The acid activation of south Tunisian bentonitic clay leads to a porous material with very enhanced bleaching properties for sofa and colza oils. The experimental investigation is performed in accordance with the methodology of the factorial design of experiments. A descriptive statistical model linking the decoloration effect to the reaction parameters is established and used to find the optimal activation conditions. The effect of the reaction conditions on the solid structure is investigated.
A. Gannouni, A. Bellagi
argile, activation acide, decoloration des huiles vegetales, planification d'experiences, optimisation
Pages 1357-1369
The geothite precipitation from amorphous ferrihydrite in alkaline medium at 70°C has been studied by single wave length ellipsometric data. Optical parameters such as ψ, Δ, n and k of the precipitates obtained at different reaction times have been determined. Goethite content of the precipitates have been determined by XR diffraction and 1R spectroscopy. Variations of n and ψ are particularly significant, the former decreases from 2.65 to 2.198 and the later increases from 1.09 to 7.40 degrees. Both of parameters are suitable to be used as goethite crystallization indicators. At the same time, the colors of precipitates have been determined in the L*a*b* color space. b* has been verified as simple indicator of goethite crystallization and a positive relationship has been established between n , ψ and b*.
A. Hamzaoui, M. Soua, M. El Maaoui
Goethite, Ferrihydrite, color, refractive index, crystallisation
Pages 1371-1381
Iron(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes of type ML2Cl2, where M is FeII, CoII, NiII, CuII, ZnII and CdII and L is Schiff base formed by condensation of 2-thiophenecarboxaldehyde (TFCA) and methylamine (MA), N-[2-thienylmethylidene] methanamine (TNAM), have been prepared and characterized by elemental analysis, magnetic and spectroscopic measurements. Elemental analysis suggests the stoichiometry to be 1:2 (metal:ligand). Magnetic susceptibility data coupled with electronic and ESR spectra suggest a distorted octahedral structure for the Fe(II), Co(II) and Ni(II) complexes, a square-planar geometry for the Cu(II) compound and an tetrahedral geometry for Zn(II) and Cd(II) complexes. Infrared and NMR spectra of the complexes agree with the co-ordination to the central metal atom through nitrogen and sulphur atoms. Conductance measurements suggest the non-electrolytic nature of the complexes, a except the Cu(II), Zn(II) and Cd(II) complexes which are 1:2 electrolytes.
C. Spinu, A. Kriza, M. Mateescu, L. Spinu
Schiff base, 2-thiophenecarboxaldehyde, N-[2-thienylmethylidenej methanamine
Pages 1383-1387
The effect of sulphide ions on the corrosion behaviour of an austenitic alloy 904L (Z1CNDU 25-20) in phosphoric media and especially on the nature and the composition of the layer formed at the material surface has been studied using electrochemical methods (polarization curves) and spectroscopic techniques (XPS, Auger and IR). The electrochemical study shows that the sulphide ions induce the depolarization of anodic processes resulting in a increase of material dissolution kinetics and hence a decrease of corrosion resistance. In such conditions, information obtained on the passivity film using surface analysis techniques revealed enrichment or impoverishment in some elements. So, the external layer is characterized by the presence of phosphate and metallic sulphide, while the internal layer contains some oxides and hydroxides. The micrographic test obtained by SEM showed localized attacks at the material surface in the presence of sulphide ions.
A. Bellaouchou, A. Guenbour, A. Benbachir, L. Aries
Corrosion, Stainless Steel, Phosphoric Medium, Sulphides ions
Pages 1389-1398