PRODUCTION of THERMAL PHOTONS IN VISCOUS FLUID DYNAMICS WITH TEMPERATURE-DEPENDENT SHEAR VISCOSITY

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

Shear viscosity from thermal fluctuations in relativistic conformal fluid dynamics

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

Study of structural evolution and photoluminescent properties at room temperature of Ca(Zr, Ti)O-3 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Metamorphic evolution of a subduction complex, South Shetland Islands, Antarctica

A subduction complex composed of ocean floor material mixed with arc-derived metasediments crops out in the Elephant Island group and at Smith Island, South Shetland Islands, Antarctica, with metamorphic ages of 120-80 Ma and 58-47 Ma? respectively. Seven metamorphic zones (I-VII) mapped on Elephant Island delineate a gradual increase in metamorphic grade from the pumpellyite-actinolite facies, through the crossite-epidote blueschist facies, to the lower amphibolite facies. Geothermometry in garnet-amphibole and garnet-biotite pairs yields temperatures of about 350 degrees C in zone III to about 525 degrees C in zone VII. Pressures were estimated on the basis of Si content in white mica, Al2O3 content in alkali amphibole, Na-M4/Al-IV in sodic-calcic and calcic amphibole, Al-VI/Si in calcic amphibole, and jadeite content in clinopyroxene. Mean values vary from about 6-7.5 kbar in zone II to about 5 kbar in zone VII. Results from the other islands of the Elephant Island group are comparable to those from the main island; Smith Island yielded slightly higher pressures, up to 8 kbar, with temperatures estimated between 300 and 350 degrees C. Zoned minerals and other textural indications locally enable inference of P-T-t trajectories, all with a clockwise evolution. A reconstruction in space and time of these P-T-t paths allows an estimate of the thermal structure in the upper crust during the two ductile deformation phases (D-1 & D-2) that affected the area. This thermal structure is in good agreement with the one expected for a subduction zone. The arrival and collision of thickened oceanic crust may have caused the accretion and preservation of the subduction complex. In this model, D-1 represents the subduction movements expressed by the first vector of the clockwise P-T-t path, D-2 reflects the collision corresponding to the second vector with increasing temperature and decreasing pressure, and D-3 corresponds to isostatic uplift accompanied by erosion, under circumstances of decreasing temperature and pressure.

The use of apatite fission track thermochronology to constrain fault movements and sedimentary basin evolution in northeastern Brazil

An apatite fission track study of crystalline rocks underlying sedimentary basins in northeastern Brazil indicate that crustal blocks that occur on opposite sides of a geological fault experienced different thermal histories. Samples collected on the West block yielded corrected fission-track ages from 140 to 375 Ma, whereas samples collected on the East block yielded ages between 90 and 125 Ma. The thermal models suggest that each block experienced two cooling events separated by a heating event at different times. We concluded that the West block moved downward relative to the East block ca. 140 Ma ago, when sediments eroded from the East side were deposited on the West side. This process represents the early stage of sedimentary basin formation and the opening of the South Atlantic Ocean in the region. Downward and upward movements related to heating and cooling events of these crustal blocks at different periods until recent times are proposed. (c) 2005 Elsevier Ltd. All rights reserved.

Structural evolution up to 1100 degrees C of xerogels prepared from TEOS sonohydrolysis and liquid phase exchanged by acetone

Silica xerogels were prepared from sonohydrolysis of tetraethoxysilane and exchange of the liquid phase of the wet gel by acetone. Monolithic xerogels were obtained by slow evaporation of acetone. The structural characteristics of the xerogels were studied as a function of temperature up to 1100 degrees C by means of bulk and skeletal density measurements, linear shrinkage measurements and thermal analyses (DTA, TG and DL). The results were correlated with the evolution in the UV-Vis absorption. Particularly, the initial pore structure of the dried acetone-exchanged xerogel was studied by small-angle X-ray scattering and nitrogen adsorption. The acetone-exchanged xerogels exhibit greater porosity in the mesopore region presenting greater mean pore size (similar to 4 nm) when compared to non-exchanged xerogels. The porosity of the xerogels is practically stable in the temperature range between 200 degrees C and 800 degrees C. Evolution in the structure of the solid particles (silica network) is the predominant process upon heating up to about 400 degrees C and pore elimination is the predominant process above 900 degrees C. At 1000 degrees C the xerogels are still monolithic and retain about 5 vol.% pores. The xerogels exhibited foaming phenomenon after hold for 10 h at 1100 degrees C. This temperature is even higher than that found for foaming of non-exchanged xerogels. (c) 2005 Elsevier B.V. All rights reserved.

