Operating Temperature Limit Research Articles

A Wide-Temperature-Range, Low-Cost, Fluorine-Free Battery Electrolyte Based On Sodium Bis(Oxalate)Borate

Common battery electrolytes comprise organic carbonate solvents and fluorinated salts based on hexafluorophosphate (PF6–) anions. However, these electrolytes suffer from high flammability, limited operating temperature window, and high cost. To address those issues, we here propose a fluorine-free electrolyte based on sodium bis(oxalate)borate (NaBOB). Although lithium bis(oxalate)borate (LiBOB) has previously been investigated for lithium-ion batteries, NaBOB was considered too insoluble in organic solvents to be used in practice. Here, we show that NaBOB can be dissolved in mixtures of N-methyl-2-pyrrolidone (NMP) and trimethyl phosphate (TMP) and in each sole solvent. NMP provides higher solubility of NaBOB with a concentration of almost 0.7 M, resulting in an ionic conductivity up to 8.83 mS cm–1 at room temperature. The physical and electrochemical properties of electrolytes based on NaBOB salt dissolved in NMP and TMP solvents and their binary mixtures are here investigated. The results include the thermal behavior of the sole solvents and their mixtures, flammability tests, NaBOB solubility, and ionic conductivity measurements of the electrolyte mixtures. Full-cell sodium-ion batteries based on hard carbon anodes and Prussian white cathodes were evaluated at room temperature and 55 °C using the aforementioned electrolytes. The results show a much improved performance compared to conventional electrolytes of 1 M NaPF6 in carbonate solvents at high currents and elevated temperatures. The proposed electrolytes provide a high ionic conductivity at a wide temperature range from room temperature to −60 °C as NMP–TMP mixtures have low freezing points. The flammability tests indicate that NaBOB in NMP–TMP electrolytes are nonflammable when the electrolyte contains more than 30 vol % TMP.

Impact of materials technology on the breeding blanket design – Recent progress and case studies in materials technology

A major part in the EUROfusion materials research program is dedicated to characterize and quantify nuclear fusion specific neutron damage in structural materials. While the majority of irradiation data gives a relatively clear view on the displacement damage, the effect of transmutation – i.e. especially hydrogen and helium production in steels – is not yet explored very well. However, few available results indicate that EUROFER-type steels will reach their operating limit as soon as the formation of helium bubbles reaches a critical amount or size. At that point, the material would fail due to embrittlement at the considered load.This paper presents a strategy for the mitigation of the before-mentioned problem using the following facts:•the neutron dose and related transmutation rate decreases quickly inside the first wall, that is, only a plasma-near area is extremely loaded•nanostructured oxide dispersion strengthened (ODS) steels may have an enormous trapping effect on helium and hydrogen, which would suppress the formation of large helium bubbles•compared to conventional steels, ODS steels show improved irradiation tensile ductility and creep strengthIn summary, producing the plasma facing, highly neutron and heat loaded part of blankets by an ODS steel, while using EUROFER97 for everything else, would allow a higher heat flux as well as a longer operating period.Consequently, we (1) developed and produced 14 % Cr ferritic ODS steel plates. (2) We fabricated a mockup with 5 cooling channels and a plated first wall of ODS steel, using the same production processes as for a real component. And finally, (3) we performed high heat flux tests in the HELOKA facility (Helium Loop Karlsruhe at KIT) applying short and up to 2 h long pulses, in which the operating temperature limit for EUROFER97 (i.e., 550 °C) was finally exceeded by 100 K. Thereafter, microstructure and defect analyses did not reveal defects or recognizable damage. Only a heat affected zone in the EUROFER/ODS steel interface could be detected. This demonstrates that the use of ODS steel could make a decisive difference in the future design and performance of breeding blankets.

