The physico-geometrical reaction pathway and kinetics of multistep thermal dehydration of calcium chloride dihydrate in a dry nitrogen stream

Abstract

Several inorganic hydrates exhibit reversible reactions of thermal dehydration and rehydration, which is potentially applicable to thermochemical energy storage. Detailed kinetic information on both forward and reverse reactions is essential...

Water vapor effect on the physico-geometrical reaction pathway and kinetics of the multistep thermal dehydration of calcium chloride dihydrate

“…The magnitude relation of the mass loss values of the first and second mass loss steps, Δ m 1 and Δ m 2 , respectively, was Δ m 1 > Δ m 2 at low p (H 2 O), aligning with that in a stream of dry N 2 . 31 However, with increasing p (H 2 O), Δ m 1 gradually decreased until it equaled Δ m 2 in a p (H 2 O) range of 2.6–4.7 kPa. Further increase in p (H 2 O) led to an additional mass loss step emerging toward the end of the first mass loss step, causing a decrease in the Δ m 2 value.…”

“…The mass loss process involved two steps, akin to that in a stream of dry N 2 . 31 The mass loss values of the first and second mass loss steps vary with increasing p (H 2 O) value. The magnitude relation of the mass loss values of the first and second mass loss steps, Δ m 1 and Δ m 2 , respectively, was Δ m 1 > Δ m 2 at low p (H 2 O), aligning with that in a stream of dry N 2 .…”

“…The same CC-DH sample used in our previous study to monitor the thermal decomposition process in a stream of dry N 2 31 was used in this study, focusing on examining the effect of water vapor on the thermal dehydration pathway and kinetics. The CC-DH sample (special grade, >99.9%, FUJIFILM Wako Chem.)…”

“…Those sampling procedures including m 0 value, sample pan, and pretreatment in the TG–DTA instrument are the same with those used for the TG–DTA measurements in a stream of dry N 2 in our previous study. 31 The sample temperature was increased at a β of 2 K min −1 in steps with 10 min-isothermal holding sections inserted every 10 K to a temperature below the reaction initiation temperature. In addition, the p (H 2 O) value in the flowing gas was increased with a step-by-step manner at each isothermal holding section to attain the preset p (H 2 O) value for the TG–DTA measurements, after switching the flowing gas to wet N 2 ( q v = 200 cm 3 min −1 ) generated by the humidity controller.…”

“…In our previous study, 31 we examined the thermal dehydration of CC-DH in a stream of dry N 2 to understand the impact of self-generated water vapor on the reaction pathway and kinetics of the component reaction steps. The process was comprised of three distinct steps: (1) direct dehydration of CC-DH to CC-AH on the particle surface, resulting in a core–shell structure with CC-DH core and CC-AH shell; (2) contraction of the CC-DH core with the three-dimensional (3D) interface shrinkage to form CC-MH; and (3) contraction of the CC-MH core with the 3D interface shrinkage to form CC-AH.…”