Hume-Rothery compounds Table

Table 9.4. Electron compounds (Hume-Rothery phases).

Hume-Rothery phases (brass phases, electron compounds ) are certain alloys with the structures of the different types of brass (brass = Cu-Zn alloys). They are classical examples of the structure-determining influence of the valence electron concentration (VEC) in metals. VEC = (number of valence electrons)/(number of atoms). A survey is given in Table 15.1. 

It is just as incomprehensible that, as appears from Table 27, compounds of completely different composition, such as Cu5Zn8, Cu9A14, Cu31Sn8, Fe5Zn21, nevertheless crystallize in the same type of lattice. Hume-Rothery pointed out that in these cases it is not the atom ratio which is characteristic but... 

The circumstances under which intermetallics form were elucidated by the British metallurgist William Hume-Rothery (1899-1968) for compounds between the noble metals and the elements to their right in the periodic table (Hume-Rothery, 1934 Reynolds and Hume-Rothery, 1937). These are now applied to all intermetaUic compounds, in general. The converse to an intermetaUic, a solid solution, is only stable for certain valence-electron count per atom ratios, and with minimal differences in the atomic radii, electronegativities, and crystal structures (bonding preferences) of the pure components. For example, it is a mle-of-thumb that elements with atomic radii differing by more than 15 percent generally have very little solid phase miscibility. 

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