Silver redox systems

Hydroquinone [123-31 -9] represents a class of commercially important black-and-white chemical reducing agents (see Hydroquinone,RESORCINOL, AND catechol). The following scheme for silver haUde development with hydroquinone shows the quantitative importance of hydrogen ion and haUde ion concentrations on the two half-ceU reactions that describe the silver—hydroquinone redox system ... 

As early as 1937, Kolthoff and Sanders32) used silver halide discs as ion-sensitive membranes for the corresponding anion. They found that interferences through redox-systems were negligible with those membranes compared to electrodes of... 

Figure 4 shows what is known to date about the standard potential of the silver microelectrode as a function of the agglomeration number n f For n = 1, i.e. the redox system... 

We have prepared a series of copolymers under the conditions shown in Table 2. The monomer feed was always a 50 50 ratio of chloroprene to sulfur dioxide. Copolymerizations were carried out in bulk at temperatures from -78 to 100°. Initiators were tertiary butyl hydroperoxide at low temperatures, where it forms a redox system with the SO2 and is more effective than one might otherwise expect. Silver nitrate was used at 0° and 25°, azoiso-butyronitrile at 40° and 60°, and azodicyclohexanecarbonitrile... 

Several other imaging systems based on Com/developer amplification are known, including systems with various diffusion transfer imaging chemistries. The principles are the same as those outlined here. Basically, most imaging chemistries useful with silver halide systems can be transformed into a low-silver or (sometimes) non-silver system with a suitable developer/Com complex redox combination for amplification on imagewise catalytic nuclei. 

A number of redox couples at platinum electrodes (with both species soluble in the solvent) have been important to the establishment of a relation between potential scales in different solvents. Although they are useful in the comparison of redox potentials, they appear to have no advantages over the silver-silver ion system in the preparation of practical reference electrodes. 

In many cases platinum or silver wires serve as quasireference electrodes, however, they have to be calibrated by a reference redox systems. [The term pseudoreference (literally false reference) electrode is also used in the literature, however, the term quasireference electrode is preferred]. 

In a unique experiment Wetzel et determined the dependence of SERS of pyridine on a silver sol on the electric potential, which was maintained by a reversible redox system (europium +3, +2) added to the suspension. The relative concentration of the europium ions was maintained by means of an electrode whose potential was controlled with standard electrochemical equipment. They found that the ratio between the two main bands behaved similarly on an electrode and on a sol. Also frequency shifts were seen. They interpreted these results as indicating that the same SERS mechanisms are operative on the sol and in electrochemical systems. 

Since colloidal particles of silver and gold also give large SERS effects, it is useful to consider these as disconnected microelectrodes. Controlled variations in the potential at the interface between silver sol particles and electrolyte solution have been achieved by adding the Eu3+/Eu2+ redox system and varying the concentration ratio [22]. From measurements of SER spectra of pyridine adsorbed on the silver sol, the potential-dependent effects have been found to be identical with those given by bulk silver electrodes. These experiments also demonstrated that the intensity ratio of the pyridine Raman bands at ca. 1010 and 1040 cm-1 may be used as a simple but effective measure of sin-face potential for colloidal metals. 

The advantage of this technique is to be seen in the transformation of an original silver shape into a hollow gold architecture. This process can also be applied to other metals, examples being the redox systems Ag-Pd " and Ag-Pt, with corresponding results. 

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