Low Melting Point Metal Research Articles

Microstructure, mechanical, wave-transparent and heat insulation properties of Si3N4 foam ceramic by organic foam impregnation combined with CVI

An ultralight and high-strength Silicon nitride (Si3N4) foam ceramic with highly efficient wave-transparent and heat insulation properties was successfully prepared using the organic foam impregnation technique combined with chemical vapor infiltration (CVI) process. The microstructure of Si3N4 foam ceramic inherits the pore structure characteristics of the template, and the ceramic skeleton is formed by coupling the Si3N4 whiskers with the CVI Si3N4 matrix. The use of CVI process avoids the volume shrinkage problem during the ceramic formation process by traditional sintering method at high temperature, and ensures the near-net-shape preparation of ceramic. Meanwhile, CVI Si3N4 matrix has pure components without impurities like low melting point metal oxides by sintering method or free carbon by polymer-derived ceramic method, which is beneficial to the improvement of wave-transparent ability and thermal stability. The addition of whisker reinforcement greatly increases the compressive strength of ceramic through whisker pulling out, crack deflection and other strengthening and toughening mechanisms. Moreover, we discuss in detail the relationship between the structural parameters of Si3N4 foam ceramic, such as whiskers-matrix solid content ratio, open-closed porosity ratio, pore size and mechanical, wave-transparent as well as heat insulation properties. In this study, the compressive strength of 40PPI Si3N4 foam ceramic with total porosity of 91.97% is 1.06 MPa, the thermal conductivity is only 0.624 W/(m·K) at 25 °C and the dielectric constant and loss tangent are 1.40 (10 GHz) and 6.35 × 10−3 (10 GHz), respectively.

Experimental investigation on ex-vessel debris bed formation using low melting-point melt of binary metals

During severe accidents in a light water reactor, the core melt (corium) may relocate to the lower head and fail the reactor pressure vessel (RPV). The corium will be ejected to the reactor cavity upon the RPV failure and undergo melt coolant interactions (FCI) if the cavity is flooded with water. The FCI process does not only determines the characteristics of the resulting debris bed which are important to coolability, but also induces a steam explosion risk which may threaten containment integrity. The present study is concerned with characterization of debris bed formed from FCI of metal-rich corium failing into a deep water pool in the reactor cavity. Low melting-point metals Tin and Tin–Bismuth (20 kg) were employed as the simulant materials of metal-rich corium melt. Ten tests were carried out on the DEFOR-M test facility at KTH to investigate the effects of various parameters on debris bed formation, such as melt superheat, coolant subcooling, material. The melt jet fragmentation and fragments movement in the water pool as well as debris deposition on the pool floor were recorded by high-speed cameras. Melt sensors and weight sensors were installed to detect the period of melt jet discharge and the mass of forming debris bed. The porosity of debris bed was obtained through the debris bed volume measured by a three-dimensional laser scanner and the pore volume measured by water absorption. The final configuration of debris bed was also reconstructed through the laser scanner data, and the debris particles were sieved for their size distribution. The experimental results revealed the FCI phenomena and debris bed characteristics including configuration and porosity of debris bed as well as morphology and size distribution of debris particles under different melt superheats, coolant subcooling, materials.

A liquid metal-polydopamine composite for cell culture and electro-stimulation.

Gallium (Ga) is a low melting point metal in the liquid state in the biological environment which presents a unique combination of fluidity, softness, and metallic electrical and thermal properties. In this work, liquid Ga is proposed as a biocompatible electrode material for cell culture by electro-stimulation since the cytotoxicity of Ga is generally considered low and some Ga compounds have been reported to exhibit anti-bacterial and anti-inflammatory activities. Complementarily, polydopamine (PDA) was coated on liquid Ga to increase the attachment capability of cells on the liquid Ga electrode and provide enhanced biocompatibility. The liquid Ga layer could be readily painted at room temperature on a solid inert substrate, followed by the formation of a nanoscale PDA coating layer resulting in a conformable and biocompatible composite electrode. The PDA layer was shown to coordinate with Ga3+, which is sourced from liquid Ga, providing electrical conductivity in the cell culture medium. The PDA-Ga3+ composite acted as a conductive substrate for advanced electro-stimulation for cell culture methods of representative animal fibroblasts. The cell proliferation was observed to increase by ∼143% as compared to a standard glass coverslip at a low potential of 0.1 V of direct coupling stimulation. This novel PDA-Ga3+ composite has potential applications in cell culture and regenerative medicine.

