Spontaneous electrodeposition

A special transistorized circuit was also constructed (118) to minimize spontaneous electrodeposition. Siver adsorption occurred when tertrate, citrate, EDTA or their mixtures were present, and the response to silver was linear in the range 2 x 10 - 1 x 10 M after 10 min from a 1 mM EDTA/3mM tartrate solution. No significant interfernces were noted, including mercury(II) and copper(II). 

Electrodeposition on metal disks is used to prepare very thin sources of the radionuclides discussed in Section 3.7. At very low concentrations in water, certain radionuclides may be deposited on metal disks by sorption or spontaneous electrodeposition (Blanchard et al. 1960). The former yields a relatively low percent deposition on more noble metals, as in the case of deposited on gold. In contrast, spontaneous electrodepostion results in near 100% yield on a less noble metal, for example, in depositing n Ag or divalent Fe on magnesium. Yield must be determined separately for this source preparation step and then combined with the yield observed for the chemical purification steps. 

Switzer et al. found that CU/CU2O layered nanostructures are electrodeposited with spontaneous potential oscillations from alkaline Cu(II)-lactate solution in a self-... 

Saliba, R., Mingotaud, C., Argoul, F. and Ravaine, S. (2002) Spontaneous oscillations in gold electrodeposition. Electrochem. Commun., 4, 629-632. 

Electrodeposition of metal onto structured objects, such as circuits, is controlled in part by a template. At the same time, the deposit must fill all the recesses uniformly and seamlessly, the texture and crystal structure must fall within tolerances, and the quality of the features must be sustained over a large workpiece. The distribution of material within recesses or onto widely separated portions of the workpiece is subject to a limited number of macroscopic control-parameters such as applied potential and plating bath composition. Success therefore depends on exploitation of the natural pathways of the process. The spontaneous and unconstrained development of structure must be taken into consideration in the production of highly organized and functional patterns. 

Polonium may be purified by various processes. Such purification methods include precipitation of polonium as sulfide and then decomposing the sulfide at elevated temperatures spontaneous decomposition of polonium onto a nickel or copper surface and electrolysis of nitric acid solutions of polonium-bismuth mixture. In electrolytic purification polonium is electrodeposited onto a platinum, gold, nickel, or carbon electrode. 

Much of the early literature of polonium describes methods for separating it from these mixtures many of these have subsequently been adapted to the separation of milligram amounts of polonium from irradiated bismuth and to its purification. The methods range from a simple chemical separation of the element with a tellurium carrier to its electrodeposition on to a more noble metal or its spontaneous electrochemical replacement on the surface of a less noble metal. 

Electrochemical cells may be one of two types. Should a current spontaneously flow on connecting the electrodes via a conductor, the cell is a galvanic cell. An electrolytic cell is one in which reactions occur when an external voltage greater than the reversible potential of the cell is applied. Simple examples involving copper are given in Figure 1. It is the electrolytic cell which is of interest in the electrodeposition of metals. 

Solutions containing the metal, most commonly in nitric acid, will deposit the metal on a platinnm electrode by electrodeposition. Polonium metal is deposited spontaneously from such solutions on to metals such as silver or nickel. The metal can be sublimed off such support metals at low pressures. Thermal decomposition of polonium sulfide also yields the metal. In much the same way as tellurium, the metal can be obtained from its solutions by the action of reducing agents such as hydrazine, tin(II) ion, titanium(III) ion, and dithionite. Such metal precipitates appear as gray-black powders. Thin foils, silvery in color, have been prepared by vacuum sublimation of the metal. 

In order to decrease dispersion in particle size during electrodeposition, two important principles should be taken into account. Firstly, the crystal seed formation has to occur spontaneously, thus preventing progressive nucleation. Secondly, the crystal growth has to be conducted at a slow rate, that is, at low overpotential. Penner et al. [22-26] has elucidated the importance and coherence of these fundamental principles. 

Ru-decorated Pt surfaces obtained by spontaneous deposition. These studies were reviewed recently here we give a brief summary. Several methods were used to obtain Ru-modified Pt surfaces, including electrodeposition of Ru ad-atoms,electrochemical, spontaneous deposition, UHV deposition" and organometallic chemistry. However, these various methodologies produce different amounts of metallic vs. oxidized Ru at-... 

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