Dissolution magnesium alloys

Moreover, the magnesinm deposition on silver substrate from 0.25 M solution of 60a in THE is accompanied " by the formation of silver-magnesium alloy, which decreases the overpotential of deposition-dissolution processes and promotes the cychng efficiency. 

Galvanized steel is a common example of galvanic coupling where steel (Fe), with a standard electrode potential of —0.440 V vs. SHE, is cathodicaUy protected by zinc, which has a more active standard electrode potential of —0.763 V. Obviously, zinc is not a corrosion-resistant metal and cannot be classified as a barrier coating. It protects steel from corrosion through its sacrificial properties. Because zinc is less noble than iron in terms of the standard electrode potentials, it acts as an anode. The sacrificial anode (zinc) is continuously consumed by anodic dissolution reaction and protects the underlying metal (iron in steel) from corrosion. In practice, sacrificial anodes are comprised of zinc, magnesium alloys, or aluminum. 

Lead hydride is the least well characterized of the Group IVB hydrides. It is formed along with hydrogen, on the electrolysis of dilute sulphuric add with lead electrodes, and by the dissolution of lead-magnesium alloy in dilute add. The hydride of lead formed in small quantities is assumed to be PbH4 (b.p.--13°C)m. 

The unequal attack which occurs in tap water, condensate and other mild electrolytes may lead to perforations of thin-gauge sheet and even to deep pitting of castings. In stronger electrolytes the effect is variable. In chloride solutions such as sea-water, attack on the metal usually results in the pitting of some areas only, but where the metal surface has been rendered reactive, as by shot blasting, attack may be so rapid that uniform dissolution over the whole surface may occur. In either case magnesium-base alloys are not usually suitable for use in aqueous liquids since they are not intrinsically resistant to these electrolytes. 

Induced dissolution is also a well known phenomenon and frequently applied in chemical analysis. To dissolve platinum easily it was suggested by Ropp that the sample should be alloyed with silver or copper, the alloys being easily soluble even in dilute acids. Anhydrous chromic chloride, insoluble in water and dilute acids, becomes easily soluble by adding metallic magnesium or zinc to the dilute acid . In this case the chromium(III) compound is reduced to chro-mium(II), which will be oxidized by the solvent to water-soluble chromium(III)... 

The anodic dissolution of magnesium. Mg, has been reported as possible in the basic or buffered ionic liquids that consist of EMI+ and DMPI [20]. However, the deposition of Mg is impossible due to the instability of metallic Mg against these organic cations, whereas the formation of Al-Mg alloys containing Mg up to 2.2 at% has been observed in the acidic EMICI-AICI3 ionic liquid [21]. Calcium and strontium dichlorides, CaCla and SrCla, are soluble in an acidic EMICI-AICI3 ionic liquid and the co-deposition of calcium and strontium with bismuth and copper has been examined in the acidic ionic liquid [22]. 

It is well known that aluminum as such is fairly passive, because a very dense and uniform aluminum oxide AI2O3 layer is formed onto the metal to protect the metal from corrosion. Highly ductile light weight aluminum alloys that are passed through specific heat treatments can, however, make aluminum susceptible to corrosion. These materials may contain alloying elements such as magnesium and/or copper, which alter and complicate the corrosion behavior of aluminum. Typical forms of corrosion for the alloys are localized and pit corrosion. Due to the dense structure of the aluminum oxide layer, the corrosion rate of aluminum alloys is, however, substantially slower compared with corrosion/dissolution of CRS or HDG steel [15]. 

This chapter provides an overview of the corrosion mechanisms of typical Mg alloys, most of which contain two or more phases. Magnesium (Mg) is a reactive metal and corrosion protection is an issue of importance [1] particularly for the automobile industry. The rapid increase in Mg use is due to its lightweight and good casting capabilities, particularly its ability to be diecast into large, thin sections. Typical examples are automobile seats, instrument panels, computer cases, etc. Reviews [1-4] and our early research [5-9] have indicated that the poor corrosion resistance of Mg alloys results from (a) the high intrinsic dissolution tendency of magnesium, which... 

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