Preparation And Characterizations Of Al₂O₃Ultrafine Particles

Ceramic materials, especially alumina ceramic, due to its high hardness, high strength, corrosion resistance, good biocompatibility and excellent electrical insulation properties, have a very wide range of applications in many areas. But alumina ceramics’ brittleness has limited its wider application at room temperature. For solving this problem, with different methods and ideas, preparation of alumina nano-ceramic can fundamentally solve this problem. Mono-disperse, spherical, ultrafine alumina particles is a prerequisite for the preparation of alumina nano-ceramic.Common method for preparing aluminum ultrafine particles is calcine precursor which is prepared by liquid phase chemical and has good morphology, good dispersion at a high temperature. But after a calcination treatment at a high temperature, the α-Al2O3particles have obvious sintering and agglomeration, which are not ideal. Therefore, try to look for a relatively low temperature to calcine precursor, the phase change is not complete at this low temperature, only a portion of precursor is transformed to the thermodynamically stable α-Al2O3, mostly in the form of transition phases of Al2O3. As α-Al2O3is different with transition phases of Al2O3in the structure, resulting in the different chemical activity between them. If find a suitable condition which can separate α-Al2O3and transition phases of Al2O3, then α-Al2O3can be obtained at a relatively low calcination temperature. After the experimental exploration, discovery that under the high temperature and high pressure, hydrochloric acid solution can act as this medium. Transition phases of Al2O3are corroded in that condition. Due to the chemical stability, α-Al2O3can exist, so that can get α-Al2O3.This work reports the preparation of Al2O3ultrafine particles by precipitation reaction of aluminum nitrate and ammonium bicarbonate and the hydrolysis reaction of aluminum isopropoxide as well as calcination and corrosion via hydrochloric acid. Aluminum nitrate was used as the aluminum source, polyethylene glycol as surfactant, ammonium bicarbonate as precipitant to prepare aluminum ammonium carbonate (AACH). After calcinating AACH at980℃,1010℃, and1020℃and corrosion via hydrochloric acid, two-phase mixed Al2O3, namely, α-Al2O3accompanied by θ-Al2O3, was obtained; and its average particle sizes are about30nm. The obtained two-phase mixed Al2O3particles have relatively regular shape and no agglomeration. Aluminum isopropoxide was used as the aluminum source, citric acid as surfactant to prepare boehmite (y-AlOOH) via the hydrolysis of aluminum isopropoxide. After calcinating γ-AlOOH at900℃and corrosion via hydrochloric acid,θ-Al2O3particles were obtained; they have a regular shape, good dispersity, and an average particle size of13.3nm. After calcinating y-AlOOH at980℃and corrosion via hydrochloric acid, α-Al2O3particles were obtained; they have severe sintering and agglomeration.