Multi-step hydration/dehydration mechanisms of rhombohedral Y(2)(SO(4))(3): a candidate material for low-temperature thermochemical heat storage.
Multi-step hydration/dehydration mechanisms of rhombohedral Y(2)(SO(4))(3): a candidate material for low-temperature thermochemical heat storage.
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为了评价菱面体Y2(SO4)3作为低温热化学储能新材料的潜力，研究了其热行为、相变和水化/脱水反应机理。菱面体Y2(SO4)3在130℃以下表现出可逆的水化/脱水行为，热滞较小(小于50℃)。在约0.02atm的水蒸气压力下，反应通过两个反应步骤进行，即在80~130℃的“高温反应”和在30~100℃的“低温反应”。高温反应是通过将水插入到菱面体Y2(SO4)3主体结构中形成菱面体Y2(SO4)3·xH2O(x=∼1)进行的。在低温反应中，菱面体Y2(SO4)3·xH2O容纳了额外的水分子(x>；1)，并最终水合成Y2(SO4)3·8H2O(单斜晶系)，主体结构发生了变化。当水蒸气压力高于0.08atm时，出现中间产物Y2(SO4)3·3H2O。绘制了水合物的相稳定图，并对Y2(SO4)3在热能升级中的潜在用途进行了评估。在反应温度和水蒸气压力方面，高温反应可能与现有的候选CaSO4·0.5H2O相似。此外，菱面体Y2(SO4)3·xH2O水合成Y2(SO4)3·3H2O应具有较大的储热能力。在反应动力学方面，Y2(SO4)3·8H2O的初始脱水为菱面体Y2(SO4)3，引入了微米级的微孔结构，这可能会提高反应速度。为了评价菱面体Y2(SO4)3作为低温热化学储能新材料的潜力，研究了其热行为、相变和水化/脱水反应机理。
To evaluate rhombohedral Y2(SO4)3 as a new potential material for low-temperature thermochemical energy storage, its thermal behavior, phase changes, and hydration/dehydration reaction mechanisms are investigated. Rhombohedral Y2(SO4)3 exhibits reversible hydration/dehydration below 130 °C with relatively small thermal hysteresis (less than 50 °C). The reactions proceed via two reaction steps in approximately 0.02 atm of water vapor pressure, i.e. “high-temperature reaction” at 80–130 °C and “low-temperature reaction” at 30–100 °C. The high-temperature reaction proceeds by water insertion into the rhombohedral Y2(SO4)3 host structure to form rhombohedral Y2(SO4)3·xH2O (x = ∼1). For the low-temperature reaction, rhombohedral Y2(SO4)3·xH2O accommodates additional water molecules (x > 1) and is eventually hydrated to Y2(SO4)3·8H2O (monoclinic) with changes in the host structure. At a water vapor pressure above 0.08 atm, intermediate Y2(SO4)3·3H2O appears. A phase stability diagram of the hydrates is constructed and the potential usage of Y2(SO4)3 for thermal energy upgrades is assessed. The high-temperature reaction may act similarly to an existing candidate, CaSO4·0.5H2O, in terms of reaction temperature and water vapor pressure. Additionally, the hydration of rhombohedral Y2(SO4)3·xH2O to Y2(SO4)3·3H2O should exhibit a larger heat storage capacity. With respect to the reaction kinetics, the initial dehydration of Y2(SO4)3·8H2O to rhombohedral Y2(SO4)3 introduces a microstructure with pores on the micron order, which might enhance the reaction rate. To evaluate rhombohedral Y2(SO4)3 as a new potential material for low-temperature thermochemical energy storage, its thermal behavior, phase changes, and hydration/dehydration reaction mechanisms are investigated.
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