Moderate Temperature Range Research Articles

Excellent strength-ductility synergy assisted by dislocation dipole-induced plasticity in Co-free precipitate-strengthened medium-entropy alloy

Precipitation strengthening is one of the most effective approaches for developing advanced structural materials with outstanding strength-ductility combinations. However, most compositional designs of precipitate-strengthened HEAs/MEAs compromise the cost-property tradeoff owing to the addition of expensive Co element. In this study, a Co-free FeCrNi-based precipitate-strengthened medium entropy alloy (denoted as Al0.2Cr0.9FeNi2.2Ti0.2) with a near-equiatomic FeCrNi matrix and a high content (∼ 35 %) L12 nanoprecipitates was designed using a mixing strategy. The microstructural features, mechanical performance, deformation substructure evolution, and strengthening mechanisms were systematically investigated using EBSD, TEM, and APT. Tensile tests indicated that the current alloy aged within a moderate temperature range achieved an exceptional strength-ductility combination compared to existing Co-containing and Co-free HEAs/MEAs. Particularly, the alloy aged at 700 ℃ (denoted as 700A) demonstrated a high ultimate tensile strength of 1606 MPa and a large ductility of 25 %, benefiting from both precipitation hardening and an unusual strain-hardening sustainability. Such anomalous strain-hardening sustainability can be attributed to the dislocation dipole-induced plasticity. High-density dislocation dipoles can simultaneously provide additional strain hardening by reducing the dislocation mean free path and enhance plastic deformation compatibility by acting as stress delocalization origins, thereby contributing to excellent strength-ductility synergy. These findings will not only open a new door for the future development of high-performance Co-free precipitate-strengthened HEAs/MEAs, but also deepen the understanding of the work-hardening mechanisms in these alloys.

Breaking the trade-off between proton conductivity and mechanical stability through liquid-crystal-modified aramid fibers in sulfonated polyether ether ketone membranes

In the quest for sustainable and high-performance hydrogen fuel cells, proton exchange membranes (PEMs) stand as a pivotal research focus. To overcome the significant challenge posed by the traditional trade-offs between proton conductivity and mechanical stability, this work introduces liquid-crystal-modified aramid fibers (DBAF) with highly ordered molecular arrangements and abundant sulfonic acid groups on the side chains as proton-hopping sites into a sulfonated poly (ether ether ketone) (SPEEK) matrix. The inclusion of components not only improves the proton conductivity of the membrane, but also boosts its mechanical strength. The results of our study demonstrate that the externally attached sulfonic acid groups create extra channels for the transport of protons. Additionally, the organized and consistently stable hydrogen-bond network enables the Grotthuss transport mechanism within the SPEEK membrane. The 1 wt% DBAF-SPEEK composite membrane exhibits a maximum proton conductivity of 0.23 S cm−1 at 80 °C, representing a 64% increase over the baseline SPEEK membrane's 0.14 S cm−1. Simultaneously, the tensile strength at normal room temperature is 39.7 MPa, exhibiting an improvement of 86% compared to the initial value of 21.3 MPa. Additionally, the swelling ratio is lowered by 18.69%. Compared with the baseline membrane, the DBAF-enhanced SPEEK composite membrane exhibits superior mechanical stability and proton conductivity within a moderate temperature range (30–80 °C). Consequently, this work offers valuable insights for the development of novel proton-conductive materials.

