Long-term Thermal Stability Research Articles

Highly Efficient, Flexible, and Eco-Friendly Manganese(II) Halide Nanocrystal Membrane with Low Light Scattering for High-Resolution X-ray Imaging.

Scintillators enable invisible X-ray to be converted into ultraviolet (UV)/visible light that can be collected using a sensor array and is the core component of the X-ray imaging system. However, combining the excellent properties of high light output, high spatial resolution, flexibility, non-toxicity, and cost effectiveness into a single X-ray scintillator remains a great challenge. Herein, a novel scintillator based on benzyltriphenylphosphonium manganese(II) bromide (BTP2MnBr4) nanocrystal (NC) membranes was developed by the in situ fabrication strategy. The long Mn-Mn distance provided by the large BTP cation allows the nonradiative energy dissipation in this manganese(II) halide to be significantly suppressed. As a result, the flexible BTP2MnBr4 NC scintillator shows an excellent linear response to the X-ray dose rate, a high light yield of ∼71,000 photon/MeV, a low detection limit of 86.2 nGyair/s at a signal-to-noise ratio of 3, a strong radiation hardness, and a long-term thermal stability. Thanks to the low Rayleigh scattering associated with the dense distribution of nanometer-scale emitters, light cross-talk in X-ray imaging is greatly suppressed. The impressively high-spatial resolution X-ray imaging (23.8 lp/mm at modulation transfer function = 0.2 and >20 lp/mm for a standard pattern chart) was achieved on this scintillator. Moreover, well-resolved 3D dynamic rendering X-ray projections were also successfully demonstrated using this scintillator. These results shed light on designing efficient, flexible, and eco-friendly scintillators for high-resolution X-ray imaging.

Surface and optical properties of phase-pure silver iodobismuthate nanocrystals.

The study of surface defects is one of the forefronts of halide perovskite research. In the nanoscale regime, where the surface-to-volume ratio is high, the surface plays a key role in determining the electronic properties of perovskites. Perovskite-inspired silver iodobismuthates are promising photovoltaic absorbers. Herein, we demonstrate the colloidal synthesis of phase pure and highly crystalline AgBiI4 nanocrystals (NCs). Surface-sensitive spectroscopic techniques reveal the rich surface features of the NCs that enable their impressive long-term environmental and thermal stabilities. Notably, the surface termination and its passivation effects on the electronic properties of AgBiI4 are investigated. Our atomistic simulations suggest that a bismuth iodide-rich surface, as in the case of AgBiI4 NCs, does not introduce surface trap states within the band gap region of AgBiI4, unlike a silver iodide-rich surface. These findings may encourage the investigation of surfaces of other lead-free perovskite-inspired materials.

Excellent yellow emission of Si3N4:Eu nanorods derived from waster silicon with better thermal stability for white LEDs

The core issue of light emitting diodes (LEDs) for actual application is the thermal stability of phosphors. Silicon nitride (Si 3 N 4 ) is generally recognized as especially important structural material due to its excellent mechanical properties at extreme high temperature. In this work, Si 3 N 4 : Eu was demonstrated to be an excellent luminescence functional material for LEDs. The discarded corner-waster silicon raw material was utilized to act as the precursor. The Si 3 N 4 :Eu phosphor was synthesized by a facile nitriding process at elevated temperature. The pure α-Si 3 N 4 :Eu nanorods were successfully obtained by adjusting the doping concentration of Eu. It is coexistence with mixed-valence (divalent and trivalent) for Eu in α-Si 3 N 4 according to X-ray photoelectron spectroscopy. The synthesized α-Si 3 N 4 :Eu nanorods showed bright yellow under the excitation of 365 nm (UV) and white luminescence by 460 nm chip (Blue). The Si 3 N 4 :Eu nanorods possess excellent thermal stability, maintains nearly 70% of the origin intensity even at temperatures over 300 °C. The Si 3 N 4 :Eu nanorods demonstrated comparable performance to commercial YAG:Ce 3+ (YAG). Moreover, the long-term thermal stability of Si 3 N 4 :Eu nanorods is superior to commercial YAG, revealing the enhanced service performance. This work not only presents a facile Si 3 N 4 :Eu nanorods green synthesis route from waste utilization, but also offers an enhanced service performance for the high temperature LEDs application.

