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.
Direct observation of mesopore closure in silica powders at temperature up to 1150C was carried out using TEM. It was determined that collapsing of pores started arouns 1000C and at 1150C they completely collapsed.