Silver formation

The generation of Oj in suspensions of ZnO containing Ag" ions, which has been known for a long time has again been studied in recent years 210,211) experiments on colloidal solutions have also been carried out in our laboratory. Hada et al. measured the quantum yield of silver formation as a function of Ag concentration They found that the quantum yield q> could be expressed as... 

AgN03 in cone, solutions, white precipitate—AgCH02, turning dark even in cold, owing to deposition of metallic silver. This decomposition of silver formate does not take place in presence of excess ammonia. 

Both reduction centers and latent image centers are composed of silver, and to Moisar "it seems safe to assume that the silver specks formed by reduction are identical to those which somehow appear as subspecks and alleged intermediate entities during photolytic silver formation" (93). He proposed that Ag2 centers formed by exposure by light can act as hole traps and Agj centers act as subdevelopable precursors of latent image centers but, as Hamilton and Baetzold comment (96),... 

Silver nitrate solution white precipitate of silver formate in neutral solutions, slowly reduced at room temperature and more rapidly on warming, a black precipitate of silver being formed (distinction from acetate). With very dilute solutions, the silver may be deposited in the form of a mirror on the walls of the tube. 

Silver salts. Silver formate and silver oxalate readily decompose below about 420 K, but salts containing more complicated anions that yield carbon in the residue, breakdown at higher temperatures (above 440 K for the malonate, mellitate, squarate, maleate and fumarate [129]). The formate and oxalate of this less electropositive element are less stable than the corresponding nickel and copper salts, but the differences are less marked where the residual product retained carbon. The reaction of silver squarate was not a silver promoted nucleation and growth process, but proceeded with the intervention of silver oxide [114],... 

A second important decay mechanism for the iridium-associated trapped electron center involves the thermally assisted excitation of the trapped carrier to the conduction band. It is retrapped many times at other Ir3 + sites, so that the time before the electron is permanently annihilated by silver formation at an intrinsic sensitivity center or recombination is increased. When this decay mechanism predominates, the addition of Ir3 + reduces the emulsion s high intensity reciprocity failure (see Section I.B). 

Silver formate undergoes a decomposition similar to that expressed by the last equation. All the reactions described above are of value in identifying a formate. 

One form of Ag was oriented relative to the original AgNa lattice and the other was not. The decomposition and silver formation was thought to be primarily due to thermal effects, although evidence was found that the form of silver is different in the case of simple thermal decomposition thus irradiation effects play some role in the electron-beam-induced decomposition. These studies are reviewed more fully by Bowden and Yoffe [100]. 

According to UV-Vis and DSC observations, the mechanism for zero-valence silver formation inside polystyrene matrices should involve a reduction of silver ions by hydrogen atoms generated from polystyrene during thermolysis. In particular, according to the DSC thermogram, the Ag-mercaptide... 

Whatever the explanation for the color change, the interesting fact remains that in molten potassium or sodium thiocyanate the sulphur is highly reactive and displays reactions which are not realizable in aqueous solutions of alkali thiocyanates. Among such reactions are formation of silver sulfide from metallic silver formation of sodium thiosulfate with sodium sulfite conversion of metal oxides and sulfates (even lead sulfate)... 

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