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

小行星9617392 一种用于确定氧化铝中孔的平衡形状的实验技术已经被开发并应用于未掺杂和钛掺杂的蓝宝石。 Ti掺杂改变了氧化铝的Wulff形状。 与此同时，使用预扰动的孔隙通道提高了瑞利不稳定性的研究到一个新的水平，允许定量测量的关键热力学和动力学参数，在评估表面扩散系数的各向异性效应校正的框架已经开发。 钛掺杂影响的形态稳定性，但似乎只有一个温和的影响表面扩散。最后，Ti掺杂已经显示出促进高度各向异性的晶粒生长，导致细长晶粒的形成，并显著改变晶界迁移率。 拟议的工作建立在并扩展了这一先前工作的前两个组成部分。 具体而言，通过使用光刻引入的孔和原子力显微镜（AFM），以评估平衡孔的形状，我们建议，以确定钛，铬，钙和镁添加剂的相对能量和热力学稳定性的范围内的低指数表面蓝宝石的效果。 此外，光刻引入的孔隙通道与已知的，但系统地变化的振幅和波长的预先存在的有限扰动的不稳定性将被检查。 掺杂剂和晶体取向的扰动演化的热力学和动力学特性的独立影响将被确定。 这种确定表面扩散率的方法和更传统的划痕平滑方法将被用于串联比较表观表面扩散率的条件下获得的表面扰动的幅度随时间增加，并随时间减少，分别。使用这两种互补的方法确定的扩散系数将进行比较，可以从孔隙边界分离条件的分析得到的扩散系数。 比较可能有助于确定这两种方法（如果有的话），用于确定表面扩散率提供的数据，是有用的预测和描述陶瓷的微观结构演变。 该研究将有助于提高我们对陶瓷表面扩散的理解。 通过研究掺杂剂和晶体取向的影响，可以确定表面扩散的能量，从而确定能量和动力学性质的变化如何影响陶瓷中的微观结构演变。 这些过程在设计最佳性能的微观结构方面很重要。 ***

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. ***