Síntese e caracterização de PSFC (Pr0,5Sr0,5Fe1-xCuxO3-δ, sendo x=0,2 e x=0,4) para aplicação como catodo de células a combustível de óxido sólido

The PSFC (Pr0.5Sr0.5Fe1-xCuxO3-δ) is a new mixed oxide perovskite and has been studied and evaluated the cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs), mainly due to its good compatibility with the electrolyte (CGO) and its high ionic conductivity and electronic in intermediate temperature. In this work, PSFC powders with two different compositions (Pr0,5Sr0,5Fe0,8Cu0,2O3- PSFC5582 and Pr0,5Sr0,5Fe0,6Cu0,4O3-PSFC5564) were synthesized by the citrate method using a new route. The powders obtained were characterized by thermal analysis (Differential Scanning Calorimetry and Thermogravimetry), and the material calcined at 800, 900 and 1000 °C for 5h were analyzed by X-ray diffractometry (XRD), with the Rietveld refinement of the diffraction data and dilatometry. PSFC5582 composite films were obtained by screen printing of powder calcined at 1000 °C. The films were deposited on substrate ceria doped with gadolinia (CGO) and then sintered at 1050 °C for 2h. The electrochemical performance of the electrodes was evaluated by impedance spectroscopy and the interface electrode/electrolyte was observed by scanning electron microscopy (SEM). The specific resistance area (ASR) was 0.44 Ω.cm² at 800 °C, slightly lower than those reported in the literature for cathodes containing cobalt. The thermal expansion coefficients of both the PSFC compositions were obtained and varied between 13 and 15 x 10-6 °C-1 , in a temperature range of 200 to 650 °C, demonstrating the good thermal compatibility of cathodes with Ce0,9Gd0,1O1,95 electrolytes (CET = 12 x 10-6 °C).

Estudo da influência de sistemas microemulsionados na molhabilidade de arenitos e na recuperação avançada de petróleo

Sandstone-type reservoir rocks are commonly responsible for oil accumulation. The wettability is an important parameter for the physical properties of the container, since it interferes in characteristics such as relative permeability to the aqueous phase, residual oil distribution in the reservoir, operating characteristics with waterflood and recovery of crude oil. This study applied different types of microemulsion systems - MES - in sandstone reservoirs and evaluated their influences on wettability and residual oil recovery. For this purpose, four microemulsion were prepared by changing the nature of ionic surfactants (ionic and nonionic). Microemulsions could then be characterized by surface tension analysis, density, particle diameter and viscosity in the temperature range 30° C to 70° C. The studied oil was described as light and the sandstone rock was derived from the Botucatu formation. The study of the influence of microemulsion systems on sandstone wettability was performed by contact angle measurements using as parameters the rock treatment time with the MES and the time after the brine surface contact by checking the angle variation behavior. In the study results, the rock was initially wettable to oil and had its wettability changed to mixed wettability after treatment with MES, obtaining preference for water. Regarding rock-MES contact time, it was observed that the rock wettability changed more when the contact time between the surface and the microemulsion systems was longer. It was also noted only a significant reduction for the first 5 minutes of interaction between the treated surface and brine. The synthesized anionic surfactant, commercial cationic, commercial anionic and commercial nonionic microemulsion systems presented the best results, respectively. With regard to enhanced oil recovery performance, all systems showed a significant percentage of recovered oil, with the anionic systems presenting the best results. A percentage of 80% recovery was reached, confirming the wettability study results, which pointed the influence of this property on the interaction of fluids and reservoir rock, and the ability of microemulsion systems to perform enhanced oil recovery in sandstone reservoirs.

Estudo da influência de sistemas microemulsionados na molhabilidade de arenitos e na recuperação avançada de petróleo

Sandstone-type reservoir rocks are commonly responsible for oil accumulation. The wettability is an important parameter for the physical properties of the container, since it interferes in characteristics such as relative permeability to the aqueous phase, residual oil distribution in the reservoir, operating characteristics with waterflood and recovery of crude oil. This study applied different types of microemulsion systems - MES - in sandstone reservoirs and evaluated their influences on wettability and residual oil recovery. For this purpose, four microemulsion were prepared by changing the nature of ionic surfactants (ionic and nonionic). Microemulsions could then be characterized by surface tension analysis, density, particle diameter and viscosity in the temperature range 30° C to 70° C. The studied oil was described as light and the sandstone rock was derived from the Botucatu formation. The study of the influence of microemulsion systems on sandstone wettability was performed by contact angle measurements using as parameters the rock treatment time with the MES and the time after the brine surface contact by checking the angle variation behavior. In the study results, the rock was initially wettable to oil and had its wettability changed to mixed wettability after treatment with MES, obtaining preference for water. Regarding rock-MES contact time, it was observed that the rock wettability changed more when the contact time between the surface and the microemulsion systems was longer. It was also noted only a significant reduction for the first 5 minutes of interaction between the treated surface and brine. The synthesized anionic surfactant, commercial cationic, commercial anionic and commercial nonionic microemulsion systems presented the best results, respectively. With regard to enhanced oil recovery performance, all systems showed a significant percentage of recovered oil, with the anionic systems presenting the best results. A percentage of 80% recovery was reached, confirming the wettability study results, which pointed the influence of this property on the interaction of fluids and reservoir rock, and the ability of microemulsion systems to perform enhanced oil recovery in sandstone reservoirs.

