Direct Joule Heating Research Articles

Platinum-Ruthenium Bimetallic Nanoparticle Catalysts Synthesized Via Direct Joule Heating for Methanol Fuel Cells.

Platinum-Ruthenium (PtRu) bimetallic nanoparticles are promising catalysts for methanol oxidation reaction (MOR) required by direct methanol fuel cells. However, existing catalyst synthesis methods have difficulty controlling their composition and structures. Here, a direct Joule heating method to yield highly active and stable PtRu catalysts for MOR is shown. The optimized Joule heating condition at 1000°C over 50 microseconds produces uniform PtRu nanoparticles (6.32wt.% Pt and 2.97 wt% Ru) with an average size of 2.0 ± 0.5 nanometers supported on carbon black substrates. They have a large electrochemically active surface area (ECSA) of 239 m2 g-1 and a high ECSA normalized specific activity of 0.295mA cm-2. They demonstrate a peak mass activity of 705.9mA mgPt -1 for MOR, 2.8 times that of commercial 20 wt.% platinum/carbon catalysts, and much superior to PtRu catalysts obtained by standard hydrothermal synthesis. Theoretical calculation results indicate that the superior catalytic activity can be attributed to modified Pt sites in PtRu nanoparticles, enabling strong methanol adsorption and weak carbon monoxide binding. Further, the PtRu catalyst demonstrates excellent stability in two-electrode methanol fuel cell tests with 85.3% current density retention and minimum Pt surface oxidation after 24 h.

Sub-minute carbonization of polymer/carbon nanotube films by microwave induction heating for ultrafast preparation of hard carbon anodes for sodium-ion batteries

Hard carbons (HCs) are excellent anode materials for sodium-ion batteries (SIBs). However, the carbonization and granulation of HC powders involve complex processes and require considerable energy. Here, we developed a facile method for manufacturing HC anodes for SIBs via a novel microwave induction heating (MIH) process for polymer/single-walled carbon nanotube (SWCNT) films. Numerical simulations solving electromagnetic field and heat transfer problems revealed the MIH mechanism; the electric current induced by the applied microwave enables direct Joule heating of the SWCNT networks in the composite film. Consequently, the composite films could be heated to the target temperatures (800–1400 °C) and free-standing HC/SWCNT anodes could be prepared by applying MIH for only 30 s. Comparative analyses confirmed that ultrafast MIH is a reliable technique for producing HC anodes and can replace conventional carbonization processes which require a high-temperature furnace. Moreover, the HC/SWCNT anodes prepared by the ultrafast MIH were successfully applied to the SIB full cells. Finally, the feasibility of MIH for scalable roll-to-roll production of HC anodes was verified through local heating tests using a circular sheet larger than a resonator.

Capturing carbon dioxide from air with charged-sorbents

Emissions reduction and greenhouse gas removal from the atmosphere are both necessary to achieve net-zero emissions and limit climate change1. There is thus a need for improved sorbents for the capture of carbon dioxide from the atmosphere, a process known as direct air capture. In particular, low-cost materials that can be regenerated at low temperatures would overcome the limitations of current technologies. In this work, we introduce a new class of designer sorbent materials known as ‘charged-sorbents’. These materials are prepared through a battery-like charging process that accumulates ions in the pores of low-cost activated carbons, with the inserted ions then serving as sites for carbon dioxide adsorption. We use our charging process to accumulate reactive hydroxide ions in the pores of a carbon electrode, and find that the resulting sorbent material can rapidly capture carbon dioxide from ambient air by means of (bi)carbonate formation. Unlike traditional bulk carbonates, charged-sorbent regeneration can be achieved at low temperatures (90–100 °C) and the sorbent’s conductive nature permits direct Joule heating regeneration2,3 using renewable electricity. Given their highly tailorable pore environments and low cost, we anticipate that charged-sorbents will find numerous potential applications in chemical separations, catalysis and beyond.

