Metal Field Research Articles

Self-healing carbon fiber/epoxy laminates with particulate interlayers of a low-melting-point alloy

In order to prolong the service life of fiber-reinforced polymer composites, the implementation of self-healing ability with the micro-encapsulated healing agent has been extensively studied. However, such microcapsule-based self-healing composites typically suffer from degraded mechanical properties due to the liquid-phase inclusions, thereby limiting their proliferation. Here, a low-melting-point alloy is utilized as the particulate inclusions of carbon fiber/epoxy laminated composites. Field's Metal particles (melting point: 62 °C) are distributed between woven carbon fiber preforms followed by the resin impregnation to realize laminated composites with a Field's Metal-enhanced interlayer(s). The resulting laminated composites demonstrate the autonomic repair of interlaminar failure with a 40 % of healing efficiency. Most of all, the mechanical properties of these self-healing laminated composites are comparable to the conventional laminated composites attributed to the rigid inclusions that can be compressed to increase the fiber volume. Since the Field's Metal particle inclusions can bestow polymer composites with self-healing ability and the potential increase in mechanical properties, Field's Metal-enhanced fiber-reinforced polymer composites are expected to unlock the practical utility of self-healing composites.

Photovoltaic enhancement in OSCs based on PM6:Y7 when doping the active layer with Ag2S nanoparticles

Herein, silver sulfide (Ag2S) nanoparticles (NPs) with an average size of 31 nm ± 4 nm were synthesized using a simple, economic, and eco-friendly method assisted by ultrasonic bathing; the reaction was carried out in a non-polluting aqueous medium. These Ag2S NPs were suspended in ethanol and used to dope the active layer of Organic Solar Cells (OSCs) based on PM6 (donor) and Y7 (acceptor) by adding 2 v/v % of a suspension to the PM6:Y7 solution in chlorobenzene (CB). The entire fabrication process and testing was carried out under normal atmospheric conditions. Field's metal (FM) was used as the top electrode of the OSCs, which is a eutectic alloy of bismuth, indium, and tin (Bi 32.5 %, In 51 %, and Sn 16.5 %) with a melting point above 62 °C deposited by free evaporation techniques. The average Power Conversion Efficiency (PCE) for the reference and doped OSCs were 9.19 % (9.43 % the best) and 10.31 % (10.77 % the best), respectively; representing an increase of more than 14 % in the PCE value when Ag2S NPs are added to the active layer. It can be attributed to different optical phenomena, among which could be the enhance in the internal light reflection processes (scattering) and the Local Surface Plasmon Resonance (LSPR) effect.

Thermal response to periodic heating of a heat sink incorporating a phase change material

Phase change materials (PCMs) can effectively dampen temperature fluctuations due to their high latent heat capacity, leading to decreased average cooling requirements in various engineering applications. However, there are few design guidelines for PCM-based heat sinks and there is limited experimental research on their performance in high heat flux, periodic heating conditions. In this work, we present a 0-D and 1-D nondimensional analytic model for PCM-based heat sinks subject to sinusoidal heating. We formally define the four possible responses of PCM-based heat sinks and derive expressions to predict their effectiveness. We test experimentally two PCM-based heat sinks to validate these expressions – an air-cooled system and a water-cooled system. The operating PCM is Field's metal (32.5-Bi, 51-In, 16.5-Sn), a eutectic alloy with a melting temperature of 60 °C. Thermocouples are embedded in the system to measure the evolution of the system's temperature over time. We apply a sinusoidal heat input and study the parametric response of these heat sinks under a wide range of heat flux amplitudes (1-100 W/cm2) and periods (5–640 s), while also varying the external heat transfer coefficient (1,700-18,700 W/m2K), ambient temperature (20–45 °C), and thickness of PCM (1–4.4 mm) to comprehensively validate these proposed models. The experimental results are plotted in phase space and show good agreement with the analytic predictions.

