Robust mesoporous silica compacts: multi-scale characterization of microstructural changes related to physical–mechanical properties
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Spark plasma sintering (SPS) was used to compact chemically synthesized mesoporous silica powders with ordered hexagonal nanopore channels (~5 nm). Solid compact disks (~19 mm diameter) densified at processing temperatures from 600 to 1000 °C were characterized at multiple length scales using scanning electron microscopy, transmission electron microscopy, Vickers hardness tests, and Brunauer–Emmett–Teller gas adsorption measurements. Microscopy revealed both micro- and nanoporosity in the compacted disks and the hexagonal mesopore channels in the starting powders were retained during SPS at temperatures up to 850 °C under a uniaxial pressure of 10.6 MPa. The degree of macroporosity in SPS samples was correlated to the mechanical properties, surface area, and pore morphology. The macroporosity is retained up to 950 °C under the same pressure, and the degree of macroporosity increases when the mesopores collapse due to individual particle shrinkage. The results of multi-scale characterization of the mesoporous silica compacts were used to shed light on the role of nanostructure and microstructure on the mechanical and physical properties of SPS processed compacted disks.