Tooling in Spark Plasma Sintering Technology: Design, Optimization, and Application

Spark plasma sintering as the prominent field‐assisted sintering technique (FAST/SPS) is a novel technology for the rapid, pressure‐assisted consolidation of powder materials. The main feature of FAST/SPS is the direct Joule heating of the applied tooling. Tooling is a challenging part of the FAST/SPS setup, which must withstand high pressure at elevated temperatures and ensure a uniform temperature distribution in the sintered part. This review looks at the standard FAST/SPS tooling, the specific tooling for sintering complex‐shaped parts, and for pressureless sintering. A particular focus lies on graphite, the commonly used tooling material, and on alternative materials such as steel, alloys, ceramics, and composites. The review also considers the add‐on tooling elements, such as spacers, foils, and thermal insulation. Furthermore, the article discusses the basics of FAST/SPS modeling, and the computer‐based optimization of FAST/SPS tooling, the procedure used, and the modeling accuracy. The review briefly describes the tooling and equipment for manufacturing upsized parts and large‐scale production. In addition, the article considers the tooling for FAST/SPS sintering under high pressure (up to 1 GPa) and ultra‐high pressure (over 1 GPa). The article concludes with an analysis of the challenges and prospectives for the smart design of FAST/SPS tooling.

Improved heating method for shape-memory alloy using carbon nanotube and silver paste

Shape memory alloys (SMAs) have a special ability to remember their initial shape and return from operating temperature. For this special ability, there are many studies in the field of smart wearables to replace rigid, heavy, and large electric actuators with SMAs that can be a fabrication. The usual operating method of the SMA is heating the SMA by direct Joule heating with electricity. Although direct Joule heating is fast and easy, there is overshooting, unstable, and high-power consumption. For these issues to use the SMA as textile actuators, this research suggested a heating method with silver paste required lower power consumption and coating the basic fabric with carbon nanotubes (CNTs) to support heating stability and heat uniformity. The heating method evaluated the efficiency of heat by comparing direct heating and silver layer heating and the uniformity of heat with the infrared images of whether CNTs coated or not. In this research, we reached higher temperatures with lower power than direct Joule heating using wearable heaters manufactured using silver paste. In addition, we confirmed that coating the basic fabric with carbon nanotubes reduce the temperature imbalance, and improved the heating stability. This research is expected that SMA will be used as a wearable actuator to help develop wearable devices that can move.

Electrified CO2 valorization driven by direct Joule heating of catalytic cellular substrates

The growing environmental concerns have driven catalytic CO2 valorization as a forward-looking solution to mitigate the carbon footprint of valuable chemical products. CO2 conversion processes into synthesis gas, such as CO2 reforming of methane (CRM) or reverse water–gas shift (RWGS), may have a strategic role for the future sustainable production of chemicals and energy carriers. However, fuel combustion to supply the heat of the associated endothermic reactions would result in unwanted CO2 emissions, frustrating the overall objective. Electrification of the endothermic processes may represent the technological solution to such an issue. Here we report a promising approach for the direct electrification of the CO2 reforming of methane (eCRM) and reverse water–gas shift (eRWGS) processes in washcoated structured reactors. We employ catalytically activated open-cell foams that provide optimal heat and mass transfer properties and serve as Joule heating substrates for the catalytic conversion of CO2 via reaction with methane or hydrogen. The proposed reactor system with Joule-heated Rh/Al2O3-coated foam exhibited excellent catalytic and electrical stability for more than 75 h, operating up to 800 °C and approaching equilibrium conversion at high space velocity, i.e., GHSV of 600 and 100 kNl/kgcat/h for eRWGS and eCRM, respectively. Such a reactor concept has potential to ensure remarkably low specific energy demand for CO2 valorization. Assuming an optimized process configuration approx. 0.7 kWh/Nm3CO2 is calculated for eRWGS. By replacing fuel combustion with Joule heating driven by renewable electricity, the electrified CO2 valorization processes provide an important approach for dealing with the intermittent nature of renewable sources by storing the energy in chemicals with a low carbon footprint.