Effect of doping the PM6:Y7 active layer with MoS2 nanospheres in organic solar cells

Herein, MoS2 nanostructures were synthetized and characterized, as well as PM6:Y7 based organic solar cells (OSCs) were fabricated, tested, and modelled through SCAPS-1D software. Devices were assembled and tested under regular atmosphere conditions including the top electrode Field's Metal (FM), which is a eutectic alloy of Bi, In and Sn easily deposited by melting it at ∼ 95 °C. The modelled binary OSCs through SCAPS-1D achieved a PCE of 14.2%. The active layer was doped with MoS2 nanoparticles at two different concentrations, 1 and 2% v/v, the reached experimental average PCE values were 9.1%, 10.2% and 9.3% for control devices, and for the two doping concentrations, respectively; it means a PCE percentage enhancement of 11.2% when doping at 1% of MoS2. The enhanced experimental PCE value could be partially explained because of the light absorption into the active layer through the localized surface plasmonic resonance (LSPR) phenomenon induced by the nanostructures, among other optical phenomena such as light reflection and interference effects.

Hydration behavior and microstructure of cement-based materials modified by Field’s metal particles

The hydration of cement-based materials, especially at early ages, directly affects the development of matrix strength and the later durability. In this paper, in order to explore the hydration behavior and microstructure of cement-based composites modified by low melting point Field's Metal Particles (FMP), inverted cone method, standard Vicatometer method, isothermal calorimetry, and compressive strength test, TGA, SEM, and XRD are used to investigate the fresh properties, heat of hydration, matrix strength, hydration products and transition zone between FMP and cement matrix. The results show that the incorporation of FMP can improve the fluidity of cementitious composites by 31.6%, due to the hydrophilicity of FMP. Meanwhile, due to the small heat capacity and large thermal conductivity of low-melting FMP, the heat stored in FMP is naturally released and used to promote hydration reaction when the hydration rate slows down. Additionally, FMP does not affect the types of hydration products in cement-based composites, but the total amount of hydration products increased at 7 d, especially calcium hydroxide (CH). Unexpectedly, FMP can reduce the compressive strength of the hardened paste, due to the large particle size of FMP than cement particles and the presence of directionally growing CH crystals in the interface transition zone between FMP and cement matrix.

Anti-leakage and recyclable phase change thermal conductive films with ultralow thermal impedance enabled by Field’s metal via the generation and internalization of metal oxides

The heat dissipation performance of a thermal interface material (TIM) is greatly dependent on its total thermal impedance, which can be effectively reduced by introducing a solid–liquid phase change material (PCM). However, previously reported phase change TIMs (PCTIMs) have been developed only based on organic PCMs with low thermal conductivities; thus, they cannot achieve low thermal impedance. Herein, Field’s metal (FM), which is a metal phase change material with a melting point of approximately 60 ℃, is first employed to develop a novel PCTIM with an ultralow thermal impedance. Trace oxidation is conducted on FM, and Bi2O3 and SnO are thus generated, followed by forming nanoscale particles by internalization. The formation of the nanoscale metal oxides increases the surface free energy and interfacial interaction force, thereby increasing the viscosity and improving the film-forming ability of the oxidized FM. The phase change thermal conductive films with different thicknesses, which are fabricated from the optimal oxidized FM, exhibit little liquid leakage, even at a pressure of 200 psi, and reach an ultralow thermal impedance of 0.03 cm2·K·W−1 at a thickness of 100 μm after the solid–liquid phase change, which is lower than those of the previously reported PCTIMs. The optimal film possesses good thermal reliability and recyclability, and shows a significantly better cooling effect than a commercial PCTIM with an identical thickness. These ideal characteristics make the FM-based phase change thermal conductive films up-and-coming in practical applications.

