The dynamic behavior of the complex structures of liquid oxides determines the glass formation tendency of these materials. Structural relaxations at high temperatures are difficult to study because of the high reactivity of these compounds. In this project, we use the Brillouin scattering technique to determine the viscoelastic characteristics of oxide melts and their glasses. We are particularly interested in the phenomena that constitute the glass transition. The experimental results will be compared with the coefficients determined by molecular dynamics simulations to elucidate the relation between structure and dynamic behavior in glass-forming systems.

The heat capacity, thermal conductivity, and thermal expansion coefficients of materials are intimately related with their phonon density of states. In highly disordered materials the spectrum of elastic vibrations deviates significantly from that of a typical three-dimensional solid, and is characterized by a high degree of localization. Such modes are called fractons because the arrangement of allowed wavevectors obeys fractal geometries. This project combines small-angle neutron scattering for the structural analysis, inelastic neutron, and light scattering for the investigation of dynamic properties and molecular dynamic simulations for the interpretation of the results. Investigated systems include aerogels, xerogels, and glass-ceramic composites.

The research focuses on thermal inducibility of the PE and CE transformation in a fibrous ceramic. It is of scientific and engineering interest to study the effects of phase transformation weakening in a tailored design. An adapted version of the so-called fibrous monolithic ceramic approach is used to fabricate dense, fibrous ceramics for three-point flexure analysis so as to examine the mechanical response of hot-pressed, then annealed samples. Optimal binder burnout, densification, and annealing schedules are to be developed for this system. As far as characterizing the physical and crystallographic nature of phase transformation weakening in a fibrous ceramic, SEM and XRD are used.

Kinetics and mechanisms of fluid-assisted cracking are examined in Si;i3N;i4 and Al;i2O;i3 ceramics to elucidate the synergistic effect of stress and surface chemistry on microfracture. Three different techniques are being used to measure this effect: the repeated indentation technique, which follows the development of indentation cracks leading to surface microfracture, small crack experiments where the growth of penny-shaped surface cracks is monitored, and fracture mechanics technique with through-thickness cracks. Possible influences of fluid viscosity, temperature, grain size, grain boundary phase, and loading rate on cracking kinetics are investigated.