High-powered superhydrophobic pyroelectric generator via droplet impact

Recent studies on water-based pyroelectric generators (PEGs), which convert thermal energy to electrical energy, have focused on different operational modes like water evaporation, water stream, and droplet sliding. However, the development of sustainable, high-powered generators and comprehensive theoretical models has been limited. In response, our research introduces a droplet-based superhydrophobic pyroelectric generator (S-DPEG), exploiting the characteristics of lead magnesium niobate-lead titanate (PMN-0.3PT) coated with titanium dioxide nanoparticles. We analyzed power density by considering the phase transient temperature that maximizes the pyroelectric coefficient of PMN-0.3PT, testing various Weber numbers and droplet diameters within a moderate operating temperature range of 40°C to 80°C. Considering the dynamic characteristics of water droplet on superhydrophobic surfaces, we suggest a peak current model that can accurately predict the peak current within ∼15% of error. Also, the maximum power density of 54.5 μW/cm2 at a droplet diameter of 3.6 mm and a temperature of 80°C, a noteworthy improvement over 3 times higher than previous water-based PEGs. Our results enhance the understanding of the pyroelectric effect coupled with drop impact dynamics and outline novel strategies for designing high-performance water-based PEGs.

Hydrochar Derived from Sewage Sludge and Water Hyacinth and Its Characterization

Population and urbanization increase the sewage generation. Sewage treatment plant (STP) generates the sewage sludge. Agricultural runoff and sewage water discharge into water bodies proliferates the growth of water hyacinth and creates environmental issues. Managing the sewage sludge and water hyacinth are difficult task because of high water content, environmental concerns, regulatory measures and high operational cost. Hydrothermal carbonization (HTC) converts the wet biomass into condensed solid product called hydrochar at moderate temperature range of 180 – 250°C under auto generated pressure. Through HTC process, the sewage sludge and water hyacinth were mixed and converted into hydrochar @ temperature of 200℃ and 4h resident time with L/S ratio of 9:1. The produced hydrochar showed desired functional groups viz., CH – methyl groups, C-O-C – alcohol groups, esters, ethers and Oxygenic functional groups (-C=O, -OH, -CO-O, C-O-C) with particle size of 494.8 nm, BET surface area of 369.70 m2 g-1, Zeta Potential of -27.9 mV. The hydrochar recorded slightly acidic pH (5.8) with appreciable levels of C (24.4%), N (2.51%), P (0.44%), K (0.98%), Ca (1.24%), Mg (0.68%). These properties of sewage sludge and water hyacinth derived hydrochar exhibits its potential use in agricultural and environmental applications.

Transmission Mechanism and Logical Operation of Graphene-Doped Poly(vinyl alcohol) Composite-Based Memristor.

Memristors are considered the best candidates for nonvolatile memory and advanced computing technologies, and polymer and two-dimensional (2D) materials have been developed as functional layer materials in memristors with high-performance resistive switching characteristics. In this work, a polymer memristor with a graphene (Gr)-doped poly(vinyl alcohol) (PVA) composite acting as the functional layer was prepared. The memristor device exhibited superior performance with good retention and a comparatively large ON/OFF ratio at room temperature. Additionally, excellent logic operations were achieved. These satisfactory properties can be attributed to trap-induced carrier trapping and detrapping. In addition, the device exhibited stable bipolar resistive switching behavior over a moderate temperature range. This work provides insight into the transmission mechanism of polymer-based memristors and the reasons why they become unstable at high temperatures, demonstrating the potential applications of PVA-Gr-based polymer memristors as logic circuit units in integrated chips and artificial intelligence.

Metal-Al layered double hydroxides synthesized from aluminum slags as efficient CO2 adsorbents at pre- and post-combustion temperature

