Showing papers on "Atmospheric temperature range published in 2020"

A highly scalable dielectric metamaterial with superior capacitor performance over a broad temperature

Abstract: Although many polymers exhibit excellent dielectric performance including high energy density with high efficiency at room temperature, their electric and dielectric performance deteriorates at high temperatures (~150°C). Here, we show that nanofillers at very low volume content in a high-temperature (high–glass transition temperature) semicrystalline dipolar polymer, poly(arylene ether urea), can generate local structural changes, leading to a marked increase in both dielectric constant and breakdown field, and substantially reduce conduction losses at high electric fields and over a broad temperature range. Consequently, the polymer with a low nanofiller loading (0.2 volume %) generates a high discharged energy density of ca. 5 J/cm3 with high efficiency at 150°C. The experimental data reveal microstructure changes in the nanocomposites, which, at 0.2 volume % nanofiller loading, reduce constraints on dipole motions locally in the glassy state of the polymer, reduce the mean free path for the mobile charges, and enhance the deep trap level.

High temperature lead-free BNT-based ceramics with stable energy storage and dielectric properties

Abstract: High-temperature dielectric ceramics are in urgent demand due to the rapid development of numerous emerging applications. However, producing dielectric ceramics with favorable temperature, frequency and electric field stability is still a huge challenge. The construction of multi-phase coexistence material systems is an effective way to obtain stable dielectric and energy storage properties. In this work, NaNbO3 (NN) modified 0.95Bi0.5Na0.5TiO3–0.05SrZrO3 (BNTSZ) ceramics ((1 − x)BNTSZ–xNN) are designed to achieve the coexistence of rhombohedral and tetragonal phases. The variation in the dielectric permittivity of the 0.8BNTSZ–0.2NN ceramic is less than ±15% over the temperature range from −55 °C to 545 °C, which is the reported record-high upper operating temperature, with a high room-temperature dielectric permittivity of 1170. The 0.8BNTSZ–0.2NN ceramic exhibits excellent frequency and electric field stability as well. Additionally, a large discharge energy density of 3.14 J cm−3 is obtained in the 0.85BNTSZ–0.15NN ceramic with an energy efficiency of 79% at a high temperature of 120 °C under 230 kV cm−1, with the variation in the discharge energy density being less than ±4% in the temperature range from 25 °C to 180 °C under 120 kV cm−1. All these features demonstrate that the (1 − x)BNTSZ–xNN ceramics are promising candidates for use at extremely high temperature in both dielectric and energy storage capacitor applications.

High energy-storage density under low electric fields and improved optical transparency in novel sodium bismuth titanate-based lead-free ceramics

Abstract: A novel (1-x)Na0.5Bi0.5TiO3-xBaHfO3 (abbreviated as (1-x)NBT-xBH) transparent ceramic was fabricated by the solid state reaction method. X-ray diffraction analysis showed that NBT-based transparent ceramics exhibit a cubic-like perovskite structure and the solid solubility of BH in NBT reached to 0.15. The Landau-Devonshire theory and I-E curves revealed that the transition between the antiferroelectric like phase and the ferroelectric phase deeply relies on the variation of composition and free energy. One sample (x = 0.15) was found to show a high dielectric constant (˜2418±10%) over the temperature range 57–400 °C. These ceramics also exhibited a high discharge energy density (Wd) of 2.1 J/cm3 and a high maximum polarization Pm of 34 μC/cm2 under relatively low electric fields which were less than 175 kV/cm. There was also high transparency in the visible spectra (more than 0.5) when the sample thickness was 250 μm.

Enhanced Energy Storage Performance of Sodium Niobate-Based Relaxor Dielectrics by a Ramp-to-Spike Sintering Profile.

Abstract: Sodium niobate (NaNbO3)-based lead-free ceramics have been actively studied for energy storage applications because of their antiferroelectric and/or relaxor features achieved in modified systems The P–E loops of NaNbO3-based ceramics are usually hysteretic because of the existence of a metastable ferroelectric phase at room temperature In this study, by introducing aliovalent cations and A-site vacancies, the relaxor characteristics are greatly enhanced in (Na1–2xBix)­(Nb1–xZrx)­O3 ceramics, leading to a high energy storage efficiency of above 90% In addition, sintering aid CuO and a special ramp-to-spike sintering profile were employed to decrease the sintering temperature and reduce the grain size The modified ceramic exhibits improved insulating properties and hence a higher breakdown strength, leading to a high recoverable energy density of 49 J/cm3 and a high energy efficiency of 88% at 430 kV/cm The ceramic also exhibits satisfactory temperature stability over a wide temperature range from 25 to 125 °C and charge–discharge performance, making it a promising candidate for high-power dielectric energy storage applications

