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Crystallization and relative stabilities of Polymorphs of Niobium(V) Oxide under hydrothermal conditions
Author(s) -
Izumi F.,
Kodama H.
Publication year - 1978
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.19784400115
Subject(s) - hydrochloric acid , niobium oxide , crystallization , dissolution , nitric acid , chemistry , inorganic chemistry , amorphous solid , niobium , precipitation , oxide , hydrothermal circulation , hydrolysis , isothermal process , sulfuric acid , nuclear chemistry , crystallography , organic chemistry , chemical engineering , physics , meteorology , engineering , thermodynamics
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.