Preparation of intermetallics

Another application of the electrolysis of tantalum and niobium in fluoride melts is in the preparation of intermetalic compounds as a result of the interaction between the electrochemically precipitating metal and the cathode material. Based on an investigation of the electrochemical reduction of K2TaF7 or K2NbF7 in a LiF - NaF melt on nickel cathodes, Taxil and Qiao [565] determined the appropriate conditions for the formation of TaNi3 or NbNi3 in the form of stable phases in the bulk of the obtained layer. 

A chapter dedicated to the laboratory (small scale) preparation methods of inter-metallics has then been included (Chapter 6). In the preparation of intermetallic phases, indeed (or, more generally, of alloys), in comparison to other chemical compounds a number of interesting and significant peculiarities are pointed out, for instance, those related to their high melting points, insolubility in many common solvents, etc. The presentation of selected examples of preparative methods, therefore,... 

The experimental methods of determining phase diagrams will be only briefly commented upon, in order to give an idea of the problems involved and of the connection between phase diagram science and other disciplines. A few special points will be considered in Chapter 6, dedicated to the preparation of intermetallics. 

In the following paragraphs an indication will be given of a few (mainly laboratory) methods which can be used in the preparation of intermetallic phases and compounds. Without any claim of being exhaustive, we will discuss a few characteristic manipulations and devices frequently employed in an intermetallic chemistry laboratory. This will also introduce general aspects of the intermetallic reactivity, while underlining some of its peculiarities. 

Miscellaneous, special processing techniques and heat treatments In the preparation of intermetallic alloys, both in massive quantities for commercial purposes, or as small specimens for laboratory investigations, very often the alloys must be subjected to selected and well-defined heat treatments, in some cases in addition to mechanical treatments, in order to have their full characterization and/or optimal performance. 

Both in the preparation of intermetallics and in their handling, special problems are encountered due to impurities present in the materials involved or produced by unwanted side reactions, such as reactions with the atmosphere, the containers, etc. The purity control is especially important when working at high temperature. It is well-known that the fundamental law of high-temperature chemistry is that . .. everything reacts with everything ... 

In the following paragraphs a few examples of the preparation of intermetallic phases in various metallic and non-metallic solvents are reported. 

Percheron-Guegan, A. and Welter, J.-M. (1988) Preparation of intermetallics and hydrides, in Hydrogen in Intermetallic Compounds I (ed. L. Schlapbach), Springer-Verlag, Berlin, p. 11. 

The preparation of intermetallic compounds, solid solutions, interstitional alloys, and substitutional alloys is generally accomplished from a melt of the constituent metallic elements. Alloy syntheses are a branch of metallurgy and require the use of pure metallic reagents, high temperature, and inert containers and atmospheres. 

The majority of synthetic efforts have overwhelmingly focused on the preparation of intermetallic clathrates in bulk form by the methods described above. To date, comparatively fewer efforts to prepare thin film and nanostructured materials have been reported. 

A Percheron Guegan, J M Welter. Preparation of intermetallics and hydrides. In L. Schlapbach, Ed. Hydrogen in Intermetallic Compounds I, Vol 63 of Topics in Applied Physics. Berlin Springer Verlag, 1988, p 11. 

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