Intermetallic phase synthesis

Equilibrium conditions for the synthesis of intermetallic phases and compounds are summarized as a function of temperature and composition in the form of phase diagrams. Consequently, in the following subsections, phase relationships for group-IIA-group-IB metal systems are reviewed. Phase diagrams in ref. 1 are used as a baseline work published before this compilation is not specifically referred to, but that reported subsequently is used, as appropriate, to modify or replace these phase diagrams. 

A number of intermetallic phases may be prepared directly starting from the pure components suitably mixed together. The synthesis reaction may then be performed... 

SYNTHESIS OF INTERMETALLIC PHASES BY EXCHANGE REACTIONS (METATHESIS REACTIONS)... 

Comparison of the potassium content of the cetineite crystals to the composition of the synthesis mixture shows a preferred incorporation of potassium into the structure. Although this compound with 50 atoms per unit cell is a highly complex structure, it seems to follow the empirical Vegard s rule similar to homogeneous mixed crystals and for intermetallic phases of the Laves type as well as to microporous tin(IV)thioselenides of type SnSi.xSex.i.[13]... 

Occasionally, a pure component (a) phase may exhibit properties markedly different from those of the intermetallic phase which is vicinal to it on the constitutional diagram. Thus, the a-phase may dissolve more readily in a solvent or it may be attacked more readily by a reagent. In such cases it may be possible to use an excess of the pure component during the high-temperature synthesis and then liberate the intermetallic product by leaching out the matrix phase. Occasionally, also, slow cooling of the alloy melt may yield well-formed crystals of the intermetallic phase embedded in the pure component matrix, which may then be removed by some solvent. Dependii on circumstances, the matrix phase may be removed by electrolytic oxidation, by aqueous acids, by bases, or by liquid NHa. For example ... 

From the perspective of a materials scientist, tellurium is certainly the most attractive element, and it has found applications mainly in the electronics industry because of its p-type semiconducting properties. It can also be used for the synthesis of so-called II-VI semiconductors (such as MgTe) or may be alloyed to yield superior intermetallic phases. In addition, some Te alloys are under investigation in the realm of phase-change media for rapid data storage [273]. 

Ghosh T, Leonard BM, Zhou Q, DiSalvo FJ (2010) Pt alloy and intermetallic phases with V, Cr, Mn, Ni, and Cu synthesis as nanomaterials and possible applications as fuel cell catalysts. Chem Mater 22 2190-2202... 

Cisar, A., J. D. Corbett, and D. J. Merryman. Polybismuth anions - Synthesis and crystal structure of a salt of tetrabismuthide(2-) ion, bi (2-) basis for interpretation of structure of some complex intermetallic phases. Inorg. Chem. 16 (1977) 2482. 

Among catalysts derived from intermetallic compounds, titanium-iron systems have received some attention. The precise course of reactions involved is not clear. For example, it is claimed that the catalyst derived from a suitably activated TiFe intermetallic phase is TiN + Fe. The TiN is said to react with molecular hydro-gen. On the other hand, in a series of patents on Fe-Ti systems, covering a range of iron-to-titanium ratios, with or without addition transition elements, it is quite clearly regarded that the titanium is capable of forming hydrides. Whatever the mechanism, such systems appear capable of promoting ammonia synthesis in commercial yields at 300 °C, 80 atm, while some are even claimed to be active at 125 °C and 1 atm. Rare earth metals, in combination with iron, ruthenium, or cobalt, can also function as catalysts. Again, the rare earth metals seem to be... 

The successful use of the Zintl-Klemm concept in the synthesis of complex intermetallics is represented by the work of Schaefer and co-workers in Darmstadt [41]. The extensive investigations on Zind phases mainly by von Schnering... 

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. 

Synthesis in liquidAl Al as a reactive solvent Several intermetallic alu-minides have been prepared from liquid aluminium very often the separation of the compounds may be achieved through the dissolution of Al which dissolves readily in several non-oxidizing acids (for instance HC1). For a review on the reactions carried out in liquid aluminium and on several compounds prepared, see Kanatzidis et al. (2005) binary compounds are listed (Re-Al, Co-Al, Ir-Al) as well as ternary phases (lanthanide and actinide-transition metal aluminides). Examples of quaternary compounds (alumino-silicides, alumino-germanides of lanthanides and transition metals) have also been described. As an example, a few preparative details of specific compounds are reported in the following. 

---