Elevated Temperatures Research Articles

Serum levels of soluble receptor activator for nuclear factor kB ligand play a crucial role in the association of osteoprotegerin with coronary artery disease.

Osteoprotegerin (OPG) is a soluble decoy receptor for receptor activator of nuclear factor kB ligand (RANKL), and is implicated in the pathogenesis of atherosclerosis. The aim of the present study was to examine the hypothesis that serum OPG concentrations are increased in patients with stable coronary artery disease (CAD) at different serum levels of soluble RANKL (sRANKL). The study used a case-control design in which consecutively hospitalized individuals were recruited. Fasting blood samples were taken upon admission for serum testing. Participants with previously diagnosed CAD that was asymptomatic or had controlled symptoms constituted the stable CAD group, whereas patients with negative coronary computed tomography angiography results constituted the control non-CAD group. Exclusion criteria included recent acute coronary syndrome, severe heart failure, CAD-complicating autoimmune, blood or thyroid diseases, cancer, elevated temperature with or without infection, severe liver or kidney dysfunction, abnormal calcium metabolism, recent surgery and trauma history. A total of 118 individuals were included in the study. Smoothed plots generated using the recursive method and multivariate models showed that the incidence of stable CAD increased with serum OPG level up to the turning point of 18 pg/ml. This trend was observed at both high [odds ratio (OR), 1.61; 95% confidence interval (CI), 1.04-2.50; P=0.032) and low sRANKL concentrations (OR, 1.52; 95% CI, 1.06-2.17; P=0.022) after adjustment for cardiovascular risk factors. In conclusion, serum OPG levels ≤18 pg/ml are positively associated with stable CAD, regardless of sRANKL levels. In addition, at the same serum OPG level, higher sRANKL levels are associated with a greater incidence of stable CAD compared with lower sRANKL levels. This study identified the relationship between OPG, sRANKL, and stable CAD, and established the reference range for future clinical use.

Study on the fire resistance of RC beams reinforced with BFRP and HFRP bars

For non-metallic reinforcement to be successfully integrated into residential and commercial construction, extensive research is required to understand the structural performance of Fiber Reinforced Polymer (FRP) reinforced concrete (RC) elements in various conditions, including the effect of elevated temperatures on structural performance. To accomplish this, a full-scale investigation was performed on the structural performance of FRP-RC elements subjected to elevated temperatures. The study involved conducting fire tests on beams, where the midsection was heated from below (tension zone) and the sides while being simultaneously loaded with 50% of their ultimate loads. The beams were reinforced with Basalt FRP (BFRP) bars and a hybrid composite of Carbon and Basalt Fibers (HFRP) bars. The HFRP-RC beams showed better resistance to the combined effect of loading and elevated temperatures compared to BFRP-RC beams. This study provides insights into the behavior of FRP materials in RC structures subjected to high temperatures, and contributes to the advancement of knowledge in this field.

Fabrication, machining (dry vs. cryogenic) and life cycle analysis of hybrid titanium composite laminates (HTCL)

Titanium-based fiber metal laminates, also known as hybrid titanium composite laminates (HTCL), are new-age potential materials used in the field of supersonic and high-speed passenger aircraft due to their better corrosion resistance, higher stiffness, fatigue and impact resistance at both elevated and room temperature. However, the difficult-to-machine nature mandates using effective but sustainable coolant during machining. Therefore, in the present study, drilling of HTCL is done in a dry and cryogenic LCO2 environment, considering various responses such as thrust force, torque, surface roughness, tool wear, chip analysis, power consumption and specific cutting energy. Further, a life-cycle analysis was carried out to evaluate the impacts of these two cutting conditions. The results indicate that cryogenic cooling improved the hole surface finish (up to 25%) by reducing the torque values significantly by 25–30%. Furthermore, tool life is improved (up to 48.6%), and power consumption is reduced (up to 13.3%). These outcomes make cryogenic with LCO2 more favorable to use over dry conditions for this novel material. Nevertheless, condensing CO2 into liquid form necessitates a higher consumption of energy and natural resources. Furthermore, its direct release into the environment results in environmental impacts (up to 17–20%) compared to dry machining.

