Why fumed and precipitated silica have different mechanical behavior: Contribution of discrete element simulations

Abstract Precipitated silica (PS) could be an interesting alternative to fumed silica (FS) for the core of Vacuum Insulation Panels (VIP), in particular to reduce their cost and widen their use. However, compacted PS exhibits, for the same density, lower mechanical properties than FS. A better understanding of the mechanical behavior of these materials would help to design PS with optimized mechanical properties for VIP. In this work, complemented with experimental characterization, Discrete Element Method (DEM) simulations are used to investigate the compaction behavior and post-compaction tensile behavior of a set of numerically generated silica aggregates with varying neck size, surface energy and morphology (primary particle size, fractal dimension and gyration radius). During the compaction stage, neck size has the largest influence on the mechanical behavior, whereas during the tensile stage the influence of surface energy predominates. These results should be taken with caution as the task of modeling such a complex system necessarily involves bias due to simplifying assumptions. However, it is believed that the experimentally observed differences between PS and FS in compaction behavior and strength may lie not only in aggregates morphological differences, but also in different surface energies and neck sizes.