Maria Veronilda Macedo Souto

Synthesis and Characterization of CuNb2O6 from an Oxalic Precursor Via Solid State Reaction

The present papers 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.

Synthesis and characterization of Mo2 C based materials over activated carbon derived from sewage sludge pyrolysis for catalytic applications

Transition metal carbides have been successfully used as substitute materials for conventional noble metal catalyst in several important industrial reactions due to their interesting physicochemical properties. Surface structure, chemical composition and metal-support interactions, as well as processing conditions, are of utmost importance in the use of such materials in catalysis. The present study aimed to synthesize and evaluate pure molybdenum carbide with and without support, and bimetallic Mo-Ni carbide over a carbon active support derived from sewage sludge pyrolysis. The support was chemically (KOH) and physically (thermal treatment) activated before use. TG/DTG, XRD, XRF, SEM, BET and particle size evaluation were performed, together with adsorption/desorption isotherms. Results indicated that the applied synthesis method was adequate for the obtainment of pure materials. The increase in surface area of the support was significant, from 13 to 141 m2.g-1 after the thermal and chemical treatment; also, supporting Mo2C over carbon provided an increase from 45 to 73 m2.g -1 in surface area, which indicated its potential as a catalytic material as well as the effectiveness of the applied methodology.

Synthesis of Nanostructured Tungsten Carbide (WC) from Ammonia Paratungstate-APT and its Characterization by XRD and Rietveld Refinement

The carbides of refractory metals like tungsten carbide (WC), tantalum carbide (TaC) and niobium carbide (NbC), has been extensively studied due to their applications in several areas of industry, because of their specific properties; such as high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The tungsten carbide, particularly, is generally used at hardmetal industries due to its high hardness and wear resistance. New synthesis techniques have been developed to reduce the synthesis temperature of refractory metal carbides using more reactive precursors and gas-solid reactions for carbon reduction. The result is producing pure carbides suitable properties for production of high quality cemented carbides and more selective catalysts. In this work, pure and nanostructured WC was obtained from the ammonium paratungstate hydrate (APT), at low temperature and short reaction time. Hydrogen (H2) and methane (CH4) were used as a reducing gas and carbon source, respectively. The precursor and obtained product were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained by diffraction of X-rays showed that complete reduction and carburization of APT have been took place resulted in pure WC formation. The average crystallite size was in nanometer order reaching values of approximately 20.8 nm and a surface area (BET) of 26.9 m2/g.

NANOMETRIC TANTALUM CARBIDE: PRODUCTION AT LOW TEMPERATURE AND CHARACTERIZATION

Tantalum carbide (TaC) is an extremely hard material with features such as high hardness, high melting point, high chemical stability, good resistance to chemical and thermal shock and excellent resistance to oxidation and corrosion. Thus, this study aimed to obtain nanostructured TaC from precursor tris (oxalate) hydrate ammonium oxitantalato through gas-solid reaction at low temperature (1000°C) and short reaction time. The materials obtained were characterized by X-ray diffraction (XRD), Rietveld refinement, Scanning Electronic Microscopy (SEM), Infrared Spectroscopy and Thermogravimetric analysis (TG). Through XRD analyses and Reitiveld refinement of TaC with S = 1.1584, the formation of pure tantalum carbide with cubic structure and average crystallite size in the order of 12.5 nanometers was observed.