Abstract

Vaporization in the Li₂O–Ta₂O₅ system is studied using the Knudsen effusion method in combination with mass-spectrometric analysis of the gas phase in the temperature range of 1570–1860 K. Saturated vapor above the system is found to consist of lithium atoms, oxygen molecules, and lithium oxide Li₂O molecules over the entire range of condensed phase compositions. The absolute partial pressures are calculated, and a p–x section of the complete p–T–x phase diagram at T = 1753 K is constructed. The experimental data made it possible to calculate the standard enthalpies of a number of heterophase reactions and the standard enthalpies of formation of lithium tantalates using the second and third laws of thermodynamics: \({{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }\)(Li₃TaO₄) = –2074.6 ± 62.9 kJ/mol, \({{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }\)(LiTaO₃) = –1403.5 ± 57.4 kJ/mol, and \({{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }\)(LiTa₃O₈) = –3466.4 ± 47.3 kJ/mol. Activities of the components at T = 1473 K and the standard enthalpy of formation of lithium heptatantalate (\({{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }\)(Li₇TaO₆) = –3383.0 kJ/mol) are estimated from the p–x section of the phase diagram.

中文翻译：

---

Li 2 O–Ta 2 O 5系统中蒸发的热力学：钽酸锂的标准形成焓

摘要

使用Knudsen渗流方法结合质谱对1570–1860 K温度范围内的气相进行了研究，研究了Li ₂ O–Ta ₂ O ₅系统中的蒸气。系统上方的饱和蒸气包括整个冷凝相组成范围内的锂原子，氧分子和氧化锂Li ₂ O分子。计算绝对分压，并在T =时完整p–T–x相图的p–x截面建造了1753K。实验数据使得可以使用第二和第三热力学定律来计算许多异相反应的标准焓和钽酸锂形成的标准焓：\（{{Delta __f）} H _ {{ {\ text {298}}} ^ {^ \ circ} \）（Li ₃ TaO ₄）= – 2074.6±62.9 kJ / mol，\（{{\ Delta __ {f}} H _ {{{\ text {298}}}} ^ {^ \ circ} \）（LiTaO ₃）= – 1403.5±57.4 kJ / mol，和\（{{\ Delta __f }} H _ {{{\ text {298}} }} ^ {^ \ circ} \）（LiTa ₃ O ₈）= – 3466.4±47.3 kJ / mol。T =时组件的活动1473 K和庚钽酸锂形成的标准焓（\（{{\ Delta __ {f}} H _ {{{\ text {298}}}} ^ {^ \ circ} \）（Li ₇ TaO ₆） = – 3383.0 kJ / mol）是根据相图的p–x部分估算的。