Formation of monosized spherical aluminum hydroxide particles by urea method

Monosized spherical aluminum hydroxide particles were first prepared by homogeneous precipitation using the urea method below its boiling temperature. To obtain monosized particles a careful control is needed of the precipitation process, such as factors like temperature, hold time and concentration of Al³⁺. The formation chemistry of monosized particles is studied through the measurement of pH and concentration of Al³⁺ during precipitation. It is found that when the nucleation limit of aluminum hydroxide is reached only once monosized particles are formed; and in contrast, when the nucleation limit is attained more than once it will cause a multisize distribution of particles. Besides factors like temperature and hold time, anions would also affect the formation of monosized particles; monosized particles can only be obtained with SO^2-₄, not with NO^-₃ or Cl^-.