Why is aluminium powder sticky? Aluminium powder is used in applications like the “etch-a-sketch” toy because it tends to stick to surfaces. Also it tends to clog abrasive tools like files and grinding wheels or stones, and the chips are quite annoying to clean after machining, because they tend to stick everywhere.
What are the specific reasons related to its atomic structure for this phenomenon?
 A: For powders where the mass of an individual particle is small relative to the size of the electrostatic effects due to slight charge differences on surfaces, "sticking" to those surfaces is common.
The reason why aluminum "loads" grinding wheels and files is 1) its ductility and 2) the fact that it exhibits galling- in which pieces of aluminum, when rubbed together under pressure, tend to friction-weld themselves together at asperities on their facing surfaces and then roll up into globs of aluminum that get sheared between the surfaces, glue themselves onto them, and then get sheared loose while tearing loose fresh aluminum from the now-roughened surfaces. So when a bit of loose aluminum gets jammed inbetween the teeth of a file, that aluminum rubs against the workpiece, galls itself into the interface, and then gets caught between more teeth on the file, etc., etc.
One reason this happens with aluminum is that when fresh aluminum surfaces are exposed to air, a very thin oxide film quickly forms on them- which can be rubbed away with sliding action to bring fresh, unoxidized aluminum on those surfaces into direct contact where "pressure welding" can occur, and the galling process initiated.