A new approach of preheating and powder sintering in electron beam powder bed fusion

Preheating is an essential process step in electron beam powder bed fusion. It has the purpose of establishing a sintered powder bed and maintaining an elevated temperature. The sintered powder bed reduces the risk of smoke and in combination with the elevated temperature improves the processability. Today, the line-ordering preheating scheme is widely used. This scheme does not take the previously built layers into account and results in an inhomogeneous elevated temperature and consequently in a variety of sinter degrees, which is disadvantageous for the process. The main challenge is now to modify this scheme to establish a homogeneous temperature distribution. This study addresses this challenge and analyses as well as optimises this scheme. A GPU-parallelised thermal model reveals a heterogeneous temperature distribution during preheating because of varying thermal conditions within a build job. In addition, a work-of-sintering model predicts that the sinter degree of the current powder layer on top of previously consolidated material is smaller than on top of the surrounding powder bed. This work aims to invert this trend to improve powder re-usage and material consolidation. Consequently, this work proposes an extension of the current scheme, compensating for the specific energy loss with local adjustments to the energy input. This adaption results in a uniform temperature distribution and advantageous sintering. Applying the proposed numerical model proves to be an effective method to analyse the evolving process conditions and tailor the local energy input, thereby improving the efficiency of the preheating step.

A Comprehensive Study on the Production and Characterization of Eco-Friendly Biodegradable Plastic Films from Dent Corn Starch

The increasing demand for eco-conscious and sustainable biomaterials has propelled the exploration of alternatives to petroleum-derived materials. This study delves into the utilization of dent corn (Zea mays L.) starch as a renewable resource for crafting biodegradable packaging solutions. The physicochemical properties of dent corn starch were meticulously assessed through a series of preparation steps, encompassing washing, cutting, grinding, drying, and pulverizing. Despite the inherent variability in dent corn sourced from local markets, the resulting starch exhibited commendable characteristics, including a pH of 7.02, moisture content of 6.50%, ash content of 0.20%, bulk density of 0.47 g/ml, gelatinization temperature of 61.2 ˚C, protein content of 2%, and a yield of 64%. Subsequently, employing the casting method, bioplastic films were synthesized using starch powder, water, and glycerol as a plasticizer. A comprehensive evaluation of the chemical, mechanical, solubility, and biodegradability properties of the films ensued. Remarkably, the films demonstrated notable values for tensile strength (2.58 MPa), elongation at break (24%), and film thickness (1.4 mm), alongside exhibiting low absorption rates in various media and remaining insoluble in solvents, even at elevated temperatures. Notably, the influence of glycerol content on the tensile strength and biodegradability of the films was elucidated through a least squares model, underscoring its pivotal role. These findings highlights the potential of dent corn starch as a viable alternative for the development of biodegradable packaging materials, despite the variability inherent in its sourcing from local markets. The study significantly contributes to ongoing endeavors aimed at fostering sustainability and reducing reliance on petroleum-derived materials, aligning with the escalating environmental consciousness.

Electrocatalysis in Solid Oxide Fuel Cells and Electrolyzers.

Interest in energy-to-X and X-to-energy (where X represents green hydrogen, carbon-based fuels, or ammonia) technologies has expanded the field of electrochemical conversion and storage. Solid oxide electrochemical cells (SOCs) are among the most promising technologies for these processes. Their unmatched conversion efficiencies result from favorable thermodynamics and kinetics at elevated operating temperatures (400-900 °C). These solid-state electrochemical systems exhibit flexibility in reversible operation between fuel cell and electrolysis modes and can efficiently utilize a variety of fuels. However, electrocatalytic materials at SOC electrodes remain nonoptimal for facilitating reversible operation and fuel flexibility. In this Review, we explore the diverse range of electrocatalytic materials utilized in oxygen-ion-conducting SOCs (O-SOCs) and proton-conducting SOCs (H-SOCs). We examine their electrochemical activity as a function of composition and structure across different electrochemical reactions to highlight characteristics that lead to optimal catalytic performance. Catalyst deactivation mechanisms under different operating conditions are discussed to assess the bottlenecks in performance. We conclude by providing guidelines for evaluating the electrochemical performance of electrode catalysts in SOCs and for designing effective catalysts to achieve flexibility in fuel usage and mode of operation.

