Low-temperature Metal Research Articles

Synergistically improved thermal conductivity of polyamide-6 with low melting temperature metal and graphite

Synergistically improved thermal conductivity of polyamide-6 with low melting temperature metal and graphite

Evolution of Phase Transition and Oxidation of Copper in Electrical Fires

Based on the theories of low-temperature plasma and metal solidification, the similarities and differences between anode melted marks (AMMs) and cathode melted marks (CMMs) in direct current (DC) short circuits were characterized, and the phase transition and oxidation of copper melted marks were analyzed. These data were used to ascertain which melted marks were suitable for identification of evidence of electrical fire materials. These parameters were assessed using metallographic microscopy, X-ray diffraction, laser micro-Raman spectroscopy, scanning electron microscopy and energy-dispersive spectrometry. The grain size of AMMs was 20–40nm and that of CMMs was 20–35nm at a DC of 600A. The oxygen: copper ratio on the three types of regions of AMM surfaces displayed an inverted U-shaped with increasing DC. The oxygen: copper ratio on rough surfaces was <1.3, on smooth surfaces were <0.8, and in gas holes were <1.2. Furthermore, the ratio on longitudinal sections of CMMs showed a similar trend, and was <0.8. Copper (I) oxide appeared only on the surfaces of SSMs (secondary short-circuited melted marks).

An Electrochemical and Photoelectron Spectroscopy Study of a Low Temperature Liquid Metal Battery Based on an Ionic Liquid Electrolyte

We report the design of a low-temperature liquid metal battery (LMB). Li and Ga as the negative and positive electrode, respectively, are used in combination with a room temperature ionic liquid as an electrolyte. 1 mol/L lithium bis(trifluoromethylsulfonyl)imide (Li[TFSI]) in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide is chosen as electrolyte. The battery operates at 220°C which is a relatively low temperature for a LMB and shows good electrochemical performance at low current density. The cells were cycled for more than 600 h and achieved a round-trip Coulombic efficiency close to 100% and an average voltage efficiency of 66% resulting in an overall energy efficiency of 65%. At higher current densities, however, the system showed up to 75% irreversible capacity loss after three cycles. To understand the origin of this strong deterioration, we characterized the surface and the bulk properties of the Ga cathode using X-ray Photoelectron Spectroscopy. Especially at higher current densities a decomposition of the electrolyte was found. The chemical changes that occurred and the elemental distribution at the Ga cathode are analyzed based on XPS measurements at different stages of the battery charge/discharge cycling.

Impact of Post-deposition Plasma Treatment on Surface Passivation Quality of Silicon Nitride Films

Exposing a plasma-enhanced chemical vapor deposition-deposited silicon nitride (SiNx) film to an inert gasoxidizing plasma ambient results in a significant reduction in background plating in the case of electroplated Ni-Cu metallization on c-Si solar cells. However, plasma treatment of SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> is known to result in a degradation of the Si-SiNx interface. In this paper, we investigate the impact of an Ar/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma treatment process on the surface passivation properties of SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> film. Following the plasma treatment, effective minority carrier lifetime (τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ) is seen to improve from 266 to 864 μs at a minority carrier density of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The interface-state density (Dit) at the Si-SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> interface also decreases by an order of magnitude, following the Ar/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O plasma treatment. Enhancement in τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> is found to be stable for annealing temperatures up to 450°C, which is typically used for Ni-Cu contact sintering. Substrate annealing during the post-deposition plasma treatment process is seen to play a major role in improving the τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> . Coupled with its potential for reducing the background plating, the proposed process is a promising candidate for developing the passivation layers for cell technologies with low-temperature metallization schemes.

