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Multicomponent Diffusion in Natural Silicate Melts

天然硅酸盐熔体中的多组分扩散

基本信息

批准号：
1829822
负责人：
Youxue Zhang
金额：
$ 43.21万
依托单位：
Regents of the University of Michigan - Ann Arbor
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-07-01 至 2022-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1829822&HistoricalAwards=false
关键词：
Multicomponent Diffusion Natural Silicate Melts

项目摘要

Diffusion is a ubiquitous and fundamental process arising from the random motion of atoms, ions and molecules in a phase. If there is inhomogeneity, the random motion of diffusion results in net mass transfer from high concentration to low concentration to eliminate the inhomogeneity. Although it is a microscopic process, diffusion plays a crucial role in numerous macroscopic phenomena ranging from nutrient transfer in the human body, dispersion of pollutants, to a variety of igneous processes, such as explosive volcanic eruptions and igneous rock formation. Explosive volcanic eruptions begin with bubble growth, whose rate is controlled by the diffusion of gas molecules from the melt into the bubbles. Igneous rock formation is the collective effect of crystal growth in magma, in which diffusion plays an important role. The more generalized concept of diffusion has also been applied to understand the mean elevation of continents. The goal of this research is to understand diffusion in natural silicate melts. A natural silicate melt typically contains many major oxide components. Diffusion in a multicomponent (meaning three or more components) system is complicated because different oxide components may move in a coordinated fashion. Hence, the diffusion of one component is affected not only by itself, but also by other components. Therefore, even though the ultimate effect of diffusion is to homogenize, the complicated diffusion may lead some oxides in silicate melts to diffuse from low to high concentration, termed uphill diffusion. In the literature, diffusion in natural silicate melts was treated only partially: If a component shows "normal" diffusion behavior, meaning the flux is from high to low concentration, it is quantified to obtain the effective binary diffusivity. Otherwise, researchers simply note the uphill diffusion behavior, and then shy away from it without quantification. Such uphill diffusion is frequently encountered in experiments as well as in natural systems. With a prior NSF grant, Youxue Zhang's research group at the University of Michigan investigated multicomponent diffusion and made remarkable progress in the last three years. The new grant will enable continued research and development. Diffusion in melts with natural basalt and dacite compositions will be studied. There are 8 major oxide components and the diffusion is described by a 7 by 7 diffusion matrix (49 unknowns). Glasses with appropriate compositions will be synthesized to form diffusion couples. High-temperature and high-pressure diffusion couple experiments will be carried out. The compositional profiles in the quenched glass will be measured using an electron microprobe. The data will be fit using the Levenberg-Marquardt algorithm to extract the diffusion matrix. One working hypothesis is that the diffusion eigenvectors for natural silicate melts are independent of temperature and melt composition, which will be evaluated. The obtained diffusion matrix will be applied to calculate diffusion profiles in mineral dissolution experiments, and to predict diffusion in natural magmas during a variety of processes, including crystal growth and dissolution, magma mixing, and post-entrapment interaction between a melt inclusion and the host mineral. The results will be published and disseminated in scientific meetings and in teaching.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

扩散是一种普遍存在的基本过程，它是由原子、离子和分子在一个相中的随机运动引起的。如果存在非均匀性，则扩散的随机运动导致从高浓度到低浓度的净传质以消除非均匀性。虽然这是一个微观过程，扩散在许多宏观现象中起着至关重要的作用，从人体内的营养物质转移，污染物的分散，到各种火成岩过程，如火山爆发和火成岩形成。爆炸性火山爆发开始与气泡的增长，其速度是由气体分子从熔体扩散到气泡控制。岩浆岩的形成是岩浆中晶体生长的集体效应，其中扩散作用起着重要作用。更广义的扩散概念也被用来理解大陆的平均海拔。本研究的目的是了解天然硅酸盐熔体中的扩散。天然硅酸盐熔体通常含有许多主要氧化物组分。多组分（意味着三种或更多种组分）系统中的扩散是复杂的，因为不同的氧化物组分可能以协调的方式移动。因此，一种组分的扩散不仅受其本身的影响，而且受其他组分的影响。因此，尽管扩散的最终作用是均匀化，但复杂的扩散可能导致硅酸盐熔体中的某些氧化物从低浓度向高浓度扩散，称为上坡扩散。在文献中，仅部分处理了天然硅酸盐熔体中的扩散：如果组分显示“正常”扩散行为，意味着通量从高到低浓度，则将其量化以获得有效二元扩散率。否则，研究人员只是注意到上坡扩散行为，然后回避它而不量化。这种上坡扩散在实验和自然系统中经常遇到。在美国国家科学基金会的资助下，密歇根大学张友学的研究小组研究了多组分扩散，并在过去三年中取得了显着进展。新的赠款将使继续研究和发展。将研究天然玄武岩和英安岩组成的熔体中的扩散。有8种主要的氧化物成分，扩散由7 × 7扩散矩阵（49个未知数）描述。将合成具有适当组成的玻璃以形成扩散偶。将进行高温高压扩散偶实验。将使用电子显微探针测量淬火玻璃中的组成分布。将使用Levenberg-Marquardt算法拟合数据，以提取扩散矩阵。一个工作假设是，天然硅酸盐熔体的扩散特征向量是独立的温度和熔体组成，这将被评估。所得到的扩散矩阵将用于计算矿物溶解实验中的扩散剖面，并预测天然岩浆在各种过程中的扩散，包括晶体生长和溶解，岩浆混合，和后熔体包裹体和主矿物之间的包裹作用。研究结果将在科学会议和教学中发表和传播。该奖项反映了NSF的法定使命，通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。