Thermal behavior of jeriva oil (Syagrus romanzoffiana)

The jeriva is a well-known fruit, which belongs to the Arecaceae family, Syagrus romanzoffiana species frequently found in Brazil. Extraction of the jeriva oil was carried out, and the fatty acid profile of this oil indicates the linoleic and oleic acid presence, around 29.35 and 28.89%, respectively. Thermogravimetry (TG), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) were used to characterize this oil. Additionally, this oil was evaluated by DSC from 25 to -80 A degrees C, and the crystallization behavior was verified. Details concerning the thermal behavior as well as data of kinetic parameters of these stages have been described here. The obtained data were evaluated, and the values were plotted in activation energy (E (a)/kJ mol(-1)) in function of the conversion degree (alpha).

Thermal characterization of the interaction of poly(3-hydroxybutyrate) with maleic anhydride

Poly(3-hydroxybutyrate), PHB, has been structurally modified with maleic anhydride, MA, in the presence of triethylamine, TEA. Glass transition, melting, and crystallization temperature, obtained from DSC curves, and thermal degradation temperatures obtained from TG ones, were employed to evaluate the influence of the MA proportion on the modification in the PHB chain. According to the results, most of chain modification reactions are the 80/20 and 90/10 proportions. Observations suggest that most chain modification reactions occur when the ratio of PHB/MA is 80/20 or 90/10. This suggests that modifications of PHB in the presence of MA involve main chain scission.

Y2O3:Eu3+ (5 mol%) with Ag nanoparticles prepared by citrate precursor

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structure Elucidation and Absolute Stereochemistry of Isomeric Monoterpene Chromane Esters

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural and optical properties of GdAlO3:RE3+ (RE = Eu or Tb) prepared by the Pechini method for application as X-ray phosphors

In this work, GdAlO3:RE3+ (RE = Eu or Tb) was successfully prepared by the Pechini method at lower temperatures when compared to others methods as solid-state synthesis and sol-gel process. In accordance to the XRD data, the fully crystalline single-phase GdAlO3 could be obtained at 900 degrees C. The differential thermal analysis (DTA) shows a crystallization peak at 850 degrees C. The samples are composed by monocrystalline particles (50-120 nm) exhibiting the formation of aggregates among them, which indicates the beginning of the sinterization process. This feature indicates a strong tendency to the formation of aggregates, which is a suitable ability for the close-packing of particles, and hence a potential application in X-ray intensifying screens. Luminescence measurements indicate Gd3+ -> RE3+ energy transfer. The Eu3+ emission spectra exhibit all the characteristics D-5(0) -> F-7(j) transitions and the observed profile suggests that RE3+ ions occupy at least one site without center of symmetry. For terbium-doped samples, the D-5(3) -> F-7(j) (blue emission) and D-5(4) -> F-7(j) (green emission) transitions were observed and the ratio between them may depend on the Tb3+ content due to cross-relaxation processes. (C) 2009 Elsevier B.V. All rights reserved.

Structural Investigations of Glass Ceramics in the Ga2S3-GeS2-CsCl System

Transparent glass ceramics have been prepared in the Ga2S3-GeS2-CsCI pseudoternary system appropriate heat treatment time and temperature. In situ X-ray diffraction at the heat treatment temperature and Cs-133 and Ga-71 solid-state nuclear magnetic resonance have been performed in function of annealing time to understand the crystallization process. Both techniques have evidenced the nucleating agent role played by gallium with the formation of Ga2S3 nanocrystals. on the other hand, cesium is incorporated very much later into the crystallites during the ceramization. Moreover, the addition of CsCl, which is readily integrated into the glassy network, permits us to shift the optical band gap toward shorter wavelength. Thus, new glass ceramics transmitting in the whole visible range up to 11.5 mu m have been Successfully synthesized from the (Ga2S3)(35)-(GeS2)(25)-CsCl40 base glass composition.

Local order around rare earth ions during the devitrification of oxyfluoride glasses

Erbium L-3-edge extended x-ray absorption fine structure (EXAFS) measurements were performed on rare earth doped fluorosilicate and fluoroborate glasses and glass ceramics. The well known nucleating effects of erbium ions for the crystallization of cubic lead fluoride (based on x-ray diffraction measurements) and the fact that the rare earth ions are present in the crystalline phase (as indicated by Er3+ emission spectra) seem in contradiction with the present EXAFS analysis, which indicates a lack of medium range structural ordering around the Er3+ ions and suggests that the lead fluoride crystallization does not occur in the nearest neighbor distance of the rare earth ion. Molecular dynamics simulations of the devitrification process of a lead fluoride glass doped with Er3+ ions were performed, and results indicate that Er3+ ions lower the devitrification temperature of PbF2, in good agreement with the experimental results. The genuine role of Er3+ ions in the devitrification process of PbF2 has been investigated. Although Er3+ ions could indeed act as seeds for crystallization, as experiments suggest, molecular dynamics simulation results corroborate the experimental EXAFS observation that the devitrification does not occur at its nearest neighbor distance. (c) 2008 American Institute of Physics.

Spatial variability of the physical and mineralogical properties of the soil from the areas with variation in landscape shapes

Este trabalho teve como objetivo avaliar a influência das formas do relevo na variabilidade espacial de atributos físicos e suas relações com a mineralogia da argila de um Latossolo Vermelho eutroférrico, utilizando a técnica da geoestatística. Os solos foram amostrados nos pontos de cruzamento de uma malha, com intervalos regulares de 10 m, nas profundidades de 0,0-0,2 m, 0,2-0,4 m e 0,4-0,6 m para os atributos físicos e 0,6-0,8 m para os atributos mineralógicos. Os valores médios para a densidade do solo e resistência do solo à penetração são maiores no compartimento I onde a relação Ct/Ct+Gb é relativamente maior, indicando a presença de maior teor de caulinita. No compartimento II a condutividade hidráulica e a macroporsidade são maiores, influenciados provavelmente pelo predomínio da gibbsita. Portanto, conclui-se que a identificação das pedoformas é muito eficiente para compreender a variabilidade espacial de propriedades do solo. Sendo que, as variações na forma da paisagem promovem variabilidade espacial diferenciada das propriedades físicas e mineralógicas do solo.

