High Temperature Operating Conditions Research Articles

MWIR barrier detectors versus HgCdTe photodiodes

New trends to reach high operating temperature (HOT) conditions to include AIIIBV bulk materials and type-II superlattices barrier structures have been observed. The barrier structures are designed to limit dark current associated with Shockley–Read–Hall (SRH) generation–recombination processes and to decrease influence of surface leakage current without impeding photocurrent. This idea is typically implemented in materials with poor SRH lifetimes, such as all AIIIBV compounds. Despite advantages of the AIIIBV barrier detectors over HgCdTe photodiodes to include reduced tunneling and surface leakage currents and suppressed Auger recombination, the performance of these detectors in comparison with HgCdTe photodiodes, has not been realized yet. It must be stressed that their dark current density is higher than that of bulk HgCdTe photodiodes, especially in mid-wave spectral range (MWIR). To explore full potential of barrier detectors, the technological restrictions such as short carrier lifetime and passivation issues must be overcome.

Fundamental limits of MWIR HgCdTe barrier detectors operating under non-equilibrium mode

The paper presents numerical considerations of temperature-dependent performance of different mid-wave infrared HgCdTe detectors (with p- and n-type active layer) for non-equilibrium operation. Current–voltage characteristics of double heterostructure PpN photodiode, pBppN barrier photodiode, nBnn and nBnnN barrier detectors are compared to find an optimal architecture for high-operating temperature conditions. Using our model, the calculated characteristics of the devices are fitted to the experimental results for HgCdTe photodiode grown on GaAs substrate by metal organic chemical vapour deposition.The performance of photodiodes with p-type absorber are limited by the generation current associated with the Shockley–Read–Hall process, while nBnn type devices (with the n-type absorber) indicate a diffusion limited dark currents associated with Auger processes. At high values of the reverse bias (over 1V), the trap states located at dislocations lead to strong band-to-band and trap-assisted tunnelling due to high electric field within the depletion layer.

The effects of thermal aging on metallic interconnects of solid oxide fuel cells

For solid oxide fuel cells (SOFCs), metallic interconnects (ICs) are crucial components to add to the electrochemical catalyst electrodes. The high temperature operation condition in SOFCs is an extremely degrading factor for metallic ICs. Three metallic ICs have been selected in this thermal aging study. IC-1 and IC-2 contain similar Mn/Cr compositions. The thermal mechanical property of IC-2 is better than that of IC-1, attributed to the inclusion of rare earth elements. IC-3 has lower chromia composition, whereas IC-1 and IC-2 have higher Cr contents. Thermal aging is introduced under ambient atmosphere at 800°C from 0 to 100 h. X-ray diffraction study of the IC oxide scales shows growth of (MnCr)3O4 with the spinel structures. Scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS) reveal the thickness and spinel particles for the three ICs, the oxide layers at about 0·9–1·3 μm thick and the spinel sizes at 1·0–1·3 μm. The oxide weight gain studies have shown that IC-3 is the more readily oxidised IC, with an estimated oxidation rate of ∼1·98×10−7 g2 cm−4 s−1 at 800°C. Thus, IC-3 should be better coated with a protective layer for SOFC applications. For the thermal Cr diffusion study, we applied homemade glass sealant on the surface of IC-1. After thermal aging for 1000 h under ambient atmosphere at 800°C, we examined the sample with micro-Raman. The cross-sectional microstructures were studied with SEM/EDS. Both Raman and SEM/EDS results indicated that the Cr ions penetrated into the glass sealant by ∼65 μm. The oxide scales on ICs are influential on the electrical conductivity. The electrochemical impedance spectroscopy study on IC-2 samples after thermal aging is also shown.

Analysis of Tritium/Deuterium Retention and Permeation in FW/Divertor Including Geometric and Temperature Operating Features

Available data and mathematical formulations concerning tritium transport in the FW/Divertor with tungsten and beryllium as plasma facing materials were implemented in the commercial code COMSOL Multiphysics. The goal is to develop a CAD-based multiphysics modeling capability so that FW/Divertor temperature and geometric features can be readily taken into consideration while tritium permeation to the primary coolant in a prototypical PFC can be more realistically addressed. This development began with the simulation of ion implantation experiments, validated against existing laboratory experimental results. Analysis shows that with ITER FW where Be is used as the plasma facing material, the low operating temperature, erosion, and the dwell time greatly hinder tritium bulk diffusion, permeation, and inventory accumulation. However, under DEMO high-temperature operating conditions, tritium can quickly diffuse through tungsten to structural material and reach a steady state inventory after a relatively short time. Additionally, its permeation to the coolant can be reduced when the Soret effect is considered. The findings and challenges of developing a 3-D predictive capability for tritium transport in a FW/Divertor PFC are discussed.

