Water diffusion in potassium-rich phonolitic and trachytic melts
Water diffusion in potassium-rich phonolitic and trachytic melts
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DOI：
10.1016/j.chemgeo.2012.09.030
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发表时间：
2013-05
期刊：
影响因子：
3.9
通讯作者：
S. Fanara;H. Behrens;Youxue Zhang
中科院分区：
文献类型：
--
作者：
S. Fanara;H. Behrens;Youxue Zhang
研究了水在含重达6wt的声质体和粗溶性熔体中的扩散率。使用扩散偶联技术，在1373K和1673K之间的温度下，运行时间为108至1186秒。实验分别在压力为0.2或0.3GPa的内加热气体压力容器（IHPV）和压力为0.5至2.5GPa的活塞缸装置（PCA）中进行。采用一种新研制的快速加热和快速淬火装置对人乳头状瘤病毒进行短期实验。利用红外微光谱法沿扩散样品的圆柱形轴测量含水物质（OH基团和H2O分子）和总水（OH和H2O分子的体积水浓度之和）的浓度分布。红外光谱技术是用卡尔-费舍尔滴定法测量的一组样品的散装水含量来校准的。电子探针显示沿H2O剖面无水组分的相对比例没有显著变化，表明我们的数据可以被视为H2O和其余硅酸盐熔体之间有效的二元扩散。总体水扩散系数采用改进的Boltzmann-Matano方法，并使用假设总水扩散系数（DH2Ot）与总水浓度（CH2Ot）之间存在函数关系的附件，从总水剖面中得到。剖面的拟合表明，对于声质体熔体，水扩散系数与含水量大致成正比。在T- 1373 ~ 1673K和CH2Ot范围内，总水扩散率（m2/s）作为T (K)的函数的预测推导出以下公式：实验数据由此关系式再现，标准差为0.07log单位。在相同条件下，滑脱熔体中的水扩散率是相似的。在0.2 ~ 2.5GPa范围内，声母状或滑脱状熔体的压力对水扩散率的影响无法解决。
Water diffusivity was investigated in phonolitic and trachytic melts containing up to 6wt.% of dissolved water at temperatures between 1373K and 1673K for running time of 108 to 1186s using the diffusion couple technique. The experiments were performed in an internally heated gas pressure vessel (IHPV) at pressures of 0.2 or 0.3GPa and in a piston cylinder apparatus (PCA) at pressures between 0.5 and 2.5GPa. A newly developed rapid heating and rapid quench device was used for short term experiments in the IHPV. Concentration profiles of hydrous species (OH groups and H2O molecules) and total water (bulk water concentration as sum of OH and H2O molecules) were measured along the cylindrical axis of the diffusion sample using IR micro-spectroscopy. The IR spectroscopic technique was calibrated using a set of samples with bulk water contents measured by Karl–Fischer titration. Electron microprobe traverses show no significant change in relative proportions of anhydrous components along H2O profiles, indicating that our data can be treated as effective binary diffusion between H2O and the rest of the silicate melt. Bulk water diffusivity was derived from profiles of total water using a modified Boltzmann–Matano method as well as using fittings assuming a functional relationship between the total water diffusivity (DH2Ot) and the total water concentration (CH2Ot). The fitting of the profiles indicates that for phonolitic melt the water diffusivity is roughly proportional to water content. The following formulation was derived for the prediction of total water diffusivity (m2/s) as a function of T (K) in the T-range of 1373 to 1673K and CH2Ot: The experimental data are reproduced by this relationship with a standard deviation of 0.07log units. Water diffusivity in trachytic melts is similar at the same conditions. A pressure effect on water diffusivity could not be resolved in the range 0.2 to 2.5GPa for phonolitic or trachytic melts.