Síntese e caracterização do carbeto misto de nióbio e tântalo nanoestruturado a partir da columbita [(Fe,Mn)(Nb,Ta)2O6]

Abstract

This study proposes a new possibility for synthesizing mixed carbide of niobium and tantalum nanostructured from based mineral columbite – an orthorhombic mineral extracted in the city of Currais Novos, RN –, under low temperature and through gas-solid reactions. Firstly this starting mineral (columbite) was submitted to a quartering process, followed by grinding and sieving operations, with its characterization being performed through X-ray fluorescence (XRF) and X-ray diffraction (XRD), which showed satisfactory caracteristics for the synthesis. Then, the application of the mineral treatments were tested for about 3, 5 and 8 hours, respectively – and the 8-hour treatment showed the best result. After that, the precursor synthesis took place – a much more reactive reagent used in the carbide synthesis trough a gas-solid reaction. It is important to register that the synthesized component was the complex hydrated ammonium [(NH4)3(Nb(1-x)Tax)O(C2O4)3.nH2O] tri(oxalate) oxiniobiotantalatum, which showed high reactivity when used as solid reactant in the production of Nb(1-x)Ta(x)C nanostructured, due to the shape and size of the particles (close to 2 um) and to its porosity, as well. This precursor was characterized by a particle size analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), thermo gravimetric, thermodifferential analysis and differential scanning (TG/ATD/DSC), Infrared Spectroscopy (IRS), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The synthesis reaction, then, occurs between the precursor and gaseous mixture of H2/CH4, in which hydrogen is the reducing gas and the methane is the carbon source. The Nb(1-x)Ta(x)C nanostructured was produced from a new methodology at lower time and temperatures (between 930 0C and 980 0C, 2 and half hours) as it is used in the conventional method, which is based on solid state reaction, and controlled by diffusion and phase transformations. The synthesis of mixed carbide of niobium and tantalum nanostructured was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD) with the Rietveld refinement, Analysis of specific surface area (BET), scanning electron microscopy (SEM) and spectroscopy of dispersive energy (EDS). Results showed that the synthesis technique used in the process is capable for the production of carbide of niobium and tantalum mixed carbide nanostructured