Investigations on the Chilean kelp crab Taliepus dentatus

Physiological responses of larval stages can differ from those of the adults, affecting key ecological processes. Therefore, developing a mechanistic understanding of larval responses to environmental conditions is essential vis-à-vis climate change. We studied the thermal tolerance windows, defined by lower and upper pejus (Tp) and critical temperatures (Tc), of zoea I, II, and megalopa stages of the Chilean kelp crab Taliepus dentatus. Tp limits determine the temperature range where aerobic scope is maximal and functioning of the organism is unrestrained and were estimated from direct observations of larval activity. Tc limits define the transition from aerobic to anaerobic metabolism, and were estimated from the relationship between standard metabolic rate and temperature. Zoea I showed the broadest, Zoea II an intermediate, and megalopae the narrowest tolerance window (Tp). Optimum performance in megalopae was limited to Tp between 11 and 15°C, while their Tc ranged between 7 and 19°C. Although Tc may be seldom encountered by larvae, the narrower Tp temperatures can frequently expose larvae to unfavorable conditions that can drastically constrain their performance. Temperatures beyond the Tp range of megalopae have been observed in most spring and summer months in central Chile, and can have important consequences for larval swimming performance and impair their ability to avoid predators or settle successfully. Besides the well-documented effects of temperature on development time, variability in field temperatures beyond Tp can affect performance of particular larval stages, which could drive large-scale variability in recruitment and population dynamics of T. dentatus and possibly other invertebrate species.

Table 1 Core site, fractional abundance of individual isoprenoid GDGTs and TEX86 values

TEXL86 and TEXH86 are organic palaeothermometers based on the lipids of Group 1 Crenarchaeota, recently proposed as a modified version of the original TEX86 index, but with significantly improved geographical coverage. Since few data from the global core top calibration are from the Pacific, this study was carried out to assess whether the global core top calibration is regionally biased or not. The result of principal components analysis of the fractional abundance of GDGTs, an analysis of variance (ANOVA) and the comparison of the residuals of TEXH 86 derived sea surface temperature (SST) estimates of the Pacific subset with that of the global data set suggest that the Pacific subset has a similar TEXH 86-SST relationship with the global data set. However, the regression line through the Pacific data and an ANOVA on the residuals of TEXL 86 derived SST estimates suggest otherwise. The contradictory findings are likely to stem from the large scatter in the Pacific TEXL 86 values in the mid temperature range. While regionality does not seem to exert a strong bias on TEXL 86 and TEXH 86 calibration, it appears that there is a strong need to resolve the large scatter in the global data set, especially in the mid and high latitudes, in order to improve the calibration for a better SST estimation.

Stable oxygen isotope and Mg/Ca ratios on Globorotalia inflata

We present a species-specific Mg/Ca-calcification temperature calibration for Globorotalia inflata from a suite of 38 core top samples from the South Atlantic (from 8° to 49°S). G. inflata is a deep-dwelling planktonic foraminifer commonly occurring in subtropical to subpolar conditions, which qualifies it for reconstructions of the permanent thermocline. Apparent calcification depths and calcification temperatures were determined by comparing measured d18O with equilibrium d18O of calcite based on water column properties. Based on our core top samples, G. inflata apparent calcification depth is constant throughout the South Atlantic mid-latitudes with a depth of 350-400 m within the permanent thermocline. The resulting Mg/Ca-calcification temperature calibration is Mg/Ca = 0.72 +/-0.045/0.042 exp (0.076 +0.006 calcification 2 temperature) (r2 = 0.81) and covers the temperature range 3.1-16.5°C. We applied our Mg/Ca calibration to gravity core PS2495-3 from the Mid-Atlantic Ridge at ca. 41°S to test its validity by reconstructing a low-resolution record covering the last two glacial-interglacial cycles. Our paleotemperature record reveals large changes in temperature for Terminations I and II, when permanent thermocline temperature increased by as much as 8°C. The G. inflata paleotemperature record suggests that oceanic fronts repeatedly migrated over the location of site PS2495-3 during the last 160 kyr. This study shows the potential of G. inflata Mg/Ca to reconstruct paleotemperatures in the permanent thermocline.

