Synthesis Of α-Al₂O₃ Nanoparticles By High Energy Ball Mill

Alumina ceramics have a wide range of applications, such as electronic devices, high temperature materials, and composite materials, because of its high strength and corrosion resistance etc. Recently, much attention have focused on the ultrafine a-Al2O3 nanoparticles since compared to the traditional alumina ceramics, the alumina nanoceramics composed of ultrafine a-Al2O3 crystallites may possesses good ductility, which is significant for the applications of alumina ceramics. Thus, it is necessary to study the preparation of the a-Al2O3 nanoparticles with smaller sizes and narrow particle size distributions. Generally, the particle size and particle size distribution of a-Al2O3 nanoparticles prepared by wet chemical methods is large and wide, and the hard agglomerations of a-Al2O3 nanoparticles usually formed during the sintering among particles. In present study, a-Al2O3 nanoparticles were prepared by the mechanochemical reaction, that is, the mixture of CoO and Al powders was milled to induce the reduction reaction to form the Co/a-Al2O3 nanocomposites. Then α-Al2O3 nanoparticles can be obtained by removing the Co with HCl; and the impurities such as Fe and Cr arising from the ball milling could also be removed. Then the particles size and dispersion of a-Al2O3 nanoparticles were studied systematically by changing the milling parameters, such as milling speed, ball to powder ratio (BPR) and milling time. The results are as follows.1. With increasing the revolution speed from 200 to 250 rpm (the milling time and BPR are 20 h and 20:1, respectively and kept constant during the milling.), the average particle size of a-Al2O3 nanoparticles decreases from 100 to 40nm. When the revolution speed increased to 300 rpm, the average particle size of a-Al2O3 nanoparticles is 45 nm. At 250 rpm, the average particle size of a-Al2O3 nanoparticles is the smallest (40 nm).2. With increasing BPR (the revolution speed and time are 250 rpm and 20 h, respectively and kept constant during the milling), the particle sizes of a-Al2O3 nanoparticles decreases firstly and then increases slightly. At BPR of 10:1, the average particle size is 50 nm; at BPR of 50:1, the average particle size is 15 run, and when BPR reaches to 100:1, the average particle size is 35 nm.3. With increasing the milling time (the revolution speed and BPR are 250 rpm and 50:1, respectively and kept constant during milling), the average particle size decreases from 50 nm at 10 h to 15 nm at 20 h; and with milling time increasing to 50 h, the average particle size increases to 45 nm. For the milling time of 100 h, the XRD patterns show the absence of the diffraction peaks of a-Al2O3. Maybe the a-Al2O3 phase transforms to amorphous phase for such a long milling time, and thus no Al2O3 nanoparticles can be obtained due to the dissolution of amorphous Al2I3 in HCl.Based on the above results, the particle sizes of a-Al2O3 nanoparticles can be controlled by adjusting the milling parameters (revolution speed, BPR and milling time). The optimized conditions for preparing a-Al2O3 nanoparticles are the revolution speed of 250 rpm, BPR of 50:1 and milling time of 20 h. Under these conditions, the a-Al2O3 nanoparticles with an average particle size of 15 nm and good dispersivity can be obtained. The ICP-MS results for this sample show that the obtained a-Al2O3 nanoparticles are pure; the mass percentage of Co, Fe,Cr in a-Al2O3 nanoparticles are 0,0.12 wt% and 0.002 wt%, respectively.