High-temperature Characteristics Research Articles

Investigation on performance and mechanism of grafting activated waste leather powder modified asphalt

The objective of this study is to seek a methodology to recycle the waste leather in an efficient and eco-friendly way. In this study, modified asphalts samples containing 9% and 12% waste leather powder (WL) and Maleic anhydride grafted waste leather (MAH-WL), as well as base asphalt sample, were prepared. In addition, these tests of penetration, softening point, ductility, DSR, MSCR, fluorescence microscope, FTIR and SEM were applied to investigate the conventional physical performance, high-temperature rheological characteristic and storage stability of asphalt samples. The results indicated that under the same content of waste leather powder, grafting activation could reduce the penetration of asphalt and greatly improve the softening point and the ductility. Furthermore, the high-temperature rheological characteristic of MAH-WLMA was improved compared with base asphalt and WLMA. The storage stability of modified asphalt was also greatly enhanced after grafting Maleic anhydride to waste leather. The result of FTIR manifested that chemical reaction was occurred between the grafting activated waste leather powder and base asphalt, while the modification of waste leather without grafting was merely a physical process. Overall, using grafting activated waste leather as a bio-modifier of asphalt is feasible and promising, while some limits do exist. To comprehensively master the modification mechanism and apply MAH-WLMA to practical projects, further experiments need to be conducted. A range of performance of grafting activated waste leather asphalt mixture should also be investigated in the future.

Modified thermal energy storage unit for solar cookers using iterative design algorithm

The use of phase change materials (PCMs) as thermal energy storage (TES) mediums has gained notable attention in recent years due to their high energy density and constant temperature characteristics which makes them suitable for solar cookers (SCs). Therefore, the primary objective of this study is to develop a modified TES unit containing PCM as heat storage medium incorporated with cooking vessel for SCs. The TES units use PCM filled on all sides, including the lid, enhancing heat transfer to food load. The design of TES unit is carried out by developing computational procedure. MATLAB code is written to implement the iterative procedure, simplifying exhaustive calculations required for optimizing and designing the TES unit. The present work also aims to design, fabricate and test different geometries of TES units using paraffin wax as the PCM. After six hours, cooking load temperature in all geometries of TES units reached the melting point of PCM. TES units with cylindrical shapes perform best among hexagon and square designs. Through computational procedure, cylindrical configuration is the best as it takes least amount of PCM to keep steady temperature over a specific period. Based on the computational procedure developed in this study, TES container will be designed to enhance SC performance during sundown hours and maximize the use of latent heat stored within the PCM.

High-Temperature Deformation Characteristics of Cu<sub>3</sub>Sn Evaluated by the Tests Using Composite Copper Wire Specimen.

In recent years, the propulsive movement of electrification of automobiles and airplanes is accelerating to realize a decarbonized society. Along with this movement, lightening of electric mobility is also required to reduce electricity consumption. The power modules used in electric mobility control high voltage and great current and are subjected to high temperature. Since most of the power modules employ Si semiconductor chips which can’t work in such a high-temperature range, cooling systems must be installed to prevent their failure. Therefore, next-generation power semiconductor chips using SiC or GaN, which can work properly in a high-temperature environment of over 200 ℃, are expected to be mounted in power modules to lighten them by eliminating cooling system. Cu3Sn intermetallic bonding technique which can form joints having a high melting point has attracted attention to achieve the mounting of the chips. To put the technique into practical use, the high-temperature deformation characteristics of Cu3Sn must be clarified. We previously proposed a materials testing method using a composite copper wire (CCW) specimen having a Cu3Sn layer to estimate the tensile characteristics of Cu3Sn. In this study, we conducted tensile tests, tension-strain maintenance tests, and cyclic tension-compression loading tests using the CCW specimen to evaluate the deformation characteristics of Cu3Sn in the temperature range between room temperature and 200 ℃.

