Silver electrodeposition processes

The current density on the electrode from Fig. 12b, with a coverage of about 20%, is practically the same as on a completely covered graphite electrode, as can be seen from Fig. 11 at an overpotential of 120 mV This is because the exchange current density for the silver electrodeposition process from nitrate baths is extremely large.27,46... 

Application of complex salt electrolytes in metal electrodeposition processes was examined by comparison of silver electrodeposition processes from the simple (nitrate) and complex (ammonium) electrolytes [15]. Silver was deposited from 0.10 M AgNOs in 0.20 M HNO3 (the simple electrolyte) and 0.10 M AgNOs in 0.50 M (NH4)2S04 to which was added ammonium hydroxide to dissolve the precipitate of Ag sulfate (the complex electrolyte). The conductivities of both electrolytes were almost the same [3]. Silver was deposited onto a stationary vertical Pt cathode (1x1) cm placed in the middle of a cylindrical cell (diameter 6 cm and height 5 cm). The surface of the cell was covered by anode of a high purity Ag plate. Polarization curves were recorded at the Pt wire electrodes at which Ag from the ammonium complex electrolyte was previously electrodeposited. 

Based on a model on the features of the double-pulse technique, various structures of silver nanoparticles grown onto a thin ITO film covered glass plate were generated and characterized [30]. With this method, the conflict between both optimal conditions for nucleation and growth is partially defused. This is due to the amount of small seed additionally nucleated at the higher polarization and resolved as soon as the potential is switched over to the lower polarization of the growth pulse. The interaction of the pulse parameters was modeled, thus forming the basis for how the electrodeposition process of noble metal clusters can be variably controlled. 

Electrodeposition Processes Hasse et al. [366] have used in situ AFM for the detection of silver nucleation at the three-phase junction of the type metal-sUver halide-electrolyte solution. At this phase boundary, electrochemical reduction of submicrometer size silver halide crystals immobilized on the surface of gold and platinum electrodes took place. Following nucleation, the reaction advanced until the entire surface of the silver halide crystals was covered with 20 atomic layers of silver. Then, reduction was terminated. The obtained silver layer could be oxidized and the next layer of silver halide crystals became accessible for further reduction. 

Silica, silver, bioactive glass, heparin, and CaSiOs have been incorporated into the electrodeposition process of chitosan and HA to try and improve performance of composite coatings for biomedical implants that interface with bone tissue [116, 119, 134, 139, 149]. While the electrodeposition methods and mechanical and adhesion strength of the coatings are commonly reported in these studies, little biological data has been gathered on the response of cells or tissues to these composite coatings. 

Where the corrosion resistance of a coating depends upon its passivity, it is common to follow plating with a conversion coating process to strengthen the passive film. Zinc, cadmium and tin in particular are treated with chromate solutions which thicken their protective oxides and also incorporate in it complex chromates (see Section 1S.3). There are many proprietary processes, especially for zinc and cadmium. Simple immersion processes are used for all three coatings, while electrolytic passivation is us on tinplate lines. Chromate immersion processes are known to benefit copper, brass and silver electrodeposits, and electrolytic chromate treatments improve the performance of nickel and chromium coatings, but they are not used to the extent common for the three first named. 

The typical Pb granules obtained in the potentiostatic regime of electrolysis are shown in Fig. 2.34. Similar to silver granules, granules of various shapes were produced by the electrodeposition processes. The granules, such as octahedrons and hexagons, as weU as many various types of twinned particles single-twinned, multiply-twinned (MTPs), lamellar-twinned (LTPs), and many other complicated... 

Popov KI, Zivkovic PM, Nikolic ND (2012) Formation of disperse silver deposits by the electrodeposition processes at high overpotentials. Int J Electrochem Sci 7 686-696... 

They were obtained first with silver in the earliest experiments in electrochemistry (Pristley, 1803), and a large number of metals have been obtained in that form by electrodeposition processes since that time. Examples include Cu, Ni, Co, Fe, Pb, Sn, Mn, Zn, Cd, Pd, W, Pt. Detailed surveys of the field are available. 