Experimental investigation on submerged arc welding of Cr–Mo–V steel

Welding aspects of a high-quality Cr–Mo–V steel are investigated in the present work. Cr–Mo–V steel can be suggested as a best choice for fabrication of pressure vessels to be operated in high-temperature operating conditions. Welding of this group of steel demands very critical attention on the parameters setting of chosen welding process. Only a few researchers had carried out research on the optimization aspects of the submerged arc welding of Cr–Mo–V steel. In the present work, complete experimental analysis is carried out on the submerged arc welding of Cr–Mo–V steel. The important input process parameters considered are welding current, voltage, welding speed, and wire feed. The effect of these input parameters is studied on various responses related to weld bead geometry and few mechanical properties. Taguchi’s L9 orthogonal array is used for design of experiment and the mathematical models are developed for the responses using MINITAB 15 software. The models developed are validated by conducting more experiments. Optimised parameter setting is also obtained by using a recently developed teaching–learning-based optimization algorithm.

An X-ray Radiography Study of the Effect of Thermal Cycling on Damage Evolution in Large-Area Sn-3.5Ag Solder Joints

There is a need for next-generation, high-performance power electronic packages and systems utilizing wide-band-gap devices to operate at high temperatures in automotive and electricity transmission applications. Sn-3.5Ag solder is a candidate for use in such packages with potential maximum operating temperatures of about 200°C. However, there is a need to understand the thermal cycling reliability of Sn-3.5Ag solders subject to such high-temperature operating conditions. The results of a study on the damage evolution occurring in large-area Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates with Au/Ni-P metallization subject to thermal cycling between 200°C and 5°C are presented in this paper. Interface structure evolution and damage accumulation were followed using high-resolution X-ray radiography, cross-sectional optical and scanning electron microscopies, and X-ray microanalysis in these joints for up to 3000 thermal cycles. Optical and scanning electron microscopy results showed that the stresses introduced by the thermal cycling result in cracking and delamination at the copper–intermetallic compound interface. X-ray microanalysis showed that stresses due to thermal cycling resulted in physical cracking and breakdown of the Ni-P barrier layer, facilitating Cu-Sn interdiffusion. This interdiffusion resulted in the formation of Cu-Sn intermetallic compounds underneath the Ni-P layer, subsequently leading to delamination between the Ni-rich layer and Cu-Sn intermetallic compounds.

Exceptional Activity for Methane Combustion over Modular Pd@CeO 2 Subunits on Functionalized Al 2 O 3

There is a critical need for improved methane-oxidation catalysts to both reduce emissions of methane, a greenhouse gas, and improve the performance of gas turbines. However, materials that are currently available either have low activity below 400°C or are unstable at higher temperatures. Here, we describe a supramolecular approach in which single units composed of a palladium (Pd) core and a ceria (CeO(2)) shell are preorganized in solution and then homogeneously deposited onto a modified hydrophobic alumina. Electron microscopy and other structural methods revealed that the Pd cores remained isolated even after heating the catalyst to 850°C. Enhanced metal-support interactions led to exceptionally high methane oxidation, with complete conversion below 400°C and outstanding thermal stability under demanding conditions.

이산화탄소를 이용한 가스터빈 블레이드 막냉각 특성 연구

In order to cool the turbine blade under high temperature operating conditions, the film-cooling method is generally applied. In this study, CO2 was used as working fluid and it helped the operating system to prevent the loss of compressed air. The trapezoidal diffuser shape was adopted at the cross section of hole and the characteristics of heat flow with various working fluids were numerically studied. In particular, the different mixture ratios of CO2, such as various density ratios of 0.2, 0.8, and 1.0, respectively, were considered. Numerical results are graphically depicted with various conditions.

Pressureless Sintering Progression of a Silver Nanoparticle Attach Material Via Micrographic Analysis

Increasing demand for reliable power electronics for harsh environments, together with regulations in packaging materials, have resulted in new efforts in research and development in this area. The need for an attach material that can be processed at a relatively low temperature yet able to withstand the expected high temperature operating conditions is of particular interest. In this work, sintering of silver nanoparticles is examined through microstructural evolution. An image analysis technique was developed and used to analyze SEM micrographs. Results showed a strong correlation between characteristic structural features and the degree of nanoparticle arrangement prior to the sintering stage. The initial ordering of the nanopowder within the paste, and the availability of smaller particles acting as satellites were found to be pivotal for the progression of the sintering as observed from the formation of continuous structures at a larger length scale. The advancement presented in this work is a useful tool to analyze the progression of the sintering mechanism which can lead to a better understanding and control of particle coagulation and coordination which may result in properties close to that of the bulk material.