An Overview of Current Printing Technologies for Large-Scale Perovskite Solar Cell Development

The power conversion efficiencies (PCEs) of Perovskite solar cells (PSCs) have seen significant performance improvements between 2012 and 2022. PSCs have excellent optoelectronic properties and can be built using low-cost materials. In order to compete with first-generation photovoltaic technologies, it will be necessary to scale up production. This review article explores the advancements in several scalable perovskite deposition techniques, including recent developments in the fabrication of high-quality perovskite film, their stabilities and commercialization status. Several scalable deposition techniques are discussed, including user-friendly solution-techniques (spin coating, slot die coating, etc.), vapour-assisted deposition approaches in the laboratory and full-scale commercial applications. The aforementioned deposition techniques have advantages compared to deposition techniques based on cost, effective mask-less patterning and unparalleled-design freedom. Other potential advantages include optimal use of materials, scalability, contactless deposition in high-resolution and a rapid transformation from small laboratory-scale work to large industrial-scale roll-to-roll production. Most recent technological advancements and structural developments relate to long-term thermal stability and moisture resistance. Many of the developments are still in the evolving field of lab-scale devices. The improvement roadmap and commercialization aspects of PSC manufacture involve two significant milestones: bridging the gap between the performance characteristics of small-scale and large-scale devices and the scalable printing techniques for all the layers in the device.

Cooling Subgrade Effectiveness by L-Shaped Two-Phase Closed Thermosyphons with Different Inclination Angles and XPS Insulation Boards in Permafrost Regions

This study focused on the coupling heat transfer mechanism and the cooling efficiency of L-shaped two-phase closed thermosyphons (L-shaped TPCTs) in the wide subgrade of permafrost regions. Considering the fact that time-space dynamics change the effects of the air temperature, wind speed, and geotemperature, a coupled air temperature-L-shaped TPCT-subgrade soil heat transfer model was established using the ANSYS 15.0 software platform, and the rationality of the model was verified through measured data. The heat-transfer characteristics of the L-shaped TPCTs and the long-term thermal stability of the subgrade were studied under different inclination angles of the evaporator (α = 15°, 30°, 50°, 70°, and 90°). Then, the cooling effectiveness of a composite subgrade with TPCTs and an XPS insulation board was numerically calculated. The results show that the heat flux of the L-shaped TPCT was the greatest when α = 50°, and the heat flux reached the maximum value of 165.7 W·m-2 in January. The L-shaped TPCT had a relatively good cooling effect on the subgrade as a whole when α = 50° and 70°, but the thawing depth at the center of the subgrade with L-shaped TPCTs reached 9.0 m below the ground surface in the 30th year. The composite subgrade with L-shaped TPCTs/vertical TPCT/XPS insulation board is an effective method to protect the permafrost foundation and improve the long-term thermal stability of the wide subgrade. The maximum heat flux of evaporation section of the L-shaped TPCT is 18.8% higher than that of the vertical TPCT during the working period of the TPCTs of the composite subgrade.

Thermal stability and behaviour of paraffin nano Al2O3, graphene and surfactant sodium oleate composite as phase change material

Organic phase change materials like paraffin possess high latent heat yet incredibly low thermal conductivity. For improving the thermal conductivity, nanomaterials are introduced into the phase change materials. Thermal energy storage applications benefit from the use of phase transition materials with high thermal conductivity and latent heat of fusion. In this work to increase the dispersion of the alumina and graphene nanoparticles, a novel nanocomposite phase change material was produced by utilizing sodium oleate as a surfactant. The surfactant sodium oleate is prepared with oleic acid and methanol, The mixture is prepared using sodium oleate, Alumina Nanoparticle, and Graphene in the mass ratio of 1:3:0.5 is mixed with paraffin in the weight percentage of 7.5 and 10 and thermal stability study was carried out. Alumina nanoparticles were synthesized and prepared by using a microwave-assisted chemical precipitation approach which is more effective and graphene nanoparticles were prepared by using modified hummer’s method. Thermocycling was used for up to 100 cycles to determine the melting point, latent heat, and long-term thermal stability of nanocomposites with phase change material. Differential Scanning Calorimetry (DSC) was used to evaluate the heat storage behaviour of the samples, and the heating rate of nanocomposites containing PCMs was investigated. The transient hot wire method was then utilised to assess the PCM’s actual thermal conductivity. From the obtained results, nanocomposite with 7.5 wt% additives show maximum thermal stability and latent heat (161.09 KJ Kg−1) for 100 cycles with an increase in 42% effective thermal conductivity, Nanocomposite with 10 wt% shows 57% higher thermal conductivity. But shows lower thermal stability and very low latent heat (120.44 KJ Kg−1). It is understood from the results that nanoparticle and surfactant addition gives a positive rise in latent heat.