Layered double hydroxides (LDH) have been proposed as the materials that offer the best performance in the moderate-temperature range, between 200 and 450 °C, for CO2 adsorption, so the effect of some synthesis parameters and surface modification on their adsorption capacities is herein investigated. This work reports the use of M2+ (Co, Mg, Ni and Zn)/Al layered double hydroxides synthesized with a 3:1 molar ratio by the co-precipitation method and using aluminum extracted from saline slags as source of this metal as CO2 adsorbents. The synthesis and use of Zn/TiAl is also reported considering several proportions of Al-Ti. Structural characterization and comparison of the series has been achieved using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen physisorption at 196 °C and thermogravimetry measurements (TGA). The performance of calcined LDH as CO2 adsorbents was evaluated in the 50 – 400 °C temperature range and 80 kPa and results show that Ni6Al2 and Mg6Al2 samples present a significant adsorption capacity at low temperature (0.382 and 0.292 mmolCO2/g, respectively). At 400 °C only Mg6Al2 maintains its high adsorption capacity (0.275 mmolCO2/g) compared to the other calcined LDH. Its adsorption capacity at moderate-temperature range was proven to be better than that of a commercial Mg6Al2 sample. In all materials the CO2 adsorption capacity at 200–450 °C increased by incorporating potassium (K2CO3 and KOH as sources) up to 0.58 mmolCO2/g for Mg6Al2 +K2CO3. The addition of the amine TEPA in the low-temperature range worked for Co6Al2 and Mg6Al2 (increment > 40 %). In the case of Zn6Al2, the partial substitution of Al by Ti also increased the CO2 adsorption capacity from 0.177 to 0.244 mmolCO2/g, finding isosteric heats between 17.07 and 23.30 kJ/mol using the Clausius-Clapeyron equation.

Significance of temperature as a key driver in ZVI PRB applications for PCE degradation

We report on the potential of elevated groundwater temperatures and zero-valent iron permeable reactive barriers (ZVI PRBs), for example, through a combination with underground thermal energy storage (UTES), to achieve enhanced remediation of chlorinated hydrocarbon (CHC) contaminated groundwater. Building on earlier findings concerning deionized solutions, we created a database for mineralized groundwater based on temperature dependence of tetrachloroethylene (PCE) degradation using two popular ZVIs (i.e., Gotthart–Maier cast iron [GM] and ISPAT sponge iron [IS]) in column experiments at 25 °C–70 °C to establish a temperature-dependent ZVI PRB dimensioning approach. Scenario analysis revealed that a heated ZVI PRB system in a moderate temperature range up to 40 °C showed the greatest efficiency, with potential material savings of ~55% to 75%, compared to 10 °C, considering manageability and longevity. With a 25 °C–70 °C temperature increase, rate coefficients of PCE degradation increased from 0.4 ± 0.0 h−1 to 2.9 ± 2.2 h−1 (GM) and 0.1 ± 0.1 h−1 to 1.8 ± 0.0 h−1 (IS), while TCE rate coefficients increased from 0.6 ± 0.1 h−1 to 5.1 ± 3.9 h−1 at GM. Activation energies for PCE degradation yielded 32 kJ mol−1 (GM) and 56 kJ mol−1 (IS). Temperature-dependent anaerobic iron corrosion was key in regulating mineral precipitation and passivation of the iron surface as well as porosity reduction due to gas production.

Severe ethanol stress inhibits yeast proteasome activity at moderate temperatures but not at low temperatures.

Since yeast research under laboratory conditions is usually conducted at 25-30°C (moderate temperature range), most of the findings on yeast physiology are based on analyses in this temperature range. Due to inefficiencies in cultivation and analysis, insufficient information is available on yeast physiology in the low-temperature range, although alcoholic beverage production is often conducted at relatively low temperatures (around 15°C). Recently, we reported that severe ethanol stress (10% v/v) inhibits proteasomal proteolysis in yeast cells under laboratory conditions at 28°C. In this study, proteasomal proteolysis at a low temperature (15°C) was evaluated using cycloheximide chase analysis of a short-lived protein (Gic2-3HA), an auxin-inducible degron system (Paf1-AID*-6FLAG), and Spe1-3HA, which is degraded ubiquitin-independently by the proteasome. At 15°C, proteasomal proteolysis was not inhibited under severe ethanol stress, and sufficient proteasomal activity was maintained. These results provide novel insights into the effects of low temperature and ethanol on yeast physiology.

