CeO 2 solid solutions synthesized by different chemical routes: crystal structure and local order

Acu˜na, L. M.¹, Zimicz, M. G.¹, Lamas, D. G.¹, Fuentes, R. O.¹, S.A. Larrondo², Fantini, M. C. A.³, and Craievich AF³

1 Consejo Nacional de Investigaciones Cient´ıficas y T´ecnicas - Buenos Aires Argentina

2 Universidad de Buenos Aires - Buenos Aires CapFe Argentina

3 Universidade de S˜ao Paulo - S˜ao Paulo - S˜ao Paulo SP Brazil

ZrO2-CeO2substitutional solid solutions have found application as redox or oxygen storage promoters in three-way catalysts because of their high oxygen storage ca- pacity (OSC). Also, due to their excellent catalytic properties for direct oxidation of hydrocarbons, these materials have been proposed as anodes in intermediate temperature solid oxide fuel cells (IT-SOFCs). In particular, the electrical and catalytic properties are close related to the crystal structure of the powders. In previous XRD studies at LNLS, we found a tetragonal-to-cubic transition as a function of composition and also a tetragonal-to-cubic phase transition as function of temperature in ZrO2-50 and 65 mol% CeO2 nanopowders. In both cases, the cation-oxygen bond was also studied by EXAFS, finding a correlation between the structural and local changes.

In this work, we studied the influence of the synthesis methods on the structure and local order of ZrO2-50, 70 and 90 mol% CeO2nanopowders. Compositionally homogeneous nanopowders were synthesized by gel-combustion and citrate com- plexation methods. Measurements were carried out at the D10B-XPD and D04B- XAFS1 beamlines of the LNLS. We found that the crystallite size and morphology of the powders have been strongly influenced by the synthesis method. Lattice pa- rameters were refined by Rietveld method and local order around Zr cations were studied.

Acknowledgements: This work has been supported by the Brazilian Synchrotron Light Laboratory (LNLS) under proposals D04B - XAFS1 - 4700 and 6706, Agencia Nacional de Promoci´on Cient´ıfica y Tecnol´ogica (Argentina, PICT No. 14268 and PICT No. 38309), CONICET (Argentina, PIP No. 6559), CNPq (Brazil, PROSUL Program) and CAPES-

Characterization of a new material based on polyaniline doped with [Cs][In(dmit)

], (cesium)

[bis(1,3-dithiole-2-thione-4,5-dithiolato)indium (III)] by X-Ray Photoelectron Spectroscopy

Picciani, P.H.S¹, Comerlato, N.M.¹, Soares, B.G.¹, and Souza Jr, F. G.¹ Universidade Federal do Rio de Janeiro - Rio de Janeiro RJ Brazil

A novel conducting hybrid material based on polyaniline doped with a monoan- ion derived from [cesium][bis(1,3-dithiole-2-thione-4,5-dithiolato)indium(III)], ([Cs]

[In(dmit)2]), were prepared. The X-ray photoelectron spectroscopies confirmed that the [Cs] [In(dmit)2] acts as the doping agent for the emeraldine base (insulat- ing form of the polyaniline). This new material presented lower electrical resistivity values than the starting materials, and also formed a flexible, self-supporting film with good homogeneity. The XPS analysis constitutes a powerful tool for character- izing the doping degree of conducting polyaniline. From the characteristic binding energies of the photoelectron, the elements involved can be identified and the peak intensity can be directly related to the atomic concentration in the sample surface.

In addition, the various intrinsic redox states of PAni as well as the different neutral and positive nitrogen spectra can be quantified from the properly curve-fitted N 1s core-level spectrum. The spectrum of the EB sample displayed peaks with binding energies at 397.4 and 399.4 eV, which are related to the imine and amine groups, re- spectively. In addition, one can observe a small signal at around 402 eV, attributed to the positively charged nitrogens. A very interesting result was observed in the spectrum of EB/[Cs][In(dmit)2] (1:1 wt.) blend. This pattern is very similar to that found in polyanilines doped with hydrochloric acid. Furthermore, the polyaniline doped with dmit presented higher amount of the charged nitrogens (56.8 percent) indicating higher doping degree than the sample doped with HCl (46.4 percent).

