Preparation And Characterizations Of Al₂O₃Nanoparticles

Alumina ceramic materials have received much attention and applications because of their superior performance. In order to solve the brittleness problem, we tried to prepare alumina nanoceramic. Preparation of monodisperse alumina nanoparticles is a premise for the preparation of alumina nanoceramic. Particle sintering and aggregation problem has been the focus of our concerns all the time. We have prepared the precursor by simple and cost low precipitation method. We studied the effect of the preparation conditions on the formation and phase transformation of the precursor (ammonium aluminum carbonate hydroxide). We added acetic acid to improve the AACH morphology; and the basic aluminum acetate is prepared. We studied the preparation conditions for the basic aluminum acetate and its topography as well as the phase transformation. Then we combined AACH with the polymer network method and studied the phase transformation of gel formed from the AACH added into the polymer network, as well as the morphology of the calcined sample. We also tried a new method, pickling corrosion method, to solve the problem of the particle sintering in phase transformation. The crystal structures and morphology of the pickling-etched sample were characterized.(1) Al (NO3)3·9H2O was used as the aluminum source; and the ammonium bicarbonate is dissolved in deionized water as the precipitating agent. Then aluminum nitrate was titrated in the ammonium bicarbonate solution. During this process, the aqueous ammonia of3mol/L was dropped into the reaction solution to maintain the pH value (pH=9). When the aluminum nitrate concentration is0.07mol/L or more, the expected AACH can be obtained, whereas when the aluminum nitrate concentration is less than0.07mol/L, the product is AIOOH (amorphous) or boehmite. The proportion of aluminum nitrate and ammonium bicarbonate has little effect on the the precursor.0.07mol/L of aluminum nitrate solution was added to2mol/L ammonium bicarbonate solution to prepare AACH particles; the resulting particles are10-20nm in size, well disperse and uniform in size. Mixed acrylamide and N, N’-methylene acrylamide were added to AACH solution. The temperature of the solution is80℃. The ammonium persulfate was used as catalyst coagulant. After the prepared gels were dried,a-Al2O3particles are obtained by calcining these dry gels at1000℃for2h. However, the obtained a-Al2O3particles are severely sintered and aggregated and100-200nm in size. Under air-free condition, the gels were calcined at800℃to remove carbon; and the as-prepared sample is y-phase alumina with good dispersibility. The particle sizes of the calcined y-alumina are10-20nm, which is a narrow size distribution.(2) Different mounts of AACH with poor morphology was added to the acetic to react for different times. When the reaction time is15hour and AACH concentration is0.004mol/L, we obtained the precursor particles of good dispersivity, with particle sizes in10-20nm; the precursor is aluminum acetate mixed with small amount of unreacted AACH. Polymer network for the first part of our work was easily decomposed at high temperature. This precursor was calcined at about1000℃for0.5h and then pickling-etched at120℃for20hours; finally pure a-Al2O3was obtained. The obtained a-Al2O3particles are sintered and agregated; the pickling corrosion treatment did not produce satisfactory a-Al2O3particles. The precursor was calcined at970℃for20min and then pickling-etched at100℃for20hours; finally pure γ-Al2O3was obtained. The resulting particles are10-20nm in size, with narrow size distribution.