Study of the aluminothermic reduction of niobium pentoxide through thermal analysis experiments and high energy milling processing

Abstract

Aluminothermic reduction of niobium pentoxide was studied through thermal analysis techniques such as differential thermal analysis (DTA) and thermogravimetry (TG) as well as through high energy milling processing. Reactants mixtures were composed by powders of Nb2O5 and Al. In the case of DTA-TG experiments, different molar ratios Nb2O5:Al were heated in a dynamic atmosphere of synthetic air under controlled conditions. The high energy milling runs were carried out via SPEX vibratory mill under argon atmosphere and with milling power equal to 7:1 (ratio of mass of balls to mass of mixture) with 10 pct excess of Al over the stoichiometric mass of aluminum necessary. In both kinds of experiments, X ray diffraction was used in order to identify the products of reaction. From DTA-TG experiments, it was possible to determine the experimental value of the enthalpy change (-595.9 kJ.mol-1), which is near to the theoretical one. From the milling experiments, it was possible to verify the possibility of the occurance of aluminothermic reducion of niobium pentoxide via this kind of processing

Influence of sintering temperature on the morphology of ceramic hollow fibers prepared from niobium pentoxide

“…According to Yu et al and Sreethawong et al, these endothermic peaks may result from not only the crystallization process of the sample but also the burnout of a small portion of some organic residues as well as the dehydration and evaporation of chemisorbed water molecules. De Lazzari et al studied the aluminothermic reduction in niobium pentoxide and related the exothermic DTA peak around 1000°C to the overall enthalpy change in the system.…”

Interface structures in Al-Nb2O5 nanocomposites processed by high-pressure torsion at room temperature

“…Thermodynamically, pure Al and Al 3 Nb are the stable phases at room temperature in the Al-Nb system [32,33]. The enthalpy of formation of Al 3 Nb at 298 K is ~121 kJ/mol [34] and the heat of reaction of the aluminothermic reduction of Nb 2 O 5 is ~890 kJ/mol [35]. In high energy milling experiments of the Al and Nb 2 O 5 powders for 45, 75, and 120 minutes at 298 K, X-ray diffraction of the milled mixtures detected the presence of Al 2 O 3 and Nb as result of the aluminothermic reduction of niobium pentoxide only after 75 minutes [34].…”

Metallic Niobium Powder Reduced by Atmospheric Magnesium Gas with Niobium Pentoxide Powder

“…Although the agent is favorable at high temperatures and for mass production, it is difficult to remove the Al 2 O 3 mixed with the product and easily contaminated by undesired aluminum content. 7,8) Also, some studies reported reducing Nb 2 O 5 with silicon. In this process, niobium silicide (NbSi 2 ) can be formed as an intermediate compound during the reduction, because silicon is soluble in solid niobium.…”