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

2004; Wiley; Volume: 39; Issue: 11 Linguagem: Inglês

10.1002/crat.200410287

1521-4079

V. Koleva, Veronika Karadjova, M. P. Georgiev,

Inorganic Fluorides and Related Compounds

Abstract BeSeO 4 .2H 2 O and BeSeO 4 have been studied röntgenographically: BeSeO 4 .2H 2 O 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) Å 3 . The crystals of BeSeO 4 are tetragonal: a = 4.648(1) Å; c = 7.084 (3) Å; V = 153.1(1) Å 3 , SG I $ \bar 4 $ . The thermal dehydration of BeSeO 4 .4H 2 O has been studied by TG, DTA and DSC methods. The dehydration occurs in four steps and intermediate hydrates BeSeO 4 .2H 2 O, BeSeO 4 .H 2 O and BeSeO 4 .0.5H 2 O are formed. The enthalpies of dehydration of the observed dehydration processes have been determined. The higher value of ΔH deh of BeSeO 4 .4H 2 O as compared to those of other metal selenate tetrahydrates is discussed in terms of the strong Be–H 2 O interaction. The enthalpies of formation of BeSeO 4 .4H 2 O and BeSeO 4 .2H 2 O have been calculated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)