Nanotechnology is blossoming into one of the premiere technologies of this century, but the key to its progress lies in developing more efficient nanosynthesis methods. Variations in synthetic technique, however, can cause variations in size, structure, and surface characteristics, thereby altering the physical properties and functionality of the particles. Careful structural characterizations are thus essential for understanding the properties and appropriate applications for particles produced by new synthetic techniques.In this work, a new ‘solvent-deficient’ method is presented for the synthesis of an unprecedentedly wide range of metal oxide nanomaterials including at least one metal oxide from each group in Groups 3-4, 6-15, and the Lanthanides. XRD, BET, and TEM structural characterizations as well as chemical purity analyses of the products are given. The intermediates associated with the method are also investigated, allowing the reaction parameters to be rationalized and culminating in a proposed mechanism for the reaction. Several of the reaction intermediates are themselves useful products, expanding the range of this already versatile method. Optimized synthesis parameters as well as structural characterizations are presented for one such intermediate product, the iron oxyhydroxide called ferrihydrite.The Al2O3 nanoparticles produced by the new method show promise in catalyst support applications, and the synthesis and structural analysis (XRD, X-ray PDF, 27Al NMR, TG/DTA-MS) of these nanoparticles is provided. The XRD, PDF, and NMR analyses reveal that the initial boehmite-like phase transforms to the catalytically useful gamma-Al2O3 phase at unusually low temperatures (300-400°C), but boehmite-like local structure defects remain which heal slowly with increasing temperature up to 800°C. The ‘pure’ gamma-Al2O3 may still contain randomized, non-cubic, local structure distortions, and it transforms directly to alpha-Al2O3 at ~1050°C. To rationalize the local structure and the absence of the delta- and theta-Al2O3 phases during the alpha-phase transition, relationships between the many Al2O3 phases are presented via innovative symmetry-mode analyses, revealing a potential quazi-topotactic mechanism for the gamma-to-alpha transition.To stabilize the gamma-Al2O3 phase to higher temperatures for catalyst applications, 3 wt% of a lanthanum dopant was added via a new, 1-pot process based on the new solvent-deficient method. This process is described and X-ray PDF, TEM, 27Al NMR, and EXAFS analyses of the La-doped gamma-Al2O3 nanoparticles reveal that the dopant resides as isolated, adsorbed atoms on the gamma-Al2O3 surface. The first coordination shell of the isolated La is increasingly La2O3-like as calcination temperature increases but changes drastically to be more LaAlO3-like after the alpha-phase transition, which is delayed ~100°C by the La dopant. Combining the EXAFS, PDF, NMR, and symmetry-mode analyses, we provide new insight into the mechanism of stabilization provided by the La dopant.

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No description available.

The ever-growing Internet of Things is promoting more data acquisition, data exchange and fewer human interactions, engendering a higher demand for sensors and therefore power. While in most cases it is possible to directly connect these sensors to the power grid, it will not always be feasible with emerging technologies, especially in remote areas where human access is limited. Moisture-Electric Energy Transformation (MEET) devices are components that use moisture as a “fuel” to generate electrical power. Upon contact with moisture, a potential difference results from a diffusion mechanism, allowing charge to be stored locally in capacitors or rechargeable batteries to be utilized for useful work. The focus of the present work was to investigate the potential of Cold Gas Dynamic Spray (CGDS) as an additive manufacturing (AM) process for the fabrication of MEET devices. Following a layer-by-layer approach, MEET devices were successfully built by CGDS, by combining aluminum (electrode material) and an in-situ composite of polyether ether ketone (PEEK) and alumina (diffusion medium). The main challenges of this work were the determination of the spray parameters of PEEK and the investigation of the MEET capability of the manufactured devices. On the other hand, the main contributions of this work were the demonstration of the viability of CGDS in the deposition of PEEK/Al2O3 on aluminum 6061-T6 substrates, as well as the potential of PEEK as a MEET-capable material. The diffusion mechanisms that govern power generation were also hypothesized, explained and summarized. Initial tests of a MEET device of 66 mm x 34 mm indicate an uninterrupted power generation cycle of over 30 hours, and a maximum output voltage of 268 mV with a 6.8 MΩ load. The output power and power per unit area of the device were computed to be 10.63 nW and 4.736 µW/m2 respectively. The output current and current density were evaluated to 39.53 nA and 17.62 µA/m2.

