Jean-Hugues Thomassin

Experimental seawater-basaltic glass interaction at 50°C: Study of early developed phases by electron microscopy and X-ray photoelectron spectrometry

Experiments on seawater-basaltic glass interaction were made using a particulary high seawater-basaltic glass ratio (14.5 g/cm2; weight ratio: 50). A layered alteration skin is observed at the glass surface, while the variations in the composition of the seawater are imperceptible. Three zones of different composition and structure are distinguished: 1. 1) An external zone, the composition of which evolved to saponite. 2. 2) A median zone of hydrotalcite-like hydroxycarbonate (Mg6Al2CO3(OH)164H2O). 3. 3) An internal zone, between glass and hydroxycarbonates, richer in Fe and in Mg and in which a 10 A interval is observed (by dark field examination) compatible with a TOT type clay mineral. The composition of this zone indicates a mixing of poorly crystalline products. The principal chemical exchanges between glass and solution are the release of Ca in solution and the contribution of Mg and CO2 from seawater to form hydroxycarbonates, which are considered precursors of phyllosilicates. Comparison with natural phenomena (palagonitization) is made.

An XPS study of the dissolution kinetics of chrysotile in 0.1 N oxalic acid at different temperatures

The dissolution of chrysotile is studied in regard to the surfaces analysis by photoelectron spectrometry. After leaching of chrysotile (Provenance: Thetford; about 200 mg of fibers of 1 cm length) in nonstirred 0.1 N oxalic conditions, the composition of the mineral surfaces is determined by XPS; kinetic curves of dissolution are given in the range 22–80°C.Two conditions for the rate-limiting step are involved for the explanation of the dissolution: diffusion of Mg2+ through the fibrous gel or dissociation of chrysotile. By the former, some values of the diffusion coefficient are proposed: D varies from 5·10−19 cm2s−1 to 5·10−16 cm2s−1, in the range 22–80°C. By the second model, the leaching rate is estimated from 3 Å (22°C) per h to 250 Å (80°C) per h. For the 2 models, the activation heat energy is in the range 15–20 Kcal.

Study of the early hydration of Ca3SiO5 by X-ray photoelectron spectrometry

C3S pastes (W/S = 0.5), have been studied from 5 seconds to 4 hours by X-ray Photoelectron Spectrometry. XPS reveals surface transformations of C3S grains from very early ages of hydration. The modifications have been evidenced by a change in the environment of Si atoms and a variation of the Ca/Si ratio. A Primary Hydrate (C/S << 3), a Secondary Hydrate (C/S ⋍2) and a Tertiary Hydrate (CSH type I) have been identified. XPS is a sensitive and reproducible method for the study of the surface C3S hydration.

Experimental hydration of two synthetic glassy blast furnace slags in water and alkaline solutions (NaOH and KOH 0.1 N) at 40° C: structure, composition and origin of the hydrated layer

The hydration of blast furnace slags has been modelled using two synthetic (CaO, SiO2, Al2O3, MgO) glasses with different Al2O3/MgO values. Experiments (duration: 16 h to 150 d) were performed at 40° C in deionized water (pH 6.5) and in NaOH and KOH (0.1 N) solutions (pH=12.9). The hydrated layer was characterized from a combination of several techniques at different scales: surface analysis by XPS and SEM; TEM of ultrathin diamond-cut sections including electron microdiffraction and EDS analysis; X-ray diffraction of scratched powders. In water, the hydrated zone is only about 0.5μm thick after 150 d with a leached layer covered by a thin siliceous film on which are scattered rare amorphous lamellae. In alkali media, the hydrated zone is composed of three parts: an inner layer made of modified residual glass, calcium-depleted and richer in magnesium and aluminium than the initial glass; an intermediate lamellar of constant thickness (O.3μm) after 15 d with magnesium and aluminium as major components (“hydrotalcite type” composition) and labelling the initial solid-solution interface, an outer layer with initially abundant C-S-H more or less carbonated after reaction with atmospheric CO2. The “hydrotalcite-type” layer separates the inner domain dominated by the formation and evolution of a leached glass layer from an outer one, where the precipitation of C-S-H and other amorphous or crystalline compounds, followed by carbonation, are the major processes.

