997 resultados para 650-degrees-c
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The high-temperature oxidation behavior of modified 304 austenitic stainless steels in a water vapor atmosphere was investigated. Samples were prepared by various thermo mechanical treatments to result in different grain sizes in the range 8-30 mu m. Similar I 3 pound grain boundary fraction was achieved to eliminate any grain-boundary characteristics effect. Samples were oxidized in an air furnace at 700 A degrees C with 20 % water vapor atmosphere. On the fine-grained sample, a uniform Cr2O3 layer was formed, which increased the overall oxidation resistance. Whereas on the coarse-grained sample, an additional Fe2O3 layer formed on the Cr-rich oxide layer, which resulted in a relatively high oxidation rate. In the fine-grained sample, grain boundaries act as rapid diffusion paths for Cr and provided enough Cr to form Cr2O3 oxide on the entire sample surface.
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In this study tensile properties of consolidated magnesium chips obtained from solid state re-cycling (SSR) has been examined and correlated with the microstructure. Chips machined from as-cast billet of pure magnesium were consolidated through SSR technique, comprising of compaction at ambient conditions followed by hot extrusion at four different temperatures viz., 250, 300, 350 and 400 degrees C. The extruded rods were characterized for microstructure and their room temperature tensile properties. Both ultimate tensile strength and 0.2% proof stress of these consolidated materials are higher by 15-35% compared to reference material (as cast and extruded). Further these materials obey Hall-Petch relation with respect to strength dependence of grain size. Strain hardening behavior, measured in terms of hardening exponent, hardening capacity and hardening rate was found to be distinctly different in chip consolidated material compared to reference material. Strength asymmetry, measured as a ratio of compressive proof stress to tensile proof stress was higher in chip consolidated material. (C) 2012 Elsevier B.V. All rights reserved.
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The fracture of eutectic Si particles dictates the fracture characteristics of Al-Si based cast alloys. The morphology of these particles is found to play an important role in fracture initiation. In the current study, the effects of strain rate, temperature, strain, and heat treatment on Si particle fracture under compression were investigated. Strain rates ranging from 3 x 10(-4)/s to 10(2)/s and three temperatures RT, 373 K, and 473 K (100 A degrees C and 200 A degrees C) are considered in this study. It is found that the Si particle fracture shows a small increase with increase in strain rate and decreases with increase in temperature at 10 pct strain. The flow stress at 10 pct strain exhibits the trend similar to particle fracture with strain rate and temperature. Particle fracture also increases with increase in strain. Large and elongated particles show a greater tendency for cracking. Most fracture occurs on particles oriented nearly perpendicular to the loading axis, and the cracks are found to occur almost parallel to the loading axis. At any strain rate, temperature, and strain, the Si particle fracture is greater for the heat-treated condition than for the non-heat-treated condition because of higher flow stress in the heat-treated condition. In addition to Si particle fracture, elongated Fe-rich intermetallic particles are also seen to fracture. These particles have specific crystallographic orientations and fracture along their major axis with the cleavage planes for their fracture being (100). Fracture of these particles might also play a role in the overall fracture behavior of this alloy since these particles cleave along their major axis leading to cracks longer than 200 mu m.
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This paper deals with a combined forming and fracture limit diagram and void coalescence analysis for the aluminum alloy Al 1145 alloy sheets of 1.8 mm thickness, annealed at four different temperatures, namely 200, 250, 300, and 350 A degrees C. At different annealing temperatures these sheets were examined for their effects on microstructure, tensile properties, formability, void coalescence, and texture. Scanning electron microscope (SEM) images taken from the fractured surfaces were examined. The tensile properties and formability of sheet metals were correlated with fractography features and void analysis. The variation of formability parameters, normal anisotropy of sheet metals, and void coalescence parameters were compared with texture analysis.
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The paper reports the synthesis of Nb/Si multilayers (48/27 nm) deposited on Si single crystal substrate by sequential laser ablation of elemental Nb and Si. Significant amount of Nb is found in the amorphous Si layer (similar to 25-35 at.% Nb). The Nb layer is found to be polycrystalline. The phase evolution of the multilayer has been studied by annealing at 600 degrees C for various times and carrying out cross sectional electron microscopic studies. We report the formation of amorphous silicide layer at the Nb/Si interface followed by the formation of the NbSi2 phase in the Si layer. Further annealing leads to the nucleation of hexagonal Nb5Si3 grains in amorphous silicide layers at Nb/NbSi2 interfaces. These results are different from those reported for sputter deposited multilayer. (C) 2013 Elsevier B. V. All rights reserved.