Plasmonic Temperature Sensor Using D-shaped Photonic Crystal Fiber

Abstract: Simple structure and high sensitivity with a broad detection range are highly desirable for temperature sensor. This work presents a highly sensitive plasmonic sensor based on D-shaped photonic crystal fiber (PCF) in the near infrared region (900-1900 nm) for temperature measurement. The proposed sensor is designed by finite element method (FEM) based simulation tool and sensing properties are investigated by means of wavelength interrogation method (WIM). To support the surface plasmon oscillation, 45 nm gold film is deposited on the flat portion of the D-shaped PCF which consists of pure silica. Benzene is used as the temperature sensitive material that offers large propagation loss (PL) peak shift. Simulation outcome shows that the maximum possible sensitivity of 110 nm/°C in the temperature range from 10 °C to 70 °C. To our knowledge, the achieved sensitivity is the highest for temperature sensing in the existing literature. In addition, the proposed sensor exhibits the maximum figure of merit (FOM) of 5.5 /°C, resolution of 9.09 × 10–4 °C, and excellent fitting characteristics of PL peak wavelengths. Moreover, low PL of the proposed sensor helps to extend the sensor length up to few centimeters. Such excellent results and wider temperature range make sure that the proposed sensor can be an appropriate choice for temperature measurement even in the remote sensing application.

Engineering excited state absorption based nanothermometry for temperature sensing and imaging.

Abstract: Current luminescence nanothermometry exploits either temperature dependent quenching, temperature dependent energy transfer or thermal equilibrium between two metastable emitting levels, which are quantified to convert spectral features into absolute temperature. Although widely used and feasible, these methods are not always reliable enough in terms of flexibility, optimum temperature operating range and often require relatively complicated and expensive detection instrumentation, which may hinder wider adoption of luminescence based nanothermometry in technology and biomedical sciences. Therefore, not only more sensitive, brighter and robust phosphors are sought, but also novel temperature sensing schemes, which may potentially simplify remote quantification and imaging of temperature. In this work, we demonstrate the concept of contactless temperature readout and 2D temperature mapping by using excited state absorption (ESA) process instead of conventional approach based on ground state absorption (GSA) combined with multi-colour emission. The analysis of the excitation spectra of LiLaP4O12:Eu3+ nanocrystalline powders in a wide temperature range confirmed that the probability of populating higher levels of the ground 7FJ multiplet increases at increased temperatures. The Single Band Ratiometric Luminescent Thermometry (SBR-LT) opens new possibilities and offers luminescent thermometry at single emission band (5D0 → 7F1) under different excitation lines (7F2,3,4 → 5D0). In consequence, technically simple, temperature range adjustable, fast and affordable optical temperature imaging can be performed with high sensitivity reaching over 2.17% per °C in an unprecedentedly wide temperature range from -150 to 400 °C.

Structural stability enables high thermoelectric performance in room temperature Ag2Se

Abstract: Ag2Se is considered as an attractive candidate for use in room-temperature thermoelectric applications owing to its unique transport properties, such as glass-like thermal conductivity and good electrical conductivity. However, understanding the correlation between composition (Ag/Se ratio), defect structure, and transport properties is an important prerequisite to optimize its figure of merit (ZT). Using in-depth microscopic analysis, this study reveals the coexistence of a metastable and the main orthorhombic crystal structure in stoichiometric Ag2Se. The formation of the metastable structure was found to be detrimental to the transport properties of bulk Ag2Se. We were able to successfully inhibit its formation and stabilize the main orthorhombic structure via small anion (Se and S) excess. The compositions Ag2SeChy (y ≤ 0.01; Ch = Se, S) yielded 40–70% rise in carrier mobility with a value of 2510 cm2 V−1 s−1 at 300 K and extremely low lattice-thermal-conductivity (0.2–0.1 W m−1 K−1 over 300–375 K). This combination of transport properties yielded a room-temperature power factor of 3.2 mW m−1 K−2 and a nearly flat ZT value of ∼1.0 over the 300–375 K temperature range. Additionally, a record-high conversion efficiency (ηmax) of 3.7% was theoretically obtained for single-leg Ag2Se for a small temperature gradient of ∼80 K.