Terrigenous input and marine productivity for the Pacific sector of the Southern Ocean based on lipid biomarkers

In this study, we present a new multiproxy data set of terrigenous input, marine productivity and sea surface temperature (SST) from 52 surface sediment samples collected along E-W transects in the Pacific sector of the Southern Ocean. Allochtonous terrigenous input was characterized by the distribution of plant wax n-alkanes and soil-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs). 230Th-normalized burial rates of both compound groups were highest close to the potential sources in Australia and New Zealand and are strongly related to lithogenic contents, indicating common sources and transport. Detection of both long-chain n-alkanes and brGDGTs at the most remote sites in the open ocean strongly suggests a primarily eolian transport mechanism to at least 110°W, i.e. by prevailing westerly winds. Two independent organic SST proxies were used, the UK'37 based on long-chain alkenones, and the TEX86 based on isoprenoid GDGTs. Both, UK'37 and TEX86 indices show robust relationships with temperature over a temperature range between 0.5 and 20°C, likely implying different seasonal and regional imprints on the temperature signal. While alkenone-based temperature estimates reliably reflect modern SST even at the low temperature end, large temperature residuals are observed for the polar ocean using the TEX86 index. 230Th-normalized burial rates of alkenones are highest close to the Subtropical Front and are positively related to lithogenic fluxes throughout the study area. In contrast, highest isoGDGT burial south of the Antarctic Polar Front is not related with dust flux but may be largely controlled by diatom blooms, and thus high opal fluxes during austral summer.

Stable carbon and oxygen isotope ratios of foraminifera from Cretaceous and Paleocene sediments

Detailed analysis of over 200 samples of uppermost Cretaceous and Paleocene sediments from Atlantic Ocean DSDP Sites 384, 86, 95, 152, 144, 20C, 21, 356, 357, and 329 provides new information on the temperature stratification of Paleocene planktonic foraminifera, the temperature and carbon isotopic changes across the Cretaceous/Tertiary boundary, and the fluctuating temperature and carbon isotopic records through the Paleocene ~64.5-54 m.y.). There was a significant temperature rise across the Cretaceous/Tertiary boundary both at the surface and in deep waters of the Atlantic Ocean. This temperature rise occurred before the basal Tertiary 'Globigerina' eugubina Zone, so that in the oldest Paleocene sample yet analyzed from the deep sea (Site 356) temperatures are already three degrees higher at the bottom and at the surface than in the Cretaceous. The temperature rise across the boundaryis more pronounced on the bottom and in samples from higher latitudes. Accompanying the temperature rise across the boundary there is a significant shift in the carbon isotope profile. In the basal Paleocene the foraminifera of the surface zone demonstrate very negative carbon isotope values (unlike in the Cretaceous of today's ocean), while deeper dwelling species have more positive values which then decrease to the bottom. The unusual carbon isotope gradients persist through the first three million years of the Paleocene until towards the top of planktonic foraminiferal Zone P.1 (G. trinidadensis Zone) the foraminifera record a profile more positive at the surface and decreasing towards the bottom (as in today's ocean). During the Paleocene there are two noteworthy rises in surface water temperature; the first around 62-61 m.y. (G. trinidadensis Zone), and the second near the base of the Globorotalia angulata Zone, 60-59 m.y. At this time surface temperatures at low to mid latitudes reached values near 25°C, while at mid-latitude Site 384 temperature highs near 22°C were registered. At a sample spacing of around one per million years, we have only produced some of the detail of these temperature fluctuations. The later Paleocene is generally cooler and there do not seem to be any large variations either through time or latitude. Middle-latitude sites average temperatures near 15°C at the surface, while high lower latitude site temperatures range near 18°C. The most salient feature of the bottom temperature record (based on multispecific samples) through the Paleocene is its lack of fluctuations. There is an overall temperature range of 5°C at these intermediate depth sites (paleodepth estimates between 1500 and 3000 m). Higher values near 13°C accompany the surface temperature peaks around 62 and 60 m.y., while low values near 8°C occur in Zone P.2 (61-60 m.y.). We detected no change in bottom temperature across the paleocene/Eocene boundary in the few samples studied so far. While there are several fluctuations in the carbon isotope values through the early Paleocene, the general trend is one of increasingly positive values at the surface and at depth. This trend culminates in the late Paleocene (upper Zone P.4, about 56-57 m.y.) with a major excursion in the carbon isotope values. At low latitudes the range between the surface and the deepest planktonic foraminifera is a delta13C of 4 per mil as compared with a range of 2 per mil today. The carbon values drop off slightly, but remain strongly positive through the remainder of the Paleocene at most sites. Accompanying the carbon isotope excursion at Site 384 is a productivity increase and a proposed rise in the CCD.

