The Free Energy Diagram of the Vanadium-Oxygen System

A review of a number of earlier works permits the derivation of the free energy diagram of the system vanadium‐oxygen from composition V 2 O 5 down to beyond composition VO . It is shown that most of the earlier results agree fairly well if correctly interpreted. Results of some hydrogen reduction experiments are in accordance with the energy relations derived. The slope of the energy curve at low concentrations of oxygen has been determined by establishing equilibria between vanadium‐oxygen solutions and molten barium, magnesium, or calcium. The oxygen contents in vanadium thus obtained were determined by the vacuum fusion method. With these results the free energy curve for vanadium‐ oxygen has been completed. The results further suggest that the solubility of oxygen in vanadium is much lower than has been assumed hitherto, being possibly 0.25 per cent oxygen at 1000°C.