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Nanomaterials contract and expand: The spacing between the atoms initially decreases as the grain size becomes smaller; below a critical grain size, the spacing expands again. The reason for this is that the surface stress and excess volume compete with one another and the latter wins the upper hand below the critical grain size. © Eric Mittemeijer & Sairam Meka

It’s the fineness of the grind

In nanomaterials, the structure of the individual crystals changes with grain size

  • 22 July 2013

The properties of nanomaterials could be easier to predict in future. Scientists from the Max Planck Institute for Intelligent Systems in Stuttgart have ground metal into continuously finer powders in steps and prepared a detailed catalogue of how the structure of the metal grains changes depending on grain size. They discovered that the crystal lattices initially shrink, but expand again below a certain threshold grain size. The arrangement and spacing of the atoms determine numerous properties of a material. If it is possible to accurately characterise crystal lattices as a function of the particle size, it may also be possible thereby to more accurately calculate how nanoparticles of a particular size behave.


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