The effect of oxygen partial pressure on the growth of ZnO nanostructure on Cu_0.62Zn_0.38 brass during thermal oxidation

Cu_0.62Zn_0.38 brass foils were thermally oxidized at 500 °C under various gaseous environments, including nitrogen, air and mixture of N₂O₂ at a pressure of 1 atm for 3 h. The oxidized specimens were characterized with a scanning electron microscope, an X-ray diffractometer and a transmission electron microscope. Optical property of oxidized products was characterized by photoluminescence. It is found that the nanowires and/or nanowalls are formed from hexagon ZnO crystals under N ₂O₂ gases and air. However, nanowires and nanowalls cannot form on the specimens oxidized in N₂. When oxygen partial pressure of environment is over a critical value, increasing oxygen partial pressure is of disbenefit to the growth of nanowires and nanowalls and reduces the thickness of oxide scale on a specimen. The experimental results are explained by the defect equilibrium theory of oxide scale and the compressive growth stresses occurred during oxidation.