In der vorliegenden Arbeit werden Al2O3-geträgerte Eisenoxid-Katalysatoren auf ihre Eignung in der Nachbehandlung von Dieselabgasen getestet. Hierbei werden die Oxidationsreaktionen von Kohlenmonoxid, Propen, Stickstoffmonoxid sowie Ammoniak getestet. Weiterhin wird die Katalysatoraktivität bei der Stickoxidminderung nach dem SCR-Verfahren untersucht. Basierend auf einer detaillierten Charakterisierung wird eine Struktur-Aktivitäts-Korrelation entwickelt, auf deren Basis ein Verständnis für die Art der aktiven Zentren solcher Katalysatoren generiert wird. Zudem wird ein Modell entwickelt, mit Hilfe dessen die spezifische Aktivität der verschiedenen Typen an aktiven Zentren bewertet werden kann. Darüber hinaus wird in dieser Arbeit auf die Stickoxidminderung nach dem SCR-Verfahren fokussiert, was die Untersuchungen des Reaktionsmechanismus sowie die Struktur-Aktivitäts-Korrelation an hydrothermal gealterten Katalysatoren beinhaltet.

Neste trabalho foi investigado o processamento e propriedades mecânicas e tribológicas do compósito cerâmico Al2O3- NbC com o objetivo de desenvolver um compósito cerâmico com melhores propriedades do que a alumina pura. Como material para comparação foi utlizado a alumina que é uma cerâmica tradicionalmente aplicada onde é necessária elevada resistência mecânica e ao desgaste. A composição Al2O3-0,5%wtY2O3-20%wtNbC, que origina o compósito, passou por moagem e mistura em moinho tipo atrittor e secagem em evaporador rotativo. O pó obtido foi caracterizado quanto a distribuição granulométrica e morfologia. A alumina seguiu a rota tradicional de moagem e mistura em moinho de bolas, secagem em spray dryer; e mesma caracterização realizada para o compósito. Foi realizado estudo da sinterização em dilatômetro para os dois materiais com intuito de determinar as condições ideais de sinterização. Por meio de prensagem uniaxial seguida de prensagem isostática a frio foram confeccionadas amostras na forma de discos e pinos. Os materiais densos foram obtidos por sinterização normal sendo que a alumina ao ar e o compósito em atmosfera de argônio. As fases formadas no dois materiais foram determinadas por difração de raios X. As microestruturas foram estudas em microscópio eletrônico de varredura nas superfícies polidas e atacadas. Entre as propriedades mecânicas foram medidas o módulo elástico, a dureza e a tenacidade à fratura por meio de impressões Vickers. O compósito desenvolvido apresentou valores superiores em todas estas propriedades em relação a alumina. O estudo do comportamento tribológico foi realizado por meio do deslizamento de pinos, com extremidade cônica, de alumina e do compósito cerâmico sobre discos de alumina. Os ensaios foram realizados com a velocidade de 0,4m/s e com carregamento, por meio de peso morto, de 10N sob diferentes níveis de umidade relativa ( 26,8; 48 e 76,3%). O coeficiente de atrito cinético médio, assim como a taxa de desgaste, diminuiu em todos os ensaios com o aumento da umidade relativa, para os dois materiais. Este comportamento foi relacionado com a formação de uma camada na interface de contato entre as superfícies do pino e do disco de hidróxido de alumínio. O compósito demostrou maior resistência ao desgaste em todas as condições tribológicas estudadas. O compósito cerâmico desenvolvido claramente possui boas perspectivas como um novo material cerâmico em importantes aplicações técnicas. / In the present work processing, and mechanical and tribological properties of a ceramic composite Al2O3-NbC were investigated in order to develop a ceramic material with superior properties. Alumina was chosen as a reference since it is a traditional ceramic material for applications where elevated mechanical properties and wear resistance are required. The composition Al2O3 - 0.5 wt%Y2O3-20 wt%NbC was prepared by attrition milling followed by drying in a rotaevaporator. The resulting powder mixture was characterized for granulometry and powder particles morphology. Alumina was processed according to the traditional route of ball milling followed by passing through a spray drier, and the processed powder was then characterized the same way as the composite. Dilatometry was accomplished for both materials in order to define the ideal sintering conditions. Samples with the shape of discs and pins were compacted by uniaxial pressing followed by cold isostatic pressing. Densification was achieved by sintering in air and in argon for alumina and the composite, respectively. Phase composition of sintered materials was studied by X-ray diffraction (XRD). Microstructure was investigated by means of scanning electron microscopy (SEM) on polished and etched surfaces. Materials were also characterized for a number of mechanical properties, in particular for Young modulus, hardness, and fracture toughness by Vickers indentation method. The developed composite exhibited superior mechanical properties as compared to alumina. Tribological behavior was investigated by means of a sliding pin on disk test with pins of a conical shape prepared both from alumina and the composite, and an alumina disk. Tests were performed with the sliding speed of 0.4 m/s and 10N load under varying humidity conditions (26.8; 48, and 76.3%). Both the mean coefficient of friction and the wear rate diminished in all tests with the increase of humidity for both materials. Such behavior was attributed to a aluminum hydroxide layer formation between the pin and the disk surfaces. The developed composite exhibited better wear resistance under all tribologic conditions studied. The developed ceramic composite obviously has good perspectives as a new material for a variety of important technical applications.