Bioleaching of Chalcopyrite by Thermophilic Archaea

Bioleaching and biooxidation of sulfidicores and concentrates generate very high acidities and a great of heat, which rise the temperature in the reactors or heaps, and accumulate the sulfur on the surface of the ores. Extremely thermoacidophilic archaea, mainly from the genus ofAcidianus, Sulfolobus,Metallosphaeraandsulfurisphaera, have great potential to contribute to biomining processes for their inherent tolerance for low pH, high temperature, and high-soluble metal concentrations. Species of the genusMetallosphaeratypically grow by aerobic respiration on CO2with S0, tetrathionate (S4O62+), and Fe2+as electron donors, particularly suitble for metal extraction under high temperature by their iron- and sulfur-oxidation ability. Several species fromMetallosphaeraandAcidianusgenerawere investigated for their ability and conditions to dissolve various ores under a range of conditions. All of them showed good performance in copper extraction from chalcopyrite, with strainM.cuprinaAr-4 displaying higher activity than others. Surface analysis of chalcopyrite leached with the strain showed the leaching products accumulated on the ores. Our study will cover new understandings on the application of these thermoacidophilic archaea in biomining.

Substrate temperature control for the formation of metal nanohelices by glancing angle deposition

The targets of this study are to develop a device to precisely control the temperature during glancing angle deposition, to make films consisting of low melting temperature metal nanoelements with a controlled shape (helix), and to explore the substrate temperature for controlling the nanoshapes. A vacuum evaporation system capable of both cooling a substrate and measurement of its temperature was used to form thin films consisting of arrays of Cu and Al nanohelices on silicon substrates by maintaining the substrate temperature at Ts/Tm &amp;lt; 0.22 (Ts is the substrate temperature and Tm is the melting temperature of target material). The critical Ts/Tm to produce Cu and Al nanohelices corresponds to the transitional homologous temperature between zones I and II in the structure zone model for the solid film, where surface diffusion becomes dominant. X-ray diffraction analysis indicated that the Cu and Al nanohelix thin films were composed of coarse oriented grains with diameters of several tens of nanometers.

Kinetics of Internal Methane Reforming on the Anodes of Low Temperature Ceres Power Steel Cell SOFCs

Ceres Power has developed a unique low-temperature metal supported SOFC design (the ‘Steel Cell’) based predominantly around the use of ceria. This unique design architecture offers greatly enhanced robustness to real-world operating conditions at a lower cost than conventional SOFC designs, whilst retaining the advantages of fuel flexibility, high efficiency and low degradation. A widely quoted benefit of SOFCs is the ability to carry out a significant percentage of the reforming of hydrocarbon fuels to syngas within the anode of the cells, simplifying the design of the fuel processing system by comparison with other fuel cell types. In addition performing the endothermic reforming reaction within the stack significantly reduces the requirement for air cooling, which improves the efficiency of a typical SOFC system by reducing the parasitic power demand from the cathode air blower. It has historically been viewed that a disadvantage of low temperature SOFC operation is that significant levels of internal methane reforming are no longer possible due to poor kinetics and thermodynamically limited methane conversion. The Ceres steel cell technology has been developed to perform relatively high levels (40-60%) of internal methane reforming. In this paper a method for approximately estimating the kinetics of methane reforming on Steel Cell anodes will be described, coupling experimental measurements to a mathematical model.

Ceres Power Steel Cell Technology: Rapid Progress Towards a Truly Commercially Viable SOFC

Ceres Power is continuing to make excellent progress in the development of its low-temperature metal supported SOFC design (the ‘Steel Cell’) based predominantly around the use of ceria. This unique design architecture allows for a robust, low cost, subsidy free fuel cell product, whilst retaining the advantages of fuel flexibility, high efficiency and low degradation. Over the last year, extensive development and verification of the technology has been undertaken on the latest generation of Steel Cell technology, which offers further enhancements in technology readiness level and manufacturability. Over the same period, third parties have deepened their testing and development engagements with Ceres Power for a broadening range of market applications at cell, stack, fuel cell module and product levels. This paper provides an update on Ceres’ development, verification approach and latest results.

