Disperse fine equiaxed alpha alumina nanoparticles with narrow size distribution synthesised by selective corrosion and coagulation separation

Abstract

Disperse fine equiaxed α-Al2O3 nanoparticles with narrow size distribution are important materials in nanotechnology and nanomaterials, but syntheses of disperse fine equiaxed α-Al2O3 nanoparticles usually result in fine γ-Al2O3 nanoparticles or large α-Al2O3 nanoparticles larger than 15 nm. α-Al2O3 has a higher surface energy than γ-Al2O3 and becomes thermodynamically not stable with respect to γ-Al2O3 at specific surface areas larger than 100 m2/g (at sizes smaller than 15 nm for spherical particles) at room temperature. So disperse fine equiaxed α-Al2O3 nanoparticles smaller than 15 nm with narrow size distribution are extremely difficult to synthesise. Here we show the successful synthesis of disperse fine equiaxed α-Al2O3 nanoparticles with average sizes below 10 nm and narrow size distribution by selective corrosion and refined fractionated coagulation separation. An almost fully dense nanocrystalline α-Al2O3 ceramic with a relative density of 99.5% and an average grain size of 60 nm can be sintered from disperse fine equiaxed α-Al2O3 nanoparticles with narrow size distribution.

Selective Corrosion Preparation and Sintering of Disperse α‐Al2O3 Nanoparticles

“…12,13 It is known that vermicular microstructures induce large pores and microstructural heterogeneities in green compacts which cannot be removed easily during sintering but lead to differential densification and reduced densification rates and limit the final densification. 21 But this preparation method is complicated; meanwhile the yield is low after separation. [16][17][18][19][20] For example, Li et al added 5 wt% a-Al 2 O 3 seed and lowered the formation temperature to 900°C, 16 but the obtained a-Al 2 O 3 particles are agglomerates of about 100 nm.…”

“…As the closed, isolated pores disappear, pore pinning decreases, which leads to accelerated grain growth. 21 However, these a-Al 2 O 3 nanoparticles were prepared by a very complicated process. 30 In two-step pressureless sintering, grain-boundary migration is sufficiently sluggish and the densification could occur without grain growth during the final stage of sintering.…”

“…28,29 Chen et al successfully produced fully dense nanocrystalline Y 2 O 3 ceramics by a two-step pressureless sintering. 21 Therefore, it is necessary to develop a simple method to prepare pure disperse fine equiaxed a-Al 2 O 3 nanoparticles with a narrow size distribution and to sinter the a-Al 2 O 3 nanoparticles to dense nanocrystalline a-Al 2 O 3 ceramics with finer grains. Two-step sintering was successfully applied to sinter nanocrystalline Ni-Cu-Zn ferrite, 31 barium titanate, 31,32 and zirconia 33 ceramics as well as a range of other nanocrystalline ceramics.…”

Disperse Equiaxed α‐Al2O3 Nanoparticles Without Vermicular Microstructure

“…9 Many efforts have been attempted to prepare disperse equiaxed a-Al 2 O 3 nanoparticles. 10 The size distribution of the a-Al 2 O 3 nanoparticles is quite wide. 6 But some of these a-Al 2 O 3 nanoparticles are larger than 100 nm.…”

“…Karagedov et al obtained disperse a-Al 2 O 3 nanoparticles with a mean size of 25 nm by milling large a-Al 2 O 3 particles. 10 But this separation process is complicated, and the experimental operations are difficult. In our previous work, we prepared disperse a-Al 2 O 3 nanoparticles of 2-250 nm by removing the matrixes in the a-Al 2 O 3 -NPs-embedded composites synthesized by a mechanochemical method.…”