GOALI: Fundamental Investigations of Nucleation Processes in Silicate Liquids and Glasses with a Goal of Developing Predictive Models for Glass Formation and Crystallization

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NON-TECHNICAL DESCRIPTION: Glasses have been centrally important technological materials for thousands of years. Glass ceramics (partially crystallized glasses) are also important, filling low technology applications such as stove-tops and cookware, to high technology applications such as optical waveguides, telescope mirrors, bone prosthesis and dental restorations. Used in composite armor, ceramics are able to break up impacting projectiles while a metallic backing plate absorbs the kinetic energy of the projectile. Controlling nucleation, the first step in the crystallization of a liquid or glass, is critically important for the production of glass ceramics. However, nucleation is generally understood within the context of a model that was developed for liquid formation in a gas in the early years of the last century and extended to the crystallization of liquids about 60 years ago. This model is inadequate for the level of control needed today. The previous assumptions are now questionable and so predictions often fail to agree quantitatively with experimental data. This research is aimed at developing a deeper understanding of crystal nucleation and the formulation of a more quantitative model. This new model provides a foundation for the development of computer simulations that can be used to accelerate the discovery and design of new glasses and ceramics. The project provides opportunities for graduate students to interact with industrial scientists in Corning Research and Development and leads to a career path for graduates in either industry or academia.TECHNICAL DETAILS: Glasses and glass ceramics are ubiquitous modern materials, fundamental to a wide range of applications. Understanding nucleation and growth is critical in the production of high quality glasses and ceramics and the discovery of new ones. These processes must be precisely controlled to produce the desired devitrified microstructures, including the number, type, and size of crystallites formed in the glass. Currently, gaining this control is largely empirical, resulting in long development times for new products. Glass and glass ceramics companies are therefore working to develop improved measurement and modeling capabilities, and to increase the fundamental understanding of nucleation and growth processes at or beyond the state-of-the-art in the field. This research, carried out with scientists in Corning Research and Development, focuses on the development of a deeper understanding of crystal nucleation through a coordinated experimental/modeling approach for two model silicate glasses (Ba2O-2SiO2 and Na2O-2CaO-3SiO2) Key elements include scanning calorimetric surveys to determine the temperature range of significant nucleation, measurements of the time-dependent nucleation rates as a function of temperature, X-ray and elastic neutron scattering studies of the glass and nucleating crystal phases to assess the importance of glass structure on the nucleation barrier, extending the classical theory of nucleation to include the effects of the diffuse interface between the nucleus and the liquid/glass and to take into account ordering in the liquid/glass, and incorporating computer models and simulations to test these theories. The new insights gained lay the foundation for computer models that can guide the rapid development of new glasses and glass ceramics with an optimized microstructure. These activities mirror a broad approach for accelerated materials development that is a national priority. The US is in crisis, with a decreasing number of students seeking careers in science, technology, engineering and math (STEM). This research forms an integral part of graduate student training, both in an academic and industrial environment. This project exposes students to cutting edge glass production and characterization techniques and leads to an optimal career path for graduates.