Aluminum ammonium sulfate (AA) solution (0.1 mol/l) and ammonium hydro
gen carbonate (AHC) solution (1.2 mol/l) were allowed to react at room
temperature. The precipitates formed were kept with the mother liquor
in a closed vessel and aged at 100 degrees C, Acicular-shaped crystal
line particles of Al(NH4)CO3(OH)(2), (AACH), were obtained after the e
longated aging period. Acicular alpha-alumina particles were obtained
through the thermal decomposition at 1300 degrees C out of the AACH pa
rticles which were previously treated with a small amount of tetraetho
xysilane (about 1.6 wt. % of SiO2).