Dielectric Properties, AC Conductivity, and Electric Modulus Analysis of Bulk Ethylcarbazole-Terphenyl

Abstract: Electrical and dielectric properties for bulk ethylcarbazole-terphenyl (PEcbz-Ter) have been studied over frequency range 1 kHz–2 MHz and temperature range (R.T –120°C). The copolymer PEcbz-Ter was characterised by using X-ray diffraction. The frequency dependence of the dielectric constant ( ) and dielectric loss ( ) has been investigated using the complex permittivity. of the copolymer decreases with increasing frequency and increases with temperature. AC conductivity ( ) data were analysed by the universal power law. The behaviour of increases with increasing temperature and frequency. The change of the frequency exponent (s) with temperature was analysed in terms of different conduction mechanisms, and it was found that the correlated barrier-hopping model is the predominant conduction mechanism. The electric modulus was used to analyze the relaxation phenomenon in the material.

Crystal Structure Features of CsPbBr3 Perovskite Prepared by Mechanochemical Synthesis.

Abstract: We present a mechanochemical procedure, with solvent-free, green-chemistry credentials, to grow all-inorganic CsPbBr3 perovskite. The crystal structure of this perovskite and its correlations with the physicochemical properties have been studied. Synchrotron X-ray diffraction (SXRD) and neutron powder diffraction (NPD) allowed us to follow the crystallographic behavior from 4 to 773 K. Unreported features like the observed negative thermal expansion of the b unit-cell parameter stem from octahedral distortions in the 4-100 K temperature range. The mechanochemical synthesis was designed to reduce the impact energy during the milling process, leading to a defect-free, well-crystallized sample characterized by a minimum unit-cell volume and octahedral tilting angles in the low-temperature orthorhombic perovskite framework, defined in the Pbnm space group. The UV-vis diffuse reflectance spectrum shows a reduced band gap of 2.22(3) eV, and the photocurrent characterization in a photodetector reveals excellent properties with potential applications of this material in optoelectronic devices.

An innovative approach to design SOFC air electrode materials: high entropy La1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (x = 0, 0.1, 0.2, 0.3) perovskites synthesized by the sol–gel method

Abstract: Among the for the first time reported Cr-containing high entropy La1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) perovskite-type oxides, the selected Sr-doped La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ material is documented to possess attractive properties as a candidate air electrode material for Solid Oxide Fuel Cells (SOFCs). Nanosized powders of the considered oxides are obtained using a modified Pechini sol–gel method. In the formed solid solution with a simple perovskite structure the strontium solubility limit is found to be at least x = 0.3. Room temperature (RT) structural data indicate the presence of rhombohedral structural distortion (Rc symmetry) in the materials. High-temperature structural studies for the selected La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ indicate the occurrence of a phase transition to an aristotype Pmm structure at ca. 800 °C. The linear thermal expansion coefficient in the RT-1000 °C range is found to be moderate, 16.0(3) × 10−6 K−1. The results of impedance spectroscopy measurements support the semiconducting-type behavior of the electrical conductivity for all single-phase materials, in a temperature range of RT-1000 °C. The maximum recorded conductivity for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ composition exceeds 16 S cm−1 in the 900–1000 °C range, being suitable for application. Furthermore, chemical stability toward the La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte is proven. Considering the presence of chromium, typically deleterious to the performance, the measured value of the total cathodic polarization resistance for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ-based electrode, being 0.126 Ω cm−2 at 900 °C, seems to be very attractive. The results obtained for a button-type fuel cell indicate power densities at a level of 550 mW cm−2 at 900 °C. Therefore, it can be considered that the high entropy-based approach enables to propose alternative SOFC air electrode materials, with otherwise inaccessible chemical compositions.

High-Performance Mg3Sb2-xBix Thermoelectrics: Progress and Perspective

Abstract: Since the first successful implementation of n-type doping, low-cost Mg3Sb2-xBix alloys have been rapidly developed as excellent thermoelectric materials in recent years. An average figure of merit above unity over the temperature range 300–700 K makes this new system become a promising alternative to the commercially used n-type Bi2Te3-xSex alloys for either refrigeration or low-grade heat power generation near room temperature. In this review, with the structure-property-application relationship as the mainline, we first discuss how the crystallographic, electronic, and phononic structures lay the foundation of the high thermoelectric performance. Then, optimization strategies, including the physical aspects of band engineering with Sb/Bi alloying and carrier scattering mechanism with grain boundary modification and the chemical aspects of Mg defects and aliovalent doping, are extensively reviewed. Mainstream directions targeting the improvement of near room temperature are outlined. Finally, device applications and related engineering issues are discussed. We hope this review could help to promote the understanding and future developments of low-cost Mg3Sb2-xBix alloys for practical thermoelectric applications.