Synergistic effects of a swirl generator and MXene/water nanofluids used in a heat exchanger pipe of a negative CO2 emission gas power plant

The focus on optimizing heat exchangers contributes to improved temperature control mechanisms, ensuring the sustainable operation of innovative power plants working toward negative CO2 emissions. In the realm of oxy-combustion within Negative CO2 Emission Power Plants (nCO2PP), the temperature of combustion products surpasses 3000 ( K ) . Addressing this challenge, the imperative arises to reduce these elevated temperatures to a manageable 1100 ( ° C ) . This critical cooling process is achieved through the injection of water, facilitated by the implementation of heat exchangers. The study delves into the optimization of heat transfer within the heat exchanger pipe, specifically tailored for the context of a nCO2PP. Employing a numerical simulation, the investigation explores the impact of vortex generator geometry, vane angles, single and dual propeller-type swirl generators, and the integration of a novel class of fluid, MXene/water nanofluid. Initially, the study scrutinizes propeller-type geometry at vane angles spanning from 15° to 60°. The enhanced swirl flow associated with lower vane angles leads to improved fluid mixing, fostering more effective heat transfer. Results showed that the 15-degree vane angle, with a wider circumferential coverage, may result in increased wall contact, influencing heat transfer efficiency. Subsequently, at Re = 6000, incremental rates of the Nusselt number ( Nu n − Nu s Nu s %), for θ = 15°, 30°, 45°, and 60° are 175.1, 108.8, 90.7, and 40.3%, respectively. Also, the increment rates of Friction Factor ( f n f s ) for aforementioned vane angle are 38.48, 9.26, 4.08, and 2.42%, respectively. In addition, for ∅ MXene = 0.5 % , the Nusselt number experiences considerable increments of 22.94, 24.17, 24.70, and 24.707% at Reynolds numbers of 6000, 12,000, 18,000, and 24,000, respectively, compared to pure water, emphasizing the potential of MXene to enhance heat transfer efficiency.

Electrochemical instability of room-temperature ionic liquids with LiTFSI at elevated temperature and its consequences in Li/Li-ion based half-cells and full-cells

High-temperature Li-ion batteries capable of operating up to 100 ℃ can replace lithium thionyl chloride primary batteries in specialized industrial applications. Room-temperature ionic liquids (RTIL) offer high thermal stability and can be a promising choice of electrolyte for high-temperature batteries. This work elucidates that high thermal stability alone does not guarantee effective battery operation due to the electrochemical instability observed in RTIL-LiTFSI mixtures at elevated temperatures. Here, we investigate the impact of varying electrochemical stability in RTILs on half-cell, full-cell, and calendar aging. Electrochemical instability of the electrolyte at the cathode interface injects additional electrons and Li-ions into the electrochemical cell, triggering a cascade of detrimental chain reactions that hinder efficient battery performance. We demonstrate that electrochemical information gathered from a full-cell configuration can frequently obscure the presence of electrochemical instability at the cathode surface. To accurately evaluate this instability, it is essential to perform in-depth half-cell studies and other characterizations. Our results indicate that cathode electrolyte interphase (CEI) can reach a thickness of up to 100 nm, with a depth-dependent composition showing higher concentration of inorganic species like LiF and LiNSO near the cathode surface. Further, accelerated calendar aging measurements of such cells at high temperature revealed complete irreversible self-discharge within as little as 14 days. These findings shed light on the critical factors influencing the stability and performance of cells under challenging operating conditions.