Wearable Aramid–Ceramic Aerogel Composite for Harsh Environment

High‐performance lightweight polymer fibers are attracting significant interest for wearable systems, where its thermal insulation performance is indispensable for harsh environments. However, one drawback of polymer fibers is its limited operating temperature range. Herein, a crosslinked poly(p‐phenylene terephthalamide) fiber and ceramic aerogel nanocomposite is reported, exhibiting hot and cold thermal management from cryogenic to high‐temperature condition (over 400 °C) and robust mechanical performance, which can be produced using additive textile manufacturing. The resulting ceramic aerogel nanocomposites demonstrate a low density (0.08 g cm−3), a low thermal conductivity (0.034 W m−1 K−1), and a high compressive mechanical strength of 1.1 MPa, due to the crosslinked interfacial interaction between the aramid fiber and the silica aerogel. A finite‐element model is developed to study the compression performance of aramid–aerogel composite, demonstrating that the robust mechanical performance is strengthened by interfacial bonding. These findings demonstrate that composite sheets are promising candidates for the low‐cost manufacturing of wearable textiles for applications in harsh environments.

Longitudinal-optical phonon absorption and dephasing in three-level terahertz quantum cascade structures with different injector anticrossings

The effects of longitudinal-optical phonon scattering and dephasing in quantum cascade structures are studied. Three-level longitudinal-optical phonon depopulated terahertz structures are investigated using a density matrix Monte Carlo method. Ideally, these structures do not contain energy states above the upper lasing state, which in principle, can reduce parasitic leakage. The light output and current density as a function of lattice temperature are calculated and shown to be consistent with experiment for a recently reported structure that is confirmed to be a good approximation to a three-level structure. The pure dephasing time is self-consistently found to be relatively constant over the temperature range, which differs from the previous analysis of other structures. At higher lattice temperatures, particularly at elevated temperatures beyond the lasing point, the reduction in current density is rather due largely to rapid longitudinal-optical phonon absorption, which reduces the lifetime of the ground state. It is shown that the operating temperature limit may further be improved by adequately increasing the injector anticrossing.

Design and optimization of cost-effective coldproof portable enclosures for polar environment

Based on the International Electrotechnical Commission standards, 
 the electronic devices in the industrial class (e.g., integrated circuits or batteries) can only operate at the ambient temperature between -40°C and 85°C. For the human-involved regions in Alaska, Northern Canada, and Antarctica, extreme cold condition as low as -55°C might affect sensing electronic devices utilized in the scientific or industrial applications. In this paper, we propose a design and optimization methodology for the self-heating portable enclosures, which can warm up the inner space from -55°C for encasing the low-cost industrial-class electronic devices instead of expensive military-class ones to work reliably within their allowed operating temperature limit. Among the other options, ceramic thermal resistors are selected as the heating elements inside the enclosure. The placement of the thermal resistors is studied with the aid of thermal modelling for the single heating device by using the curve fitting technique to achieve uniform temperature distribution within the enclosure. To maintain the inner temperature above -40°C but with the least power consumption from the thermal resistors, we have developed a control system based on the fuzzy logic controller. For validation, we have utilized COMSOL Multiphysics software and then one prototyped enclosure along with the fuzzy control system. Our experimental measurement exhibits its efficacy compared to the other design options.

Effect of bismuth substitution on piezoelectric coefficients and temperature and pressure-dependent dielectric and impedance properties of lead zirconate titanate ceramics

Basic Physics as well as devices fabrication required in-depth analysis of the effect of temperature, pressure, and other physical parameters on dielectric properties to understand the microstructure-property relation. In this regard, we have thoroughly investigated the temperature and pressure dependent ferroelectric, dielectric, and impedance properties of Bi-substituted Pb1-xBi2x/3(Zr0.52Ti0.48)O3 (PBiZT) (x = 0.10 to 0.40) ceramics. The maximum solubility of Bi was found near x = 0.15, and above this composition, it shows a composite phase of PBiZT and ZrO2. The remanent polarization (Pr) increases with decrease in the Bi concentration with the maximum value obtained for x = 0.15, i.e., 40 μC/cm2. Temperature-dependent dielectric constant and tangent loss were measured as function of composition to check the ferroelectric phase transition temperature (Tc) and the operating temperature limit for the material to make a device. The Tc value increases with decrease in bismuth (Bi) concentration which obtained in the range of 350 ℃ - 375 ℃. The tangent loss was observed to be near about 0.01 to 0.03 below 200 ℃ which suggests its suitability for device applications. The temperature-dependent imaginary part of impedance (Z'') was measured at various temperatures with varying frequency in the range of 100 Hz – 1 MHz. The peaks positions of the Z'' vs. frequency shift towards lower temperature side with increasing the value of x from 0.1 to 0.4 near and above Tc. The pressure-dependent dielectric constant (εr) and capacitive reactance (Xc) were also measured for varying x, and it was observed that maximum change in εr and Xc was observed for x = 0.15 i.e. 13% and 10.5%, respectively. The pressure sensitivity was obtained maximum for the composition near the maximum solubility of Bi in PbZr1-xTixO3 (PZT) matrix. The reason behind getting the highest remanent polarization and pressure sensitivity for x = 0.15 is that of the highest piezoelectric coefficients ∼ 130 pC/N.