Activated carbon supported nickel catalyst for selective CO2 hydrogenation to synthetic methane under contactless induction heating

The use of CO2 methanation in the power-to-gas (PtG) technology chains has received increasing attention in recent years for clean energy and sustainable development. In this work, macroscopic mesoporous nickel catalyst was prepared and evaluated for selective CO2 hydrogenation to CH4 using commercial activated carbon (AC) pellets. Catalyst samples were fully characterized by liquid N2 adsorption-desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), scanning and transmission electron microscopy (SEM/TEM). Catalytic performances were investigated under various reaction conditions with both direct induction heating (IH) and conventional indirect Joule heating (JH) modes. Results indicated that by simple thermal treatment, the surface and textural properties of the macroscopic carbon support could be greatly modified by improving the dispersion of metal sites and thus the catalytic performance. The advantages of IH combined with the inherent high thermal and electrical conductivity of the prepared materials could effectively avoid the temperature runaway and enhance the CO2 activation at relatively low reaction temperature. By comparison to the classical indirect JH mode, the resulting macroscopic nickel catalysts showed improving catalytic performances for CO2 methanation under IH mode. The efficient heat management under direct IH mode also prevented coke formation on the catalyst surface which contributes to its high stability as a function of time-on-stream.

Power Optimization of TiNiHf/Si Shape Memory Microactuators

We present a novel design approach for the power optimization of cantilever-based shape memory alloy (SMA)/Si bimorph microactuators as well as their microfabrication and in situ characterization. A major concern upon the miniaturization of SMA/Si bimorph microactuators in conventional double-beam cantilever designs is that direct Joule heating generates a large size-dependent temperature gradient along the length of the cantilevers, which significantly enhances the critical electrical power required to complete phase transformation. We demonstrate that this disadvantage can be mitigated by the finite element simulation-assisted design of additional folded beams in the perpendicular direction to the active cantilever beams, resulting in temperature homogenization. This approach is investigated for TiNiHf/Si microactuators with a film thickness ratio of 440 nm/2 µm, cantilever beam length of 75–100 µm and widths of 3–5 µm. Temperature-homogenized SMA/Si microactuators show a reduction in power consumption of up to 48% compared to the conventional double-beam cantilever design.

Evaluation of subcooled void fraction in downward flow under low mass flux condition by using neutron radiography

In downward flow, complex two-phase flow is caused by buoyancy of bubbles. It affects not only a void fraction profile but also a point of net vapor generation (PNVG). In order to understand the fundamental characteristics of the void fraction on subcooled boiling in downward flow, the void fraction was measured by using neutron radiography. The test sections were made of stainless steel tubes that had 400 mm in heated length with 10 and 15 mm in inner diameters. They were heated by direct Joule heating applying D.C. power. The void fraction characteristics were explained by dividing into three regions: i.e., a wall voidage region, a detached voidage region, and a bulk voidage region. PNVG was defined as the boundary between the detached voidage region and the bulk voidage region. In a downward flow, the thermal equilibrium quality at PNVG is smaller than in an upward flow. “Secondary PNVG” was also observed which was caused by the influence of a reverse flow of bubbles. A difference of thermal equilibrium quality between at primary PNVG and at secondary PNVG is lager in 15 mm in inner diameter than in 10 mm. The void fraction profile and PNVG characteristics in downward flow show dependence of inner diameter as well as mass flux. To demonstrate the void fraction profile involving with the influence of a reverse flow in a downward flow, an empirical void fraction correlation based on a drift-flux model with Lahey’s flow quality model was developed. This correlation well agreed with the experimental results.

NdFeB Magnets with Well‐Pronounced Anisotropic Magnetic Properties Made by Electric Current‐Assisted Sintering

Electric current‐assisted sintering (ECAS) technologies are highly promising for processing of NdFeB magnets. Due to the combination of direct Joule heating and application of external load, even powders, whose particle size distribution and morphology are not optimum for conventional powder processing like melt‐spun powders or magnet scrap, can be easily sintered to high densities. A systematic study is done to demonstrate the potential of field‐assisted sintering technique/spark plasma sintering (FAST/SPS) and flash spark plasma sintering (flash SPS) for sintering of NdFeB powders. Melt‐spun, commercial NdFeB powder (Magnequench MQU‐F) is used as starting material. Its platelet‐like shape makes this powder extremely difficult to sinter by conventional methods. This study clearly reveals that especially in the case of flash SPS application of external pressure in combination with short cycle times enables to achieve well‐pronounced anisotropic magnetic properties without the need of subsequent upset forging. Optimized flash SPS parameters are applied to NdFeB magnet scrap with broad particle size distribution, demonstrating the general potential of ECAS technologies for recycling of waste magnet materials. Finally, the results are benchmarked with respect to established NdFeB processing technologies and electrodischarge sintering (EDS), another promising ECAS technology with very short cycling time.

