Relative stability of hydrated/anhydrous products of calcium chloride during complete dehydration as examined by high-temperature X-ray powder diffraction

• Published in: The Journal of physics and chemistry of solids 2018-09, Vol.120, p.167-172
• Main Authors: Karunadasa, Kohobhange S.P., Manoratne, C.H., Pitawala, H.M.T.G.A., Rajapakse, R.M.G.
• Format: Article
• Language: English
• Subjects: Calcium chloride; Dehydration; High-temperature X-ray powder diffraction; Microstructure; Relative stability
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2018.04.034

The correlation between the relative stability of hydrated/anhydrous products and microstructure of calcium chloride has been investigated by high-temperature X-ray powder diffraction. The X-ray diffractograms were recorded at 25, 115, 150 and 200 °C, respectively. Results indicate that tetrahydrate and dihydrate are the major forms available at 25 °C. The first endothermic dehydration at around 115 °C is accounted for a mixture of anhydrous calcium chloride and monohydrate. The second consecutive endothermic dehydration at around 150 °C ensured complete removal of crystalline water. The complete dehydration is accounted for two different anhydrous calcium chloride phases with larger (0.324 nm3) and smaller (0.168 nm3) unit cell volume. The phase with smaller unit cell volume is the stable anhydrous form of calcium chloride beyond 150 °C. The relative stability of anhydrous/hydrated products at different temperatures simultaneously determines by respective lattice strain, crystallite size, and unit cell volume. It is also found that inferior lattice strain, larger crystallite size, and smaller unit cell volume ultimately account for dominant and more stable calcium chloride product. The moisture absorption from the material takes place towards reducing lattice strain; hence, the hygroscopic nature of calcium chloride can be somewhat related to microstructure stability at low temperatures. [Display omitted] •Dehydration of calcium chloride is completed via two consecutive endothermic steps.•Hydrated forms are rapidly converted to stable anhydrous forms upon water elimination and microstructure modifications.•Relative stability of calcium chloride products is determined by lattice strain, crystallite size and unit cell volume.