Mg/Ca and stable oxygen isotope ratios of Uvigerina spp. from the Southern Ocean

The sensitivity to temperature of Mg/Ca ratios in the shallow-infaunal benthic foraminifera Uvigerina spp. has been assessed. Core-top calibrations over ~1-20 °C show a range in sensitivity of 0.065-0.084 mmol/mol/°C but few data are available spanning the temperature range anticipated in deep-sea records over glacial-interglacial cycles. In contrast to epibenthic foraminiferal species, carbonate ion saturation appears not to affect Mg/Ca significantly. A method based on estimating the ratio of the temperature sensitivity of foraminiferal Mg/Ca to that of d18Ocalcite shows that sensitivity for Mg/Ca at the high end of the observed core-top range (~0.1 mmol/mol/°C) is required for consistency with LGM-Holocene differences in each property as constrained by independent proxy data. This is supported by a Mg/Ca record for Uvigerina spp. generated for the Southern Ocean over the past 440,000 years from Ocean Drilling Program Site 1123 (Chatham Rise, New Zealand). The record shows variability that correlates with climate oscillations. The LGM deep ocean temperature derived from the Mg/Ca record is -1.1 ± 0.3 °C. Transformation to temperature allows estimates to be made of changes in bottom water temperature and seawater d18O and comparison made with literature records. Analysis reveals a ~2.5-kyr lead in the record of temperature over calcite d18O and a longer lead over seawater d18O. This is a reflection of larger phase offsets at eccentricity periods; phase offsets at tilt and precession are within error zero.

Modeling and simulation of bulk gallium nitride power semiconductor devices

Bulk gallium nitride (GaN) power semiconductor devices are gaining significant interest in recent years, creating the need for technology computer aided design (TCAD) simulation to accurately model and optimize these devices. This paper comprehensively reviews and compares different GaN physical models and model parameters in the literature, and discusses the appropriate selection of these models and parameters for TCAD simulation. 2-D drift-diffusion semi-classical simulation is carried out for 2.6 kV and 3.7 kV bulk GaN vertical PN diodes. The simulated forward current-voltage and reverse breakdown characteristics are in good agreement with the measurement data even over a wide temperature range.

Energy transfer rates and population inversion investigation of sup(1)Gsub(4) and sup(1)Dsub(2) excited states of Tmsup(3+) in Yb:Tm:Nd:KYsub(3)Fsub(10) crystals

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

Nafion-based composite electrolytes for proton exchange membrane fuel cells operating above 120C with titania nanoparticles and nanotubes as fillers

FAPESP:5150

Catalizzatori polifunzionali per la sintesi di Metil Isobutil Chetone

In this work, we have examined the activity and selectivity of new catalysts for the single-stage production of methyl isobutyl ketone (MIBK, 4- methyl-2-pentanone) from acetone (both in liquid and gas phase), using a fixed bed reactor operated in the temperature range between 373 and 473 K. The main reaction pathways for the synthesis of MIBK from acetone are given in Fig.1. The first step is the self condensation of acetone to diacetone alcohol (DAA, 4-hydroxy-4-methyl-2-pentanone); the second step is the dehydration of DAA to mesityl oxide (MO, 4-methyl-3-penten-2-one); the final step is the selective hydrogenation of the carbon–carbon double bond of MO to form MIBK. The most commonly observed side reactions are over-condensations and unselective hydrogenations (also shown in Fig.1). Two types of catalysts were studied: i)Pd supported on MgO-SiO2 mixed oxides with ratio of Mg to Si, synthetized using Ohnishi’s method and ii)Pd supported on alumina doped with 5% or 10% of MgO. The different Mg-Si and Mg-Al catalysts were characterized by different techniques (XRD, BET, SEM, NH3-TPD and CO2-TPD) and tested under different conditions in the condensation of acetone to diacetone alcohol and its dehydration to mesityl oxide to enhance the activity. Palladium was chosen as metal component, and its hydrogenation activity was studied. A low hydrogenation activity negatively affects the acetone conversion and promotes the production of mesityl oxide. Hydrogenation conditions being too severe may favor the unwanted hydrogenation of acetone to 2-propanol and of MIBK to methyl isobutyl carbinol (MIBC, 4-methyl-2-pentanol) but this effect is less detrimental to the MIBK selectivity than an unsufficient hydrogenation activity.

