A Study of the Morphological Changes and the Growth Kinetics of the Oxides Formed by the High Temperature Oxidation of Cu-32.02% Zn-2.30% Pb Brass

Abstract

The high temperature oxidation of Cu-32.02% Zn-2.30%Pb brass was carried in N₂-5wt.% O₂ and N₂-12 wt.% O₂ atmospheres. The amounts of oxygen in the oxidizing atmospheres and the time of the oxidation affected the oxide morphologies and kinetics of the oxide growth. In the first hour of the oxidation at 650 °C, oxide nanowires were noted. The average diameter, length and distance between the observed nanowires were 27 ± 0.01 nm, 0.20 ± 0.04 µm and 0.20 ± 0.04 µm respectively for the samples oxidized in N₂-5wt.% O₂ atmosphere and 102 ± 23 nm, 0.36 ± 0.24 μm and 0.24 ± 0.08 μm respectively for the samples oxidized in N₂-12wt.% O₂ atmosphere. The EDX and XRD analyses of the nanowires and the oxide granules confirmed ZnO nanowires and a continuous oxide layer of ZnO. The x-ray diffraction confirmed minor presence of PbO. The oxide growth kinetics followed the linear oxide growth model, for the alloy samples that were thermally oxidized in N₂-5 wt.% O₂ atmposphere and parabolic growth model for those thermally oxidized in N₂-12 wt.% O₂ atmospheres respectively. The values of 6.8 µm/hour and 23.03 µm/(hour)^1/2were determined for growth constant (k), based on the two models respectively.

Keywords:
Thermal oxidation; growth kinetics; brass