A solid-state lithium metal battery with extended cycling and rate performance using a low-melting alloy interface

The anode with a low-melting alloy interlayer shows dendrite-free behavior, alleviating side reactions on the interface. Liquid metal alloy achieves close contact between lithium and solid-state electrolytes at room temperature.

Overall Carbon‐neutral Electrochemical Reduction of CO2 in Molten Salts using a Liquid Metal Sn Cathode

AbstractAn overall carbon‐neutral CO2 electroreduction requires enhanced conversion efficiency and intensified functionality of CO2‐derived products to balance the carbon footprint from CO2 electroreduction against fixed CO2. A liquid Sn cathode is herein introduced into electrochemical reduction of CO2 in molten salts to fabricate core–shell Sn−C spheres (Sn@C). An in situ generated Li2SnO3/C directs a self‐template formation of Sn@C. Benefitting from the accelerated reaction kinetics from the liquid Sn cathode and the core–shell structure of Sn@C, a CO2‐fixation current efficiency higher than 84 % and a high reversible lithium‐storage capacity of Sn@C are achieved. The versatility of this strategy is demonstrated by other low melting point metals, such as Zn and Bi. This process integrates energy‐efficient CO2 conversion and template‐free fabrication of value‐added metal‐carbon, achieving an overall carbon‐neutral electrochemical reduction of CO2.

Overall Carbon-neutral Electrochemical Reduction of CO2 in Molten Salts using a Liquid Metal Sn Cathode.

An overall carbon-neutral CO2 electroreduction requires enhanced conversion efficiency and intensified functionality of CO2-derived products to balance the carbon footprint from CO2 electroreduction against fixed CO2. A liquid Sn cathode is herein introduced into electrochemical reduction of CO2 in molten salts to fabricate core-shell Sn-C spheres (Sn@C). An in-situ generated Li2SnO3/C directs a self-template formation of Sn@C. Benefitting from the accelerated reaction kinetics from the liquid Sn cathode and the core-shell structure of Sn@C, a CO2-fixation current efficiency higher than 84% and a high reversible lithium-storage capacity of Sn@C are achieved. The versatility of this strategy is demonstrated by other low melting point metals, such as Zn and Bi. This process integrates energy-efficient CO2 conversion and template-free fabrication of value-added metal-carbon, achieving an overall carbon-neutral electrochemical reduction of CO2.

Intermetallic growth and thermal impedance at the In32.5Bi16.5Sn/Cu interface

Present developing trends in the miniaturization and power escalation on electronic components have driven research interest in thermal interface materials (TIMs) to solve the fundamental issue of heat dissipation. Among the various TIMs, the In32.5Bi16.5Sn low melting alloy (LMA) has drawn much attention owing to its low melting point and great bondability, which could mitigate the warpage issue and provide very low thermal interface resistance. In this study, the Cu/In32.5Bi16.5Sn/Cu structure was used to simulate the practical conditions of the application of TIM in joining the substrate and heat sink. The thermal properties before and after an aging test at 80 °C were measured with a thermal tester, and the growth kinetics of the intermetallic compound (IMC) at the In32.5Bi16.5Sn/Cu interface were investigated. Without fast dissolution of Cu into the In32.5Bi16.5Sn alloy, the growth kinetics of the IMC at the interface were found to be diffusion-controlled at the temperature studied. It was found that the main change in the Cu/In32.5Bi16.5Sn/Cu system after the aging test was the thickening of the IMC, and the interface was free of cracks. As the aging time increased, the thermal impedance increased to twice that of the initial value, showing parabolic degradation, which is relevant to the growth kinetics of the IMC at the interface. Implications for the degradation of the thermal performance and further research are also discussed.

