Amane Jada

Preparation and microelectrophoresis characterisation of calcium carbonate particles in the presence of anionic polyelectrolyte

Abstract Calcium carbonate (CaCO3) crystal growth experiments in the presence of the polystyrene sulfonate were made at ambient temperature. This polyelectrolyte inhibits the crystal growth in all directions and modifies the crystal structure and morphology. Further, the unstable vaterite CaCO3 crystalline structure was stabilized in the precipitation medium in the presence of the polyelectrolyte. Thus, at moderate polyelectrolyte concentration, spherical CaCO3 particles are obtained having a smaller size compared to the rhombohedral particles obtained in the absence of the polyelectrolyte. By increasing the polyelectrolyte concentration, the CaCO3 particles mean size and size-polydispersity index decrease. The microelectrophoresis studies indicate that in the presence of the anionic polyelectrolyte, the CaCO3 particles are negatively surface charged. The results obtained indicate a correlation between the CaCO3 particle sizes, their surface charges and the equilibrium pH of the aqueous CaCO3 dispersion. Finally, the data obtained was used to throw light on the mechanism by which polymeric additives affect the morphology, size and crystalline structure of calcium carbonate CaCO3.

STUDY OF THE STABILITY OF BITUMEN EMULSIONS BY APPLICATION OF DLVO THEORY

Abstract The stability of bitumen emulsions was compared with the chemical and interfacial properties of the bitumens. The chemical properties of the bitumens were studied by determining their asphaltenes and resins contents and the interfacial properties by measuring the zeta potential of bitumen dispersions in acid water. The DLVO theory was applied to evaluate the stability of the emulsions. This theory was improved by taking account of additional interaction energies: hydrophilic and hydrophobic interactions (extended DLVO theory). Experimental results showed that it is possible to predict the stability of the emulsions from the chemical and interfacial properties of the bitumens. It seems that the resins/asphaltenes ratio affects the dispersion and emulsion stability by controlling the distribution of polar components inside the bitumen during the dispersion or emulsion manufacturing.

Relationship between the chemical properties of bitumens and their colloidal properties in water

The chemical properties of different bitumens were characterized by determining their asphaltene and resin contents and acid-base properties by carrying out titrations in organic media. Furthermore, the colloidal properties of the bitumens in water, i.e. their electrical interfacial properties, were evaluated by measuring the zeta potentials of bitumen dispersions in water. Comparison between the chemical and colloidal properties of the bitumens shows that it could be possible to predict the dispersion stability from the chemical properties of the bitumens. The resins/asphaltenes ratio can affect the dispersion stability by controlling the arrangement of the bitumen components inside the droplet and also at the interface during dispersion manufacture.

Surface properties of petroleum oil polar fraction as investigated by Zetametry and DRIFT spectroscopy

The polar fractions of various transformer petroleum oils (one new and two used oils) were extracted from the neat oils using silica as solid support. We found that the amount of the polar fraction adsorbed on the silica was higher for the used oils as compared to the new one. Such oil polar fractions are insoluble in low molecular weight paraffins (n-hexane and n-heptane) and are soluble in ethanol. The analysis of the diffuse reflectance infrared Fourier transform (DRIFT) spectra of the silica samples coated with oil polar components indicate the presence of oil polar functional groups such as hydroxyl, aromatic and carboxyl groups resembling asphaltenes or resins. In addition, we studied the electrical properties of the oil polar fraction by determining the ζ potential, in water, of the coated silica. In order to compare the modified and the non-modified silica surface properties, we made blank experiments by measuring the surface charge in water of the bare SiO2 particles. The negative surface charge at the water/oil–silica interface was found to increase with pH, resulting from the increase in ionisation of the oil polar fraction acidic surface groups. The objective of varying the pH was to analyse the possible acid–base interactions at the water–oil interface for substrates having various oil polar fraction contents. The polar components in the neat oil adsorb on the silica surface and increase its surface charge and stabilisation in water. We found a good correlation between the amounts of the oil polar fractions, the surface concentration of their functional groups (carboxylic and phenolic groups) and the magnitude of their ζ potential at the water/oil–silica interface.

