Deoxidation of solid niobium using metallic liquid calcium or magnesium was
studied. In the temperature range of 973K to 1473K, the equilibrium oxygen
concentrations under the coexistence of the reductant and its oxide were
analyzed. An oxygen level of a few tens of mass ppm was found when Ca and CaO
coexisted, and a level of an about 100 ppm when Mg and MgO coexisted. Ca
deoxidation could be applied under an inert gas atmosphere even at temperatures
about 200K lower than those applied for the Ti external gettering. The
thermodynamic data reported in the binary system of Nb-O in the high oxygen
concentration range or at higher temperatures could not explain the measured
oxygen solubilities in Nb under the coexistence of Ca-CaO or Mg-MgO.