Recrystallization suppression through dispersion-strengthening of tungsten

Tungsten is the material of choice for the divertor region of future nuclear fusion reactors, an environment that will expose plasma-facing components (e.g. divertor, etc...) to high temperatures and transient high heat flux events. Under these conditions, recrystallization and grain growth of tungsten can occur, leading to undesirable microstructural and mechanical property changes. Therefore, there is a need to raise the recrystallization temperature of tungsten and limit the kinetics of the recrystallization and grain growth processes. In this work, we examine the effect of different types (TiC vs. TaC vs. ZrC) and different concentrations (1.1 vs. 5 vs. 10 wt.%) of dispersed second phase particles in a tungsten matrix on the high temperature performance. The addition of second-phase particles effectively increases the temperature of and time for recrystallization and slow grain growth; however, the addition of a high weight fraction of particles alters the surface chemistry, which may impact subsequent plasma-surface interactions. These results show that the addition of small concentrations of dispersed particles can be effectively employed in tungsten to raise the upper operating temperature limit for tungsten in a fusion reactor.

The SEM and TEM Analysis of IN718 Alloy after Fatigue Push-Pull Loading at 700°C

Specimens from Ni-Cr-Fe wrought superalloy INCONEL 718 were used for fatigue push-pull test at elevated temperature 700 °C. Fatigue loading was with the coefficient of cycle asymmetry R = -1. Temperature of fatigue test was chosen from two reasons; one is that limit operating temperature for this type of alloy is 650 – 700 °C due to precipitation of stable but incoherent orthorhombic Ni3Nb delta phase; the second reason for this temperature is fact that metastable body-centred tetragonal Ni3Nb gamma double prime phase starts to transform to delta phase and from that reason there is an expectation for mechanical properties decreasing due to increased volume of delta phase. For evaluation of fatigued specimens were Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observation used. Also methods of quantitative metallography – coherent testing grids were used for evaluation of delta phase volume. Some references describe that higher volume of delta phase, mostly situated at grain boundaries, act as initiation sites for cracks and therefore decreasing mechanical properties. Employed SEM and TEM analysis confirm the increased volume of delta phase in specimens after fatigue loading but a negative influence on dynamic properties, such fatigue lifetime, for this alloy was not confirmed.

Design of an Optimized Thermal Management System for Li-Ion Batteries under Different Discharging Conditions

The design of an optimized thermal management system for Li-ion batteries has challenges because of their stringent operating temperature limit and thermal runaway, which may lead to an explosion. In this paper, an optimized cooling system is proposed for kW scale Li-ion battery stack. A comparative study of the existing cooling systems; air cooling and liquid cooling respectively, has been carried out on three cell stack 70Ah LiFePO4 battery at a high discharging rate of 2C. It has been found that the liquid cooling is more efficient than air cooling as the peak temperature of the battery stack gets reduced by 30.62% using air cooling whereas using the liquid cooling method it gets reduced by 38.40%. The performance of the liquid cooling system can further be improved if the contact area between the coolant and battery stack is increased. Therefore, in this work, an immersion-based liquid cooling system has been designed to ensure the maximum heat dissipation. The battery stack having a peak temperature of 49.76 °C at 2C discharging rate is reduced by 44.87% to 27.43 °C after using the immersion-based cooling technique. The proposed thermal management scheme is generalized and thus can be very useful for scalable Li-ion battery storage applications also.

Optimum liquid filling capacity and explosion limits of naphthalene gravity heat pipes

AbstractIn this study, naphthalene heat pipes were produced and filled with different materials to test the heat transfer performance. The relationship between the pipes' diameters, liquid content, wall temperature distribution, and transmission power was studied. An explosion test was designed to assess the operating temperature limit of the naphthalene heat pipes. The results demonstrated an optimum filling amount to optimize the pipes' heat transfer performance. In practical applications, it is very important to strictly control the wall temperature of naphthalene heat pipes. When the wall temperature of the evaporation section reaches approximately 600°C, they can easily explode.

