Jacky Laureyns

Synergy in intumescence—application to β-cyclodextrin carbonisation agent in intumescent additives for fire retardant polyethylene formulations

Abstract The study first compares the FR performances of ammonium pyrophosphate (PY)-xylitol, PY-d-sorbitol and PY-β-cyclodextrin additives systems with the classical ammonium polyphosphate-pentaerythritol intumescent system in low density polyethylene(LDPE)-based formulations. It shows that β-cyclodextrin, a starch derivative, whose thermal degradation leads to high amounts of carbonaceous residue, is not a carbon source of interest in intumescent FR additives for LDPE-based formulations. A comparative study using X-ray diffraction and Raman spectroscopy shows that the absence of the FR property may be connected both to the development of a free radical reaction in the additive system in the temperature range corresponding to processing reactions and to the presence of a crystalline phase in the carbonaceous materials formed from the additive. Secondly, it is shown using the Sheffe procedure for experiments with mixtures that a synergistic effect exists in the ammonium pyrophosphate-d-sorbitol-β-cyclodextrin system. In particular, the method gives the corresponding composition of the additive mixture. The improved performance is explained by the formation of a large amount of carbonaceous residue when the formulation degrades. Moreover, the synergistic effect is discussed as a competition between antagonistic effects related to chemical characteristics of the char: amounts of free radical in carbon, structural organisation of the char and the presence of crystalline phases.

Microscopic and imaging Raman scattering study of PbS and its photo‐oxidation products

Spatially resolved molecular information on galena (PbS) crystals was obtained by microspectrometric Raman mapping through a high numerical aperture objective. Different experimental conditions were used: excitation wavelength, excitation power, crystal size and temperature. Spatially guided analysis was obtained from the spectra recorded in the point-by-point microprobe mapping mode with 1 µm spacing between the points. Multivariate data processing yielded the typical spectra of PbS and its degradation products. The Raman features of PbS were found to be weak under non-damaging excitation conditions. The laser-damaging effect generates complete and irreversible oxidation of PbS to α-PbO for particles of size of the order of micrometres. For larger PbS crystals, several lead oxysulphates including 4PbO·PbSO4 and 3PbO·PbSO4 were located in the vicinity of the illuminated spot by Raman mapping. Copyright

Chemistry of metal sulfides in anoxic sediments

Using sequential extraction of solid sulfides, the determination of acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS) in anoxic sediments from the Authie Bay (in northern France) has been undertaken because of the importance of the sediments as sinks for iron, sulfur and trace metals and as possible sources of pollution when reduced sediments are mixed with oxic waters (as a result of a sediment remobilization induced by physical disturbances such as tidal currents and dredgings), and subsequently oxidized. Chemical analysis of solutions recovered after sequential leaching of sediments with 1 M HCl, 1 M HF and concentrated HNO3 has enabled us to obtain profiles, s. sediment depth, of trace metals associated with pyrite. Porewater concentration profiles s. depth have been determined for several cations (Ca2+, Cd2+, Cu2+, Fe2+, Mg2+, Mn2+, Na+, Pb2+, Sr2+ and Zn2+) and anions (CO32−, PO43−, SO42− and S2−). Using the chemical equilibrium modeling program MINEQL+ with these analytical data, thermodynamic calculations have given information about the possibility of precipitation of discrete metal sulfide phases (FeS as greigite and amorphous FeS; ZnS, PbS, CuS and CdS), and coprecipitation with adsorption on solid FeS to produce solid solutions with iron sulfides. The degree of trace metal pyritization, DTMP, has been determined for these metals and compared to the degree of pyritization, DOP. The findings suggest that in Authie-bay sediments Mn is well pyritized; whereas Zn, Cu, Ni and above all Cd are weakly pyritized (MnZn≃Cu>NiCd). These observations seem to be intimately related to the existence of the discrete/separate solid phases CuS, CdS and ZnS, as predicted by thermodynamic calculations. Finally, analysis of crude sediments, heavy minerals and pyrite extracted by a heavy liquid density separation method, has been performed with a Raman microprobe to gain information about the geochemical and mineralogical characteristics of these sediments. The efficiency of sequential leachings of sediments (which were used for sedimentary pyrite recovery/attack and analysis of pyritic Fe and trace metal) has also been evaluated by these techniques.