Beneath the Skin: Nanostructure in the Sub‐Oxide Region of Liquid Metal Nanodroplets

AbstractLiquid metals (LMs) are emerging as unique fluids for a variety of applications, but their nanoscale solvation properties remain largely understudied. In this work, a combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations are used to investigate the structure of the interface between the bulk room temperature liquid metal (RTLM) and the LM oxide in nanodroplet systems of gallium, EGaIn (75.5% gallium, 24.5% indium), and Galinstan (68.5% gallium, 21.5% indium, 10% tin). Field's metal (51% indium, 32.5% bismuth, 16.5% tin) is also investigated, which melts at ≈62 °C, as a contrast to the other systems. AFM measurements reveal distinct sub‐oxide nanostructured layering in all three RTLM systems, and Field's metal above the melting point, to differing degrees. EGaIn and Galinstan show multiple penetration events between 20 and 30 nm, with smaller, less complex events in Ga. MD simulations suggest that this layering is a result of the near‐surface ordering of LM atoms beneath the oxide layer. Importantly, the atoms in this region do not behave as solids but are more ordered than in a pure disordered liquid system. The surface nanostructure elucidated here significantly expands the understanding of LM systems and their behavior at interfaces.

3D‐Architected low melting point alloys foam microstructure‐reinforced polymer composite with superior stiffness‐switchable for soft actuator

AbstractStiffness variable materials have aroused extensive research interest in smart devices, especially in soft actuators. However, achieving materials with high stiffness switch range remains challenging. Here, a novel three‐dimensional (3D) lightweight Field's metal (FM) foam was developed. Meanwhile, the polymer composite (SUFF) with superior stiffness switchable capacity was fabricated by embedding FM foam into a kind of designed stiffness variable polymer. The SUFF shows outstanding conductivity under relatively low FM volume fraction of 20.6%. Impressively, because of the extremely high modulus and fast transition of FM foam, the stiffness switch ratio of the SUFF are able to reach an ultra‐high value of 6987.5‐folds. Apart from its exceptional stiffness switchable capacity, the SUFF also possesses remarkable shape memory and self‐healing characteristics. Next, the SUFF was then fastened to a soft actuator as the stiffness changing units. The obtained actuator was able to exhibit a short heating–cooling cycle time of 44 s while using 10 A of current and 4°C water for cooling. Moreover, the actuator can reach remarkable values of 973 mN/mm and 4729 mN, respectively, for its stiffness and net force. Then, a soft robot gripper made up of three obtained actuators mounted on a base demonstrates its excellent load and stiffness switchable ability. It can lift a variety of objects with various forms with weights up to more than 3 kg. This study might provide a reference for application of stiffness variable materials in soft actuators.Highlights The FM foam were designed and synthetized by lost‐wax casting method. The polymer composite exhibits large stiffness switching range. The polymer composite achieves 6987.5‐folds rigid/soft stiffness ratio. A 3D‐printing soft actuator was fabricated using obtained polymer composite. The assembled robotic gripper can lift weights up to more than 3 kg.

Silver Nanoparticle-PEDOT:PSS Composites as Water-Processable Anodes: Correlation between the Synthetic Parameters and the Optical/Morphological Properties.

The morphological, spectroscopic and rheological properties of silver nanoparticles (AgNPs) synthesized in situ within commercial PEDOT:PSS formulations, labeled PP@NPs, were systematically investigated by varying different synthetic parameters (NaBH4/AgNO3 molar ratio, PEDOT:PSS formulation and silver and PEDOT:PSS concentration in the reaction medium), revealing that only the reagent ratio affected the properties of the resulting nanoparticles. Combining the results obtained from the field-emission scanning electron microscopy analysis and UV-Vis characterization, it could be assumed that PP@NPs' stabilization occurs by means of PSS chains, preferably outside of the PEDOT:PSS domains with low silver content. Conversely, with high silver content, the particles also formed in PEDOT-rich domains with the consequent perturbation of the polaron absorption features of the conjugated polymer. Atomic force microscopy was used to characterize the films deposited on glass from the particle-containing PEDOT:PSS suspensions. The film with an optimized morphology, obtained from the suspension sample characterized by the lowest silver and NaBH4 content, was used to fabricate a very initial prototype of a water-processable anode in a solar cell prepared with an active layer constituted by the benchmark blend poly(3-hexylthiophene) and [6,6]-Phenyl C61 butyric acid methyl ester (PC60BM) and a low-temperature, not-evaporated cathode (Field's metal).

