Review of thermo‐kinetic correlation during grain growth in nanocrystalline materials

Abstract

Nanocrystalline (NC) materials exhibit many unique properties over their coarse‐grained counterparts due to the high grain boundary density and the small grain size, but they are too difficult to be used in engineering environment because of the poor thermal stability. With regard of this, two strategies are previously proposed to enhance the thermal stability (or impede the grain growth) of NC materials, that is, the thermodynamic and the kinetic approaches. Recent investigations increasingly support that the two approaches may be physically interacted and acted on each other, and they can be treated together within a unified thermo‐kinetic framework. This paper reviews the progress in the investigation of thermo‐kinetic correlation during grain growth in NC materials. First, the theoretical models to describe the concept of the thermo‐kinetic correlation and the grain growth equations developed based on the thermo‐kinetic correlation are reviewed. Second, experimental and simulated evidences to support the coexistence of thermodynamic and kinetic effects are summarized. Third, the potential application of thermo‐kinetic correlation is analyzed and discussed. This paper shows that the stabilization of NC materials can be tailored by the selection of the suitable strategies. Finally, several directions that require further exploration are identified.

Thermodynamic and kinetic analyses of sintering in Al‐doped Y2O3 nanoparticles

“…10,[13][14][15] Specifically, dopants can extend the stability of single phase regions in the diagram, a phenomenon fundamentally related to the stabilization of interfaces (i.e., interfacial energy lowering). 15 This phenomenon has been observed in various doped nanocrystalline oxide systems, and it is possible Al 3+ ion enrichment at the interfaces may affect Y 2 O 3 densification. 11,[16][17][18][19] Wang et al studied the role of Al 2 O 3 on the sintering of Y 2 O 3 containing small amounts of Tm and Zr.…”

“…The diagram indicates that even at low Al 3+ ion concentration, Al‐rich eutectic monoclinic Y 4 Al 2 O 9 phase is formed along with Y 2 O 3 , suggesting that the second phase formation is more energetically favorable than the formation of solid solution in Al‐doped Y 2 O 3 12 . However, bulk phase diagrams do not take interfacial energies into consideration, while it has been demonstrated that the high interface to volume ratio in nanoscale materials can lead to non‐negligible interfacial energy contributions to the phase diagram, deviating it from bulk equilibrium values 10,13–15 . Specifically, dopants can extend the stability of single phase regions in the diagram, a phenomenon fundamentally related to the stabilization of interfaces (i.e., interfacial energy lowering) 15 …”

Improving Thermodynamic Stability of nano-LiMn2O4 for Li-Ion Battery Cathode

“…In general, at the nanoscale, properties and processes, such as fracture toughness, reactivity, phase transitions, and coarsening, are strongly dependent on interfacial characteristics. − In particular, interfacial energies, which include both solid–vapor (surface) and solid–solid (grain boundaries, resulting from aggregation or partial sintering), are key parameters controlling coarsening, phase equilibrium, and other physical properties . For instance, the stability of MgAl 2 O 4 as a catalytic support is strongly affected by its surface energy, and the material shows improved resistance to coarsening when the surface energy is lowered by the addition of dopants .…”

“…As a novel strategy to manipulate the functional properties of nanomaterials, Hasan et al demonstrated by atomistic simulations and experiments (calorimetry) that surface energies of MgAl 2 O 4 can be reduced by using dopants prone to segregation. , The segregation was in fact a spontaneous formation of surface excess where trivalent dopants substituted Al 3+ at the surfaces, leading to a surface energy decrease due to a better satisfied coordination of local ions. While all surface energies were generally reduced, some surface planes were affected more strongly than others, resulting in an increase in the fraction of the (111) surface .…”

Development of functional layers for direct ethanol solid oxide fuel cells

“…However, in systems composed of random-sized nanoparticles with a high surface area it becomes even harder to predict the sintering mechanisms. It is proposed that a thermokinetic correlation considering both interfacial energies and diffusion coefficients define the sintering mechanisms of densification or non-densification [136,137].…”