Electrolyte, dissolution

In some cases, particularly with iaactive metals, electrolytic cells are the primary method of manufacture of the fluoroborate solution. The manufacture of Sn, Pb, Cu, and Ni fluoroborates by electrolytic dissolution (87,88) is patented. A typical cell for continous production consists of a polyethylene-lined tank with tin anodes at the bottom and a mercury pool (ia a porous basket) cathode near the top (88). Pluoroboric acid is added to the cell and electrolysis is begun. As tin fluoroborate is generated, differences ia specific gravity cause the product to layer at the bottom of the cell. When the desired concentration is reached ia this layer, the heavy solution is drawn from the bottom and fresh HBP is added to the top of the cell continuously. The direct reaction of tin with HBP is slow but can be accelerated by passiag air or oxygen through the solution (89). The stannic fluoroborate is reduced by reaction with mossy tin under an iaert atmosphere. In earlier procedures, HBP reacted with hydrated stannous oxide. 

Electrical conductivity is a critical issue in nonaqueous electrochemistry, since the use of nonaqueous solvents, which are usually less polar than water, means worse electrolyte dissolution, worse charge separation, and, hence, worse electrical conductivity compared with aqueous solutions. In this section, a short course on electrical conductivity in liquid solutions is given, followed by several useful tables summarizing representative data on solution conductivity and conductivity parameters. 

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. 

The situation here is very unusual in that the breaking of a single chemical bond at a solid surface can be direcdy recognized. Fig. 3 shows the electrolytic dissolution of two n-type Ge electrodes, where the supply of holes is limited, which is to be contrasted to the dissolution of a p-type electrode where there is an unlimited supply of holes at the surface (7). As shown in Fig. 4, the dissolution rate can also be limited by the supply of chemical species needed for the formation of the final ions in solution (7). Fig. 4 also shows that hydroxyl ions lead to formation of metagermanate ions much faster than do water molecules. A similar behavior has also been found with fluoride ions. 

Dissolution and Deposition Potentials.—If a metal is placed in a solution of its ions a reversible electrode represented by M, is set up suppose its potential is E, Imagine now that an external source of potential is applied to this electrode so as to make it an anode of an electrolytic cell (p. 8) this will have the effect of increasing the potential, and since the electrode is reversible it will immediately commence to dissolve (cf. p. 184). It follows, therefore, that when a metallic electrode is made an anode, it wnll begin to dissolve as soon as its potential exceeds the reversible value E by an infinitesimal amount. In other words, the electrolytic dissolution potential of a metal when made an anode should be equal to its reversible (oxidation) potential (cf. p. 243) in the given electrolyte. The actual value depends, of course, on the concentration, or activity, in the solution of the ions with respect to which the metal is reversible. On the other hand, if the particular electrode under consideration is made a cathode, so that its potential is reduced below the reversible value, the reverse process, viz., deposition... 

Pretorius et al. proposed the electrolytic dissolution of iron in a tapwater/NaCl electrolyte using mild steel electrodes as a means of producing ferrous ions that could be used to precipitate phosphorus from wastewater [55]. The cost of this electrolyti-cally produced iron was found to compare favorably with commercially available iron salts which tend to contaminate water supplies. 

Chemical or electrolytic dissolution. The disadvantage of this method is the non-uniform removal of the target layers. Different crystallographic faces, local structures and small regions with different electrolytical behavior dissolve at different rates. 

The first-cycle raffinate wastes produced at the ICPP are the acid aluminum waste from various test reactor fuels, fluoride-bearing waste from zirconium-matrix fuel, a small amount of stainless steel sulfate waste from fuel from developmental reactors such as the Organic Moderated Reactor Experiment (OMRE), acid stainless steel nitrate waste from the electrolytic dissolution of Experimental Breeder Reactor-II (EBR-II) reactor fuel, and an acid waste from the recovery of uranium... 

Electrolytic Dissolution. The electrolytic dissolution of tungsten and tungsten alloy scrap in alkaline media (NaOH, Na2C03, NH3, (NH4)2C03) is used technically to recycle tungsten into the APT production (see Section 5.2.3.6.). 

TABLE 5.3. Typical Energetic and Dissolution Parameters of the Electrolytic Dissolution Process for Different Timgsten Scraps [5.30]... 

Flow analysis is associated with wet chemistry thus, solid samples of diverse origin, e.g., alloys, soils, sediments, sludges and foodstuffs, are normally subjected to in-line treatment in order to form a liquid analyte zone. The two most common examples are in-line sample electrolytic dissolution, where the analyte zone is formed as a consequence of applying a direct electric current to the solid sample, and sequential extractions of soils and sediments. 

Since the pioneering work of Chimside et al. on the spectrophotometric determination of boron in metallic nickel [23], electrolytic dissolution has been exploited for the direct analysis of several solid conductive materials, including metals, ores and alloys. 

