The Effect of Coalescence on AgBr Tabular Grain Formation

摘要

In the precipitation of tabular AgBr crystals in aqueous gelatin solutions, experimental results reveal a strong correlation between the degree of flocculation during nucleation and the resulting tabular grain fraction. In addition, large changes in the final tabular crystal population can be produced by changes made solely in the nucleation step, indicating that in such cases twinning occurs during nucleation. Because in the presence of gelatin, flocculation always precedes coalescence, it is concluded that coalescence plays an important role in twinning and the generation of tabular crystals. Possible coalescence mechanisms for twinning are discussed. It is also demonstrated that high populations of tabular AgBr grains can be obtained at various nucleation pBr conditions, thus raising questions about the validity of AgBr twinning mechanisms invoking solution properties that prevail only at low pBr. The results of this study also suggest a turbidi-metric method for monitoring, controlling, and generally optimizing the formation of tabular crystals during the nucleation step.