PREPARATION OF γ-Al2O3 NANOPARTICLES BY MECHANO-CHEMICAL AND SONOCHEMICAL REACTION

Bo Xu, Shengjuan Li, Shulin Wang, Laiqiang Li

1 INTRODUCTION

The γ-Al2O3 nanosolids, a kind of porous activated alumina, are widely used in plastic, rubber, ceramics and fireproofing materials as the reinforcing agent, where its characteristics of high thermal stability, adhesion resistance, high mechanical strength and wear resistance are required. It has more remarkable advantages of enhancing ceramic in its compactness, finish, fracture toughness, resistance to creep and abradability of macromolecule materials. Besides, γ-Al2O3 is also a good dispersant, which can be uniformly dispersed in many solvents, e.g. water, ethanol, acetone, benzene and xylene etc

In this paper, a novel method is applied to prepare porous γ-Al2O3 nanoparticles. At first, the 2h-milled aluminum powders are prepared as the starting material, then the powders react with water to produce Al(OH)3 collosol in an ultrasonic water-bath, lastly, dehydrating, grinding, and roasting the Al(OH)3 colloid at a given temperature to produce the porous γ-Al2 O3 nanosolids. This method, which combines mechano-chemical and sonochemical reaction, is extremely innovative, and it may inspire new ideas for preparation of nanomaterials.

2 EXPERIMENTS

2.1 Preparation of aluminum ultra-fine particles

Experiment was conducted in a dry roller vibration mill (RVM) at room temperature. The RVM has a chamber of 2.5L, equipped with a motor of 0.12kW. To provide proper atmosphere and prevent dust explosion, the entire operation was performed in a glove box filled with argon. In a typical experiment, 100g raw aluminum powder (with average sizes of 150µm, purity higher than 99.5%, purchased from Guoyao group chemical reagent Co. Ltd., China) is placed in the grinding chamber with the stainless steel rods as grinding medium, and the weight ratio between the medium and powder is 60:1. The 2h-milled sample is then collected for later use.

2.2 Synthesis of γ-Al2O3 porous nanoparticles

2.0g of 2h-milled aluminum powder was put into a beaker with the water of 50mL The beaker was placed in an ultrasonic water-bath (DL-120J, made in China), setting the supersonic frequency of 100kHz at the room temperature. Under the high temperature and high pressure circumstances generated by the ultrasonic cavitation, the energy stored in the material was fully released, and the particles reacted with water to produce Al(OH)3 white latex. In succession, it was dehydrated in a drying cabinet (101 A-1, made in China) at 80°C for 6h to remove the excess water. Lastly, grind the gel into white powder and place it in an electrical resistance furnace (SX2-5, made in China) to calcined 4h at 160°C, the porous γ-Al2O3 nanoparticles were obtained. The experimental flow chart is shown in Figure 1.

2.3 Characterizations of the particles

Structural phase analysis was carried out with D/max-γA X-ray diffractometer (XRD), using Ni-filtered Cu-Kα radiation as the X-ray source. The scanning speed was 4°/min. The morphology of the sample was observed using a FEI Quanta 450 scanning electron microscope (SEM), and the accelerating voltage was 20 KV. Transmission electron microscopy (TEM) image was recorded on Tecnai G2 20 S-Twin electron microscopy at 200 kV. All measurements were carried out at room temperature.

3 RESULTS AND DISCUSSION

3.1 The structure analysis of aluminum powders

From the SEM image (Figure 2a), we can see that the particles sizes are in the range of 0.5-0.8µm after milled for 2h, the size is in good agreement with the particle size measured from TEM image in Figure 2b, and the SEM image shows a uniform, flaky crystal pattern with 0.5µm in width and 0.8µm in length. The microstructure of the nanoparticle is also confirmed by HRTEM (Figure 2c). The result shows that the solid particles, under the action of mechanical force, generate a mass of deformation and dislocation flaws, leading to the material to a metastable high-energy state, which is favorable for mechano-chemical reaction.

Figure 3 illustrates the XRD patterns of the raw and the 2h-milled aluminum powders respectively. In Figure 3, after two hours of milling, the diffraction peaks are still indexed to the face-centered cubic lattice aluminum, but Al(OH)3 should be recognized as a minor phase. This is because the material is in a metastable, high-energy activity state during the...