Sintering Simulation of Periodic Macro Porous Alumina

Abstract

Three-dimensionally ordered macroporous (3DOM) ceramic materials are considered for a variety of applications. One of its many subclasses, inverse opals, is constituted by the ordered arrangement of the pores, resulting in the functionality of a photonic crystal and leading to strong reflection of incident electromagnetic radiation. Exposing these porous structures to high temperatures, however, can lead to sintering of the desired structure and loss of functionality. Therefore, discrete element method (DEM) simulations are performed on inverse opal structures with random homogenous distributed alumina particles forming the struts and nodes. Grain-boundary diffusion as well as surface diffusion are modeled via respective parameters of a contact model applied in MUSEN-DEM. Furthermore, the void to particle size ratio is varied to simulate fine and coarse grained 3DOM ceramics. Results indicate that nodes densify at higher rates and to a larger extent when compared to struts. An increase in the void to particle size ratio results in similar trends but with lower densification rates. This behavior is observed regardless whether surface or grain-boundary diffusion is considered as the dominant transport mechanism, with the latter giving higher densification rates. Variations in particle coordination due to the initial random packing favor local desintering, thereby causing the formation of defects/crack nuclei.