Thermal Stability of Spherical Nanoporous Aggregates and Formation of Hollow Structures by Sintering—A Phase-Field Study

Abstract

Nanoporous structures are widely used for many applications and hence it is important to investigate their thermal stability. We study the stability of spherical nanoporous aggregates using phase-field simulations that explore systematically the effect of grain boundary diffusion, surface diffusion, and grain boundary mobility on the pathways for microstructural evolution. Our simulations for different combinations of surface and GB diffusivity and GB mobility show four distinct microstructural pathways en route to 100% density: multiple closed pores, hollow shells, hollow shells with a core, and multiple interconnected pores. The microstructures from our simulations are consistent with experimental observations in several different systems. Our results have important implications for rational synthesis of hollow nanostructures or aggregates with open pores, and for controlling the stability of nanoporous aggregates that are widely used for many applications.

Mechanistic Insights into a Non‐Classical Diffusion Pathway for the Formation of Hollow Intermetallics: A Route to Multicomponent Hollow Structures

“…In our case a polycrystalline aggregate of Pt is transformed to a single crystalline structure on forming intermetallic with Bi. The experimental observation of the transformation of polycrystalline aggregate of single component systems including Pt, CeO 2 , SnO 2 and TiO 2 to hollow particle and the phase‐field modelling on such a system have been reported earlier . We propose that a similar mechanism could be operational in this case even though we have a multi‐component system.…”

“…Thus, by in situ TEM study of the microstructural changes during the sintering of porous aggregates of nanoparticles, various stages of porous to hollow transformation are captured. The formation of sintered surface shell during the initial stage of sintering due to the dominating surface diffusion was theoretically predicted as a necessary condition in obtaining hollow structure . Here, a direct evidence has been presented for this mechanism.…”

“…The formation of hollow intermetallic PtBi can be explained by a mechanism we proposed recently for the formation of hollow structures of metals and oxides by partial sintering of porous aggregates of nanoparticles . The mechanism involves a rapid surface sintering resulting in the formation of a sintered surface shell on the nanoparticle aggregate and subsequent inside‐out mass transport due to curvature effect leading to a thickening of the shell.…”

Grain boundary driven Plateau–Rayleigh instability in multilayer nanocrystalline thin film: A phase-field study

“…The mechanisms involved are atomic diffusion and grain boundary migration. Therefore, phase-field modeling technique is ideally suited to model this phenomenon [12]. It can also allow different grain boundary mobility in different phases, which can play an important part in the temporal evolution of the system.…”

Multiphase-field model for surface diffusion and attachment kinetics in the grand-potential framework

“…In such systems of equations, one can also derive a case where the interphase boundary moves via surface diffusion and the grain boundary is governed by curvature. These systems of equations have been employed in a multitude of problems, ranging from sintering [52,[62][63][64][65] to the interaction between pores and grain boundaries [66][67][68], grain boundary grooving [54,63,69,70], grain growth in porous solids [57,58,71], additive manufacturing processes, such as selective laser sintering [72], and direct ink writing [53].…”