UC Davis

Nanoceramics have unique properties compared to bulk materials, primarily because of their large interfacial areas. This gives rise to considerable surface and grain boundary energies that play an important role in thermodynamic stability and the sintering process. During sintering, densification of the nanoceramic occurs by the mass transport phenomena, and the reduction of interfacial energy is the driving force for this process. Experimental thermodynamic data on surface energies, and in particular on free surface energies, is lacking, though. Yttrium oxide is selected as a model material because of its wide range of applications and abundant sintering studies in the literature. Faceted nanocrystalline yttrium oxide was synthesized by hydrothermal synthesis, and the morphology of these nanoceramics was studied using electron microscopy. Surface energies of specific planes were determined experimentally by water adsorption calorimetry using an experimental setup that includes a water micro-dosimeter combined with a micro-calorimeter. This characterization technique is based on the thermodynamics of water adsorption on the anhydrous surface of the ceramics. Molecular dynamic simulations were also performed to estimate the free surface energies as a function of the surface normal, and corroborate the experimental results.