André Rulmont

MORPHOLOGICAL STUDY OF MAGNESIUM HYDROXIDE NANOPARTICLES PRECIPITATED IN DILUTE AQUEOUS SOLUTION

Abstract Among other applications, magnesium hydroxide is commonly used as a flame-retardant filler in composite materials, as well as a precursor for magnesium oxide refractory ceramic. The microstructure of the powder is of prime importance in both technical applications. The influence of synthesis parameters on the morphological characteristics of magnesium hydroxide nanoparticles precipitated in dilute aqueous medium was studied. Several parameters were envisaged such as chemical nature of the base precipitant, type of counter-ion, temperature and hydrothermal treatment. Special attention was given to the obtaining of platelet-shaped, nanometric and de-agglomerated powders. The powders were characterized in terms of particle size distribution, crystal habits, morphology and ability to be re-dispersed in water. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and laser diffusion analyses were used for this purpose.

Polymer/layered silicate nanocomposites by combined intercalative polymerization and melt intercalation: a masterbatch process

Abstract Poly(e-caprolactone) (PCL) and poly(vinyl chloride) (PVC) layered silicate nanocomposites were prepared by combination of intercalative polymerization and melt intercalation. In a first step, high clay content PCL nanocomposites were prepared by in situ polymerization of e-caprolactone intercalated between selected organo-modified silicate layers. The polymerization was catalyzed with dibutyltin dimethoxide in the presence of montmorillonites, the surface of which were previously exchanged with (functionalized) long alkyl chains ammonium cations. Then, these highly filled PCL nanocomposites were added as masterbatches in commercial PCL and PVC by melt blending. The intercalation of PCL chains within the silicate layers by in situ polymerization proved to be very efficient, leading to the formation of intercalated and/or exfoliated structures depending on the organo-clay. These masterbatches were readily dispersed into the molten PCL and PVC matrices yielding intercalated/exfoliated layered silicate nanocomposites which could not be obtained by melt blending the matrix directly with the same organo-modified clays. The formation of nanocomposites was assessed both by X-ray diffraction and transmission electronic microscopy. Interestingly, this so-called ‘masterbatch’ two-step process allowed for preparing PCL nanocomposites even with non-modified natural clay, i.e. sodium montmorillonite, which showed a material stiffness much higher than the corresponding microcomposites recovered by direct melt intercalation. The thermal stability of PCL nanocomposites as a function of clay content was investigated by thermogravimetry (TGA).

Vibrational spectroscopy and solid state chemistry

Abstract Some aspects of the application of vibrational spectroscopy to problems of solid state chemistry are reviewed and discussed in the light of the work carried out in the laboratory of inorganic structural chemistry of the University of Liege. The following topics have been considered: Methods of interpretation of the spectra: isomorphic replacements and the vibrational behaviour of solid solutions; isotopic replacement, its possibilities and limitations. Local symmetry of a complex anion: vibrational behaviour of “dilute” solid solutions. Correlations between the coordination of a cation, the cation-oxygen distances and the cation-oxygen vibrational frequencies; application to compounds with unknown structure; detailed discussion of the specific case of titanium in titanates and titano-silicates. Order-disorder phenomena; interest of the simultaneous use of vibrational spectroscopy and X-ray diffraction. Glasses; structural analogies or differences between a crystalline compound and the corresponding glass. Dual structural role of lead in lead borate glasses. Metamict state; evidence of intermediate stages during a recrystallisation process.

Vibrational spectra and structures of double diphosphates M2CdP2O7 (M = Li, Na, K, Rb, Cs)

The cadmium double diphosphates M2CdP2O7 (M = Li, Na, K, Rb, Cs) have been investigated by X-ray diffraction and vibrational spectroscopy. The X-ray diffraction patterns of the Li, Rb, Cs compounds were indexed and their unit-cell parameters determined. The infrared and Raman spectra of these salts are interpreted, and the factor group analysis can be made only for the K2CdP2O7 compound. Non-coincidence of the majority of the Raman and infrared spectra bands confirms a centrosymmetric structure for K2CdP2O7. The vibrational spectra point to a bent POP bridge angle in all these compounds, and their values are estimated using the Lazarev relationship: Δ = (vas POP − vs POP)(vas POP + vsPOP).

Study of the morphology of copper hydroxynitrate nanoplatelets obtained by controlled double jet precipitation and urea hydrolysis

A copper hydroxynitrate of stoichiometry Cu2(OH)3NO3, analogous to the layered double hydroxide family, was synthesized by the so-called controlled double jet precipitation technique, and by hydrolysis of urea in the presence of copper nitrate. Special attention has been focused on the size, morphology and agglomeration tendency of the particles. The aim of this work is to define the optimum precipitation conditions in terms of quality and dispersability of the recovered product. Such platelet-like particles can be used as anisotropic fillers in nanocomposite materials. Several reaction parameters such as flow and concentration of the reactant solutions, design of the reactor and addition of a growth modifier were studied. r 2003 Published by Elsevier Science B.V.

Synthesis and characterization of new inorganic polymeric composites based on kaolin or white clay and on ground-granulated blast furnace slag

Alkali activation of dehydroxylated kaolin or clay yielded high-strength polymeric materials, so-called geopolymers. They were synthesized by mixing the aluminosilicate with solutions of sodium metasilicate and KOH followed by adding 45 wt.% of ground-granulated blast furnace slag. The influence of the aluminosilicate source, its activation temperature, and the order of mixing raw materials were studied on the workability of the blending paste, the microstructure, and the Vickers hardness of the geopolymer samples. The polymeric material is completely amorphous according to x-ray diffraction. Solid-state 2 7 A1 and 2 9 Si magic-angle-spinning nuclear magnetic resonance showed that the geopolymer consists of AlO 4 and SiO 4 tetrahedra linked together through a polymeric network constituted by branched entities SiQ 4 (4A1) and SiQ 4 (3A1), but also by less-polymerized silicates SiQ 1 and SiQ 2 . Scanning electron microscopy showed a homogeneous polymeric gel matrix containing unreacted slag (and quartz) grains; thermogravimetric analysis and differential scanning calorimetry exhibited a high content of water and an elevated melting point (1260 °C). Vickers hardness values are in the range of 200 MPa.

