Silver nuclei formation

Simmons, W., Gonnissen, D., and Hubin, A. 1997. Study of the initial stages of silver electrocrystallisation from silver thiosulphate complexes Part I. Modelling of the silver nuclei formation during the induction period. Journal of Electroanalytical Chemistry 433, 141-151. 

The validity of the Poisson distribution for silver nucleation is demonstrated in Fig. 5.48B. The assumption for this kind of treatment is that the nucleus formation is irreversible and that the event is binary consisting of a discontinuous process (nucleus formation) and a continuous process (flow of... 

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. 

Spherical silver nanoparticles (NPs) were obtained by silver ions reduction with hydrazine in the presence of sodium citrate as a stabilizer. It has been investigated the kinetic regularities of the silver NPs nucleuses formation and their propagation depending on the starting concentration of the hydroxide ions and silver ions. It was investigated the influence of the s mthesis conditions on the average diameter of the obtained silver NPs. It was shown the dependence of the obtained silver NPs on kinetic parameters of the process. 

To of the voltage drop was considered as the time of appearance of the first new-phase nuclei oti the electrode surface. As is known, if nonstationary effects can be neglected, the average value of tq is inversely proportional to the stationary rate of nucleus formation (to = l//st)> and this is the way in which Kaischev, Scheludko, and Bliznakov [48] determined for the first time this important physical quantity in the case of silver electrodeposition on a platinum electrode. The data for... 

If the lifetime of a single silver atom in or on the silver halide grain is only a small fraction of a second, as assumed in some detailed formulations of latent image growth, silver atoms could form, dissociate, re-form, and so on, many times before the final formation of silver at a growing nucleus site. If, however, the lifetime is of the order of seconds, the dissociation and re-formation sequence is less attractive as a means of transporting silver atoms on or in the crystal. An alternative is the migration of the undissociated silver atom... 

The exact mechanism of propylene glow discharge polymerization is not known. The presence of a terminal acetylene (presumable propyne) in the gaseous products of propylene polymerization was indicated by the interaction of the cold trap gaseous condensates with 1% alcoholic or ammonlacal AgNO sol.(22) after the polymerization was over. An immediate formation of an explosive silver acetyllde was detected. Intermediate formation of propyne is also indicated by the IR spectra of the yellow relatively less volatile liquid left in the cold trap after the polymerization was over. Sharp but weak absorptions at 3310 cm l and 1270 cm are indications of a substituted acetylenic compound. The IR spectra of the yellow liquid also points to the presence of mono, dl- and trl-substituted aromatic compounds in the mixture (i.e. sharp absorption bands at 3080 cm l, 1640 cm l, 920 cm , 810 cm and a multiple band in the 1000-1120 cm l region are observed). The NMR spectra in deuterated acetone indicated the presence of an aromatic nucleus in the yellow liquid obtained from the cold trap. The formation of aromatic compounds can be explained if a propynyllc Intermediate is involved. 

Ag—Si02 and Agl—Si02 in water (core diameter 8 nm, total diameter 16 nm) are shown as well. The excellent agreement confirms that the observed absorption changes are due to metallic silver oxidation and formation of colloidal Agl, and demonstrates that molecular iodine can diffuse through the 10 nm silica shell and completely oxidize the silver cores. The fundamental mechanistic problem is that the molar volume of the hexagonal P-Agl phase is 41 cm moP, whilst that of face-centerd cubic silver is just 10.26 cm mol . Thus the core volume must quadruple in size in order to accommodate the nascent Agl nucleus. There appear to be only two ways for such a drastic volmne increase to be realized. Either the silica shell has an enormous porosity and can accommodate the silver iodide as a myriad nanoporous filaments, or more catastrophically, the silica shell must undergo violent rupture when iodine is added to the solution. 

As we can see, the starting section of the kinetic curve corresponds to the stage of the nucleus centers formation and the following sharp decrease of the concentration of silver ions corresponds to their growth stage. 

The rates of the nucleus centers formation (WO = 1/t of silver nanoparticles were calculated on the basis of the time length (t ) of the starting section of the kinetic curve. 

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