Variable temperature PXRD investigation of the phase changes during the dehydration of potassium Tutton salts

• Published in: Journal of thermal analysis and calorimetry Vol. 132; no. 3; pp. 1523 - 1534
• Main Authors: Morales, Ana C., Cooper, Nicholas D., Reisner, Barbara A., DeVore, Thomas C.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.06.2018; Springer; Springer Nature B.V
• Subjects: Analysis; Analytical Chemistry; Calorimetry; Chemistry; Chemistry and Materials Science; Copper; Decomposition; Dehydration; Dehydration (Physiology); Differential scanning calorimetry; Gravimetric analysis; Hydration; Inorganic Chemistry; Investigations; Measurement Science and Instrumentation; Nickel; Phase transitions; Physical Chemistry; Polymer Sciences; Potassium; Thermal analysis; Thermal decomposition; X ray powder diffraction; X-ray diffraction; Zinc; Dehydration pathways; FTIR; Thermal dehydration; Author contact information; Tutton salts; Thermal gravimetric analysis; Powder X-ray diffraction
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-018-7107-0

The thermal dehydration of the potassium Tutton salts K 2 M(SO 4 ) 2 ·6H 2 O (M = Mg, Co, Ni, Cu, Zn) was investigated using thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), FTIR, and variable temperature powder X-ray diffraction. While each Tutton salts lost all six waters of hydration when heated to 500 K, the decomposition pathway depended on the divalent metal cation. K 2 Ni(SO 4 ) 2 ·6H 2 O lost all six waters in a single step, and K 2 Cu(SO 4 ) 2 ·6H 2 O consistently lost water in two steps in capped and uncapped cells. In contrast, multiple decomposition pathways were observed for the magnesium, cobalt, and zinc Tutton salts when capped and uncapped TG cells were used. K 2 Zn(SO 4 ) 2 ·6H 2 O lost the waters of hydration in a single step in an uncapped cell and in two steps in a capped cell. Both K 2 Mg(SO 4 ) 2 ·6H 2 O and K 2 Co(SO 4 ) 2 ·6H 2 O decomposed in a series of steps where the stability of the intermediates depended on the cell configuration. A greater number of phases were often observed in DSC and capped-cells TG experiments. A quasi-equilibrium model is presented that could explain this observation. These results highlight that experimental conditions play a critical role in the observed thermal decomposition pathway of Tutton salts.