X-ray photoelectron spectroscopy and chemical study of the adsorption of biological molecules on chrysotile asbestos surface☆

Abstract The sorptive properties of chrysotile and Mg-depleted chrysotile fibers were determined. Chemical analysis and X-ray photoelectron spectroscopy (XPS) were used in order to study the adsorption of albumin and of dipalmitoyl phosphatidyl choline liposomes on the fibers. The macromolecules are adsorbed on the surface of chrysotile fibers, the albumin being in the “end-on” position. The adsorption on Mg-depleted chrysotile fibers is different, there is a bulk incorporation of the macro-molecules in the fibers. However, the chemical analysis shows that similar amounts of macromolecules were adsorbed on the undepleted or Mg-depleted fibers. These observations suggest that some biological effects of chrysotile fibers may be related to their physicochemical properties.

Blast-furnace slag hydration. Surface analysis

Abstract X-ray photoelectron spectrometry (XPS) was used to determine the variation of the characteristic ratios Ca/Si, Al/Si and Mg/Si of two different slags (one in granulated, the other in pelletized form) during hydration. The results show that the slag surface is modified as soon as it becomes in contact with water or alkaline solution. The hydrated superficial layer is depleted of calcium but contains alkali ions if instead of water, NaOH or KOH solutions are used in mixing.

Hydrotalcite-like solid solutions with variable SO 4 2− and CO 3 2− contents at 50° C

Hydrotalcite-like solid solutions have been synthesized by coprecipitation in basic solutions with variable SO42−/CO32−ratios. Chemical determination of CO32−in the interlayer was impossible because of the presence of minor hydromagnesite. SO42−was determined both by chemical analysis and X-ray photoelectron spectroscopy (XPS), the two methods giving similar results. A Raman spectrometry gave additional data on the SO42−/CO32−ratio. Then, the stoichiometry of the anionic interlayers, Xs, Xc, and XOHwere determined, and the influence of Xson the c′ parameter (increasing from c′=7.97 Å to c′=8.63 Å between Xs=0 and Xs=1) was characterized. In addition, a partitioning curve of SO42−and CO32−between aqueous solutions and hydrotalcite-like compounds was established. Its general shape strongly suggests a miscibility gap between a sulfate-rich end and a carbonate-rich solid solution (maximum SO42−/CO32−about 0.2). This result explains why most of the hydrotalcites synthesized during experimental alteration of basaltic glasses by sea-water (a sulfate-rich solution) are CO32−-rich solid solutions.

Photoelectron spectroscopy analysis of asbestos dissolution in acidic media of biological interest

Abstract Many authors have studied asbestos dissolution, in relation with physical and chemical properties and/or biological effects. Most often, the experiments have been carried out under conditions poorly related to health problems. A possible conclusion is a correlation between the reactivity of leached mineral surfaces and the cancerigenic power. In earlier works (Thomassin et al. 1977) we have studied the dissolution kinetics of chrysotile using XPS analysis of the solids, after leaching in non-stirred media by strong reagents (0.1 n oxalic acid and 6 n HCl). It appears that the two possible rate-limiting steps are: • -diffusion of Mg++ through an external silica gel, • -chemical reaction. Complementary experiments carried out with 0.01 n HCl favor a rate mechanism involving a chemical reaction, followed by diffusion through a silica layer and a chemical reaction after some collapse or corrosion of the ordered silica gel. Using XPS, we have studied three aspects of asbestos dissolution related to biological problems: 1. 1.comparative leaching study of various asbestos minerals (chrysotile, crocidolite, amosite and anthophyllite) by 0.1 n chemical reagents from the Krebs cycle (pyruvic, citric and oxalo-acetic acids); 2. 2.study of the dissolution mechanism of chrysotile at very low concentrations of oxalic acid (10−4 and 10−6 n ); 3. 3.study of the effects of grinding: The most soluble asbestos is chrysotile, the best of the investigated reagents being pyruvic acid, which is not so active as oxalic acid at the same concentration. At low concentrations, the dissolution of chrysotile in oxalic acid is limited to the first brucite layer; grinding of crocidolite favors significantly its dissolution. These few experiments enable us to suggest that in the human body, except in the stomach, asbestos dissolution is very low, favored by grinding and leaves a surface layer having ordered silanols groups, the high reactivity of which has been demonstrated in the case of chrysotile (pacco et al., 1976).