Abstract:

The dehydration processes of three selected inorganic salt hydrates, CuSO₄·5H₂O, Na₂HPO₄·12H₂O and Na₂SO₄·10H₂O, were respectively investigated to obtain the influence of water on the latent heat. Simultaneous DSC (differential scanning calorimetry)-TG (thermogravimetry) combined with Raman spectroscopy were employed to monitored the dehydration processes and the structural variations. The result reveals that for those salt hydrates which dehydrate mainly crystal water at melting point, the role of water in the structure directly influences not merely the thermal effect but the latent heat. For most salt hydrates, the water content exhibits a negative correlation with the latent heat for per mole water. Na₂HPO₄·12H₂O melts to a salt hydrate with fewer moles of water, whereas Na₂SO₄·10H₂O melts to its anhydrous form. Previous studies claim that there exists a quantitative relationship between the latent heat of salt hydrate and the number of crystal water. However, the comparison of the dehydration processes of Na₂HPO₄·12H₂O and Na₂SO₄·10H₂O indicates that whether this conclusion is generally applicable needs further study.

Key words: inorganic salt hydrate, crystal structure, latent heat

摘要：

选择3种典型的样品CuSO₄·5H₂O (胆矾)、Na₂HPO₄·12H₂O和Na₂SO₄·10H₂O (芒硝)进行测试, 利用热重?差式扫描量热(TG-DSC)同步测试仪检测样品的热效应, 并通过拉曼光谱进行结构分析。结果表明, 对于在相变点以脱结晶水为主的相变材料, 水在晶体中的状态不同, 会使相变材料在脱水过程中产生不同的热效应, 直接影响相变潜热的大小, 但并非所有无机水合盐的相变潜热都随着结晶水数目增多而增大。大部分无机水合盐所带结晶水数目越少, 每摩尔水的平均潜热越高。通过对在相变点脱去部分结晶水的Na₂HPO₄·12H₂O与在相变点脱去全部结晶水的Na₂SO₄·10H₂O的对比研究认为, 对于前人关于无机水合盐的潜热大小与结晶水数目之间普遍存在定量关系这一结论是否具有普适性还有待进一步研究。

关键词: 无机水合盐, 晶体结构, 相变潜热