Indium, anodic dissolution

Electrolysis in the cell Pt/MeC02H H20(trace)/In caused dissolution of the indium anode and formation of fine feathery crystals of the metal on the cathode. This material slowly reacted with the electrolyte to give crystals of In(OAc)2 which could be converted to In(OAc)3 on boiling with glacial acetic acid. It seems likely that the crystal lattice consists of In1 4- In111 + OAc-, but no detailed structure could be obtained.31 This system warrants further investigation in view of work on the analogous thallium system (see below). 

With particular attention to excess interface electrons, an anodic procedure has been performed for n-type InP (100). The anodic voltammogram was similar to Figure 15. No specific characteristics have been observed and a stable overlayer of indium sulfide has been formed. Equations 4, 5 and 6 show the reaction mechanism of aqueous (NH S solution with the InP substrate during anodic sulfidation. Equation 5 is responsible for the anodic dissolution of InP in (NH S solution when the hydroxyl group is dominating the solution. Equation 6 is the one responsible for sulfidation and depositing sulfides. 

It is generally assumed that ions which can accelerate either or both partial reactions in a corrosion process are capable of being adsorbed on the iron surface. Thus it is known that hydrogen sulfide ions which accelerate both partial reactions of acid corrosion (although predominantly the anodic one), and formic acid molecules which catalyze the cathodic partial reaction but inhibit the anodic one, as well as commercial inhibitors which reduce both partial reactions, are in fact adsorbed on the iron surface. As a consequence the mere fact that adsorption takes place cannot be used to predict an expected change in corrosion rate as it is also known that halide ions cat-alize the anodic dissolution of indium, while hydroxyl adsorption catalyzes the anodic dissolution of iron. Furthermore, it is also known that certain ions can act either as a catalyst or an inhibitor when adsorbed on the metal surface depending on the type of metal considered. Kolotyrkin (18) observed that the adsorp-... 

Cathodic polarization of /7-type InP single crystals in 1N H2SO4 leads to phosphane and metallic indium [31] according to InP + 3H+ + 3e" PH3 + In. In IN KOH or IN KF, formation of PH3 and indium is only observed at current densities 10 A/cm. Anodic dissolution of p-InP in KOH solution yields PH3, probably by disproportionation of the intermediately formed H3PO3. Phosphane also forms in acidic (1N H2SO4,1N NH4F HF, 1N HF) or neutral electrolytes (0.8N KF, IN NH4F) [31]. 

Another approach to metal deposition involves formation of metal ions by anodic dissolution of a microelectrode made of the same metal to be deposited (119d-119f, 124). In one example, gold patterns were fabricated in this way on indium tin oxide (124). The An UME was anodically dissolved in bromide-containing solution to form AuBr4 ions, which diffused to the negatively biased indium tin oxide substrate and were reduced to form micropattems of Au. 

Contact with steel, though less harmful, may accelerate attack on aluminium, but in some natural waters and other special cases aluminium can be protected at the expense of ferrous materials. Stainless steels may increase attack on aluminium, notably in sea-water or marine atmospheres, but the high electrical resistance of the two surface oxide films minimises bimetallic effects in less aggressive environments. Titanium appears to behave in a similar manner to steel. Aluminium-zinc alloys are used as sacrificial anodes for steel structures, usually with trace additions of tin, indium or mercury to enhance dissolution characteristics and render the operating potential more electronegative. 

In principle, the same observations have been made with InP. In this case, however, it is more difficult to find the proper conditions for electrochemical measurements. This is caused by the fact that InP is rather easily reduced under cathodic polarization, leading to the formation of metallic indium at the surface. Subsequent anodic polarization then leads to the formation of In203 which can easily influence the corresponding current-potential curves [44]. The anodic corrosion of InP was investigated with respect to the participation of electrons in the dissolution mechanism, including IMPS measurements [45]. These measurements have yielded y = 3 at low intensities. Accordingly, three electrons are injected into the conduction band besides the consumption of three holes, whereas at higher intensities five holes are used for the dissolution process and one electron is in-... 

Taking into account the dissolution potential of aluminium, anodes can be made either in zinc or in a special aluminium alloy called Hydral , which contains indium (0.015-0.025%) or tin (0.10-0.20%). Magnesium anodes must not be used, because they lower the potential too much and will thus lead to severe cathodic corrosion of aluminium. 

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