Photographic developer threshold

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],...

Optical microscopy photographs of typical indentations on treated samples are reported in Figure 10. If the indentation load is 40 N no cracks are generated conversely, at 50 N well-developed cracks are generated therefore, a threshold load for crack formation can be pointed out for the strengthened samples, which is much higher than that for as-received glass, estimated equal to about 4 N. The effect of the compressive residual stress is absolutely clear. 

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