Preparation of ultrafine spherical AlOOH and Al2O3 powders by aqueous precipitation method with mixed surfactants

Ultrafine spherical boehmite (AlOOH) particles were prepared from aluminum sulfate and aluminum chloride solution with urea as precipitant at 90 °C. It was observed that mixed surfactants tween80-sodium stearate could improve dispersion of AlOOH particles. While the concentrations of tween80 and sodium stearate were 0.75 wt.% and 0.14 wt.% respectively, particles with spherical degree of 1.1 and size of 0.36 μm could be achieved. The thermogravimetric (TG) and Fourier transform infrared spectroscopy (FTIR) showed that sodium stearate molecules were bonded upon the surface of particles forming a coating layer to prevent agglomeration. Addition of NaCl could further improve dispersion of particles, spherical AlOOH particles with average size of 0.38 μm and nanosized spherical particles could be obtained when the concentration of NaCl was 0.05 M and 0.1 M. At the same time, Al2O3 powders obtained from precursor with NaCl showed much better sintering behavior.