## 3 Results and Discussion
### Dehydration/Hydration Stability  
After structural and thermal characterization of as synthesized materials, cyclic TG experiments were carried out in order to assess the dehydration/hydration stability of all batches. Figure 8 shows the whole first thermogravimetric cycle for CA-11H/32H and CA-SH, and the highlighted sections 1-6 correspond to the analysis steps previously reported in Section 2.3.3 and listed in Table 3. The plot is useful to visually perceive how the material's mass changes along each step, relating these transitions to the dehydration and hydration reactions. Initially, a heating phase and subsequent sustainment of 250 \({}^{\circ}\)C were applied (steps 1 and 2). As shown, this temperature allowed the materials to be dehydrated in a relatively short time. In fact, already at about 200-220 \({}^{\circ}\)C the material began to undergo a partial dehydration, which was completed when the temperature plateau is reached. The time that lapsed between the achievement of the onset temperature and the end of the process (identified as weight loss stabilization) was around 40 min. The dehydration results at equilibrium were compatible to TGA ones. This means that the chosen operating \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample ID** & \(\mathbf{T_{onset}}\) (\({}^{\circ}\)C) & **Weight Loss (\%)** & **Heat (kJ/kg)** & **Katoite (\%)** \\ \hline CA-32H & 247.5 & \(-19.04\) & 655.8 & 88.9 \\ CA-11H & 245.8 & \(-21.12\) & 807.0 & 98.6 \\ CA-SH & 248.7 & \(-10.15\) & 530.2 & \(<\)46.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Thermogravimetric analysis (TGA) and DSC characterization results. Figure 8: First dehydration/hydration cycle for CA-32H (red), CA-11H (blue) and CA-SH (orange). temperature was adequate to obtain a complete reaction conversion of the materials into their respective dehydrated forms. Step 3 and 4 are necessary after the dehydration reaction to decrease and stabilize the system at the target hydration temperature (125 \({}^{\circ}\)C) before the atmosphere shift. Hydration kinetics on co-precipitated batches was faster; the mass suddenly increased when the water vapor was supplied (5), reaching a plateau after 35-40 min. CA-32H exhibited a slightly higher hydration rate and, at the same time, a more marked slope variation. In contrast, CA-11H exhibited a larger yield at the end of the hydration process. However, both co-precipitated batches exhibited a comparable hydration trend. This behavior could be related to their similar composition (katoite, mostly) and morphology (different sized hexagonal plates). CA-SH had a different hydration kinetic; the mass gain associated to the hydration reaction was more gradual, if compared to the other two batches. This behavior could be related to its structural heterogeneity that kinetically limited the hydration processes. The release of physisorbed water (6) occurred when the water vapor supply was over and led to a small weight loss for all the materials; hence, it was deducted that just a limited portion of adsorbed water was not chemically bonded. However, to estimate the effective yield of the hydration reaction, this surplus of mass was not calculated, since the surface interaction with physisorbed water clearly had a weaker energy than a chemisorption. Hence, to avoid an overestimation of the released heat, the real hydration conversion in mass was calculated as the difference between the mass at the end of Section 6 and the beginning of Section 5. Additionally, in Section 6, the cycle drift is evidenced (double pointed arrow). It shows a less hydration yield than the previous dehydration, which led to an efficiency loss throughout the cycle. This aspect therefore involved an evaluation of the behavior in subsequent cycles. Table 5 lists the conversion values for each dehydration and hydration step, related to a five-cycle experiment.