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首页> 美国卫生研究院文献>Astrobiology >Experimentally Determined Standard Thermodynamic Properties of Synthetic MgSO4·4H2O (Starkeyite) and MgSO4·3H2O: A Revised Internally Consistent Thermodynamic Data Set for Magnesium Sulfate Hydrates
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Experimentally Determined Standard Thermodynamic Properties of Synthetic MgSO4·4H2O (Starkeyite) and MgSO4·3H2O: A Revised Internally Consistent Thermodynamic Data Set for Magnesium Sulfate Hydrates

机译：实验确定的合成MgSO4·4H2O（Starkeyite）和MgSO4·3H2O的标准热力学性质：硫酸镁水合物的修正的内部一致热力学数据集

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The enthalpies of formation of synthetic MgSO4·4H2O (starkeyite) and MgSO4·3H2O were obtained by solution calorimetry at T=298.15 K. The resulting enthalpies of formation from the elements are (starkeyite)=−2498.7±1.1 kJ·mol−1 and (MgSO4·3H2O)=−2210.3±1.3 kJ·mol−1. The standard entropy of starkeyite was derived from low-temperature heat capacity measurements acquired with a physical property measurement system (PPMS) in the temperature range 5 K<T<300 K: (starkeyite)=254.48±2.0 J·K−1·mol−1.Additionally, differential scanning calorimetry (DSC) measurements with a Perkin Elmer Diamond DSC in the temperature range 270 K<T<300 K were performed to check the reproducibility of the PPMS measurements around ambient temperature.The experimental Cp data of starkeyite between 229 and 303 K were fitted with a Maier-Kelley polynomial, yielding Cp(T)=107.925+0.5532·T−1048894·T−2.The hydration state of all Mg sulfate hydrates changes in response to local temperature and humidity conditions. Based on recently reported equilibrium relative humidities and the new standard properties described above, the internally consistent thermodynamic database for the MgSO4·nH2O system was refined by a mathematical programming (MAP) analysis.As can be seen from the resulting phase diagrams, starkeyite is metastable in the entire T-%RH range. Due to kinetic limitations of kieserite formation, metastable occurrence of starkeyite might be possible under martian conditions. Key Words: Mg sulfates—Starkeyite—Thermodynamic data—Entropy—Enthalpy—Calorimetry. Astrobiology 12, 1042–1054.
机译：通过溶液量热法在T = 298.15 K下获得合成的MgSO4·4H2O（starkeyite）和MgSO4·3H2O的形成焓。由元素生成的形成焓为（starkeyite）=-2498.7±1.1 kJ·mol -1 和（MgSO4·3H2O）= − 2210.3±1.3 kJ·mol -1 。从在5 K - 1 ·mol -1 。另外，使用Perkin Elmer Diamond DSC在270 K -2 。所有硫酸镁水合物的水合状态会根据当地的温度和湿度条件而变化。基于最近报道的平衡相对湿度和上述新的标准特性，通过数学编程（MAP）分析完善了MgSO4·nH2O系统的内部一致的热力学数据库。从生成的相图中可以看出，星晶石是亚稳的在整个T-％RH范围内。由于钾长石形成的动力学局限性，在火星条件下可能会发生亚稳的星基石。关键字：硫酸镁-Starkeyite-热力学数据-熵-焓-量热法。天体生物学12，1042–1054。

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