Nano a-alumina is one of the most important oxides for a wide
range of applications in ceramic, high strength materials,
functional materials, adsorbents, catalysts, catalyst support and
transparent armours for ballistic performance [1–4], which are
attributed to its excellent performance such as high mechanical
strength, good wear resistance, low conductivity, high refractoriness,
high hardness and high corrosion resistance.
In order to prepare nano a-alumina powder with good
performance, a lot of approaches such as mechanical milling [5],
vapor phase reaction [6–7], microemulsions [8–9], precipitation
[10], sol–gel [11–12], hydrothermal [13–14] and combustion
methods [15] have been developed. However, alumina powder
exists in a lot of metastable transition phases, the transformation
proceeds of a-Al2O3 usually through the following sequence:
g-Al2O3!s-Al2O3!u-Al2O3!ba-Al2O3 [16]. While the nanoscale
a-alumina powder is difficult to obtain, because of the following
reasons: first, the a-Al2O3 is the most thermodynamically stable
phase after calcination at high temperature, the transformation of
a-Al2O3 from u-Al2O3 always relates to a significant change in the
oxygen sublattice from cubic peaking to hexagonal close packing