A solution and solid state study of niobium complexes University of ...
A solution and solid state study of niobium complexes University of ...
A solution and solid state study of niobium complexes University of ...
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Chapter 2<br />
Buachuang et al. 16 reported the separation <strong>of</strong> tantalum <strong>and</strong> <strong>niobium</strong> from dilute<br />
hydr<strong>of</strong>luoric media through a hollow fibre supported liquid membrane (HFSLM).<br />
Quaternary ammonium salt diluted in kerosene was used as a carrier. The best<br />
conditions were 0.3 M HF, 3 % (v/v) ammonium salt diluted in kerosene <strong>and</strong> 0.2 M <strong>of</strong><br />
stripping <strong>solution</strong> (NaClO4).<br />
2.3 Purification<br />
Three types <strong>of</strong> impurity elements are considered in the purification <strong>of</strong> <strong>niobium</strong>:<br />
Impurity elements with a higher vapour pressure than Nb. These elements<br />
can easily be removed by electron beam melting or high vacuum arc melting.<br />
Refractory impurity metals with a similar vapour pressure as Nb can only be<br />
removed by chemical or physical methods. These methods utilise the<br />
difference in kinetic behaviour <strong>and</strong> thermodynamic properties <strong>of</strong> the impurity<br />
element. Suitable methods are sublimation, electrolysis, distillation, etc.<br />
The removal <strong>of</strong> interstitial impurity elements involves high temperature<br />
annealing treatments in gas <strong>and</strong> high vacuum atmospheres.<br />
Niobium oxide (Nb2O5) is the starting material for the production <strong>of</strong> other <strong>niobium</strong><br />
compounds, such as lithium niobate (LiNbO3) <strong>and</strong> <strong>niobium</strong> chloride (NbCl5). Niobium<br />
oxide can be reduced with carbon in a two-step reaction, known as the Balke-<br />
process. 7 The first step is the formation <strong>of</strong> the carbide. The oxide is mixed with a<br />
stoichiometric amount <strong>of</strong> carbon black, placed in a carbon vessel <strong>and</strong> heated in<br />
vacuum to 1800 °C:<br />
Nb2O5 + 7 C → 2 NbC + 5 CO (2.1)<br />
16 D. Buachuang, P. Ramakul, N. Leepipatpiboon, U. Pancharoen, J. Alloys Compd., 509, 9549, 2011.<br />
12