Léo Mazerolles

Synthesis of brookite TiO2 nanoparticlesby thermolysis of TiCl4 in strongly acidic aqueous media

Nanometric particles of titania, brookite and rutile polymorphs were synthesised by thermolysis of TiCl4 in concentrated HCl solutions. The Cl∶Ti molar ratio seems to be the key factor in determining the crystalline phases and their relative proportions as well as the particle size and a large proportion of brookite can be obtained under specific conditions. The complex Ti(OH)2(Cl)2(OH2)2 seems to be the precursor of the brookite phase. The presence of chloride ions is also necessary to stabilise brookite in suspension. Depending on the acidity and the ageing conditions, different morphologies of brookite nanoparticles are obtained, namely spheroidal particles or platelets. Stable sols of pure brookite are obtained by peptization of the solid phase.

Fracture of metastable tetragonal zirconia crystals

Crystals of single-phased metastable tetragonal zirconia (MTZ) were prepared from skullmelting at the composition ZrO2-3 mol % M2O3 (M = Y, Yb or Gd). The fracture of the tetragonal crystals occurred differently than for the cubic stabilized zirconia ones. The toughness was much higher for the tetragonal specimens and the cleavage planes were not the same as for the fluorite crystals. The results were interpreted by considering the domain microstructure induced by the cubic → tetragonal phase transformation undergone by the crystals.

Highly oriented 3D-hexagonal silica thinfilms produced with cetyltrimethylammonium bromide

Mesoporous silica thin films have been produced by sol–gel chemistry in the presence of cetyltrimethylammonium bromide (CTAB) template. The films were deposited on silicon or glass substrates by dip-coating and underwent different treatments to eliminate the CTAB and create porosity. As-prepared and treated coatings exhibit good optical quality. Their structures were fully characterised by transmission electron microscopy (TEM) performed on film cross-sections and by X-ray diffraction (XRD) in θ–2θ scan mode, as well as in transmission mode using two different scattering geometries. The films exhibit large and homogeneous domains organised in a 3D-hexagonal (P63/mmc) structure with the c axis normal to the surface throughout their whole thickness. Numerical analysis of the TEM pictures confirms the space group deduced from the XRD measurements. To our knowledge, these are the first reported thin films obtained by dip-coating in the presence of CTAB which show such extended and highly mono-oriented 3D-hexagonal (P63/mmc) domains. The film thickness, porosity and refractive index were evaluated by ellipsometry for the various treated films.

Morphology and surface heterogeneities in synthetic goethites

In the framework on a study of the acido-basic and sorption properties of iron oxides, a thorough characterization of two types of goethite powders was performed in several laboratories joined in a common project. Chemical analysis by ICPAES; high-resolution SEM, TEM, and AFM observations; XRD with line width analysis; and argon and nitrogen sorption isotherms were used for that purpose. The main crystallographic faces of goethite particles could be identified as {001}, {101}, and {121}, and their abundance correlated with the distribution of low-pressure argon adsorption local isotherms. These results will be very useful for further studies on the relationship between surface reactivity in aqueous solution and orientation of solid surfaces.

Microstructure and metal-insulating transition of vo2 thin films

Abstract Vanadium oxide thin films were deposited from alkoxide precursors. Upon a thermal treatment under a reducing atmosphere, they led to crystalline VO2, which exhibited the well-known metal-semiconducting transition. The shape and width of the hysteresis curve were related to the microstructure of the films and strongly depend on the preparation procedure.

Sorption kinetics and diffusion of cadmium in calcium hydroxyapatites

Abstract The kinetics of Cd Sorption from aqueous solution on a synthetic calcium hydroxyapatite was investigated at 18, 28 and 75 °C in batch experiments, using also X-ray diffraction, electron microscopy and nuclear microprobe analysis. Cadmium is incorporated into the hydroxyapatite structure via diffusion and substitution for calcium ions, but exchange equilibrium is not achieved even after 12 days of contact at 75 °C and sorption is only partly reversible. Values of diffusion coefficients were estimated from X-ray line broadening and sorption kinetics. The fact that Cd is incorporated into the bulk of the apatite with partial reversibility is important in the context of the safe storage of used sorbent material after decontamination of water polluted by cadmium.

