Monodisperse Sols of Barium Sulfate. I. Preparation of Stable Sols

Monodisperse sols of barium sulfate were prepared by a modified method of homogeneous precipitation and characterized by electron microscopy. The particles were spindle-shaped and of a rather uniform distribution when prepared with concentrations of barium and sulfate ions of 4 X 10·3 M. The degree of monodispersity obtained depends on the cleanliness of solutions and glassware, and good results were obtained by filtration of solutions and careful cleaning of glassware. Morphological changes in the particles during the reaction are studied. Monodisperse particles dispersed in the mother liquor are not stable, since they aggregate and recrystallize by aging. However, addition of nonionic detergents stabilizes the particles for longer periods, as detected by electron microscopy and ultramicroscopy. Stable sols of barium sulfate of particle size from 195 to 480 mμ for the longer axis, and from 95 to 188 m~t for the shorter axis, respectively, were prepared