The influence of defect structures at reaction interfaces and shear-deformation on reaction rim growth kinetics in the MgO-Al2O3 system

反应环是变质岩中的常见特征，当两个接触的固相在其界面处反应形成新相时，反应环就形成了。反应环已广泛应用于材料科学和地球科学中，以推断环境条件和反应系统的速率信息。深入了解反应边缘形成过程中有效的基本过程，对于正确解释岩石中的显微结构、纹理和矿物成分是必要的。拟议的研究是基于在研究小组的第一个资助期内进行的前体项目"运输控制矿物反应与差异应力之间的反馈"期间获得的结果。我们的目标是确定和平衡有效的机制，支配反应边缘生长动力学的合成系统MgO-Al2O3，其中MgO（方镁石）和Al2O3（尖晶石）反应形成MgAl2O4（尖晶石）在规定的实验条件下。在前体项目期间，出现了新的研究问题，需要通过完成研究并扩大方法来解决这些问题。我们提出了补充调查，重点放在两个方面的反应缘生长：A）原子结构在两个传播的反应前沿将通过高分辨率的分析方法（SEM，TEM）进行研究，以获得信息的局部缺陷结构的反应物和产品的定义晶体取向关系的接口。当我们考虑到渐进反应边缘生长过程中局部缺陷结构的变化时，我们将初始生长阶段的样品与长期实验运行的样品进行了比较。B）此外，我们研究了外部施加的变形对整体边缘生长速率以及对微观结构和织构演变的影响。我们打算用Paterson型气体介质装置进行单晶反应扩散偶的扭转实验。由此，我们将获得暴露于从核心到边缘逐渐增加的有限剪切应变的样品。从高空间分辨率的微观结构和织构分析（SEM-EBSD，SEM-FSD，（S）TEM），我们打算破译变形和动态再结晶的反应进程和微观结构和织构发展的影响。我们还将通过EMPA分析直接反应前沿的相组成，以将微观结构和织构与偏离局部化学平衡的程度相关联。以往的研究表明，在静态条件下，生长机制和拓扑关系控制的微观结构和织构的反应轮辋。在动态环境中进行额外的实验，预计将完成系统如何响应外部施加的应力，变形和化学反应如何在相变过程中相互作用，以及在轮辋生长过程中微观结构和纹理形成的机制的理解。

Reaction rims are common features in metamorphic rocks, which form, when two solid phases that are in contact react to form a new phase at their interface. Reaction rims have been widely used in Material Sciences and Earth Sciences to infer environmental conditions and rate information from reactive systems. In depth knowledge of the underlying processes that are effective during reaction rim formation is mandatory for properly interpreting microstructures, textures and mineral compositions in rocks. The proposed study is based on results obtained during the precursor project ‘Feedback between transport-controlled mineral reactions und differential stress’ in the first funding period of the Research Group. We aim to identify and balance effective mechanisms that govern reaction rim growth kinetics in the synthetic system MgO-Al2O3, where MgO (periclase) and Al2O3 (corundum) react to form MgAl2O4 (spinel) under defined experimental conditions. During the precursor project new research questions have arisen which need to be addressed by completing the study with a methodological extension. We propose complementary investigations that focus on two aspects of reaction rim growth: A) Atomic structures at both propagating reaction fronts will be investigated by high resolution analytical methods (SEM, TEM) in order to obtain information on the local defect structure at interfaces with defined crystallographic orientation relation of reactants and product. As we account for changes in the local defect structure during progressive reaction rim growth, we compare samples from initial growth stages with those from long-term experiment-runs. B) In addition, we investigate the effect of externally imposed deformation on the overall rim growth rate and on the microstructure and texture evolution. We intend to perform torsion experiments of single-crystal reaction-diffusion couples using a Paterson-type gas-medium apparatus. Therefrom we will obtain samples exposed to increasing finite shear-strain from the core to the rim. From microstructural and textural analyses at high spatial resolution (SEM-EBSD, SEM-FSD, (S)TEM) we intend to decipher the influence of deformation and dynamic recrystallization on the reaction progress and the microstructure and texture development. We will also analyse the phase compositions at the immediate reaction front by EMPA in order to correlate microstructures and textures with the grade of deviation from local chemical equilibrium. Previous investigations have shown that growth mechanisms and topotactic relations control the microstructure and texture of reaction rims under static conditions. Performing additional experiments in a dynamic setting is expected to accomplish the understanding of how the system responds to externally applied stress, how deformation and chemical reactions interact during phase transformation and which mechanisms underlie microstructure and texture formation during rim growth.