Enhanced high-temperature capacitive performance through introduction of polar groups in poly(aryl ether ketone) dielectric polymer

High-temperature poly(aryl ether ketone) dielectrics have attracted application prospects in the field of polymer film capacitors. However, the investigations on improving the capacitive properties of poly(aryl ether ketone) based on molecular structure design strategies were absent. Herein, a series of poly(aryl ether ketone) bearing phthalazinone moiety were synthesized, and the effect of chemical structures on the capacitive properties of the resultant polymers was investigated by experimental data and density functional theory calculation. The introduction of the sulfone group could not only improve the permittivity but also construct deep carrier traps to enhance the breakdown strength, leading to high discharge energy density (Ue) value of the poly(phthalazinone ether sulfone ketone) (PPESK). For the poly(phthalazinone ether nitrile ketone) (PPENK), the introduction of the nitrile group could improve the Ue at room temperature, but reduce the value at elevated temperatures. As a result, at room temperature, the maximum Ue of both the PPESK (4.56 J/cm3) and the PPENK (3.40 J/cm3) was higher than that of the PPEK (3.02 J/cm3). Notably, the maximum Ue of the PPESK reached 3.07 J/cm3 at 150 °C, which is twice that of commercially bi-oriented polypropylene (BOPP) film (1.5 J/cm3 at 70 °C). Additionally, at the electric field of 200 MV/m and 150 °C, the PPESK films exhibited the Ue of 0.72 J/cm3 with charge-discharge efficiency (η) of 97.2 %, which was obviously superior to those of the BOPP (Ue = 0.4 J/cm3 with η of 96 % at 70 °C). This study presents an in-depth analysis regarding the relationship between the sulfone and nitrile groups and the capacitive performance of poly(aryl ether ketone) bearing phthalazinone moiety, which is informative for designing high-temperature dielectric polymers.

Do the expected heatwaves pose a threat to lichens?: Linkage between a passive decline in water content in thalli and response to heat stress.

Being poikilohydric, lichens are inherently exposed to alternating desiccation and hydration cycles. They can exhibit extraordinary resistance to extreme temperatures in a dehydrated state but thermal thresholds for hydrated lichens are lower. The ability of the lichen Cetraria aculeata to recovery after high temperature treatment (40°C, 60°C) at different air humidity levels (relative humidity [RH]: <15%, 25%, 50%, 75%, ≅100%) was examined to find a linkage between passive dehydration of the lichen and its physiological resistance to heat stress. The response to heating was determined by measuring parameters related to photosynthesis and respiration after 2- and 24-h recovery. A higher RH level resulted in a slower decline in relative water content (RWC) in hydrated thalli. In turn, the stress resistance of active thalli depended on the ambient humidity and associated RWC reduction. Elevated temperature had a negative impact on bioenergetic processes, but only an unnatural state of permanent full hydration during heat stress resulted in a lethal effect. Hydrated lichen thalli heated at 40°C and 50% relative humidity (RH) tended to be least susceptible to stress-induced damage. Although atypical climatic conditions may lead lichens to lethal thresholds, the actual likelihood of deadly threat to lichens due to heat events per se is debatable.

Response of 11B enriched ZrB2 ultra-high temperature ceramic to neutron irradiation at elevated temperatures

ZrB2, an ultra-high temperature ceramic (UHTC) is being considered for use in fusion reactor first-wall structures, yet its response to irradiation remains poorly understood. This study employed scanning/transmission electron microscopy (S/TEM), synchrotron X-ray diffraction (XRD), finite element calculations, and thermal property measurements to thoroughly investigate the neutron-irradiation effects on 11B-enriched ZrB2. Neutron irradiations were conducted at 220 °C and 620 °C, with a neutron fluence of 2.2 × 1025 neutron/m2 (energy > 0.1 MeV), resulting in 3.9 dpa and 4200 appm He. The study revealed the unusual prevalence of prism loops and a > c anisotropic lattice swelling, likely linked to the low c/a ratio of ZrB2, leading to grain boundary microcracking. Reducing the grain sizes was effective in reducing intergranular cracking and macroscopic swelling. The observation of cavities in ZrB2 irradiated at 620 °C, as opposed to 220 °C, prompts questions about the temperature at which vacancies in ZrB2 become mobile, and the role of neutron absorption by 10B in elevating irradiation temperatures. Isotopic enrichment in 11B proves to be a viable strategy for mitigating helium production in transition-metal diborides, which is a critical consideration for nuclear applications. Irradiation-induced defects reduce the thermal diffusivity and conductivity of ZrB2 by a factor of 4–9, which has important implications for its role as a plasma-facing material in fusion reactors that drive high heat fluxes through first-wall materials. This comprehensive study lays the foundation for understanding ZrB2 behavior under neutron irradiation and highlights important phenomena to consider for various material applications.

