《High-surface-area corundum nanoparticles by resistive hotspot-induced phase transformation. 》
Authors：Bing Deng, Paul A. Advincula, Duy Xuan Luong, Jingan Zhou, Boyu Zhang, Zhe Wang, Emily A. McHugh, Jinhang Chen, Robert A. Carter, Carter Kittrell, Jun Lou, Yuji Zhao, Boris I. Yakobson, Yufeng Zhao & James M. Tour.
High-surface-area α-Al2O3 nanoparticles are used in high-strength ceramics and stable catalyst supports. The production of α-Al2O3 by phase transformation from γ-Al2O3 is hampered by a high activation energy barrier, which usually requires extended high-temperature annealing (~1500 K, > 10 h) and suffers from aggregation. Here, we report the synthesis of dehydrated α-Al2O3 nanoparticles (phase purity ~100%, particle size ~23 nm, surface area ~65 m2 g−1) by a pulsed direct current Joule heating of γ-Al2O3. The phase transformation is completed at a reduced bulk temperature and duration (~573 K, < 1 s) via an intermediate δʹ-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 γ- to δʹ- to α-Al2O3) is driven by their surface energy differences. The α-Al2O3 nanoparticles are sintered to nanograined ceramics with hardness superior to commercial alumina and approaching that of sapphire.
