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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >Energetics of metastudtite and implications for nuclear waste alteration
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Energetics of metastudtite and implications for nuclear waste alteration

机译：准硬石的能量学及其对核废料改造的影响

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摘要

Metastudtite, (UO2)O2(H2O)2, is one of two known natural peroxide minerals, but little is established about its thermodynamic stability. In this work, its standard enthalpy of formation, −1,779.6 ± 1.9 kJ/mol, was obtained by high temperature oxide melt drop solution calorimetry. Decomposition of synthetic metastudtite was characterized by thermogravimetry and differential scanning calorimetry (DSC) with ex situ X-ray diffraction analysis. Four decomposition steps were observed in oxygen atmosphere: water loss around 220 °C associated with an endothermic heat effect accompanied by amorphization; another water loss from 400 °C to 530 °C; oxygen loss from amorphous UO3 to crystallize orthorhombic α-UO2.9; and reduction to crystalline U3O8. This detailed characterization allowed calculation of formation enthalpy from heat effects on decomposition measured by DSC and by transposed temperature drop calorimetry, and both these values agree with that from drop solution calorimetry. The data explain the irreversible transformation from studtite to metastudtite, the conditions under which metastudtite may form, and its significant role in the oxidation, corrosion, and dissolution of nuclear fuel in contact with water.
机译：偏硅酸盐（UO2）O2（H2O）2是两种已知的天然过氧化物矿物质之一，但对其热力学稳定性的了解很少。在这项工作中，通过高温氧化物熔滴溶液量热法获得了其标准的形成焓-1,779.6±1.9 kJ / mol。通过热重分析和差示扫描量热法（DSC）以及异位X射线衍射分析来表征合成偏硅酸盐的分解。在氧气气氛中观察到四个分解步骤：失水约220°C，伴有吸热效应和非晶化；从400°C到530°C的另一个失水;非晶态UO3结晶正交α-UO2.9的氧气损失;并还原为结晶​​U3O8。这种详细的表征可以根据由DSC和转置式降温量热法测得的分解热效应计算地层焓，这两个值与滴定液量热法相符。数据解释了从辉石到偏辉石的不可逆转变，偏辉石可能形成的条件及其在与水接触的核燃料的氧化，腐蚀和溶解中的重要作用。

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