Clay Hunt Doctoral Defense
- Thursday, November 16, 2017 at 2:00pm
- Barnard Hall, Room 126 - view map
Sintering and Atomic Transport in Oxide Ceramics – Modeling the Diffusion Process
The practice of sintering is around 27,000 years old. Without sintering we would have no clay pottery, ceramic cutlery, or oxygen sensors for internal combustion engines. What is sintering? It is the process of fusing the particles of a powdered material into a solid without melting the powder.
The bonding of particles that occurs during sintering is achieved via diffusion of the atoms (ions) that compose said powder particles. As sintering progresses, a net shape change of the powder compact occurs. This shape change is a result of the centers of the particles that compose the sintering powder moving closer together, and is referred to as densification. A measure of this shape change can be used to estimate activation energy, the energy required for an atom or ion to diffuse.
Efforts of this study were first directed toward determining the activation energy of yttrium-stabilized zirconia with transition-metal oxide impurities as sintering aids. Literature review found that current activation energy estimates suggest decreasing activation energy with increasing density. These results suggest that the mobility of the atoms (ions) of a crystal structure increases as these atoms (ions) move to positions in the crystal structure with relatively lower potential energy. This is a contradiction.
The results of several sintering models indicated the necessity of a clear approach. This led to an in-depth study of a 1990 sintering model that relates sintering rate to processing parameters such as temperature. This model is widely-accepted despite the undefined function of density factor. A key result of this work is a proposed definition of this function for constant rate of heating and constant temperature sintering. Definitions of this function of density have been incorporated, and the model has been numerically integrated for the first time. Integration results have been compared to density profiles. Good agreement between measurements and corresponding numerical integration validates the proposed definitions of the undefined function of density, and the activation energy values that are constant with respect to density.
- Department of Mechanical & Industrial Engineering