H. Van Damme

Surface properties of an activated bentonite — Decolorisation of rape-seed oils

Abstract The decolorisation of rape-seed oils by a recently discovered Tunisian bentonite was tested. It is proved that this clay has a valuable high decolorizing power after appropriate activation by acids. We have tried to relate the adsorption of a model colored molecule (β-carotene) with the modified surface properties of the activated clay, such as surface area, pore volume, CEC measurements, surface polarity, fractal surface dimension, and data given by IR and XRD spectra. The results of this study show that only a few strong acidic sites due to activation are responsible for the partial removal of the pigments coloring the oils.

Water retention and granular rheological behavior of fresh C3S paste as a function of concentration

Abstract Water retention and rheological behavior of fresh C3S paste have been analysed as a function of C3S volume fraction. Three investigation techniques have been used : (1) the test of water demand, (2) filtration under gas pressure, and (3) shear rheology with normal stress measurements. Cross correlations between shear rheological parameters, dilatancy, and water retention measurement results allow for the construction of a concentration-rheology “phase diagram,” ranging from the concentrated suspension regime, where rheology is dominated by hydrodynamic interactions and follows Krieger-Dougherty equation, to the granular paste regime, where rheology is dominated by fluctuations of solid contacts and where dilatancy sets in.

Preliminary results on the properties of pillared clays by mixed AlCu solutions

Abstract Three crude bentonites samples from USA (W), Tunisia (H) and Algeria (MR) have been used in order to prepare Cu-exchanged and new mixed AlCu pillared clays by three methods (i) a classical ‘dilute suspension and solution’ method by adding the nitrate pillaring solution to a 2% clay suspension, (ii) a ‘powder in solution’ method where the clay powder is dispersed in the pillaring solution and (iii) a ‘concentrated slurry’ method in which a dialysis bag containing clay-water slurry (33% w/w) is placed in the pillaring solution. These three methods are called D, P and CS respectively. Pillaring reactions was performed at 40°C with a OH/(Al + Cu) molar ratio ( R ) equal to 2 and at Cu/(Al + Cu) ratio of 0, 5 and 10%, respectively. Chemical analysis, X-ray diffraction, N 2 BET surface area and cation exchange capacity measurements were carried out to characterize the pillared materials. The results show that after calcination at 300°C, the three pillaring methods lead to a d 001 peak at about 1.8 urn which subsists after one year ageing, and which remains at 1.6 nm even at 800°C for some samples. Catalytic tests in oxidation reaction of phenol by H 2 O 2 in diluted aqueous solution performed at room temperature show an interesting activity of the Cu-clays.

Controlled rate thermal treatment of reactive powder concretes

Abstract Controlled rate thermal analysis (CRTA) was applied to the thermal curing of a reactive powder concrete. Heating was adjusted to keep the rate of gas evolution constant and in dynamic equilibrium at a pressure of 3 Pa. In this way, all internal gradients were kept constant and homogeneous samples were produced. Six different solid-state transformations were detected below 900°C, four of them occurring below 250°C. Under these conditions, no xonotlite or other crystalline silicate hydrates were detected even up to temperatures of 250°C, contrary to what is observed when heating is carried out in regular, nonkinetically controlled conditions, which generate local hydrothermal water vapor pressures inside of the samples. Our results show that controlled rate thermal treatment in dynamic equilibrium with fixed water vapor pressures is a promising method for the accurate control of hydrate crystallization.

Evaluation of the energy barrier for dehydration of homoionic (Li, Na, Cs, Mg, Ca, Ba, Alx(OH)z+y and La)-montmorillonite by a differentiation method

Abstract The thermal energy necessary for the removal of molecular water from Li+-, Na+-, Cs+-, Mg2+-, Ca2+-, Ba2+-, Alx(OH)yz+- and La3+-homoionic montmorillonite powders was determined by thermogravimetric analysis under atmospheric pressure. The weight loss curves and their derivatives exhibit one or several features related to the various populations of water molecules. The activation energy for water removal, which is the sum of the adsorption energy and the activation energy for diffusion, was calculated in each case using a simple first-order differentiation method. The results allow the physisorbed water and the water coordinated to the cations to be clearly separated. For the later population and with the exception of the Na-clay, a good correlation was found between the temperatures and activation energies for water removal and the polarizing power of the cations. Comparison with the results of mechanical tests performed on similar samples suggests that the creep of smectite clays is not controlled by mobility of the individual water molecules but by the mobility of the interlayer cations surrounded by their hydration shell.

Microstructure, permeability and rheology of bentonite — cement slurries

Abstract The microtexture, the water loss, the permeability, and the flow behaviour of bentonite-cement slurries has been interpreted in terms of two major effects : a large calcium ions concentration, on one hand, and a high pH on the other hand.

Polyether-modified fullerenes

SummaryPolyether-modified fullerenes have been prepared under mild conditions by reacting C60 or C70 in toluene with a precursor poly(oxyethylene) or poly(oxypropylene) polymer possessing amino end-groups. In the early stages of the interaction, soluble products are formed. Later, cross-linking proceeds between the polyfunctional fullerenes and the bifunctional polyethers. The non-crosslinked fullerene derivatives are soluble both in toluene and water; by evaporation of toluene, very adhesive films are formed.

A NMR investigation of adsorption/desorption hysteresis in porous silica gels.

The purpose of this study is to investigate possible differences in geometry and connectivity of the liquid phase in a partially water-satured porous medium between the adsorption and the desorption branches, using a series of silica gels. This was done by comparing the T1 and T2 relaxation times (in 1H and 2H nuclear magnetic resonance (NMR) relaxation) as well as the water self-diffusion coefficient D (in 1H) along the two branches of the adsorption/desorption isotherms. The results show that the two relaxation times and the diffusion coefficient are strongly dependent on the water content (saturation level). When plotted in normalized coordinates, the T1 and T2 vs. P/Po curves fit closely the adsorption/desorption isotherms, which validates the two-population, fast-exchange model. Furthermore, because at equivalent saturation levels, there is no difference between the relaxation times and diffusion coefficients obtained along the adsorption branch and those obtained along the desorption branch, one is led to the conclusion that despite different equilibrium conditions, the geometry and connectivity of the liquid phase are statistically the same along the two branches.

A Scaling Model of the Microstructural Evolution in C3S/C-S-H Pastes

In order to build a reliable and multiscale morphological model for the solid-void interface in hardened cement pastes, the textural evolution of hardened C-S-H pastes were characterized at all length scales between the size of the elementary colloidal gel particles and the size of the largest voids, using several nondestructive or mildly destructive structural techniques. The starting samples were all prepared at the same W/C ratio (0.4). Their evolution was monitored between one day and one year. The C3S/C-S-H ratio was measured by X-ray diffraction. Mercury intrusion was used as a standard reference method in order to measure the pore-size distribution and the pore-scaling properties between 1 μm and 10 nm. The specific surface area accessible to water molecules in saturated conditions was measured by proton NMR. Small-angle X-ray scattering was used to determine the scaling properties between 45 nm and 3 nm. A multifractal analysis was performed on digitized transmission electron micrographs obtained from ultrathin (50 nm) slices after stepwise solvent exchange and inclusion.

About Surface Area and Porosity Measurements in Pillared Clays

We discuss the problems raised by chemical heterogeneity and geometrical confinement in pillared clays for the measure of their surface area and their porosity by physical adsorption.