Visualization of quench-rewetting phenomena of liquid-film falling during dryout and rewetting on fuel rods in high temperature and pressure BWR operating conditions

Thermal and hydraulic phenomena of the dryout and rewetting on a fuel rod were discussed, based on the transient process observed visually with the surface-temperature variations measured during the transition from dryout to rewetting with a high-speed CCD video movie under BWR-rated high pressure and temperature conditions of 7 MPa and ~559 K (~286°C) in a thermal-hydraulics experimental loop. Liquid film was observed falling under CCFL from the downstream spacer placed in upper side on the electrically heated rod after the dryout. The heater rod surface could be cooled with the liquid film falling in the early stage of the rewetting and then the surface temperatures recovered from unusually elevated levels with quench-rewetting.

Design and analysis of a high pressure and high temperature sulfuric acid experimental system

We discuss the design and analysis of a small scale sulfuric acid experimental system that can simulate a part of the hydrogen production module. Because nuclear hydrogen coupled components such as a SO3 decomposer and a sulfuric acid evaporator should be tested under high pressure and high temperature operating conditions, we developed the sulfuric acid loop to satisfy design specifications of 900°C in temperature and 1.0MPa in pressure. The components for the sulfuric acid loop were specially designed using a combination of materials with good corrosion resistance; a ceramic and Hastelloy-C276. The design feature of the loop was tested for performance in a 10h sulfuric acid experiment and optimized using Aspen+ code simulation.

Hybrid Silicon Laser Technology: A Thermal Perspective

In this paper, the hybrid silicon laser integration platform is analyzed from a thermal perspective. Key laser performance limitations are identified under high temperature and high electrical power operating conditions. Particular attention is paid to the low thermal conductivity buried oxide layer that is utilized for optical confinement. A novel approach is presented and demonstrated to reduce the effect of the buried oxide and its application to a variety of thermally limited hybrid silicon devices is discussed.

Accelerated Life Testing in Epoxy Packaged High Luminosity Light Emitting Diodes

In this work, we have evaluated the reliability of epoxy packaged light emitting diodes (LEDs) for outdoor applications by specific tests to enhance catastrophic failures that appear under high temperature and humidity operation conditions. The different failure mechanisms were analyzed observing two main types: one is open circuit catastrophic failures induced by moisture and the other one power luminosity degradation. The influence of temperature and humidity on catastrophic failures was modelled using the Arrhenius–Peck law obtaining an activation energy of 0.87 eV and a Peck parameter of 2.29. MTTF value of 1.582 × 106 h at low bias current, 10 mA, has been evaluated.

Microstructural anisotropy effect on the mechanical properties of a 14Cr ODS steel

During the last years in the field of materials for energy production, oxide dispersion strengthened (ODS) alloys have been reintroduced as candidate materials for high temperature and aggressive operating conditions. In particular, the Fe-ODS alloys developed in the 1970s for fast reactor cladding are being improved under various national and international projects. One of the main open issues in the use of ODS alloys as fuel cladding is their anisotropy, characteristic of extruded alloys. The aim of this work is to investigate the effect of the anisotropy of an extruded bar of a14Cr ODS on the tensile properties. The microstructure in longitudinal direction (L, parallel to the extrusion direction) is characterized by grains elongated along the extrusion direction, while in the transverse direction (T, perpendicular to the direction of extrusion) grains are smaller and more equiaxed. This microstructural anisotropy is reflected in a loss of ductility in the transverse direction. Furthermore, after tensile tests different fracture mode are observed depending on the orientation under study.

Indentation based life assessment for boiler tubes of fossil power plants

Boiler tubes of fossil power plant are used in high temperature and high pressure operating conditions are required to resist creep damage, fatigue cracking, and corrosion damages. Especially, X20CrMoV12.1 (12%Cr) steel has been widely used for superheater and reheater tubes of power plants due to its improved creep strength and higher oxidation resistance. Long-term service at the elevated temperature causes deterioration of mechanical property of materials as a result of changes in micro structure. Thus the accurate knowledge of degradation or life consumption level considering strength decrease is necessary to make a plan for the effective operation and maintenance. In this paper, some material properties such as yield strength, tensile strength, of X20CrMoV12.1 steel tubes were experimentally evaluated by portable indentation tester. Also damage evolution parameters of continuum damage models are modified to determine remaining life of boiler tubes. Which methodology was developed for the in-situ experiment for plant facilities.