Determination of the Corrosion–Oxidation Turning Point at the Field’s Metal/Chromium Interface by Electrical Contact Resistance Measurement

The correlation of the electrical contact resistance measurement and microanalysis of the Field’s metal (FM)/Cr interface was used to determine the temperature-dependent reactions at the interface. Oxidation of Cr by oxygen contained in FM was identified through a sharp increase of the contact resistance around a certain temperature, above which the following resistance decrease was associated to a corrosion process. The corrosion–oxidation turning point was observed around 390 ± 1.7 °C. Cr saturation in FM combined with complete consumption of the oxygen contained in the FM induced a stabilization of the interface giving a specific contact resistance of about 30 µΩ·cm2.

Low melting point alloy modified polymer composite with sharp stiffness switch for soft actuator

Materials possessing switchable stiffness, particularly dynamically switchable stiffness, have generated a lot of attention in the soft actuator. Herein, we proposed a facial poly (vinyl alcohol) (PVA) coating method to fabricate the micron-sized Field's metal (FM) phase-changing particles with an average particle size of about 1.2 μm, and obtained a series of stiffness variable polymer composites via incorporating FM particles into the designed stiffness variable polymer matrix. Owing to the rapid solid-liquid change and ultra-high modulus of FM, the rigid/soft stiffness ratio of the composites improved to 1442-folds. Moreover, the shape fixity (Rf) and shape recovery ratio (Rr) values of the shape memory properties could reach up to ultra-high values of 99.4% and 99.6%, respectively. Subsequently, the prepared composites were selected and used a 3D printing soft actuator as the stiffness variable units. The soft actuator exhibits short heating-cooling time of 36s under 1.2A current and with 4 °C water as the coolant, and it is able to lift a 200 g weight at the rigid state. Furthermore, the stiffness of obtained actuator can achieve high value 779 mN/mm. The results indicate that the obtained soft actuator possesses excellent actuate behavior and stiffness switchable ability. This work might provide faster and more rigid variable stiffness materials for soft actuators application in the real world.

Strain-rate sensitivity of cement composites: Insights from field's metal nano-inclusions

In this study, we investigated the effects of Field's metal (FM) nanoparticles (NPs) on the mechanical behaviour of cement paste under quasi-static (QS) and dynamic strain rates. We found the highest mechanical improvement under QS loading with 1 % FM dosage, beyond which boosting the dosage diminished its contribution to the mechanical performance. Conversely, under dynamic loadings, boosting the dosage from 1 % to 4 % FM significantly and progressively enhanced the overall mechanical performance. These results indicated that the mechanical impacts that ensue from the microstructural modification effects of FM differ with dosage and strain rates. Under QS loading, the pore-refining effect of the NPs was predominant, whereas, under dynamic loadings, the reinforcing effect of the NPs was the primary factor. Furthermore, by comparing the effects of FM and nanosilica NPs, our findings underscored the pronounced effect of the nanomaterial physical and mechanical properties on the strain-rate sensitivity of cementitious nanocomposites.

Robust cement composite with low hydration temperature and high mechanical performance achieved by Field's metal and acrylic acid-acrylamide copolymer

Concrete as an artificial stone owns the weakness of high brittleness and poor flexural strength, dramatically restricting its potential. Therefore, it is crucial to reduce the brittleness and increase the flexural strength of concrete to prolong its service life. Herein, we developed a cement composite with low hydration temperature and high mechanical strength (especially in flexural strength) by combining Field’s metal with in situ polymerization of acrylic acid (AA) and acrylamide (AM). A cement composite with compressive and flexural strength increased by 8.2% and 174.2% was achieved by tuning the dosage of Field's metal and AA-AM copolymer. The hydration temperature was significantly reduced with the assistance of Field’s metal and AA-AM copolymer, inhibiting the formation of the thermal crack. In situ polymerization of AA and AM monomers was responsible for improving the intrinsic toughness of cement hydrates by constructing a polymer-cement network, significantly enhancing flexural strength. The in situ polymerized AA-AM copolymer acted as a bridge between Field’s metal and the cement matrix, improving their interface and contributing to the increased mechanical strength. The filling effect of Field’s metal and AA-AM copolymer refined the pore structure of the composite as well. Overall, our findings may offer a promising strategy for developing more robust, resilient, and sustainable cementitious materials.

