JOURNAL of the Tunisian Chemical Society

serving the Research, the Education and the Industry

Structure defects and electrochemical study of copper processed by equal channel angular pressing

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Ultra-fine grained (UFG) pure copper of 99.99 wt.% purity has been successfully obtained at room temperature by Equal Channel Angular Pressing (ECAP), with the grain size about 200 nm after 2 passes. X-ray diffraction and Transmission Electron Microscopy (TEM) were used to characterize the microstructure evolution. The effect of ECAP passes on the electrochemical behavior of copper were investigated by potentiodynamic polarization test. The UFG copper display a higher corrosion resistance, despite the increase of the defect density, such as dislocations and grain boundaries.

R. Daly, M. Masmoudi

​​​​ECAP, X-ray diffraction profile analysis, TEM, potentiodynamic polarization, Corrosion

Pages: 183-190

Réactivité du 4-phénoxy-7-nitrobenzofurazane: Mécanisme et corrélations structure-réactivité

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The bimolecular rate constants for the reaction of coupling of a series of para-substituted anilines 2a-f with 4-phenoxy-7-nitrobenzofurazan 1 were determined in dimethyl sulfoxide (DMSO) at 25 °C. The Hammett plot for the reactions of anilines 2a-f with benzofuroxane 1 consists of two intersecting straight lines, while the corresponding Yukawa-Tsuno plot is linear. However, the nonlinear Hammett plot indicate a change in mechanism from the polar SNAr process for the electron-donating substituent X (X = Cl and CN) to a single electron transfer (SET) for the electron-withdrawing substituent X (X = OH, OCH3 and CH3). On the other hand, satisfactory correlation between the logarithm of the bimolecular rate constants (k1) and oxidation potentials (E°) of anilines 2a-d support a SET mechanism for this process.

I. Jamaoui, T. Boubaker, R. Goumont

Kinetic, Hammett relationship, Yukawa Tsuno eqution and SET mechanism

Pages: 191-200

Synthesis and characterization of sodium and carbonate-co-substituted fluorapatites

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Sodium and carbonate co-substituted fluorapatites (Ca10-xNax(PO4)6-x(CO3)xF2, 0≤ x≤3) were prepared via the hydrothermal method. The obtained powders were investigated by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and specific surface area measurements. Results indicate that both Na+ and CO32- ions were incorporated into the apatite structure only until x=2. Above this value, the excess of CaCO3 remained unreacted. For the monosubstituted sample, the structural refinement using the Rietveld method showed that Na+ is distributed between the two cationic sites. No carbonate ions were detected in the apatite anionic channel, indicating that the synthesised carbonated fluorapatite is of B-type. The CO32- group substituting the PO43- one is located in positions corresponding to two faces of the phosphate tetrahedron. The specific surface area of the substituted powders increased with the rise of the carbonate amount. When calcined at 1000°C in air atmosphere, the carbonated fluorapatite decomposed with a release of CO2 and formation of CaO.

E. Ben Salem, S. Nasr, P. Gravereau, K. Bouzouita

Fluorapatite, Carbonate, Sodium, Substitution, Hydrothermal synthesis

Pages: 201-210

Etude physico-chimique de deux molybdo-arséniates NaAg2Mo3AsO13 et Na2AgMo3AsO13 Corrélations structures-propriétés électriques

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Structural study of NaAg2Mo3AsO13 and Na2AgMo3AsO13 compounds confirms that they were build by one dimensional framework formed by ribbons running along [100] direction. Ag+ and Na+ ions are located in the inter ribbons space. Those phases were characterized by powder and single–crystal X-ray analysis, scanning electronic microscopy (S.E.M.) and infrared spectroscopy (I.R.). The conductivity study was realized by complex impedance spectrometry (I.C.S.) and the differential scanning calorimetric analysis (D.S.C.).

H. Hamza, M.F. Zid, A. Driss

molybdo-arsenates, X-ray analysis, complex impedance, ionic conductivity

Pages: 211-223

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