Malick Jean

Atmospheric corrosion of nickel in various outdoor environments

As part of a field exposure program in the north-west of France on atmospheric corrosion of metal and alloys, this study presents the results of the behaviour of nickel panels exposed in industrial, urban and rural atmospheres. Mass measurements were investigated during the exposure and adherent corrosion layers were followed by means of several methods of analysis: Fourier transform infrared reflection–absorption spectroscopy, X-ray diffraction and scanning electron microscopy with X-ray microanalysis. In order to determine all the chemical species formed in the corrosion layers, corrosion products released from the surface by rainfall were also studied by collecting the streaming water from the nickel surfaces. Anionic and cationic quantities in the streaming water were determined respectively with ionic chromatography and polarography. The nickel attack appears as a pitting corrosion process accompanied by the formation of soluble corrosion products in dry exposure periods, these being regularly dissolved by rainfall events. Pits are associated with the formation of nickel salts, mainly sulphates and chlorides with small amounts of nitrate, and surrounded by carbonate species. The corrosion rate increases from rural to industrial areas.

Simultaneous copper runoff and copper surface analysis in an outdoor area

Simultaneous copper runoff and copper surface analysis has been performed during a field exposure in a French industrial area. Corrosion layer composition was studied with fourier transform infrared reflection-absorption spectroscopy, x-ray diffraction and scanning electron microscopy with energy-dispensive scattering analysis, revealing cuprite, basic copper sulphates (brochantite and posjnakite) and copper sulphate pentahydrate (CuSO 4 .5H 2 O) as the main corrosion products after 3 months of exposure. In order to determine the soluble corrosion compounds carried with rain, the water streaming over a copper coupon was collected and analysed by means of ionic chromatography and potentiometric stripping analysis. Significant sulphate and copper concentrations were detected in water and interpreted as resulting from the dissolution of copper sulphate compounds.

Characterization of nanocrystalline Mn-Zn ferrites obtained by mechanosynthesis

Different Zn and Mn-Zn ferrites have been obtained by High Energy Ball Milling (HEBM) from elemental oxides. By varying the rotation speed of vials and main disk, several modes of milling can be obtained. In this paper, the materials prepared by two modes of milling, called shock (S) and high shock (HS), are studied by XRD and Mössbauer spectroscopy. Several mechanisms for spinel phase formation have been proposed. In particular, a reduction of Fe(III) occurs for the S mode, which leads to the formation of a wüstite-type phase which disappears after a long milling time.

Mössbauer study on LiFePO4 cathode material for lithium ion batteries

Crystalline LiFePO4 has been synthesized using solid-state, spray pyrolysis, and wet chemical methods. The crystal parameters were obtained from Rietveld’s refinement methods of the X-ray diffraction patterns. A detailed investigation of the Fe valency carried out using Mössbauer spectroscopy at room temperature indicates that Fe is predominantly present in its bivalent state.

Atomic-scale investigation and magnetic properties of Cu80Co20 nanowires

Cu80Co20 granular alloy nanowires were synthesized by electrodeposition method and investigated by x-ray diffraction (XRD), Laser Assisted Wide Angle Tomographic Atom Probe (LAWATAP), and SQUID magnetometry. XRD results reveal the existence of a fcc Cu matrix and fcc Co-rich nanograins, with a preferred orientation along the [200] direction (perpendicular to the substrate surface). The Co-rich nanograins could be coherent with the Cu matrix. 3D reconstructions of a nano-sized volume, obtained by LAWATAP, reveal the heterogeneous aspect of the Cu80Co20 nanowires: Co-rich nanoclusters with size between 2 and 10 nm are detected, and the presence of Cu and Co oxides is evidenced. Magnetization measurements indicate that the Co-rich nanoclusters are superparamagnetic, with a blocking temperature that extends up to, at least, room temperature. The presence of ferromagnetic domains at room temperature indicates that some Co-rich nanoclusters are correlated within a volume that corresponds to a so-called interact...