Papers by Author: Ludovic Douminge

Abstract: Ultraviolet radiation is one of the major factors that affect weathering of polymers. Indeed, diffusion of oxygen containing groups [-C-O, C=O and C(=O)O-] into the molecular chains of polymers is particularly enhanced by UV irradiation in air, thus entailing structural and chemical changes such as polymeric chain breaking, cross-linking and oxidation. The goal of this study is to predict the photo-chemical ageing of polymers upon UV radiation through a non destructive method: fluorescence spectroscopy. In the case of high density polyethylene (HDPE) the addition of fluorophore is required to make it fluorescent. The spectral features of fluorescence are very sensitive to the interactions between the excited molecules and the matrix. In this way, Fourier-Transform InfraRed spectrophotometry (FTIR) and Differential Scanning calorimetry (DSC) have been employed to correlate the fluorescence spectra with the degradation phenomena.

Abstract: The performance of Ni-based alloys at high temperature strongly depends on the formation of a protective chromia scale which prevents from fast growth NiO scale. The evolution of the oxide scales will be shown to be strongly dependent on the chromium content especially for the shortest oxidation times. Indeed, transient stages will be reported to condition the subsequent oxidation behavior at longer times until the oxidation rate constant becomes invariant. To this end, a comparative study on the outward and inward diffusion of species upon oxidation at 800°C for short times (0.5 / 1 / 2 / 4 / 8 h) has been evaluated on commercial available Ni20Cr and Ni30Cr alloys through in-situ Raman spectroscopy and supported by post-mortem X-ray diffraction (XRD) as well as scanning electron microscopy coupled to energy dispersive spectrometry (FEG-ESEM / EDS) investigations.