Electrochemical liquid-liquid-solid (ec-LLS) crystal growth: a low-temperature strategy for covalent semiconductor crystal growth.

This Account describes a new electrochemical synthetic strategy for direct growth of crystalline covalent group IV and III-V semiconductor materials at or near ambient temperature conditions. This strategy, which we call "electrochemical liquid-liquid-solid" (ec-LLS) crystal growth, marries the semiconductor solvation properties of liquid metal melts with the utility and simplicity of conventional electrodeposition. A low-temperature liquid metal (i.e., Hg, Ga, or alloy thereof) acts simultaneously as the source of electrons for the heterogeneous reduction of oxidized semiconductor precursors dissolved in an electrolyte as well as the solvent for dissolution of the zero-valent semiconductor. Supersaturation of the semiconductor in the liquid metal triggers eventual crystal nucleation and growth. In this way, the liquid electrolyte-liquid metal-solid crystal phase boundary strongly influences crystal growth. As a synthetic strategy, ec-LLS has several intrinsic features that are attractive for preparing covalent semiconductor crystals. First, ec-LLS does not require high temperatures, toxic precursors, or high-energy-density semiconductor reagents. This largely simplifies equipment complexity and expense. In practice, ec-LLS can be performed with only a beaker filled with electrolyte and an electrical circuit capable of supplying a defined current (e.g., a battery in series with a resistor). By this same token, ec-LLS is compatible with thermally and chemically sensitive substrates (e.g., plastics) that cannot be used as deposition substrates in conventional syntheses of covalent semiconductors. Second, ec-LLS affords control over a host of crystal shapes and sizes through simple changes in common experimental parameters. As described in detail herein, large and small semiconductor crystals can be grown both homogeneously within a liquid metal electrode and heterogeneously at the interface of a liquid metal electrode and a seed substrate, depending on the particular details chosen for ec-LLS. Third, the rate of introduction of zero-valent materials into the liquid metal is precisely gated with a high degree of resolution by the applied potential/current. The intent of this Account is to summarize the key elements of ec-LLS identified to date, first contextualizing this method with respect to other semiconductor crystal growth methods and then highlighting some unique capabilities of ec-LLS. Specifically, we detail ec-LLS as a platform to prepare Ge and Si crystals from bulk- (∼1 cm(3)), micro- (∼10(-10) cm(3)), and nano-sized (∼10(-16) cm(3)) liquid metal electrodes in common solvents at low temperature. In addition, we describe our successes in the preparation of more compositionally complex binary covalent III-V semiconductors.

Carbon deposition behaviour in metal-infiltrated gadolinia doped ceria electrodes for simulated biogas upgrading in solid oxide electrolysis cells

One of the attractive applications for reversible Solid Oxide Cells (SOCs) is to convert CO2 into CO via high temperature electrolysis, which is particularly important for biogas upgrading. To improve biogas utility, the CO2 component can be converted into fuel via electrolysis. A significant issue for SOC operation on biogas is carbon-induced catalyst deactivation. Nickel is widely used in SOC electrodes for reasons of cost and performance, but it has a low tolerance to carbon deposition. Two different modes of carbon formation on Ni-based electrodes are proposed in the present work based on ex-situ Raman measurements which are in agreement with previous studies. While copper is known to be resistant towards carbon formation, two significant issues have prevented its application in SOC electrodes – namely its relatively low melting temperature, inhibiting high temperature sintering, and low catalytic activity for hydrogen oxidation. In this study, the electrodes were prepared through a low temperature metal infiltration technique. Since the metal infiltration technique avoids high sintering temperatures, Cu–Ce0.9Gd0.1O2−δ (Cu-CGO) electrodes were fabricated and tested as an alternative to Ni-CGO electrodes. We demonstrate that the performance of Cu-CGO electrodes is equivalent to Ni-CGO electrodes, whilst carbon formation is fully suppressed when operated on biogas mixture.