O uso do óxido de nióbio como promotor e como suporte tem sido investigado em numerosas aplicações catalíticas, tais como, na oxidação seletiva, conversão de hidrocarbonetos, polimerização, eliminação de poluentes (NOx), desidrogenação, etc. Sabe-se que a adição de nióbio na γ-Al2O3 melhora a acidez, a seletividade e a estabilidade térmica e, conseqüentemente, a atividade catalítica desses materiais. A atividade catalítica dos sistemas contendo nióbia suportada é decorrente das diferentes espécies redox do óxido de nióbio presentes nas superfícies do sólido. O presente trabalho tem como objetivo avaliar a influência do teor de nióbio e vanádio no sistema catalítico V2O5/Nb2O5-Al2O3 na reação de desidrogenação oxidativa do propano. A fim de alcançar o objetivo deste trabalho, as seguintes técnicas de caracterização foram utilizadas: volumetria de N2 (área específica e volume de poros), redução a temperatura programada, difratometria de raios X (DRX) e espectroscopia Raman. As propriedades ácidas e/ou básicas dos suportes e catalisadores foram avaliadas através da reação de decomposição do isopropanol. / The use of niobium oxide as a promoter and as a support has been investigated in various catalyst applications, such as selective oxidation, hydrocarbonate conversion, polymerization, elimination of (NOx) pollutants, dehydrogenation, etc. It is known that adding niobium to γ-Al2O3 improves acidity, selectivity and thermal stability and consequently the catalyst activity of these materials. The catalyst activity of systems containing supported niobium is due to the different redox species of niobium oxide present on the solid surface. This study aims to evaluate the influence of the niobium and vanadium content in the V2O5/Nb2O5-Al2O3 catalyst system in the propane oxidative dehydrogenation reaction. Aiming the target of this study, the following characterization techniques were used: N2 volumetry (specific area and pore volume), temperature-programmed reduction, X-ray diffractometry (DRX), and Raman spectroscopy. The acid-base properties of the supports and catalysts were studied through isopropanol decomposition reaction.

Estudamos o efeito de Conjugação de Fase por Mistura Degenenerada de Quatro Ondas em Al2O3:Cr+3 (Rubi) e GdAlO3:Cr+3 com um laser de Ar (λ=5145 Å). Obtivemos eficiência aproximadamente quatro vezes maior no GdAlO3:Cr+3 (onde este trabalho é original) que no Rubi o que nos motivou a investigar as propriedades físicas que são relevantes para o fenômeno nestes sistemas (isto não foi bem compreendido no trabalho anterior em Rubi). Desenvolvemos um método interferométrico muito sensível para medida dos coeficientes não lineares do índice de refração n2 destes materiais (que não eram conhecidos) Com estes valores de n2 calculamos a eficiência de Conjugação de Fase em bom acordo com experiência. / We have studied the effect of Phase Conjugation by Degenerate Four Wave Mixing in Al2O3:Cr+3 (Rubi) and GdAlO3:Cr+3 with an Ar (λ=5145 Å). We obtained efficiency ?approximately? 4 times greater in GdAlO3:Cr+3 (where this work is original) than in Rubi and this have motivated us to investigate the physical properties that are important to explain this phenomenon in these materials (what wasn\'t well understood in the previous paper on Rubi(10)). We developed an interferometric method very sensitive to measure the nonlinear coeficient of refractive index n2 of these materials (what wasn\'t known). With these values of n2 we calculated the efficiency of the Phase Conjugation in good agreement with the experience.