Experimental and parametric numerical investigation of finned heat sinks with organic and metallic phase-change materials

The use of phase change materials (PCMs) has gained much attention for applications of transient thermal management of electronic systems due to their high latent heat and ability to absorb heat near-isothermally. Because of their low thermal conductivity, PCMs are usually integrated with heat sinks to be used more efficiently. In this study a PCM-based heat sink with a generic structure of plate fins was investigated experimentally and numerically. The intentionally simple fin topology allowed focusing on the effects of various material properties rather than the commonly investigated geometry effects. Hence, two types of heat sink material, copper and aluminum, were examined, and two PCMs with similar melting temperatures but distinctly different thermal properties – a metallic alloy (Field's metal) and an organic paraffin (n-Octacosane), were used. Experimental findings allowed for validation of the numerical approach, used for a comprehensive parametric numerical study. The latter facilitated a more detailed investigation of the transient heat transfer processes, such as melting patterns and heat accumulation analyses, where the superior thermal properties of the metallic PCM manifested in more efficient latent heat accumulation, resulting in reduced system peak temperatures. It was found that systems with Field's metal were able to accommodate up to 80% of the energy in the form of latent heat, which is 10 percentage points higher than achieved using the organic paraffin. A dimensional analysis accounting for power inputs and material properties was conducted, and a generalized behavior was achieved for a normalized time in terms of Fourier and Stefan numbers, and thermal diffusivities ratio.

Blade Coating of Alloy as Top Electrodes for Efficient All‐Printed Organic Photovoltaics

AbstractAll printing of organic photovoltaics (OPVs) including the top electrode is highly desirable for achieving cost‐effective, high‐throughput, and large‐area photovoltaic manufacturing. Here, the printing of a low‐melting‐point alloy as top electrodes in OPVs via blade coating is investigated. The Field's metal (FM) with the melting point of 62 °C is adopted for the top electrodes, because FM can be printed under moderate temperatures without harming the active layers while remaining solid state under solar irradiation. The correlations between the processing parameters and properties of the blade‐coated electrodes are elucidated. OPVs based on the D18:Y6 active layer and blade‐coated FM electrodes achieve a highest power conversion efficiency of 17.28%. The OPVs with FM‐electrode demonstrate much higher thermal stability than that of the Ag‐electrode devices. All‐printed OPVs, in which the FM electrode is blade coated and the other layers are prepared by flexible micro‐comb printing, exhibit an efficiency of 16.07%. The results represent the records of evaporation‐free and all‐printed OPVs, demonstrating that printing FM as OPV electrodes is a cost‐effective and time‐saving strategy to substitute the vacuum‐evaporated metals, as well as a feasible route toward high‐performance all‐printed OPVs.

Self-Reconfigurable Soft-Rigid Mobile Agent With Variable Stiffness and Adaptive Morphology

In this letter, we propose a novel design of a hybrid mobile robot with controllable stiffness and deformable shape. Compared to conventional mobile agents, our system can switch between rigid and compliant phases by solidifying or melting Field's metal in its structure and, thus, alter the shape through the motion of its active components. In the soft state, the robot's main body can bend into circular arcs, which enables it to conform to surrounding curved objects. This variable geometry of the robot creates new motion modes which cannot be described by standard (i.e., fixed geometry) models. To this end, we develop a unified mathematical model that captures the differential kinematics of both rigid and soft states. An optimised control strategy is further proposed to select the most appropriate phase states and motion modes needed to reach a target pose-shape configuration. The performance of our new method is validated with numerical simulations and experiments conducted on a prototype system.