Highly anisotropic metallized wood obtained by filling basswood channels with low-melting-point Sn-Bi alloy

Basswood and Sn-Bi alloy have several complementary properties—the former has a low density, no electromagnetic shielding, poor thermal and electrical conductivity, and low impact toughness, while the latter has exactly the opposite properties. Combining the natural porous structure of basswood with a low-melting Sn-Bi alloy can produce a composite with the merits of both materials. In this study, basswood was pretreated with 5 % ammonia water, and then the Sn-Bi alloy was filled into the cell lumens and vessels without lignin at 138 ℃ and 3000 Pa. After metallization, the density of the basswood increased from 0.5 g·cm−3 to 3.0 g·cm−3, reaching six times its initial value, which also doubled the impact toughness. The total electromagnetic interference shielding effectiveness of the metallized basswood obtained using different filling methods ranged from 45 dB to 70 dB. Heat-transfer simulations and circuit experiments were carried out to investigate the thermal and electrical conductivity of this composite, and the results demonstrated its anisotropic conductivity. These properties showed that the metallized basswood could be used as a functional or structural material in different fields.

Observation of Pattern Formation during Electromagnetic Levitation Using High-Speed Thermography

Electromagnetic levitation (EML) was employed for studying the velocity and morphology of the solidification front as a function of undercooling of metallic materials. The limitation of the EML technique with respect to low melting alloys that emit outside the visible light spectrum was overcome by employing state-of-the-art high-speed mid-wavelength infrared cameras (MWIR cameras) with a photon detector. Due to the additional thermography contrast provided by the emission contrast of the solid and liquid phases, conductor, and semi-conductor, the pattern formation of Al-based alloys was studied in detail, revealing information on the nucleation, phase selection during solidification, and the influence of convection.

3D Printed Electronic Circuits from Fusible Alloys

This work aims to evaluate the possibility of fabricating conductive paths for printed circuit boards from low-temperature melting metal alloys on low-temperature 3D printed substrates and mounting through-hole electronic components using the fused deposition modeling for metals (FDMm) for structural electronics applications. The conductive materials are flux-cored solder wires Sn60Pb40 and Sn99Ag0.3Cu0.7. The deposition was achieved with a specially adapted nozzle. A comparison of solder wires with and without flux cores is discussed to determine whether the solder alloys exhibit adequate wettability and adhesion to the polymer substrate. The symmetrical astable multivibrator circuit based on bipolar junction transistors (BJT) was fabricated to demonstrate the possibility of simultaneous production of conductive tracks and through-hole mountings with this additive technique. Additional perspectives for applying this technique to 3D-printed structural electronic circuits are also discussed.

PREDICTION OF THE TENSILE STRENGTH OF STEEL FORGINGS

Great attention is paid to the issues of improving the methods of product quality prediction, in particular, a comprehensive approach to its evaluation is being developed based on the principles of qualimetry. The example of experimental approach is provided to predict one of the mechanical properties ‒ tensile strength which is an important indicator of the steel forgings quality. The investigation has been carried out to estimate the accumulated strain degree, chemical composition, friction conditions at contact surface influencing on temporal resistance distribution in the forging volume. The accumulation of strain degree was carried out by crimping of cubic billets in three mutually perpendicular directions with different number of crimping cycles according to cube‒cube scheme. The distribution of strain degree over the volume of a deformed billet was experimentally determined for lead samples by coordinate grid technique. The lead cubic billets were cut in half. A square grid was applied to one of the halves, and then the halves were fused with a fusible Wood alloy and subjected to the first upsetting. After upsetting the sample was unsoldered and the Λ value in each cell was calculated from the curvature of the coordinate grid. The forging of steel billets was carried out in a similar way. After forging the steel billets, the specimens were cut out for mechanical testing. As a result of experimental data processing, the equation of regression has been received, which enables to predict the level of forgings’ tensile strength at the known technological parameters. Significance of the coefficients of the obtained equation was validated by the Student's criterion and the adequacy by the Fisher's criterion. The developed technique can be applied for selection of rational mode of deformation during forging for maintenance of the given level of mechanical properties.