중간층이 DLC 코팅에 미치는 영향

DLC is considered as the candidate material for application of moving parts in automotive components relatively in high pressure and temperature operating conditions for its high hardness with self lubrication and chemical inertness. The properties of interlayer between the substrate and the DLC film were studied. Arc ion plating method have been employed to deposit onto substrate and sputtering method was used for synthesizing DLC onto interlayer. Among these six types of interlayer, deposited DLC film onto TiCN showed excellent value for characteristics. From the results of analysis for physical properties of DLC films, it seems that the adhesion forces were more important factors than intrinsic mechanical properties such as hardness, roughness and wear resistance of DLC films. AFM(Atomic Force Microscope) was used for understanding roughness of DLC films. Hardnesses of the coating layers were identified by nano-indentation method and adhesions were checked by scratch method.

Synthesis and Electro-Optical Properties of 9,10-Substituted Anthracene Derivatives for Flexible OLED Devices

A silylated anthracene derivative, bis[2-(p-trimethylsilyl)phenylethynyl]anthracene (1), was synthesized by using Sonogashira reaction. Compound 1 showed two absorption maxia(λmax,abs) at 444 and 447 nm, and fluorescence maximum (λmax,em) at 478 nm. Compound 1 had higher melting temperature of 274°C compared to anthracene 210°C presumably due to confinement of π-conjugated system by trimethylsilyl end-capping, which will be beneficial in the high temperature operation condition of OLED devices. As compared to the commercially available, blue-light emitting, material 4 and tert-butylated compound 2, the compound 1 showed small red-shift of 9 nm in the OLED emission from the by PL λmax due to the increased electron density in the anthracene ring. The compound 1 was also found to be easily fabricated in the flexible OLED devices and showed a low threshold voltage and high current efficiency compared with other anthracene derivatives.

Kinetics of crystallization of a Fe-based multicomponent amorphous alloy

The Fe-based multicomponent amorphous alloys (also referred to as metallic glasses) are known to exhibit soft magnetic properties and, it makes them important for many technological applications. However, metallic glasses are in a thermodynamically metastable state and in case of high temperature operating conditions, the thermally activated crystallization would be detrimental to their magnetic properties. The study of crystallization kinetics of metallic glasses gives useful insight about its thermal stability. In the present work, crystallization study of Fe67Co18B14Si1 (2605CO) metallic glass has been carried out using differential scanning calorimetry (DSC) technique. Mössbauer study has also been undertaken to know the phases formed during the crystallization process. The alloy shows two-stage crystallization. The activation energy has been derived using the Kissinger method. It is found to be equal to 220 kJ/mol and 349 kJ/mol for the first and second crystallization peaks, respectively. The Mössbauer study indicates the formation of α-(Fe, Co) and (Fe, Co)3B phases in the alloy.

증착방법에 따른 DLC 막의 마찰-마모 특성평가

DLC is considered as the candidate material for application of moving parts in automotive components relatively in high pressure and temperature operating conditions for its high hardness with self lubrication and chemical inertness. Different deposition method such as arc plating, ion gun plating and PECVD were used for comparing mechanical and tribological properties of each DLCs deposited on stainless steel with 1 um thick respectively. Among these 3 types of DLCs, the arc plated DLC film showed highest value for wear resistance in dry condition. From the results of analysis for physical properties of DLC films, it seems that the adhesion force and crack initiation modes were more important factors than intrinsic mechanical properties such as hardness, elastic modulus and/ or roughness to the wear resistance of DLC films. Raman spectroscopy was used for understanding chemical bonding natures of each type of DLC films. Typical D and G peaks were identified based on the deposition method. Hardness of the coating layers were identified by nanoindentation method and the adhesions were checked by scratch method.

Modeling and performance assessment of Pd- and Pd/Au-based catalytic membrane reactors for hydrogen production

A mathematical steady-state modeling framework for the isothermal operation of a membrane reactor for methane steam reforming is developed, and a comparative performance assessment of the catalytic membrane reactor (CMR) versus a conventional packed bed reactor (PBR) is accordingly conducted. A detailed literature benchmarking suggests that the models developed in the present study predict total methane conversion levels within 99% of the experimental values reported in the literature. The proposed Pd- and Pd/Au-based CMR model is utilized for the aforementioned performance analysis under a broad range of reactor operating conditions such as temperature (350–750 °C), pressure (2–30 bars), steam to methane ratio (1–15), membrane thickness (1–50 µm), and permeate-side sweep ratio (1–100). In all simulation runs conducted, the superior performance of both the Pd- and Pd/Au-based CMR over the PBR was amply demonstrated. Furthermore, within the proposed CMR modeling framework, an index-based analysis is conducted that concretely quantifies progress towards the attainment of key process intensification objectives. In particular, by appropriately defining the Δ-index, which explicitly captures potential performance and process intensification benefits associated with attainable total CH4 conversion levels under different reactor operating conditions, it is shown that the optimum CMR performance is achieved at high pressure and low temperature operating conditions, which was particularly suitable for the attainment of key process intensification objectives as well as optimum performance target levels.