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Abstract Nanostructured niobium nitride was synthesized through a solid-gas reaction in an atmosphere of nitrogen and hydrogen using an oxalic niobium precursor. Crystal phases evolution throughout the reactive processes were evaluated using X-Ray Diffraction, reaction parameters modifications were performed in isotherm time, gas flow, and precursors’ mass. It was verified the synthesis of a stable NbN material with a hexagonal structure under the following conditions: 1g of precursor, 300 min of isotherm at 1100 °C and, the gas flow of N2 = 40% (v/v), and H2 = 60% (v/v). The increase in gas phase flow and the decrease of solid load favored the process, and a pure and single-phase powder was obtained. This set indicates the importance of physical resistance in the fluid-particle interaction process. Under these conditions, the solid obtained had a crystallite size of 30 - 50 nm.

BaCeO3-based ceramics are ionic and electronic conductors that can be applied to oxygen sensors, solid oxide fuel cells and oxygen permeable membranes. However, the low chemical stability at high temperatures of these materials motivates studies involving doping of A and/or B sites of the perovskite structure. In this context, the present work aimed to synthesize a new BaCe0.8Pr0.05Cu0.15O3-δ material using the chemical route of complexation which combines EDTA-Citrate with pH variation. The powders obtained at pH 3 or 11 and calcined up to 900 ºC are thermally unstable. The cubic perovskite BaCe0.8Pr0.05Cu0.15O3-δ with crystallite size between 99.4 nm and 131.6 nm was obtained along with barium carbonate traces. In the powders calcined at 1000 ºC the pH increase decreases the amount of barium carbonate (17.3% to pH 3, 3.4% to pH 7 and 1.8% to pH 11), but increases the size of grains with irregular shapes.

Cerium molybdate semiconductive nanoparticles were synthesized by the EDTA-citrate combined complexation method. Gel thermal degradation behavior, phase formation, morphology, composition and band gap of cerium molybdate powders were characterized by TG/DSC, XRD, SEM/EDS and DRS analysis, respectively. The nanoparticles were synthesized by fixing the pH of the reaction medium to 9, producing an organometallic gel which was heated to 230 ºC obtaining a precursor powder. The precursors were calcined in a temperature range of 450 - 800 ºC for 3 h. The cerium molybdate powders were characterized and the phase evolution, morphology and band gap changes with the increase of calcining temperature were investigated. It was observed that the calcining temperature directly influences the formation of the crystalline structure, appearance of other phases in the materials and the particle size.

The objective of this work is obtaining W-30 wt% Cu composite powder from ammonium paratungstate hydrated (APT) and hydrated copper nitrate and investigating the influence of some production process parameters of W- 30 wt% Cu in particles form which results in high sinterability and densification of W-30 wt% Cu composite. To achieve this objective, the powder was obtained by manually mixing the APT and copper nitrate and reducing under a hydrogen atmosphere at 800 °C and then compacting at 500 MPa and sintering in a tubular furnace at 1200 °C for 60 minutes. The obtained materials were characterized by XRD, SEM, EDS, particle size analysis, density and microhardness measurements. The composite powder showed a good homogenization of Cu in W with very fine and agglomerated particles and a mean crystallite size of 25.64 nm. SEM coupled with EDS with mapping analysis revealed a homogeneous distribution of Cu and W in the sintered sample. The composite had a relative density of 96.77% and a microhardness of 523.66 HV. Therefore the method of obtaining the composite powder is feasible to sinter W-30 wt% Cu powder due to a greater dispersion and homogenization of phases and the average particle size.

The present paper's objective was to synthesize and characterize both the oxalic niobium precursor (NH4)3NbO(C2O4)3.H2O, and the product of its doping with Cu and calcining, CuNb2O6. In order to obtain the niobium precursor, commercially available niobium oxide (Nb2O5) was subject to fusion with potassium bisulfate (KHSO4). Once leached with water, the powder was complexed with oxalic acid and ammonium oxalate. The as produced material was manually mixed with copper nitrate Cu(NO3)2.2H2O (25% Cu molar) and calcined at 1000°C in a muffle furnace. CuNb2O6 was then obtained. The precursor was characterized by XRD, SEM, FT-IR, XRF, TG/DTG. The calcination product was characterized by XRD, XRF and SEM. Results show that single phase CuNb2O6 could be obtained by this method without Nb2O5 contamination.

Esta trabalho enfoca o método de síntese de coprecipitação para preparação da perovsquita SrCo0,8Fe0,2O3-d e suas caracterizações, desenvolvendo uma rota metodológica alternativa de síntese a partir da coprecipitação via meio oxalato. No intuito de verificar a influência do método, a perovsquita foi sintetizada também com base no método de complexação combinando EDTA - Citrato. Ambos os métodos de síntese permitiram obter pós monofásicos. A síntese com base no método via coprecipitação em meio oxalato permitiu obter tamanho de partículas na mesma ordem de grandeza que os obtidos a partir do método de complexação combinando EDTA – Citrato. A natureza do reagente utilizado no método via coprecipitação em meio oxalato produziu um material com aproximadamente 80 % menor em relação ao tamanho médio de cristalito. Além disso, o método via coprecipitação em meio oxalato obteve precursores em estado sólido, em baixa temperatura (~26oC), menor tempo de síntese, maior estabilidade térmica e um rendimento maior da ordem 90 a 95%, mantendo na mesma ordem de grandeza o tamanho médio de cristalito que o método de complexação combinando EDTA - Citrato