Magnetic Properties and Microstructure of Ce-Cu-Al Low Melting Alloy Bonding Sm2Fe17N3 Magnet Fabricated by the Hot-Pressing Method

Sm2Fe17N3 compounds, having excellent intrinsic magnetic properties, are prone to decomposition at high temperatures; thus, a low melting point metal binder is the key to prepare high performance bulk magnets at low temperatures. In this paper, a new low melting point alloy Ce72Cu28-xAlx was used as the binders, and high-performance Ce-based alloy bonding Sm2Fe17N3 magnets were realized by the hot-pressing method. The experimental results demonstrated that the content of Al in the Ce-based alloys had an important influence on the performance of the magnets. High performance Sm-Fe-N bonded magnets with remanence of 10.19 KGs and maximum magnetic energy product of 21.06 MGOe were achieved by using 5 wt.% Ce72Cu22Al6 alloy as a binder. At the same time, it was found that the Ce72Cu28-xAlx alloy has a lower density and better bonding effect than the common Zn binder. Its bonding magnets still have higher performance even with extremely high oxygen content. Therefore, Ce72Cu28-xAlx alloy with low melting point is a promising new rare earth-based alloy binder. If the oxygen content of the alloy powders could be reduced, higher performance Sm2Fe17N3 bonded magnets can be prepared.

Shape-stable Bi-Sn-In alloy/Ag/copper foam composite phase change material for thermal storage and management

With the increasing challenge of heat dissipation in electronic device, the development of rapid thermal storage and management materials with high thermal conductivity becomes an important topic. This study developed a novel low melting point metal composite phase change material composed of Bi-Sn-In alloy, Ag particles (1–4 wt%) and copper foam (apertures 0.25–0.64 mm) using high thermal conductivity synergetic enhanced effect. The Ag particles were uniformly distributed in Bi-Sn-In alloy and they changed to Ag strips with high Ag content, and Bi-Sn-In alloy/Ag can be evenly filled in apertures of copper foam. Bi-Sn-In alloy/Ag/copper foam composite with optimal aperture of 0.42 mm exhibited highest shape stability, because it avoided molten alloy leakage for larger apertures and residual alloy which was not pressed into copper foam for small apertures. As Ag content increases, the melting points of Bi-Sn-In alloy/Ag and Bi-Sn-In alloy/Ag/copper foam with Ag content of 4 wt% respectively increased by 4.91 % and 2.46 %, while their enthalpy slightly decreases by 10.9 % and 2.49 %. More importantly, the synergistic effect of Ag strips and copper skeleton addition formed continuous channels for heat transfer. The thermal conductivities of alloy/Ag (4 wt%) and alloy/Ag (4 wt%)/copper foam were respectively 22.4 and 42.7 Wm−1 °C−1, and they were remarkably higher than that of Bi-Sn-In alloy (16.4 Wm−1 °C−1). Furthermore, thermal management test showed that Bi-Sn-In alloy/Ag/foam copper had the most prominent endothermic and exothermic properties. The outstanding performance of present Bi-Sn-In alloy/Ag/copper foam demonstrates a promising prospect for solving the thermal management problems of contemporary electronic devices.

