The partial pressure of oxygen in equilibrium with a niobium dioxide‐niobium pentoxide mixture was determined from electrochemical cell measurements over the range 800° to 1070°C and from thermogravimetric gas‐equilibrium measurements at 1000° and 1200°C. These measurements compare favorably with those of previous investigators. An isopiestic technique was used to determine the composition at 100°C intervals for nonstoichiometric Nb 2 O 5 in equilibrium with NbO 2 between 900° and 1100°C. The departure from stoichiometry for Nb 2 O 5 decreased from Nb 2 O 4 . 81 at 1090°C to Nb 2 0 4.887 at 889°C. The partial pressure of oxygen in equilibrium with different compositions of nonstoichiometric Nb 2 O 5 was determined from electrochemical cell measurements over the range 800° to 1070°C and from thermogravimetric measurements by equilibrating the nonstoichiometric Nb 2 O 5 specimen with an H 2 /H 2 O gaseous mixture at 900° to 1200°C. Th_e relative partial molar enthalpy of oxygen, Δ II O 2 for the Nb 2 O 5 ‐χ phase (calculated from the cell measurements) was independent, within experimental error, of both temperature and composition, the average value being ‐164 kcal/ mole. These equilibrium measurements were compared with the therrnogravimetric study of nonstoichiometric Nb 2 O 5 by Kofstad and Anderson and a departure from their relation χ (Nb 2 O 5 ‐χ) ∝ p O 2 ‐ 1 /6 was observed at the low oxygen end of the homogeneous phase field.
No takes yet. Share an insight, caveat, or question.
Blumenthal et al. (1965) studied this question.