Latent image oxidation

Fig. 9. Corrosion model of silver development. As the haUde ion, X, is removed into solution at the etch pit, the silver ion,, travels interstitiaHy, Ag/ to the site of the latent image where it is converted to silver metal by reaction with the color developer, Dev. Dev represents oxidized developer.

In these processes, metal complexes find a number of uses as light-sensitive latent-image-catalyst formers, catalyst replacements for image silver in low-silver systems, and oxidants for various developers in image amplification baths. 

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. 

Photochemical Decomposition of Solids. Defect ionic solids frequently undergo photochemical degradation on absorption of quanta of appropriate energy. The formation of the latent image in silver halides and the photolysis of sulphides and oxides in moist air are of this class. 

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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