Phase separation and anomalous shape transformation in frozen microscale eutectic indium-gallium upon remelting

The eutectic Ga-In (EGaIn) alloy has low vapour pressure, low toxicity, high thermal and electrical conductivities, and thus has shown a great potential for smart material applications. For such applications, EGaIn is maintained above its melting point, below which it undergoes solidification and phase separation. A scientific understanding of the structural and compositional evolution during thermal cycling could help further assess the application range of low-melting-point fusible alloys. Here, we use an integrated suite of cryogenically-enabled advanced microscopy & microanalysis to better understand phase separation and (re)mixing processes in EGaIn. We reveal an overlooked thermal-stimulus-response behaviour for frozen mesoscale EGaIn at cryogenic temperatures, with a sudden apparent volume expansion observed during in-situ heat-cycling, associated with the immiscibility between Ga and In during cooling and the formation of metastable Ga phases. These results emphasize the importance of the kinetics of rejuvenation, and open new paths for EGaIn as a self-healing material.

Effects of particle size and oxide shell on variable stiffness performance of phase-changing materials

Phase-changing materials have recently found use as particulate fillers to engender stiffness-changing behavior in composites. In the transition from solid to liquid particles, the composite modulus can be significantly reduced, and then raised again as the particles are allowed to solidify. While the general effect of stiffness tuning in phase-changing composites has been demonstrated in a range of studies and applications, the most drastic stiffness ranges are provided by fusible metallic alloys, which are commonly subject to the formation of oxide shells on their surfaces. In this work, we examine the effect these oxide surfaces have on variable-stiffness performance, and investigate the corresponding role of particle size. In particular, we study particles of a low-melting-point metallic alloy, Field’s Metal, and we also present a facile method of manufacture that allows for control of particle size. We then manufacture a set of stiffness-changing composites using these particles and characterize mechanical performance, with the aim of controlling particle size to increase the total stiffness ratio while resisting material failure.

Accurately tailoring yolk-shell spheres to balance cycling stability and volumetric capacity of lithium storage

Yolk-shell structure is a promising material design for alloying type anode due to its void space accommodating the volume change during battery cycle life. However, the coordination between void space and core size is an issue for yolk-shell structured anode materials achieving excellent cycling stability and reasonable high volumetric energy density. Herein, we propose a strategy of in-situ shell-to-core evolution to accurately control the void space and core size in yolk-shelled spheres. Based on this approach, we have synthesized a yolk shelled composite with a Sn nanoparticle encapsulated in a N doped C shell ([email protected]@NxC). The controlled core size and void space, and their relationship with anode electrochemical performance have been systematically studied. The optimal [email protected]@NxC electrode demonstrates excellent cycling stability of 1110 mAh cm−3 for volumetric capacity and 820 mAh g−1 for gravimetric capacity after 1000 cycles at 1 C (1 C = 1000 mA g−1). We believe that the facile yolk-shelled structure designing strategy in this work could be extended to synthesize other low melting point metals, such as Bi, Pb, In, Ge, etc., for their functional applications.

Design, Fabrication and Performance Evaluation of a Dual Powered Crucible Furnace for Aluminium Cans Recycling

There is great need for metal scraps recycling and commercialization in Nigeria owning to the abundant and indiscriminate disposal of metal scraps which constitute health hazard to citizens through the blockage of drainage systems, causing erosion and flooding, defaces the aesthetics of the cities through mounting heaps of metallic waste. This research work designed and fabricated a manually operated dual powered tilting crucible furnace suitable for laboratory and workshop practice for recycling of aluminium cans and scraps and other low melting metals and alloys. It consists of a cylindrical stainless steel pot contained in a refractory lined mild steel square box, fired with both gas and electricity and incorporates a K-type digital thermocouple for temperature measurement. The stainless steel crucible pot has a diameter of 195mm, 312mm high and 3mm thick. The refractory material was locally developed from asbestos, clay, cement and perlite combined in the ratio 1:1:1:5 by volume. The fabricated furnace was tested for performance evaluation by melting different samples of aluminium cans using both gas and electricity. It was found that the furnace has fairly uniform melting rate with both gas and electric powered operations but has varying heating rate which decreased with increasing charge mass. The furnace also has no-load heating rates of 28.7oC/min and 20.1oC/min when powered with gas and electricity respectively. The furnace has a melting capacity of 〖0.0093m〗^3 for 25kg of aluminium charge with total output heat of 199.93MJ and thus suitable for use in small scale foundries and tertiary institutions

