Aluminium solid-solution

Fig. 1.2. Optical micrographs of the transition zone between commercial purity iron or steel and aluminium. The Fe2Al5 intermetallic compound layer becomes progressively flatter and thinner with increasing carbon content of steel. The A1 + an intermetallic compound eutectic is distributed at grain boundaries of aluminium solid solutions.

Of 2.5 mass % Fe and 0.28 mass % Ni added initially to aluminium in order to obtain the saturated melt at 700°C, only 0.41 mass % (0.20 at.%) Fe and 0.05 mass % (0.03 at.%) Ni is retained in an aluminium solid solution during cooling down the aluminium melt. The remaining iron and nickel react with aluminium to form a eutectic and intermetallic grains distributed at random in the aluminium matrix. Microhardness, HV 50, was found to be 2.0 GPa for the Fe-Ni alloy base, 9.3 GPa for the intermetallic layer and 0.5 GPa for the aluminium matrix. The relative error of its measurement was around 10 %. 

The contents of iron and nickel in the aluminium solid solution were around 1.30 mass % (0.63 at.%) Fe and 0.47 mass % (0.22 at.%) Ni. Note that initially 2.5 mass % Fe and 0.86 mass % Ni were added to aluminium... 

Unlike preceding cases, the broad fine-grained two-phase zone, 2 mm thick, is formed at the interface between a 20 mass % Fe-80 mass % Ni alloy and the saturated aluminium melt (Fig. 5.16e). The same applies to a 15 mass % Fe-85 mass % Ni alloy, the thickness of the two-phase zone being 1.7 mm. The FeNiAl9 compound is dominant in the two-phase zone. Its fine crystals form a framework whose pores are filled with an aluminium solid solution. The NiAl3 inclusions are relatively seldom. 

Table3.1-12 Solubility of some elements in aluminium solid solutions [1.16,18]...

Of the generic aluminium alloys (see Chapter 1, Table 1.4), the 5000 series derives most of its strength from solution hardening. The Al-Mg phase diagram (Fig. 10.1) shows why at room temperature aluminium can dissolve up to 1.8 wt% magnesium at equilibrium. In practice, Al-Mg alloys can contain as much as 5.5 wt% Mg in solid solution at room temperature - a supersaturation of 5.5 - 1.8 = 3.7 wt%. In order to get this supersaturation the alloy is given the following schedule of heat treatments. 

Solution hardening is not confined to 5000 series aluminium alloys. The other alloy series all have elements dissolved in solid solution and they are all solution strengthened to some degree. But most aluminium alloys owe their strength to fine precipitates of intermetallic compounds, and solution strengthening is not dominant... 

Aluminium and magnesium melt at just over 900 K. Room temperature is 0.3 T and 100°C is 0.4 T, . Substantial diffusion can take place in these alloys if they are used for long periods at temperatures approaching 80-100°C. Several processes can occur to reduce the yield strength loss of solutes from supersaturated solid solution, overageing of precipitates and recrystallisation of cold-worked microstructures. 

The alloy aluminium-4 wt% copper forms the basis of the 2000 series (Duralumin, or Dural for short). It melts at about 650°C. At 500°C, solid A1 dissolves as much as 4 wt% of Cu completely. At 20°C its equilibrium solubility is only 0.1 wt% Cu. If the material is slowly cooled from 500°C to 20°C, 4 wt% - 0.1 wt% = 3.9 wt% copper separates out from the aluminium as large lumps of a new phase not pure copper, but of the compound CuAlj. If, instead, the material is quenched (cooled very rapidly, often by dropping it into cold water) from 500°C to 20°C, there is not time for the dissolved copper atoms to move together, by diffusion, to form CuAlj, and the alloy remains a solid solution. 

Single-phase solid solution of copper in aluminium... 

Because of the interest in its use in elevated-temperature molten salt electrolyte batteries, one of the first binary alloy systems studied in detail was the lithium-aluminium system. As shown in Fig. 1, the potential-composition behavior shows a long plateau between the lithium-saturated terminal solid solution and the intermediate P phase "LiAl", and a shorter one between the composition limits of the P and y phases, as well as composition-dependent values in the single-phase regions [35], This is as expected for a binary system with complete equilibrium. The potential of the first plateau varies linearly with temperature, as shown in Fig. 2. 