Evaluation of the long-term thermal stability of a crushed-rock revetment embankment in pan-Arctic permafrost regions under the effect of snow drift

In the pan-Arctic region, snow drift events usually result in heavy snow accumulations on both sides of road embankment which severely affects the energy exchange process at the embankment slopes and further changes the temperature distribution in the embankment and its subsoil. However, there is a lack of research on the prediction of snow distribution patterns around the embankment, which makes it difficult to accurately assess the impact of snowdrift on the thermal stability of the embankment in permafrost regions, and the embankment structure cannot be reasonably optimized accordingly. Herein, using the theories of two-phase flow and heat transfer, a numerical model is developed to evaluate the long-term thermal stability of embankments with different structures under the effect of snow drift. The results show that snow deposition occurs at the toe of the windward side slope and the whole leeward side of the embankment under the effect of snow drift. If the side slope of the embankment is reduced from 1:2 to 1:5 (vertical:horizontal), the snow accumulations on both sides of the embankment are significantly reduced, and the subsoil refreezes more effectively in cold season. When a crushed-rock revetment embankment (CRRE) with 1:5 side slopes is used, the soil beneath the embankment is sufficiently cooled, the warming of permafrost beneath both sides of the embankment caused by snow accumulation is eliminated, and the temperature distribution in the embankment and subsoil has a good symmetry in warm season. The crushed-rock revetment is thus proved to be an applicable and effective structure to ensure the long-term stability of the embankment in pan-Arctic permafrost regions.

MOFs-mediated nanoscale Turing structure in polyamide membrane for enhanced nanofiltration

This work reported the successful preparation of a novel nano-Turing structure polyamide membrane. By introducing polyvinylpyrrolidone (PVP) into UiO-66-NH2, PVP-UiO-66-NH2 with high water hydrophilicity and low particle size was synthesized. The aqueous phase dispersion containing PVP-UiO-66-NH2 was loaded on the support through vacuum filtration method, and PVP-UiO-66-NH2 was fused in the polyamide layer via traditional interfacial polymerization (IP) technology. The existence of PVP-UiO-66-NH2 induced the occurrence of “local activation and lateral inhibition” in the IP system, resulting in the appearance of nano-Turing structure on the membrane surface. The successful preparation of PVP-UiO-66-NH2@polyamide composite membrane with uniform distribution of PVP-UiO-66-NH2 was proved. The PVP-UiO-66-NH2@polyamide composite membrane showed excellent water permeability of 32.95 L·m−2·h−1·bar−1 and stable Na2SO4 removal rate of 99.35 %, compared with 17.56 L·m−2·h−1·bar−1 and 99.56 % of pure polyamide membrane under the same conditions. In addition, the PVP-UiO-66-NH2@polyamide composite membrane exhibited excellent long-term filtration stability, thermal stability and antibacterial property.

A Feasible and Promising Strategy for Improving the Solar Selectivity and Thermal Stability of Cermet-Based Photothermal Conversion Coatings.

