistentes al desgaste por vía pulvimetalúrgica. Sin embargo, el uso de TaC suele venir limitado por su alto precio, por lo que en ocasiones se utiliza carburo de tantalio con conteniendo de niobio, más barato. En el presente trabajo se estudia la obtención de carburos complejos de tantalio y de niobio a partir de un concentrado mineral de columbotantalita de procedencia española, mediante un proceso relativamente barato y sencillo, como es la reducción carbotérmica. Se describe el afino previo del mineral y su posterior reducción, así como la caracterización de los productos obtenidos. Tantalum and niobium carbides are characterized by its high hardness and chemical corrosion resistance. Both carbides, but mainly TaC, are used in hard metals (sintered carbides), together with other carbides, to manufacture cutting tools and dies and in special machining applications involving mechanical shock at high temperature. Its use as reinforcement of wear resistant materials through powder metallurgy techniques are being investigated. However, the use of TaC is usually limited because of its high cost. Therefore tantalum carbide with niobium content, which is cheaper, is used. In this work the obtention of complex tantalum and niobium carbides from a Spanish columbotantalite ore is studied through a relatively cheap and simple process as it is carbothermic reduction. Concentration of the ore, its reduction and the characterization of products are described. Este trabajo ha sido posible gracias a la financiación por la CICYT del proyecto MAT96-0542, ya finalizado, y del proyecto MAT97-0695, actualmente en curso, y a los trabajos realizados con anterioridad por el Dr. J. C. Ruiz Sierra, iniciador e impulsor de ambos proyectos y de esta línea de investigación.

The effect of Nb microalloying on structure and physical properties of quenched and tempered 13%Cr martensitic stainless steel was investigated. Excellent strength and adequate toughness properties were obtained by 0.10 wt% Nb addition to low interstitial (N 0.01wt%, C < 0.02wt%) steel. The effect of Nb in 13%Cr steels with high N content was also studied in a commercial martensitic stainless steel sample containing higher levels of N and also alloyed with V. The microstructure, precipitate morphology and dispersion and volume fraction of reverse austenite were characterized. The strength properties obtained in the steel with 0.10%Nb are significantly higher than those of the V-containing steel. The study shows that whereas amount, size and dispersion of precipitates of microalloying elements contribute to enhanced strength, the optimum volume fraction of reverse austenite formed contributes to enhanced ductility and toughness properties. More importantly, high Nb additions to low N -13%Cr-1%Mo steel are found to improve significantly resistance against pitting corrosion significantly. O efeito da adição de Nb, na microestrutura e nas propriedades mecânicas e de resistência à corrosão dos aços martensíticos com 13% Cr, foi investigado. Excelente resistência mecânica final e suficiente tenacidade e alongamento foram obtidos em aços contendo baixo teor de elementos intersticiais (0.01%N e C < 0.02%) e com adição de 0.10%Nb. O efeito do Nb, também, foi estudado em uma amostra industrial contendo maiores teores de N e adição de V. As propriedades mecânicas obtidas, no aço contendo 0.10% Nb, mostraram-se, significativamente, maiores que aquelas obtidas com o aço contendo V e maior teor de N. A microestrutura, morfologia e dispersão de precipitados, bem como a fração volumétrica de austenita revertida, foram, também, caracterizadas. O tamanho e a dispersão dos precipitados formados a partir dos elementos microligantes contribuem para aumentar a resistência mecânica, enquanto a formação de austenita revertida auxilia na obtenção de tenacidade e ductilidade. Quanto à resistência à corrosão por pite, o desempenho do aço 13Cr5Ni1Mo com maior teor de Nb e menor quantidade de N foi, surpreendentemente, melhor em comparação ao desempenho das demais composições estudadas.

