| Autor: |
Pillai SB; Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States., Wilcox RJ; Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States., Hillis BG; Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States., Losey BP; Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States., Martin JD; Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States. |
| Abstrakt: |
Using a series of time- and temperature-resolved synchrotron diffraction experiments, the relationship between multiple polymorphs of ZnCl 2 and its respective hydrates is established. The δ-phase is found to be the pure anhydrous phase, while the α, β, and γ phases result from partial hydration. Diffraction, gravimetric, and calorimetric measurements across the entire ZnCl 2 · R H 2 O, 0 > R > ∞ composition range using ultrapure, doubly sublimed ZnCl 2 establish the ZnCl 2 : H 2 O phase diagram. The results are consistent with the existence of crystalline hydrates at R = 1.33, 3, and 4.5 and identify a mechanistic pathway for hydration. All water is not removed from hydrated ZnCl 2 until the system is heated above its melting point. While hydration/dehydration is reversible in concentrated solutions, dehydration from dilute aqueous solutions can result in loss of HCl, the source of hydroxide impurities commonly found in commercial ZnCl 2 preparations. The strong interaction between ZnCl 2 and water exerts a significant impact on the solvent water such that the system exhibits a deep eutectic at a composition of about R = 7 (87.5 mol %) and a eutectic temperature below -60 °C. |