Nanofluid-based pulsating heat pipe for thermal management of lithium-ion batteries for electric vehicles

Abstract: The battery is the core component of electric vehicles (EVs). Effective thermal management of batteries directly influences the power, driving mileage, and safety of EVs. This experimental study has been conducted on a thermal management system based on a pulsating heat pipe (PHP) with a TiO2 containing nanofluid for lithium-ion batteries in EVs under different ambient temperatures and operating conditions. This study shows that when the ambient temperature was increased, the PHP suppressed the rise in the maximum temperature on the surface of the lithium battery. In the process of continuous discharge at an ambient temperature of 35 oC and discharge rate of 1C, the maximum temperature of the battery does not exceed 42.22 oC, and the maximum temperature gradient across the battery is less than 2 oC. The distribution of temperature across the surface of the battery is more uniform, and the effective improvement rate is up to 60%. Also, at the end of discharge for 0.5C, 1C, and 1.5C, the lithium-ion batteries performed well with reference to the maximum temperature, surface temperature gradient, and temperature rise. These observations prove that the thermal management system based on PHP with a TiO2-based nanofluid has excellent heat dissipation performance which can minimize the temperature gradient and increase the thermal uniformity on the battery surface. Therefore, the TiO2-PHP ensures that lithium-ion battery performs well within the appropriate temperature range (20 oC–50 oC).

Comparative study on the physical properties of rare-earth-substituted nano-sized CoFe 2 O 4

Abstract: Nanotechnology manufacturing is rapidly developing and promises that the essential changes will have significant commercial and scientific impacts be applicable in an extensive range of areas. In this area, cobalt ferrite nanoparticles have been considered as one of the competitive candidates. The present study is based on the investigation of the effect of rare-earth (RE) incorporation on the physical properties of CoFe2O4. Rare-earth ions doped cobalt ferrites with composition CoRE0.025Fe1.975O4 where RE are Ce, Er and Sm have been synthesized by citrate auto combustion technique. Characterization is achieved using X-Ray diffraction (XRD) technique for structural analysis. The obtained data show that the samples exhibit a single-phase spinel structure. RE is successfully substituted into the spinel lattice without any distortion and it acts as inhibiting agent for grain growth. Room temperature M–H curves exhibit ferrimagnetism behavior with a decrease in saturation magnetization and coercivity indicating these materials can be applicable for magnetic data storage and magneto-recording devices. The electrical conductivity is studied as a function of frequency in the temperature range of 300–700 K. The conduction mechanism is attributed to the hopping mechanism. The Seebeck coefficient S is found to be positive for Ce indicating that Co/Ce ferrite behaves as a p-type semiconductor. While it is fluctuated between positive and negative for Er/Sm-doped samples throughout the studied temperature range. The cobalt doped with Er3+ and Sm3+ exhibits degenerated semiconductor trends at higher temperatures. Such data offer a new opportunity for optimizing and improving the performance of cobalt ferrite where the physical properties are decisive.

Ultra-large electric field─induced strain in potassium sodium niobate crystals

Abstract: Electromechanical coupling in piezoelectric materials allows direct conversion of electrical energy into mechanical energy and vice versa. Here, we demonstrate lead-free (KxNa1−x)NbO3 single crystals with an ultrahigh large-signal piezoelectric coefficient d33* of 9000 pm V−1, which is superior to the highest value reported in state-of-the-art lead-based single crystals (~2500 pm V−1). The enhanced electromechanical properties in our crystals are realized by an engineered compositional gradient in the as-grown crystal, allowing notable reversible non-180° domain wall motion. Moreover, our crystals exhibit temperature-insensitive strain performance within the temperature range of 25°C to 125°C. The enhanced temperature stability of the response also allows the materials to be used in a wider range of applications that exceed the temperature limits of current lead-based piezoelectric crystals.

Phonon hydrodynamics and ultrahigh-room-temperature thermal conductivity in thin graphite.

