Solid state deoxidation of niobium by calcium and magnesium

Deoxidation of solid niobium using metallic liquid calcium or magnesium was studied. In the temperature range from 973 to 1473 K, the equilibrium oxygen concentrations under the coexistence of the reductant and its oxide were analyzed. A oxygen level of a few tens of mass ppm was found when Ca and CaO coexisted, and a level of about 100 ppm when Mg and MgO coexisted. Ca deoxidation could be applied under an inert gas atmosphere even at temperatures around 200 K 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. (C) 1998 Elsevier Science S.A.