Synthesis and Structural Studies of Er3+ Containing Lead Cadmium Fluoroborate Glasses and Glass-Ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Filmes finos de SrBi2Ta2O9 processados em forno microondas

Filmes finos de SrBi2Ta2O9 foram depositados em substratos de Pt/Ti/SiO2/Si e, pela primeira vez, sinterizados em forno microondas doméstico. Os padrões de difração de raios X mostraram que os filmes são policristalinos. O processamento por microondas permite utilizar baixa temperatura na síntese e obter filmes com boas propriedades elétricas. Ensaios de microscopia eletrônica de varredura (MEV) e de Força Atômica (MFA) revelam boa aderência entre filme e substrato, com microestrutura de superfície apresentando grãos finos e esféricos e rugosidade de 4,7 nm. A constante dielétrica e o fator de dissipação, para freqüência de 100 KHz, à temperatura ambiente, foram de 77 e 0,04, respectivamente. A polarização remanescente (2Pr) e o campo coercitivo (Ec) foram 1,04 miC/cm² e 33 kV/cm. O comportamento da densidade de corrente de fuga revela três mecanismos de condução: linear, ôhmico e outro mecanismo que pode ser atribuído à corrente de Schottky. Dos padrões de DRX, análises das imagens por MEV e topografia de superfície por MFA observa-se que 10 min de tratamento térmico a 550 ºC, em forno microondas, é tempo suficiente para se obter a cristalização do filme.

Sinterização de filmes finos de LiNbO3 em forno microondas: estudo da influência da direção do fluxo de calor

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Obtenção in situ do compósito alfa-SiAlON-SiC

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Epitaxially grown LiNbO3 thin films by polymeric precursor method

LiNbO3 thin films were grown on (0001) sapphire substrates by a chemical route, using the polymeric precursor method. The overall process consists of preparing a coating solution from the Pechini process, based on metallic citrate polymerization, the precursor films, deposited by dip coating, are then heat treated to eliminate the organic material and to synthesize the phase. In this work, we studied the influence of the heat treatment on the structural and optical properties of single-layered films. Two routes were also investigated to increase the film thickness: increasing the viscosity of the coating solution and/or increasing the number of successively deposited layers. The x-ray diffraction theta -2 theta scans revealed the c-axis orientation of the single- and multilayered films and showed that efficient crystallization can be obtained at temperatures as low as 400 degreesC, the phi-scan diffraction evidenced the epitaxial growth with two in-plane variants, A microstructural study revealed that the films were crack free, homogeneous, and relatively dense. Finally, the investigation of the optical properties (optical transmittance and refractive index) confirmed the good quality of the films. These results indicate that the polymeric precursor method is a promising process to develop lithium niobate waveguides.

Ferroelectric and microstructural characteristics of SrBi2Ta2O9 thin films crystallized by the rapid thermal annealing process

Ferroelectric SrBi2Ta2O9 thin films on Pt/Ti/SiO2/Si were successfully synthesized by the modified polymeric precursor method. The films were deposited by spin coating and crystallized by rapid thermal annealing in a halogen lamp furnace, followed by postannealing at temperatures ranging from 700 degreesC to 800 degreesC in an oxygen atmosphere. Microstructural and phase evaluations were followed by x-ray diffraction and atomic force microscopy. The films displayed spherical grain structures with a superficial roughness of approximately 3-6 nm. The dielectric constant values were 121 and 248 for films treated at 700 degreesC and 800 degreesC, respectively. The P-E curve showed a voltage shift toward the positive side, which was attributed to crystallization under the halogen illumination. The remanent polarization (2P(r)) and coercive field (E-c) were 7.1 muC/cm(2) and 113 kV/cm, and 18.8 muC/cm(2) and 93 kV/cm for the films treated at 700 degreesC and 800 degreesC, respectively. (C) 2001 American Institute of Physics.

Time dependence and energy-transfer mechanisms in Tm3+Ho3+ and Tm3+-Ho3+ co-doped alkali niobium tellurite glasses sensitized by Yb3+

Glass samples with the composition (mol%) 80TeO(2)-10Nb(2)O(5)-5K(2)O-5Li(2)O, stable against crystallization, were prepared containing Yb3+, Tm3+ and Ho3+. The energy transfer and energy back transfer mechanisms in samples containing 5% Yb3+-5% Tm3+ and 5% Yb3+-5% Tm3+-0.5% Ho3+ were estimated by measuring the absorption and fluorescence spectra together with the time dependence of the Yb3+ F-2(5/2) excited state. A good fit for the luminescence time evolution was obtained with the Yokota-Tanimoto's diffusion-limited model. The up-conversion fluorescence was also studied in 5% Yb-5% Tm. 5% Yb-0.5% Ho and 5% Yb-5% Tm-0.5% Ho tellurite glasses under laser excitation at 975 nm. Strong emission was observed from (1)G(4) and F-3(2) Tm3+ energy levels in all samples. The S-5(2) Ho3+ emission was observed only in Yb3+Ho3+ samples being completely quenched in Yb3+/Tm3+/Tm3+ samples. (C) 2001 Elsevier B.V. B.V. All rights reserved.