An explanation that may be suggested of these facts is that solid solutions of a quadrivalent metal (zinc) in a tervalent metal (aluminium) tend to be unstable because of the difficulty of saturating the valency of isolated quadrivalent atoms by bonds to its lower-valent ligates. With zinc as the solute an increase in free energy at the lower temperatures would accompany the separation into the zinc-poor a phase, in which the versatile zinc atoms tend to assume the valency 3 (less stable, however, for them than their normal valency) in order to fit into the aluminium structure, and the zinc-rich a phase, in which the concentration of zinc atoms is great enough to permit the extra valency of zinc to be satisfied through the formation of Zn-Zn bonds. 

Titanium and zirconium intermetallics. Various metals of practical relevance (Ti, and also Nb, Fe, Ni) form several fields of solid solutions with aluminium in presence, often, of rather complex phase equilibria. Several investigations and re-examinations of such systems, performed in the course of time, have been reviewed and assessed during the European Congress EUROMAT 2005... 

Wolska, E. (1990) Studies on the ordered and disordered aluminium substituted maghemites. Solid State Ionics 44 119-123 Wolska, E. Szajda.W. Piszora, P. (1992) Determination of solid solution limits based on the thermal behaviour of aluminium substituted iron hydroxides and oxides. J. Thermal Analysis 38 2115-2122 Wolski.W. (1985) Das Eisenoxidgelb. Farbe Lack 91 184-189... 

In the context of bidentate ligands, and in a similar vein to the polyfunctional aryloxides discussed above [141, 142, 146, 147], the chelation of a metal centre by deprotonated j5-diketones is a recurrent feature of monomeric organooxide complexes of aluminium. The employment of such ligands results in the observation of simple hexa-coordinate complexes which incorporate three [RC(0)C(H)C(0)R ] moieties (R = R = Me [177,178], CF3 [179], Ph [180, 181] R = f-Bu, R = CF3 [182]). More recently, the cocrystallisation of M(acac)3 (M = Al, Cr) has allowed the crystallographic study of metal disorder in a series of solid solutions of stoichiometry Ali, cCi x(acac)3 (x = 0.02-0.91) [183, 184]. Chelation of the metal centre similar to that reported in monomeric ] -diketonates has also been noted in the presence of... 

Arsenic triiodide also dissolves, the saturated solution at 15° C. having density 3-661. Other soluble halides are potassium bromide, anhydrous ferric and aluminium chlorides 6 and tetramethyl ammonium iodide but the iodides of rubidium, cadmium, manganese and cobalt, also mercuric and stannic iodides, and cobalt and stannic bromides, are insoluble or only very slightly soluble in arsenic tribromide. The liquid also dissolves phosphoryl bromide and, very slightly, ammonium thiocyanate. In the mixed solutions of halides, the components may react chemically (cf. p. 106), but such is not always the case for example, with antimony tribromide a continuous series of solid solutions is formed.7... 

Bragt R. C., 1967, Chromium Oxide Solid Solution Hardening of Aluminium Oxide, J. Am. Cer. Soc., 50-54. 

Fig. 5.12. Relationship between hardness H of solid solution crystals and composition of aluminium-niobium and aluminium-tantalum alloys after melting at different temperature, and limited solubility curves for tantalum in aluminium.

Thermolysis of tin and lead alkoxozirconates leads to the formation of metals. The mass-spectral data indicate the presence ofbarium and aluminium derivatives in the gas phase, but no preparative data are accessible for them. The major application of zirconium and hafnium alkoxides lies now in the sol-gel technology of zirconate-titanate and solid solutions Zr02-Y203 (see Section 10.3), Except in the synthesis of oxide materials, the alkoxides of zirconium and hafnium are traditionally used in the polymer chemistry, where they are applied as the components in catalysts [1278, 1269] and as additives to polymers, improving their characteristics [825, 1403] and so on. Already in 1930s Meerwein has proposed the use of zirconium alkoxides for the reduction of aldehydes intoprimary alcohols (Meerwein-Schmidt reaction) [1420],... 

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