Nouvelles solutions solides LI(MIV)2−x(NIV)x(PO4)3 (L = Li,Na M,N = Ge,Sn,Ti,Zr,Hf) synthèse et étude par diffraction x et conductivité ionique

Abstract Definite Nasicon-like compounds LI(MIV)2(PO4)2 and new solid solutions LI(MIV)2−x(NIV)x(PO4)3 (L = Li,Na, M,N = Ge,Sn,Ti,Zr,Hf) have been synthesized and studied by X-ray powder diffraction and ionic conductivity measurements. A new single phase of the compound LiSn2(PO4)3 has been obtained for the first time. Concerning the solid solutions, continuous series of well-crystallized single phases can be synthesized in the Ti ↔ Ge, Sn ↔ Ti, and Sn ↔ Zr systems, but not in the Ge ↔ Zr, Zr ↔ Ti, and Sn ↔ Ge systems, because of important differences of ionic radii. When solid solutions are possible, the variation of ionic conductivity with x is regular except in LiSn2−xZrx(PO4)3, where it reaches a maximum near x = 1 (σ ≈ 7 10−3 Ω−1 cm−1 at 600 K).

Ionic conductivity of the Na1+xM x III Zr2?x(PO4)3 systems (M = Al, Ga, Cr, Fe, Sc, In, Y, Yb)

The existence and ionic conductivity of solid solutions Na1+xMxIIIZr2−x(PO4)3 with Nasicon-like structure have been investigated and the results compared with literature data. A limited range of solid solutions is formed with MIII = aluminium, gallium, yttrium, ytterbium, whereas a continuous series is obtained for MIII = chromium, iron, scandium, indium. The pure end member Na3ln2(PO4)3 is reported for the first time; according to powder diffraction data, it is hexagonal witha = 0.8966(1) andc = 2.2104(4) nm. The small monoclinic distortion already known for MIII = chromium, iron and scandium is restricted tox values very close to 2. Ionic conductivity measurements show that for a given value ofx, the mobility of the Na+ ions is strongly influenced both by the ionic radius and the type of electronic structure of the MIII ion. However, no simple correlation can be found.

Lanthanide borogermanates LnBGeO5: synthesis and structural study by X-ray diffractometry and vibrational spectroscopy

Abstract Ln BGeO 5 borogermanates have been synthesized by solid-state reaction and investigated by powder X-ray diffractometry, infrared, and Raman spectroscopy. A hexagonal, stillwellite-like phase is obtained for Ln = La, Pr, and Nd (low-temperature phase). Smaller cations (Nd to Er and Y) lead to a monoclinic phase, Z = 4, with a = 9.80–10.03, b = 7.42–7.60, c = 4.79–4.96 A, and β = 91°14′–91°54′, depending on the ionic radius of the rare earth. For the smallest lanthanides (Tm, Yb, Lu), no monoclinic phase is obtained: Ln 2 Ge 2 O 7 is eventually formed, with a total loss of B 2 O 3 . The vibrational spectrum of the monoclinic phase points to some analogies with the stillwellite structure, namely a tetrahedral coordination of boron, and an ordered distribution of the BO 4 and GeO 4 tetrahedra.

Synthese et etude de nouveaux arseniates (MI)3(NIII)2(AsO4)3 et de solutions solides (MI)3(NIII)2(AsO4)x(PO4)3−x (M = Li, Na; N = Fe, Sc, In, Cr)

Abstract New compounds ( M I ) 3 ( N III ) 2 (AsO 4 ) 3 ( M = Li, Na; N = Cr, Fe, In, Sc) have been studied by X-ray powder diffraction, infrared and Raman spectroscopies, and ionic conductivity measurements. The powder diagram of Na 3 In 2 (AsO 4 ) 3 has not been indexed. Li 3 Cr 2 (AsO 4 ) 3 has a garnet structure, in which Li + ions are eightfold coordinated. Na 3 Sc 2 (AsO 4 ) 3 is structurally related to γ-Na 3 Sc 2 (PO 4 ) 3 (hexagonal Nasicon-like structure) whereas the three compounds Li 3 (Fe, In, Sc) 2 (AsO 4 ) 3 are structurally related to monoclinic Fe 2 (SO 4 ) 3 . These two structures are related, but sufficiently different to prohibit solid-solutions. Li 3 (Fe, In, Sc) 2 (AsO 4 ) 3 and Na 3 Sc 2 (AsO 4 ) 3 form continuous solid-solutions with the corresponding phosphates. In the Li 3 (Fe, In, Sc) 2 (AsO 4 ) x (PO 4 ) 3− x solid-solutions, the ionic conductivity reaches a maximum near x = 1 or 2; so, the conductivities of Li 3 Sc 2 (AsO 4 )(PO 4 ) 2 and Li 3 Fe 2 (AsO 4 ) 2 (PO 4 ) are equal to 5.10 −2 Ω −1 cm −1 at 600 K, which is an excellent value for Li + conductors. No simple relationship can be established between ionic conductivity and chemical formula or cell parameters.