The effect of water on diffusion-controlled reaction rim growth (TP3)

水对扩散控制反应边缘生长的影响 (TP3)

• 批准号: 33832673
• 负责人: Professor Dr. Wilhelm Heinrich
• 金额: --
• 依托单位: Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum (GFZ)
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2007
• 资助国家: 德国
• 起止时间: 2006-12-31 至 2013-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/33832673?language=en
• 关键词: effect; water; diffusion; controlled; reaction

Our recent high temperature - high pressure experiments and modelling of simple and complex reaction rim growth in the two component MgO-SiO2 (MS) and the three component CaO-MgO-SiO2 (CMS) systems have shown that rim growth is strongly affected by minute amounts of water present in the system. Traces of water may either be inherited from the reactants, particularly when mineral powders are used, or introduced via water diffusion from the pressure medium through the noble metal capsule into the reacting system in hydrothermal, piston-cylinder, and multianvil devices. Traces of water do not only affect the absolute growth rates, which can be faster by up to several orders of magnitude in „wet“ experiments than in “dry” experiments, but also the relative mobilities of the diffusing species/components, so that in the CMS system, for example, different rim sequences are produced for “wet” and “dry” setups. The driest conditions are achieved in IHPV single crystal experiments, whereas several “levels” of humidity were found in using piston cylinder experiments with different pressure media. We now have some qualitative understanding about the effect of water; quantitative information is, however, missing. We suggest a series of experiments with minute and clearly defined amounts of water present in both the MS and CMS systems to evaluate the dependence of the kinetic parameters such as nucleation, grain growth, diffusivity patterns, diffusivities, etc., on water fugacities. This will be done by loading the reactants with OH-defects and subsequently reacting them to grow rims in IHPV and piston-cylinder apparatuses. This issue calls for more detailed investigation because the effect of traces of water is of paramount importance for reaction kinetics in natural rocks. Whereas a large amount of recent work deals with the storage capacity and incorporation mechanisms of water into nominally anhydrous minerals including work on OH-dependent transformation kinetics of mantle phases, there is very little information about the effect of OH in NAMs on net-transfer reactions generally, and on reaction rim formation specifically. The project fills the space between the multitude of available data on OH incorporation into NAMs and their implications for reaction kinetics.

我们最近在二元系和CaO-MgO-SiO_2系(CMS)中进行的简单和复杂反应轮缘生长的高温高压实验和模拟表明，体系中的微量水对轮缘生长有很大的影响。微量的水可以从反应物中继承，特别是在使用矿物粉末时，或者通过水从压力介质通过贵金属胶囊扩散进入水热、活塞-圆柱体和多顶锤装置中的反应系统。水的痕量不仅影响绝对生长速度，在“湿”实验中可能比“干”实验快几个数量级，而且还影响扩散物种/组分的相对迁移率，因此在CMS系统中，例如，为“湿”和“干”设置产生不同的轮缘序列。在IHPV单晶实验中获得了最干燥的条件，而在使用不同压力介质的活塞筒实验中发现了几个“水平”的湿度。我们现在对水的影响有了一些定性的了解；然而，缺乏定量的信息。我们建议对MS和CMS系统中存在的微量和明确定义的水进行一系列实验，以评估成核、颗粒生长、扩散系数图样和扩散系数等动力学参数对水逸度的依赖关系。这将通过在反应物中加载OH-缺陷并随后使它们在IHPV和活塞-圆柱体装置中生长轮缘来实现。这个问题需要更详细的研究，因为微量水的影响对天然岩石中的反应动力学是至关重要的。尽管最近的大量工作涉及水在名义上无水的矿物中的储存能力和结合机制，包括对依赖于OH的地幔相转化动力学的研究，但关于NaMS中的OH对净转移反应的影响，以及对反应圈形成的具体影响的信息很少。该项目填补了关于氢氧化氢并入NAMS的大量可用数据与它们对反应动力学的影响之间的空白。