Intermetallic alloy formation

Hot Dipped Coatings Major attempts have been made to improve the quality of aluminised steel strip. Requirements on coating thickness and uniformity have been imposed. It is the speed of sheet movement, length of path in the molten bath, temperature and composition of the bath that control the thickness of the intermetallic layer which lies below the aluminium outer surface. The process of intermetallic alloy formation is diffusion controlled, and it is usual that some dissolution of iron into the molten aluminium does occur at a rate, Ac/At, which is given by... 

M. Nastasi Ion-Irradiation-Induced-Transformations in Intermetallic Alloys Formation and Stability. Ph.D, Thesis, Cornell University (1986)... 

At the m.p. of aluminium (600°C) an aluminium-sheathed palladium thermocouple formed an alloy with a flash and an exotherm to 2800°C [1]. The use of thin layers of palladium or platinum on aluminium foil or wire as igniters derives from the intense heat of alloy formation, which is sufficient to melt the intermetallic compounds [2],... 

Thermochemistry of cluster compounds. In this short summary of cluster structures and their bonding, a few remarks on their thermochemical behaviour are given, in view of a possible relationship with the intermetallic alloy properties. To this end we remember that for molecular compounds, as for several organic compounds, concepts such as bond energies and their relation to atomization energies and thermodynamic formation functions play an important role in the description of these compounds and their properties. A classical example is given by some binary hydrocarbon compounds. 

Intermetallic compound formation may be observed as the result from the diffusion across an interface between the two solids. The transient formation of a liquid phase may aid the synthesis and densification processes. A further aid to the reaction speed and completeness may come from the non-negligible volatility of the component(s). An important factor influencing the feasibility of the reactions between mixed powders is represented by the heat of formation of the desired alloy the reaction will be easier if it is more exothermic. Heat must generally be supplied to start the reaction but then an exothermic reaction can become self-sustaining. Such reactions are also known as combustion synthesis, reactive synthesis, self-propagating high-temperature synthesis. 

Chapter 10 provides an exhaustive description of how these techniques can be applied to a large number of industrial alloys and other materials. This includes a discussion of solution and substance databases and step-by-step examples of multi-component calculations. Validation of calculated equilibria in multi-component alloys is given by a detailed comparison with experimental results for a variety of steels, titanium- and nickel-base alloys. Further selected examples include the formation of deleterious phases, complex precipitation sequences, sensitivity factor analysis, intermetallic alloys, alloy design, slag, slag-metal and other complex chemical equilibria and nuclear applications. 

Formation of several successive layers of bulk intermetallic compounds has been shown. Also, Lee et al. [480] have detected, during Al UPD, the formation of two alloys on polycrystalline Au electrodes from acidic l-ethyl-3-methylimidazolium chloroaluminate that melt at room temperature. Moreover, in the Al UPD region, fast phase transition between these two intermetallic compounds has been evidenced. Later, the same group of researchers [481] has performed EQCM studies on Al deposition and alloy formation on Au(lll) in ambient temperature molten salts/benzene mixtures. 

Aluminium is known to form a number of binary142 145 221 and tema-ry intermetallics with iron and nickel or chromium. In this section, the intermetallic compound formation at the interface between a solid iron-nickel or iron-chromium alloy and the aluminium melt saturated with alloy constituents at 700°C, will be described. Also, the effect of dissolution on the process of layer growth will be illustrated.344 345... 

Consider first the Al-Fe-Ni system. Generally, the equilibrium phase diagram is known to be helpful in analysing the process of intermetallic layer formation. Projection of the liquidus surface on the concentration triangle and distribution of the phase fields in the solid state for Al-rich Al-Fe-Ni alloys are shown in Fig. 5.15. 

An attractive, semiempirical application of physical insight into alloy formation is found in classifications of alloy phase data into structure maps, quantum diagrams, and so on (see Structure Property Maps for Inorganic Solids) where a necessarily limited number of coordinates (one to three) must reflect the physical parameters determining the property of interest. An example is given below in the Pettifor map for Ti-Al intermetallics. Further developments in the mapping of intermetallics are due to Ceder. ... 

The solubilities of uranium, plutonium, and thorium in magnesium at 650°C are 0.002 wt %, 55 wt %, and 44 wt %, respectively. Thus, assuming no solute interaction, uranium is essentially insoluble in magnesium, while plutonium is quite soluble and good separation may be effected. While precipitation of an insoluble phase from solution would appear to be a straightforward process, the behavior of a solute in a given metal or alloy may differ from its behavior when influenced by the inclusion of other solutes. One element may increase or suppress the solubility of another through coprecipitation or intermetallic compound formation. Such effects must be determined experimentally. 

Platinum promotes Ru/ZrOz through the formation of intermetallic alloys, or a strong interaction between the two metallic phases for the two bimetallic precursors, although this phenomenon is less marked in the coimpregnated sample. The incorporation of platinum reduces TOF values and the selectivity to products of deep hydrogenolysis with respect to monometallic catalysts. The order of activity can be established for the five catalytic series as ID > CID > CAD = AD >CAC. 

The gases that are generated when an encapsulant resin is exposed to a high temperature were analyzed by GC-MS to disclose the cause for resin degradation and chip failure. This paper describes the cause for chip failure, and also presents a method for controlling the formation of intermetallic alloys. 

A monolayer of Sm is formed on Ru(OOl) surface which transforms into surface intermetallic phase at higher doses of Sm. It is possible to produce SmRu intermetallic phases of different composition using this method. Alloy formation is confirmed from Ru 3d low binding energy feature at 279 eV. Molecular CO adsorption occurs on open Ru sites as evidenced by twin TPD peaks. The partly oxidized Sm20x species attracts CO molecules for... 

Ma, Akis, Ayturk, Guazzone, EngwaU, MardUovich. Characterization of intermetallic diffusion barrier and alloy formation for pd/cu and pd/ag porous stainless steel composite membranes. Ind Eng Chem Res. 2004 43 2936 5. 

---