The Effect of CO2 Reduction in Low-Water Melts at Low Hydrogen Fugacity: Experiment at 500 MPa and Thermodynamic Model

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
A. G. Simakin, V. N. Devyatova, G. V. Bondarenko
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Abstract

Formation of graphite was observed in experiments on synthesis of dry carbon-bearing albite glasses in platinum capsules in an Internally Heated Pressure Vessel at 500 MPa and Т = 1200–1250°С. A thermodynamic model is proposed that explains the achievement of low oxygen fugacity near QFM-2 in the melt at low fugacity of hydrogen formed due to the decomposition of trace amounts of water in a compression medium (Ar gas). The unexpectedly low fugacity of oxygen is explained by the shift of equilibrium between the gases dissolved in the melt CO2 + H2 = H2O + CO to the right due to the low activity of molecular water at a low total content of H2O ~ 0.1–0.5 wt %. The high local СО concentrations in the melt lead to the platinum dissolution in form of carbonyl, corrosion of capsule walls, and redeposition of the metal at the contact with melt. With increase of water concentration in the melt (>1 wt %), the effect of reduction disappears.

Abstract Image

低氢逸度低水熔体中CO2还原的影响:500 MPa实验和热力学模型
在内热压力容器中,在500 MPa和Т = 1200 ~ 1250°С条件下,用铂胶囊合成干含碳钠长石玻璃,观察了石墨的形成。提出了一个热力学模型,解释了熔体在QFM-2附近低氧逸度的实现,这是由于在压缩介质(Ar气体)中分解微量水而形成的氢的低逸度。氧的逸度之所以如此之低,是由于在H2O总含量(0.1-0.5 wt %)低的情况下,水分子的活度较低,导致熔体中溶解的气体CO2 + H2 = H2O + CO的平衡向右移动。熔体中较高的СО局部浓度导致铂以羰基形式溶解,胶囊壁腐蚀,金属在与熔体接触处再沉积。随着熔体中水浓度的增加(1 wt %),还原效果消失。
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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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