High-temperature deformation characteristics of 3D printing of nano-ceramic materials

High-temperature deformation characteristics of 3D printing of nano-ceramic materials

The Fabrication Method and Tribological Properties of Co-TiC Sintered High-Temperature Alloy

Turbine blades of aircraft gas-turbine engines were always the place to apply novel materials and technologies. Special attention was paid to strength, corrosion-oxidation, and tribological performance. The blade top-shrouds are one of the most vulnerable places from the point of wear resistance. This problem was usually solved by applying coatings (weld-deposition, electro-spark coating, gas-spray coatings). The new method proposed here is to use soldering technology: the to-size plate manufactured of wear-resistant material is bonded to the friction surface by the solder with the composition close to the composition of the turbine blade. In this work, we propose the method and the material for improving the wear resistance of the turbine blade’s top shrouds. The cobalt-based materials (Co-15Cr-2.5Fe-2.5Al-36TiC) seem very promising for this. In the present work, the manufacturing technology of the alloy by HIP method, microstructure, and high-temperature fretting-wear characteristics (1050?C) are discussed.

High-Temperature Deformation Characteristics and Constitutive Models of Inconel 625 Superalloy

High-Temperature Deformation Characteristics and Constitutive Models of Inconel 625 Superalloy

Low and High Temperature Characteristics of Compounded and Modified Bitumens

Low and High Temperature Characteristics of Compounded and Modified Bitumens

Biaxial film bulk acoustic resonator magnetic sensor based on the Fe80Ga20 anisotropic ΔE effect

With the increasing application of personal navigation systems in consumer electronics, the demand for multi-axis magnetic sensors based on MEMS is growing. We report a biaxial MEMS DC magnetic sensor consisting of an Mo/AlN/Fe80Ga20 film bulk acoustic resonator, with anisotropy ΔE effect-based sensing principle. Different from the previously reported 1D magnetic sensor based on the ΔE effect, the anisotropic ΔE effect was used to realize in-plane and out-of-plane 2D magnetic field responses on a discrete sensor, and the sensor had two readout methods: resonant frequency f and return loss S11. The magnetic sensor realized the resonant frequency f shifted by 1.03 MHz and 0.2 MHz in the 567 Oe in-plane magnetic field and 720 Oe out-of-plane magnetic field, respectively, and the S11 changes by −30.2 dB and −0.92 dB. As the applied magnetic field increases, the −3 dB bandwidth quality factor Q 3dB of the S11 curve gradually increases, and its maximum values in the in-plane and out-of-plane magnetic fields are 77 143 and 1828, respectively, which reduces the detection limit of the magnetic sensor. The resonant magnetic sensor has stable high linear temperature and frequency drift characteristics, and its temperature frequency coefficient is −48.7 ppm °C−1.

Comparative Stability Analysis of Boron Nitride Nanotube using MD Simulation and Nonlocal Elasticity Theory

Boron Nitride Nanotube (BNNT) is a promising nano sized structure with superior electrical, physical, and mechanical properties comparing to Carbon nanotube. Higher Young’s modulus, oxidation resistance, hardness, corrosion resistance, durability in high temperature, piezoelectric and pyroelectric characteristics are some featured characteristics of BNNT. In this paper the critical buckling load of Boron Nitride Nanotube is investigated. Two different method is used. First Eringen’s nonlocal elasticity theory is employed to obtain size-dependent critical buckling loads. Then, LAMMPS software is used to simulate molecular dynamics and obtain critical buckling loads. Zigzag (5,5) BNNT with 400 atoms is examined into MD simulation analyzes.

Study of High-Temperature Corrosion Characteristics Fe-2.25Cr-1.6W Steel for Eco-friendly Power Plants

To evaluate the corrosion mechanism of Fe-2.25Cr-1.6W(wt.%) steels were corroded between 600 and 800 ℃ for up to 200 h in Na2SO4. Corrosion rates increased progressively as the corrosion time increased. The formed outer scale grew into the air by the salt during corrosion, which facilitated outward diffusion of Fe2+ ions. The inner mixed layer grew by the inward diffusion of oxygen ions. The Fe-2.25Cr-1.6W(wt.%) steel corroded little fast, forming thick scales that consisted primarily of an outer and middle Fe-O layer and an inner (Fe, Cr, O)-mixed layer. At the interface of the outer and inner scales, voids developed and cracking occurred. Fe-2.25Cr-1.6W(wt.%) steel had a small amount of Cr, which cannot decreased the scaling rate and the adhesion of scale.

