Abstract
Reactions of niobium metal powder with high temperature-high pressure water were studied in an open system under the conditions of 300°-800°C, 10-100MPa and 3-72h. Niobium pentaoxide (Nb2O5), niobium hydride (NbHx), and NbO2 were obtained from niobium. Niobium changed into orthorhombic Nb2O5 and niobium hydride at 400°C under 100MPa for 3h. Only orthorhombic, or/and monoclinic Nb2O5 were obtained above 700°C under 100MPa for 3h. The formation of oxides and hydrides caused cracking on the surface above 400°C (100MPa, 3h) resulting in disintegration of grains above 500°C (100MPa, 3h). The partial crystal growth of Nb2O5 was observed above 700°C (100MPa, 3h). Temperature and reaction duration affected the hydrothermal oxidation of Nb metal, but pressure did not.
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