Abstract In this paper, we report the results of the first study focused on the thermal stability and dehydration dynamics of the natural zeolite mineral ferrierite. A sample from Monastir, Sardinia [(Na0.56K1.19Mg2.02Ca0.52 Sr0.14) (Al6.89Si29.04)O72·17.86H2O; a = 19.2241(3) Å; b = 14.1563(2) Å; c = 7.5106(1) Å, V = 2043.95(7) Å3] was investigated by thermogravimetric analysis and in-situ synchrotron X‑ray powder diffraction. Thermogravimetric data show that H2O release begins already in the range 50–100 °C and is complete at ~600 °C. The results of the structure refinements performed in Immm space group by Rietveld analysis with data collected up to 670 °C show that ferrierite belongs to the group of zeolites that do not undergo phase transitions. Upon heating to 670 °C, ferrierite behaves as a non-collapsible structure displaying only a slight contraction of the unit-cell volume (ΔV = –3%). The unit-cell parameter reductions are anisotropic, more pronounced for a than for b and c (Δa = –1.6%; Δb = –0.76%; Δc = –0.70%). This anisotropic response to a temperature increase is interpreted as due to the presence in the ferrierite framework of five-membered ring chains of SiO4 tetrahedra, which impart a higher structural rigidity along b and c. Upon dehydration we observe: (1) the gradual H2O loss, beginning with the molecules hosted in the 10MR channel, is almost complete at 670 °C, in good agreement with the TG data; (2) as a consequence of the decreased H2O content, Mg and K migrate from their original positions, moving from the center of the 10MR channel toward the walls to coordinate the framework oxygen atoms. The observation of transmission electron microscopy selected-area electron diffraction patterns revealed defective crystals with an occasional and moderate structural disorder. Beyond providing information on the thermal stability and behavior of natural ferrierite, the results of this work have significant implications for possible technological applications. These data allow for comparison with the dehydration kinetics/mechanisms of the corresponding synthetic phases, clarifying the role played by framework and extra-framework species on the high-temperature behavior of porous materials with ferrierite topology. Moreover, the information on the thermal behavior of natural ferrierite can be used to predict the energetic performances of analogous synthetic Si-pure counterparts, namely “zeosil-electrolyte” systems, under non-ambient conditions. Specifically, the very high thermal stability of ferrierite determined in this study, coupled with the baric behavior determined in other investigations, suggests that the “Si-FER–electrolyte” system may be an excellent candidate for use as an energy reservoir. Indeed, ferrierite exhibits the so-called “spring behavior,” i.e., upon compression in water or in an electrolyte solution, it converts the mechanical energy into interfacial energy, and—when pressure is released—it can completely restore the supplied mechanical energy accumulated during the compression step.

中文翻译：

---

天然镁碱沸石的高温行为：原位同步加速器 X 射线粉末衍射研究

摘要 在本文中，我们报告了第一项关于天然沸石矿物镁碱沸石的热稳定性和脱水动力学的研究结果。来自撒丁岛莫纳斯提尔的样品 [(Na0.56K1.19Mg2.02Ca0.52 Sr0.14) (Al6.89Si29.04)O72·17.86H2O; a = 19.2241(3) Å；b = 14.1563(2) Å；c = 7.5106(1) Å, V = 2043.95(7) Å3] 通过热重分析和原位同步加速器 X 射线粉末衍射进行研究。热重数据显示 H2O 的释放在 50–100 °C 范围内已经开始，并在 ~600 °C 时完成。通过 Rietveld 分析在 Immm 空间群中进行的结构改进结果表明，镁碱沸石属于不发生相变的沸石群。加热到 670 °C 时，镁碱沸石表现为不可折叠的结构，仅显示晶胞体积的轻微收缩 (ΔV = –3%)。晶胞参数降低是各向异性的，a 比 b 和 c 更明显（Δa = –1.6%；Δb = –0.76%；Δc = –0.70%）。这种对温度升高的各向异性响应被解释为由于 SiO4 四面体的五元环链在镁碱沸石骨架中的存在，它赋予沿 b 和 c 更高的结构刚度。脱水后我们观察到：（1）H2O 逐渐丢失，从 10MR 通道中的分子开始，在 670°C 时几乎完成，与 TG 数据非常吻合；(2) 由于 H2O 含量降低，Mg 和 K 从其原始位置迁移，从 10MR 通道的中心向壁移动以协调骨架氧原子。透射电子显微镜选定区域电子衍射图案的观察显示有缺陷的晶体，偶尔有中度结构紊乱。除了提供有关天然镁碱沸石的热稳定性和行为的信息外，这项工作的结果对可能的技术应用具有重要意义。这些数据允许与相应合成相的脱水动力学/机理进行比较，阐明骨架和骨架外物质对具有镁碱沸石拓扑结构的多孔材料的高温行为所起的作用。此外，天然镁碱沸石的热行为信息可用于预测类似的合成纯硅对应物，即“沸石-电解质”系统，在非环境条件下的能量性能。具体而言，本研究中确定的镁碱沸石具有非常高的热稳定性，再加上其他研究中确定的重压行为，表明“Si-FER-电解质”系统可能是用作能量储存器的绝佳候选者。事实上，镁碱沸石表现出所谓的“弹簧行为”，即在水中或电解质溶液中压缩时，它将机械能转化为界面能，并且——当压力释放时——它可以完全恢复所提供的累积机械能在压缩步骤中。