Sodium and potassium carbonates and their mixtures are important for different applications, e.g. for latent thermal energy storage, die-casting processes and molten carbonate fuel cells. In this work the phase diagram and thermodynamic properties of Na₂CO₃–K₂CO₃ system were studied by differential thermal analysis, differential scanning calorimetry and high temperature X-ray diffraction. Three carbonate mixtures (56, 25 and 75 mol% of Na₂CO₃) have solid-solid transition in a wide temperature range between 648 K and 823 K. The high temperature XRD analysis has shown that this transition is a continuous process of changing of the unit cell volume without structural changing of the hexagonal lattice. This phenomenon has also been observed on the measured heat capacity curves. The obtained experimental results were compared with calculations performed using the previous thermodynamic datasets. The comparison of these results shows that further thermochemical assessment of this system needs to be performed to achieve better agreement with the available experimental data.

碳酸钠和碳酸钾及其混合物对于不同的应用非常重要，例如对于潜在的热能存储，压铸工艺和熔融碳酸盐燃料电池而言。在这项工作中，通过差热分析，差示扫描量热法和高温X射线衍射研究了Na ₂ CO ₃ -K ₂ CO ₃体系的相图和热力学性质。三种碳酸盐混合物（Na ₂ CO ₃的56、25和75 mol％）在648 K和823 K之间的较宽温度范围内具有固-固转变。高温XRD分析表明，这种转变是单位晶胞体积变化的连续过程，而六角形晶格没有结构变化。在测得的热容曲线上也观察到了这种现象。将获得的实验结果与使用以前的热力学数据集进行的计算进行比较。这些结果的比较表明，需要对该系统进行进一步的热化学评估，以与现有实验数据更好地吻合。