Monodisperse Sols of Barium Sulfate. II. Morphological Characteristics, Aging and Dissolution of Particles

A morphological study is made of barium sulfate particles precipitated from a homogeneous solution at 25° and 50° C in the presence of various foreign substances and without them. As foreign substances several types of compounds were chosen: a nonionic detergent (Triton X-100), an anionic detergent (Aerosol MA), and complexing agents (citrate and EDTA). The particles were studied by electron microscopy. In all cases anisotropic particles were formed with more or less defined structures, and most of the systems were monodisperse. The appearance of twins, grown together in different profile planes, was observed. The aging of particles in mother liquor was studied, as well as the dissolution of particles in water. On the basis of particle slize data, the morphological characteristics of particles, and their aging and dissolution, the mechanisms of particle foTmation were discussed. The -i!nfluence of foreign substances is discussed in terms of their chemical properties. lt lis sugges,ted that particles of barium sulfate are predominantly formed by aggregation of primary particles, whilst pure diffusion growth is encountered only under restricted conditions