Monolithic Si-Based AlGaN/GaN MIS-HEMTs Comparator and Its High Temperature Characteristics

Monolithic GaN High Electron Mobility Transistor (HEMT)-integrated circuits are a promising application of wide band-gap materials. To date, most GaN-based devices behave as NMOS-like transistors. As only NMOS GaN HEMT is currently commercially available, its control circuit requires special design if monolithic integration is desired. This article analyzes the schematics of a GaN-based comparator, and three comparator structures are compared through ADS simulation. The optimal structure with the bootstrapped technique is fabricated based on AlGaN/GaN Metal–Insulator–Semiconductor (MIS) HEMT with the recessed gate method. The comparator has excellent static characteristics when the reference voltage increases from 3 V to 8 V. Dynamic waveforms from 10 kHz to 1 MHz are also obtained. High-temperature tests from 25 °C to 250 °C are applied upon both DC and AC characteristics. The mechanisms of instability issues are explained under dynamic working condition. The results prove that the comparator can be used in the state-of-art mixed-signal circuits, demonstrating the potential for the monolithic all-GaN integrated circuits.

High temperature characteristics of nitric oxide annealed p-channel 4H-SiC metal oxide semiconductor field effect transistors

In this work, p-channel 4H-SiC MOSFETs were fabricated and analyzed at high temperature. It is demonstrated that nitridation of the gate oxide enables enhancement mode operation in these devices. Nitrogen incorporation at the 4H-SiC/SiO2 interface by nitric oxide annealing reduces the interface trap density energetically located in the lower half of the 4H-SiC bandgap, resulting in viable high temperature p-channel devices. In the 27–300 °C temperature range, the threshold voltage decreases with increasing temperature, consistent with the reduction of occupied interface traps at higher temperatures. The hole channel mobility is weakly temperature dependent under strong inversion conditions. Hall measurements support that above the threshold voltage, the mobility is limited by surface roughness scattering. In weaker inversion, the channel conductivity is limited by interface hole trapping and Coulomb scattering. In addition, high temperature bias stress measurements confirm a temperature activated hole trapping under negative gate bias, which requires further investigations.

Metallic Oxides for Innovative Refrigerant Thermo-Physical Properties: Mathematical Models

Nano-refrigerant is announced to become an excellent refrigerant, which often improves heat transfer efficiency in the cooling systems. Different materials can be applied to be suspended in traditional coolants in the same way as nanoparticles. In this comprehensive research, mathematical modeling was used to investigate the effect of suspended nanoparticles (Al2O3, CuO, SiO2 and ZnO) on 1,1,1,2-Tetrafluoroethane, R-134a. The thermal conductivity, dynamic viscosity, density and specific heat capacity of the nano-refrigerant in an evaporator pipe were investigated. Compared to conventional refrigerants, the maximum increase in thermal conductivity was achieved by Al2O3/R-134a (96.23%) at a volume concentration of 0.04. At the same time, all nano-refrigerant types presented the same viscosity enhancement of(45.89%) at the same conditions. These types of complex thermophysical properties have enhanced the heat transfer tendencies in the pipe. Finally, the nano-refrigerant could be a likely working fluid generally used in the cooling unit to improve high-temperature transfer characteristics and save energy use.

High-Temperature Rheological Characteristics of Asphalt Binder Incorporated with Graphene Oxide and Predicting Its Rutting Potential Using Response Surface Method

AbstractRutting is one of the most common types of asphalt pavement failures. This study has investigated the high temperature performance of asphalt binders incorporating graphene oxide (GO). To t...

Nanoscale Functional Additives Application in the Low Temperature Greases.