Mechanical analysis of a stitched sandwich structure and its SiO2f/SiO2 panels: Experimental and numerical investigation on compression and shear performances

The compression and shear performances of the stitched sandwich thermal protection structure (SSTPS) was systematically investigated through experimental and simulation methods in this study. Compression and shear testing methods were designed, and macroscopic performance data for SiO2f/SiO2 thin panels and SSTPS were successfully obtained, thereby validating the rationality of the experimental approach. By establishing mechanical experimental methods, the correlation between microscopic structural features and macroscopic mechanical performance was revealed, and mechanical modeling and analysis work was conducted. The experimental and numerical results indicate that compression and shear failure of thin panels mainly occur at the intersections of fiber bundles, exhibiting non-brittle failure. The delamination of sandwich materials or the buckling deformation of panels is identified as the primary cause of the nonlinear response in SSTPS. Elevated temperatures induce an increase in the modulus and strength of SSTPS and a decrease in toughness, correlated with the high-temperature densification of the matrix structure. Finite element simulations reveal the critical role of component and interface damage in macroscopic nonlinear mechanical responses. The research demonstrates that, the compressive and shear failure mechanisms of SiO2f/SiO2 thin panels and SSTPS were successfully elucidated through the implementation of an innovative experimental methodology.

Effect of elevated temperatures (550–860 K) on the laminar flame speeds of methane/hydrogen blends

Experimental determination of laminar flame speeds was performed for methane/hydrogen mixtures in a 79% Ar/21% O2 oxidizer (referred to as “airgon”) at 1 atm. The shock-tube flame speed method enabled the first measurements at temperatures above 650 K and was employed to study binary fuel blends with various hydrogen fuel fractions (xH2 = 0.1–0.4) at equivalence ratios of 0.8, 1.0, and 1.2 in the unburned-gas temperature range of 550–860 K. Results were compared against simulations conducted using the GRI-3.0, FFCM-2 and Stagni et al. models. Good agreement between all three models and measurements was observed at lean and stoichiometric conditions, while the three models and data diverge in the rich case. Equivalent fuel/air flame speeds were computed from fuel/airgon measurements by applying a mixture-dependent scaling ratio. The scaled air equivalent data were compared against literature data and showed good agreement. Through sensitivity analyses, it was found that reactions related to neat methane combustion are highly relevant at all conditions, while H2-specific reactions only become important with high hydrogen content (xH2 ≥ 0.4). Additionally, differences in sensitivity coefficients were identified across the models, providing useful information for potential refinement of reaction rates, and consequently, the development of models which better represent new experimental data.

Scalable multilayered dielectric polymer film exhibiting significantly improved high-temperature energy density

Dielectric polymers, serving as crucial dielectric media in high-power-density energy storage devices, play a pivotal part in modern industries and electrical systems. However, the rapid degradation of breakdown strength and charge-discharge efficiency in elevated temperature environment imposes formidable limitations on the utilization of polymer dielectric under extreme conditions. Here, a series of polyetherimide/polysulfone alternating multilayer composite films are prepared using a non-equilibrium processing method, which effectively blocks the development of breakdown paths by the interface barriers in the multilayer structure. The deep trap sites within the interface capture the charge carriers excited at high temperatures, thus decreasing conduction loss and enhancing the efficiency and breakdown field strength of the dielectric polymer. Consequently, excellent capacitive performances including a high energy density of 5.4 J cm−3 with an efficiency exceeding 90% at 200 °C and cycle stability up to 106 cycles have been obtained. Furthermore, the multilayer polymer capacitors (MLPC) constructed from composite films also exhibit significant flexibility and thermal stability. This work provides valuable insights for the advancement of high-temperature energy storage polymers with commercial application value.