Temperature Dependences of IR Spectral Bands of Humic Substances of Silicate-Based Soils

Temperature-dependent IR spectroscopy capable of revealing specific changes in the band intensities, positions, and shape was used to increase the information on humic substances (HS) from soils. Temperature dependences of IR spectra of HS isolated from silicate-based soils differing in the contents and nature of organic matter, chernozem and soddy podzolic soil, were investigated by attenuated total internal reflection FTIR in the mid-IR region (4000–400 cm−1) in the air within the moderate temperature range of 25–215 °C (298–488 K) with a step of 2.5 °C. The dependences of shifts in frequency (wavenumber) corresponding to band maxima and integrated band intensities were built for all major bands. Observed reversible frequency shifts upon heating and cooling can be interpreted as forming structures in the dry state. The behavior of integrated intensities of bands assigned to C–H and C–C vibrations, characteristic vibrations of polyaromatic compounds, carboxylic acids, and carboxylates were shown, and similar behavior for the same group (symmetric and antisymmetric stretches) were revealed. Differences in the temperature trends in chernozem and soddy podzolic soils due to different structures (aliphatic and aromatic) and functional groups (carboxylic and carboxylate) are shown. The different behavior of the bands corresponding to carboxylic groups and skeletal vibrations differentiates soil types with different organic matter. The temperature trends of band maximum and intensity shifts are less prone to measurement conditions and may serve as qualitative parameters characterizing the composition of soil humic substances.

Optimized global reaction mechanisms for H2, CO, CH4, and their mixtures

Global reaction mechanisms (GRMs) are widely used in combustion engineering. However, it is difficult to find GRMs commonly available for various mixtures of H2, CO, and CH4 (with air), which are likely to be the primary fuels in the future. In this study, a series of GRMs were optimized to follow the results of the five detailed reaction mechanisms (GRI 3.0, USC II, San Diego, FFCM-1, CRECK) for the essential fuels (H2, CO, CH4) and their mixtures (at 300 K and 1 bar). At first, a 1-step GRM of H2+air (R1) and another of CO + air (R2), were optimized to reproduce their respective laminar burning velocities (LBVs). After that, an additional water-gas shift reaction (R3) was suggested to improve the prediction for the H2+CO + air mixture. Similarly, a 1-step GRM (M1) was developed for the fuel-lean mixtures of CH4+air, and a 2-step GRM (R1+M1) was proposed for the fuel-lean mixtures of H2+CH4+air. In the case of the mixture of H2+CO + CH4+air, an additional methane oxidation reaction (M1L) producing H2 and CO was suggested, and a 4-step GRM (R1+R2+R3+M1L) showed reliable results in the fuel-lean conditions. However, to get reliable LBVs over all equivalence ratios, two additional reactions (M2+M3) were proposed to reflect the endothermic reaction. Furthermore, the pre-exponential factor of the methane oxidation reaction (M1R) varied as a function of the hydrogen concentration in the fuel. Conclusively, acceptable LBVs could be obtained for the H2+CO + CH4+air mixtures in a moderate temperature range (300 K–600 K).

Thermo‐Responsive Nanocomposite Bioink with Growth‐Factor Holding and its Application to Bone Regeneration (Small 9/2023)

Thermo-Responsive Nanocomposite Bioinks Poly(organophosphazene)-based thermo-responsive nanocomposite bioink, with tunable mechanical property under a moderate temperature range, exhibits good 3D printing outcomes without additional chemical crosslinking process. The bioink encapsulates growth factors through physical interaction, exhibiting biological activities and therapeutic potential for bone defect repair. More details can be found in article number 2203464 by Soo-Chang Song and co-workers.

Energetic costs of bill heat exchange demonstrate contributions to thermoregulation at high temperatures in toco toucans (Ramphastos toco).

