High Heating Rates Research Articles

Fast self-preheating system and energy conversion model for lithium-ion batteries under low-temperature conditions

Low temperature is one of the major drawbacks of electric cars in high latitudes. This problem can be addressed using a battery self-preheating system. The existing self-heating systems have problems, such as slow heating rate, complex control system, single thermal management function and poor safety. Herein, we propose a conductive phase change material (cPCM)-based self-preheating system that generates heat simultaneously using the internal resistance of cells and external resistance of the cPCM. This self-preheating system shows a high heating rate of 17.14 °C/min and excellent temperature uniformity (temperature difference of 3.58 °C). The system can preheat the battery safely in the capacity range of 20%–100%. When the battery pack is set in −20 °C, the effective electric energy can be increased by 550% after preheating. An energy conversion model is also built to measure the relationship between the energy improvement of battery and the energy consumption by preheating. This energy conversion model can help the system to make the optimal preheating strategy and obtain the maximum discharge energy. Nevertheless, based on the outcome of this study, this self-preheating strategy can effectively solve the problem of battery in low temperatures and maximize the effective electric energy of the battery.

On the confluence of ultrafast high‐temperature sintering and flash sintering phenomena

AbstractUltrafast high‐temperature sintering (UHS) and flash sintering are novel methods for rapid sintering of ceramics, often completed in just a few seconds. Here, we show that both also share two additional features: an abrupt rise in electrical conductivity, which is electronic, and electroluminescence. More fundamentally, both are related to phonon physics where MD calculations have shown that proliferation of phonons at the edge of the Brillouin zone can induce Frenkel pairs without the application of electrical fields. Here, we show that, indeed, heating without the application of electric field, can also induce flash: Rapid heating processes of thin films of an oxide‐salt deposited on silk fibers, with a propane torch, are shown to induce electronic conductivity, electroluminescence, and rapid sintering of the oxide. The discussion in this article harkens back to two inventions, more than a century ago, which can now be related to flash and UHS: (i) the Nernst glow lamp circa 1900, made from zirconia, and (ii) the Welsbach mantle, constituted from ceria doped thorium oxide, in the late nineteenth century. Thus, the confluence between high heating rate and electric field induced flash phenomena links the past to the new. The emerging question is how injection of phonons that has been shown to create Frenkels can further induce high electronic conductivity and electroluminescence in oxides. Both electronic conductivity and luminescence are likely related to the generation of electron–hole pairs.

Synthesis and Properties of Silicon Carbide (Review)

Silicon carbide is an extremely hard material that exhibits exceptional corrosion resistance as well as thermal shock resistance. Its high mechanical properties determine the increased performance of materials based on it. The combination of high thermal conductivity and low thermal expansion coefficient determines the stability of silicon carbide at high heating rates and under stationary thermal conditions. To date, significant progress has been made in the development of methods for the synthesis of various materials based on silicon carbide. The main synthesis methods that scientists use in their research are the sol-gel method, sintering, pyrolysis, microwave synthesis, chemical vapor deposition, etc. The use of "green" techniques in the synthesis of SiC has gained wide popularity due to environmental friendliness, renewability, and ease of implementation. This review analyzes modern research in the field of silicon carbide synthesis published in peer-reviewed professional journals.

Novel solid-state calcium carbide synthesis from calcium oxide and walnut shell char by in-situ induction heating

Calcium carbide (CaC2) is a platform chemical to synthesize many polymers. It has been produced in industry by reacting CaO with coal derived coke in electrical arc furnaces for more than a century at temperatures higher than 2000 °C to ensure the formation of CaC2-CaO eutectics at the furnace bottom, which completes the electrical arc circuit but inevitably limits the molten product discharge to a periodical mode. Here we report new observations that under electromagnetic induction of 400 kHz, walnut shell char can be rapidly heated to high temperatures and so be the pellets containing CaO and walnut shell char (CaO-C) prepared from pyrolysis of calcium hydroxide and walnut shell. For the induction heating (IH) of the char to take place the threshold temperature of pyrolysis is around 800 °C and threshold CaO-C pellet size is Φ12 × 12 mm. The pellets with the stoichiometric C/Ca molar ratio of 3 or higher yield solid-state CaC2 under IH. A higher C/Ca ratio results in a higher heating rate, a higher maximum temperature, and a higher CaC2 yield. A CaC2 yield (CaO based) of 99.6% is obtained in 10 min for pellets with a C/Ca ratio of 10, a size of Φ15 × 15 mm and the maximum pellet temperature of higher than 1726 °C.

