气体混合炉中氧逸度控制

Oxygen fugacity buffering in a gas-mixing furnace

氧逸度是影响地质体系性质的物理化学变量之一。实验岩石学中常利用氧逸度可控的气体混合炉进行设定氧逸度下的实验。常用的混合气体组合包括CO_2-CO、CO_2-H_2和H_2-H_2O体系。然而,混合气体配比涉及到的较复杂的热力学计算以及老旧的热力学数据阻碍了该项技术在实验岩石学中的应用。本文根据新的物理化学数据,对不同混合气体体系(如CO_2-CO,CO_2-H_2和H_2-H_2O)温度-氧逸度-气体混合比例关系进行了重新计算和评估。另外,还计算了O_2-惰性气体、CO_2-O_2和H_2O-O_2体系,弥补了前人CO_2-CO、CO_2-H_2和H_2-H_2O体系不能控制高氧逸度(大于CO_2体系)的缺陷。最后,比较了应用新旧不同热力学数据库算出的结果,认为随着基础物理化学数据的不断更新,温度-氧逸度-气体混合比例关系也应不断更新。

Oxygen fugacity is a physicochemical parameter which has a great impact on the nature of geologic systems. In order to get meaningful results, oxygen fugacity must be buffered in experimental petrology. Gas-mixing furnace is a widely used apparatus for oxygen fugacity buffered high-temperature experiments at 1 atm. The CO2-CO, CO2-H2, H2-H2O gas-mixing systems are commomly applied in gas-mixing furnaces and a desired oxygen fugacity value is reached by changing the flux ratio between the gases poured into the furnaces. However, the application of gas-mixing technique in experimental petrology has been hampered because the calculation of gas-mixing ratio needs a complex physicochemical consideration and also some thermodynamic data have been out of date. In this paper, re-calculation and evaluation on the relations of temperature-oxygen fugacity-gas mixture ratioes in the O2-inert gas, CO2-O2 and H2O-O2 systems have been presented based on the updated physicochemical data. The results make up the previous defects. It is concluded that the accuracy of gas-mixing oxygen fugacity calculation depends on the choice of basic physicochemical data. It is pointed out that as the basic physicochemical data are renewed, gas-mixing oxygen fugacity calculation should be constantly updated.