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[IEEE 2018 2nd International Conference on Engineering Innovation (ICEI) - Bangkok (2018.7.5-2018.7.6)] 2018 2nd International Conference on Engineering Innovation (ICEI) - Schottky's Barrier Height of T91/Cr2O3 Heterojunction in Dry and Wet Conditions: Effects of WaterVapor Onto Accelerated High Temperature Oxidation
摘要： Increasing the operating temperature in thermal power plant will further accelerate the high temperature oxidation with the presence of water vapor. It is hypothesized that water vapor provides hydrogen that dissolves into the ferritic alloy susbstrate, hence altering their electronic state at the metal-semiconductor (oxide) interface. This study aims to quantitatively prove above postulation by comparing their Schottky’s Barrier Height (SBH) in dry and wet environment. The Schottky’s barrier was prepared by sputtering Cr2O3 onto the T91 boiler tube in high vacuum condition using RF power 150W for an hour. The T91/Cr2O3 junction was then connected with platinum wire for capacitance-voltage, C-V test at high temperature. The value of Vbi was used to calculate the SBH, which increase proportionately with built in voltage. It is clearly shown that the SBH value in wet condition is higher than that in dry condition by 10.3%. This is explained by the formation of space charge layer at metal/oxide interface due to dissolved hydrogen in metal, thus may change the transport property and accelerate the oxidation rate in water vapor.
关键词： T91 alloy,Cr2O3,Schottky’s barrier,High temperature oxidation
更新于2025-09-04 15:30:14
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Additive-Manufacturing of 3D Glass-Ceramics down to Nanoscale Resolution
摘要： Fabrication of a true-3D inorganic ceramic with resolution down to nanoscale (～ 100 nm) using sol-gel resist precursor is demonstrated. The method has an unrestricted free-form capability, control of the ?ll-factor, and high fabrication throughput. A systematic study of the proposed approach based on ultrafast laser 3D lithography of organic-inorganic hybrid sol-gel resin followed by a heat treatment enabled formation of inorganic amorphous and crystalline composites guided by the composition of the initial resin. The achieved resolution of 100 nm was obtained for 3D patterns of complex free-form architectures. Fabrication throughput of 50 × 103 voxels/s is achieved; voxel - a single volume element recorded by a single pulse exposure. A post-exposure thermal treatment was used to form a ceramic phase which composition and structure were dependent on the temperature and duration of the heat treatment as revealed by Raman micro-spectroscopy. The X-ray diffraction (XRD) showed a gradual emergence of the crystalline phases at higher temperatures with a signature of cristobalite SiO2, a high-temperature polymorph. Also, a tetragonal ZrO2 phase known for its high fracture strength was observed. This 3D nano-sintering technique is scalable from nanoscale to millimeter dimensions and opens a conceptually novel route for optical 3D nano-printing of various crystalline inorganic materials de?ned by an initial composition for diverse applications for microdevices designed to function in harsh physical and chemical environments and at high temperatures.
关键词： ultrafast 3D laser nanolithography,3D nanoscale optical printing,inorganic 3D structures,high-temperature glass-ceramic materials,calcination
更新于2025-09-04 15:30:14
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Effect of Tm3+ Sensitization to Ho3+ Doped GeO2-B2O3-BaF2-Al2O3-ZnO2-Na2O Glass on Spectral Properties
摘要： A series of Tm3+/Ho3+ sensitized 65GeO2-7BaF2-10B2O3-4Al2O3-4ZnO2-10Na2O glass samples were synthesized by using high temperature melting method. The spectral properties were systematically studied when Ho3+ concentration was 0.1, 0.3, 0.5 mol % and Tm2O3 changed from 0.3 to 2.5 mol %. Differential thermal analysis showed that ?T was higher than 190 oC, which illustrated this kind of matrix glass have better thermal stability. The absorption cross section peak height, free energy of Ho3+ from 5I8 to 5I7 and emission cross section were calculated according to Mc-Cumber theory. Under the excitation of 808 nm laser diode, fluorescence intensity at 1954 nm reached the highest value when the concentration of Ho3+ was 0.1 mol % and Tm3+ was 0.7 mol %. However the fluorescence intensity reduced greatly when Ho3+ concentration was 0.5 mol % and Tm3+ exceeded 1.5 mol %. The sensitized function and influence of different Tm3+/Ho3+ doped ion ratios on the spectral properties was studied.
关键词： Glasses,Growth from high temperature solutions,Rare earth compounds,Adsorption
更新于2025-09-04 15:30:14
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Regenerated fiber Bragg grating sensing system for ultrasonic detection in a 900 °C environment
摘要： Heat-resistant composites, such as ceramic matrix composites (CMCs) and heat-resistant carbon fiber reinforced plastics (CFRPs), are expected to be used for aircraft engine parts. The development of reliable heat-resistant composite materials requires the use of nondestructive test (NDT) techniques for evaluating the progression of damage during material testing at elevated temperatures. Furthermore, structural health monitoring (SHM) technologies that operate under harsh environments are expected to be realized for monitoring heat-resistant composite structures. To provide potential solutions for the establishment of such technologies, this research developed a heat-resistant ultrasonic sensor based on a regenerated fiber-optic Bragg grating (RFBG). First, we fabricated an RFBG by annealing a normal FBG sensor. Because the RFBG exhibits high heat resistance at temperatures of 1000 °C, the sensor achieved stable ultrasonic detection at an elevated temperature. In addition, we attempted to use a π-phase-shifted FBG (PSFBG) as the seed grating to construct an ultrasonic sensor with enhanced performance. As a result, the R(PS)FBG sensor possessed a very short effective gauge length and achieved a broad frequency response to ultrasonic waves with frequencies greater than 1.5 MHz. The broadband detectability enables the R(PS)FBG sensor to acquire an accurate response to ultrasonic waves. Hence, we believe the regenerated Bragg grating-based ultrasonic sensors can contribute to establishing an effective nondestructive evaluation method for composite materials, thereby enabling a structural health monitoring system for a composite-made structure operating under extreme high-temperature environments.
