| About this Abstract |
| Meeting |
2020 TMS Annual Meeting & Exhibition
|
| Symposium
|
Advances and Discoveries in Non-equilibrium Driven Nanomaterials and Thin Films
|
| Presentation Title |
Heat Capacity and Free Energy of Ni-Fe Nanocrystals |
| Author(s) |
Stefan Lohaus, Michel B. Johnson, Peter Ahnn, Mary Anne White, Brent Fultz |
| On-Site Speaker (Planned) |
Stefan Lohaus |
| Abstract Scope |
The thermodynamic stability of fcc nanocrystalline Ni-Fe with respect to a control sample with larger crystallites was studied through heat capacity measurements from 0.5 - 300 K. The heat capacity, dominated by phonons, was integrated to obtain the temperature dependence and grain size dependence of the enthalpy, entropy, and free energy. The nanomaterial, with an average crystallite size of 6 nm, was synthesized by high energy ball milling. It was also used in prior work to measure the phonon density of states. Vibrations cause a larger heat capacity of the nanomaterial, resulting in an excess entropy with respect to the control sample. The nanomaterial also has an excess enthalpy from grain boundaries and defects of approximately 2 kJ/mol. This excess enthalpy causes the free energy of the nanomaterial to exceed that of large-grained material, and entropic effects are not sufficient to alter significantly the relative stability of the nanomaterial. |
| Proceedings Inclusion? |
Planned: Supplemental Proceedings volume |