On the Formation of Solid Solutions with Blödite- and Kröhnkite-Type Structures. II. Structural and Thermal Investigations of Solid Solutions Na2Zn1-xCux(SO4)2×4H2O(0 < x < 0.14)

Authors

  • D. Marinova  Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
  • M. Georgiev  Department of Inorganic Chemistry, University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria
  • Tsv. Bancheva  Department of Inorganic Chemistry, University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria
  • D. Stoilova  Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Keywords:

Na2Zn1-xCux(SO4)2∙4H2O solid solutions; X-ray powder diffraction; Enthalpy of dehydration; Enthalpy of formation; Infrared spectra.

Abstract

Structural and thermal investigations of solid solutions Na2Zn1-xCux(SO4)2×4H2O (0 < x < 0.14) of a blödite-type structure are reported in the present paper. The replacement of the zinc ions by copper ones in the crystals of the blödite-type structure do not change considerably the lattice parameters and the volumes of the unit cells of the solid solutions due probably to the buffer effect of the sodium cations. However, the degree of distortion of the [M(H2O)4(SO4)2] clusters in the solid solutions is larger than that in Na2Zn(SO4)2×4H2O as deduced from the single crystal X-ray diffraction due to the Jahn-Teller effect (DI has value of 0.011 and 0.018 for the neat zinc blödite and solid solutions, respectively).

On the basis of TG-DTA-DSC methods combined with X-ray powder diffraction at elevated temperature, it has been found that the dehydration of blödite phases occurs stepwise, thus forming intermediate dehydrate (at about 130 ºC) and two polymorphic modifications of anhydrous compounds. The form (I) of Na2Zn(SO4)2 and Na2Zn0.86Cu0.14(SO4)2 is stable in the temperature interval of about 200-280 ºC and the from (II) - in the temperature interval of about 330-380 ºC. The incorporation of copper ions in the zinc blödite results in increasing in the values of DHdeh and decreasing in the values of DHf with increasing in the copper content. The water molecule in the kröhnkite compound Na2Cu(SO4)2×2H2O are separated in one step (the dihydrate is stable up to 250 ºC) and after heating at higher temperature it transforms into an anhydrous compound (300-380 ºC). Additionally, the anhydrous Na2Zn(SO4)2, Na2Cu(SO4)2 and Na2Zn0.86Cu0.14(SO4)2 were characterized structurally using both X-ray diffraction and spectroscopic techniques. The infrared spectroscopic experiments add an additional information about the structural properties of the anhydrous compounds. For example, the sulfate tetrahedra in the anhydrous compounds are distorted in a higher degree in comparison to those in the hydrated ones.

References

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International Journal of Scientific Research in Science and Technology

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Published

2016-12-30

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Volume 2, Issue 6 , November-December-2016

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Research Articles

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[1]
D. Marinova, M. Georgiev, Tsv. Bancheva, D. Stoilova, " On the Formation of Solid Solutions with Blödite- and Kröhnkite-Type Structures. II. Structural and Thermal Investigations of Solid Solutions Na2Zn1-xCux(SO4)2×4H2O(0 < x < 0.14), International Journal of Scientific Research in Science and Technology(IJSRST), Online ISSN : 2395-602X, Print ISSN : 2395-6011, Volume 2, Issue 6 , pp.283-295, November-December-2016.