A novel multilayer, solar selective absorbing coating that contains lamellar-distributed nanoparticles in its cermet-absorbing sublayers has been fabricated using ion-source-assisted cathodic arc plating. The multilayer coating shows an outstanding selectivity, i.e., a high solar absorptance (0.909), yet it has a low thermal emittance (0.163). More importantly, the long-term thermal stability tests demonstrate that the lamellar-structured absorbers can remain stable, even when annealed at 500 °C for 1000 h in ambient air. The coating’s enhanced selectivity and thermal stability were attributed to the formation of lamellar-distributed nanoparticles in the absorbing sublayer, which form many asymmetric Fabry–Pérot cavities. In this case, the light would be held in the Fabry–Pérot cavities and thus boost the absorptivity due to the increase in interaction time. Meanwhile, the unique distribution of the nanoparticles is also beneficial for enhancing the surface plasmon resonance absorption, and thus promoting the increase in solar selectivity. Furthermore, the excellent thermal stability is ascribed to the existence of amorphous matrices, which separate and seal the nanoparticles into honeycomb shells. In this case, the atomic diffusion in the nanoparticles would be significantly retarded as the amorphous matrices can remain stable below the crystallization temperatures, which can effectively slow down the growth and agglomeration of the nanoparticles.

Long-term thermal stability and failure mechanisms of Pyromark 2500 for high-temperature solar thermal receivers

Pyromark 2500 is widely used as a concentrating solar power absorber coating because of its relatively high absorptance and its ease in application onto large-scale solar thermal receiver surfaces. However, it cannot withstand many years at elevated temperatures (>700 °C), degrading significantly within the first years of operation, and eventually failing unless costly maintenance procedures are carried out. This work aims to further the understanding of the reasons for Pyromark degradation and failure. Pyromark samples deposited on Inconel 625 and stainless steel 316L were analysed after undergoing extensive isothermal aging testing at 800 and 900 °C for 3000 h. Pyromark on Inconel 625 was shown to be optically stable at 800 °C for 3000 h, retaining a high figure of merit, which includes the impact of radiative losses as well as absorption, with a value of 90.7% after this time. In contrast, at 900 °C, the solar absorptance and optical performance of the coating trended consistently downward, with mechanical failure after 1200 h. Part of the optical degradation was associated with observed changes in morphology and the formation of new phases. Spallation was identified as the main physical degradation mechanism. The analysis suggested that the coating spalled due to two main factors: a reduction in bonding strength owing to micro-defects and the formation of oxide layers; and stress caused by the thermal expansion coefficient mismatch between layers. At higher temperatures, a more significant reduction in bonding strength, combined with higher thermal stresses, led to the rapid failure of the coating. • Optical and physical degradation of Pyromark is studied after long-term aging. • Pyromark on Inconel 625 was optically stable at 800 °C, while it failed at 900 °C. • New phase formation and changes in morphology impact optical performance. • Spallation failure is a result of increasing stress and reducing bonding strength. • Residual thermal stress between coating and substrate increases over aging time.

Influence of Nanoparticles on Long-Term Thermal Stability of Vegetable Insulating Oil

Although vegetable oil is the best substitute for mineral oil, it exhibits numerous disadvantages, including a high dielectric loss factor, low volume resistivity, and high viscosity. Nanoparticle modification may improve the electrical properties of vegetable oil considerably. In this study, vegetable oil infused with Fe3O4, TiO2, and Al2O3 nanoparticles was investigated. Thermal aging experiments were performed at 100 °C, 130 °C, and 150 °C. The aged vegetable insulating oil was periodically sampled and tested. The results revealed that the nanoparticles with a mass fraction of 0.001% exhibited the best modification effect. The electrical properties of the vegetable insulating oil modified with magnetic nanoparticles were pronounced, whereas the modification effect of nonmagnetic nanoparticles was mild. The general trend of the modification effect of the nanoparticles on vegetable oil became obvious with the increase in the temperature. At the same content, the modification effect of nano-Fe3O4 was superior to that of nano-TiO2 and nano-Al2O3. The results of this study provide experimental and theoretical support for the mechanism of long-term stability of vegetable insulating oil with nanoparticles and can be used to improve the long-term stability of vegetable insulating oil.

