Souza, Carlson Pereira deMedeiros, Francisca de Fátima Pegado de2022-08-162022-08-162002-05-03MEDEIROS, Francisca de Fátima Pegado de. Síntese de carbetos de tungsténio e nióbio a baixa temperatura, através de reação gás-sólido em reator de leito fixo. 2002. 144f. Tese (Doutorado em Engenharia Química) - Centro de Tecnologia, Universidade Federal do Rio Grande do Norte, Natal, 2002.https://repositorio.ufrn.br/handle/123456789/49153This work presents a method for producing carbides of tungsten and niobium at low temperature through a gas-soiid reaction by using more reactive raw materiais. The reaction occurs between a solid W and Nb containing product and a H2/CH4 gaseous mixture. Hydrogen acts as a reducer and methane acts as a carburizer agent. Niobium and tungsten carbides were produced in the temperature range of 820° - 950°C for a reaction time between 1 and 2 hours. These values are much lower than the temperature and time used in the conventional technique for producing these carbides (above 1400°C and longer than 6 hours). The conventional method is based on solid State reaction, controlled by diffusion and phase transformation. Ammonium paratungstate (APT) and ammonium (tris)oxalateoxiniobate are the source of tungsten and niobium respectively. APT is a commercial product and the niobium precursor was synthesized from a commercial Nb2O5. These materiais are highly reactive powders. During the reduction and carburization reactions the precursors decompose. Gases are evolved and the particles become porous. The high surface area ofthe solid increases the contact area between the solid and gaseous reactants. Thus, the reaction rate is increased. The process of carburization was studied. The steps of the reduction and carburization reactions were determined. The influence of some parameters such as temperature, precursor charge, gas flow and H2/CH4 ratio on the reaction time was investigated. The intermediate phases and evolved phases were identified. The percent amount and the crystallite size of the intermediate phases were determined by the Rietveld refinement method and the broadness of X Ray diffraction peaks, respectively. Carbide powders with high specific surface area (35m2/g) and small crystallite size (18nm) were produced. These carbides can be used in hardmetal alloys and in catalysis. The niobium Carbide powder was used as WC grain growth inhibitor in a hardmetal alloy. Its performance was comparable with that of a commercial NbC powder.CarbonetoCarbeto de nióbioCarbetos de metais refratáriosReações gás-sólidoSíntese e caracterizaçãodoctoralThesisCNPQ::ENGENHARIAS::ENGENHARIA QUIMICA