Adsorption and surface properties of silica with transformer insulating oils

Abstract The presence of polar species in transformer insulating oil may cause degradation and electric discharges in the power transformer. Such oil polar fraction can originate either from the neat oil and/or from its oxidative degradation in the power transformer. The aim of this study is to examine the relation between the insulating oil and the electrical properties of its polar fraction in order to predict eventual failure in the power transformer. We investigate at ambient temperature the adsorption of the polar fractions of various transformers insulating oils (a new and two used oils) from the neat oils onto silica particles. The adsorbed amount was higher for the used oils as compared to the new one. Infrared spectra of the polar fraction indicate the presence of hydroxyl, aromatic and carboxyl functional groups that are found in the asphaltenes compounds. Microelectrophoresis study of the oil polar fraction covered silica particles gives negatively charged oil polar fraction. Such oil surface charge depends on the pH and results from the ionisation of the oil acidic surface groups. Finally, we obtain a good correlation between the amount of the oil polar fraction and the magnitude of the zeta potential at the water/oil–silica interface.

Smooth and rough spherical calcium carbonate particles

Several studies dealing with crystallization of calcium carbonate (CaCO3) on solid surface [1] or in solution [2] have shown that the morphology and the growth of the crystal may be affected by the presence of foreign compounds or additives. Almost all such additives, which are organic or inorganic in nature, prevent or reduce the rate of CaCO3 crystallization from supersaturated solutions. Such studies are useful for many industrial applications, such as the production at large-scale of spherical CaCO3 particles with uniform size, and in preventing the precipitation of calcium carbonate in steam boilers. Furthermore in the biological mineralization, the calcium containing salts are the major constituents of mollusk shells. In these mineralized tissues, precipitation of oriented aragonite and calcite CaCO3 forms occur within polymeric tissues matrices. Acidic protein [3] which are located at the surfaces of the matrix interact from the solution with the growing CaCO3 crystals and are responsible for both nucleation and inhibition of crystallization. In the present work crystallisation of calcium carbonate (CaCO3) from supersaturated solutions and in the presence of polystyrene sulfonate (PSS1) and/or polystyrene-polyethylene oxide (SE10-30) copolymer has been investigated. The polyelectrolyte (PSS1) purchased from Aldrich and the copolymer (SE10-30), have molecular weights values equal to, respectively, 7£10 4 and 4000. The polystyrene and the polyethylene blocks of the copolymer SE 10-30 have molecular weights equal to, respectively, 1000 and 3000, and the sample is the same as used elsewhere [4]. Supersaturated solutions for crystal growth experiments were prepared by rapid addition of equal volumes of sodium carbonate (Na2CO3) to calcium nitrate (Ca(NO3)2 4H2O) solutions. In the case of the additives, the polymers aqueous solutions of PSS1 and/or SE10-30 were first added to calcium nitrate solution and the mixtures were stirred for about 15 min prior the rapid addition of Na2CO3 solutions. The crystal growth experiments were made at ambient temperature in a water-jacketed Pyrex glass vessel of 300-ml capacity. The precipitated CaCO3 crystals were recovered by filtration and the dried crystals were gold coated in vacuum and examined by scanning electron microscope at magnifications from£2000 to 30 000.

Adsorption at the solid—solution interface and micelle formation in water of the poly(oxyethylene—styrene—oxyethylene) triblock copolymer

Abstract ABA-type copolymers composed of polystyrene (PS) as the B block and polyoxyethylene (POE) as the A block, having weight fractions (nps) of PS and Mn values in the ranges 16–35% and 12000–27000 respectively, were synthesized by sequential anionic polymerization. Micelle formation in water by triblock copolymers in the concentration range 10−5–1 g dm−3 was investigated by fluorescence probing (FP) and small-angle X-ray scattering (SAXS) methods. The data obtained by the FP method indicate that the CMC is extremely small and not observable over the concentration range studied. The micelle size determined by SAXS was found to increase with the total copolymer chain length. The results are in good agreement with the Star model, and a power-law dependence is found between the radius of gyration R of the micelles and the Mn values of the copolymers investigated. Adsorption measurements from water onto titanium dioxide particles were made with copolymer concentrations ranging from 10−1 to 1 g dm−3. The maximum amount adsorbed and the surface density were found to decrease with increasing nps and molecular weight of the PS block respectively.