Due to the fact that the application of AW and EP additives in low-temperature greases may lead to worse high-temperature and anti-corrosion characteristics as well as additional burden on the environment due to the content of aggressive components, in this paper, the possibility of replacing these additives with NFA, which do not have these disadvantages, was investigated. The analysis of nanosized particles being used as functional additives in greases was carried out. The morphology of the following nanoparticles was studied: montmorillonite K 10, silica, calcium car-bonate and borate, halloysite, and molybdenum disulfide incorporated in halloysite tubes. The effect of nanostructured components on the physicochemical characteristics and anti-wear and anti-scuffing properties of complex lithium, polyurea, and polymer greases were studied. Maximal improvement of anti-wear and anti-scuffing characteristics of cLi-greases was reached when using silica and calcium borate. Maximal improvement of anti-scuffing properties of PU-lubricant was reached when using calcium carbonate and the two-component NFA based on halloysite, for anti-wear properties when adding silicon dioxide and halloysite. When the concentrations of silicon dioxide and calcium carbonate was increased from 1 to 3 wt.%, there was a decrease in yield stress of the structural frame of the PU-lubricant and its colloidal stability was worse. The increase of the concentration of calcium carbonate and borate nanoparticles in the studied range led to a significant improvement of the anti-wear and anti-scuffing characteristics of the PU grease, respectively. The greases properties’ dependence from the nanostructured functional additives’ introduction method and their concentration were investigated. Nanoparticles were added into the test lubricants before and after the thermo-mechanical dispersion stage. The addition of silicon dioxide and calcium carbonate NFA after the heat treatment stage led to worsening of the characteristics of the plastic material, and the increase of their concentration from 1 to 3 wt.% formed a harder structure of Li-grease. On the contrary, the addition of calcium borate NFA is recommended after the thermomechanical dispersion. The choice of nanoparticles and the method of their addition to the lubricants of various types was carried out according to the results of the previous stage of the research. Along with the analysis of the physicochemical characteristics and anti-wear and anti-scuffing properties of the lubricants, the structure of the dispersion phase of nanomodified lubricants were studied.

Evaluation of the Creep Rupture Behavior of Alloy 690 Steam Generator Tubes Considering the Pressure Ramp Rate

Abstract Steam generator tubes are among the main components that form the pressure boundary of a nuclear power plant and studies of ruptures of steam generator (SG) tubes are important because they can ensure the safety of a nuclear power plant in case of a severe accident. The materials used previously for SG tubes around the world have been replaced and will be replaced by Alloy 690 given its improved corrosion resistance relative to that of Alloy 600. However, studies of the high-temperature creep and creep-rupture characteristics of SG tubes made of Alloy 690 are insufficient compared to those focusing on Alloy 600. In this study, several creep tests were conducted using half-tube shape specimens of the Alloy 690 material at temperatures ranging from 650 °C to 850 °C and stresses in the range of 30–350 MPa, with failure times to creep rupture ranging from 3 h to 870 h. Based on the creep test results, creep life predictions were then made using the well-known Larson–Miller parameter (LMP) method. Steam generator tube rupture tests were also conducted under the conditions of a constant temperature and pressure ramp using SG tube specimens. As the pressure ramp rate increases, the failure behavior changes due to the rapid change in strain near the crack tip. The rupture test equipment was designed and manufactured to simulate the transient state (rapid temperature and pressure changes) in the event of a severe accident condition. After the rupture test, the damage to the SG tubes was predicted using a creep rupture model and a flow stress model. A modified creep rupture model for Alloy 690 SG tube material is proposed based on the experimental results. A correction factor of 1.7 in the modified creep rupture model was derived for the Alloy 690 material. The predicted failure pressure was in good agreement with the experimental failure pressure.

Study on controlled rolling and cooling process of CH1T steel High speed wire 1# shaoguan steel

Under the background that the high-grade industrial wire rod such as cold heading steel is mainly developed in the first line of Shaoguan Iron and Steel Co., Ltd., the controlled rolling and controlled cooling process of ultra-low carbon cold heading steel ch1t is studied in this paper. A large number of high-temperature tensile tests for CH1T are carried out on Gleeble 3800 thermal simulation testing machine, and the high-temperature plastic characteristics of CH1T and stress-strain curves at different temperatures are obtained, At the same time, the transformation points Ac1, Ac3, Ar1 and Ar3 of ch1t steel and the dynamic CCT curve were measured, and the process improvement measures were formulated on the basis of experimental research. The field practice shows that the proposed process improvement measures have greatly improved the problem of low yield of ch1t cold heading steel in the first high line of Shaoguan Iron and Steel Co., and achieved remarkable economic benefits.

