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1

Simulated catalytic properties of Ce02 and Ru02 nanostructured dioxides under air-CH4 gas flow

Nowakowski P., Villain S., Gavarri J. R., Kopia A., Kusinski J.

Inżynieria Materiałowa

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2007

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Vol. 28, nr 3-4

313-316

EN

In this work, we present the elaboration of nanostructured powders of cerium dioxide (Ce02.z) and ruthenium dioxide Ru02 by sol gel wute and their catalytic activities in presence of air methane mixtures. Prom Fourier transform infrared spectroscopy, the conversion rate of CH4 into C02 and H20 was determined as function of time. Nanostructured powders of Ce02 and Ru02 presented very different activities in presence of air-CH4 flows. We propose a semi-empirical Avrami' s approach of catalytic kinetics for these two different systems exposed to gas reduction during long times.

2

Lanthanum hydroxycarbonates and langasite ceramics: staility, infrared spectroscopy and electrical behaviors

Ouzaouit K., Bakiz L., Villain S., Benlhachemi A., Essoumhi A., Benyaich H., Guinneton F., Gavarri J-R.

Inżynieria Materiałowa

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2007

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Vol. 28, nr 3-4

330-333

EN

Optimized synthesis routes allowed preparing polycrystalline hydroxycarbonate La203_x(OH)y(C03)z and langasite La3Ga5Si014. Langasite precursor was used to form a first langasite polycrystalline thin film. The thermal stability of lanthanum hydroxycarbonates La203_x(OH)y(C03)z (noted LHC) resulting from surface hydration and carbonation of La203 was studied by Fourier Transform infrared spectroscopy and electrical impedance analysis. Piezoelectric oxide La3Ga5SiO|4 might be used as a piezoelectric substrate associated with catalytic LHC systems, in gas sensor devices

3

Porównanie własności katalitycznych nanokrystalicznych tlenków ceru CeO2 i rutenu RuO2

Kopia A., Nowakowski P., Suliga I., Villain S., Gavarri J.R.

Inżynieria Materiałowa

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2006

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Vol. 27, nr 5

1069-1072

PL

W pracy porównano własności katalityczne tlenków Ce02 i Ru02. Do wytworzenia proszków i cienkich warstw zastosowano technikę zol-żel. Prekursorami były odpowiednio RuCl3xH20 i (NH4)2Ce(N03)6 mieszane z etanolem przez 24h i starzone przez 7 dni. Z tak otrzymanych zoli wytwarzano nanoproszki i warstwy, z wykorzystaniem techniki spin coating. Próbki poddano badaniom struktury: na dyfraktometrze rentgenowskim, mikroskopie skaningowym oraz transmisyjnym mikroskopie elektronowym Własności katalityczne wytworzonych tlenków badano za pomocą spektroskopii w podczerwieni w transformacji Fouriera. Stwierdzono doskonałe własności katalityczne obu tlenków dla reakcji utleniania metanu CH4. Tlenek ceru Ce02 wykazywał silniejszą tendencję do starzenia, a tlenek rutenu Ru02 charakteryzował się szybką regenerację miejsc aktywnych.

EN

In his work we compared the catalytic properties of the nanocrystaline oxides Ce02 and R11O2. The powder and the thin films were prepared by the sol-gel techniques using the RUCl3xH2O and (NH4)2Ce(N03)6 precursors. The thin films were deposited on the Si (100) oriented substrate using spin coating techniques. All samples were examined by X-ray difractometer, scanning electron microscope and high-resolution electron microscope. Nanocrystalline powders were investigated as catalyst for CH4 oxidation. The catalytic test of CH4 at the temperature T=350°C was verified by infrared spectroscopy. In RuO2 we observed the regeneration of the active site, this effect is not observed in the cerium dioxide.

4

Analiza własności katalitycznych i elektrycznych cienkich warstw Ce02 domieszkowanych Nd wytworzonych techniką ablacji laserowej

Kopia A., Chmielowska M., Villain S., Kusiński J., Gavarri J. R.

Inżynieria Materiałowa

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2005

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Vol. 26, nr 5

330-331

PL

Analiza własności katalitycznych i elektrycznych cienkich warstw Ce02 domieszkowanych Nd wytworzonych techniką ablacji laserowej W artykule omówiono wpływ domieszkowania Nd na własności katalityczne i elektryczne cienkich warstw CeO2. Warstwy wytworzono techniką ablacji laserowej na podkładkach Si (001) przy różnych czasach ekspozycji t= 90, 180, 360 s i różnej zawartości procentowej Nd203 (6.5, 15, 21.5, 27 % at.). Uzyskane materiały poddano badaniom struktury: na dyfraktometrze rentgenowskim, mikroskopie skaningowym oraz transmisyjnym mikroskopie elektronowym. Wyniki dyfrakcyjnej analizy fazowej warstw Nd203-Ce02 wykazały obecność fazy CeO2 i brak linii od fazy Nd203. Stwierdzono silne steksturowanie wytworzonych warstw wraz ze wzrostem udziału procentowego Nd203 o czym świadczy zmiana orientacji krystalograficznej z preferowanej (111) na (200). Pomiary własności katalitycznych przeprowadzone w atmosferze CH4. wykazały tylko częściowe utlenianie gazu do H20 i CO2. Pomiary przewodności warstw domieszkowanych w funkcji temperatury wykazały polepszenie własności w stosunku do czystych warstw CeO2.