Fast pyrolysis of pulverized coal at high temperatures and fuel nitrogen migration characteristics in a wire mesh reactor

ABSTRACT Pulverized coal (PC) pyrolysis is an indispensable process for coal thermal conversion and utilization. The transformation of fuel-N into fast pyrolysis is a basis for the investigation of nitrogen migration in coal combustion. In this paper, a wire mesh reactor was used to study the initial decomposition processes and to reveal the final pyrolysis yield and composition distribution during the fast pyrolysis process. Furthermore, the initial pyrolysis characteristics of PC with different ash contents were presented and compared. The results showed that both Huangling coal (with higher volatile) and Wuhai coal (with higher ash content) showed a similar trend, and the pyrolysis ratio increased with the increased pyrolysis final temperature. The pyrolysis ratio at the high heating rate was estimated to exceed that at the low heating rate by 2%–10%. With the temperature increased, the char-N yield decreased first and then tended to be stable, and most of nitrogen remained in the char (more than 55%). An increase in heating rate made the pyrolysis zone to shift toward higher temperature, and it enhanced the yields of volatile and tar as well as the proportion of tar in volatile. Besides, the heating rate increased from 10°C·s−1 to 1500°C·s−1, the yield of tar-N increased from 4% to 14% and gas-N decreased from 28% to 19%. Overall, NH3 yielded was higher than HCN, which became more apparent at high heating rates. The content of the N-6 was positively related to the coal pyrolysis ratio.

Electrical-to-thermal energy conversion efficiency of conductive concrete

New cement-based materials designed with advanced electrical and thermal properties could allow for effective electrical to thermal energy conversion, empowering novel energy related functionalities in sustainable concrete construction. In this study, the electrical-to-thermal energy conversion ability of mortars reinforced with carbon nanotubes (CNTs) and nanofibers (CNFs) was evaluated by adjusting their conductivity and energy storage properties, as prior assessment has been limited to the evaluation of the temperature rise and/or heating rate. It was found that the degree of CNT and CNF dispersion, high values of electrical and thermal conductivity, and negligible values of electrical and thermal storage capacity are critical in achieving an almost complete conversion of electrical to thermal energy, reaching electrothermal efficiency as high as 99.4%. The optimization of the electrothermal efficiency of mortars reinforced with low amounts of uniformly dispersed CNTs and CNFs, resulted in high heating rates under the application of AC voltages as low as 2V. This low voltage ensures negligible potential for cracking and damage due to thermal shock.

Engineering austenite/martensite mesostructured materials by controlled localised laser treatments in a Fe–Ni–C alloy

Localised laser treatments enable the creation of sophisticated austenite/martensite mesostructures in Fe–Ni–C steel with the potential of achieving enhanced mechanical performance. The control of phase topology is essential to modify the properties of these structures on demand and requires a profound understanding of the effect of the processing parameters on the development of the different phases upon the application of laser treatment. In this work, the microstructure evolution under exceptional gradients in temperature and heating rates is thoroughly investigated. The extent of the laser-affected zone and the heat input were tailored by varying laser parameters and specimen thickness, based on a model that considers transient material properties and the coupling between temperature and microstructure. The predicted temperature fields resulted in a complex interplay between martensite to austenite phase transformation and martensite tempering. Considering the high heating rates of up to 25000 K/s and the observed microstructures, it is suggested that austenite was formed by a pseudo-displacive mechanism and subsequently fully recrystallised in the zones most directly affected by the laser heat source. A smooth strength transition from austenite to martensite, affected by the laser parameters, could be exploited for more effective deformation mechanisms and improved material mechanical properties.