In 1983, electrolytic dissolution was exploited in the metallurgical industry for the batchwise determination of soluble aluminium in steels by flame atomic absorption spectrometry [27]. A specially designed spoon transferred a few millilitres of the red-hot molten material to a diskshaped mould where the material solidified when cooled. The resulting pellet was placed on the electrolytic chamber and, after the dissolution step, an aliquot of the electrolytic solution was taken and analysed for aluminium. With an advanced electrolytic chamber design, electrolysis time was reduced to about 40 s. The feasibility of batchwise electrolytic... 

For flow analysis incorporating electrolytic dissolution, very small characteristic masses, often below the ng level, are reported for metal determinations. This is a consequence of the analytical sensitivity and the small sample volume required, and is an attractive feature of in-line electrolytic dissolution. As a very small dissolved mass is required, rapid electrolysis (a few seconds) under a moderate current (mA) is sufficient. This was demonstrated in the flow-based spectrophotometric determination of aluminium in steels [29]. The analyte was oxidised and dissolved in a flowing acidic electrolytic solution that also acted as the sample carrier stream of the flow analyser. This innovation was further applied to the spectrophotometric determination of molybdenum in alloys [30]. In both applications, the anode was the polished metallic sample, and the cathode was a gold or silver coated electrode placed at the bottom of the electrolytic chamber (Fig. 8.4). A silicone rubber sheet (adapter) was placed between the solid sample and the chamber walls in order to avoid leakage and to define the sample surface area to be dissolved. This classical geometry is the most commonly used. 

Sampling by means of electrolytic dissolution permits concentration gradients along the metallic sample to be determined, thereby providing information on sample homogeneity and/or changes in analyte concentration near the alloy surface. Surprisingly, the potential of this approach has not been exploited. 

Spectrophotometry was used in the original proposal for electrolytic dissolution [23] and in the first flow-based applications [24,29] but detection techniques such as ICP-OES [31—33], ICP-MS [34], FAAS [26,35] and ET-AAS [36] are now more commonly used. In order to avoid the need for certified reference materials to determine accuracy, alternative procedures for calibration have been proposed [25]. The fundamental aspects of the technique and applications have been reviewed elsewhere [37]. 

I.G. Souza, H. Bergamin-Filho, F.J. Krug, J.A. Nobrega, P.V. Oliveira, B.F. Reis, M.F. Gine, On-line electrolytic dissolution of alloys in flow-injection analysis. Part 3. Multi-elemental analysis of stainless steels by inductively coupled plasma atomic emission spectrometry, Anal. Chim. Acta 245 (1991) 211. 

M. Aimoto, H. Kondo, A. Ono, Determination of silicon in high-silicon electrical steel by ICP-AES with on-line sample electrolytic dissolution, Anal. Sci. 23 (2007) 1367. 

D.X. Yuan, X.R. Wang, P.Y. Yang, B.L. Huang, On-line electrolytic dissolution of solid metal samples and determination of copper in aluminium alloys by flame atomic absorption spectrometry, Anal. Chim. Acta 243 (1991) 65. 

Electrolytic dissolution in nitric acid has been used at the Savannah River [B22] and Idaho Qiemical Processing plants [AlO, All] to dissolve a wide variety of fuels and cladding materials, including uranium alloys, stainless steel, aluminum, zircaloy, and nichrome. The electrolytic dissolver developed by du Pont [B22], pictured in Fig. 10.4, uses niobium anodes and cathodes, with the former coated with 0.25 mm of platinum to prevent anodic corrosion. Metallic fuel to be dissolved is held in an alundum insulating frame supported by a niobium basket placed between anode and cathode and electrically insulated from them. Fuel surfaces facing the cathode undergo anodic dissolution in a reaction such as... 

A10. Aylward, J. R., and E. M. Whitener Electrolytic Dissolution of Nuclear Fuels, Part II. 

H. Bergamin F-, F. J. Krug, E. A. G. Zagatto, E. C. Arruda, and C. A. Coutinho, On-Line Electrolytic Dissolution of Alloys in Flow-Injection Analysis. Part 1. Principles and Application in the Determination of Soluble Aluminium in Steels. Anal. Chim. Acta, 190 (1986) 177. 

The chemistry of the process is presented in Figure 9.1, whereas the mechanism of the process is presented in Figure 9.2. The rate of bond metal dissolution is highest at the metal-diamond interface particles in other words, the tendency of electrolytic dissolution is to expose the diamond particles (Chen and Li I, 2000). In addition, the metal dissolution rate increases with diamond concentration particles (Chen and Li 1,2000). 

Similarly, the electrolytic dissolution of Fe anode in water produces ... 

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