Body temperature regulation under changes in ambient temperature involves adjustments in heat production and heat exchange rates between the animal and the environment. One mechanism involves the modulation of the surface temperature of specific areas of the body through vasomotor adjustment. In homeotherms, this thermoregulatory adjustment is essential for the maintenance of body temperature over a moderate temperature range, known as the thermal neutral zone (TNZ). The bill of the toco toucan (Ramphastos toco) has been described as a highly efficient thermal window and hypothesized to assist in the thermal homeostasis of this bird. Herein, we directly evaluated the contribution of heat exchange through the bill of the toco toucan and role of the bill in the delimitation of the TNZ. To do this, we measured metabolic rate (MR), via oxygen consumption, over a range of ambient temperatures from 0 to 35°C. MR measurements were made in birds with the bill intact and with the bill insulated. The limits of the TNZ did not differ between treatments, ranging from 10.8 to 25.0°C. The MR differed among treatments only at elevated temperatures (30 and 35°C), reaching 0.92±0.11ml O2g-1h-1 (mean±s.d.) for the intact group and 1.13±0.13ml O2g-1h-1 for the insulated group. These results indicate that although heat dissipation through the bill does not contribute significantly to widening of the TNZ, it may well be critically important in assisting body temperature regulation at higher temperatures extending above the upper limit of the TNZ.

Investigation of Effective Thermal Conductivity of Spherical Packed Beds Using In-Line Contacting Three-Dimensional Cubic Unit Cell Model

This paper estimates the effective stagnant thermal conductivity of a spherical packed bed using an experimentally validated modified collocated unit cell model. The study focused on the effect of primary and secondary parameters on effective thermal conductivity. The effects of concentration of the spherical packed bed, thermal conductivity ratio, contact conductance resulting from particle-to-particle contact, and moderate temperature are studied in detail. Analytical expressions are derived for the in-line contacting three-dimensional solid cubic arrays by adopting the unit-cell-based thermal resistance method for determining the effective stagnant thermal conductivity. The effective thermal conductivity of different heterogeneous packed beds with solid-fluid materials possessing conductivity ratio in the range of 1–1000 and concentrations in the range of 0–1 are predicted for various temperatures at constant pressure regimes using the developed model. Furthermore, the developed model is used to estimate the effective stagnant thermal conductivities of packed beds filled with glass and ceramic bead materials, which are compared with values measured using the steady-state square guarded hot plate apparatus over the moderate temperature range of 323–673 K. The values for both uniform-sized glass and ceramic beads are found to be within ±11.26% and ±13.35% of each other.

Thermal performance assessment of the coaxial pipe evacuated tube solar air heater in Bilaspur climatic conditions

The present era finds the implementation of small-scale solar thermal applications to overcome emissions caused by fossil fuels. In this connection, a forced convection co-axial pipe evacuated tube solar air heater is fabricated and examined under various operating parameters and in Bilaspur Chhattisgarh climatic conditions in the months from October 2021 to March 2022. The performance parameters under consideration were outlet air temperature, collector efficiency, exergy efficiency, and overall system efficiency. The experiments have been performed for different mass flow rates 9.36, 15.84, 18.36, 22.32, and 26.28 kg/h of air. The ambient air temperature varied in the range of 20.8 °C to 41.6 °C. The air temperature at the inlet of the heater varies from 28.4 °C to 66.7 °C. The maximum outlet air temperature and temperature rise recorded were 82.9 °C and 37.2 °C in the month of March and February, respectively, for the low mass flow rate of 9.36 kg/h. It was observed that the maximum collector efficiency, exergy efficiency, and overall system efficiency were achieved as 82.95%, 6.4%, and 81.92%, respectively, for a moderate mass flow rate of 15.84 kg/h. All the performance parameters seem to be strongly dependent on the solar intensity and were found to be highest when the intensity was at its peak value. It is found that the increase in mass flow rates beyond 15.84 kg/h tends to decrease the temperature rise as well as the efficiency of the solar heater. No significant temperature rise is observed for a mass flow rate beyond 26.28 kg/h. The study finds that the fabricated setup can effectively produce a low to moderate temperature range (40 °C–80 °C) and can be used for domestic as well as small-scale industrial applications.

