High aspect ratio silver bromoiodide emulsions and processes for their preparation

摘要

A tabular grain silver halide emulsion is disclosed comprised of a dispersing medium and silver bromoiodide grains. Tabular silver bromoiodide grains having a thickness less than 0.3 micron and a diameter of at least 0.6 micron have an average aspect ratio of greater than 8:1 and account for at least 50 percent of the total projected area of the silver bromoiodide grains. The high aspect ratio silver bromoiodide grains are prepared by concurrently running silver, bromide, and iodide salts into a reaction vessel while controlling pBr. Prior to the concurrent addition of silver and iodide salts the reaction vessel is substantially free of iodide.