EN

CeO2 thin films doped with neodymium oxides for gas sensor application were elaborated by pulsed laser deposition technique. The films were deposited on oriented Si (100) substrates with variable deposition times t=90, 180, 360 s and atomic fractions of Nd203 (6.5, 15,21.5,27 %at.) using the excimer laser system (Complex 301 L=248 mm from Lambda Physics Germany). The structure of thin films were characterized by means of X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy both equipment with EDS microanalysis. The catalysis properties was examined by infrared spectroscopy at temperature T=623 K in CH4. gas. The conductivity was determined under air, in the temperature range T=473-873 K.

5

Structure of ferroelectric Aurivillius phases studied by transmission electron microscopy

Madigou V., Villain S., Nihoul G.

Inżynieria Materiałowa

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2004

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R. XXV, nr 3

389-392

EN

We present some results obtained by High Resolution Electron Microscopy (HREM) showing the existence of structural defects in the ferroelectric Aurivillius phases used in non volatile memories FeRAM. These defects are well explained by the particular crystallography of the Aurivillius phases; their existence is important when building FeRAM.

6

Structural and optical properties of thermochromic bilayers CeO2-VO2

Saitzek S., Guirleo G., Guinneton F., Sauques L., Villain S., Aguir K., Leroux C., Gavarri J.R.

Inżynieria Materiałowa

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2004

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R. XXV, nr 3

653-655

EN

Using Radio-Frequency reactive sputtering techniques, thin films of thermochromic vanadium dioxide (presenting a insulator-metal phase transition at Tc = 68°C) were covered by a cerium dioxide layer. Cerium dioxide was chosen for its chemical stability, infrared optical transparency and strong optical absorption in the ultrafiolet range. Vanadium dioxide was first deposited on a silica substrate by Radio Frequency reactive sputtering. Then, a ceria thin film was deposited on the vanadium dioxide film by the same technique. The bilayers were characterized by X-ray diffraction measurements, scanning electron microscopy, transmission electron microscopy and ellipsometry techniques. Optical properties were studied by infrared spectroscopy. The optical properties of these bilayers are similar to optical properties observed for non-coated pure vanadium dioxide films.

7

Nanostructured pure and doped ceria catalysts for gas sensor applications

Saitzek S., Villain S., Fremy M.-A., Leroux C., Nolibe G., Gavarri J.-R.

Inżynieria Materiałowa

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2004

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R. XXV, nr 3

231-233

EN

For many years, CeO2 -based materials have been used as three-ways catalysts (TWC). They are also of great interest as solid electrolytes. It was already shown that nano-structured powders of cerium dioxide are more sensitive than micronic powders, for the detection of carbon monoxide CO or methane CH4 in air. By doping the cerium dioxide with various elements (Cu, V, Mn, ...), we try to improve the selectivity of the detection. The nanopowders of pure and doped cerium oxide were elaborated from "Sol-Gel" process. The structural characterization of these powders was carried out by X-ray diffraction and transmission electron microscopy. The atom fraction of doping element and the homogeneity of the powders were investigated by Energy Dispersive Spectrometry (EDS) microanalysis techniques. Finally, the catalytic activity was determined from (BET) adsorption techniques, spectrometry IR and electrical measurements involing a homemade device.

8

New materials for memories (FeRAM): study of SrBi2Ta2O9 (SBT) thin films on a conductive oxide substrate.

Nihoul G., Villain S., Madigou V., Nigrelli E.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

663-663

9

Nanoparticles of cerium dioxides for gas sensor applications.

Villain S., Leroux C., Musso J., Fremy M.A., Pischedda M.H., Gavarri J.R.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

935-938

EN

The aim of this work is to elaborate nanostructured cerium dioxides for catalytic and gas sensor applications. Nanosized cerium oxide powders were prepared via three chemical routes: 1) chemical precipitation followed by high-energy mechanical milling; 2) soft chemical preparation, 3) an unusual method of pulverization of liquid solution developed in our laboratory. The obtained powders were characterized using X-Ray diffraction analyses and Transmission Electron Microscopy experiments. Nanoparticles of pure CeO2 oxide having their sizes ranging from 2 to 10 nanometers have been obtained.

10

Degradation and percolation in composite materials.

Gavarri J.R., Thommerel E., Villain S., Musso J., Valmalette J.C., Kopia A., Suliga I., Kusiński J.

Inżynieria Materiałowa

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2001

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R. XXII, nr 4

332-332

EN

In this work, we present various modelling approaches available for describing the chemical evolution of a solid polycrystalline system made of at least two phases: these phases can be insulating or conducting, they can be corroded in aggressive environments, or react together at high temperature. Generally, in the case of heterogeneous systems, Avrami models seem to be well adapted to interpret the experimental data. To follow the chemical evolutions as a function of time or composition, we make use of a main technique the electrical complex impedance spectroscopy (ECIS) in a large frequency range (from 10 to the -1 to 10 to the 7 Hz).