Defect dynamics studies during heat treatments in plastically deformed metals predicted for nuclear applications

We report on defects dynamics during heat treatment in plastically deformed metallic materials using positron annihilation lifetime spectroscopy carried out on the intense pulsed positron beam. The conducted experiment allowed us to observe the changes in the concentration and sizes of vacancy-like defects observed during in situ annealing. We monitored heat treatments up to 300 °C in hydrostatic extruded Ti and cavitation peened V–4Cr–4Ti alloy. We were able to track the recovery processes in Ti and redistribution of large voids at the surface of cavitation peened V–4Cr–4Ti alloy. The relaxation time during recovery was about 20 min. Performed experiments show that in cold-worked metallic materials significant changes in vacancy clusters concentrations occur at mildly elevated temperatures. The presented results give opportunity to the application of in situ observation of defects dynamic to similar problems related to thermomechanical processing of metallic materials.Graphical abstract

Investigation of the addition of fins in the collector of water/Al2O3-based PV/T system: Validation of 3D CFD with experimental study

Photovoltaic solar cells, known for their high efficiency and durability, offer a promising renewable energy solution. However, they are susceptible to weather conditions, have low energy density, and require regular maintenance. Elevated operating temperatures can diminish efficiency, power output, and voltage. This study explores the incorporation of fins into PV/T system collectors using Al2O3 nanofluid, validated through 3D computational fluid dynamics (CFD) simulations and laboratory experiments conducted in Surakarta, Indonesia. The research reveals that adding fins to the system reduces PV temperature by expanding the heat transfer area from the collector to the working fluid. Working fluid Water/Al2O3, at 0.6 % concentration, exhibits the highest electrical energy conversion rates at 13.39 %. Adding fins also improves thermal performance based on the working fluid used. The use of fins concentrates the heat transfer flow in the fluid. The PV/T-Fin system has more temperature color contour distribution than the PV/T system. The direction of flow distribution is based on the geometry of the fins added to the PV/T system collector. In addition, when the viscous effect decreases, the temperature decreases towards the center of the flow. This research was validated using Mean Absolute Percentage Error (MAPE), with the most significant error observed in PV/T thermal efficiency being 13.5 %. ANOVA was used to analyze the impact of additional fins and working fluid factors on the PV/T system. The results indicate no significant difference in electrical energy conversion between adding fins and the working fluid Water/Al2O3.

Detection of Cyclic Imines (CIs) Toxins in Whole Body of Shellfishes: First Monitoring Report of CIs in South Korea Shellfishes

Cyclic imines (CIs) produced by microalgal species that accumulate in the food chains of marine organisms are novel biotoxins that do not belong to the classic group of marine biotoxins. In the past, CIs were found only in limited areas; however, in recent years, rapid changes in marine ecosystems have led to widespread CIs and increased exposure to toxic risks. In this study, we analyzed seven CI toxins, GYM-A, SPX (13-desmethyl spirolide C, 13, 19-dideMe spirolide C, 20-methyl spirolide G), and PnTX-E, F, and G, using LC/MRM-MS. Shellfish samples were purchased from a domestic Korean fish market (67 samples in 2021 and 216 samples in 2022). The entire body of the shellfish was ground and extracted with 50% methanol, followed by lipophilic-specific SPE. Only GYM-A, PnTX-G, and 13-desmethyl spirolide C were detected in all analyzed samples. The maximum concentrations of GYM-A is maximum 179 ppt (ng/kg) in Crassostrea nippona (March 2022), PnTX-G is maximum 7 ppt in Anadara broughtonii (April 2022), 13-desmethyl SPX C is maximum 58 ppt in Crassostrea nippona (April 2022). The southern coast exhibited the highest frequency of detection of these toxins, which was attributed to elevated sea-surface temperatures, aligned with conducive conditions for toxin-producing phytoplankton. According to the monitoring results, there were no significant CI toxins in the shellfish; however, it is important to monitor CI toxin accumulation in shellfish because of their high risk of toxicity.