The electrodeposition process can also be combined with an AAO template for the fabrication of a metal-embedded hollow nanotube structure, that is, Ni-embedded silica nanotubes, as demonstrated by Xu et al. [79]. The fabrication starts with the electrodeposition of multiple segments of Ag/Ni/Ag (3 pm/3 pm/ 3 pm) nanowires with a diameter of 300 nm on nanoporous AAO templates (Figure 13.7d). Subsequently, a hydrolysis reaction of tetraethyl orthosiUcate was performed for 2-5 h to coat a 70 nm thick silica layer. Then, Ag was selectively etched in a mixture (4 1 1) of methanol, hydrogen peroxide, and ammonia hydroxide to produce a hollow structure. Finally, Ag nanoparticles were functionalized on the surface by the reduction of Ag ions at 70 °C for 7 h in a composite solution of PVP (2.5xlO M in ethanol), silver nitrate (0.06 M), and ammonia hydroxide (0.12 M). The synthesized silica nanotubes exhibited a Ni-embedded hollow structure with Ag nanoparticles functionalized on the surface... 

Despite the fact that the electrodeposition of copper and silver at the water-DCE and the water-dichloromethane interfaces has been generally regarded as the first experimental evidence for heterogeneous ET at externally biased ITIES [171], a very limited amount of work has dealt with this type of process. This reaction has also theoretical interest because the molecular liquid-liquid interface can be seen as an ideal substrate for electrochemical nucleation studies due to the weak interactions between the interface and the newly formed phase and the lack of preferential nucleation sites always present at metallic electrodes. 

It is interesting to conclude this section with an example that, in a sense, brings the chapter full circle. The metallization of plastic materials used as metal substitutes is a process with actual and future commercial potential. Usually, plastics are plated after appropriate sensitization by an electroless process which involves reduction of metal ions (e.g. Ni2+, Cu2+) by chemical rather than electrical means.19 There seems no reason why the reducing agent should not be incorporated in the polymer and Murray and his collaborators101 have demonstrated that copper, silver, cobalt and nickel may each be electrodeposited on to films of [poly-Ru(bipy)2(4-vinylpyridine)2]2+ coated on to platinum electrodes. The metal reductions are mediated by the Ru1 and Ru° states of the polymer. 

The electrodeposition of thallium on Ag(l 10) is similar to that which takes place on the (111) face of silver [122]. The voltammogram shows well-defined structure in the formation of the first monolayer, and further deposition occurs before formation of the bulk deposit. Fig. 5.16c and d display the results for the isotropic and anisotropic response respectively. The magnitude and phase of o 2 were modeled by a constant contribution from the adatoms throughout the adsorption process (Eq. (5.4)). Values of x /Xin = 0-94 and a phase shift of 131° were obtained. As with Ag(lll), an enhancement in the anisotropic response was observed beyond 1 monolayer and was attributed to a similar resonance effect. 

Classical electrodeposition has limited application today because of the development of more sophisticated methods. It is a slow and tedious process, and there is a need for large samples. However, it still represents one of the most precise quantitative techniques for the determination of copper, cadmium, silver, and nickel. The best conditions for the determination of these and other ions by electrodeposition are summarized in Table 3.5. 

The electrodeposition of silver from chloroaluminate ionic liquids has been studied by several authors [45-47], Katayama et al. [48] reported that the room-temperature ionic liquid l-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) is applicable as an alternative electroplating bath for silver. The ionic liquid [EMIM]BF4 is superior to the chloroaluminate systems since the electrodeposition of silver can be performed without contamination of aluminum. Electrodeposition of silver in the ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and l-butyl-3-methylimidazoliumhexafluorophosphate was also reported [49], Recently we showed that isolated silver nanoparticles can be deposited on the surface of the ionic liquid Tbutyl-3-methylimidazolium trifluoromethylsulfonate ([BMIMJTfO) by electrochemical reduction with free electrons from low-temperature plasma [50] (see Chapter 10). This unusual reaction represents a novel electrochemical process, leading to the reproducible growth of nanoscale materials. In our experience silver is quite easy to deposit in many air- and water-stable ionic liquids. 

Electrolytic dissolution processes will be discussed here since it is normally very difficult to electrodeposit semiconductors. Results obtained with silver on one hand and with germanium on the other will be presented since these cases are best understood. 

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