Mechanisms of Incongruent Reduction

将固体氧化物转化为新的流体和固体产物的化学反应，其组成与初始氧化物不同，被认为是“不一致的”(例如，不一致的熔化、不一致的溶解)。虽然某些类型的不一致反应已被很好地理解，但氧化物与熔融金属进行“不一致还原”的基本动力学机制尚不清楚。这项研究的目的是对固体氧化物与活性金属液体进行不一致还原的动力学机制(限速步骤、微观结构演变)有一个基本的了解。在这项工作中，将研究氧化铝在与镁铝液体接触时的不一致还原(这涉及到固体镁铝尖晶石的形成)。新的原位x射线衍射实验将被用来实时跟踪在熔融的镁铝层下浸泡的尖晶石氧化铝表面的形成。在稳态条件下，还将研究氧化铝在镁铝熔体中浸泡时的重量变化动力学。这些动力学测量(相变、质量变化)将结合氧化铝/熔体界面的微观化学和微观结构分析来确定不一致氧化铝还原的速率限制步骤(S)。%陶瓷与液体金属之间的反应速度对于一些先进技术至关重要，如：1)汽车应用(例如气缸套、刹车部件、轴承套)的新型、低成本、反应浸渗工艺，以及2)用于飞机轻质和坚固结构部件的先进钛合金的熔模铸造。这项研究的目的是为了更好地从根本上了解固体陶瓷与液态金属之间的反应机理，以便更好地预测和控制此类反应的速度。这项研究将涉及使用最先进的分析设备来实时跟踪固体陶瓷与液态金属界面上的此类反应的进展。

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.