## 3 Results and Discussion
### Dehydration/Hydration Stability
The reported data are expressed by means of \(R_{d/h}\) (%), which is the normalized conversion obtained by Equation (7):  
\[R_{d/h}(\%)\ =\frac{\Delta m_{d/h}}{\Delta m_{1^{\circ}d}}\cdot 100 \tag{7}\]  
where \(d\) and \(h\) refer to the dehydration and hydration steps, respectively. The term \(\Delta m\) refers to the mass variation at the end of the considered process, while \(\Delta m_{1^{\circ}d}\) is the mass variation relative to the first dehydration, which is supposed to correspond to a 100% yield. Normalized conversions represent the most proper method to compare how the materials work along the cycling, taking into account their different katoite content. The previously described cycle drift could be numerically evaluated by observing the hydration \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample ID** & **Cycle** & **Dehydration T\({}_{\text{onset}}\) (\({}^{\circ}\)C)** & **Rd (\%)** & **Rh (\%)** \\ \hline CA-32H & 1 & 241.5 & 100 & 66.5 \\  & 2 & 231.1 & 67.6 & 50.9 \\  & 3 & 229.8 & 45.7 & 40.4 \\  & 4 & 230.2 & 40.4 & 40.2 \\  & 5 & 230.0 & 40.1 & 39.8 \\ \hline CA-11H & 1 & 242.7 & 100 & 67.5 \\  & 2 & 231.4 & 68.1 & 48.3 \\  & 3 & 229.4 & 47.6 & 37.1 \\  & 4 & 229.3 & 42.5 & 33.6 \\  & 5 & 229.6 & 33.3 & 32.5 \\ \hline CA-SH & 1 & 241.0 & 100 & 52.7 \\  & 2 & 233.2 & 51.0 & 31.7 \\  & 3 & 233.3 & 32.1 & 15.4 \\  & 4 & 231.7 & 12.2 & 11.0 \\  & 5 & 230.5 & 11.4 & 8.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Thermogravimetric performances per cycle. yields: co-precipitated presented a similar R\({}_{\rm h1^{\circ}}\) (66.5% and 67.49% for CA-32H and CA-11H, respectively), while the solid-solid one was moderately lower (52.68%) at the first cycle. This effect, however, became less enhanced cycle by cycle. Figure 9 graphically shows the cycle drift reduction, where the single normalized dehydations and hydrations are plotted for each material. CA-32H (a) reached comparable conversions from the end of the third cycle, corresponding to a R\({}_{\rm h}\) around 40%. Similar conversions were also appreciable for CA-11H at the end of the last two cycles, around a R\({}_{\rm h}\) of 33%. The solid-solid sample, on the contrary, did not reach a stable conversion throughout the experiment, and its conversion at the end of the fifth cycle was much lower than the other two materials (8.51%). The progressive decrease suggests that the material may have become totally deactivated in the subsequent cycles. The nonpurity of the CA-SH sample had, therefore, a detrimental effect on the thermal stability of the hydration process. Still in Figure 9, it should be noted that the hydration kinetic of the second cycle undergoes a clear change with respect to the first cycle but then remains similar for the following ones. An explanation could be related to a structural change that occurred during the first cycle, which involved rearrangements that persisted until a condition of stability was achieved. The number of cycles required to achieve a structural stabilization depended on the kind of material and the conditions applied during cycling. The structural change that the materials gradually underwent was coupled with a reduction of the dehydration onset temperature, T\({}_{\rm onset}\), which was observable after the first cycle (Table 5). This tem  
Figure 9: The 1 st, 2 nd, 3 rd, 4 th and 5 th normalized dehydration/hydration curves for CA-32H (red), CA-11H (blue) and CA-SH (orange). perature was found to be settled at an almost constant value from the third cycle for the co-precipitated batches (around 230 \({}^{\circ}\)C), simultaneously with an occurring conversion stabilization, as described before. For CA-SH, contrarily, the onset temperature was still decreasing at the fifth cycle.