Study of the nanostructuration of ZrAu alloy near the ambient temperature by X-ray diffraction and thermal analyses

摘要

Spontaneous nanostructuration in air of the crystallized ZrAu alloy has been followed by X-ray diffraction using both synchrotron radiation and conventional laboratory X-ray source. This has allowed the study of the degradation of this compound from 25 to 150 deg C with an accurate step in time adapted to the very fast oxidation kinetic (2 mum of oxide layer per day at room temperature). From these experiments the activation energy (E_a) of the mechanism has been determined by the way of an original approach consisting in the analysis of the temperature dependent evolution of the integrated intensity of a selected ZrAu diffraction peak. Furthermore, this activation energy has been compared with the one obtained from thermogravimetric analysis. The two independent techniques giving consistent information, average activation energy of 55 kJ mol~(-1) was associated with this unusual phenomenon. We have shown that no significant oxidation behavior is observed under pure oxygen below 100 deg C. The study of the phenomenon under pure oxygen, the microstructural analysis of the oxide layer and the study of the influence of relative humidity (RH) on the oxidation rate, allows us to attribute the oxidation mechanism to an atmospheric oxidation mechanism controlled by the dissociation of gaseous oxidative species at the alloy/air interface.