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。它们也可以发生化学反应，彼此之间以及与周围的其他物质（矿物质）发生化学反应。它们溶解的程度，以及它们所经历的反应的性质和程度，影响着各种各样的现象，如不同矿物的结晶和导致火山爆发的岩浆的形成。该项目旨在确定在各种压力和温度下，有多少水可以溶解为二氧化碳，有多少二氧化碳可以溶解为水，以及当它们溶解时发生的化学变化。除了地质学的角度来看，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;它可能会导致，例如，设计二元的，化学可调的“绿色”溶剂，用于在压力和温度下，它们是相互溶解的。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混合流体在适当的高压和高温下的情况，将研究水和二氧化碳的高压高温混合物的性质，其条件范围高达100，000个大气压和1000 ℃。将在所述范围内获得两种组分的相容性程度，从而获得关于在何处（在压力、温度和组成方面）可以存在单一均匀流体以及在何处相反地必须分离成两种共存流体的简单和基本的知识。一个更基本的角度来看，这些发现将寻求通过调查的化学物种，实际上存在于解决方案。特别地，二氧化碳将与水反应并首先解离成碳酸氢根离子，然后解离成碳酸根的程度将被定量。该工作还将包括添加各种溶质（例如，氯化钠）加入到水/二氧化碳混合物中，并确定二氧化碳的比例多大会影响矿物如碳酸钙和石英的溶解度。水和二氧化碳将被装入一个高压金刚石砧室，然后将其放入烤箱。将升高温度，直到池的内容物形成均匀溶液，之后将降低温度，并且视觉上确定溶解度的极限为第二（不同且共存的）流体出现时的温度。类似地，用视觉确定负载有流体的矿物的溶解度。目前的物种，以及它们的浓度，将通过使用拉曼光谱，光学技术非常适合于金刚石砧细胞来确定。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.