Theoretical Investigation of Diffusional Phase Transformations and the Possibility of Stable Nanoscale Structures in Ionic Ceramics

离子陶瓷中扩散相变和稳定纳米结构的可能性的理论研究

• 批准号: 9311898
• 负责人: Long-Qing Chen
• 金额: $ 13.8万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-07-15 至 1997-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9311898&HistoricalAwards=false
• 关键词: Theoretical; Investigation; Diffusional; Phase; Transformations

9311898 Chen A theoretical investigation will be carried out on the thermodynamics and kinetics of continuous phase transformations and on the possibility of stable nanoscale structures in multicomponent ceramic materials. The main objective is to develop theories and computer simulation techniques for understanding the fundamental thermodynamic and kinetic origins leading to the formation of an important class of self-assembled nanocomposites which resist continuous coarsening. To reach this objective, systematic phase stability analysis and phase diagram calculations for ionic systems with stable nanoscale structures will be performed. The key structural and thermodynamic factors leading to the formation of thermodynamically stable nanoscale phases will be identified. Extensive computer modeling will be conducted of the kinetics of atomic ordering, compositional clustering and microstructural coarsening in systems involving both short-range chemical and long- range Coulomb interactions. A computer simulation technique will be developed which can describe the coarsening dynamics of domains interacting with each other through electric dipole-dipole interactions, elastic interactions and Coulomb interactions. The focus will be on the diffusional transformations in the self- assembled relaxor nanocomposites. The relation of atomic ordering and compositional clustering tendencies to the atomic sizes and charge valences of cations will be investigated through a combination of modern statistical mechanics theory of order- disorder transformations and atomistic computer simulations using shell-model interatomic potentials. %%% This theoretical research grant involves both analytical theory and computer simulation to study the properties of ceramic materials which undergo changes of phase into materials having novel structures. The research will identify the conditions which control the formation of these structures during the phase change. The research is com plicated by the fact that the materials are ionic. This causes additional forces over long distances which are difficult to handle theoretically. However, the results of this work will have important ramifications for understanding and processing these technologically important materials. ***

9311898 CHEN A将对连续相变的热力学和动力学以及多组分陶瓷材料中稳定的纳米级结构的可能性进行理论研究。 主要目的是开发理论和计算机仿真技术，以理解基本的热力学和动力学起源，从而形成一类重要的自组装纳米复合材料，这些纳米复合材料可以抵抗连续的块状。 为了达到这一目标，将对具有稳定纳米级结构的离子系统进行系统的相位稳定性分析和相图计算。 将确定导致热力学稳定纳米级阶段形成的关键结构和热力学因素。 在涉及短距离化学和长距离库仑相互作用的系统中，将对原子量有序，组成聚类和微观结构的动力学进行广泛的计算机建模。 将开发一种计算机仿真技术，可以通过电动偶极 - 偶极相互作用，弹性相互作用和库仑相互作用来描述域相互作用的粗糙动力学。 重点将放在自组装弛豫纳米复合材料中的扩散转换上。 原子量有序和组成聚类趋势与原子大小和阳离子的电荷率的关系将通过现代统计力学理论的秩序疾病转化理论和使用壳体模型的原子质势能的结合来研究。 %% %%这项理论研究赠款涉及分析理论和计算机模拟，以研究陶瓷材料的特性，这些陶瓷材料将相变成具有新结构的材料。 该研究将确定控制这些结构在相变的形成的条件。 这项研究是由于材料是离子化的事实而进行的。 这会导致远距离的额外力，而这些力在理论上很难处理。 但是，这项工作的结果将对理解和处理这些技术重要的材料产生重要的影响。 ***