JOURNAL OF MATERIALS SCIENCE 37 (2 0 0 2 ) 2117 – 2123 Elaboration of mixed tantalum and niobium carbides from tantalite mineral (Fe,Mn)(Ta 1−x Nb x ) 2 O 6 C. CIARAVINO Laboratory of Physico-Chemistry of Materials, University of Toulon and Var, 83957 La Garde C ´ edex, France E-mail: ciara@univ-tln.fr F. F. P. MEDEIROS, C. P. DE SOUZA Laboratory of Reactors and Thermodynamic, University Federal Rio Grande do Norte—CT-DEQ/PPGEQ, Campus Universitario—Lagoa Nova 59072-970 Natal—RN, Brazil; Laboratory of Experimental Physic, University Federal Rio Grande do Norte—CT-DEQ/PPGEQ, Campus Universitario—Lagoa Nova 59072-970 Natal—RN, Brazil M. ROUBIN Laboratory of Physico-Chemistry of Materials, University of Toulon and Var, 83957 La Garde C ´ edex, France This paper presents an original method of synthesis of mixed tantalum and niobium carbides from an oxalic precursor elaborated from the tantalite mineral (Fe,Mn)(Ta 1−x Nb x ) 2 O 6 . The process of elaboration consists initially in melting the ore with potassium pyrosulphate, then performing a lixiviation with a concentrated hydrochloric acid solution. During the latter reaction, iron and manganese oxides are converted into water-soluble chlorides while the fused mass containing potassium, niobium and tantalum is not dissolved. Traces of chlorides are eliminated by filtration with boiling aqueous solution. Then, the solid is dissolved slowly in hot concentrated sulphuric acid solution. Adding ammonium hydroxide up to a pH of 8 completes the precipitation of niobium and tantalum hydroxides. The precipitate (Ta 1−x Nb x )(OH) 5 is washed and submitted to a reaction of complexation with oxalate ions in an aqueous environment. This reaction involves the formation of a water-soluble oxalic complex containing tantalum and niobium. The excess of water is eliminated by evaporation at 333 K. The tantalum and niobium carbides are obtained by submitting the oxalic complex of chemical formula (NH 4 ) 3 (Ta 1−x Nb x )O(C 2 O 4 ) 3 · nH 2 O to a gas-solid reaction in a methane-hydrogen atmosphere at 1273 K. The oxalic precursor and their resultant mixed carbides are characterized by atomic absorption and Infra-Red spectroscopies, thermogravimetric-differential thermal analysis coupled, laser granulometry, X-ray diffraction and transmission electronic microscopy. C  2002 Kluwer Academic Publishers 1. Introduction Due to their physicochemical properties, interests in the manufacturing of the niobium and tantalum carbides are growing up for industrial applications. The classical manufacturing route for the synthesis of those carbides is based on the solid-state diffusion of the carbon in the transition metal. The process is activated by high temperature treatment up to 1473 K for long periods of time [1, 2]. Among all the minerals in which tantalum and niobium are found, the main source is the tantalo-columbite mineral (Fe,Mn)(Ta 1−x Nb x ) 2 O 6 where they occur in combination with iron and man- ganese. Previous works focused on the direct carburization of tantalo-columbite concentrate (Fe,Mn)(Ta 1−x Nb x ) 2 O 6 [3, 4], however the temperature reached 1673 K for few hours. An alternative route to decrease the temperature and the time of synthesis of tantalum and niobium carbides consists of the carburization of an oxalic precursor. This method has been applied successfully in the preparation of TaC [5] and NbC [6] from tantalum and niobium pentoxides as raw materials. This study extends the process to the elaboration of a mixed tantalum-niobium carbide: the oxalic precursor is elaborated from tantalite mineral and then submitted to the carburant atmosphere. The first part of the present contribution reports the different steps of the synthesis of the precursor: the melting of the mineral with potassium hydrogen 0022–2461 C  2002 Kluwer Academic Publishers 2117