Printing of Low‐Melting‐Point Alloy as Top Electrode for Organic Solar Cells

AbstractThe top electrodes of organic solar cells (OSCs) are usually deposited by thermal evaporation in vacuum, which has become the major obstacle toward fully‐printed OSCs. The vacuum‐free printed top electrodes are highly desirable for the continuous production of OSCs. Here, the printing of low‐melting‐point alloy (LMPA) as cathodes in OSCs based on the D18:Y6 system is investigated. The Field's metal (FM) is focused with a melting point of 62 °C, which could be printed under moderate temperatures that are harmless to the active layers and solidifies at room temperature. More importantly, FM will not melt by solar radiation under practical scenarios. Direct ink writing is used to print the FM cathodes. Two printing modes are identified: the dragging mode in the far field to obtain rod electrodes, and the shearing mode in the near field to achieve relatively flat lamellas. The correlations between processing parameters and properties of the printed electrodes are elucidated. OSCs with printed FM cathodes exhibit the highest power conversion efficiency of 16.44%. The results demonstrate that this facile and robust direct LMPA writing technique is promising for high‐performance fully‐printed OSCs.

A Liquid Metal Encapsulation for Analyzing Porous Nanomaterials by Atom Probe Tomography

Abstract Analyzing porous (nano)materials via atom probe tomography has been notoriously difficult. Voids and pores act as concentrators of the electrostatic pressure, which results in premature specimen failure, and the electrostatic field distribution near voids leads to aberrations that are difficult to predict. In this study, we propose a new encapsulating method for porous samples using a low melting point Bi–In–Sn alloy, known as Field's metal. As a model material, we used porous iron made by direct-hydrogen reduction of single-crystalline wüstite. The complete encapsulation was performed using in situ heating on the stage of a scanning electron microscope. No visible corrosion nor dissolution of the sample occurred. Subsequently, specimens were shaped by focused ion-beam milling under cryogenic conditions at −190°C. The proposed approach is versatile and can be applied to provide good quality atom probe datasets from micro/nanoporous materials.

Thermophysical Characteristics of Liquid Metal In-Bi-Sn Eutectic (Field's Metal) as a Similarity Coolant

Abstract This work investigated the thermophysical characteristics of liquid indium–bismuth–tin eutectic alloy also known as Field's Metal for the purposes of use as a similar fluid for liquid metal reactors. The density, specific heat capacity, viscosity, thermal conductivity, and the coefficient of thermal expansion were determined for liquid Field's Metal for temperature ranges from its melting point 333 K to 423 K. The work captured the effect of temperature on these properties and each property's magnitude. The findings were used to create mathematical correlations to predict the value of the thermophysical property at a specified temperature for use in natural circulation studies. Notably, the work also observed non-Newtonian shear thinning behavior of the alloy near the melting point and that the non-Newtonian behavior relaxes as the material obtains more energy. The results are consistent with the behavior of other liquid metals including variances that occur close to the melting point.

Electric Field Assisted Direct Writing and 3D Printing of Low‐Melting Alloy

Metal additive manufacturing plays a vital role in new generations of manufacturing. As one of the most used alloys, field's metal can be used in many applications such as mold fabrication, radiation shielding, and more. This research demonstrates the ability to fabricate functional parts using the field's alloy at the micron level. With the good thermal conductivity and low thermal negative thermal expansion coefficient, printing temperatures and printing speed are mapped for single layer printing at a given nozzle size for printing width and height performance stability optimization. Printing temperatures and printing speeds were optimized with the same evaluation criteria. Classic 3D printing challenges have been printed testing technology readiness including overhang, bridges, and infills. Varieties of 3D parts are fabricated and prove functional for computed tomography imagery marking tags and micro‐volume liquid capacitance measurements. It demonstrates that the capability of high‐resolution printing also improves the printing time efficiency when small features are not required.