The thermal conductivity of wurtzite and zinc blende indium arsenide nanowires was measured using a microfabricated device, with the crystal structure of each sample controlled during growth and determined by transmis...
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The thermal conductivity of wurtzite and zinc blende indium arsenide nanowires was measured using a microfabricated device, with the crystal structure of each sample controlled during growth and determined by transmission electron microscopy. Nanowires of both phases showed a reduction of the thermal conductivity by a factor of 2 or more compared to values reported for zinc blende indium arsenide bulk crystals within the measured temperature range. Theoretical models were developed to analyze the measurement results and determine the effect of phase on phonon transport. Branch-specific phonon dispersion data within the discretized first Brillouin zone were calculated from first principles and used in numerical models of volumetric heat capacity and thermal conductivity. The combined results of the experimental and theoretical studies suggest that wurtzite indium arsenide possesses similar volumetric heat capacity, weighted average group velocity, weighted average phonon-phonon scattering mean free path, and anharmonic scattering-limited thermal conductivity as the zinc blende phase. Hence, we attribute the differing thermal conductivity values observed in the indium arsenide nanowires of different phases to differences in the surface scattering mean free paths between the nanowire samples.
The creep strength enhanced ferritic (CSEF) steels P91 and P92 are extensively used in fossil supercritical power plants due to their improved creep strength at elevated temperatures. Loss of creep strength and/or duc...
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The creep strength enhanced ferritic (CSEF) steels P91 and P92 are extensively used in fossil supercritical power plants due to their improved creep strength at elevated temperatures. Loss of creep strength and/or duc...
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ISBN:
(纸本)9781935117131
The creep strength enhanced ferritic (CSEF) steels P91 and P92 are extensively used in fossil supercritical power plants due to their improved creep strength at elevated temperatures. Loss of creep strength and/or ductility may occur in CSEF steel welds due to formation of fresh martensite, ferrite, or retained austenite during welding and post weld heat treatment (PWHT). Predicting the critical phase transformation temperatures is of practical importance for the development of appropriate welding and PWHT procedures. The available empirical formulae for the determination of critical temperature:;are not applicable for the CSEF steels. A Design of Experiment (DOE) based approach and fractional data analysis were applied to develop formulae for predicting A1 temperature in P91 and P92 steels. The significant factors in the DOE were screened out by factorial experiments based on measurements and thermodynamic simulations. Test samples within the CSEF steels composition ranges were produced by button melting, rolling, normalizing, and tempering. The critical temperatures in these samples were measured by Single Sensor Differential Thermal Analysis (SS-DTA). The results of the DOE and of the fractional data analysis were used to develop predictive formulae for the A 1 temperature in P91 and P92 steels. The predictions of these formulae were validated by comparison to measured values.
Self-assembly of bridged silsesquioxanes with a chemical structure of (RO)3Si-R′-Si(OR)3 represents an efficient approach to design and to fabricate functional organic/inorganic nanocomposites. The desired functional...
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Self-assembly of bridged silsesquioxanes with a chemical structure of (RO)3Si-R′-Si(OR)3 represents an efficient approach to design and to fabricate functional organic/inorganic nanocomposites. The desired functionalities are mainly incorporated into the R′ with R of a hydrolysable alkoxide group such as CH3 or CH3CH2. This feature article discusses two typical assembly approaches: self-directed assembly aiming at ordered solid materials and surfactant-directed assembly aiming at periodic mesoporous organosilica, with emphasis on the bridged silsesquioxanes in which conjugated functional organic groups are incorporated. The conjugated moieties are shown to be critical to the resulting assembly structure, morphology, and property. Self-assembly of three bridged silsesquioxanes based on polydiacetylene, perylene, and porphyrin has been detailed, respectively.
Very High Power Ultrasonic Additive Manufacturing (VHP-UAM) system was used to produce aluminum parts from 150 μm thick Al3003-H18 foils. The build was processed at 36 μm vibration amplitude, 8 kN normal load, and 3...
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Very High Power Ultrasonic Additive Manufacturing (VHP-UAM) system was used to produce aluminum parts from 150 μm thick Al3003-H18 foils. The build was processed at 36 μm vibration amplitude, 8 kN normal load, and 35.6 mm/s weld speed at 20 kHz frequency. Almost 100% linear weld density was achieved. A deformation-interaction volume of 20 μm was observed below the bonded interface. The microstructural stability including grain boundary structures, and crystallographic orientations was evaluated after annealing these samples at 343°C for 2 hours and 450°C for 2 hours. After heat treatment, small grains persisted at the interfaces with sluggish grain growth kinetics. In contrast, normal grain growth kinetics was observed in the middle of the foils. Possible mechanisms for such phenomena are discussed.
The Structural properties of Europium (Eu) doped GaN and its relation with optical properties were studied. Concentration quenching of the intensity of the Eu related luminescence observed when Eu concentration exceed...
The Structural properties of Europium (Eu) doped GaN and its relation with optical properties were studied. Concentration quenching of the intensity of the Eu related luminescence observed when Eu concentration exceeds 3 at.%. In situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were carried out to study this luminescence quenching and it was discovered that there is close relationship between the luminescence intensity at 622 nm and structural properties. The cause of the concentration quenching is likely related to the polycrystalline growth as well as to the EuN formation.
Magnetic semiconductors are of interest for emerging spintronic applications, such as the integration of electronic information processing with magnetic data storage. We report on a new approach - furnace annealing un...
Magnetic semiconductors are of interest for emerging spintronic applications, such as the integration of electronic information processing with magnetic data storage. We report on a new approach - furnace annealing under controlled ambients – aimed at increasing Mn incorporation and synthesizing new magnetic semiconductors with Tc greater than/around room temperature. These annealing treatments are hypothesized to reduce the effect of Mn interstitials. We have obtained preliminary SQUID magnetometry results which indicate ferromagnetic Curie temperatures of around 130 K in (In,Mn) Sb and 60 K in (In, Mn)P. X-ray diffraction was used to characterize phase homogeneity.
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