FORMATION OF SENSITIVITY DUE TO FORMS MODIFICATION OF THE (111) AGBR EMULSIONS GRAINS DURING RIPENING WITHOUT PHOTOGRAPHICALLY ACTIVE AGENTS

摘要

The formation of sensitivity effect in AgBr (111) emulsion microcrystals without the addition of photographically active compounds, called by us, spontaneous ripening, is found out. The Ag_n sensitivity centers are formed during habit microcrystals modification at supersaturation in the system owing to the difference of chemical potentials of silver on the crystal surface μ(111)-μ(100). The efficiency of ripening process of AgBr(111) increases with the microcrystals sizes and achieves a maximum at d=0.9-1.2μm. This value can be compared to lengths of photoelectron diffusion pass in silver halides microcrystals and with optimal quantity of ionic conductivity for the formation of centers of the latent image. The influence of added Cd~(2+) on spontaneous ripening processes was investigated. At small concentrations (up to 0.1 mol.%), the additive Cd~(2+) does not hinder the process of modification of the surface and ripening of microcrystals. With concentration Cd~(2+) change up to 1 mol.%, the increase of velocity of ripening and reaching of maximal sensitivity at concentration Cd~(2+)=0.5 mol.% can be connected with optimal value of ionic conductivity for shaping centers of the latent image. The values of supersaturation, critical supersaturation, growth rate of MC AgBr (111) and size of a critical nucleus for our experiments of synthesis are spotted. It is shown, that in the used crystallization requirements the growth rate G is more than critical growth rate G~*, that probably results in shaping nonuniform crystal structure. Influence of Gibbs-Thomson effect on the process of spontaneous ripening of MC AgBr (111) are discussed. It is shown that the shaping of sensitivity in the process of spontaneous ripening of MC AgBr (111) is due to the result of modification of the form and habit change MC from (111) up to (100) and spherical form.