Catalisadores baseados em óxidos metálicos têm sido muito utilizados nos últimos anos para a desidrogenação oxidativa de alcanos leves. Dentre os principais catalisadores, estão os sistemas contendo V2O5, Nb2O5 e Al2O3. O processo de desidrogenação oxidativa do propano (DOP) representa uma via alternativa importante para a produção de propileno sob menores temperaturas, porém sua prática vem sendo limitada pela diminuição dos valores de seletividade ao propeno com o aumento da conversão do reagente. Metais alcalinos, dentre eles o potássio, são frequentemente utilizados como promotores em reações de oxidação seletiva com o objetivo de proporcionar melhores seletividades catalíticas aos mecanismos de reação, devido à redução da acidez e ao aumento da basicidade na superfície dos catalisadores. O projeto proposto tem como objetivo principal criar uma metodologia de síntese de novos suportes Nb2O5-Al2O3 e catalisadores V2O5-Nb2O5-Al2O3 dopados com potássio a serem utilizados em processos petroquímicos para a produção de olefinas leves. Para tanto, as seguintes técnicas de caracterização foram utilizadas: espectrometria de absorção atômica, espectroscopia de emissão atômica com plasma indutivamente acoplado (ICP-OES), volumetria de N2, difratometria de raios X (DRX) e redução à temperatura programada (RTP). As características ácidas e/ou básicas e a atividade catalítica dos suportes e catalisadores foram medidas pelas reações de decomposição do isopropanol e de desidrogenação oxidativa do propano, respectivamente. / Catalysts based on metal oxides have been extensively used in recent years for the oxidative dehydrogenation of light alkanes. Among the main catalysts, there are the systems containing V2O5, Nb2O5 e Al2O3. The oxidative dehydrogenation of propane (ODH) provides a potential low-temperature route for the synthesis of propylene, but its practice has been limited by a marked decrease in propene selectivity with increasing conversion of reactant. Alkali metals, such as potassium, are frequently used as promoters in selective oxidation reactions with the objective of providing higher selectivity in catalytic reaction mechanisms, due to the reduced acidity and increasing basicity of the catalysts surface. The considered project has as major objective create a new synthesis methodology of Nb2O5-Al2O3 supports and V2O5-Nb2O5-Al2O3 potassium-doped catalysts to be used in petrochemical processes for the production of light olefins. For in such a way, the following characterization techniques were used: atomic absorption spectrometry, inductively coupled plasma optic emission spectroscopy (ICP-OES), N2 volumetry, X-ray diffractometry (XRD) and temperature programmed reduction (TPR). The properties acid and/or basic and the catalytic activity of supports and catalysts were evaluated by the isopropanol decomposition and oxidative dehydrogenation of propane reactions, respectively.

Filmes amorfos de nitreto de alumínio (AlN) foram preparados por sputtering de rádio frequência convencional em um alvo de Al+Cr e plasma de nitrogênio puro. A área relativa de Al-Cr determina o conteúdo de Cr, o qual esteve em um intervalo de concentração de ~ 0 3.33 at.% no presente estudo. A deposição dos filmes foi seguida por tratamento térmico das amostras até 1050 ºC e por caracterização espectroscópica através de medidas de EDS (Energy Dispersive Spectrometry), Foto-luminescência e Transmissão Óptica. De acordo com os resultados experimentais, as propriedades óptico-eletrônicas dos filmes de AlN contendo Cr são altamente influenciadas tanto pela concentração de Cr como pela temperatura de tratamento térmico. Na verdade, o tratamento térmico a 1050 ºC induz o desenvolvimento de estruturas que, devido ao seu tamanho típico e características espectrais exclusivas, foram designadas por micro-estruturas de rubi (RbMSs). Estas RbMSs são rodeadas por um meio rico em nitrogênio no qual os íons Cr3+ apresentam características luminescentes não encontradas na literatura. A emissão de luz apresentada pelas RbMSs e suas vizinhanças foram investigadas de acordo com o conteúdo de Cr e a temperatura de medida permitindo a identificação de várias linhas luminescentes relatadas do Cr3+. As principais características destas linhas luminescentes e correspondentes processos de recombinação-excitação são apresentados e discutidos tendo em vista uma análise espectroscópica detalhada. / Films of amorphous aluminum-nitride (AlN) were prepared by conventional radio frequency sputtering of an Al+Cr target in a plasma of pure nitrogen. The Cr-to-Al relative area determines the chromium content, which stayed in the ~ 0 3.33 at.% concentration range in the present study. Film deposition was followed by thermal annealing the samples up to 1050 ºC and by spectroscopic characterization through energy dispersive spectrometry (EDS), Photo-luminescence and Optical Transmission measurements. According to the experimental results, the optical-electronic properties of the Cr-containing AlN films are highly influenced by both the Cr concentration and the temperature of the thermal treatments. In fact, thermal annealing at 1050 °C induces the development of structures which, because of their typical size and unique spectral characteristics, were designated by ruby microstructures (RbMS\'s). These RbMS\'s are surrounded by a nitrogen-rich environment in which Cr3+ ions exhibit luminescent features with no counterpart in the literature. The light emission presented by the RbMS\'s and surroundings were investigated according to the Cr content and temperature of measurement allowing the identification of several Cr3+-related luminescent lines. The main characteristics of these luminescent lines and corresponding excitation-recombination processes are presented and discussed in view of a detailed spectroscopic analysis.