Abstract
It was reported that the ultrafine particles of alumina was prepared by the neaction of NH3 gas and AlCl3 solution. A particle size decreased with decreasing NH3 gas composition or AlCl3 concentration. The particles of less than 50Å in size were prepared.The formation mechanism was discussed as follows. While a mass of AlCl3 solution falls from the top to the bottom of a stream in a flask, NH3 gas is absorbed from the surface of a mass. The generation zone on the surface of solution defined in preceding paper shifts toward the innerpart of mother liquid during the very short exposure time for NH3 gas, so that the ultrafine particles and excess OH- ions remain in the stocking zone behind the generation zone. The particles and OH- ions are carried into the mother liquid by the stream in the flask and the excess OH- ions make the relatively large particles by inhomogeneous reaction with Al3+ ions there. The partcles exist in the mother liquid as a stable colloid for the very near equilibrium state of the mother liquid.
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