Thermodynamic mixing properties of disordered alkali feldspar solid-solution from Na–K partitioning and low-temperature calorimetry

IF 1.2 4区地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY

Physics and Chemistry of Minerals Pub Date : 2024-02-26 DOI:10.1007/s00269-024-01270-z

D. Heuser, E. Petrishcheva, F. Ingegneri, C. L. Lengauer, E. Dachs, C. Hauzenberger, R. Abart

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Abstract

The equilibrium partitioning of Na and K between alkali feldspar and NaCl–KCl salt melt was determined at 800 $^\circ$C, 850 $^\circ$C, 900 $^\circ$C, 950 $^\circ$C and 1000 $^\circ$C and close to ambient pressure. Four different natural gem-quality alkali feldspars with low degree of Al–Si ordering covering the range from orthoclase to high sanidine and with slightly different minor element concentrations were used as starting materials. The partitioning curves obtained for the four feldspars are indistinguishable indicating that Na–K partitioning independent of the differences of Al–Si ordering state and minor element concentrations existing amongst these feldspars. A sub-regular two parameter Margules type solution model was fitted to the partitioning data, and the excess Gibbs energy describing the thermodynamic non-ideality of the alkali feldspar solid-solution and the respective Margules parameters $W_{\text {g}\text {K}}$ and $W_{\text {g}\text {Na}}$ including their temperature dependence expressed as $W_g=W_h-TW_s$ were determined:

$$\begin{aligned} W_{\text {g}\text {K}}&= 19754 \pm 3140 J\cdot \,\,{\hbox {mol}}\,\,^{-1} - T \cdot 2.33 \pm 2.67 J\cdot \,\,{\hbox {mol}}\,\,^{-1}\cdot K^{-1} \\ W_{\text {g}\text {Na}}&= 14916 \pm 4272 J\cdot \,\,{\hbox {mol}}\,\,^{-1} - T \cdot 3.55 \pm 3.64 J\cdot {\hbox {mol}}\,\,^{-1}\cdot K^{-1} \\ \end{aligned}$$

The corresponding solvus has a critical temperature slightly above 650 $^\circ$C and is well comparable with earlier direct experimental determinations of the low-sanidine-albite solvus curve. Comparison of the vibrational excess entropy determined from low-temperature heat capacity measurements with the total excess entropy derived from the temperature dependence of the excess Gibbs energy yields a negative configurational contribution to the excess entropy pointing towards short-range Na–K ordering on the alkali site.

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从 Na-K 分配法和低温量热法看无序碱长石固溶体的热力学混合特性

摘要碱长石和NaCl-KCl盐熔体之间Na和K的平衡分配是在800℃、850℃、900℃、950℃和1000℃以及接近环境压力下测定的。四种不同的天然宝石级碱长石被用作起始材料，它们的铝硅有序度较低，范围从正长石到高辉石，次要元素浓度略有不同。四种长石获得的分配曲线没有区别，这表明 Na-K 分配与这些长石之间存在的 Al-Si 排序状态和次要元素浓度差异无关。对分区数据拟合了一个亚规则双参数 Margules 型溶液模型，并确定了描述碱长石固溶体热力学非惰性的过剩吉布斯能以及各自的 Margules 参数（W_{text {g}\text {K}\} ）和（W_{text {g}\text {Na}}），包括以 $W_g=W_h-TW_s$ 表示的它们的温度依赖性：$$begin{aligned}(W_{text {g}\text {K}\}) 和 $W_{text {g}\text {Na}\}(W_{text {g}\text {Na}})。W_{text {g}\text {K}}&= 19754 \pm 3140 J\cdot \,\,{hbox {mol}}\,^{-1} - T \cdot 2.33 \pm 2.67 J\cdot \,{\hbox {mol}\,^{-1}\cdot K^{-1} W_{text {g}\text {Na}}&= 14916 \pm 4272 J\cdot \,{\hbox {mol}\,^{-1} - T \cdot 3.55 \pm 3.64 J\cdot {\hbox {mol}\,^{-1}\cdot K^{-1} （end{aligned}$$相应的溶解度临界温度略高于 650 \(^\circ$ C，并且与早期直接试验测定的低闪锌矿-闪锌矿溶解度曲线相当。将根据低温热容测量确定的振动过量熵与根据过量吉布斯能的温度依赖性得出的总过量熵进行比较，得出过量熵的负构型贡献指向碱位点上的短程 Na-K 排序。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Physics and Chemistry of Minerals 地学-材料科学：综合

CiteScore

2.90

自引率

14.30%

发文量

审稿时长

3 months

期刊介绍： Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)