Gallium Nitride (GaN) Nanostructures and Their Gas Sensing Properties: A Review.

In the last two decades, GaN nanostructures of various forms like nanowires (NWs), nanotubes (NTs), nanofibers (NFs), nanoparticles (NPs) and nanonetworks (NNs) have been reported for gas sensing applications. In this paper, we have reviewed our group’s work and the works published by other groups on the advances in GaN nanostructures-based sensors for detection of gases such as hydrogen (H2), alcohols (R-OH), methane (CH4), benzene and its derivatives, nitric oxide (NO), nitrogen dioxide (NO2), sulfur-dioxide (SO2), ammonia (NH3), hydrogen sulfide (H2S) and carbon dioxide (CO2). The important sensing performance parameters like limit of detection, response/recovery time and operating temperature for different type of sensors have been summarized and tabulated to provide a thorough performance comparison. A novel metric, the product of response time and limit of detection, has been established, to quantify and compare the overall sensing performance of GaN nanostructure-based devices reported so far. According to this metric, it was found that the InGaN/GaN NW-based sensor exhibits superior overall sensing performance for H2 gas sensing, whereas the GaN/(TiO2–Pt) nanowire-nanoclusters (NWNCs)-based sensor is better for ethanol sensing. The GaN/TiO2 NWNC-based sensor is also well suited for TNT sensing. This paper has also reviewed density-functional theory (DFT)-based first principle studies on the interaction between gas molecules and GaN. The implementation of machine learning algorithms on GaN nanostructured sensors and sensor array has been analyzed as well. Finally, gas sensing mechanism on GaN nanostructure-based sensors at room temperature has been discussed.

Numerical and experimental analysis of the energy performance of an air-source heat pump (ASHP) coupled with a horizontal earth-to-air heat exchanger (EAHX) in different climates

Geothermal energy has a huge potential in building applications. This paper proposes the use of an Air-Source Heat Pump (ASHP) system coupled with a Horizontal Earth-To-Air Heat Exchanger (EAHX) to reduce energy consumption in buildings.The novelty is to geothermally pre-heat or pre-cool the air source of the ASHP through the EAHX, reducing the electric power needed, keeping constant heating/cooling capacity. The behaviour of ASHP-EAHX system has been investigated by a numerical model implemented in TRNSYS. A total of 54 combinations have been obtained and tested varying ground thermal properties, burial depth, air flow rate and pipe length. The model has been validated with a real case showing a good agreement between simulated and monitored data.The study is focused on the city of Turin (North of Italy), compared with Brindisi (South of Italy), and extremely cold and hot climates like Tromsø (Norway) and Béchar (Algeria), respectively.The ASHP-EAXH performance has been investigated, by the comparison with the traditional ASHP, using different coefficients, such as the Coefficient of Performance (COP), the Energy Efficiency Ratio (EER), the Seasonal Coefficient of Performance (SCOP), and the Seasonal Energy Efficiency Ratio (SEER).The paper reveals how the ASHP-EAHX system show higher performance compared to the traditional ASHP, in all seasons.The overall merit is, for cold extremely climate, the reduction of the shutdown periods, when the outside temperature is below the limit operating temperature, and to allow the extension of the use of the heat pump to locations, where it is currently not convenient for the average outside temperature lower than the limit operating temperature of the heat pump.

Synthesis and Characterization of Zinc Oxide-Reduced Graphene Oxide Hybrid Materials and their Application for Nitrogen Dioxide Detection