Raman analysis of materials corrosion: The example of SiC fibers

Advanced materials (ceramics, fibers, composites...) exhibit unique high temperature properties but long term durability assessment is mandatory on account of high processing costs. We used Raman micro-spectroscopy to analyze the corrosion resistance of commercially available SiC fibers versus Na+ ions, with or without fiber thermal treatment (in air or in a reducing atmosphere) prior to sodium attack. The lateral resolution of the technique approaches the submicron scale and the analysis of colored materials can be limited to a few tens of nanometers in-depth, which makes Raman micro-spectrometry well suited for the analysis of corrosion films. Although corrosion starts with localized defects in pristine NicalonTM fibers attacked with Na+ (in oxidizing conditions), a protective effect of a silica film is clear for oxidized fibers. The corrosion of SiC crystals seems to be related to stacking faults. Raman-Analyse der Werkstoffkorrosion am Beispiel von SiC-Fasern Fortschrittliche Werkstoffe (Keramiken, Fasern, Verbundwerkstoffe) weisen einzigartige Hochtemperatureigenschaften auf; wegen der hohen Herstellungskosten muss obligatorisch aber auch die Langzeitbestandigkeit beurteilt werden. Um den Korrosionswiderstand von kommerziell erhaltlichen SiC-Fasern gegenuber Na+-Ionen, mit und ohne thermische Behandlung (in Luft oder in einer reduzierenden Atmosphare) vor dem Natriumangriff, zu analysieren, wurde in der vorliegenden Untersuchung die Raman-Mikrospektroskopie eingesetzt. Die laterale Auflosung der Technik bewegt sich im Submikronmasstab und die Analyse des gefarbten Werkstoffes kann auf wenige Zehntel Nanometer in der Tiefe begrenzt werden, wodurch sich die Raman-Mikrospektroskopie fur die Analyse von Korrosionsfilmen gut eignet. Wenn auch die Korrosion mit lokalen Defekten in ursprunglichen NicalonTM-Fasern, die durch Na+ (in oxidierenden Bedingungen) angegriffen wurden, beginnt, so ist doch ein schutzender Effekt des Siliciumoxidfilms fur die oxidierten Fasern erkennbar. Die Korrosion der SiC-Kristalle scheint mit Stapelfehlern in Zusammenhang zu stehen.

Nanocomposites in mullite-ZrO2 and mullite-TiO2 systems synthesised through alkoxide hydrolysis gel routes : microstructure and fractography

The sol-gel process allows preparation of very homogeneous and reactive monolithic, optically clear gels. Low-temperature thermal treatments (700–1000 °C) lead to amorphous optically clear samples (“glass”). Amorphous mullite compositions (0.4Al2O3-0.6SiO2 to 0.8Al2O3-0.2SiO2) retain large amounts of Ti and Zr elements. The crystallization has been studied by differential thermal analysis, dilatometry, X-ray and electron diffraction and Raman scattering. The nucleation begins above 1000 °C with the departure of the last protonic species, the amorphous matrix being completely crystallized only above 1400 °C. The addition of Zr and Ti elements leads to a homogeneous nucleation of phases with a composition close to ZrO2 and Al2Ti3O9 (EDX analysis) above the solubility limit. TEM and SEM analyses show that the precipitate size remains submicrometric over a wide temperature range (1000–1400 °C) and consequently glass-like mechanical properties, as well as toughening effects, caused by the presence of nanoprecipitates, are observed.

Sub-micron sized Al2TiO5 powders prepared by high-energy ball milling

High energy ball milling to obtain ultrafine aluminium titanate particles has been investigated. Tempered steel has been selected as material for the containers and balls because the desirable properties of aluminium titanate are not degraded by small amounts of Fe2O3. The starting powders have been milled during different periods (1–60 h) and the evolution of the morphology and crystallinity of the treated powders as well as the extent of contamination from the milling media have been characterised. Different experimental techniques, X-ray diffraction, BET-analysis, chemical analysis, scanning electron microscopy and low and high resolution transmission electron microscopy have been used. High energy ball milling has been proved to be an efficient route to obtain submicron sized (50–100 nm) aluminium titanate powders, but further milling of the powders is accompanied by contamination from the milling media and the formation of hard agglomerates.

New Method of Porous Oxide Synthesis: Alumina and Alumina Based Compounds

Novelty of the synthesis method is the use of alumina hydroxides with very low initial density ~0.02 g/cm 3 . This porous alumina monolith (PAM) is obtained first by active oxidation of aluminum in a humid atmosphere through a liquid mercury layer. Then, in the second step, a thermal treatment of PAM between 1000 and 1700 °C allows sintering of porous alumina with the density varying between 0.04 and 3 g/cm 3 consisting of - or - alumina crystallites with submicron or micron size and with specific surface area up to ~100 m 2 /g. Fibrous structures have a high surface to volume ratio and transport is possible only along fibers - this determines the kinetics of structure formation and transformations during synthesis. Due to very high porosity, these materials can have different applications: high temperature filters, substrate for the catalysts and nuclear waste storage. Porous aluminas can be impregnated by liquid or gaseous species and after drying and solidification can be used as precursors for subsequent synthesis of porous compounds. Impregnation by magnesium, nickel or cobalt nitrate solutions followed by thermal treatment leads to spinels; synthesis of mullite can be provided using silicon species. The obtained porous spinels have finer microstructures and higher specific surface areas than those formed with -alumina. However, the nanometric size of Al2O3 allows reaction at lower temperatures. Materials, having low density or high porosity, high specific surface area and fine grain structure, are needed for catalysts, sensors, filtration membranes, composites, etc. The range of technological applications of these materials depends on possibilities to obtain and control the required microstructure or/and chemical composition. This paper describes a new approach to the problem of synthesis of porous materials based on alumina and alumina compounds. 2. Nanostructured Alumina