Deposition of silver

The surface area of paper pulp fibers has been determined by the deposition of a continuous film of metallic silver on the surface by use of the reducing properties of cellulose [77]. The amount of metal deposited was determined by its ability to decompose hydrogen peroxide catalytically. A standard surface, e.g. regenerated cellulose film, is requir for calibration. 

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All the silver halides are sensitive to light, decomposing eventually to silver. In sunlight, silver chloride turns first violet and finally black. The use of these compounds in photography depends on this (see below). (All silver salts are, in fact, photosensitive—the neck of a silver nitrate bottle is black owing to a deposit of silver.)... 

Electroplating. Most silver-plating baths employ alkaline solutions of silver cyanide. The silver cyanide complexes that are obtained in a very low concentration of free silver ion in solution produce a much firmer deposit of silver during electroplating than solutions that contain higher concentrations. An excess of cyanide beyond that needed to form the Ag(CN)2 complex is employed to control the concentration. The silver is added to the solution either directly as silver cyanide or by oxidation of a silver-rod electrode. Plating baths frequently contain 40—140 g/L of silver cyanide... 

Ag(I) and Cu(II) are readily used in neutral solution, although oxidations by Ag(I) are often affected by the deposition of silver metal. Theoretically Cu(II) can behave either as a two- or a one-equivalent reagent, but it usually functions as the latter. The tendency of Cu(I) to disproportionate is normally suppressed by working with solvents such as pyridine which form stable complexes with this oxidation state. 

Aslan, K., Leonenko, Z., Lakowicz, J.R. and Geddes, C.D. (2005) Fast and slow deposition of silver nanorods on planar surfaces Application to metal-enhanced fluorescence. The Journal of Physical Chemistry. B, 109, 3157-3162. 

Room temperature deposition of silver on Pd(lOO) produces a rather sharp Ag/Pd interface [62]. The interaction with a palladium surface induces a shift of Ag 3d core levels to lower binding energies (up to 0.7 eV) while the Pd 3d level BE, is virtually unchanged. In the same time silver deposition alters the palladium valence band already at small silver coverage. Annealing of the Ag/Pd system at 520 K induces inter-diffusion of Ag and Pd atoms at all silver coverage. In the case when silver multilayer was deposited on the palladium surface, the layered silver transforms into a clustered structure slightly enriched with Pd atoms. A hybridization of the localized Pd 4d level and the silver sp-band produces virtual bound state at 2eV below the Fermi level. 

The present technique enables light-induced redox reaction UV light-induced oxidative dissolution and visible light-induced reductive deposition of silver nanoparticles. Reversible control of the particle size is therefore possible in principle. The reversible redox process can be applied to surface patterning and a photoelectrochemical actuator, besides the multicolor photochromism. 

Figure 2. UV light-induced deposition of silver nanoparticles (al-a3) and wavelength-selective visible light-induced dissolution of silver nanoparticles (bl-b3).

This conclusion is proved by the element analysis of sensors which have registered more than 30 portions of silver emitted from the surface of substrate after completion of deposition of silver on its surface. The experiments on local analysis of tiie sensor indicated that such sensor has areas containing up to 0.3 wt.% of silver in 1 pm. The total amount of silver atoms incident on sensor was 7-10. This means that silver atoms get deposited on the surface of the sensor inhomogeneously, being localized close to defect allocation area which made it possible to detect... 

We heated the substrate of zinc oxide containing 10 cm 2 of silver atoms (in this case there was already no emission after completion of deposition) at 300 C. Such thermal treatment results in formation of microcrystals, rather than evaporation adatoms on the surface of the substrate made of zinc oxide. In paper [34] it was shown that microcrystals with diameter 100 A deposited on the zinc oxide surface are acceptors of electrons, therefore the formation of microcrystals results in increase of resistivity of a sensor substrate above the initial value (prior to silver deposition). In this case the initial value of the resistance of sensor-substrate was 2.1 MOhm, after adsorption of silver atoms it became 700 kOhm, and as a result of heating at 300°C and formation of microcrystals - acceptors of electrons it in increased up to 12 MOhm. If such a substrate is subject to deposition of 3-10 5 cjjj-2 silver again, then emission of silver atoms gets detected. From the change of resistivity of sensor-detector due to deposition of silver atoms one can conclude that in this case the emission of atoms is 4 times as low than in experiment with pure substrate made of zinc oxide, which confirms the supposition made on the mechanism of emission of adatoms. 

