Abstract:

Starting niobium samples with different oxygen contents were produced by arc melting and electron beam melting respectively. The equilibrium oxygen contents of the niobium metal have been measured in the temperature range of 1173-1473K for Ca-CaO-Nb and of 973 and1173K for Mg-MgO-Nb by an inert gas fusion infrared absorption method. The equilibrium oxygen contents in Nb increases with temperature, which is independent of oxygen concentration of the starting Nb samples. Based on the equilibrium oxygen contents, the Gibbs free energy of the oxygen dissolution in niobium metal, as well as the expressions of oxygen pressure temperature component ( p t x ) for theses two equilibrium systems were obtained. The acquired free energy values a less than that reported in the literature. This difference is mainly attributed to the adoption of different standard formation free energy of CaO.

Key words: Deoxidation of niobium, Thermodynamics, Gibbs free energy, High purity niobium