Ceres Power Steel Cell Technology: Rapid Progress Towards a Truly Commercially Viable SOFC

Ceres Power is continuing to make excellent progress in the development of its low-temperature metal supported SOFC design (the ‘Steel Cell’) based predominantly around the use of ceria. This unique design architecture allows for a robust, low cost, subsidy free fuel cell product, whilst retaining the advantages of fuel flexibility, high efficiency and low degradation. Over the last year, extensive development and verification of the technology has been undertaken on the latest generation of Steel Cell technology, which offers further enhancements in technology readiness level and manufacturability. Over the same period, third parties have deepened their testing and development engagements with Ceres Power for a broadening range of market applications at cell, stack, fuel cell module and product levels. This paper provides an update on Ceres’ development, verification approach and latest results.

Kinetics of Internal Methane Reforming on the Anodes of Low Temperature Ceres Power Steel Cell SOFCs

Ceres Power has developed a unique low-temperature metal supported SOFC design (the ‘Steel Cell’) based predominantly around the use of ceria. This unique design architecture offers greatly enhanced robustness to real-world operating conditions at a lower cost than conventional SOFC designs, whilst retaining the advantages of fuel flexibility, high efficiency and low degradation. A widely quoted benefit of SOFCs is the ability to carry reforming of hydrocarbon fuels to syngas within the anode of the cells, simplifying the design of the fuel processing system. A perceived disadvantage of low temperature SOFC operation is that significant levels of internal methane reforming are no longer possible due to poor kinetics and thermodynamically limited methane conversion. The Ceres steel cell technology has been developed and demonstrated to perform high levels (40-60%) of internal methane reforming. In this paper a method for approximately estimating the kinetics of methane reforming on Steel Cell anodes will be described, coupling experimental measurements to a mathematical model.

Patterning for Plated Heterojunction Cells

This paper describes a patterning and plated metallization process that can be used for bifacial heterojunction silicon solar cells. Patterning was achieved by inkjet printing a functional fluid onto a resist surface, the fluid being able to chemically inhibit resist cross-linking in a subsequent thermal process. Copper/tin plated fingers as narrow as 20 μm were achieved on both surfaces of the cell. The low temperature metallization process was demonstrated on 156 mm heterojunction cells where the finger metallization was interconnected using SmartWire Connection Technology resulting in mini modules with efficiencies as high as 18.8%.

Thermal boundary conductance accumulation and interfacial phonon transmission: Measurements and theory

The advances in phonon spectroscopy in homogeneous solids have unveiled extremely useful physics regarding the contribution of phonon energies and mean-free paths to the thermal transport in solids. However, as material systems decrease to length scales less than the phonon mean-free paths, thermal transport can become much more impacted by scattering and transmission across interfaces between two materials than the intrinsic relaxation in the homogeneous solid. To elucidate the fundamental interactions driving this thermally limiting interfacial phonon scattering process, we analytically derive and experimentally measure a thermal boundary conductance accumulation function. We develop a semiclassical theory to calculate the thermal boundary conductance accumulation function across interfaces using the diffuse mismatch model, and validate this derivation by measuring the interface conductance between eight different metals on native oxide/silicon substrates and four different metals on sapphire substrates. Measurements were performed at room temperature using time-domain thermoreflectance and represent the first-reported values for interface conductance across several metal/native oxide/silicon and metal/sapphire interfaces. The various metal films provide a variable bandwidth of phonons incident on the metal/substrate interface. This method of varying phonons' cutoff frequency in the film while keeping the same substrate allows us to mimic the accumulation of thermal boundary conductance and thus provides a direct method to experimentally validate our theory. We show that the accumulation function can be written as the product of a weighted average of the interfacial phonon transmission function and the accumulation of the temperature derivative of the phonon flux incident on the interface; this provides the framework to extract an average, spectrally dependent phonon transmissivity from a series of thermal boundary conductance measurements. Our approach provides a platform for analyzing the spectral phononic contribution to interfacial thermal transport in our experimentally measured data of metal/substrate thermal boundary conductance. Based on the assumptions made in this work and the measurement results on different metals on native oxide/silicon and sapphire substrates, we demonstrate that high-frequency phonons dictate the transport across metal/Si interfaces, especially in low Debye temperature metals with low-cutoff frequencies.