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This work presents micro-actuation of atomic force microscopy (AFM) cantilevers using piezoelectric Zinc Oxide (ZnO) thin film. In tapping mode AFM, the cantilever is driven near its resonant frequency by an external oscillator such as piezotube or stack of piezoelectric material. Use of integrated piezoelectric thin film for AFM cantilever eliminates the problems like inaccurate tuning and unwanted vibration modes. In this work, silicon AFM cantilevers were sputter deposited with ZnO piezoelectric film along with top and bottom metallic electrodes. The self-excitation of the ZnO coated AFM cantilever was studied using Laser Doppler Vibrometer (LDV). At its resonant frequency (227.11 kHz), the cantilever displacement varies linearly with applied excitation voltage. We observed an increase in the actuation response (131nm/V) due to improved quality of ZnO films deposited at 200 degrees C.
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In this paper, we report a novel piezoelectric ZnO nanogenerator on flexible metal alloy substrate (Phynox alloy) for energy harvesting and sensing applications. The vertically aligned ZnO nanowires are sandwiched between Au electrodes. The aligned growth of ZnO nanowires have been successfully synthesized on Au coated metal alloy substrate by hydrothermal method at low temperature (95 +/- 1 degrees C). The as-synthesized vertically aligned ZnO nanowires were characterized using FE-SEM. Further, PMMA is spin coated over the aligned ZnO nanowires for the purpose of their long term stability. The fabricated nanogenerator is of size 30mm x 6mm. From energy harvesting point of view, the response of the nanogenerator due to finger tip impacts ranges from 0.9 V to 1.4V. Also for sensing application, the maximum output voltage response of the nanogenerator is found to be 2.86V due to stainless steel (SS) ball impact and 0.92 V due to plastic ball impact.
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In plants, calcium-dependent protein kinases (CDPKs) are key intermediates in calcium-mediated signaling that couple changes in Ca2+ levels to a specific response. In the present study, we report the high-level soluble expression of calcium-dependent protein kinase1 from Cicer arietinum (CaCDPK1) in Escherichia coli. The expression of soluble CaCDPK1 was temperature dependent with a yield of 3-4 mg/l of bacterial culture. CaCDPK1 expressed as histidine-tag fusion protein was purified using Ni-NTA affinity chromatography till homogeneity. The recombinant CaCDPK1 protein exhibited both calcium-dependent autophosphorylation and substrate phosphorylation activities with a V (max) and K (m) value of 13.2 nmol/min/mg and 34.3 mu M, respectively, for histone III-S as substrate. Maximum autophosphorylation was seen only in the presence of calcium. Optimum temperature for autophosphorylation was found to be 37 A degrees C. The recombinant protein showed optimum pH range of 6-9. The role of autophosphorylation in substrate phosphorylation was investigated using histone III-S as exogenous substrate. Our results show that autophosphorylation happens before substrate phosphorylation and it happens via intra-molecular mechanism as the activity linearly depends on enzyme concentrations. Autophosphorylation enhances the kinase activity and reduces the lag phase of activation, and CaCDPK1 can utilize both ATP and GTP as phosphodonor but ATP is preferred than GTP.
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This paper reports an experimental investigation of oscillating temperature field beneath a single isolated nucleation site using a non-invasive TLC (thermochromic liquid crystal) based thermography technique. Empirical correlations are presented to demonstrate the influence of system pressure and wall heat flux on different ebullition characteristics in the nucleate pool boiling regime of refrigerant R-134a. TLC transient response and two-phase flow structure are captured using synchronized, high resolution imaging. It is observed that the area of influence of nucleation site exhibits a two-part distinct transient behavior during the bubble growth period and broadens to a maximum of 1.57 times the bubble diameter at the instant of bubble departure. This is accompanied by a sharp fall of 2.5 degrees C in the local excess temperature at the nucleation site, which results in momentary augmentation (similar to 40%) in the local heat transfer coefficient at the nucleation origin. The enhanced heat transfer rate observed during the bubble peel-off event is primarily due to transient micro-convection in the wake of the retreating bubble. Further, the results indicate that a slight increase in system pressure from 813.6 to 882.5 kPa has no considerable effect on either the wall superheat or the overall heat transfer coefficient and ebullition frequency. In addition, correlations have been obtained for bubble Reynolds number, Jackob number and the dimensionless bubble generation frequency in terms of modified boiling number.
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Calcium titanate (CaTiO3) nanophosphors were synthesized by three different routes namely solution combustion (SC), modified solid-state reaction (MSS) and solid-state (SS) methods. Rietveld refinement studies revealed the presence of an orthorhombic structure with traces of CaCO3. The crystallite sizes were found to be in the 43-45 nm range. TEM studies also confirm the nano size with well crystalline nature. EPR spectrum for SS method exhibits a broad resonance signal at g = 2.027 is attributed to TiO6](9-) center, whereas in MSS sample the resonance signals are attributed to surface electron and hole trapping sites. The TL behavior has been investigated for the first time using gamma-irradiation. TL glow peak at 169 degrees C were recorded in CaTiO3 prepared by SC, MSS and SS methods. The trapping parameters such as activation energy (E) and order of kinetics (b) were estimated using peak shape method and results are discussed in detail. (C) 2013 Elsevier Ltd. All rights reserved.
