Amorphous Materials: Properties, structure, and durability: Oxidation state of iron in hydrous phono-tephritic melts
Amorphous Materials: Properties, structure, and durability: Oxidation state of iron in hydrous phono-tephritic melts
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非晶材料：性能、结构和耐久性：水合声软石熔体中铁的氧化态
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
C. Freda
中科院分区：
文献类型：
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作者：
J. Schuessler;R. Botcharnikov;H. Behrens;V. Misiti;C. Freda
在1200和1250 °C、50 ~ 500 MPa压力下，对与H2O-CO2混合流体共存的含水超钾质（音纹质）熔体中Fe的氧化态进行了实验研究。相对于Ni-NiO氧缓冲剂（NNO），氧逸度（fO）从NNO-2.9变化到NNO+2.6（log fO），如由实验容器中的外部氧化还原条件和胶囊内部的水活度从0.05变化到1所施加的。用比色湿化学分析法测定了急冷熔体中Fe的氧化还原状态。该分析方法经优化后可测定毫克级样品的Fe ~（2+）/Fe ~（2+）比值在±0.03（2σ）以内。用国际标准物质和其他方法分析的标准品检测准确度和精密度。实验玻璃的Fe 2 +/Fe 3 + Fe比范围为0.41至0.85。在给定的fO值下，发现溶解水对Fe 2 +/Fe 3Fe有较小的负面影响，这与Moretti（2005）的热力学模型一致。在所研究的P-T范围内，压力和温度对Fe的氧化还原态没有明显的影响。含水铁玄武质熔体相比，以前在类似的条件下研究，系统较低的Fe 2 +/Fe 3Fe比被发现的phono-tephritic熔体，特别是在低氧逸度。这种效应归因于声子软玉的高得多的K2 O含量（7.5wt%比0.3wt%），但是FeOT的差异（声子软玉中的7.8wt%和铁玄武岩中的12.9wt%）也可能具有影响。比较实验获得的关系log fO和Fe 3 +/Fe 2+的研究含水超钾质熔体与常用的经验和热力学模型表明，这些模型可以成功地应用于phono-tephritc熔体，虽然这样的组合物没有实施的模型校准。此外，新的数据可以用来改善模型的组成变量，如H2O或K2 O，在硅酸盐熔体中的Fe的氧化还原状态的影响。
Abstract The oxidation state of Fe in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed H2O-CO2 fluids was studied experimentally at 1200 and 1250 °C and pressures from 50 to 500 MPa. The oxygen fugacity (fO₂) varied from NNO-2.9 to NNO+2.6 in log fO₂, relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The Fe redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the Fe2+/ΣFe ratio of milligram-sized samples within ±0.03 (2σ). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The Fe2+/ΣFe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on Fe2+/ΣFe at given fO₂ was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of Fe was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower Fe2+/ΣFe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher K2O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in FeOT (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between log fO₂ and Fe3+/Fe2+ for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as H2O or K2O, on the redox state of Fe in silicate melts.