Evaluation of the thermal diffusivity of vegetable oils during frying by Thermal Lens Spectrometry

In this work we report on the use of the Thermal Lens method to verify the evolution of the thermal diffusivity of sunflower and soybean vegetable oils utilized in preparation of twenty five snacks portions. Our results show that the thermal diffusivity for sunflower oil does not change between 1 and 25 portions of fried snacks. By another hand, the soybean thermal diffusivity exhibits a little decrease for higher portion of fried snacks, indicating that for this oil the triglyceride level is reduced as a degradation process.

Morphological evolution of zinc oxide originating from zinc hydroxide carbonate

Zinc oxide can be obtained by thermal decomposition of hydrozincite, a topochemical reaction. This work reports the relation between zinc oxide morphology and the precursor zinc hydroxide carbonate precipitation time. The morphological evolution was monitored by SEM, IR and XRD. Zinc oxide obtained from initially precipitated hydrozincite consists of porous spherical aggregates and shows a single Zn-O IR vibrational band. At longer periods of precipitation time the aggregates were transformed into spherulitic-shaped zinc oxide particles showing the Zn-O split vibrational band. X-ray patterns show that the hexagonal zinc oxide phase is substantially increased as a function of hydrozincite precipitation time. © 1997 Elsevier Science S.A.

Short Range Order Evolution in the Preparation of SnO2 Based Materials

The evolution of Eu3+ doped SnO2 xerogels to the cassiterite structure observed during sintering was studied by means of Eu3+ spectroscopy, XRD and EXAFS at the Sn K-edge. Eu3+ ions adsorbed at the surface of colloidal particles present a broad distribution of sites, typical of oxide glasses. With sintering at 300°C, this distribution is still broadened. Crystallization is clearly observed by the three techniques with increasing sintering temperature. It is found that the addition of Eu3+ limits the crystallite growth.

EXAFS and XRD Study of the Structural Evolution during Isothermal Sintering of SnO2 Xerogels

The formation of an ordered (crystalline) phase during isothermal sintering of SnO2 monolithic xerogels, at 200, 250, 300, 400, 500, 600 and 700°C, has been analyzed by the combined use of EXAFS and XRD techniques. For the desiccated gel (110°C), EXAFS results show the formation of small microcrystallites with the incipient cassiterite structure. Between 110 and 250°C, the dehydratation reaction leads to an amorphization evidenced by a decrease of the long and short range crystallographic order. It is due to fissure formation in the xerogel network. For higher temperatures, a continuous coagulation of the crystallites occurs, leading to grain growth. Grain and pore growth obeys the same kinetic relation, so that the microstructure grows by simple enlargement while its morphology is static.

Study of crystallite size and strain as a function of morphological evolution in zinc oxide powder obtained from hydroxycarbonate precursor

In this work, zinc oxide samples were obtained from hydroxycarbonate by thermal decomposition at 300°C. Zinc hydroxycarbonate samples were produced by homogeneous precipitation over different periods of time. The method used to obtain zinc oxide produces different morphologies as a function of the precursor precipitation time. Among the obtained particle shapes were porous spherical aggregates, spherulitic needle aggregates, and single acicular particles. This work investigated spherulitic needle-aggregate formation and the correlation among morphology, domain size, and microstrain. Transmission electron microscopy data revealed that the acicular particles that form the spherulitic needle aggregates consist of nanometer crystallites. Apparent crystallite size and microstrain in the directions perpendicular to (h00), (h0l), (hk0), and (00l) planes were invariable as a function of precursor precipitation time. From the results, it was possible to conclude that the precursor precipitation period directly influenced the morphology of the zinc oxide but did not influence average crystallite size and microstrain for ZnO samples. Therefore, using this route, it was possible to prepare zinc oxide with different morphologies without microstructural alterations. © 2001 International Centre for Diffraction Data.