Thermodynamics and Heat Transport of doped Spin-Ice Materials

In this thesis the low-temperature magnetism of the spin-ice systems Dy2Ti2O7 and Ho2Ti2O7 is investigated. In general, a clear experimental evidence for a sizable magnetic contribution kappa_{mag} to the low-temperature, zero-field heat transport of both spin-ice materials is observed. This kappa_{mag} can be attributed to the magnetic monopole excitations, which are highly mobile in zero field and are suppressed by a rather small external field resulting in a drop of kappa(H). Towards higher magnetic fields, significant field dependencies of the phononic heat conductivities kappa_{ph}(H) of Ho2Ti2O7 and Dy2Ti2O7 are found, which are, however, of opposite signs, as it is also found for the highly dilute reference materials (Ho0.5Y0.5)2Ti2O7 and (Dy0.5Y0.5)2Ti2O7. The dominant effect in the Ho-based materials is the scattering of phonons by spin flips which appears to be significantly stronger than in the Dy-based materials. Here, the thermal conductivity is suppressed due to enhanced lattice distortions observed in the magnetostriction. Furthermore, the thermal conductivity of Dy2Ti2O7 has been investigated concerning strong hysteresis effects and slow-relaxation processes towards equilibrium states in the low-temperature and low-field regime. The thermal conductivity in the hysteretic regions slowly relaxes towards larger values suggesting that there is an additional suppression of the heat transport by disorder in the non-equilibrium states. The equilibration can even be governed by the heat current for particular configurations. A special focus was put on the dilution series Dy2Ti2O7x. From specific heat measurements, it was found that the ultra-slow thermal equilibration in pure spin ice Dy2Ti2O7 is rapidly suppressed upon dilution with non-magnetic yttrium and vanishes completely for x>=0.2 down to the lowest accessible temperatures. In general, the low-temperature entropy of (Dy1-xYx)2Ti2O7, considerably decreases with increasing x, whereas its temperature-dependence drastically increases. Thus, it could be clarified that there is no experimental evidence for a finite zero-temperature entropy in (Dy1-xYx)2Ti2O7 above x>=0.2, in clear contrast to the finite residual entropy S_{P}(x) expected from a generalized Pauling approximation. A similar discrepancy is also present between S_{P}(x) and the low-temperature entropy obtained by Monte Carlo simulations, which reproduce the experimental data from 25 K down to 0.7 K, whereas the data at 0.4 K are overestimated. A straightforward description of the field-dependence kappa(H) of the dilution series with qualitative models justifies the extraction of kappa_{mag}. It was observed that kappa_{mag} systematically scales with the degree of dilution and its low-field decrease is related to the monopole excitation energy. The diffusion coefficient D_{mag} for the monopole excitations was calculated by means of c_{mag} and kappa_{mag}. It exhibits a broad maximum around 1.6 K and is suppressed for T<=0.5 K, indicating a non-degenerate ground state in the long-time limit, and in the high-temperature range for T>=4 K where spin-ice physics is eliminated. A mean-free path of 0.3 mum is obtained for Dy2Ti2O7 at about 1 K within the kinetic gas theory.

Tris(2-ethylhexyl) trimellitate (TOTM) as a potential industrial reference fluid for viscosity at high temperatures and high pressures: New viscosity, density and surface tension measurements

Tris(2-ethylhexyl) trimellitate (TOTM) was recently suggested as a reference fluid for industrial use associated with high viscosity at elevated temperature and pressure. Viscosity and density data have already been published on one sample covering the temperature range (303-373) K and at pressures up to about 65 MPa. The viscosity covered a range from about (9 to 460) mPa s. In the present article we study several other characteristics of TOTM that must be available if it were to be adopted as a standard. First, we present values for the viscosity and density obtained with a different sample of TOTM to examine the important feature of consistency among different samples. Vibrating-wire viscosity measurements were performed at pressures from (5 to 100) MPa, along 6 isotherms between (303 and 373) K. Density measurements were carried out from (293 to 373) K up to 68 MPa, along 4 isotherms, using an Anton Paar DMA HP vibrating U-tube densimeter. Secondly, we report a study of the effect of water contamination on the viscosity of TOTM, performed using an Ubbelhode viscometer under atmospheric pressure. Finally, in order to support the use of TOTM as a reference liquid for the calibration of capillary viscometers, values of its surface tension, obtained by the pendant drop method, are provided. (C) 2016 Elsevier B.V. All rights reserved.