First principles thermodynamic assessment of the MgO–SiO2 system

IF 2.1 4区 综合性期刊 Q2 MULTIDISCIPLINARY SCIENCES Rendiconti Lincei-Scienze Fisiche E Naturali Pub Date : 2024-08-05 DOI:10.1007/s12210-024-01258-5
Giulio Ottonello
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Abstract

Application of the Polarized Continuum Model to molten oxides in the MgO–SiO2 system combined with all-electron ab initio calculations of the thermodynamic and thermophysical properties of all the solid phases nucleating in the system permits the computation of the phase diagram topology at high pressure and temperature up to deep Earth’s conditions. The first principle parameterization reproduces satisfactorily the extrinsic stability fields of the various metasilicate and orthosilicate polymorphs at subsolidus conditions. The extrinsic stability field of Anhydrous-B (Mg14Si5O24; Anh-B) with respect to a Mg2SiO4 + MgO assemblage opens up at pressures higher than 10 GPa and widens with temperature to form a triangular pressure–temperature stability field. Superimposing the mantle adiabat Anh-B appears to predate the Mg2SiO4 + MgO assemblage with increasing pressure in a range comprised from roughly 10 to 20 GPa. Interactions among components in the liquid are addressed through the Hybrid Polymeric Approach (HPA). The P = 1 bar mixing properties of the liquid are consistent with a simple acid–base interaction according to Lux-Flood notation and with some experimental evidence concerning the enthalpy of fusion of stoichiometric compounds along the binary system. Limited strain energy contributions, which arise from loss of vibrational entropy in the mixture, are responsible for the liquid–liquid miscibility gap experimentally observed at room conditions. Disappearance of the miscibility gap at high P (i.e. P > 5 GPa) is due to the progressively vanishing effect of strain energy, counterbalanced by quite limited (and P-dependent) excess volumes of mixing (Vexc). The metasilicate melts congruently at P > 0 GPa. Forsterite forms peritectically at P ≤ 5 GPa.

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氧化镁-二氧化硅体系的第一原理热力学评估
将极化连续模型应用于 MgO-SiO2 系统中的熔融氧化物,并结合该系统中成核的所有固相的热力学和热物理性质的全电子 ab initio 计算,可以计算出高压和高温直至地球深处条件下的相图拓扑。第一原理参数化令人满意地再现了亚固态条件下各种偏硅酸盐和正硅酸盐多晶体的外稳定性场。无水-B(Mg14Si5O24;Anh-B)相对于 Mg2SiO4 + MgO 组合的外稳定性场在压力高于 10 GPa 时打开,并随温度升高而扩大,形成一个三角形的压力-温度稳定性场。在大约 10 到 20 GPa 的范围内,随着压力的增加,叠加地幔 adiabat Anh-B 似乎早于 Mg2SiO4 + MgO 组合。液体中各组分之间的相互作用是通过混合聚合物方法(HPA)来解决的。液体的 P = 1 bar 混合特性符合根据 Lux-Flood 符号得出的简单酸碱相互作用,也符合有关二元体系中化学计量化合物熔融焓的一些实验证据。由于混合物中振动熵的损失而产生的有限应变能是在室温条件下实验观察到的液-液混溶差距的原因。在高 P 值(即 P > 5 GPa)条件下,由于应变能的影响逐渐消失,而相当有限的(并与 P 值有关的)过量混合体积(Vexc)则抵消了应变能的影响,因此混溶间隙消失了。偏硅酸盐在 P > 0 GPa 时熔化。透闪石在 P≤5 GPa 时形成透闪石。
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来源期刊
Rendiconti Lincei-Scienze Fisiche E Naturali
Rendiconti Lincei-Scienze Fisiche E Naturali MULTIDISCIPLINARY SCIENCES-
CiteScore
4.10
自引率
10.00%
发文量
70
审稿时长
>12 weeks
期刊介绍: Rendiconti is the interdisciplinary scientific journal of the Accademia dei Lincei, the Italian National Academy, situated in Rome, which publishes original articles in the fi elds of geosciences, envi ronmental sciences, and biological and biomedi cal sciences. Particular interest is accorded to papers dealing with modern trends in the natural sciences, with interdisciplinary relationships and with the roots and historical development of these disciplines.
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