Makoto Okaji

An Empirical Rule to Modify the Crystal Habit of Silver Chloride to Form Tabular Grains in an Emulsion

AbstractThe purpose of this study is to indicate an empirical rule to form tabular silver chloride grains, in double-jet precipitations, which controls the growth, form and morphology of the crystals. This rule relates intrinsic conditions (formation constants, bond-nature (electronegativity), molecular size (ionic or molecular radii) and number of points of attachment (denticity) of the silver ligands added as impurities to silver chloride) to the production of tabular grains. The rule was examined by adding various silver ligands (CN-, SCN-, 1-, S2O32-, SO32-, thiourea and its derivatives) to excess Cl- aqueous solution. Thus, the silver chloride tabular grains were found to be produced in the case of adding SCN-, thiourea and its derivatives (methyl-thiourea, ethyl-thiourea, N,N’.dimethyl thiourea and N,N’diethyl thiourea). Especially, we obtained the high aspectratio tabular crystals with [111] faces, for silver chloride grai/ls involving N,N’-dimethyl and N,N’.diethyl thiourea.