Metallic Aluminum Forms Tetrahedrons | March 28, 2011 Issue - Vol. 89 Issue 13 | Chemical & Engineering News
Volume 89 Issue 13 | p. 36 | Concentrates
Issue Date: March 28, 2011

Metallic Aluminum Forms Tetrahedrons

Electron distribution maps provide a better explanation for some of bulk aluminum’s properties
Department: Science & Technology
Keywords: aluminum, metal, electron diffraction, electron density, bonding
Pockets of high-bonding electron density (red) are shown between tetrahedrally arranged aluminum atoms (blue).
Credit: Philip Nakashima
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Pockets of high-bonding electron density (red) are shown between tetrahedrally arranged aluminum atoms (blue).
Credit: Philip Nakashima

Atoms in aluminum metal are bound together in a tetrahedral geometry, a finding by researchers at Australia’s Monash University that better explains some of bulk aluminum’s properties (Science, DOI: 10.1126/science.1198543). The traditional view of a metal as an array of ions in a mobile sea of electrons works well to explain properties such as conductivity. But it doesn’t explain some mechanical qualities, such as why aluminum is more elastic in some directions than others, which would arise from directional bonding. In the sea of electron density, however, it is difficult to pick up localized electron distribution to identify bonds between atoms. Monash’s Philip N. H. Nakashima and colleagues used convergent-beam electron diffraction to map electron distribution in aluminum and observed that the atoms are bound together in a tetrahedral geometry, rather than in an octahedral or other fashion. The results agree with aluminum’s mechanical properties: The metal’s strongest axis passes through areas of highest bonding electron density within the tetrahedrons, whereas its weakest axis corresponds to holes in the electron density.

 
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