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成果報告書詳細
管理番号20170000000459
タイトル*平成28年度中間年報 未利用熱エネルギーの革新的活用技術研究開発 技術シーズ発掘のための小規模研究開発(蓄熱) 余剰希土類元素を使用した新型化学蓄熱材の研究開発
公開日2018/3/8
報告書年度2016 - 2017
委託先名国立大学法人京都大学
プロジェクト番号P15007
部署名省エネルギー部
和文要約
英文要約Title: Research and Development Project for Innovative Thermal Management Materials and Technologies/ Incubation Research on Innovative Technologies in the Thermal Energy Storage Materials/ Development of Thermochemical Energy Storage Materials using Surplus Rare Earth Elements

(1) Fundamental thermal properties and reactivity of rare earth sulfate hydrate

This development item is aimed at improving the energy density and tuning working temperature of La2(SO4)3 by exploring new gaseous species which react with La2(SO4)3. In this year, the reactivity of La2(SO4)3 with NH3 and CO2 gases has been investigated by thermogravimetry (TG) and X-ray diffraction analysis.
La2(SO4)3・9H2O (Wako Pure Chemical Industries) was used as the starting material. TG analysis was conducted by the following procedure: La2(SO4)3・9H2O was heated to 350 °C under a dry Ar atmosphere for complete dehydration to take place, and then it was cooled down under dry CO2 or NH3 atmospheres at a rate of 20 °C/min. XRD analysis was applied for the sample heat-treated under a dry CO2 atmosphere at 366 °C for 10 min and cooled down at a rate of 5 °C/min.
The results indicate that La2(SO4)3 does not react with CO2 gas, as neither significant weight change nor phase change was observed under the CO2 atmosphere. By contrast, weight gain was observed by cooling La2(SO4)3 to 250 °C under the NH3 atmosphere. It suggests that La2(SO4)3 reacts with NH3 gas. Further investigation is needed to reveal the reaction mechanism and reaction enthalpy.

(2) Materials design of rare earth sulfate hydrate for improving energy density and lowering working temperature

For materials design of controlling the thermal storage properties of La2(SO4)3・H2O, the effects of partial substitution by various dopants, such as Y, Al, Mg, Ca, Sr, and Ba, are examined in the present study. In this year, the effects of Y and Al substitution have been examined using first-principles calculations.
Prior to investigation of the substitution effects, the stable state of H2O incorporated in the dopant-free La2(SO4)3 was clarified. As a result, H2O in the crystal was found to be keep the shape of the molecule (OH bond length: 0.98 Angstrom, HOH angle: 107degree). In addition, the OH bonds direct towards a neighboring O ion located at a corner of SO4 units in the host crystal to form the OH-O bond like the hydrogen bond.
The stability of the incorporated H2O is varied by dopant substitution on the La sites. The calculated stabilization energies between dopants and H2O indicates Al substitution was found to be more effective for the H2O stability than Y substitution. Specifically, the stabilization energy is 0.5 eV by Al substitution, in which a strong Al-O bond is formed between Al and O in the H2O molecule. By contrast, Y substitution has little effect on the H2O stability in the crystal, meaning that Al substitution is more effective to improve the thermal storage density of La2(SO4)3・H2O.
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