Acid-leaching of sodium brannerite: Synthesis and structure of Na{sub 0.13}(V{sub 0.13}Mo{sub 0.87})O{sub 3} {center_dot} nH{sub 2}O
- Univ. of Pennsylvania, Philadelphia, PA (United States)
In dilute hydrochloric acid NaVMoO{sub 6}, which has a layered {open_quotes}brannerite{close_quotes} structure, participates in an acid-leaching reaction that results in the formation of a metastable compound with the stoichiometry Na{sub 0.13}(V{sub 0.13}Mo{sub 0.87})O{sub 3} {center_dot} nH{sub 2}O and the structure of {open_quotes}hexagonal{close_quotes} MoO{sub 3}. The locations of the sodium ions and water molecules in the channels of this structure, space group P6{sub 3} with a = 10.628(1) {angstrom} and c = 3.6975(7) {angstrom}, were determined through Rietveld refinement of powder neutron diffraction data collected on deuterated samples. The water molecules are important in providing a stable environment for the sodium ions, which are octahedrally coordinated by four framework oxygen atoms and two water molecules. In an attempt to understand the mechanistic aspects of the acid-leaching reaction, samples of the hexagonal phase were formed with a range of V:Mo contents from aqueous Na-V-Mo solutions via conventional precipitation methods. Although phases could be stabilized with the same crystallography as the brannerite-derived products, the solution precipitates contained vacancies in the transition metal framework and a higher concentration of sodium in the channels. These compositional differences led to a significant reduction in the apparent high-temperature stability of the solution-derived phases compared to that of their brannerite-derived counterparts. There is some evidence to suggest that the structural filiation between brannerite and hexagonal MoO{sub 3} may be responsible for the unique stoichiometry and stability of the products of the acid-leaching reactions and that the acid-leaching reactions do not proceed through a simple dissolution/precipitation mechanism.
- OSTI ID:
- 237565
- Journal Information:
- Journal of Solid State Chemistry, Vol. 119, Issue 1; Other Information: PBD: Oct 1995
- Country of Publication:
- United States
- Language:
- English
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