Thus, co-deposition of silver and copper can take place only when the silver concentration in the electrolyte falls to a very low level. This clearly indicates that the electrolytic process can, instead, be used for separating copper from silver. When both silver and copper ions are present, the initial deposition will mainly be of silver and the deposition of copper will take place only when the concentration of silver becomes very low. Another example worth considering here is the co-deposition of copper and zinc. Under normal conditions, the co-deposition of copper and zinc from an electrolyte containing copper and zinc sulfates is not feasible because of the large difference in the electrode potentials. If, however, an excess of alkali cyanides is added to the solution, both the metals form complex cyanides the cuprocyanide complex is much more stable than the zinc cyanide complex and thus the concentration of the free copper ions available for deposition is considerably reduced. As a result of this, the deposition potentials for copper and zinc become very close and their co-deposition can take place to form alloys. 

In the first case, the rate of deposition depends on the equilibrium concentration of ad-atoms, on their diffusion coefficient, on the exchange current density and on the overpotential. In the second case, the rate of deposition is a function, besides of the geometric factors of the surface, of the exchange current and the overpotential. This mechanism is valid, for example, in the deposition of silver from a AgN03 solution. 

The basic condition for experimental study of nucleation on an identical surface requires that this surface be a single crystal face without screw dislocations (page 306). Such a surface was obtained by Budevski et at. when silver was deposited in a narrow capillary. During subsequent deposition of silver layers the screw dislocations died out so that finally a surface of required properties was obtained. 

Further deposition of silver on such a surface is connected with a cathodic current randomly oscillating around the mean value... 

Fig. 5.47 Deposition of silver on (100) face of a silver electrode in absence of screw dislocations. A—time dependence of current pulses,...

Pol VG, Srivastava DN, Palchik O, Palchik V, Slifkin MA, Weiss AM, Gedanken A (2000) Sonochemical deposition of silver nanoparticles on silica spheres. Langmuir 18(8) 3352-3357... 

Figure 11.3 Dependence of the exchange current density jo for the deposition of silver on the concentration of cyanide. Data taken from Ref. 2.

As an example of the determination of electrochemical reaction orders, we consider the deposition of silver from an aqueous solution containing cyanide. The latter forms various complexes with silver ions, such as AgCN, Ag(CN) ", Ag(CN)3. Therefore, in the bulk of the solution reactions of the type ... 

The silver deposition experiments of Sonnenfeld and Schardt (94) provide a representative example. After the deposition of silver on HOPG, the freshly plated surface was imaged in the presence of aqueous 0.05 M AgClO (Fig. 7)(94). Assuming a positive tip polarity is used, the STM tip will function as an anode and its potential will be that necessary to oxidize water, Ea jj2q/02 - -+0.95 V (pH - 7). The substrate cathode will drive the reduction of silver ion at the silver plated substrate at a formal potential of Ec Ag+/Ag V. Thus, an imaging window of AEp - 230 mV is... 

In a related study, silver microtubules were produced by chemical deposition [38]. Similar to electrochemical deposition, the surface of the membrane must first be modified, not with a silane but with a catalyst such as Sn ions. Initially, one side of the membrane is protected by tape (Figure 1.12b) and then the surface is activated with SnCh (Figure 1.12c). The activated membrane was then placed into a solution of silver-plating solution (Figure 1.12d). This resulted in the deposition of silver over the activated surface finally the alumina membrane was dissolved away. 

Figure 1.12 Stepwise synthesis scheme for chemical deposition of silver into an alumina membrane. (With kind permission from Springer Science + Business Media [38]. A. Huczko, Applied Physic A, 70, (2000), 365-376 Figure 1.7 Reprinted with permission from The Materials Research Society.)...

Platinum is the 75th most abundant element and, unlike many elements, is found in its pure elemental form in nature, as are deposits of silver and gold. Platinum is widely distributed over the Earth and is mined mainly in the Ural Mountains in Russia and in South Africa, Alaska, the western United States, Columbia in South America, and Ontario in Canada. When found in the mineral sperryhte (PtAs ), it is dissolved with aqua regia to form a precipitate called sponge that is then converted into platinum metal. It is also recovered as a by-product of nickel mining, mainly in Ontario, Canada. 

Argyrosis (deposition of silver in the eyes) appears to be the critical effect and is observed in workers exposed to silver compounds at concentrations in the range of 0.005-0.38mg/mh Disturbances with night vision and lens changes without visual impairment have been associated with argyrosis. ... 

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