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Hydrothermal equilibria and crystal chemistry of phases in the oxide-hydroxide-sulfate systems of La, Pr, and Nd

Journal Article · · J. Solid State Chem.; (United States)
Equilibria of the aqueous Ln + O + SO/sub 4/ (Ln = La, Pr, Nd) system have been investigated at water pressure of 120 +/- 20 MPa and temperatures of 450 +/- 50/sup 0/C. At low sulfate contents, the UCl/sub 3/-type trihydroxides coexist with the orthorhombic dioxide monosulfates. A second two-phase region, Ln/sub 2/O/sub 2/SO/sub 4/ + Ln(OH)SO/sub 4/, appearing at higher sulfate concentrations is followed by a third two-phase region, Ln(OH)SO/sub 4/ + Ln/sub 2/(SO/sub 4/)/sub 3/ x nH/sub 2/O. Whereas the monohydroxide monosulfates all have the same monoclinic structure, several new hydrate compositions and structures form in hydrothermal media. X-ray diffraction data indicate that the n = 7 hydrates of La and Pr and the monohydrate of La have closely related orthorhombic structures similar to that of the anhydrous La/sub 2/(SO/sub 4/)/sub 3/ phase obtained by decomposition of the hydrates at low temperature. The n = 5 sulfate hydrates of Pr and Nd have also been characterized, and a metastable La/sub 2/(OH)/sub 4/SO/sub 4/ phase has been identified. Lattice parameters and diffraction data obtained by powder and single crystal methods are reported, and the thermal decomposition reactions of the products are described.
Research Organization:
Rockwell International, Golden, CO (USA)
OSTI ID:
6976688
Journal Information:
J. Solid State Chem.; (United States), Journal Name: J. Solid State Chem.; (United States) Vol. 73:1; ISSN JSSCB
Country of Publication:
United States
Language:
English