The reduction of niobium and tantalum pentoxides by silicon in vacuum

• Published in: Journal of alloys and compounds Vol. 315; no. 1; pp. 187 - 192
• Main Authors: Awasthi, Alok, Bhatt, Y.J., Krishnamurthy, N., Ueda, Y., Garg, S.P.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 09.02.2001; Elsevier
• Subjects: Applied sciences; Chemical synthesis; Exact sciences and technology; Metals; Metals. Metallurgy; Production of metals; Production of non ferrous metals. Process materials; Production of pure metals; Solid state reaction; Chemical synthesis; Metals; Solid state reaction; Under vacuum; Thermogravimetry; Theoretical study; Niobium production; Thermal reaction; Phase analysis; Experimental study; Reducing agent; X ray diffraction; Chemical reduction; Tantalum production; Niobium Oxides; Silicon; Silicothermy; Tantalum Oxides
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/S0925-8388(00)01274-3

The use of silicon as a reducing agent for Nb 2O 5 and Ta 2O 5 to obtain the metals under pyrovacuum conditions has been investigated. Reduction occurs due to the removal of oxygen by evaporation of volatile silicon monoxide, SiO (v). Pourbaix–Ellingham diagrams for Nb–Si–O and Ta–Si–O systems were constructed using the published thermodynamic data. The sequences of reduction, as indicated by these diagrams, were also observed by vacuum thermogravimetry experiments and X-ray diffraction (XRD) analysis of products. The reduction starts at around 1150°C for both niobium and tantalum systems and proceeds smoothly as the temperature is raised to 1600°C under vacuum. The extents of reduction were found to be more than that observed in carbothermic reductions at comparable levels of temperature, pressure and durations. The product was an Nb–Si–O or Ta–Si–O alloy, which is refineable to the pure metal by pyrovacuum treatment at a higher temperature.