Herein, we report a facile synthesis of zinc oxide-reduced graphene oxide (ZnO-rGO) hybrid materials by two-step method. Firstly, rGO was synthesized by using graphite powder mixed with sodium nitrate, sulfuric acid and potassium permanganate via Hummers method. Synthesized rGO were dispersed in ethanol by ultra-sonication for a designated time period. Then, zinc oxide (ZnO) powder was added into rGO-ethanol solution and transferred into Teflon-lined stainless steel autoclave. The ZnO-rGO was produced by hydrothermal method at 180 °C for 120 and 180 min (here after referred to as ZnO(120)-rGO and ZnO(180)-rGO, respectively). The morphological and crystalline structures of synthesized rGO and ZnO-rGO were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Synthesized ZnO-rGO was exposed to 100 parts per million (ppm) nitrogen dioxide (NO2) gas at room temperature, 50 °C and 75 °C for testing its sensing performance. The results show that ZnO(180)-rGO hybrid materials exhibit high response to NO2 gas at 50 °C and 75 °C. The electrical resistance of ZnO-rGO sensors decreased when the sensors responded to NO2 gas, indicating a p-type behavior. Moreover, the ZnO-rGO hybrid materials can detect 100 ppm NO2 gas with an operating temperature limit at 50 °C. The results imply that synthesized ZnO-rGO hybrid materials could be used as gas sensing device for ppm-level NO2 detection at low temperature and consume low power.

Systematic study of the response of single crystal diamond neutron detectors at high temperature

For many years artificial diamond detectors have been studied for application in high temperature environments. An open question is whether the performance of such detectors is influenced by the electrical contacts. In the attempt to better understand this point, a systematic study of electrical contacts deposited with different techniques and materials on top of commercial artificial single crystal diamond (SCD) films was performed. In this paper we report on the results obtained using three types of electric contacts produced both using metal and not metal layers: a) double Schottky, b) double ohmic; c) Schottky-ohmic contacts. The detectors were studied under 14 MeV neutron irradiation, and were operated in pulse mode. The pulse height spectra (PHS) produced by the 14 MeV neutrons were recorded as a function of temperature and the detector behaviour was studied by analysing the variation of the peak produced in the PHS by the 12C(n,α)9Be reaction induced by 14 MeV neutrons in carbon. The maximum operational temperature limit of the tested detectors was found to be around 230̂C and it resulted to be slightly dependent, within ±10̂C, upon the type of the electrical contact. It turned out that, together with the type of the electrical contact, other parameters such as the intrinsic diamond properties and the film thickness have to be considered to understand the response of the detector at high temperature.

All-Metal Scroll Vacuum Pumps for Tritium Processing Systems

Over the past decade, Air Squared has been actively developing and improving the highly anticipated 15 m3/h tritium vacuum pump to replace the obsolete industry standard Normetex scroll pump. The all-metal pump features a metal bellows that hermetically seals all tritium gas from any material other than metal. Air Squared has listened to the tritium market’s needs and is currently developing the latest addition to the Air Squared tritium vacuum pump line: the 150 m3/h liquid cooled all-metal (LCAM) scroll vacuum pump. Through numerous hours of testing, Air Squared has demonstrated the advantages of LCAM scroll vacuum pumps. The effect that thermal expansion has on highly toleranced all-metal pumps has been observed and characterized to predict pump performance as well as provide safe operational temperature limits. Performance characteristics of the 15 m3/h pump have been analyzed with different process gases to understand the effects of pumping light gases. Vacuum pumping speed curves have been generated at various interstage pressures to understand the advantages that roughing pump systems have when used in series with all-metal scroll vacuum pumps. This paper presents Air Squared’s 15 m3/h designs and highlights the performance characteristics. The effects that pump temperature, process gas, and fore-vacuum have on all-metal scroll vacuum pumps are explained with empirical data collected over a decade of research. With the knowledge and data collected, Air Squared has a pathway for a new industry standard 15 m3/h and 150 m3/h positive displacement scroll pump for tritium service to support international nuclear fusion and tritium research.

Suppression of Dielectric Loss at High Temperature in (Bi1/2Na1/2)TiO3 Ceramic by Controlling A-site Cation Deficiency and Heat Treatment

Dielectric capacitors are integral components in electronic devices that protect the electric circuit by providing modulated steady voltage. Explosive growth of the electric automobile market has resulted in an increasing demand for dielectric capacitors that can operate at temperatures as high as 400 ℃. To surpass the operation temperature limit of currently available commercial capacitors that operate in temperatures up to 125 ℃, Bi1/2Na1/2TiO3 (BNT), which has a large temperature-insensitive dielectric response with a maximum dielectric permittivity temperature of 300 ℃, was selected. By introducing an intentional A-site cation deficiency and post-heat treatment, we successfully manage to control the dielectric properties of BNT to use it for high-temperature applications. The key feature of this new BNT is remarkable reduction in dielectric loss (0.36 to 0.018) at high temperature (300 ℃). Structural, dielectric, and electrical properties of this newly developed BNT were systematically investigated to understand the underlying mechanism.