The ability of [Cs][In(dmit)2] complex in doping polyaniline was also evaluated by others spectroscopic techniques as fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible spectroscopy. Reference: Paulo H.S. Picciani, Fernando G.

Souza Jr., Nadia M. Comerlato, Bluma G. Soares. Synthetic Metals (2007) 157, 1074-1079.

XANES Study of Si and Zr in Composite Hollow Spheres

Andrini, L.¹, Arnal, P. M.², and Requejo, F. G.¹

1 Universidad Nacional de La Plata - La Plata Bs.As Argentina

2 Universidad Nacional de La Plata - La PLata B.A. Argentina

Zirconia is an extremely important material with wide-ranging applications includ- ing as a high-performance transformation-toughened structural engineering ceramic and as a solid electrolyte, and has also found application as a catalyst and catalyst support, especially when durability to chemical attack is required [1].

The Zr L2-L3 and Si K-edges XANES measurements were carried out at D04A- SXS beamline at LNLS. The preparation of nanocrystalline zirconia and hollows spheres (@ZrO₂) were already reported elsewhere [2].

In this work we report a XANES study of Zr and Si present in @ZrO2to obtain information about the electronic and local morphological structure of Zr and Si.

These hollow spheres are made of nanometer-sized zirconia domains surrounded at least partially by a Si-containing material. A pore structure extends from the inner surface, which defines the inner macropore, to the external surface of the spheres, allowing mater diffusion across the shell [3].

According to white line (WL) intensity and the feature of the Si K-edge ab- sorption spectra, the Si atoms in @ZrO2 samples have similar neighborhood that Si in SiO2and they are not forming ZrSiO4. The evaluation of the splitting at the WL of the Zr L2,3 XANES spectra of the samples indicates that, for low treat- ments temperatures (293 K), the local environment of Zr is similar to ZrO2, and for temperatures higher than 973 K, the phase of Zr in @ZrO2 samples is similar to BaZrO3, where Zr is octahedrally coordinated.

References

1. A. V. Chadwick et al., Chem. Mater. 13, 1219 (2001).

2. P.M. Arnal et al., Chem. Mater. 18, 1068 (2006).

3. P.M. Arnal et al., Angewandte Chemie Internation Edition, 45 (2006).

Acknowledgements:

Microstructural Evaluation of Rapidly Solidified Ti-Si-B Alloys via High Resolution TEM

Candioto, K.C.G.¹, Nunes, C. A.¹, and Coelho, G. C.¹

Escola de Engenharia de Lorena - Universidade de S˜ao Paulo - Lorena SP Brazil

Rapidly solidification refers to rapid cooling of liquid metals/alloys at rates higher than 104 K.s-1, which may produce: refinement of the grain size, extension of the solubility limits; formation of nanocrystals; production of metallic glasses. In general, the produced materials present high chemical homogeneity and fine mi- crostructure. In this study, Ti-Si-B samples ( 80 mg) with near sphere shape were levitated, melted and quenched under argon in a splat-cooler apparatus, pro- ducing discs of approximately 20 mm diameter by 0.05 mm thickness. The disks were characterized via X-ray diffraction (XRD) at room temperature and High- Resolution Transmission Electron Microscopy (HRTEM). The XRD results of sev- eral compositions indicated the possible formation of amorphous/nanocrystalline microstructures. Thus, HRTEM was carried out in order to fully characterize the microstructures. Four of the alloys were fully amorphous and seven presented an amorphous matrix with dispersed nanocrystalline regions.

Acknowledgements: This work has been supported by the Brazilian Synchroton Light Laboratory (LNLS) under proposal TEM 7415, CNPq (Proc. 142242/2007-1) and FAPESP (proc. 01/09529-7)

Structural features on corrosion inhibiting properties of siloxane-PMMA hybrid coatings by SAXS and XPS

Sarmento, V.H.V¹, Hammer, P.¹, Pulcinelli, S.H.¹, and Santilli, C.V.¹ Universidade Estadual Paulista - Araraquara - Araraquara SP Brazil

Siloxane-poly(methyl methacrylate), PMMA, hybrid films were deposited by dip- coating on different substrates from a sol prepared by acid hydrolysis and conden- sation of silicon alkoxides: tetraethoxysilane (TEOS) and 3-methacryloxy propy- ltrimethoxysilane (MPTS) and by initialization of the methyl methacrylate (MMA) polymerization with benzoyl peroxide (BPO). The structural features of the films with varying TEOS/MPTS ratio and MMA/MPTS ratio were analyzed by Small Angle X-ray Scattering (SAXS) and X-ray photoelectron Spectroscopy (XPS) and the results were correlated with corrosion protection efficiency in saline environ- ment through electrochemical classic techniques. It was found that the hybrids with TEOS/MPTS and MMA/MPTS ratios of 2 exhibit a highly crosslinked structure.