Abstract: Allotropes of carbon, such as diamond and graphene, are among the best conductors of heat. We monitored the evolution of thermal conductivity in thin graphite as a function of temperature and thickness and found an intimate link between high conductivity, thickness, and phonon hydrodynamics. The room-temperature in-plane thermal conductivity of 8.5-micrometer-thick graphite was 4300 watts per meter-kelvin-a value well above that for diamond and slightly larger than in isotopically purified graphene. Warming enhances thermal diffusivity across a wide temperature range, supporting partially hydrodynamic phonon flow. The enhancement of thermal conductivity that we observed with decreasing thickness points to a correlation between the out-of-plane momentum of phonons and the fraction of momentum-relaxing collisions. We argue that this is due to the extreme phonon dispersion anisotropy in graphite.

Development of highly sensitive temperature sensor made of graphene monolayers doped P(VDF-TrFE) nanocomposites

Abstract: New series of nanocomposites composed of graphene and P(VDF-TrFE) have been developed for the manufacturing of ultrasensitive and flexible temperature sensor for the first time. Monolayer graphene sheets were synthesized via sonochemical approach. This graphene embedded into the P(VDF-TrFE) at various concentrations (0−0.09 wt%). The developed nanocomposites were characterized via SEM, XRD, and FTIR. The P-E hysteresis and pyroelectricity measurements were carried out. The thermal stability was emphasized using TG-TDA measurements. The electrical conductivity was investigated under different temperatures. The activation energy and the positive temperature coefficient of conductivity were determined. The developed nanocomposites were examined as temperature sensor at low temperatures (-20−0 °C) and at high temperatures (0−300 °C). Among all prepared nanocomposites, it was found that the inclusion of 0.05 wt% of graphene in the P(VDF-TrFE) resulted in a highly sensitive temperature sensor along the temperature range from -20 °C to 300 °C with sensitivity of 0.025 °C−1. This sample exhibited fast detection of temperature within 4 s and fast recovery time of 3 s. This nanocomposite exhibited high repeatability, stability and reproducibility. Therefore, the developed nanocomposite may be served as efficient, low price, light weight and ultra-sensitive flexible temperature sensor for daily life use.

Temperature-Dependent Electrochemical Properties and Electrode Kinetics of Na3V2(PO4)2O2F Cathode for Sodium-Ion Batteries with High Energy Density

Abstract: Phosphate cathode materials are practical for use in sodium-ion batteries (SIBs) owing to their high stability and long-term cycle life. In this work, the temperature-dependent properties of the phosphate cathode Na3 V2 (PO4 )2 O2 F (NVPOF) are studied in a wide temperature range from -25 to 55 °C. Upon cycling at general temperature (above 0 °C), the NVPOF cathode retains an excellent charge/discharge performance, and the rate capability is noteworthy, indicating that NVPOF is a competitive candidate as a temperature-adaptive cathode for SIBs. Upon decreasing the temperature below 0 °C, the cell performance deteriorates, which may be caused by the electrolyte and Na electrode, based on the study of ionic conductivity and electrode kinetics. This work proposes a new breakthrough point for the development of SIBs with high performance over a wide temperature range for advanced power systems.

Dielectric Relaxation Behavior of Silver Nanoparticles and Graphene Oxide Embedded Poly(vinyl alcohol) Nanocomposite Film: An Effect of Ionic Liquid and Temperature.

Abstract: This paper presents the dielectric characteristics of nanocomposite films of poly(vinyl alcohol) (PVA) embedded with silver (Ag) nanoparticles and graphene oxide(GO). The nanocomposite films were fabricated by using the solvent casting approach. The morphological analysis was carried out through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The dielectric relaxation behavior of nanocomposite films was analyzed in the frequency range of 101 to 106 Hz, by varying GO loading. The temperature effect was investigated over the temperature range of 40 to 150 °C. The effect of ionic liquid (IL) was also explored by comparing the dielectric behavior of films fabricated without using ionic liquid. The conductive filler loading variation showed a significant effect on dielectric permittivity(e′), complex impedance (Z*) and electric conductivity (σac). The obtained results revealed that the dielectric permittivity (e′) increased by incorporating Ag nanoparticles and increasing GO loading in PVA matrix. An incremental trend in dielectric permittivity was observed on increasing the temperature, which is attributed to tunneling and hopping mechanism. With an increase in nanofiller loading, the real part of impedance (Z′) and imaginary part of impedance (Z″) were found to decrease. Further, the semicircular nature of Nyquist plot indicated the decrease in bulk resistivity on increasing GO loading, temperature and incorporating ionic liquid. On the basis of above findings, the obtained GO-Ag-PVA nanocomposite films can find promising applications in charge storage devices.

