| The use of three kinds of techniques: (a) precipitation from homogenous solution, (b) controlled double-jet precipitation, and (c) chemical reactions in aerosols in the preparation of uniform colloids dispersions is discussed.; Uniform spherical MgF{dollar}sb2{dollar} and cubic NaMgCl{dollar}sb3{dollar} particles were obtained by aging at 80{dollar}spcirc{dollar}C solution contained NaF and MgCl{dollar}sb2{dollar} m certain concentration ratios. The electrophoretic mobilities of these dispersions indicated the particles to be positively charged even in the presence of various excesses of F{dollar}sp-{dollar} ions. Thermal analysis and X-ray diffraction data indicated that MgF{dollar}sb2{dollar} sphere were formed by agreggation of microcrystallites, while NaMgF{dollar}sb3{dollar} cubes were generated by diffusion growth, possibly as a result of the Ostwald ripening process.; Well defined zinc oxide colloidal particles of different morphologies were produced by the controlled double-jet precipitation (CDJP) process. Scanning electron microscopy and X-ray data indicated that the solids generated under different conditions have identical crystallite structures, although they are internally composites. The growths of the subunits and of particles themselves follow different patterns. Particles formed in the presence of a surfactant (sodium dodecyl sulfate) exhibit essentially the same overall characteristics, but the particles are microporous.; Spherical silica/titania particles were prepared by nebulizing with a nozzle mixed liquids of tetraethyl orthosilicate and titanium(IV) ethoxide and contacting the resulting droplets with water vapor. The size distribution of the liquid aerosols was improved by mechanically eliminating the larger droplets and by the evaporation and condensation of the remaining droplets in the presence of AgCl nuclei introduced with the carrier gas. The composition of the resulting solids differed from that expected from the original liquids. Furthermore, the particles were not internally homogeneous; the surface layers contained a higher molar ratio of titania than the bulk. The electrokinetic data corroborated the surface composition. On calcination at 700{dollar}spcirc{dollar}C, the titania component crystallized to anatase in the originally amorphous particles. |