A Novel Approach to Analysis of Complex Crystallization Behavior in Zr-Based Bulk Metallic Glass by Non-isothermal Kinetics Studies

The complex crystallization behavior of the Zr40Ti15Cu10Ni10Be25 bulk metallic glass (BMG) produced by suction-casting method was studied with the non-isothermal DSC measurements with the heating rate from 5 to 40 K/min. Three exothermic phenomena were observed for the investigated material. The novel evaluation procedure for qualitative and quantitative analysis of intricate crystallization kinetics for Zr-based BMGs is proposed. The unusual deconvolution of the DSC curves based on a Gaussian function and a two-phase exponential decay function allowed for separate, detailed analysis of overlapped peaks. The activation energies for each crystallization stage were studied based on overall (Kissinger) and local (Kissinger–Akahira–Sunose) procedures. The KAS method applied separately for both low and high heating rates showed a significant difference in local activation energies. Finally, the local Avrami exponent evaluation revealed that the first two stages of crystallization are diffusion-controlled with mainly increasing nucleation rate, whereas the third crystallization is more growth-dominated.

Fast pyrolysis behaviors of biomass with high contents of ash and nitrogen using TG-FTIR and Py-GC/MS

In order to examine the effective exploitation of high ash and high nitrogen content biomass, the fast pyrolysis behavior of mushroom bran (MB) and corn straw (CS) was studied utilizing high heating rate TG-FTIR and Py-GC/MS. TG was used to study the pyrolysis behavior of MB and CS under low and high heating rates followed by a seven-stage pyrolysis studies using Py-GC/MS. The results showed that at higher heating rates, there is an overlap of the decomposition of starch and hemicellulose, potentially leading to synergistic effects that would promote the formation of furan and furfural. At heating rates greater than 200 °C/min, nitrogen has a tendency to migrate from hydrogen cyanide to NH3 before 450 °C. Deoxidation and denitrification mainly occurred between the pyrolysis temperature range of 300 °C to 350 °C, which merits further research. Staged pyrolysis interrupts the oil's continuous deoxidation process in comparison to direct pyrolysis, and it reduces the selectivity of aldehydes and ketones in MB and CS pyrolysis by 12.57% and 12.25%, respectively. More importantly, the study of staged pyrolysis in this work provides detailed pyrolysis characteristics for high nitrogen and ash content biomass, allowing for a better understanding of the pyrolysis behavior of such biomass.

Experimental investigation of variable fin length on melting performance in a rectangular enclosure containing phase change material

The present study proposes a new technique to determine liquid fractions of phase change material during the melting process in a left-side heated rectangular enclosure. The effects of variable fin length arrangements on the melting performance of phase change material (PCM) were also investigated experimentally. Detailed information about solid, mushy, and liquid ratios was obtained by analysing the temperature histograms of real thermal images of the melting zone. In accordance with the nature of the melting, the use of variable-length fins shortens the melting time by 14.9% compared to the equal-length fin arrangement. Similarly, variable-length fins reduce the average temperature of the latent heat thermal energy storage (LHTES) by around 10 °C compared to the equal-length fin arrangement. The use of variable length fin arrangements ensures a more homogeneous melting process within the LHTES. The fin arrangement evenly distributed to the entire heating source is more effective at low heating rates. In contrast, fin arrangements evenly distributed over the lower half of the heating source are more efficient at high heating rates.

