High-surface-area corundum nanoparticles by resistive hotspot-induced phase transformation

High-surface-area alpha-Al2O3 nanoparticles are used in high-strength ceramics and stable catalyst supports. The production of alpha-Al2O3 by phase transformation from gamma-Al2O3 is hampered by a high activation energy barrier, which usually requires extended high-temperature annealing (similar to 1500 K, > 10 h) and suffers from aggregation. Here, we report the synthesis of dehydrated alpha-Al2O3 nanoparticles (phase purity similar to 100%, particle size similar to 23 nm, surface area similar to 65 m(2) g(-1)) by a pulsed direct current Joule heating of gamma-Al2O3. The phase transformation is completed at a reduced bulk temperature and duration (similar to 573 K, < 1 s) via an intermediate delta'-Al2O3 phase. Numerical simulations reveal the resistive hotspot-induced local heating in the pulsed current process enables the rapid transformation. Theoretical calculations show the topotactic transition (from gamma- to delta'- to alpha-Al2O3) is driven by their surface energy differences. The alpha-Al2O3 nanoparticles are sintered to nanograined ceramics with hardness superior to commercial alumina and approaching that of sapphire.

Automated summary

In this study, dehydrated alpha-Al2O3 nanoparticles were synthesized by pulsed direct current Joule heating of gamma-Al2O3. The rapid phase transformation at reduced temperature and time resulted in nanograined ceramics with superior hardness.