Carlosbarbosaite, ideally (UO2)2Nb2O6(OH)2·2H2O, is a new mineral which occurs as a late cavity filling in albite in the Jaguaraçu pegmatite, Jaguaraçu municipality, Minas Gerais, Brazil. The name honours Carlos do Prado Barbosa (1917–2003). Carlosbarbosaite forms long flattened lath-like crystals with a very simple orthorhombic morphology. The crystals are elongated along [001] and flattened on (100); they are up to 120 μm long and 2–5 μm thick. The colour is cream to pale yellow, the streak yellowish white and the lustre vitreous. The mineral is transparent (as individual crystals) to translucent (massive). It is not fluorescent under either long-wave or short-wave ultraviolet radiation. Carlosbarbosaite is biaxial(+) with α = 1.760(5), β = 1.775(5), γ = 1.795(5), 2Vmeas. = 70(1)º, 2Vcalc. = 83º. The orientation is X || a, Y || b, Z || c. Pleochroism is weak, in yellowish green shades, which are most intense in the Z direction. Two samples were analysed. For sample 1, the composition is: UO3 54.52, CaO 2.07, Ce2O3 0.33, Nd2O3 0.49, Nb2O5 14.11, Ta2O5 15.25, TiO2 2.20, SiO2 2.14, Fe2O3 1.08, Al2O3 0.73, H2O (calc.) 11.49, total 104.41 wt.%; the empirical formula is (□0.68Ca0.28Nd0.02Ce0.02)Σ=1.00[U1.44□0.56O2.88(H2O)1.12](Nb0.80Ta0.52Si0.27Ti0.21Al0.11Fe0.10)Σ=2.01 O4.72(OH)3.20(H2O)2.08. For sample 2, the composition is: UO3 41.83, CaO 2.10, Ce2O3 0.31, Nd2O3 1.12, Nb2 O5 14.64, Ta2O5 16.34, TiO2 0.95, SiO2 3.55, Fe2O3 0.89, Al2O3 0.71, H2O (calc.) 14.99, total 97.43 wt.%; the empirical formula is (□0.67Ca0.27Nd0.05Ce0.01)Σ=1.00[U1.04□0.96O2.08(H2O)1.92] (Nb0.79Ta0.53Si0.42Ti0.08Al0.10Fe0.08)Σ=2.00O4.00(OH)3.96(H2O)2.04. The ideal endmember formula is (UO2)2Nb2O6(OH)2·2H2O. Calculated densities are 4.713 g cm-3 (sample 1) and 4.172 g cm-3 (sample 2). Infrared spectra show that both (OH) and H2O are present. The strongest eight X-ray powder-diffraction lines [listed as d in Å (I)(hkl)] are: 8.405(8)(110), 7.081(10)(200), 4.201(9)(220), 3.333(6)(202), 3.053(8)(022), 2.931(7)(420), 2.803(6)(222) and 2.589(5)(040,402). The crystal structure was solved using single-crystal X-ray diffraction (R = 0.037) which gave the following data: orthorhombic, Cmcm, a = 14.150(6), b = 10.395(4), c = 7.529(3) Å, V = 1107(1) Å3, Z = 4. The crystal structure contains a single U site with an appreciable deficiency in electron scattering, which is populated by U atoms and vacancies. The U site is surrounded by seven O atoms in a pentagonal bipyramidal arrangement. The Nb site is coordinated by four O atoms and two OH groups in an octahedral arrangement. The half-occupied tunnel Ca site is coordinated by four O atoms and four H2O groups. Octahedrally coordinated Nb polyhedra share edges and corners to form Nb2O6(OH)2 double chains, and edge-sharing pentagonal bipyramidal U polyhedra form UO5 chains. The Nb2O6(OH)2 and UO5 chains share edges to form an open U—Nb—φ framework with tunnels along [001] that contain Ca(H2O)4 clusters. Carlosbarbosaite is closely related to a family of synthetic U–Nb–ϕ framework tunnel structures, it differs in that is has an (OH)-bearing framework and Ca(H2O)4 tunnel occupant. The structure of carlosbarbosaite resembles that of holfertite.