Structural data obtained after the corrosion tests evidence that the formation of efficient diffusion barrier is directly related to increasing cross-linking density of the hybrid network.

Acknowledgements: The authors gratefully acknowledge FAPESP and CNPQ for finan- cial support and the LNLS for the use of the SAXS beamline and the support of the line staff

Estudo das transforma¸c˜ oes estruturais de comp´ ositos de ferro nanoestruturados em materiais carbonosos porosos em fun¸c˜ ao da temperatura utilizando a linha D10B-XPD

Miguel A. Schettino Jr.¹, Freitas, JCC¹, Morigaki, M. K.¹, E. Nunes¹, Cunha, A.

G.¹, Passamani, E. C.¹, and Francisco G. Emmerich¹ Universidade Federal do Esp´ırito Santo - Vit´oria ES Brazil

Nanopart´ıculas met´alicas dispersas em matrizes de sustenta¸c˜ao tˆem atra´ıdo o in- teresse da comunidade cient´ıfica devido as suas propriedades f´ısicas, peculiares da dimensionalidade reduzida, e seu grande potencial para aplica¸c˜oes tecnol´ogicas. Es- pecificamente, materiais carbonosos contendo comp´ositos de Fe nanopart´ıculados podem ser utilizados como: a) agente de contraste magn´etico para imagem por ressonˆancia magn´etica nuclear de tecidos biol´ogicos, b) precursor para s´ıntese de nanotubos de carbono, entre outras. Este trabalho trata da produ¸c˜ao e caracter- iza¸c˜ao de comp´ositos nanoestruturados de Fe a partir da mistura de 2,0 g de carv˜ao ativado e 1, 2, 3, 4 e 5 mL de pentacarbonil ferro (Fe(CO)5) utilizando dois pro- cedimentos de prepara¸c˜ao simples e de baixo custo: i) sob atmosfera de argˆonio e com temperatura controlada em 120 C (S´erie I) e ii) em atmosfera e temper- atura ambiente (S´erie II). As amostras foram investigadas utilizando experimentos de difra¸c˜ao de raios-X (DRX, com λ=1,746 ) in situ durante o aquecimento da amostra, sob atmosfera de N2, utilizando a linha D10B-XPD do Laborat´orio Na- cional de Luz S´ıncrontron (LNLS). Amostras pr´e-determinadas foram estudadas por espectroscopia M¨ossbauer (EM) com fonte radiativa de ⁵⁷Co:Rh pelo m´etodo de transmiss˜ao. Apesar dos resultados de DRX `a temperatura ambiente eviden- ciarem reduzida cristalinidade para as amostras das S´eries I e II, ficou evidente a presen¸ca das fases α-Fe2O3 e Fe3O4 nas amostras da S´erie II, enquanto que nas amostras da S´erie I predomina apenas a fase Fe3O4. Quando submetidas ao aque- cimento t´ermico, at´e a temperatura de 550 C, os DRX indicam um progressivo estreitamento dos picos de difra¸c˜ao, confirmando a presen¸ca das citadas fases. En- tre as temperaturas de 550 e 900 C, os comp´ositos de Fe, das S´eries I e II, iniciam um processo de transforma¸c˜ao por redu¸c˜ao levando `a forma¸c˜ao do α-Fe, FeC e ainda contribuindo para o processo de grafitiza¸c˜ao do carv˜ao ativado. Os espec- tros de EM registrados `a temperatura ambiente das S´eries I e II mostraram um comportamento para ou superparamagn´etico das nanopart´ıculas dos comp´ositos de

TERMODIN ˆ AMICA DE FORMAC ¸ ˜ AO E ESTRUTURA