Latent redox potential

The redox potential and the halide potential thus determine the silver activity, and so all defect concentrations are fixed at the phase boundaries [47]. All local transport coefficients are, in turn, determined by the defect concentrations. Therefore, all the prerequisites necessary for a quantitative treatment of the developing process are satisfied, provided that the spatial distribution and size distribution of the nuclei of the latent image are known, or that plausible assumptions regarding these distributions can be made, and provided that electrical double layer and space charge effects can be neglected. 

Hillson PJ (1958) The redox potential of the latent image. J Photogr Sci 6 97... 

Another approach to estimating the size of a latent image center uses redox buffers to determine the size at the transition potential between dissolution and growth. These buffers either develop the latent image centers, bleach them, or do neither. Konstantinov and associates (203,204) used the Gibbs-Thomson equation to analyze results obtained by this method. 

Tani [90] has examined the properties of silver clusters by means of redox buffer solutions, and showed that the oxidation potential of latent images formed by sulfur-plus-gold sensitization was much more positive than for those formed in unsensitized, sulfur-sensitized, reduction-sensitized, and iridium-sensitized emulsions. The oxidation potential of fog centers with excessive sulfur sensitization was much more positive than that of fog centers with excessive reduction sensitization. In general this reflects the relative ease of bleaching of silver centers compared with silver sulfide centers. 

Figure 10 Photographic development mechanism. The reduction potential, E"(Ag+/Agn), ofthe latent image clusters, when in contact with a solution. Increases with the number of atoms n. Therefore a nuclearity threshold for developmen t is created by the redox poten tial of the developer E°(CP/D). Above the critical nuclearity n, the potential E°(Ag yAg ) is higher than E°(CA/D), and alternate electron transfer toward A g, and Ag adsorption on Err allows the cluster to grow autocatalytically. On the contrary, when l"(Ag, /Agg is lower than E°(E>-/D), corrosion ofsubcritical clusters takes place by oxidizing molecules, such as D or Ox [7],...

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