The use of niobium containing materials' has gained much attention of the scientific community in the late years due its various applications in diverse fields. NbC is a highly versatile material. Copper addition may alter several of its properties, such as morphology, crystal structure etc. as well as enhance its catalytic behavior. Nanostructured NbC with copper addition synthesis' presented here had the precursor [(NH4)3[NbO(C2O4)3]xH2O] as starting material, which was doped with Cu(NO3)2 at 5% and 10% (molar) ratios. Doped NbC was obtained via gas solid reaction in fixed bed reactor at lower temperature (980°C) and with shorter reaction time (2h) than traditional methods. Reaction products' were characterized by XRD, crystal sizes were estimated according to HWL method, and SEM, XRF, BET and laser particle size analysis were performed. XRD indicated the formation of NbC and Cu phases with cubic crystal structure of ~20nm. SEM showed slight morphological change upon increasing copper content, indicating a less porous structure, which is consistent with BET data (43.7m2/g for 5%Cu-NbC and 37m 2/g for the 10% Cu-NbC). Crystal size calculations showed that increasing dopant content particle sizes were also increased, probably due to the presence of the dopant, in some extent, in the crystal structure.

Inúmeras são as pesquisas que utilizam o método de complexação EDTA-Citrato na sintetização de materiais cerâmicos variados. No presente trabalho sintetizou-se o BaCeO3, com base neste método, visando investigar a influência do pH (7 – 11) e razão molar EDTA:ácido cítrico:íons metálicos totais (0,5:1,5:1,0; 1,0:1,0:1,0; 1,0:1,5:1,0; 1,5:1,5:1,0 e 1,0:2,0:1,0). Foram ainda realizadas duas bateladas de síntese, variando as condições do tratamento térmico: (1) 230 °C por 180 min com taxa de aquecimento de 5 °Cmin-1 e calcinação a 950 °C por 300 min com taxa de aquecimento de 5 °Cmin-1 e (2) 500 oC por 180 min com taxa de aquecimento de 10 oC min-1 e 950 oC por 300 min com taxa de aquecimento de 1 oCmin-1. Os materiais foram caracterizados por difração de raios-x e refinamento através do método Rietveld a partir do programa MAUD. As análises de difração de raios-X confirmaram a fase BaCeO3 em todas as amostras nas condições do pH ou da razão molar, com também do tratamento térmico. Todavia, foi observada uma variação significativa na pureza e no tamanho médio de cristalito do material conforme alteração na condição de síntese. Apresentando a condição (1) cerca de 2% de fase secundária (BaCO3) quando variou o pH ou razão molar. O tamanho médio de cristalito dos pós também apresentou uma variação entre aproximadamente 90 e 192 nm quando variou o pH e maior tamanho de cristalito (105-141 nm) diminuindo EDTA ou aumentando o ácido cítrico. Entretanto, a condição (2) apresenta uma amostra monofásica (pH 11 e razão molar 1,5:1,5:1,0) com tamanho médio de cristalito por volta de 180 nm. Pode-se ainda constatar que a alteração do pH e da razão molar na metodologia de síntese variou a temperatura de formação da fase e consequentemente tamanho de cristalito.

Inúmeras são as pesquisas que utilizam o método de complexação EDTA-Citrato na sintetização de materiais cerâmicos variados. No presente trabalho sintetizou-se o BaCeO3, com base neste método, visando investigar a influência do pH (7 – 11) e razão molar EDTA:ácido cítrico:íons metálicos totais (0,5:1,5:1,0; 1,0:1,0:1,0; 1,0:1,5:1,0; 1,5:1,5:1,0 e 1,0:2,0:1,0). Foram ainda realizadas duas bateladas de síntese, variando as condições do tratamento térmico: (1) 230 °C por 180 min com taxa de aquecimento de 5 °Cmin-1 e calcinação a 950 °C por 300 min com taxa de aquecimento de 5 °Cmin-1 e (2) 500 oC por 180 min com taxa de aquecimento de 10 oC min-1 e 950 oC por 300 min com taxa de aquecimento de 1 oCmin-1. Os materiais foram caracterizados por difração de raios-x e refinamento através do método Rietveld a partir do programa MAUD. As análises de difração de raios-X confirmaram a fase BaCeO3 em todas as amostras nas condições do pH ou da razão molar, com também do tratamento térmico. Todavia, foi observada uma variação significativa na pureza e no tamanho médio de cristalito do material conforme alteração na condição de síntese. Apresentando a condição (1) cerca de 2% de fase secundária (BaCO3) quando variou o pH ou razão molar. O tamanho médio de cristalito dos pós também apresentou uma variação entre aproximadamente 90 e 192 nm quando variou o pH e maior tamanho de cristalito (105-141 nm) diminuindo EDTA ou aumentando o ácido cítrico. Entretanto, a condição (2) apresenta uma amostra monofásica (pH 11 e razão molar 1,5:1,5:1,0) com tamanho médio de cristalito por volta de 180 nm. Pode-se ainda constatar que a alteração do pH e da razão molar na metodologia de síntese variou a temperatura de formação da fase e consequentemente tamanho de cristalito.