About this Abstract |
Meeting |
MS&T21: Materials Science & Technology
|
Symposium
|
Phase Transformations in Ceramics: Science and Applications
|
Presentation Title |
Phase Stability and Transformation in Borides Examined by X-ray Diffraction |
Author(s) |
James T. Cahill |
On-Site Speaker (Planned) |
James T. Cahill |
Abstract Scope |
X-ray diffraction and transmission electron microscopy are used to study the phase stability of metal hexaborides and boron nitride at elevated temperatures. The short time scales of combustion synthesis are shown to produce nanodomains of multiple solid solutions within ternary hexaboride compounds as seen by peak broadening, splitting and shifting. The transformation of boron nitride from the cubic to hexagonal phase is investigated at high temperatures and ambient pressure in dry flowing helium, and transformation rates as measured by weight fraction of the hexagonal phase correspond to a zero-order transformation of cBN to hBN, which becomes inhibited as the particle size decreases. Variations in surface growth morphology between the particle sizes suggest growth inhibition due to a reduction in nucleation site availability. |