Synthesis in solvents under fluxes

A number of reactions between metals (or metals and semi-metals) may be carried out by dissolving the elements in a suitable solvent , technically also termed a flux . The solvent may also act as a reactant and be involved in the formation of the compound (reactive solvent, reactive flux). Several fluxes, ranging from simple metallic elements up to complex substances have been used. 

An authoritative review entitled The metal flux a preparative tool for the exploration of intermetallic compounds has been published by Kanatzidis etal. (2005). In this paper, containing a long list of references, several general and experimental aspects of this technique are discussed. The paper is enriched also by beautiful photographs of intermetallic single crystals, for instance a dodecahedral Ho-Mg-Zn quasicrystal grown from an Mg and Zn-rich flux. Special attention was dedicated to the use of molten metals as media (metallic fluxes) for the synthesis of different materials, and a number of key characteristics were underlined which the metal must possess in order to be a suitable flux. The following points were noticed  

In a paper by Fisk and Remeika (1989) several points concerning the growth of single crystals from metal fluxes have been discussed. Attention has been dedicated to various aspects of the problem of separating crystal and flux, for which two main approaches, chemical and mechanical, may be considered. The following examples drawn from the preparative chemistry of the rare earth alloys were described. 

Growth of rare earth rhodium stannides from excess Sn The crystals can be leached with dilute HC1. As long as the crystals are in contact with the Sn flux, they remain shiny and metallic. Crystals separated from Sn, however, quickly form a black tarnish containing an amorphous mixture of Rh and Sn. The removal of the crystals from the leaching solution as soon as they are free of Sn flux is therefore necessary. 

Electrochemical removal of the flux By suspending the melt anode in the bath, the crystals can fall free as the etching proceeds and, if not attacked by the electrolyte, they can be easily recovered. 

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