Characterization of beryllium selenates by X-ray powder diffraction, DTA and DSC by V. G. Koleva, V. A. Karadjova, and M. P. Georgiev

Crystal Research and Technology

Cryst. Res. Technol. 39, 1020 (2004) - Abstract -

Characterization of beryllium selenates by X-ray powder diffraction, DTA and DSC

V. G. Koleva, V. A. Karadjova*, and M. P. Georgiev*

Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
*Department of Inorganic Chemistry, University of Chemical Technology and Metallurgy, 8 Kliment Ohridsky Str., 1756 Sofia, Bulgaria

Keywords	beryllium selenate tetrahydrate, beryllium selenate dihydrate, beryllium selenate, lattice parameters, enthalpy of dehydration
PACS	81.70.Pg, 61.10.Nz
DOI	10.1002/crat.200410287

BeSeO₄^.2H₂O and BeSeO₄ have been studied röntgenographically: BeSeO₄^.2H₂O forms orthorhombic crystals with lattice constants: a = 5.843(2) Å; b = 9.790(3) Å; c = 4.692(1) Å; V = 268.4(1) Å³. The crystals of BeSeO₄ are tetragonal: a = 4.648(1) Å; c = 7.084 (3) Å; V = 153.1(1) Å³, SG I-4. The thermal dehydration of BeSeO₄^.2H₂O has been studied by TG, DTA and DSC methods. The dehydration occurs in four steps and intermediate hydrates BeSeO₄^.2H₂O, BeSeO₄^.H₂O and BeSeO₄^.0.5H₂O are formed. The enthalpies of dehydration of the observed dehydration processes have been determined. The higher value of ΔH_deh of BeSeO₄^.2H₂O as compared to those of other metal selenate tetrahydrates is discussed in terms of the strong Be-2H₂O interaction. The enthalpies of formation of BeSeO₄^.4H₂O and BeSeO₄^.2H₂O have been calculated.

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