About this Abstract |
| Meeting |
MS&T25: Materials Science & Technology
|
| Symposium
|
Phase Transformations in Ceramics: Science and Applications
|
| Presentation Title |
Troubles with Tantala |
| Author(s) |
Elizabeth J. Opila, Connor Stephens, Niquana Smith |
| On-Site Speaker (Planned) |
Elizabeth J. Opila |
| Abstract Scope |
Ta and TaC are of interest for high temperature applications due to their high melting temperatures. Both form Ta<sub>2</sub>O<sub>5</sub> in high temperature oxidizing environments. Equilibrium phases include beta-Ta<sub>2</sub>O<sub>5</sub> with an orthorhombic structure undergoing a polymorphic transition at 1320°C to alpha-Ta<sub>2</sub>O<sub>5</sub> with a tetragonal structure. The melting temperature of Ta<sub>2</sub>O<sub>5</sub> is 1872°C. However, deviations from equilibrium phases have been noted for thermally grown Ta<sub>2</sub>O<sub>5</sub>. X-ray diffraction of thermally grown oxides formed at temperatures of 1300-1500°C produces patterns that are difficult to index, not matching databases. Literature indicates that Ta<sub>2</sub>O<sub>5</sub> has an incommensurate modulated structure that varies depending on formation conditions. Quenching the oxide from temperatures above the polymorphic transition temperature results in a metastable monoclinic or triclinic phase. Finally, melting was observed for thermally grown Ta<sub>2</sub>O<sub>5</sub> at 1650°C, attributed to substoichiometric Ta<sub>2</sub>O<sub>5-x</sub>. The combination of these observations results in great uncertainty regarding phase, structure, and properties of thermally grown Ta<sub>2</sub>O<sub>5</sub>. |