Polarized Single-Crystal Micro-RamanSpectroscopy of As-Synthesized Silicalite-1,Al MFI- and Fe MFI-Type Zeolites

Polarized single-crystal Raman spectra were collected from as-synthesized silicalite-1, Al MFI-type zeolites with different Si/Al ratios and Fe MFI-type zeolite using microspectrometry. These spectra are discussed in relation to the crystal structure of the as-synthesized materials. The assignment of the Raman bands to the zeolite framework and to the occluded tetrapropylammonium (TPA) ion templating the MFI structure was examined through the contribution of the different elements of the Raman tensors as functions of the Al or Fe content, respectively. The spectroscopic results are in good agreement with the conformation and location of the TPA ion in the as-synthetized MFI materials, and also with theoretical predictions of preferential substitution sites despite the low Al or Fe content of the zeolite framework.

Spectroscopic studies of vanadyl–calcite–water–oxygen systems and characterization of oxo-vanadium species deposited on CaCO3

The reactivity of vanadyl ions towards calcite has been studied in deoxygenated and oxygenated ultra-pure water at room temperature using several techniques: electron paramagnetic resonance (EPR), infrared (IR), laser Raman spectroscopy (LRS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and liquid-phase and solid-state 51V NMR. Our investigations reveal that the surface chemistry of calcite depends strongly on the concentrations of VO2+ solutions applied in the process. Indeed, for low VO2+ concentrations (⩽5×10-5 mol dm-3) in interaction with calcite (4×10-2 mol dm-3), it was found that vanadium(IV) is well dispersed on CaCO3 surface in the form of solid solutions, (VO)xCa1-xCO3, and the kinetics of its oxygenation on a monolayer type structure is relatively rapid (half-life time: 9–10 min). However , for higher VO2+ concentrations (10-4 mol dm-3), metallic multilayers (and/or clusters) grow in the medium, and a three or four components solid solution of CaCO3–VOCO3–VO(OH)2–(H2O) appears as a new phase. Such VO(II) complexes (that can be written as follows: (OH)z(H2O)y(VO)xCa1+(z/2)-xCO3) in contact with oxygen lead slowly to the generation of polyoxovanadate species at the calcite surface that contain both V(IV) and V(V) atoms. The combined use of EPR, LRS, IR, XPS and 51V NMR techniques has allowed the successful monitoring of these calcite surface phenomena, proving the existence of these layers, and even identifying the chemical composition of such coatings.

Polarization measurements in micro-Raman and microfluorescence spectrometries

Abstract The depolarization ratios of the Raman and resonance Raman bands of both isotropic and anisotropic samples performed with micro-Raman spectrometers are in good agreement with those obtained with conventional instruments, provided that corrections are made for the effects of the beam splitter and the high numerical aperture objectives. The polarization measurements have been extended to microfluorescence spectrometry and correct results are obtained.

Investigation of orientational behaviour of nematic and smectic a compounds using the Raman microprobe

Abstract The Raman microprobe technique, has been used to probe orientational order in oriented samples of nematic CB 5 and nematic and smectic CB 8 versus spatial localization of the analysed microvolume. In the nematic state, the influence of long-wavelength director fluctuations is pointed out and an elastic constant derived.

Vibrational study of the unusual phase sequence in Tl3Cr(SO4)3: A compound containing [Cr(SO43−3]∞ columns

Abstract The polarized Raman spectra of small single crystals of Tl 3 Cr(SO 4 ) 3 have been recorded using the Raman microprobe technique in the temperature range 295–660 K. The behavior of the external modes is analyzed on polycrystalline samples with conventional Raman spectrometer from 100 K to the decompositon temperature 660 K. Analysis of the spectra, in connection with dielectric measurements and X-ray data show that Tl 3 Cr(SO 4 ) 3 undergoes the following space group phase sequence P2 1 c → 340 K R 3 → 450 K R3c → 630 K R 3 c in accordance with the point group relationship 2 m → 3 →3m→ 3 m