An Assessment of Energetic and Kinetic Properties of Surfaces and Interfaces in Alumina

氧化铝表面和界面的能量和动力学性质的评估

• 批准号: 9617392
• 负责人: Andreas Glaeser
• 金额: $ 34.95万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-04-15 至 2001-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9617392&HistoricalAwards=false
• 关键词: Assessment; Energetic; Kinetic; Properties; Surfaces

9617392 Glaeser An experimental technique for determining the equilibrium shape of pores in alumina has been developed and applied to both undoped and Ti-doped sapphire. Ti doping changes the Wulff shape of alumina. Concurrently, the use of pre- perturbed pore channels has elevated studies of the Rayleigh instabilities to a new level, allowing quantitative measurement of key thermodynamic and kinetic parameters; a framework for correcting for anisotropy effects in assessing the surface diffusivity has been developed. Ti doping affects the morphological stability, but appears to have only a mild effect on the surface diffusivity. Finally, Ti doping has been shown to promote highly anisotropic grain growth, leading to the formation of elongated grains, and to substantially change the grain boundary mobility. The proposed work builds on and extends the first two components of this prior work. Specifically, by using lithographically introduced pores and atomic force microscopy (AFM) to assess the equilibrium pore shape, we propose to determine the effect of Ti, Cr, Ca and Mg additions on the relative energies and thermodynamic stabilities of a range of low index surfaces in sapphire. In addition, the instability of lithographically introduced pore channels with pre-existent finite perturbations of known but systematically varied amplitude and wavelength will be examined. The independent effects of dopants and crystallographic orientation on the thermodynamic and kinetic characteristics of perturbation evolution will be determined. This method of determining the surface diffusivity, and more conventional scratch smoothing methods will be used in tandem to compare apparent surface diffusivities obtained under conditions where the amplitude of the surface perturbation is increasing with time, and decreasing with time, respectively. The diffusivities determined using these two complementary approaches will be compared to the diffusivities that can be obtaine d from an analysis of pore-boundary separation conditions. The comparison may help to identify which (if any) of the two approaches used to determine the surface diffusivity provides data that is useful in predicting and describing microstructural evolution in ceramics. %%% The proposed research will help improve our understanding of surface diffusion in ceramics. By studying the effect of dopants and crystallographic orientation, the energetics of surface diffusion can be determined, and thus, how the changes in energetics and kinetic properties impact microstructural evolution in ceramics. These processes are important in designing optimum microstructures for properties. ***

9617392 Glaeser是一种测定氧化铝中气孔平衡形状的实验技术，已被应用于未掺杂和掺钛蓝宝石。钛掺杂改变了氧化铝的武尔夫形状。同时，预扰动孔通道的使用将瑞利不稳定性的研究提升到了一个新的水平，允许对关键的热力学和动力学参数进行定量测量；在评估表面扩散率时，已经开发了一个校正各向异性效应的框架。钛掺杂影响了薄膜的形态稳定性，但对表面扩散系数的影响不大。最后，钛掺杂促进了高度各向异性的晶体生长，导致了细长晶体的形成，并显著改变了晶界的迁移率。拟议的工作建立在先前工作的前两个组成部分的基础上，并对其进行了扩展。具体地说，通过使用光刻引入的气孔和原子力显微镜(AFM)来评估平衡孔形状，我们建议确定钛、铬、钙和镁的添加对蓝宝石中一系列低指数表面的相对能量和热力学稳定性的影响。此外，还将研究光刻引入的具有已知但系统变化的幅度和波长的有限扰动的孔道的不稳定性。将确定掺杂和晶体取向对微扰演化的热力学和动力学特征的独立影响。这种确定表面扩散系数的方法和更传统的划痕平滑方法将被串联使用，以分别比较在表面扰动幅度随时间增加和随时间减小的条件下获得的表面扩散系数。用这两种互补方法测定的扩散系数将与通过分析孔隙-边界分离条件得到的扩散系数进行比较。这种比较可能有助于确定用于确定表面扩散系数的两种方法中的哪一种(如果有的话)提供了对预测和描述陶瓷微结构演变有用的数据。所提出的研究将有助于提高我们对陶瓷表面扩散的理解。通过研究掺杂和晶体取向的影响，可以确定表面扩散的能量学，从而确定能量学和动力学性质的变化如何影响陶瓷的微观结构演变。这些工艺对设计性能最佳的微结构非常重要。***