Modeling Fertilization Outcome in a Changing World.

Marine organisms have complex life histories. For broadcast spawners, successful continuation of the population requires their small gametes to make contact in the water column for sufficiently long periods for fertilization to occur. Anthropogenic climate change has been shown to impact fertilization success in various marine invertebrates, including sea urchins which are key grazers in their habitats. Gamete performance of both sexes declined when exposed to elevated temperature and/or pCO2 levels. Examples of reduced performance included slower sperm swimming speed and thinning egg jelly coat. However, such responses to climate change stress were not uniform between individuals. Such variations could serve as the basis for selection. Fertilization kinetics has long been modeled as a particle collision process. Here, we present a modified fertilization kinetics model that incorporates individual variations in performance in a more environmentally-relevant regime, and which the performance of groups with different traits can be separately tracked in a mixture. Numerical simulations highlight that fertilization outcome is influenced by changes in gametes traits as they age in sea water and the presence of competition groups (multiple dams or sires). These results highlight the importance of considering multiple individuals and at multiple time points during in-vivo assays. We also applied our model to show that interspecific variation in climate stress vulnerabilities elevates the risk of hybridization. By making a numerical model open-source, we aim to help us better understand the fate of organisms in the face of climate change by enabling the community to consider the mean and variance of the response to capture adaptive potential.

Ultrarapid soldering Cf/Al by inactive solder by ultrasonic assistance

Ultrasonic vibration was applied when soldering carbon fiber-reinforced aluminum composites (Cf/Al) in this work. The effects of ultrasonic action time on joint formation, carbon fiber distribution, and mechanical properties of the joints were studied. Results show that, with the assistance of ultrasonic vibration, inactive solder can wet the carbon fiber within dozens of seconds at low temperature (250 °C). Short ultrasonic action time leads to minor erosion of aluminum substrate, thereby restricting the movement of carbon fibers into joint. Extensive erosion of the aluminum occurs with prolonged ultrasonic action time. A uniform distribution of carbon fibers in joint is achieved at 60 s. Wetting of carbon fiber is characterized by amorphous-nanocrystalline oxides on its surface, which can be attributed to the elevated temperature and pressure induced by the cavitation of the solder. Extending ultrasonic time enhances the hardness and the shear strength of the joint. The failure cracks propagate through the substrate when ultrasonic time exceeds 15 s. This work provides referential value when soldering materials with low surface energies.

Template-assisted growth of Ga-based nanoparticle clusters on Si: effect of post-annealing process on the Ga ion beam exposed 2D arrays fabricated by focused ion beam nanolithography.

We demonstrate template-assisted growth of Gallium-based nanoparticle clusters on Si substrate using a focused ion beam nanolithography technique. The nanolithography counterpart of the technique steers a focussed 30 kV accelerated Gallium ion beam on the surface of Si to create template patterns of two-dimensional dot arrays. Growth of the nanoparticles is governed by two vital steps namely implantation of Gallium into the substrate via Gallium beam exposure and formation of the stable nanoparticles on the surface of the substrate by subsequent annealing at elevated temperature in Ammonia atmosphere. The growth primarily depends on the dose of implanted Gallium which is in the order of 107 atoms per spot and it is also critically influenced by the temperature and duration of the post-annealing treatment. By controlling the growth parameters, it is possible to obtain one particle per spot and particle densities as high as 109 particles per square centimetre could be achieved in this case. The demonstrated growth process, utilizing the advantages of focused ion beam nanolithography, is categorized under the guided organization approach as it combines both the classical top-down and bottom-up approaches. Patterned growth of the particles could be utilized as templates or nucleation sites for the growth of an organized array of nanostructures or quantum dot structures.&#xD.