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High temperature stability of onion-like carbon vs highly oriented pyrolytic graphite
Alessandro Latini1, Massimo Tomellini2, Laura Lazzarini3
1Dipartimento di Chimica, Università di Roma La Sapienza, Roma, Italy.
Plos One
|August 26, 2014
Summary
The thermodynamic stability of onion-like carbon (OLC) was studied using solid electrolyte galvanic cells. High internal pressures in OLC, up to 7 GPa, were found to significantly influence enthalpy and entropy, primarily due to carbon defect formation.
Area of Science:
- Materials Science
- Thermodynamics
- Nanotechnology
Background:
- Onion-like carbon (OLC) nanostructures exhibit unique properties.
- Understanding the thermodynamic stability of OLC relative to graphite is crucial for its applications.
Purpose of the Study:
- To determine the thermodynamic stability of OLC compared to highly oriented pyrolytic graphite (HOPG).
- To investigate the influence of internal pressure on the thermodynamic properties of OLC.
Main Methods:
- Electromotive force (emf) measurements using a solid electrolyte galvanic cell.
- High-resolution transmission electron microscopy (HR-TEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS).
- Calculation of pressure change with temperature (dP/dT) using thermal expansion (α) and isothermal compressibility (κ) coefficients.
Main Results:
- The transformation from HOPG to OLC was found to be endothermic and entropy-driven above 920.6 K.
- OLC nanostructures were observed to be embedded in a rigid Cr3C2/CrF2 matrix, leading to high internal pressures (up to 7 GPa).
- Enthalpy and entropy changes were significantly influenced by internal pressure and attributed to the formation of carbon defects in OLC, considered as multishell fullerenes.
Conclusions:
- The high internal pressure within OLC nanostructures is a key factor governing their thermodynamic stability.
- Carbon defect formation in OLC, driven by high internal pressure, is the primary contributor to the observed enthalpy and entropy changes.
- Surface contributions to the system's energetics were found to be negligible compared to bulk effects.
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