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For the first time, high quality tin oxide (SnO2) nanowires have been synthesized at a low substrate temperature of 450 degrees C via vapor-liquid-solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2-4 mu m and diameter of 20-60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO2 nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO2 nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 x 10(-4) mbar suggested that a temperature equal to or greater than 450 degrees C was the best condition for phase pure SnO2 nanowires growth. The SnO2 nanowires grown on a SiO2 substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO2 NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 mu W/cm(2) UV lamp (330 nm) intensity on the photo detector.
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We report on the synthesis, microstructure and thermal expansion studies on Ca0 center dot 5 + x/2Sr0 center dot 5 + x/2Zr4P6 -aEuro parts per thousand 2x Si-2x O-24 (x = 0 center dot 00 to 1 center dot 00) system which belongs to NZP family of low thermal expansion ceramics. The ceramics synthesized by co-precipitation method at lower calcination and the sintering temperatures were in pure NZP phase up to x = 0 center dot 37. For x a parts per thousand yen 0 center dot 5, in addition to NZP phase, ZrSiO4 and Ca2P2O7 form as secondary phases after sintering. The bulk thermal expansion behaviour of the members of this system was studied from 30 to 850 A degrees C. The thermal expansion coefficient increases from a negative value to a positive value with the silicon substitution in place of phosphorous and a near zero thermal expansion was observed at x = 0 center dot 75. The amount of hysteresis between heating and cooling curves increases progressively from x = 0 center dot 00 to 0 center dot 37 and then decreases for x > 0 center dot 37. The results were analysed on the basis of formation of the silicon based glassy phase and increase in thermal expansion anisotropy with silicon substitution.
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The effect of strain rate, (epsilon) over dot, and temperature, T, on the tension-compression asymmetry (TCA) in a dilute and wrought Mg alloy, AM30, over a temperature range that covers both twin accommodated deformation (below 250 degrees C in compression) as well as dislocation-mediated plasticity (above 250 degrees C) has been investigated. For this purpose, uniaxial tension and compression tests were conducted at T ranging from 25 to 400 degrees C with (epsilon) over dot varying between 10(-2) and 10 s(-1). In most of the cases, the stress-strain responses in tension and compression are distinctly different; with compression responses `concaving upward,' due to {10 (1) over bar2} tensile twinning at lower plastic strains followed by slip and strain hardening at higher levels of deformation, for T below 250 degrees C. This results in significant levels of TCA at T < 250 degrees C, reducing substantially at high temperatures. At T=150 and 250 degrees C, high (epsilon) over dot leads to high TCA, in particular at T=250 degrees C and (epsilon) over dot=10 s(-1), suggesting that twin-mediated plastic deformation takes precedence at high rates of loading even at sufficiently high T. TCA becomes negligible at T=350 degrees C; however at T=400 degrees C, as (epsilon) over dot increases TCA gets higher. Microscopy of the deformed samples, carried out by using electron back-scattered diffraction (EBSD), suggests that at T > 250 degrees C dynamic recrystallization begins between accompanied by reduction in the twinned fraction that contributes to the decrease of the TCA.
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Aluminum scandium binary alloys represent a promising precipitation-hardening alloy system. However, the hardness of the binary alloys decreases with the rapid coarsening of Al3Sc precipitate during high-temperature aging. In the current study, we report a new approach to compensate for the loss of mechanical properties by combining rapid solidification with very small ternary addition of transition metal Ni. This addition yields dispersion, and at a critical concentration improves the mechanical properties. We explore additions of a maximum of 0.06 at. pct of Nickel to a binary Al-0.14 at. pct Sc alloy, which yield nickel-rich dispersions. We report two kinds of biphasic dispersions containing AlNi2Sc/Al9Ni2 and alpha-Al/Al9Ni2 phase combinations. The maximum improvement in mechanical properties occurs with the addition of 0.045 at. pct Ni with a yield strength of 239 +/- A 7 MPa for an aging treatment at 583 K (310 A degrees C) for 15 hours. DOI: 10.1007/s11661-013-1624-z (C) The Minerals, Metals & Materials Society and ASM International 2013
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Nanocrystalline delta-NbNx samples have been synthesized by reacting NbCl5 and urea at three different temperatures. A comparison of their structural, magnetic, transport and thermal properties is reported in the present study. The size of the particles and their agglomeration extent increase with increasing reaction temperature. The sample prepared at 900 degrees C showed the highest superconducting transition temperature (T-c) of 16.2 K with a transition width, similar to 1.8 K, as obtained from the resistivity measurement on cold-pressed bars. Above T-c, magnetization measurements revealed the presence of surface ferromagnetism which coexists with superconductivity below T-c. Heat capacity measurements confirm superconductivity with strong electron-phonon coupling constant. The sample prepared at 800 degrees C shows a lower T-c (10 K) while that prepared at 700 degrees C exhibit no superconductivity down to the lowest temperature (3 K) measured.