High-purity disperse α-Al2O3 nanoparticles synthesized by high-energy ball milling

The preparation of disperse fine equiaxed α-Al2O3 nanoparticles with narrow size distribution, high purity, and high yield is essential for producing Al2O3 nanocrystalline ceramic of fine grains which may exhibit a good toughness. In this work, micron-sized α-Al2O3 particles were directly ball-milled and subsequently washed with hydrochloric acid at room temperature. Fracture of large α-Al2O3 particles and cold welding of fine α-Al2O3 nanoparticles occur simultaneously during ball milling. It leads to the reduction of particle size with increasing milling duration below 80 h and reaches to a dynamic equilibrium with a minimal average particle size of 6.4 nm for milling durations over 80 h. Using the optimized high-energy ball milling parameters, we prepared high-purity disperse equiaxed α-Al2O3 nanoparticles with an average particle size of 8 nm and a purity of 99.96% (mass percent) in a high yield. After fractionated coagulation separations, disperse fine equiaxed α-Al2O3 nanoparticles with narrow size distribution were obtained. Finally, Al2O3 nanocrystalline ceramic with a relative density of 99.8% and an average grain size of 34 nm was sintered from the disperse fine equiaxed α-Al2O3 nanoparticles with an average particle size of 4.8 nm and a size distribution of 2–10 nm by pressureless two-step sintering.