Influence of nano-particle size on the oxidation behaviour of Al, Fe and Cu

The addition of ultra-fine and nano-sized particles in composite materials influences their proper I ties. In order to understand the influence of the nano-size of metal particles on the oxidation behaviour, a series of in situ studies by thermogravimetry (TG) and high temperature X-ray diffraction (XRD) was performed on Al, Fe and Cu during heating with post oxidation analysis by field emission - scanning electron microscope (FE-SEM). The oxidation reaction depends, for all three studied metals, on the particle size both in regard to transient oxide formation and formation temperatures. On a nano-scale Al forms theta-Al2O3 and gamma-Al2O3 simultaneously at 500 degrees C, but both of these oxides transforrn to alpha-Al2O3 at 975 degrees C producing nano-scaled oxide particles. Aluminium particles with sizes from 2 to 25 mu m form alpha-Al2O3 only, starting at temperatures close to the melting point. Nano-sized Fe forms on heating from 340 degrees C alpha-Fe2O3 only and no other oxides. On nano-sized Cu particles the formation of Cu2O starts at 140 degrees C, transforming completely to CuO at 300 degrees C