UNIVERSITY OF ILLINOIS
The methods for production of most ceramic materials depend on a small amount of chemical additions that distribute non-uniformly within the material; these small amounts can dominate a ceramic?s utility. These chemicals often produce additional crystalline or glassy features. By selecting the right chemicals additives it is often possible promote particular features; such approaches can often reduce the cost of production or significantly improve the properties of the material. Unfortunately, it remains an ongoing challenge to predict which chemicals should be selected for any particular system and thus progress relies on trial and error. A new approach to predicting potential chemical additives will be developed by understanding how the different crystalline and glassy features compete energetically and kinetically during their formation. A combination of various experimental and theoretical techniques will be employed to achieve this goal.The results will provide an important new predictive approach to engineering chemistry in ceramics that may lead to cost reduction and performance improvement for a variety of products. The project will fund and train two doctoral students in materials science, engineering, and teamwork throughout its duration. As part of a science outreach program, short media clips of exciting scientific phenomena will be produced for inclusion on popular viral web-media outlets such as www.YOUTube.com.
Grain boundary complexions (such as intergranular films) are analogous to grain boundary ?phases? whose stability is dependent on temperature, chemistry, and grain boundary crystallography; their thickness and structure are thermodynamic equilibrium properties. Recent studies show that complexions depend on processing and determine properties of a number of technologically important ceramic systems. Existing approaches to predicting susceptible systems are inadequate and much of our knowledge in this realm is empirical. Recent preliminary results indicate that equilibrium with relation to complexions is often not achieved and that it is important to consider competing processes such as precipitation. Furthermore, complexions will change their composition and structure in use and may serve as nucleation sites for grain boundary precipitates. Like other ?phase? selection problems in materials, this one requires a combined understanding of activation barriers, equilibrium thermodynamics, and kinetics. It is hypothesized that the activation energies of the competing processes have a dominant effect on this ?phase? selection that dramatically impacts the ultimate microstructural evolution and properties. This novel approach holds the possibility to fundamentally reshape how scientists and engineers approach this problem. The proposed work will quantify the relevant parameters necessary for determining the activation energies and change in free energy associated with the two processes, in a model ceramic system, using a combination of experimental and theoretical techniques. Graduate students will carry out this work and will be trained in such techniques as scanning probe microscopy, high-resolution transmission electron microscopy, calculated phase diagram methods, and diffuse-interface phase field approaches. The results will form the basis for new additive selection criteria for ceramics based on manipulating grain boundary complexions.