Bulk materials regardless of size exhibit identical properties but when the size approaches nano-scale, the amount of surface atoms is significant, and the properties change. For example copper at the nano-scale is brittle and not malleable like bulk copper. Nano-scale materials when in solution, neither floating or sinking but are suspended. For example magnetic materials lose their dipole direction entirely. Nano powders get their properties from their high surface area to volume ratio which makes them very reactive and this property is used in many of the applications for example as an ideal filler. But the size also raises concerns about toxicity associated with the powder. applications:Powder is used as a catalysts for chemical reactions in catalytic converters for the rapid destruction of toxic chemicals. It is used as fuel additive (from aluminum nano-powder) for boosting octane, as insulators such as SiO2 used in integrated circuits, used in sunscreens as filler to increase skin absorption, to fill in the porosity created by pressing larger particles, to fill in gaps from metal powders pressed to make gun components, allowing more weapons to be produced faster to meet standards, as nano powder coatings in automobiles( Mercedes uses metallic powders in its C-class vehicles) to provide a better reflectivity (sheen) and scratch resistance. Depending on the chemical composition, coatings can have other properties such as conductance, non-slip, porous, non-porous, and so on. Powder concerns:Their small size allows the powder to diffuse directly through the cell membrane. Long term effects of this are unknown. Trillions of nano-particles from catalytic converters fill the air every day in every city. Preliminary trials in rats show that long term exposure may cause biochemical damage to brain tissue and cells.