# What is the world's finest powder substance?

What is the world's finest powder substance that has the smallest granules but remains solid?

• Welcome to Chemistry SE! Please define, in your terms, what finest is. – Asker123 May 10 '15 at 12:27

Clusters of just a few atoms, such as gold atomic clusters, and quantum dot nanoparticles could be considered very fine powders, though they usually are suspended in another substance to keep the clusters from agglomerating. Particles this tiny have different properties from the bulk material, both because of quantum effects (there are few particles, so there is not a continuous valence band) and because more atoms are at the surface interface than are surrounded by similar atoms in the interior.

• While not quantum dots, there are some pretty small nanoparticles which can be bought in bulk as a powder. The type that come to mind the most are titanium dioxide nanoparticles, which are regularly sold in kilogram bags with particle diameters as small as $\rm{21\ nm}$. – Nicolau Saker Neto May 10 '15 at 23:48