Interfacial characteristics of petroleum bitumens in contact with acid water

The chemical and interfacial properties of two bitumens were compared. The chemical properties were characterized by determining the asphaltene and resin contents of the bitumens. The interfacial properties were studied by wettability measurements and by determining the zeta potential of bitumen dispersions in acid water, with and without maturation of asphaltene dispersions in acid water and of bitumen dispersions in acid water containing asphaltenes. The study of the influence of the maturation at 80°C for 7 h and of the addition of asphaltenes on the stability of the bitumen dispersion showed that the evolution of the interfacial properties of the bitumen depends on the resin content of the bitumen.

MINERALOGICAL AND PHYSICO-CHEMICAL CHARACTERIZATIONS OF FERRUGINOUS BEIDELLITE-RICH CLAY FROM AGADIR BASIN (MOROCCO)

The mechanism of formation of detrital, beidellite-rich clay occurring in the Agadir basin (Morocco) is well documented, but its detailed characterization is incomplete which limits its application. The aim of the present study was to provide further details of the mineralogical and physico-chemical characteristics of this clay. Bulk raw clay and its Na+-saturated, <2 μm fraction were characterized using chemical, structural, and thermal techniques. Measurements of induced streaming potential (e.g. particle charge) and of specific surface area and porous volume are reported. The raw clay contained carbonate and quartz as associated minerals along with phyllosilicates (<2 μm particle size). X-ray diffraction and scanning electron microscopy analyses showed that the <2 μm fraction was dominated by a dioctahedral smectite. Because dehydroxylation of this mineral occurred at 510°C, and because it re-expanded in ethylene glycol after Li+-saturation followed by heating at 240°C for 24 h, the mineral was shown to be a beidellite rather than montmorillonite. This assertion was further supported by 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra showing predominantly negative charges in the tetrahedral sheets due to notable Al-for-Si substitutions. The chemical composition of the <2 μm fraction showed an Fe2O3 content which was ~7.52 wt.% greater than those of other beidellite occurrences but not so much that it would be identified as a nontronite. The absence of stretching and bending absorption bands corresponding to characteristic (Fe2OH) units in mid-infrared spectra and their corresponding fundamental overtones or combination bands in near-infrared spectra supported this notion. The structural formula of the beidellite in the present study was determined to be (Si7.51Al0.49)(Al2.99Fe0.68Mg0.33) (Ca0.03Na0.54Mg0.11)O20(OH)4, having dioctahedral ferruginous characteristics with almost 60% of the negative charge found in tetrahedral sheets. The cation exchange capacity determined from the structural formula was ~108 meq/100 g. The specific surface area and total pore volume were ~82.2 m2/g and 0.136 cm3/g, respectively. Interestingly, a detrital rather than a hydrothermal-alteration origin, as reported for other beidellite occurrences, explains its natural abundance and emphasizes the great interest in it.

Photocatalytic activity of TiO2/stevensite nanocomposites for the removal of Orange G from aqueous solutions

Abstract TiO2/stevensite nanocomposite photocatalysts were synthesized by a solvothermal method using TiCl3/HCl as reactants and the stevensite clay mineral extract as support. The prepared photocatalyst samples were then characterized using various techniques such as X-ray diffraction (XRD), Infrared spectroscopy (IR) and Transmission Electron Microscopy (TEM). The Points of Zero Charge (PZC) of the various samples were evaluated by titration of the non-modified and the Ti-modified clay aqueous dispersions, with cationic surfactant solutions. The photocatalytic activity of the resulting nanocomposites samples were evaluated for the removal of Orange G (OG) from aqueous solution as a model dye pollutant. The data indicate that the formation of Na+-stevensite by the TiO2 particles leads to TiO2/stevensite nanocomposites having higher specific surface areas and mesopore volumes, and lower PZC values. Further, the photocatalytic activity was greater for the TiO2/stevensite nanocomposites having the greatest Ti amount, as compared to a pure TiO2 sample, and increased with the increase of the TiO2 content in the TiO2/stevensite nanocomposites.