摘要
Scalable pressureless sintering of nanocrystalline alumina(Al2O_(3))ceramics is a challenging problem with great scientific and technological interest.This challenge was addressed in our recent works utilizing ultrafine a-Al2O_(3) nanopowders with exceptional sinterability combined with two-step sintering technique.Here the sintering mechanism and kinetic parameters(grain boundary diffusivity and its activation energy)were analyzed from constant heating-rate sintering experiments by three different sintering models and compared with existing sintering data in the literature.We found that the lowtemperature sintering of 4.7 nm a-Al2O_(3) nanopowders can be well explained by conventional sintering mechanism via grain boundary diffusion,with reasonable activation energy of 4e5 eV that is smaller than that of coarse Al2O_(3) powders and enhanced diffusivity.However,unphysically small activation energy could be obtained if an inappropriate model was used.Lastly,successful two-step sintering was demonstrated under different heating rates.Our work illustrates that the exceptional sinterability of ultrafine a-Al2O_(3) nanopowders are most likely contributed by small size(short diffusion distance),large surface area(large sintering driving force)and good dispersity rather than new sintering mechanism,and highlights the importance of fast firing and the non-equilibrium nature for the low-temperature sintering of such nanopowders.
基金
the support by the National Natural Science Foundation of China(No.51551201 and 51772137)
the Fundamental Research Funds for the Central Universities(No.lzujbky-2019-sp03).
作者简介
Hongbing Yang is now a PhD student in the Institute of Materials Science and Engineering and MOE Key Laboratory for Special Functional Materials and Structure Design at the Lanzhou University.He obtained his BS degree in Materials Chemistry from the University of Science and Technology Liaoning in 2016.His current research interest is on structural ceramics,especially nanocrystalline alumina;Corresponding author:Yanhao Dong is now a postdoctoral researcher at the Massachusetts Institute of Technology.He obtained his BS degree in materials science in 2012 from Tsinghua University,and his MS degree in materials science in 2014,his MS degree in applied mechanics in 2015,and his PhD degree in material science in 2017,all from the University of Pennsylvania.He received several awards,including Edward C.Henry Award and the inaugural Global Distinguished Doctoral Dissertation Award from the American Ceramic Society,Acta Student Award from Acta Materialia,and Best Paper Award from Journal of the American Ceramic Society.His current research interest is on advanced ceramic and energy materials..E-mail addresses:dongyh@mit.edu;Corresponding author:Jiangong Li is a professor of materials science at Lanzhou University.He received his BS degree in metallic materials and thermal processing in 1981 from Northeastern Institute of Technology,his Dipl.-Ing.in materials science in 1989 from University of Saarland,Germany,and his Ph.D.degree in condensed matter physics in 1997 from Lanzhou University.He joined Lanzhou University in 1991.His main research includes nanocrystalline ceramics,nanoglasses,and nanocrystalline metals.His current research interest focuses on toughening of brittle materials by nanostructure.E-mail addresses:lijg@lzu.edu.cn。
