Alloy electrochemical alloying

Metal halide Eff.10 (%) alloying Electrochemical alloying efficiency of metals with lithium [27]... 

Fig. VIII-2. Scanning tunneling microscopy images illustrating the capabilities of the technique (a) a 10-nm-square scan of a silicon(lll) crystal showing defects and terraces from Ref. 21 (b) the surface of an Ag-Au alloy electrode being electrochemically roughened at 0.2 V and 2 and 42 min after reaching 0.70 V (from Ref. 22) (c) an island of CO molecules on a platinum surface formed by sliding the molecules along the surface with the STM tip (from Ref. 41).

Marcus P, Teissier A and Oudar J 1984 The influence of sulfur on the dissolution and the passivation of a nickel-iron alloy. 1. Electrochemical and radiotracer measurements Corrosion Sc . 24 259... 

Chen S J, Sanz F, Ogletree D F, Hallmark V M, Devine T M and Salmeron M 1993 Selective dissolution of copper from Au-rich Au-Cu alloys an electrochemical STS study Surf. Sc . 292 289... 

In certain alloys and under certain environmental conditions, selective removal of one metal (the most electrochemically active) can occur that results in a weakening of the strength of the component. The most common example is dezincification of brass [164, 165]. The residual copper lacks mechanical strength. 

Richarz F, Wohimann B, Vogel U, Floffschulz FI and Wandelt K 1995 Surface and electrochemical characterization of PtRu alloys Surf. Scl. 335 361-71... 

A viable electrocatalyst operating with minimal polarization for the direct electrochemical oxidation of methanol at low temperature would strongly enhance the competitive position of fuel ceU systems for transportation appHcations. Fuel ceUs that directiy oxidize CH OH would eliminate the need for an external reformer in fuel ceU systems resulting in a less complex, more lightweight system occupying less volume and having lower cost. Improvement in the performance of PFFCs for transportation appHcations, which operate close to ambient temperatures and utilize steam-reformed CH OH, would be a more CO-tolerant anode electrocatalyst. Such an electrocatalyst would reduce the need to pretreat the steam-reformed CH OH to lower the CO content in the anode fuel gas. Platinum—mthenium alloys show encouraging performance for the direct oxidation of methanol. 

Production. Indium is recovered from fumes, dusts, slags, residues, and alloys from zinc or lead—zinc smelting. The source material itself, a reduction bullion, flue dust, or electrolytic slime intermediate, is leached with sulfuric or hydrochloric acid, the solutions are concentrated, if necessary, and cmde indium is recovered as 99+% metal. This impure indium is then refined to 99.99%, 99.999%, 99.9999%, or higher grades by a variety of classical chemical and electrochemical processes. 

Lead—Calcium-Tin Alloys. Tin additions to lead—calcium and lead—calcium—aluminum alloys enhances the mechanical (8) and electrochemical properties (12). Tin additions reduce the rate of aging compared to lead—calcium binary alloys. The positive grid alloys for maintenance-free lead—calcium batteries contain 0.3—1.2 wt % tin and also aluminum. 

Tia is also used as an ahoyiag element ia lead—antimony alloys to improve fluidity and to prevent drossiag, ia lead—calcium alloys to improve mechanical properties and enhance electrochemical performance, ia lead—arsenic alloys to maintain a stable composition, and as an additive to low melting alloys. 

Manufacturing engineers wishing to use ECM processes in industry need to address the challenge of proper tool design. The cost of design can be as much as 20% of the cost of an electrochemical machine for complex components. PredictabiUty of overcuts obtained for specific appHcations and the particular electrolytes to be used for the alloy metals that have to be machined must also be considered along with specific controls and limits on the ECM equipment needed. 

G. Hor2, Electrochem. Soc. Proc. Symp. Prop. High Temp. Alloys (77-1), 753 (1976). 

The resistance to corrosion of some alloy sheet is improved by cladding the sheet with a thin layer of aluminum or aluminum alloy that is anodic to the base alloy. These anodic layers are typically 5—10% of the sheet thickness. Under corrosive conditions, the cladding provides electrochemical protection to the core at cut edges, abrasions, and fastener holes by corroding preferentially. Aircraft skin sheet is an example of such a clad product. 

Finishes for aluminum products can be both decorative and useful. Processes in use include anodic oxidation, chemical conversion coating, electrochemical graining, electroplating (qv), thin film deposition, porcelain enameling, and painting. Some alloys respond better than others to such treatments. 

The proper selection of the lead alloy depends on the intended use and the economics of the lead—acid battery appHcation. The metallurgical and electrochemical aspects of the lead are discussed in the Hterature in a comprehensive manner (81,85—87) as are trends of lead alloy use for manufacture of battery grids (88). 

Fluorine. Fluorine is the most reactive product of all electrochemical processes (63). It was first prepared in 1886, but important quantities of fluorine were not produced until the early 1940s. Fluorine was required for the production of uranium hexafluoride [7783-81 -5] UF, necessary for the enrichment of U (see DIFFUSION SEPARATION METHODS). The Manhattan Project in the United States and the Tube Alloy project in England contained parallel developments of electrolytic cells for fluorine production (63). The principal use of fluorine continues to be the production of UF from UF. ... 

The direct electrochemical oxidation of manganese alloys was developed and commercialized at the Rustavi Chemical Combine in the Georgian Repubhc (formerly the USSR). The electrode reactions are... 

Lithium. Several processes for lithium [7439-93-2], Li, metal production have been developed. The Downs cell with LiCl—KCl electrolyte produces lithium ia much the same manner as sodium is produced. Lithium metal or lithium—aluminum alloy can be produced from a mixture of fused chloride salts (108). Granular Li metal has been produced electrochemically from lithium salts ia organic solvents (109) (see LiTHlUM AND LITHIUM compounds). 

Anodic Protection This electrochemical method relies on an external potential control system (potentiostat) to maintain the metal or alloy in a noncorroding (passive) condition. Practical applications include acid coolers in sulfuric acid plants and storage tanks for sulfuric acid. 

FIG. 28-9 Typical electrochemical polarization curve for an active/passive alloy (with cathodic trace) showing active, passive, and transpassive regions and other important features. (NOTE Epp = primary passive potential, Ecaa- — freely corroding potential). 

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