Os efeitos da temperatura e do tempo sobre a cinética de revenimento foram estudados, utilizando chapas de um aço baixo carbono e microligado com Nb e de outro aço com composição química similar, porém sem Nb. A lei de cinética de revenimento foi estudada pela equação de Johnson, Mehl e Avrami, a partir da variação da dureza Vickers das amostras revenidas com a temperatura e com o tempo de revenimento para os dois aços. Para o aço sem Nb, verificou-se que a dureza praticamente não variou com o tempo de revenimento, para a temperatura de revenimento de 600°C, e que a dureza tende a saturar para altos tempos de revenimento, para as diferentes temperaturas de revenimento utilizadas. Para o aço com Nb, observou- se uma maior resistência ao revenimento para as temperaturas de revenimento de 500 e 600°C, associada à precipitação de partículas muito finas de carbonetos de Nb dispersos na ferrita. A energia de ativação, para o revenimento, para o aço sem Nb, é de 130kJ/mol e pudesse inferir que o mecanismo que limita a cinética de revenimento, é a difusão intersticial do carbono na ferrita. Para o aço com Nb, a energia de ativação, para o revenimento é de 180kJ/mol e pode-se inferir que o mecanismo que limita a cinética de revenimento é a difusão do Nb na ferrita. The effect of temperature and time on tempering kinetics was studied by using a low carbon steel microalloyed with Nb (0,031) and another steel with a similar chemical composition, however without Nb. After determining the Vickers hardness values, the kinetics law of tempering was studied by the Jonhson- Mehl-Avrami equation using a variation of temperatures and time for both steels. The hardness of the steel without Nb did not change with the tempering time at 600ºC and tended to saturate at high tempering times, for the different tempering temperatures used. For the tempering temperatures of 500 and 600ºC, the steel with Nb has a greater tempering resistance and this effect is associated to the precipitation of very fine NbC particles dispersed in ferrite matrix. The activation energy of the tempering transformation of the steel without Nb is 130kJ/mol and it could be inferred that the mechanism that controls the tempering kinetics of this steel is the interstitial diffusion of carbon in the ferrite. In the steel with Nb the activation energy is 180kJ/mol and the mechanism that controls the tempering kinetics is the Nb diffusion in the ferrite.

This paper presents the study on lithium triborate glass (LBO) in the system (1-x)|3B2O3.Li2O| (x)Nb2O5 yPr3+ zYb3+ wNd3+ with 0 £ x £ 20 mol% (y, z and w in mol%). The samples were studied by Raman spectroscopy, infrared absorption and differential thermal analysis. Pr3+-doped LBO and Pr3+/Yb3+-doped LBO samples show an increase of the glass transition and crystallization temperatures and a decrease of the fusion temperature associated with the increase of the praseodymium concentration in the LBO matrix. For the Nd3+-doped LBO and Pr3+/Yb3+-doped (LBO+Nb2O5) samples, a decrease of the glass transition temperature of the samples was observed. The increase of the rare earth doping leads to an increase of the difference between the glass transition and the crystallization temperatures. From infrared analysis it was possible to identify all the modes associated to the B-O structure. The NbO6 octahedra was also identified by IR spectroscopy for samples with x=5, 10, 15 and 20 mol% and y=0.05, z=1.1 mol%. Raman spectroscopy shows the presence of boroxol rings, tetrahedral and triangular coordination for boron. For samples containing niobium, the Raman spectra show the vibrational mode associated with the Nb-O bond in the niobium octahedra (NbO6). Este trabalho apresenta um estudo de vidros de triborato de lítio (LBO) do sistema (1-x)|3B2O3.Li2O| (x)Nb2O5 yPr3+ zYb3+ wNd3+ com 0 £ x £ 20 mol% (y, z e w em mol%). Foram feitos estudos por espectroscopia Raman, absorção no infravermelho e análise térmica diferencial. Amostras de LBO dopadas com Pr3+ e com Pr3+/Yb3+ mostram um aumento nas temperaturas de transição vítrea e de cristalização e uma diminuição na temperatura de fusão associada ao aumento da concentração de praseodímio ma matriz de LBO. Foi observada uma diminuição na temperatura de transição vítrea nas amostras de LBO dopadas com Nd3+ e nas de (LBO+Nb2O5) dopadas com Pr3+/Yb3+.O aumento no teor de dopagem de terras raras leva a um aumento na diferença das temperaturas de transição vítrea e de cristalização. A análise de espectroscopia na região do infravermelho possibilitou identificar todos os modos associados à estrutura B-O. O octaedro NbO6 foi também identificado por espectroscopia de infravermelho nas amostras com x=5, 10, 15 e 20 mol% e y=0,05, z=1,1 mol%. Os resultados de espectroscopia Raman mostram a presença de anéis boroxol, e coordenação tetraédrica e triangular para o boro. Para as amostras contendo nióbio, os espectros Raman mostram o modo vibracional associado com a ligação Nb-O no octaedro de nióbio (NbO6).