关键词： structural health monitoring (SHM),ultrasonic detection,nondestructive test (NDT),regenerated fiber-optic Bragg grating (RFBG),high-temperature environment,Heat-resistant composites
更新于2025-09-04 15:30:14
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High-temperature tungsten trioxides obtained by concentrated solar energy: physicochemical and electrochemical characterization
摘要： High-crystalline tungsten trioxides (WO3) have been synthesized by an environmentally friendly method using concentrated solar energy. The obtained tungsten trioxides (WO3) at three different temperatures and two oxygen mole fractions used for the highest synthesis temperature were characterized by XRD, SEM, and XPS. Higher crystallinity and concentration of W5+ was observed in tungsten trioxides as the synthesis temperature increased. Nevertheless, despite of the different synthetic conditions used, a mixture of two different crystalline structures was observed in all solar-prepared tungsten trioxides: monoclinic and triclinic. Comparing oxides obtained at 1000 °C, higher concentration of W5+ and more defects were found when using lower oxygen molar fraction (WO3-1000-2). Their electrochemical performance was evaluated using cyclic voltammetry (CV) in a conventional three-electrode cell in the following three aqueous electrolytes: acidic, alkaline, and neutral media. In the acidic medium, all the tungsten trioxides showed a capacitive behavior, which was enhanced for oxides obtained at 1000 °C due to a mixed valence of W. On the other hand, in the alkaline medium, a catalytic behavior was detected with higher activity towards hydrogen evolution reaction for the oxide with more defects, higher crystallinity, and monoclinic phase, obtained at 1000 °C and a lower oxygen molar fraction in the synthesis. Finally, in the neutral medium, the oxides synthesized at 1000 °C presented a capacitive behavior whereas the oxides prepared at the lowest temperatures (600 and 800 °C) presented electrochemical processes related to a catalytic behavior for water reduction, which must correspond to their minor concentration of defects, as confirmed by XPS.
关键词： High-temperature synthesis,Concentrated solar energy,Green synthesis,WO3,Tungsten trioxides
更新于2025-09-04 15:30:14
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Shock induced damage and fracture in SiC at elevated temperature and high strain rate
摘要： Large-scale molecular dynamics simulations are used to investigate shock-induced damage and fracture in 3C-SiC single crystals at an elevated initial temperature of 2000 K and a high tensile strain rate of ~1010 s-1. Three crystal orientations have been evaluated: [001], [110] and [111]. A comprehensive comparison has been made between cases at 2000 K and at 300 K to address the effects of high temperature on the mechanical performance of SiC under shock loading. Results show that for shock compression, the high temperature decreases the longitude elastic wave speeds as well as the shock stresses. The shock-induced plasticity is mainly in the form of deformation twinning at 300 K, but twinning is absent at 2000 K. The high temperature decreases the structural phase transition threshold pressure in SiC from ~90 GPa at 300 K (for all three orientations) to ~75 GPa in [001], ~57 GPa in [110] and ~64 GPa in [111] at 2000 K, with corresponding particle velocities of 2.75 km/s, 2.0 km/s, and 2.25 km/s, respectively, in agreement with trends observed in recent experiments. The spall fracture behavior reveals that high temperature reduces the spall strength with an average spall strength of ~20.7 GPa in [001], ~21.4 GPa in [110] and ~22.5 GPa in [111] at 2000 K in the classical spall regime, which are about 33% lower than strengths measured at 300 K. However, in the micro-spall regime the spall strengths are very similar at both temperatures. The corresponding thresholds of particle velocity to trigger spall decrease at elevated temperature except for [001] loading, as well as the thresholds for generating overdriven phase transition waves.
关键词： Structural phase transformation,High temperature,Silicon carbide,Plasticity,Spall
更新于2025-09-04 15:30:14
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Quasiparticle dynamics across the full Brillouin zone of Bi2Sr2CaCu2O8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy
摘要： A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy, which significantly limits the accessible momentum space. Using 20.15 eV, 12 fs pulses, we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+d and demonstrate that non-monotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in stark contrast to the monotonic relaxation in the nodal and off-nodal regions.
关键词： electron-phonon interaction,high-temperature superconductors,cuprate,time-resolved ARPES,nodal-antinodal dichotomy,angle-resolved photoemission spectroscopy,quasiparticles
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Thermal and Thermomechanical Modeling to Design a Gallium Oxide Power Electronics Package
摘要： There is significant interest in the power electronics industry in transitioning from silicon to wide-bandgap devices. Gallium oxide devices have the potential to offer comparable or even superior performance than other wide-bandgap devices, but at a much lower cost. Recent breakthroughs include demonstration of a laboratory-scale gallium oxide transistors and diodes; however, a functional power electronics package for these devices is yet to be developed. In this paper, the research methodology in designing an electronics package for gallium oxide devices is outlined. Finite element-based thermal and thermomechanical modeling simulations were conducted to realize a package design that meets the combined target of minimal thermal resistance and improved reliability. Different package designs that include various material combinations and cooling configurations were explored, and their thermal and thermomechanical performance are reported. Furthermore, the short-circuit withstanding capabilities of gallium oxide devices were studied and compared with silicon carbide.
关键词： gallium oxide,thermal modeling,thermomechanical modeling,finite-element,high-temperature packaging,power electronics,wide-bandgap devices
更新于2025-09-04 15:30:14