Solubility aluminium-iron phases

Aluminium-Iron. Figure 3.1-13 shows the Al-rich part of this system. The solubility of Fe in Al is very low. In the range shown AlsFe is formed by a peritectic reaction at 1160 °C. The eutectic between the Al phase and AIbFc crystallises in a degenerate manner to form brittle needles of Al3Fe. The formation of AIbFb needles is also occurring in Al—Fe—Si alloys such as commercially (available) pure aluminium (Fig. 3.1-14). 

Intercrystalline corrosion is caused by a difference in the electrochemical potentials between the bulk of the grain and the grain boundaries where intermetallic phases precipitate. The grain (also called the matrix) comprises a solid solution and dispersed intermetallic compounds. At room temperature, the solubility of iron, nickel, or magnesium in aluminium is so low that the solid solution has a potential very close to that of unalloyed aluminium 1050A. However, when the solid solution is supersaturated or enriched at ambient temperature, the potential depends on the concentration of the alloying element (Figure B.1.8). 

In addition to the soluble chemical species and possible solid phase species described in the previous sections no discussion on speciation can be complete without the consideration of surface species. These include the inorganic and organic ions adsorbed on the surface of particles. Natural systems such as soils, sediments and waters abound with colloids such as the hydrous oxides of iron, aluminium, manganese and silicon which have the potential to form surface complexes with the various cationic and anionic dissolved species (Evans, 1989). 

Acid (pH 3) ammonium oxalate has been widely used to dissolve iron and aluminium oxides and release bound trace metals since its introduction in 1922 (Tamm, 1922) (Tamm s reagent). Typically McLaren et al. (1986) used 0.17moll-1 ammonium oxalate +0.1 moll- 1 oxalic acid. The extraction is sensitive to light (Mitchell and Mackenzie, 1954) and particularly to ultraviolet light (Endredy, 1963). Schwertmann (1964) showed that in the dark the amorphous iron oxides were mainly attacked and under ultraviolet illumination the crystalline phases were dissolved as effectively as by the dithionite reagent. Heavy metals are released, with the exception of lead and cadmium whose oxalates are poorly soluble and which coprecipitate with calcium oxalate. The use of oxalic... 

The concentration of some ions in soil solution is controlled mainly by the presence of poorly soluble solid phase components. Good examples of this are iron and aluminium, both of which are highly insoluble at the pH of most soils, and which are controlled by the solubility of the... 

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Dar] Darken, L.S., Smith, RP., Filer, E.W., Solubility of Gaseous Nitrogen in y Iron and the Effect of Alloying Constituents - Aluminium Nitride Precipitation , Trans. Metall. Soc. AIME, 191, 1174-1179 (1951) (Phase Diagram, Phase Relations, Experimental,, 12)... 

Mae] Maekawa, S., Nagakawa, Y, Effect of Titanium, Aluminium and Oxygen on the Solubility of Nitrogen in Liquid Iron (in Japanese), Tetsu to Hagane, 46, 1438-1441 (1960) (Phase Diagram, Phase Relations, Thermodyn., Experimental, 8)... 

Wad] Wada, H., Pehike, R.D., Nitrogen Solubility and Aluminium Nitride Precipitation in Liquid Iron Alloys containing Nickel and Aluminum , Metall Trans. B, lOB, 409-412 (1979) (Phase Diagram, Phase Relations, Thermodyn., Experimental,, 4)... 

Nec] Nechaev, Yu.S., Edigarov, V.S., Pustov, Yu.A., Investigation of Iron Solubility in Aluminium and in Materials of SAP Type by Mdssbauer Spectroscopy (in Russian), Izv. V ss. Uchebn. Zaved., Chern. Metall, 5, 92-97 (1979) (Experimental, Phase Relations, 14) [1979Rou] Rousset, A., Paris, J., Chassagneux, F., Importance of Reactivity of the Finely Divided Solids for the Synthesis of New Phases (in French), Ann. Chim. Fr, 4, 115-122 (1979) (Experimental, Phase Relations, Thermodyn., 20)... 

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