Zeitschrift für anorganische und allgemeine Chemie · 1978 · 10 citations · 12 references
Natural SciencesChemistryMaterials ScienceInorganic ChemistryPhysical ChemistrySolid-state ChemistryCrystallization AnalysisCrystallization ProcessesInorganic MaterialsNucleationSolid-state SynthesisThermodynamics Of CeramicsHydrochloric Acid TreatmentHydrothermal Crystal GrowthHydrothermal SynthesisMetastable PolymorphsOxide Phase StabilityOxide PolymorphsOxide Solid-state ChemistryThermochemistry Of Oxides
Abstract The TT‐, T‐, B‐, P‐, and poorly ordered M‐forms of niobium(V) oxide were crystallized hydrothermally by treating niobic acid with pure water and acids such as hydrochloric acid, nitric acid, and sulfuric acid at 250–750°C and 15–100MPa. Triniobium chloride heptaoxide was hydrolyzed in pure water and acids solutions at 250–500°C and 15–98MPa, producing the P‐, R‐, and B‐forms. The formation of the above polymorphs involved either dissolution‐precipitation or the solid‐phase rearrangement of the structures of amorphous solids. The B‐form was shown to be the most stable phase below 760°C by an isothermal‐conversion method. The relative stabilities of seven polymorphs of niobium(V) oxide were estimated by observing the rates of conversion of metastable forms into the B‐forms in 1.2 mol/dm 3 hydrochloric acid.
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