In summary, we have successfully fabricated high-performance
porous ceramics 9PHEBs with superior mechanical and thermal
properties via a simple and effective UHTS technique. The combination of a high mechanical strength (≈337 MPa) at a porosity
of ≈50% and a low thermal conductivity (≈0.76 W m−1 K−1) endows our 9PHEB materials with great potential as reliable thermal insulation. The superior mechanical and thermal properties
are believed to result from the multiscale design: i) the ultrafine pores at the microscale, as well as strong connections and
good interfaces between building blocks at the nanoscale, can be
well constructed, owing to the ultrafast heating rate and ultrahigh
temperature of the UHTS technique; ii) the severe fluctuations of
the mass and strain fields induced by the large lattice distortion
at the atomic scale, which simultaneously improves the stiffness
of lattice and decreases the thermal conductivity of the ceramics by acting as phonon scattering barriers. Moreover, the synthesized 9PHEB show exceptional dimension and strength retention up to 2000 °C, making them suitable for use in extreme
conditions.