High-surface-area corundum nanoparticles by resistive hotspot-induced phase transformation

High-surface-area α-Al2O3 nanoparticles are used in high-strength ceramics and stable catalyst supports. The production of α-Al2O3 by phase transformation from γ-Al2O3 is hampered by a high activation energy barrier, which usually requires extended high-temperature annealing (~1500 K, > 10 h) and suffers from aggregation. Here, we report the synthesis of dehydrated α-Al2O3 nanoparticles (phase purity ~100%, particle size ~23 nm, surface area ~65 m2 g−1) by a pulsed direct current Joule heating of γ-Al2O3. The phase transformation is completed at a reduced bulk temperature and duration (~573 K, < 1 s) via an intermediate δʹ-Al2O3 phase. Numerical simulations reveal the resistive hotspot-induced local heating in the pulsed current process enables the rapid transformation. Theoretical calculations show the topotactic transition (from γ- to δʹ- to α-Al2O3) is driven by their surface energy differences. The α-Al2O3 nanoparticles are sintered to nanograined ceramics with hardness superior to commercial alumina and approaching that of sapphire.

Intermittent direct joule heating of membrane surface for seawater desalination by air gap membrane distillation

Air gap membrane distillation (AGMD) is a low-temperature separation process applied commonly to desalination of (hyper)saline feeds. The low energy efficiency of heating the bulk feed solution to drive vapor transport in MD must be addressed through novel materials and techniques. In this work, we introduce the concept of intermittent electrical heating at the membrane surface using electrically conductive carbon nanotube structure (CNS) films pressed on commercial polypropylene (PP) membranes. First, the Joule heating effect was optimized by varying the mass loading of the CNS layer between 1.4 and 4.2 mg cm −2 . The effect of mass loading on porosity, electrical properties and cross-sectional morphology of the CNS layer was also investigated. Electrical conductivity of CNS films increases with increasing CNS mass loading. A CNS loading of 1.4 mg cm −2 yielded the highest electrical resistance, which translated into higher Joule heat generation, and highest steady-state temperature in response to applied current. When an alternating current of 2 A was passed through the CNS films in air, the maximum surface temperature achieved was 184 °C, 126 °C and 100 °C at CNS loadings of 1.4 mg cm −2 , 2.8 mg cm −2 and 4.2 mg cm −2 , respectively. Maximum surface temperature and spatial temperature distribution of CNS films were verified using a steady-state thermal-electric simulation. CNS films exhibited rapid thermal cycling between on and off states, due to their low thermal mass, with low thermal time constants for both heating and cooling. CNS film with a loading of 1.4 mg cm −2 was then pressed onto a commercial PP membrane and applied to AGMD for seawater desalination, with the conductive layer in direct contact with the feed solution. Intermittent heating was carried out by passing a current of 2 A for 10 min at 20 min intervals, for 10 cycles. Feed outlet temperature increased by > 9 °C during each cycle, which improved average permeate flux by 78%. While specific thermal energy consumption increased by 34%, a 25% enhancement was found in GOR, indicative of higher thermal energy efficiency. We have demonstrated the effectiveness of intermittent membrane surface heating for simultaneous performance enhancement and improved energy efficiency for seawater desalination using MD. • Direct surface heating applied to lab-scale air gap membrane distillation system for seawater desalination. • Carbon nanotube nanostructures coated onto hydrophobic membrane to enable Joule heating. • Intermittent application of electrical field improves GOR by 25% and productivity by 78%. • Long-term application of high-grade electrical energy not required.

Electrified methane steam reforming on a washcoated SiSiC foam for low-carbon hydrogen production.