High temperature deformation behavior of Mg-5wt.%Y binary alloy: Constitutive analysis and processing maps

Abstract: The high temperature deformation behavior of a Mg-5wt.%Y (Mg–5Y) binary alloy has been investigated using uniaxial compression test in the temperature range of 523 K–723 K and strain rate of 0.001 s-1 - 10 s-1. The true stress-strain curves depict that flow stress significantly decreases with the increase in temperature and decrease in the strain rate and vice-versa. An Arrhenius based hyperbolic sine equation was used to model the flow stress of the alloy at high temperature. Processing maps were developed for true strains of 0.25 and 0.45, which represent the strain near the peak stress and steady-state region, respectively. The safe region is found to be in the strain rate range of 0.001 s-1 – 0.1 s-1 and temperature range of 623 K–723 K, while the unstable region is found to be in strain rate range of 1 s-1 – 10 s-1 at a temperature range of 523 K–723 K. In the safe region, characterization of deformed microstructures using electron backscatter diffraction (EBSD) shows that the prominent deformation mechanism is continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) with manifestation of twin induced DRX and particle stimulated nucleation (PSN). The unstable region, however, consists of cracks, voids and deformation twins with little evidence of DRX.

Low Operating Voltage Carbon-Graphene Hybrid E-textile for Temperature Sensing

Abstract: Graphene-coated polypropylene (PP) textile fibers are presented for their use as temperature sensors. These temperature sensors show a negative thermal coefficient of resistance (TCR) in a range between 30 and 45 °C with good sensitivity and reliability and can operate at voltages as low as 1 V. The analysis of the transient response of the temperature on resistance of different types of graphene produced by chemical vapor deposition (CVD) and shear exfoliation of graphite (SEG) shows that trilayer graphene (TLG) grown on copper by CVD displays better sensitivity due to the better thickness uniformity of the film and that carbon paste provides good contact for the measurements. Along with high sensitivity, TLG on PP shows not only the best response but also better transparency, mechanical stability, and washability compared to SEG. Temperature-dependent Raman analysis reveals that the temperature has no significant effect on the peak frequency of PP and expected effect on graphene in the demonstrated temperature range. The presented results demonstrate that these flexible, lightweight temperature sensors based on TLG with a negative TCR can be easily integrated in fabrics.

Experimental and theoretical evidence for temperature driving an electric-magnetic complementary effect in magnetic microwave absorbing materials

Abstract: Magnetic microwave absorbing materials (MMAMs) possess many desirable properties, including thin thickness and wide attenuation band, and thus are widely applied in many fields. However, the mechanisms of variation in performance of MMAMs at dynamic temperature are difficult to characterize and poorly understood. In this work, we combine experiments and fluctuation-induced tunneling (FIT) simulations to delineate the effects of temperature on the microwave absorption properties of MMAMs. We find that the increase in temperature weakens the complex permeability of the carbonyl iron particles (CIPs)/epoxy coating, while also strengthening the complex permittivity. FIT simulations explain the experimental observations by showing that the tunneling current between two CIPs with a gap of a few nanometers increases with increasing temperature. Furthermore, crescendo conductance loss and decrescendo magnetic loss form an electric-magnetic complementary effect, so that the coating exhibits superior microwave absorption performance (maximum effective bandwidth 8 GHz) in the temperature range of 293 K–573 K, a result with implications for the broad understanding and design of MMAMs applied at high temperatures.

Bulk and Surface Low Temperature Phase Transitions in the Mg-Alloy EZ33A

Abstract: Low-temperature phase transitions in the EZ33A Mg-cast alloy have been investigated. Based on the structure assessment of the alloy after annealing at 150 °C (1826 h) and at 200 °C (2371 h) a grain boundary wetting transition by a second solid phase was documented. Within a 50 °C temperature range, substantial differences in the α(Mg) grain boundary fraction wetted by the (Mg,Zn)12RE intermetallic were observed. In contrast to what was reported in the literature, two different types of precipitates were found within α(Mg) grains. With increasing annealing temperatures, both types of precipitates dissolved.