Evaluation of Energy Performances of Solar Dryers

In solar drying, the moisture content of a product is reduced through the use of sunlight. Solar drying is practiced since civilization for the drying of crops. The dried crop has a longer shelf life and requires less storage space. For crop drying, hot air is required in the moderate temperature range of 40 to 75℃. Solar dryer makes it possible to obtain better product quality. Over the past 20 years, numerous experimental projects have been carried out in the field of solar dryers. Most conventional dryers are not able to operate continuously during the off sunshine time. However, attempts were made to develop uninterrupted solar drying systems by incorporating an energy storage facility and a hybrid mode of operation. Sensible and latent heat storage methods are widely used to store solar energy. Heat storage materials store energy in the form of heat during sunshine and release it whenever it is required. Biogas backup, Chemical heat pump, Photo Voltaic, and Fluidized bed methods were integrated with solar dryers for uninterrupted operation. In this article, the discussion is made about different dryers. Also, the challenges and scope in the area of the solar dryer are highlighted.

Hydro-mechanical behavior of heated bentonite buffer for geologic disposal of high-level radioactive waste: A bench-scale X-ray computed tomography investigation

The behavior of heated bentonite buffer is critical for the security and long-term performance of a geological repository for high-level radioactive waste (HLW). While laboratory column experiments have been conducted to investigate compacted bentonite and coupled THMC (thermal-hydro-mechanical and chemical) processes for a moderate temperature range of up to 100 °C, data for a higher temperature range are limited. Understanding bentonite behavior and coupled THMC processes under higher temperatures (e.g., up to 200 °C) could allow for a more economic repository design and would expand the data and knowledge base for more reliable modeling. In this study, a bench-scale experiment was conducted in a compacted bentonite column experiencing both heating up to 200 °C in the center and hydration from a sand-clay boundary surrounding the column. During the experiment run for 1.5 years, frequent X-ray computed tomography (CT) scanning of bentonite provided insights into the spatiotemporal evolution of (1) hydration/dehydration, (2) clay swelling/shrinkage, (3) displacement, and (4) mineral precipitation. After the experiment, a comprehensive post-dismantling characterization of bentonite samples was conducted. Results showed that the bentonite hydration was axi-symmetrical despite the initial heterogeneity due to packing, confirming the ability of bentonite to seal fast flow/transport paths. Compared to a non-heated control experiment, the heated column showed greater CT density variations along the radial distance, indicating that homogenization of bentonite might be more difficult if a temperature gradient is maintained in the repository. Precipitation of an anhydrite layer occurred in the inner hot zone, pointing to potential concerns about salt precipitation causing canister corrosion. Ultimately, the experiments provided a high-resolution window into the strongly dynamic and coupled behavior of bentonite exposed to heating, hydration and swelling, which will be valuable for improving modeling of coupled processes, especially for the early state of a HLW repository.

Thermo-Responsive Nanocomposite Bioink with Growth-Factor Holding and its Application to Bone Regeneration.

Three-dimensional (3D) bioprinting, which is being increasingly used in tissue engineering, requires bioinks with tunable mechanical properties, biological activities, and mechanical strength for in vivo implantation. Herein, a growth-factor-holding poly(organophosphazene)-based thermo-responsive nanocomposite (TNC) bioink system is developed. The mechanical properties of the TNC bioink are easily controlled within a moderate temperature range (5-37°C). During printing, the mechanical properties of the TNC bioink, which determine the 3D printing resolution, can be tuned by varying the temperature (15-30°C). After printing, TNC bioink scaffolds exhibit maximum stiffness at 37°C. Additionally, because of its shear-thinning and self-healing properties, TNC bioinks can be extruded smoothly, demonstrating good printing outcomes. TNC bioink loaded with bone morphogenetic protein-2(BMP-2) and transforming growth factor-beta1 (TGF-β1), key growth factors for osteogenesis, is used to print a scaffold that can stimulate biological activity. A biological scaffold printed using TNC bioink loaded with both growth factors and implanted on a rat calvarial defect model reveals significantly improved bone regenerative effects. The TNC bioink system is a promising next-generation bioink platform because its mechanical properties can be tuned easily for high-resolution 3D bioprinting with long-term stability and its growth-factor holding capability has strong clinical applicability.