Effect of sodium silicate binder on the performance of ceramic coatings on copper prepared by the slurry method

Low melting point metals, such as copper, are often used as high-temperature cooling equipments and endure harsh environments during operations. This usually leads to reduced service life and reliability. To address this problem, a protective coating was prepared on copper via a slurry method. However, due to the low melting point of copper, solid-state sintering was applied. Therefore, during this process, the defects generated in the ceramic coating could affect the performance of the coating. To reduce the defects, a series of ceramic coating samples using sodium silicate water glass (SSWG) as the binder were prepared, changing the SSWG-to-aggregate mass ratio (SAMR) for each sample. The results showed that they were all related to the SAMR, and there was an optimal SAMR with minimum defects and favourable performance. The non-optimized SAMR lead to more internal defects, that is, microfractures and pores in the coating, resulting to a decline in the coating performance. By identifying the types of defects and quantifying them, the relationship between the SSWG and the generation of defects was studied, and the effect of the defects on the performance of the ceramic coating was analysed in detail. The research presented in this paper provides a method for the improvement of ceramic coatings by optimising the key factors that is the SAMR in solid-state sintering. The effect of thermal stress on the formation of microfracture defects during the sintering was investigated by experiments and simulation. It is found that with increase of sintering temperature, the thermal stress inside the coating increases gradually, resulting in more generation of microfracture defects inside the coating. The inhibition effect of SSWG on thermal stress during the sintering process was verified.

Fragmentation and solidification of fusible alloy melt by water spray

To elucidate the fragmentation and solidification processes that occur during the production of metal powders from a thermo-fluid perspective, we conducted experiments to visualize the water atomization of molten 42 Sn– 58 Bi fusible alloy and made measurements of the circularity of the resulting metal powder. The fragmentation process inside a fully developed fast water spray with a pressure up to 5 MPa was clearly captured. The time-resolved images revealed fragmentation patterns involving extending molten ligaments resulting from splashing, vapor explosions, and splitting. The time variation of the thinning of the neck diameter of the ligaments revealed that the fragmentation is rate-controlled by the capillarity of the molten drop itself, and solidification and viscosity have no influence on the pinching-point dynamics. The produced metal powder displayed size-dependent circularity, and larger particles tended to be less spherical than small particles. The mechanism is attributed to non-uniform solidification, which is enhanced at the pinching part of a droplet, consistent well with the images obtained. • Successful visualization of disintegrating alloy ligaments inside a water spray. • Fragmentation follows capillary timescale with partial stretching by impinging water. • Non-uniform solidification of elongated drops creates particles with less circularity.

A Short History of Fusible Metals and Alloys – Towards Room Temperature Liquid Metals

AbstractLiquid metals are a class of materials with a millennia‐long history, albeit until 200 years ago, mostly centered on mercury‐based applications. The knowledge of mercury's toxicity and the discovery of it's bioaccumulation and biomagnification in the late 20th century resulted in phasing out mercury for copious application. Lead‐based, bismuth‐based, and sodium‐based technology has partially replaced mercury, but due to toxicity or reactivity issues, replacements for lead and sodium are sought. The discovery of indium and, especially, gallium has allowed for the third generation of alloys with a melting point close to room temperature. This review gives a comprehensive overview of the technological developments of fusible and liquid metals, i. e., metals and alloys with melting points below ca. 250 °C, from the early days to current research and industrial application. Special emphasis is focused on important steppingstones and recent developments of gallium‐based alloys as well as how they could be used for future applications.