High performance metal hydride based thermal energy storage systems for concentrating solar power applications

Thermal energy storage systems based on metal hydride pairs using high efficiency materials are evaluated. The low temperature metal hydrides NaAlH4 and Na3AlH6 were cycled to determine stability of hydrogen capacity over extended cycling. Addition of aluminum and expanded natural graphite were found to enhance the cycling stability of NaAlH4. Potential high temperature metal hydrides were investigated based on NaMg materials. A techno-economic analysis was performed to evaluate the performance a thermal energy storage system based on two metal hydride pairs: NaMgH3:NaAlH4 and NaMgH2F:Na3AlH6. The resulting analysis suggests that the two systems have the potential to reach low cost and high efficiency performance targets.

Low-Temperature Molten Salt Electrolytes for Membrane-Free Sodium Metal Batteries

The liquid metal battery (LMB) is attractive due to its simple construction, its circumvention of solid-state failure mechanisms and resultantly long lifetimes, and its particularly low levelized cost of energy. Here, we provide a study of a unique binary electrolyte, NaOH-NaI, in order to pursue a low-cost and low-temperature sodium-based liquid metal battery (LMB) for grid-scale electricity storage. Thermodynamic studies have confirmed a low eutectic melting temperature (220°C) as well as provided data to complete the phase diagram of this system. X-ray diffraction has further supported the existence of a recently discovered compound, Na7(OH)5I2, as well as offered initial evidence toward a NaI-rich compound displaying Pm-3m symmetry. These phase equilibrium data have then been used to optimize parameters from a two-sublattice thermodynamic solution model to provide a starting point for study of higher order systems. Further, a detailed electrochemical study has identified the voltage window and related oxidation/reduction reactions and found greatly improved stability of the pure sodium electrode against the electrolyte. Finally, an Na|NaOH-NaI|Pb-Bi proof-of-concept cell was assembled. This cell achieved over 100 cycles and displayed leakage currents below 0.40 mA/cm2. These results highlight an exciting class of low-melting molten salt electrolytes that may enable low cost grid-scale storage.

Inverted InP quantum dot light-emitting diodes using low-temperature solution-processed metal–oxide as an electron transport layer

The present work shows the inverted InP quantum dot light-emitting diodes (QD-LEDs) with inorganic metal oxide layers. In the inverted structure of ITO/ZnO/InP QDs/CBP/MoO3/Al, a sol–gel derived ZnO film was used as an electron transport layer (ETL) and MoO3 was used as a hole injection layer (HIL). In contrary to high annealing temperature (>200 °C) for conventional ZnO films, low temperature annealing (∼150 °C) was performed for sol–gel derived ZnO film. The performance of the inverted QD-LEDs was efficiently improved by optimization of the annealing time and temperature of ZnO ETL. The current efficiency was significantly improved about 215% by lowering annealing temperature of ZnO ETL.

Low-temperature MOVPE using TEGa for suppressed layer undulation in InxGa1−xAs/GaAs1−yPy superlattice on vicinal substrates

