Robust bulk silicon carbide polymorphs sintered from collapsed hollow mesoporous structure

Bulk silicon carbide (SiC) ceramics are important for extreme-environment applications, but conventional synthesis demands densification temperature above 2100 °C or additives. This work introduces a straightforward strategy utilizing hollow mesoporous powder, achieving nearly full densification (99.2 ± 0.49% relative density) at 1750 °C through spark plasma sintering. The hollow structure induces intense stress accumulation around mesopores, causing instantaneous structural collapse into nanofragments (~6 nm) that greatly accelerate the densification kinetics. The resulting SiC ceramics feature fine grains (200–300 nm), clean grain boundaries, and coexisting 2H, 4H, and 3 C polytypes. These structural characteristics yield good mechanical properties: nanoindentation hardness > 35.0 GPa, Vickers hardness of 31.8 ± 1.6 GPa, and flexural strength of 625.32 ± 22.3 MPa—all exceeding conventional pure SiC. Theoretical and experimental analysis demonstrate that high-density stacking faults, nano-twins, and polytypic boundaries create substantial lattice distortions and atomic strain fields, effectively pinning dislocations and suppressing plastic deformation. Researchers synthesize dense, bulk SiC ceramics via spark plasma sintering of hollow mesoporous precursor powder. The resulting ceramics have fine grains, clean grain boundaries, and polytypes; demonstrating high hardness and flexural strength.