Evaluating the bushfire resistance of a safe room using full-scale experiments

To minimise the psychological and physiological impairment due to bushfire losses, safe rooms are identified as one of the last resort solutions. This paper proposes a safe room built with cavity insulated light gauge steel framed walls and roof lined externally with Autoclaved Aerated Concrete panels and internally with fire-rated gypsum plasterboards. Full-scale experiments of the proposed safe room were conducted at an outdoor fire testing facility to investigate its bushfire resistance under flame zone conditions. A two-source bushfire exposure was simulated to replicate an approaching bushfire and a nearby building fire. Internal and external air temperatures, surface temperatures along and across the wall and roof surfaces, heat flux, wind speed and direction were recorded to evaluate the performance of the safe room. The safe room performed well with respect to heat transfer, exhibiting a significant safety margin for 67 min duration. The external building envelope exhibited good thermal shock resistance despite the high heating rate in bushfires compared to building fires. The study was further extended to investigate the performance of the safe room under repeated bushfire exposures where the safe room exhibited similar fire resistance. The results of this study reveal that a safe room solution is feasible and will survive extreme bushfire conditions.

Temperature consistency–oriented rapid heating strategy combining pulsed operation and external thermal management for lithium-ion batteries

The poor performance of lithium-ion batteries (LIBs) at low temperatures restricts their application in electric vehicles (EVs), and existing preheating methods might lead to insufficient temperature consistency and heating rates. This study proposes an innovative method that integrates pulsed operation and external liquid circulation to heat LIBs. Experiments are performed on a LIB module under different conditions; key parameters of the proposed method are regarded as indexes to evaluate its heating effect. Furthermore, its temperature consistency is studied by both experiments and simulations. In particular, inconsistencies of the state of charge (SOC) and internal resistance among cells, and the heat preservation are examined by experiments. Among all parameters, the cooling plate layout and coolant temperature are key factors. Under inconsistent conditions, the increase in the temperature difference is less than 2 °C, even when the internal resistance of peripheral cells is 50% higher than that of other cells. For on-board applications with better heat preservation, the temperature difference can be maintained within 1 °C during heating from − 20 °C to 6 °C in 300 s, and the temperature consistency is 11 times better than that of pulsed heating only. Overall, the proposed combined heating method achieves high heating rates while ensuring excellent temperature consistency and robust performance for practical applications of EV packs. It offers significant prospects in addressing the cell degradation and potential safety hazards of LIBs at low temperatures.

The impact of flash sintering on densification and plasticity of strontium titanate: High heating rates, dislocation nucleation and plastic flow

Flash sintering involves very rapid densification of ceramic powder compacts during a thermal runaway induced by an applied voltage and current. The mechanisms of fast densification are still not well-understood. The present study investigates the impact of high heating rates during flash sintering on densification, dislocation density and plasticity of SrTiO3. After flash sintering, a high dislocation density of almost 1014 m−2 was observed by TEM. Uniaxial compression at 1150 °C revealed very high deformation rates. It is argued that for SrTiO3, dislocations are generated and migrate during flash sintering. This becomes possible by the very high heating rates, which conserve high driving forces for sintering up to high temperatures. High driving forces of several 10 MPa are preserved up to high temperatures. Thus, the sintering stress can be above the flow stress of SrTiO3 (5 MPa), and the nucleation of dislocations occurs, paving the path for plastic flow.

Preparation, Characterization and Experimental Investigation of the Separation Performance of a Novel CaO‐based CO2 Sorbent for Direct Air Capture

AbstractThe capture of CO2 from air via direct air capture (DAC) is a promising way to reduce the carbon dioxide concentration in the atmosphere. The carbonation of calcium‐based adsorbents using ambient conditions is particularly interesting for DAC due to its high theoretical CO2 uptake capacity and its low cost. In this paper, a new preparation method of synthetic calcium oxide‐based pellets for a DAC process was investigated. Their CO2 capture performance was studied experimentally in a fixed‐bed column and characterization was performed via Brunauer‐Emmett‐Teller (BET) analysis, mercury porosimetry, X‐ray diffraction, and scanning electron microscopy. Higher heating rates during the precursor calcination process and higher relative humidities during the carbonation process were found to lead to higher CO2 capture efficiencies. All prepared pellets showed good mechanical stability.

