Estudo do processo de compactação de óxidos de nióbio pelo método de centrifugação

Abstract

Brazil holds more than 90% of the world's niobium reserves and is the largest producer and exporter of this material, such as ferro-niobium alloy, niobium oxide and other products. Nevertheless, there is a need to expand the use of niobium in the country in order to make better use of it economically. The Brazilian Ministry of Mines and Energy encourages the development of technological applications to add value to niobium and its derivatives through research. The remarkable chemical and physical properties of Nb2O5 make this material promising for application as adsorbent, gas sensor, solar cells and electrochromic components. Some recent research studies have verified the possibility of several catalytic applications of niobium oxides, either as active phase or as support. A study of the consolidation of Nb2O5 suspensions by the centrifugal casting method was carried. The purpose of the present work was to investigate the efficiency of this simple and low-cost method in the preparation of ceramic supports. Initially, the slip casting method using gypsum molds was tried, but the methodology using centrifugal force proved to be much more effective. The samples were prepared by mixing Nb2O5 or Nb2O5.xH2O, PVA, agar, deionized water and boric acid dissolved in glycerin. Rotational speed was set at 10.000 rpm during various deposition times (5, 10, 20 and 30 minutes). Heat treatment was performed at different sintering temperatures varying from 1100 °C to 1400 °C. The dwell time was 4 hours. Both green and sintered bodies were characterized by scanning electron microscopy with field emission (SEM-FEG), X-ray diffraction (XRD). The density of green and sintered bodies was determined by the Archimedes method. The results showed significant influence of the sintering temperature on the contraction of the pieces, resulting in an expressive increase of the sintered density with the increase of temperature. The optimal centrifugation time was 20 minutes as it resulted in a higher green density. The packing was also evaluated through the micrographs, which evidence internal and external surfaces with good qualities compared to other ceramics in the literature. Finally, it is concluded that the methodology studied has the potential to produce substrates in specific shapes, obtaining Nb2O5 ceramics that reached 90.6% of theoretical density and 30% of porosity after sintering at 1400 °C for 4 hours.