Crystal structure, Curie temperature, and electromagnetic absorption properties in FexCo30Ni60−xSi5Al5 (x = 30, 35, 40, 45) high entropy alloys

In order to meet the requirements of future national defense for high temperature electromagnetic (EM) absorbing performance, a series of FexCo30Ni60−xSi5Al5 (x = 30, 35, 40, 45) high-entropy alloys (HEAs) powders was prepared and their Curie temperatures (TC) were measured by a self-made Wheatstone bridge. According to the results, varying the Fe/Ni ratio affected the crystal structure, Curie temperature, oxidation resistance, and electromagnetic absorbing properties of the above compounds. Since Fe has a BCC structure and is thus easier to form the solid solutions with Si and Al, the crystal structure of the alloy has changed from FCC toward BCC with increasing Fe dopant content. In turn, the Curie temperature (TC) decreased from 473.68 °C to 358.07 °C, being lower than their initial oxidation temperature (>800 °C). The reflection losses (RL) of powders at room temperature and high temperatures (≤500 °C) were calculated as well. It was found that the flake powders after ball milling gained a larger aspect ratio, resulting in the better absorption effect, which was due to high toughness and low strength characteristics of the initial FCC structure. Furthermore, the permittivity and permeability of alloys upon heating reached impedance matching at a certain temperature, thus achieving the greater RLmax value. Finally, the high-temperature EM absorption characteristics of HEAs were shown to merit a thorough study.

High-Temperature Oxidation Behaviors of TA15 Titanium Alloy after Mechanical Grinding and Laser Cleaning

This paper presents the results of a study on the high-temperature oxidation characteristics after mechanical and laser removal of TA15 titanium alloy oxide film. The morphology, components, and roughness of the surface were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and laser confocal microscope (OM). The oxide film can be effectively removed with mechanical grinding and laser cleaning, and the oxide film after mechanical grinding is thicker and looser than that of after laser cleaning. The oxide film is principally composed of TiO2, Ti2O3 and TiO. Besides, there is a small amount of aluminum oxide on the surface. The surface after mechanical grinding was rougher than that of after laser cleaning. Thus, this work indicates that laser can not only clean the oxide film completely, but also strengthen the surface, which is a promising way to favor the widespread application of laser cleaning technology.

Responses of extreme high temperatures to urbanization in the Beijing–Tianjin–Hebei urban agglomeration in the context of a changing climate

AbstractExtreme high‐temperature event is one of the most urgent climate issues faced by coordinated development of the Beijing–Tianjin–Hebei region (BTH) in the future due to global warming and urbanization. Based on the homogenized daily temperatures from 174 meteorological observation stations, six extreme hot events were detected. The results revealed the spatiotemporal change characteristics of the extreme high temperature in the BTH. The acquired evidence showed the maximum daily minimum temperature (TNx), high‐temperature days (SU35), hot night days (TR25), and heatwave spell durations (HWDI) have significantly increased, while the daily temperature range (DTR) has significantly decreased (p < 0.01) during 1961–2018. The SU35, TR25 and HWDI in 2010s were 68%, 2.8 times and 2.1 times higher than that in 1980s, respectively. Moreover, since 1961, the high‐temperature season in the BTH has been getting longer at a rate of 7.4d/10a. The study also revealed the contribution of urbanization on high‐temperature indices depends on city size and location in the BTH. The magnitudes of the indices change in the downtown area of Beijing, Tianjin and Shijiazhuang ranked top in the 13 cities of the BTH, which are closely related to the urban development. The mean contribution of urbanization on maximum daily maximum temperature (TXx), TNx, SU35 and TR25 was 68%, 45% and 27% in Beijing, Tianjin and Shijiazhuang, respectively. The socio‐economic driving factors have an important impact on the change rates of the extreme high‐temperature indices, which means that controlling population, city size and reducing energy consumption could effectively alleviate the urban heat island (UHI) effect and slow down the high‐temperature events in the BTH. In the future, it is vital to further study and investigate the mechanism of the extreme high‐temperature changes through numerical simulations and to research their impact and response in this region.