In view of largely available renewable electricity as a green future resource, here we report the electrification of a Rh/Al2O3 washcoated SiSiC foam for methane steam reforming (MSR). We show that, thanks to the suitable bulk resistivity of the SiSiC foam, its direct Joule heating up to relevant temperatures is feasible; the interconnected geometry greatly reduces heat and mass transfer limitations, which results in a highly active and energy efficient system for low-carbon H2 production. The foam-based electrified MSR (eMSR) system showed almost full methane conversion above 700°C and methane conversions approaching equilibrium were obtained in a range of conditions. Energy efficiency as high as 61% and specific power consumption as low as 2.0 kWh/ were measured at 650°C, at gas hourly space velocity (GHSV) of 150,000 cm3/h/gcat. When driven by renewable electricity, the proposed reactor configuration promises a high potential to address the decarbonization challenge in the near-term future.

Effect of Filler Aspect Ratio on Stiffness and Conductivity in Phase‐Changing Particulate Composites

AbstractVariable stiffness in elastomers can be achieved through the introduction of low melting point alloy particles, such as Field's metal (FM), enabling on‐demand switchable elasticity and anisotropy in response to thermal stimulus. Because the FM particles are thermally transitioned between solid and liquid phases, it is beneficial for the composite to be electrically conductive so the stiffness may be controlled via direct Joule heating. While FM is highly conductive, spherical particles contribute to a high percolation threshold. In this paper, it is shown that the percolation threshold of FM particulate composites can be reduced with increasing particles aspect ratio. Increasing the aspect ratio of phase‐changing fillers also increases the rigid‐to‐soft modulus ratio of the composite by raising the elastic modulus in the rigid state while preserving the low modulus in the soft state. The results indicate that lower quantities of high aspect ratio FM particles can be used to achieve both electrical conductivity and stiffness‐switching via a single solution and without introducing additional conductive fillers. This technique is applied to enable a highly stretchable, variable stiffness, and electrically conductive composite, which, when patterned around an inflatable actuator, allows for adaptable trajectories via selective softening of the surface materials.

Renewable and Electroactive Biomass-Derived Tubes for CO2 Capture in Agroindustrial Processes

Tube-shaped renewable carbon materials were developed to work as separation agents for CO2 capture in agroindustrial and intensive farming facilities. The tubes have electrical properties and moderate CO2 adsorption capacities. These materials can be heated directly through the Joule effect by applying an electric potential between the ends and thus reaching temperatures higher than 473 K in a few seconds with an applied voltage of near 10 V. The tube’s temperature can be easily controlled by manipulating the applied voltage, which is of interest for the development and design of CO2 capture processes through electric swing adsorption. The tubular form of the material also provides the alternative to be filled up with adsorbents like zeolite and metal–organic frameworks to produce highly selective structured adsorbents based on renewable carbon materials with the advantage of providing direct Joule heating. These materials were studied as separation agents to be part of cycles like vacuum swing adsorption, electric swing adsorption, and both combined. The tubes were tested through consecutive and repeated adsorption and Joule heating desorption experiments. The dynamics of the tube’s temperature and the CO2 gas-phase composition showed consistency and repeatability. The results revealed the robustness and reliability of the biomass-derived tubes to work as separation agents for CO2 capture.

Instantaneous nanowelding of ultra‐high temperature ceramics for hypersonics

AbstractUltra‐high temperature ceramics (UHTCs) are a group of advanced ceramic materials that possess excellent high temperature capabilities, which make them especially suitable for extreme environment engineering applications. As an effective assembling method, joining is frequently required for fabricating sophisticated structures for such applications due to the excessive challenges and costs in producing near‐net shapes. Here, we introduce a promising new joining technique to effectively join UHTCs called Instantaneous Nanowelding, which uses direct electric current assisted rapid Joule heating to instantaneously bond hafnium diboride (HfB2) to zirconium diboride (ZrB2) in 1 s down to atomic scale. Our approach is analogous to high temperature spot welding, and the entire process is complete in 10 min, and the instant diffusion occurs in 1 s. Seamless HfB2/ZrB2 interfaces are formed at 1750 for a duration of 1 s. A series of characterizations are done at the interfaces using techniques including SEM, WDS, EBSD, and S/TEM to observe ZrxHf1−xB2 solid solution formation. Highly coherent transition with perfect lattice alignment at atomic scale from ZrB2 to HfB2 is observed using S/TEM, meaning that the two materials are brought to atomic contact.

