Mechanisms of Incongruent Reduction

将固体氧化物转化为新的流体和具有不同于初始氧化物的组成的固体产物的化学反应被认为是“不一致的”（例如，不一致熔化，不一致溶解）。 虽然人们对某些类型的不一致反应有很好的理解，但氧化物与熔融金属发生“不一致还原”的基本动力学机制却不清楚。 本研究的目的是发展的动力学机制（限速步骤，微观结构演变）的基本理解，其中固体氧化物进行不一致的还原与反应性金属液体。 在这项工作中，氧化铝与镁铝液体接触的不一致还原（包括固体镁铝尖晶石的形成）将被检查。 新的实验与原位x射线衍射将被用来跟踪，在真实的时间，形成尖晶石氧化铝表面浸没在熔融镁铝层。 还将在稳态条件下研究浸入Mg-Al熔体中的氧化铝重量变化的动力学。 这些动力学测量（相变、质量变化）将沿着氧化铝/熔体界面的微观化学和微观结构分析，以确定不一致氧化铝还原的限速步骤。陶瓷和液态金属之间的反应速率对于许多先进技术是至关重要的，例如：1）用于汽车应用的陶瓷/金属复合材料的新型、低成本、反应渗透处理（例如，气缸套、制动器部件、轴承套）; 2）先进钛合金的熔模铸造，用于飞机中轻质和坚固的结构部件。 本研究的目的是对固体陶瓷和液体金属之间的反应机理有一个更好的基本认识，以便更好地预测和控制这种反应的速率。本研究将涉及使用最先进的分析设备来跟踪固体陶瓷和液体金属之间界面上这种反应的真实的时间进程。

Chemical reactions that convert a solid oxide into new fluid and solidproducts with compositions that differ from the initial oxide areconsidered to be "incongruent" (e.g., incongruent melting, incongruentdissolution). While some types of incongruent reactions are wellunderstood, the basic kinetic mechanisms by which oxides undergo"incongruent reduction" with molten metals are not. The objective of thisresearch is to develop a fundamental understanding of the kineticmechanisms (rate-limiting steps, microstructural evolution) by which asolid oxide undergoes incongruent reduction with a reactive metallicliquid. In this work, the incongruent reduction of aluminum oxide incontact with Mg-Al liquids (which involves the formation of solid magnesiumaluminate spinel) will be examined. Novel experiments with in-situ x-raydiffraction will be used to track, in real time, the formation of spinel onalumina surfaces immersed under molten Mg-Al layers. The kinetics ofalumina weight change upon immersion in Mg-Al melts will also be studiedunder steady-state conditions. These kinetic measurements (phase change,mass change) will be used along with microchemical and microstructuralanalyses of the alumina/melt interface to identify the rate-limitingstep(s) of incongruent alumina reduction.%%%The rate of reaction between ceramics and liquid metals is of vitalimportance for a number of advanced technologies, such as: 1) novel,low-cost, reactive infiltration processing of ceramic/metal composites forautomotive applications (e.g., cylinder liners, brake components, bearingsleeves), and 2) investment casting of advanced titanium alloys forlightweight and strong structural components in aircraft. The purpose ofthis research project is to develop a better fundamental understanding ofthe mechanisms of reactions between solid ceramics and liquid metals, sothat the rate of such reactions can be better predicted and controlled.This research will involve the use of state-of-the-art analytical equipmentto track the progress of such reactions in real time at interfaces betweensolid ceramics and liquid metals.