Comprehensive evaluation of a novel re-crosslinkable preformed particle gel for the water management of reservoir with concentrated divalent ions

As one of the most widely used technology to ameliorate the reservoir's heterogeneity, polymer gels have been applied for more than 60 years. However, how to plug fractured reservoirs with significant abnormal features, high temperature and high salinity, especially the divalent cations, is still a challenging target. This work systematically evaluated a novel salt-resistant re-crosslinkable preformed particle gel (SR-RPPG) designed for fractured reservoirs with excellent salt resistance (up to 5 % CaCl2). We evaluated the swelling kinetics, thermal stability and plugging efficiency of this SR-RPPG. We assessed the swelling kinetic and re-crosslinking behavior of the SR-RPPG through the bottle test method. High temperature-resistant glass tubes with thermally stable O-rings were employed to evaluate the long-term thermal stability of the SR-RPPG product, and the testing lasted for over 200 days. A fractured model was used to assess the plugging efficiency of the SR-RPPG product. Results showed that the SR-RPPG could swell more than 30 times its original volume in 5 % CaCl2 and a middle east formation water. Besides, the SR-RPPG gel slurry can re-crosslink to form a rubber-like elastic bulk gel at 80–100 °C, and the elastic modulus of the re-crosslinked bulk gel can reach up to 1350 Pa with a swelling ratio of 10. The SR-RPPG prepared in 1 % NaCl, 2 % KCl, middle east formation water and 5 % CaCl2 with a swelling ratio of 10 have been stable for over 200 days at 100 °C. The core flooding test demonstrated that the SR-RPPG could efficiently block the open fractures, and the water breakthrough pressure gradient reached 927.30 psi/ft (20.98 MPa/m).

Oxygen permeation properties of Bi-doped La0.8Sr0.2FeO3−δ planar ceramic membranes at intermediate temperature

Ceramic oxygen permeable membranes (COPMs) have attracted attention as a “next generation” technology for oxygen separation. However, developing new oxygen permeable membrane materials with high oxygen permeability at an intermediate operating temperature is still challengeable. In this work, a series of perovskite La0.8-xBixSr0.2FeO3-δ (LBSF, x = 0.0, 0.2, 0.3 and 0.4) oxides were synthesized and used as the oxygen permeation membrane materials. The phase structure, electrical conductivity, chemical compatibility with 3 mol% yttria-stabilized zirconia (3YSZ), O2 temperature programmed desorption (O2-TPD) have been evaluated. An asymmetric three-layer structure with “porous-transition-dense” was developed by tape casting, hot-pressing and co-sintering technology. The membrane consists of a porous 3YSZ support layer, a 3YSZ-LBSF transition layer and a dense LBSF functional layer. The oxygen permeability was tested by a new designed electrochemical device based on the limit current method. The best oxygen permeability was found in the composition of La0.4Bi0.4Sr0.2FeO3-δ measured at an intermediate temperature of 800 °C with 20% oxygen partial pressure, which could reach 1.13 mL min−1 cm−2. No obvious degradation was observed on the three-layers La0.4Bi0.4Sr0.2FeO3-δ membrane after a stability test at 800 °C for 150 h under 1.6 V and subsequent 11 times thermal cycling between 700 °C and 800 °C. The membrane exhibited excellent long-term stability and thermal cycling stability.

Recent trends and challenges in developing boride and carbide-based solar absorbers for concentrated solar power

Concentrating solar power technology has gained increased attention as a source for clean energy. However, because of low power density, it requires large areas and materials with high photothermal conversion efficiency, to harness solar energy. The solar receiver coated with solar selective material plays a critical role in efficiently converting solar energy to useful power. Because of the moderate solar selective nature and excellent thermal properties, significant efforts are currently being invested on the use of ultra-high temperature ceramics as solar selective absorbers. This literature survey presents a critical review of the research and development of early transition metal boride and carbide-based solar selective absorbers, both in bulk and tandem coating formats. In particular, we have emphasized the use of transition metal borides and carbides as intrinsic absorbers as bulk or even exploiting a multilayer design approach to improve the absorptance in the solar spectrum region. One of the key aspects is to introduce a gradient in optical constants (refractive index, extinction coefficient) to tailor high absorptance and low emissivity in tandem absorber coatings, with insightful understanding into microstructure-optical property correlation. The challenges in developing tandem solar absorbers with long-term thermal stability at mid to high temperature window in different working atmosphere are emphasized to spur the development of next generation spectrally-selective solar absorbers.

