Anodic dissolution selective

Figure 6. Bipolar precipitates consisting of an inner anion-selective layer and an outer cation-selective layer.19 When the electrode is polarized to the more noble side, protons and chloride ions are kept from permeating through the film, so that anodic dissolution of the substrate metal is blocked. (Reproduced from N. Sato, Corrosion, 45 354, 1989, Fig. 24 with permission of NACE International.)...

Bard AJ, Wrighton MS (1977) Thermodynamic potential forthe anodic dissolution of n-type semiconductors - A crucial factor controlling durability and efficiency in photoelectrochem-ical cells and an important criterion in the selection of new electrode/electrolyte systems. J Electrochem Soc 124 1706-1710... 

Different electrochemical surface treatments have found extensive use for the purposes of providing metal parts with particular properties, appearance, and shape. This includes the apphcation of superficial oxide or salt films (see Section 16.3), metal films (Section 16.5), and a number of methods that exploit the selective anodic dissolution of different segments of the metal surface. We examine briefly a few examples of the latter type. 

Different views exist as to the reasons for selective dissolution of the asperities. According to older concepts, convection of the liquid is hindered in the solution layers filling recesses hence, reaction products will accumulate there and raise the concentration and viscosity in these layers. Both factors tend to lower a metal s anodic dissolution rate relative to that at raised points. According to other concepts, a surface condition close to passive arises during electropolishing. In this case, the conditions for passivation of the metal at raised points differ from those in recesses. 

The electrochemical machining (ECM) of metals rests on the selective local anodic dissolution of metal. It is used to give metal parts the required shape and size, to drill holes, create hollows, cut shaped slots, and fashion parts of a complex pattern (e.g., the blades of gas turbines). It is an advantage of this method that it can also be used for hard metals (high-alloy steels and other alloys, metals in the quenched state, etc.). 

Dieker et al.67 used a similar method but applied a dropping amalgam electrode (DAE) and followed amperometrically by means of pulse polarography the anodic dissolution wave of mercury in the presence of an excess of ligand by appropriate choices of pH and titrant they achieved selective determinations of metal ions at low concentrations. 

The obtained results show that the surface of anodized aluminum after anodic alumina selective dissolution contains sharp stable tips. Such structures may be used for characterization of curvature radius of SPM tips, even ultra-sharp tips. The main advantages of the developed structure are simplicity and reproducibility of its fabrication. 

In early attempts to oxidize hydrocarbons electrochemically, organic solvents and corrosion-resistant electrodes (PbO, C, Pt) were used to overcome low reactant solubility and anode dissolution at extreme potentials, -I-1.8 V and up to 4.5 V (326, 327). The primary anodic reaction was usually oxygen evolution or solvent decomposition. The electrode material, nonetheless, affected the product even at the small attainable yields. Thus, toluene oxidized to traces of aldehydes on PbO2 (333), while on Pt it yielded up to 19% benzaldehyde (326). The catalytic efifect of the anode, however, on rate and selectivity was not realized. 

Huang JF, Sun IW (2004) Formation of nanoporous platinum by selective anodic dissolution of PtZn surface in Lewis addic zinc chloride -l-ethyl-3-methylimidazolium chloride ionic liquid. Chem Mater 16 1829-1835... 

Let us suppose the anodic dissolution of metals occurring under an anion-selective corrosion precipitate layer in chloride solution. The anodic corrosion current carries chloride ions across the anion-selective precipitate layer into an occluded solution under the layer as shown in... 

The STM result that dissolution of Pd atoms occurs selectively at step (disordered) sites provided the inqietus for an additional stuify which demonstrated that the I(ads)-catalyzed anodic dissolution process is able to regenerate an ordered Pd(l 11) surface from one that had been subjected to extensive Ar -ion bombardment [8]. This particular reordering reaction is unique because it occurs (i) in the absence of bulk conosive reagent, and (ii) only if a chemisorbed layer of iodine is present. This process may be viewed similarly to digital etching [9] under electrochemical conditions [10] except that (a) bulk material is not needed to replenish the adsorbed iodine that activates the surface, and (b) the dissolution process does not cease even after the atomically smooth surface has been regenerated. 

Over a decade, Bandi and co-workers have employed EGA-DTA techniques to determine second-phase compounds isolated from steels by selective chemical or anodic dissolution of the matrix. This method has been used qualitatively to identify and quantitatively to determine approximately 35 carbides, carbonitrides, and nitrides, some of which could not be identified... 

A final constraint on selection of electrode materials is frequently imposed by the problem of their corrosion, or oxidation. Thus accepting that a reduction such as that of ethene occurs over the potential range + 0.1 V to — 0.1 V, a number of metals such as Fe, Co, and Ni will not be stable, at least in more acidic solutions, but will corrode by means of the anodic dissolution reactions-... 

Fig. 2 Concentration profile of In in the near surface region of a Sngsins electrode due to the selective anodic dissolution of In in 3 N NaCi -f 0,01 N HCI at 25 °C and h = -0.47 V. Open circles from microprobe measurements, solid line calculated from Eq. (8) for = 0 and O = 5 x IQ- i cm s T (From Ref [13].)...

Fig. 5 Formation of cracks in the surface of brittle 5-Zn—Fe (ZnsiEey) due to the selective anodic dissolution ofZn (dezincification) 236 h anodic polarization in 1 N Na2SO4/0.01 N H2SO4 at room temperature and h = —0.7 V. Large pores at the bottom of the image result from the metallurgical preparation of the alloy. Light optical micrograph of metallographic cross section. (From Ref [27].)...

Fig. 10 Transmission electron micrograph of the microstructure resulting from selective anodic dissolution of Cu from a CusAu electrode (50 s anodic polarization at I = 1 mA cm in 1 M H2SO4). Black network is Au-rich Au j. jj), white spots are pores. (From Ref [52], with permission.)...

I. K. Marshakov, A. V. Vvedenskii, V. Y. Kondrashin et al., Anodnoe Rastvorenie i Sdektivnaya Korroziya Splavov (Anodic Dissolution and Selective Corrosion of Alloys), Voronezh Gos. University, Voronezh, 1988. 

Instead of chemically generated electrons as reducers, the electrolytic reduction of metal salts represents a successful alternative in cormection with the fabrication of tetra-alkylammonium salt-stabilized nanopartides [159-165]. The first step comprises an oxidative anodic dissolution of the corresponding metal, followed by the formation of zerovalent metal atoms at the cathode. Nucleation and particle growth then follow, some of which is stopped by the addition of a tetra-alkylammonium salt. This technique not only prevents the formation of byproducts but also allows a rather good size-selectivity high current densities lead to small particles, while low current densities yield larger spedes. Ammonium salt-protected nanopartides of Ti, Fe, Co, Ni, Pd, Pt, Ag, and Au may also be prepared in this way. 

In maskless EMM, there will not be any photoresist mask on the surface of the workpiece sample. Metal dissolution takes place from the desired area of the workpiece in a very selective and controlled way. Highly localized selective metal dissolution from the surface of the workpiece can generate a designed pattern or shape in a 2D or 3D scale. Anodic dissolution in maskless EMM is controlled by the current density, which depends on various predominant machining parameters and anodic reaction pattern. An lEG between the workpiece surface and tool is maintained at a very low value such that stray current effect is minimized. Passivating electrolyte is suitable for maskless EMM due to its ability to form transpassive oxide films and evolve oxygen in the stray current zone. Here, current efficiency varies as a function of the distance from the machining area hence, metal removal is more selective and localized across the zone of the workpiece surface where it faces the tool. 

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