Chlorine evolution during the fusion of chlorofluoroindate glasses

Samples with a composition of 40InF 3-20ZnF 2-5MCl- xBaF 2-ySrF 2, where M=Na, Li and x+y=35 mol%, were prepared. The thermal properties related to the Ba/Sr ratio and to the remaining chlorine content in the glasses were studied. Thermal stability is improved with the addition of chlorine. However, chlorine concentration is regulated by the sublimation of indium fluorides which takes place at about 600°C. Indium fluorides arc formed during glass fusion. The mechanisms of chlorine sublimation were studied. © 2005 Akadémiai Kiadó, Budapest.

XAS/WAXS time-resolved phase speciation of chlorine LDH thermal transformation: Emerging roles of isovalent metal substitution

The XAS/WAXS time-resolved method was applied for unraveling the complex mechanisms arising from the evolution of several metastable intermediates during the degradation of chlorine layered double hydroxide (LDH) upon heating to 450 °C, i.e., Zn2Al(OH)6·nH2O, ZnCuAl(OH)6·nH2O, Zn2Al 0.75Fe0.25(OH)6·nH2O, and ZnCuAl0.5Fe0.5(OH)6·nH2O. After a contraction of the interlamellar distance, attributed to the loss of intracrystalline water molecules, this distance experiences an expansion (T > 175-225 °C) before the breakdown of the lamellar framework around 275-295 °C. Amorphous prenucleus clusters with crystallo-chemical local order of zinc-based oxide and zinc-based spinel phases, and if any of copper-based oxide, are formed at T > 175-225 °C well before the loss of stacking of LDH layers. This distance expansion has been ascribed to the migration of Zn II from octahedral layers to tetrahedral sites in the interlayer space, nucleating the nano-ZnO or nano-ZnM2O4 (M = Al or Fe) amorphous prenuclei. The transformation of these nano-ZnO clusters toward ZnO crystallites proceeds through an agglomeration process occurring before the complete loss of layer stacking for Zn2Al(OH)6· nH2O and Zn2Al0.75Fe0.25(OH) 6·nH2O. For ZnCuAl(OH)6·nH 2O and ZnCuAl0.5Fe0.5(OH)6· nH2O, a cooperative effect between the formation of nano-CuO and nano-ZnAl2O4 amorphous clusters facilitates the topochemical transformation of LDH to spinel due to the contribution of octahedral CuII vacancy to ZnII diffusion. © 2013 American Chemical Society.

Evolution of the South Atlantic passive continental margin in southern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

The area between São Paulo and Porto Alegre in southeastern Brazil plays a key area to understand and quantify the evolution of the South Atlantic passive continental margin (SAPCM) in Brazil. In this contribution, we present new thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons from metamorphic, sedimentary and intrusive rocks. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4). Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 525.1(2.4). Ma, whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0). Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.5) and 93.0 (2.5). Ma. The spatial distribution of these ages shows three distinct blocks with a different evolution cut by old fracture zones. While the central block exhibits an old stable block, the Northern and especially the Southern block underwent complex post-rift exhumation. The sample of the Northern block shows two distinct cooling phases in the Upper Cretaceous and the Paleogene to Neogene. After sedimentation of the Permian sandstones the samples of the Central block were never heated up over 100. °C with a following moderate to fast cooling phase in Cretaceous to Eocene time and a fast cooling between Oligocene to Miocene. The five thermal models obtained in the Southern block indicate a complex evolution with three cooling phases. The exhumation events of the three blocks correspond with the Paraná-Etendekka event, the alkaline intrusions due to the Trinidad hotspot, and the evolution of the continental rift basins in SE Brazil and are, therefore, most likely to be the major force for the post-rift evolution of the passive continental margin in SE Brazil, which therefore corresponds to the three main phases of the Andean orogeny. © 2013 Elsevier B.V.

Thermal and structural study of glasses in the binary system TeO2-Pb(PO3)(2)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)