Synthesis of n-type [60]Fullerene Derivatives with Sterically Bulky tert-Butyl Groups for Vacuum Deposition Processes.

[60]Fullerene derivatives with high thermal stability can be used for vacuum deposition under heating to fabricate thin films for organic electronic devices. Here, we investigated the thermal stability of [60]fullerene derivatives with various bulky substituents for thermal evaporation under vacuum by means of thermogravimetric analysis under reduced and normal pressure. We found sterically bulky groups such as tert-butyl groups of [60]fullerene derivatives lowered the vacuum deposition temperature. Also, we performed isothermal thermogravimetric analysis to examine the long-term thermal stability of the designed compounds under heating conditions. Furthermore, we investigated the UV-Vis absorption patterns of the deposited films. Absorption in the blue wavelength range, which was attributed to intermolecular HOMO-LUMO transitions among the molecular orbitals of adjacent [60]fullerenes, was dramatically modified. These results were associated with the prevention of aggregation among neighboring [60]fullerene by the sterically bulky groups. This concept could contribute to expanding the use of evaporable [60]fullerene derivatives in organic thin-film electronics research fields.

Thermal Instability of Choline Chloride-Based Deep Eutectic Solvents and Its Influence on Their Toxicity─Important Limitations of DESs as Sustainable Materials

Deep eutectic solvents (DESs) have become a hot topic in many branches of science due to their remarkable properties. They have been studied in a wide variety of applications. In particular, choline chloride (ChCl)-based DESs are one of the most commonly used representatives of these fluids. Nevertheless, in order to apply DESs in some fields, it is essential to guarantee their stability, reusability, and biocompatibility. In this context, the long-term stability of three ChCl-based DESs formed using glucose, malonic acid, and urea as hydrogen bond donors was investigated. Furthermore, the possible formation of toxic byproducts during long-term heating was evaluated for the first time, and toxicological studies using three bacterial strains (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus) were performed. ChCl:urea DES revealed a high long-term thermal stability and was also found to be less toxic to the bacteria and thus can be considered as green solvent. ChCl:glucose DES started to decompose as a result of possible caramelization at 100 °C, and decomposition was further promoted at more elevated temperatures. Degradation of this DES did not affect greatly the toxicity toward bacteria, and low antibacterial properties were observed. The applicability of ChCl:malonic DES is not recommended as this DES was shown to be thermally unstable due to esterification and decomposition of malonic acid into acetic acid and carbon dioxide. Moreover, high toxicity of this DES in comparison to other DESs assayed in this study was reported.

Evaluation of Ultrahigh-Temperature-Resistant Preformed Particle Gels for Conformance Control in North Sea Reservoirs

Summary Preformed particle gels (PPGs) are 3D, crosslinked, dried polymer particles that can swell to several hundred times on contact with formation water. PPGs have been used extensively to control water production problems in reservoirs with conformance problems. The current state-of-the-art PPGs are polyacrylamide-based hydrogel compositions which lack long-term thermal stability under high-temperature and -salinity conditions. There are many oil reservoirs across the globe exhibiting conditions of temperatures higher than 120°C with high salinity. A novel ultrahigh-temperature-resistant PPG composition (DMA-SSS PPG) was designed to fill up the technology gap between existing polyacrylamide-based PPG technology that degrades readily over 110°C temperatures. DMA-SSS PPG exhibited excellent thermal stability for greater than 18 months in North Sea formation and formation water environments at 130°C. DMA-SSS PPG described herein showed swelling capacities of up to 30 times in different salinity North Sea brines. DMA-SSS PPG’s physiochemical properties like swelling, swelling rate, and rheological behavior were studied as a function of temperature and salinity. DMA-SSS PPGs showed excellent elastic modulus (G’) of about 3200 Pa in formation water of 90% water content. Thermostability of DMA-SSS PPGs was assessed at 130 and 150°C in North Sea brines with different salinity conditions. DMA-SSS PPGs proved to be stable for more than 18 months without losing molecular integrity. Thermostability was further confirmed through different metrics such as cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CPMAS 13C NMR), thermogravimetric analysis (TGA), and morphology. Laboratory coreflood experiments were performed to demonstrate the plugging efficiency of open fractures and effectiveness in reducing the permeability. DMA-SSS PPG comprehensive evaluation confirms its novelty for excellent hydrothermal stability, thus can be used to control water production problems for mature reservoirs exhibiting conditions of high salinity and high temperature.

