Interface Energy Measurement of MgO and ZnO: Understanding the Thermodynamic Stability of Nanoparticles

Abstract

Nanomaterials have triggered excitement in both fundamental science and technological applications in several fields. However, the same characteristic high interface area that is responsible for their unique properties causes unconventional instability, often leading to local collapsing during application. Thermodynamically, this can be attributed to an increased contribution of the interface to the free energy, activating phenomena such as sintering and grain growth. The lack of reliable interface energy data has restricted the development of conceptual models to allow the control of nanoparticle stability on a thermodynamic basis. Here we introduce a novel and accessible methodology to measure interface energy of nanoparticles exploiting the heat released during sintering to establish a quantitative relation between the solid-solid and solid-vapor interface energies. We exploited this method in MgO and ZnO nanoparticles and determined that the ratio between the solid-solid and solid-vapor interface energy is 1.1 for MgO and 0.7 for ZnO. We then discuss that this ratio is responsible for a thermodynamic metastable state that may prevent collapsing of nanoparticles and, therefore, may be used as a tool to design long-term stable nanoparticles.

Direct measurements ofquasi-zero grain boundary energies in ceramics

“…Dwelling time and the heat evolved was correlated with the microstructural evolution. 14,22,24 Because no phase separation occurred, or parallel reactions, the released heat was attributed to the change in GB area during the characteristic exothermic peak. GB areas (GBA) were calculated using a tetrakaidecahedral grain shape and a grain size distribution determined by SEM 22,25,26 using the equation…”

Evaluation of aluminosilicate glass sintering during differential scanning calorimetry

“…To support the assumption that the difference in the heat flow is observed due to the surface contact between the sample holder and the sample, a differential thermal analysis (DTA) was performed following the same 8 conditions. In the DTA the contact between the sample holder and the thermocouple is punctual, unlike in the DSC set up, where the contact occurs on the entire surface, as depicted in Fig.…”

“…Sintering processes are studied with DSC technique when particles are nanometric and the energy release is measured, generating an exothermic peak in the DSC analyses [8].…”

Li2O‐doped MgAl2O4 nanopowders: Energetics of interface segregation

“…However, the separation of the kinetic and thermodynamic contributions is difficult with the addition of additives to the material, which are usually seen as physical barriers reducing the GB mobility and are mostly studied as kinetic phenomena. With the advancements of calorimetric techniques for the measurement of the interface energy of nanoparticles, it is possible to show that the surface energy does not remain constant with an increase in the doping content; thus, the nanostability is partially attributed to thermodynamic effects …”