Insitu observations of silver bromide tabular crystal growth

Abstract

Nucleation and growth of silver bromide tabular crystals has been observed insitu for the first time by optical microscopy. Crystals were precipitated by a new method, from solutions of silver bromide and potassium bromide in DMSO. Thin tabular crystals were preferentially produced in a narrow range of silver concentration, after long nucleation periods. A twinning process occurred, generally, in a very early stage of the precipitation. Tabular crystals could appear in a single spot in the absence of other particles and they grew with a very high initial rate. Coalescence of particles was practically discarded as the main mechanism for twinning. Most tabular crystals were initially circular and then were transformed into hexagons or triangles as they developed six or three straight edges. A fast growth rate was associated with rough sides, while straight edges moved more slowly. Changes in crystal shape occurred during the growth process in a way similar to that found by Maskasky in aqueous systems by indirect mapping methods. Changes in crystal shape occurred by roughening on one, three or six crystal edges.