Mg. Antoniades et Js. Wey, EFFECT OF GELATIN ON THE AGGLOMERATION OF FINE AGBR CRYSTALS IN DOUBLE-JET PRECIPITATION, Journal of imaging science and technology, 37(3), 1993, pp. 272-280
The effect of gelatin on the agglomeration of fine AgBr crystals forme
d during the early stages of double-jet precipitation was examined by
turbidimetry. At high gelatin concentrations, the stable number of cry
stals formed increases with increasing reactant addition rate, as pred
icted by an earlier model. However, if the amount of gelatin is progre
ssively reduced, deviations from this model are exhibited. The control
ling parameter is the relative amount of gelatin available to the prec
ipitating AgBr at the silver reactant introduction point, expressed by
the gelatin-to-AgBr ratio, and is dependent on the silver reactant ad
dition rate, the gelatin concentration in the bulk suspension, and the
dilution rate of the silver reactant stream. When the gelatin-to-AgBr
ratio is decreased below a critical level (50 g/mol at 40-degrees-C),
coalescence occurs, and the number of stable crystals decreases as th
e reactant addition rate increases. This mechanism explains the deviat
ions from the earlier model and other previously reported studies. The
coalescence mechanism is further supported by electron microscopy and
x-ray diffraction. At intermediate gelatin-to-AgBr ratios (50-150 g/m
ol at pBr 2.3, pH 4.5 and 40-degrees-C) flocculation occurs. Unlike co
alescence, flocculation is reversible and does not interfere with the
nucleation and growth of the AgBr crystals.