The Chemistry of Aqueous Carbonic Fluids in Subduction

在地球内部的高压和高温下，水和二氧化碳都是流体。这些液体可以完全或部分地相互溶解。它们还可以彼此发生化学反应，也可以与周围的其他物质(矿物)发生化学反应。它们的溶解程度以及它们所经历的反应的性质和程度，影响着各种现象，如不同矿物的结晶和导致火山喷发的岩浆的形成。这个项目试图确定在不同的压力和温度下，有多少水可以分解成二氧化碳，有多少二氧化碳分解成水，以及当它们溶解时发生的化学变化。从地质学的角度来看，水和二氧化碳都是常见的工业溶剂，因此了解它们的相互作用通常是可取的；例如，这可能导致设计出在它们相互溶解的压力和温度下使用的二元、化学可控的“绿色”溶剂。此外，水和二氧化碳是现代烈性炸药的主要成分，它们的建模需要了解这些组合流体在适当的高压和温度下的知识。我们将在100,000个大气压和1000摄氏度的条件下研究高压、高温的水和二氧化碳混合物的性质。将在规定的范围内获得两种组分的混溶程度，从而获得简单而基本的知识，即在哪里可以存在一种单一的均质流体，反之，它必须分离成两种共存的流体。通过对溶液中实际存在的化学物种的调查，将寻求对这些发现的更基本的观点。特别是，二氧化碳将与水反应并首先解离成碳酸氢根离子，然后再解离成碳酸盐的程度将被量化。这项工作还将包括向水/二氧化碳混合物中添加各种溶质(如氯化钠)，以及确定二氧化碳的大比例如何影响碳酸钙和石英等矿物的溶解度。水和二氧化碳将被装入高压钻石砧座单元，然后将其放入烤箱中。温度将升高，直到槽中的内容物形成均匀的溶液，然后温度将降低，溶解极限将从视觉上确定为第二种(不同的和共存的)流体出现的温度。装载了流体的矿物的溶解度也将同样用肉眼测定。目前存在的物种及其浓度将通过使用拉曼光谱来确定，这是一种非常适合钻石砧座单元的光学技术。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

At high pressures and temperatures in parts of the Earth's interior, water and carbon dioxide are both fluids. These fluids can dissolve into each other, either fully or partially. They can also undergo chemical reactions, both with each other and with other substances (minerals) in their surroundings. The extent to which they dissolve, and the nature and extent of reactions they undergo, effect phenomena as diverse as the crystallization of different minerals and the formation of magma that leads to volcanic eruptions. This project seeks to determine how much water can be dissolved into carbon dioxide, and how much carbon dioxide into water, at various pressures and temperatures, and the chemical changes that occur when they do. Beyond the geological perspective, both water and carbon dioxide are common, industrial solvents and thus an understanding of their interactions is generally desirable; it may, for instance, lead to the design of binary, chemically tun-able "green" solvents for use at the pressures and temperatures in which they are mutually soluble. In addition, water and carbon dioxide are primary constituents of modern high explosives, and their modelling requires a knowledge of these combined fluids at suitably high pressures and temperatures.The nature of high-pressure, high-temperature mixtures of water and carbon dioxide will be investigated, across conditions ranging up to 100,000 atmospheres and 1000C. The degree of miscibility of the two components will be acquired over the stated range, leading to the simple and basic knowledge of where (in pressure, temperature and composition) a single, homogeneous fluid can exist and where, conversely, it must segregate into two, co-existing fluids. A more fundamental perspective on these findings will be sought through investigation of the chemical species which actually exist in solution. In particular, the degree to which carbon dioxide will react with water and dissociate first to bicarbonate ion, and thence to carbonate will be quantified. The work will also encompass the addition of various solutes (e.g., sodium chloride) to the water/carbon dioxide mix and a determination of how large proportions of carbon dioxide affect the solubility of minerals such as calcium carbonate and quartz. Water and carbon dioxide will be loaded into a high-pressure diamond-anvil cell, which will then be placed in an oven. Temperature will be raised until the contents of the cell have formed a homogeneous solution, following which temperature will be lowered and limits of solubility determined visually as the temperature at which a second (different and co-existing) fluid appears. Solubility of minerals loaded with the fluids will similarly be determined visually. The species present, and their concentrations, will be determined by use of Raman spectroscopy, an optical technique well-suited to the diamond-anvil cell.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.