High-Efficiency Power Cycles for Particle-Based Concentrating Solar Power Plants: Thermodynamic Optimization and Critical Comparison

This paper investigates and compares several highly efficient thermodynamic cycles that are suitable for coupling with particle-in-tube fluidized-bed solar receiver technology. In such a receiver, high-temperature particles are used as both a heat transfer fluid and a storage medium. A dense particle suspension (DPS) is created through an upward bubbling fluidized-bed (UBFB) flow inside the receiver tubes, which constitutes the “particle-in-tube” solar receiver concept. Reaching higher temperatures is seen as a key factor for future cost reductions in the solar plant, as this leads to both higher power conversion efficiency and increased energy storage density. Three advanced thermodynamic cycles are analyzed in this work: the supercritical steam Rankine cycle (s-steam), supercritical carbon dioxide cycle (s-CO2) and integrated solar combined cycle (ISCC). For each one, 100% solar contribution, which is considered the total thermal input to the power cycle, can be satisfied by the solar particle receiver. The main findings show that the s-CO2 cycle is the most suitable thermodynamic cycle for the DPS solar plant, exhibiting a net cycle efficiency above 50% for a moderate temperature range (680–730 °C). For the other advanced power cycles, 45.35% net efficiency can be achieved for the s-steam case, while the efficiency of the ISCC configuration is limited to 45.23% for the solar-only operation mode.

Ultralight Nafion/Ag composite microfiber film actuator driven by low voltage

Electrothermal actuators (ETAs) have received great attention among soft actuators due to their simple structure and light weight. Since most of the application scenarios of ETAs are on soft robots, the current research on ETAs mainly focuses on the improvement of their max deformation. In fact, important application prospects of soft actuators lie in biological and medical aspects, such as smart wearable devices. This remind us to consider the issues of safety and comfort, which have been neglected for a long time. In this work, we report an ultralight, porous Nafion/Ag composite microfiber film actuator prepared by blow-spinning. Unlike most ETAs, it has porous fibrous structure and can achieve considerable deformation in a safe temperature range for the organisms (30 °C–67 °C). The film actuator, with a low density (about 0.45 g cm−3), can bend in a short time (within 15 s) to an angle of about 91° and achieve a displacement of 11.2 mm when applied a low voltage (2.4 V). Owing to the processing method of blow-spinning, the film actuator presents a series of excellent characteristics, including softness, light weight and porosity, etc. To summarize, the Nafion/Ag composite microfiber film actuator shows great potential in soft robots and smart wearable devices due to their properties of low driven voltage, low weight and moderate working temperature range.

Mechanical and microstructural properties of alkali-activated fly ash-slag material under sustained moderate temperature effect

Alkali-activated materials are difficult to maintain strength under very high temperatures in the fire. But results are not available for those materials when subjected to sustained moderate temperature range (i.e. 60 °C–250 °C) which is a more common thermal condition in many engineering applications. In this paper, the mechanical and microscopic properties of alkali-activated fly ash-slag (AAFS) materials under sustained moderate temperature effects are studied. The microscopic properties are characterized by XRD, FT-IR, 29Si NMR-MAS, MIP and SEM-EDS. The results show that AAFS is able to maintain the compressive strength even being treated under 250 °C for 28d. The microscopic characterizations indicate that N-A-S-H gel exhibits greater thermal stability than C-A-S-H and C-S-H gels. However, after the gel loses water under sustained temperature effect, N-A-S-H is hard to reorganize. In other words, when more N-A-S-H is produced due to the addition of more slag, the AAFS becomes more porous with looser microscopic morphology leading to lower compressive strength. It is also found that, after sustained moderate temperature treatment, the gel reorganizes and agglomerates into cluster-like particles, while the matrix becomes more uniform and compact. The sustained temperature helps refine the pore size and improve the volume of connected pores and super-macropores which is helpful to maintain the compressive strength of AASF. This study provides experimental and theoretical basis for the application of alkali-activated materials subjected to sustained moderate temperature effects.