InxGa1−xAs/GaAs1−yPy strain-balanced superlattice (SL) is a promising narrow-gap material that can be lattice-matched to Ge or GaAs. When growing uniform SLs on vicinal substrates for Ge-based application, formation of step-bunching and the resultant layer undulation is a critical problem. The present paper reports low-temperature metal–organic vapor phase epitaxy (MOVPE) with triethylgallium (TEGa) to improve the stability and the uniformity of SL growth. Using trimetylgallium (TMGa), steps were severely bunched especially during InGaAs growth at high temperature, and the average reflectance of SLs significantly decreased due to lattice relaxation above 580°C. Lowering the growth temperature to 550–530°C was effective in order to grow 100-period SLs with a mirror-like surface, but an apparent lateral layer undulation was still confirmed by ex-situ X-ray-diffraction and STEM observation. Growth of SLs below 530°C with TMGa was found to result in serious crystal degradation due to unstable growth in the kinetically-limited temperature range. In contrast, use of TEGa enabled 100-period SLs to be successfully grown even at lower temperature owing to its efficient pyrolysis process. Highly uniform SLs with negligible layer undulation were grown at 510°C with TEGa, showing a photoluminescence spectrum which was as sharp as the one for SLs grown on an exact-oriented substrate. The absorption spectra for the SLs grown with TEGa showed similarly sharp edge with a strong exciton peak.

Solution-processable LaZrOx/SiO2 gate dielectric at low temperature of 180 °C for high-performance metal oxide field-effect transistors.

Although solution-processable high-k inorganic dielectrics have been implemented as a gate insulator for high-performance, low-cost transition metal oxide field-effect transistors (FETs), the high-temperature annealing (>300 °C) required to achieve acceptable insulating properties still limits the facile realization of flexible electronics. This study reports that the addition of a 2-dimetylamino-1-propanol (DMAPO) catalyst to a perhydropolysilazane (PHPS) solution enables a significant reduction of the curing temperature for the resulting SiO2 dielectrics to as low as 180 °C. The hydrolysis and condensation of the as-spun PHPS film under humidity conditions were enhanced greatly by the presence of DMAPO, even at extremely low curing temperatures, which allowed a smooth surface (roughness of 0.31 nm) and acceptable leakage characteristics (1.8 × 10(-6) A/cm(2) at an electric field of 1MV/cm) of the resulting SiO2 dielectric films. Although the resulting indium zinc oxide (IZO) FETs exhibited an apparent high mobility of 261.6 cm(2)/(V s), they suffered from a low on/off current (ION/OFF) ratio and large hysteresis due to the hygroscopic property of silazane-derived SiO2 film. The ION/OFF value and hysteresis instability of IZO FETs was improved by capping the high-k LaZrOx dielectric on a solution-processed SiO2 film via sol-gel processing at a low temperature of 180 °C while maintaining a high mobility of 24.8 cm(2)/(V s). This superior performance of the IZO FETs with a spin-coated LaZrOx/SiO2 bilayer gate insulator can be attributed to the efficient intercalation of the 5s orbital of In(3+) ion in the IZO channel, the good interface matching of IZO/LaZrOx and the carrier blocking ability of PHPS-derived SiO2 dielectric film. Therefore, the solution-processable LaZrOx/SiO2 stack can be a promising candidate as a gate dielectric for low-temperature, high-performance, and low-cost flexible metal oxide FETs.

Tracing low-temperature aqueous metal migration in mineralized watersheds with Cu isotope fractionation

Copper isotope signatures in waters emanating from mineralized watersheds provide evidence for the source aqueous copper in solution. Low-temperature aqueous oxidation of Cu sulfide minerals produces significant copper isotopic fractionation between solutions and residues. Abiotic experimental data of fractionation (defined as Δliquid–solid ‰=δ65Culiquid−δ65Cusolid) are on the order of 1–3‰ and are unique for copper rich-sulfide minerals. Data presented here from ores and waters within defined boundaries of porphyry copper, massive sulfide, skarn, and epithermal ore deposits mimic abiotic experiments. Thus, the oxidation of sulfide minerals appears to cause the signatures in the waters although significant biological, temperature, and pH variations exist in the fluids. Regardless of the deposit type, water type, concentration of Cu in solution, or location, the data provide a means to trace sources of metals in solutions. This relationship allows for tracking sources and degree of metal migration in low temperature aqueous systems and has direct application to exploration geology and environmental geochemistry.