Phase Field Modelling of Sintering of Nanoporous Aggregates

Nanoporous structures are widely used for various applications and therefore it is critical 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. For the modelling, coding was done in C using an Fourier spectral method to solve the Cahn-Hilliard and Allen-Cahn Equations. 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. Our simulations of sintering of nanoparticle aggregates show a variety of microstructural pathways for the aggregate. These pathways include a polycrystalline shell with one large pore, a polycrystalline shell containing several (possibly interconnected) pores, as well as a uniform polycrystalline aggregate with many closed pores. Some of these pathways are similar to those observed experimentally.