Abstract
The hydration structure of calcium nitrate tetrahydrate, Ca(NO3)2 · 4.1 H2O, melt at 328 K has been investigated by X-ray scattering and correlation method. Analysis of the radial distribution function and model fitting revealed that in the hydrate melt, a Ca2+ ion is surrounded by about six oxygen atoms, 4.1 of which come from water molecules at the average distance of 0.241 nm, 2.0 coming from the nitrate ions at the average distance of 0.254 nm. In the first coordination shell of the melt, the formation of a direct Ca2+-NO −3 correlation, such as contact ion pairs, was suggested. The hydration structure of the melt analysed was compared with that of Ca(NO3)2 · 3.5H2O melt previously reported, and the decrease from nine of the reported melt to six in this melt was observed in the number of the nearest neighbour oxygen atoms around a Ca2+ ion. This implies that in the highly concentrated aqueous solution, the structure of the first coordination shell around the cation changes markedly with a small difference in the water molecule content.
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Igarashi, K., Tajiri, K., Asahina, T. et al. X-ray diffraction study of calcium nitrate tetrahydrate melt at 328 K. JOURNAL OF MATERIALS SCIENCE 28, 2774–2778 (1993). https://doi.org/10.1007/BF00356217
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DOI: https://doi.org/10.1007/BF00356217