Developed silver

Coating containing a mixture of amplified latent image centers (ie, developed silver)... 

This difference is a measure of the free-energy driving force for the development reaction. If the development mechanism is treated as an electrode reaction such that the developing silver center functions as an electrode, then the electron-transfer step is first order in the concentration of D and first order in the surface area of the developing silver center (280) (Fig. 13). Phenomenologically, the rate of formation of metallic silver is given in equation 17,... 

The dyes or dye precursors may be initially diffusible in alkaU, in which case they will be immobilized imagewise, or they may be initially immobile in alkaU and released imagewise to transfer. Positive-working processes produce dye transfer density inversely related to the developed silver density conversely, negative-working processes produce dye transfer density in direct proportion to the developed silver. 

There are two basic methods by which a developed silver image can be obtained. The one commonly employed in practice is termed chemical or, better, direct development. The exposed sensitive layer is placed directly in a suitable reducing solution, and the silver image is derived from the reduction of the silver halide grains. This is the type already considered to some extent in the preceding section. 

In a modified and more complicated form (pre-fixation physical development) the exposed sensitive layer is placed directly in the developing solution without first dissolving out the silver halide. The developing solution contains a silver halide solvent in addition to the soluble silver salt, and part of the developed silver in this process comes from the original silver halide. Some direct development also occurs. 

Replacement of the latent image silver by gold in the exposed photographic sensitive layer increases the developability (James et at., 31). Since the mass of developed silver depends only upon the number of developed nuclei, the gold treatment has obviously increased the number of active nuclei. Hence, smaller gold nuclei (in terms of numbers of atoms) than silver can initiate development, unless the treatment used to effect a replacement of silver by gold has resulted in something more than a simple replacement. 

Fig. 5. Electron micrograph of two silver grains obtained by developing silver bromide grains in a distortionless hydroquinone developer.

Longer irradiation than that shown in Fig. 81 resulted in decreased absorption of AgT at 275 nm and in an increase at 380 nm, which are characteristic of a developing silver plasmon band [525, 526]. 

To allow a clear-cut distinction between the two labeled antigens after silver enhancement, the final size of the developed silver grains should be rather homogeneous and accurately predictable. The following parameters influence size, variation in size, and shape of the final gram-... 

In black and white photography, the developed visible image consists of particles of silver produced by the chemical action. By suitable processes, dye images can be formed that are related directly to the amount of developed silver... 

Direct (or chemical) development is obtained by bringing the exposed emulsion coating into contact with a solution that contains a developing agent but no silver salt. The developed silver is derived from the silver halide grains that contain the latent image centers. 

Physical development. The developer used in this process contains a soluble silver salt, and the developed image is obtained by reduction of this salt. The process is chemical, but the term is retained for historical reasons. Development by the same mechanism can occur when silver ions from silver halide grains pass into solution and are subsequently reduced at latent image centers or developed silver. This process is termed solution-physical development. 

The primary photochemical process that occurs when a photon is absorbed by the silver halide is the transfer of an electron to the conduction band. The quantum efficiency of this process is one. The efficiency of formation of a developable silver nucleus, however, depends on various chemical and physical secondary processes and may be much smaller. 

The coatings generate physically developable silver nuclei when exposed.172 One example is the merocyanine dye (95). 

When a photographic film is developed, silver bromide is reduced by hydroquinone (the developer) in a basic aqueous solution to give quinone and tiny black particles of silver metal ... 

The archivally stable Cibachrome printing process is based on the use of developed silver metal in the negative image for the imagewise reduction of azo chro-mophores 39-41 to colorless anilines under highly acidic conditions. The anilines are then dissolved away to leave a positive image in dye. This process is also known as the silver dye bleach process [56,57],... 

A highly efficient inter- and intra-molecular addition of l,3-diketones//3-keto esters to styrenes (ArCH=CH2) has been developed. Silver triflate was identified as the most efficient catalyst (10 mol%). The reaction, affording formally the Markovnikov products, is reversible through the cleavage of a carbon-carbon bond by silver at an elevated temperature.70... 

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