Experimental and numerical research on high‐temperature thermal insulation performance of lightweight porous ceramic/nanomaterial composite structure

AbstractThe thermal protection structure of hypersonic vehicles must meet the design requirements of high efficiency and light weight, and its heating surface must also be able to withstand thermal erosion by high‐speed and high‐temperature airflow. In this paper, a light‐weight porous ceramic material and a lightweight nanoscale thermal insulation material with excellent thermal insulation performance are combined to form an integrated thermal protection structure. Experimental study and numerical simulation of the structure's high‐temperature thermal insulation performance are carried out. The experimental results show that a composite sheet made from a 20 mm‐thick lightweight porous ceramic material and a 10 mm‐thick nanomaterial exhibit a temperature drop of 85 % between its back surface and front surface in four thermal environments (1200, 1000, 800 and 600 °C) at 1800 s. This indicates excellent thermal insulation performance of the composite sheet. In addition, the operating temperature limit (<1000 °C) is obtained through high‐temperature thermal performance tests on single‐layer nanomaterial sheets and scanning electron microscopy results. This provides an important basis for determining and optimizing the thickness ratio of the two materials in composite structure.

Light storage and thermal-assisted switching of SrAl2O4:Eu2+, Dy3+

In this work, we demonstrate and evaluate the viability of SrAl2O4:Eu[Formula: see text], Dy[Formula: see text] crystals for long-term light storage applications at low temperatures that can be activated at higher temperatures for on-demand lighting applications. The switching mechanism is discussed from the point of view of the possible interplay between charge transport and the persistent luminescence in this system. Step-wise temperature-dependent luminescence decay time measurement is carried out to determine the optimal temperature for photo-charging and the operational temperature limit of the crystal-under-test as light sources.

Thermally modified C-band acceleration unit for a high-repetition normal-conducting linac for free-electron lasers.

A high-repetition linear accelerator with multibeamline operation for X-rays allows users to perform multiple simultaneous experiments with an X-ray free-electron laser (XFEL) at lower actual cost per user while maintaining the availability of the laser. As the first step toward a higher pulse repetition rate (PRR), we developed radio frequency (RF) components at 5712 MHz and tested them for their feasibility at an RF PRR of 120 pulses per second (pps). To increase the RF PRR from the present value of 60 pps-at the SPring-8 Angstrom compact free-electron laser-to 120 pps, we re-examined the thermal designs of the present RF components for the XFEL. With the proposed design, the newly developed RF components worked well at 120 pps. The insulation-oil temperature in the high-voltage tank of the klystron modulator was below 70 °C, which is less than the operational temperature limit. At 5712 MHz, this is now the highest RF pulse repetition frequency yet to be achieved and represents a major step toward higher PRRs.

Hydrogen sensing and adsorption kinetics on ordered mesoporous anatase TiO2 surface

Employing TiO2 as a gas sensing material is advantageous owing to its excellent hydrogen surface receptiveness and stability under extreme conditions. However, their commercial applications are constrained by limited operating temperature range (150–400 °C) and poor selectivity. In this work, we demonstrate that the ordered mesoporous structured TiO2 is highly favourable for room temperature hydrogen sensing. The sensors prepared with evaporation induced self-assembly (EISA) showed best response ~2.98 × 102 toward 1000 ppm H2 at room temperature with a sensitivity of ~4.6 ± 1.5 × 106 ohm/ppm. Moreover, the sensor showed a response time of ~85 s (recovery time of ~198 s) with full baseline recovery and a selectivity factor of ~290 to 1000 ppm of interfering reducing gases CO and CH4 at room temperature. With a power consumption of ~1 × 10−9 W the sensors are incredibly suitable for practical applications. We performed XRD, SEM, TEM, XPS, BET and PL characterization not only to confirm the crystal structure, morphology at nanoscale, surface chemical identification, specific surface area, pore size and photo-generated charge species that contribute to the electronic transport properties but sensing mechanism also.