Direct Joule Heating as a Means to Efficiently and Homogeneously Heat Thermoplastic Prepregs

Although direct Joule heating is a known technique for heating carbon fiber reinforced plastics, it is a yet unexplored heating method for thermoplastic prepregs before back-injection molding. The knowledge obtained from resistance welding, for example, is not directly transferable because of considerably higher heated volumes and more complex shapes. In this study, the governing parameters and process limits are established for this method. The influences of the contacting, the materials used, and the size of the heated part are investigated with respect to the part temperature and heating efficiency. The findings show that the quality of heating is determined by the shape and size of the electrodes. Larger electrodes lead to a more homogeneous temperature distribution. Parts based on woven fabric can be heated more homogeneously because of the existence of intersections between rovings, generating contact between fibers. An increase in part width results in uneven heating behavior.

Correlation of electrical and magnetic properties of Co-rich amorphous ferromagnetic microwires after DC Joule heating treatment

The present work describes the investigation of electrical and magnetic properties of the glass-coated Co-rich amorphous ferromagnetic microwires, having typical metallic core diameters d = 13–20 μm and tailoring by the direct current Joule heating. During this treatment, a continuous monitoring of the microwire condition was carried out, measuring its resistance by means of a DC bridge circuit. The heating of the microwire sample was provided by a direct current in the range from 20 mA to 63 mA. In this heating currents range, the microwires show a slight change in their resistivity. After annealing the resistivity of microwires may increase of about 1% with respect to as-prepared one. Depends on the heating current, the hysteresis loops of annealed microwires demonstrated the transition from a quasi linear type to a bistable one and vice versa. The maximum of the giant magnetic impedance ratio was observed in such microwires, which had a hysteresis loops describable by a near-zero anisotropy field.

Analysis of actuation characteristics of CuAlNiMn/Polyimide thin film shape memory alloy

The article presents the study of the deformation of an SMA bimorph actuator during static heating. The thermomechanical behavior of thin film CuAlNiMn shape memory alloy (SMA) on polyimide substrate is analyzed using finite element method. The analysis is carried out for three different geometries to obtain the displacement when temperature is varied. The actuation characteristics of the SMA bimorph are studied through direct heating and joule heating techniques. The surface morphology and composition of the bimorph sample are obtained using the Scanning Electron Microscope (SEM). The numerical analysis of the thermomechanical behavior of a thin film CuAlNiMn SMA bimorph is carried out using the finite element method. The procedure is applied for a double-legged cantilever configuration of the bimorph to obtain the actuation in terms of displacement; by varying the temperature. The same is repeated for semi-circular and pentagon shapes of the bimorph to obtain the influence of area on the displacement. It is observed that SMA bimorph displaces with the rise in temperature and the magnitude of displacement increases with the increase in surface area of different geometries. The physical actuation characteristic of CuAlNiMn-polyamide bimorph is studied by thermal heating and electrical heating of the sample, which confirm the shape memory effect of the SMA and provide the displacement characteristics of the bimorph when applying an electrical current.

Soft magnetic amorphous alloys in X-ray light: Insights from ultra-fast Joule heating experiments

In this contribution a novel setup for studying rapid crystallization of metallic glasses using a time resolved in situ X-ray diffraction combined with a direct current fast Joule heating (flash-annealing) is presented. The setup was implemented and successfully tested at the P02.1 beamline of the PETRA III storage ring (DESY Hamburg, Germany). Its potential use is demonstrated by studying rapid crystallization of soft magnetic Fe73.5Cu1Nb3Si15.5B7 (at.%) metallic glass prepared by melt spinning technique. Flash-annealing experiment is realized by bursting 20 rectangular current pulses with a fixed amplitude of 1.5 A and pulse length δ is varied (30, 40 and 50 ms). A single pulse with duration of 30 ms causes temperature to rise to 770 °C with an average heating rate of 4200 K/s. Phase composition of crystallized material consist of major Fe3Si phase and small traces of boride phase Fe23B6. Consecutive pulses result in cyclic thermal expansion of a crystal lattice, which appears fully reversible. Increasing pulse width to 50 ms causes temperature to increase up to 1020 °C with an average heating rate of 5600 K/s. Differentiation of the temperature profile yields exceptionally high value of heating rate 10800 ± 2400 K/s.