Abstract: Three series of bromoiodide emulsion microcrystals with composite structure were prepared by double-jet method with automatic control pAg. The geometric properties, such as grain size, crystal habit, and the iodide distribution in the bulk and surface of microcrystal were determined as a function of iodide content, iodide introduction time and amount during the precipitation by STEM-EDS method. It was shown that the earlier the iodide was introduced and the more the iodide was incorporated, the more the iodide was enriched into the core of the microcrystals. In the microcrystals really exists the composite structure of iodide-rich and iodide-poor phases. With the iodide increase the grain size decreased, the crystal habit was transformed from regular octahedral to rounded octahedral, the iodide distribution was diffused step by step from the bulk to the surface, obscuring the boundary of composite structure of iodide-rich and iodide-poor phases.

Key words: photographic chemistry, core-shell emulsion, preparation, properties