Precipitate coarsening and mechanical properties in 6082 aluminium alloy during long-term thermal exposure

Long-term thermal stability is essential for the use of 6082 aluminium alloy in battery packaging. Precipitate coarsening and property changes in the alloy during 1000 h of thermal exposure at 100, 125, 150, and 175 °C were studied experimentally and theoretically. Variations of tensile properties were exhibited. The microstructural and nanoscale precipitates were characterized by microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Alloys exposed at 100 °C and 125 °C were thermally stable, retaining the strength above 340 MPa after a thermal exposure of 1000 h. Alloys exposed at 150 and 175 °C lost 25% and 48% of their respective strengths after 1000 h of exposure, reaching 253 and 178 MPa. Precipitates gradually increase in size with increasing thermal exposure time or temperature, while their number density decreases. After thermal exposure at 175 °C for 1000 h, the length of precipitates increased from 31 nm to 328 nm, and the coarsening rate of precipitates was 2.22 × 10−30 m3s−1. Comparing the experimental and theoretical coarsening rates showed that the Kuehmann–Voorhees (KV) model is suitable for calculating the precipitate coarsening rate of 6082 aluminium alloy. This study proposes a new method to predict the strength of aluminium alloy after thermal exposure; the effect of precipitate coarsening on alloy properties is also discussed quantitatively.

Insight into the Strategies for Improving the Thermal Stability of Efficient N-Type Mg3Sb2-Based Thermoelectric Materials.

N-type Mg3(Sb,Bi)2 compounds have recently been demonstrated as promising low-cost efficient thermoelectric materials in low and intermediate temperature ranges; however, the thermal stability of this type of material still poses a great challenge for practical applications. In this work, we conduct a systematic investigation of the thermal stability of several high-performing n-type Mg3(Sb,Bi)2-based thermoelectric materials in both bulk and powdered forms using X-ray and neutron diffraction. It is found that the bulk sample exhibits a much slower degradation rate based on the evolution of the secondary Bi/Sb phase in comparison with the powdered sample, revealing a clear kinetic effect. Moreover, the surface of the bulk sample will gradually become Mg-poor or Bi-rich even at room temperature when exposed to air for a long time, highlighting the importance of surface encapsulation for applications. An underlying mechanism based on the Mg loss/migration is proposed to account for the property degradation. Importantly, to address the property degradation, we discuss possible solutions and propose Mg-vapor annealing as an effective approach to enhance thermal stability by suppressing the Mg loss/migration through saturating grains and grain boundaries with elemental Mg. We expect a combination of the Mg-vapor annealing and surface coating to further improve the long-term thermal stability. This work sheds light on the strategies for enhancing the long-term stability of n-type Mg3Sb2-based thermoelectrics for practical applications.

The effect of traditional amur cork tree bark extract dyes on thermal stability of paper by accelerating ageing

Extracts from amur cork tree barks contain some of the most important traditional natural dyes used, especially for functional production in ancient Chinese papers, due to religious reasons and their aesthetic aspects and antibacterial properties. Some ancient paper artefacts, dyed with this colourant and scattered around the world, are currently preserved to different extents. This study aims to characterize the thermal degradation process of amur cork tree bark extracts dyed papers to improve the knowledge and effectiveness of restoration practices. The properties of extracts dyed papers treated under dry-heat accelerating ageing conditions were investigated via optical observation and scanning electron microscopy as well as with pH, tensile strength and folding endurance analyses. The results showed that the main components from extracted dyes played important roles in affecting the properties of dyed paper. The changes in surface colour, pH, morphology and mechanical properties after the artificial dry-heat ageing tests revealed the most suitable concentration of extract dyes for maintaining the long-term thermal stability of the paper.