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.

ABSTRACT The synthesis of ceramic materials such as ferrite has been widely studied in recent years, due to their properties that make these materials have excellent applications in technology, as well as in photocatalytic processes and as catalysts. To obtain the copper ferrite phase the EDTA-Citrate complexation method was used, varying pH (5, 7 and 9), temperature (600, 800 and 1000 °C) and calcination time (2, 7 and 12 h). Composition, morphology and structural analyzes were performed by X-ray fluorescence spectroscopy, X-ray dispersive energy, scanning electron microscopy and X-ray diffraction, respectively. Crystalline phase of copper ferrite (CuFe2O4) with tetragonal structure and secondary phase of Fe2O3 and CuO was verified by XRD analysis. Regarding the chemical composition analyzes, percentage deviations of the samples and the theoretical value for copper and iron were calculated. It was obtained minimum values of 0.16 - 0.08% (atomic%, EDS) and 16 - 8% (atomic%, XRF) in relation to copper and iron, respectively, for the sample obtained under pH 9, calcined at 600 °C for 12 h. The variation of the synthesis condition via EDTA-Citrate directly influenced the morphology of copper ferrite, presenting agglomerated particles, pore formation, irregular spheres, and even powder sintering.

RESUMO Nos últimos anos, pós cerâmicos à base de óxidos de estrutura do tipo perovskita ganharam atenção considerável devido às suas aplicações tecnológicas na área de membranas permeáveis de oxigênio. O óxido misto BaCeO3 apesenta-se como um material amplamente estudado em uma grande diversidade de aplicações, seja como materiais eletrolíticos em células a combustível, ou mesmo como catalisadores nas reações de catálise. Dessa forma, o presente trabalho teve como objetivo sintetizar a fase BaCeO3, pelo método de coprecipitação em meio oxalato, verificando o efeito da sinterização com diferentes aglutinantes na estabilidade térmica e densificação da membrana. A técnica de coprecipitação em meio oxalato mostrouse eficaz na obtenção da perovskita BaCeO3. As amostras obtidas durante as sínteses foram caracterizadas por difração de raios-x, observando-se a formação da fase ortorrômbica da perovskita BaCeO3. Para determinar o tamanho médio de cristalito foi utilizada a equação de Scherrer e de Williamson Hall, chegando-se a um valor próximo a de 107 nm. Conforme a literatura [1,2] e diante dos resultados apresentados definiu-se como condições favoráveis para formação de material com o menor tamanho de cristalito e maior pureza da fase formada, a amostra de pH 13 e de temperatura de calcinação de 1000 ºC. Através da microscopia eletrônica de varredura (MEV) pode-se observar a formação de cristais homogêneos. Por fim, foi possível observar que a sinterização na presença dos aglutinantes parafina e álcool polivinílico a 1300 ºC com patamar de 5 h, permitiu a obtenção de pastilhas densas com bons níveis de retração, possuindo estabilidade térmica ideal para serem utilizadas como membranas permeáveis de oxigênio e como eletrólito de células a combustível.

ABSTRACT In recent years, ceramic powders based on oxides with structure of the perovskite have gained considerable attention due their technological applications in oxygen permeable membranes. The mixed oxide BaCeO3 is introduced as a broadly studied material in a large variety of uses, either as electrolyte materials for fuel cells, or as catalysts in catalysis reactions. Thus, this study had the goal to synthesize the BaCeO3 phase by coprecipitation method amid oxalate, verifying the effect of sintering with different binders in thermal stability and densification of the membrane. The co-precipitation technique in oxalate was effective to obtain the perovskite BaCeO3. The samples obtained during the syntheses were characterized by X-ray diffraction, and it was possible to notice the formation of the orthorhombic phase of perovskite BaCeO3. To stablish the average crystallite size it was used the equation of Scherrer and Williamson Hall, coming to a value close to 107 nm As the literature [1,2] and against the results defined as favorable conditions for formation of material with the smallest size of crystallite and greater purity of the phase formed the sample pH 13 and calcination temperature of 1000° C. By scanning electron microscopy (SEM) it could be seen the formation of homogeneous crystals. Finally, it was observed that the sintering in the presence of binders paraffin and polyvinyl alcohol at 1300ºC allowed the obtaining of dense pellets with good shrinkage levels, having ideal thermal stability for use as oxygen permeable membranes and as a fuel cell electrolyte.

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.

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.