The Stability of Dense Oceanic Crust Near the Core‐Mantle Boundary

AbstractThe large low‐shear‐velocity provinces (LLSVPs) are thought to be thermo‐chemical in nature, with recycled oceanic crust (OC) being a contender for the source of the chemical heterogeneity. The melting process which forms OC concentrates heat producing elements (HPEs) within it which, over time, may cause any collected piles of OC to destabilize, limiting their suitability to explain LLSVPs. Despite this, most geodynamic studies which include recycling of OC consider only homogeneous heating rates. We perform a suite of spherical, three‐dimensional mantle convection simulations to investigate how buoyancy number, geochemical model and heating model affects the ability of recycled OC to accumulate at the core‐mantle boundary. Our results agree with others that only a narrow range of buoyancy numbers allow OC to form piles in the lower mantle which remain stable to present day. We demonstrate that heterogeneous radiogenic heating causes piles to destabilize more readily, reducing present day CMB coverage from 63% to 47%. Consequently, the choice of geochemical model can influence pile formation. Geochemical models which lead to high internal heating rates can cause more rapid replenishment of piles, increasing their longevity. Where piles do remain to present day, first order comparisons suggest that old (hot) OC material can produce seismic characteristics, such as Vs anomalies, similar to those of LLSVPs. Given the range of current density estimates for lower mantle mineral phases, subducted OC remains a contender for the chemical component of thermo‐chemical LLSVPs.

Catalytic Cleavage of the Dative Bond of Ammonia Borane by Polymeric Carbonyl Groups for Enhanced Energy Generation

Dissociation of the dative (B–N) bond of ammonia borane (NH3BH3/AB) is essential to prevent its thermochemical oligomerization to chemically resistant BNHx compounds, for its applicability as a fuel in high-energy propulsion systems. We show that when AB is incorporated into polymer matrices containing carbonyl functional groups, thermal activation causes the carbonyl groups to engage in nucleophilic interactions with AB. Such interactions catalyze the lysis of the dative B–N bond resulting in the decomposition of AB to NH3 and B2H6 gases, with no evidence of oligomerization. We find that the carbonyl groups function as catalysts and do not participate in any net reaction. In situ high-heating rate (∼105 K/s) characterizations demonstrate that facile-synthesized hierarchical (micro/nano) composite particles of AB/carbonyl-based polymers completely gasify to NH3 and B2H6 at ∼510 K, followed by spontaneous ignition in the air with negligible delay. Thus, the current chemical pathway enables the solid-state storage of reactive fuels, NH3 and B2H6, and their controlled on-demand release for high-energy applications.

Magnesium-Enhanced Reactivity of Boron Particles: Role of Mg/B2O3 Exothermic Surface Reactions

Boron offers great promise as a candidate fuel in high-energy composites as a result of its high gravimetric and volumetric energy content; however, its oxidation rate is limited by sluggish diffusion of reactive species across its low-melting oxide shell. On the other hand, Mg nanoparticles (NPs) have been shown recently to undergo fast oxidation following rapid vaporization (∼100 μs at high heating rates of ∼105 °C/s). This release of vapor-phase Mg can potentially be exploited to react exothermically (ΔHr = −420 kJ/mol) with the B2O3 layer of boron, inducing surface disrputions and promoting its combustion. In this paper, we explore this effect by evaluating Mg NPs as additive fuel to B/CuO nanoenergetic composites. We observe that incorporating Mg as an additive fuel in B/CuO composites results in a ∼6-fold enhancement in reactivity with a ∼60% reduction in burn time. Through thermal and reaction product analysis along with high-speed time-of-flight mass spectrometry (T-jump/TOFMS) and ignition characterization, we investigate the reaction mechanism of Mg/B2O3 particles as a simulant system for the interaction of Mg with the B2O3 shell of boron. These characterizations reveal that exothermic heterogeneous reactions occur between vapor-phase Mg and the molten B2O3 shell of boron at ∼500–650 °C. The role of these exothermic surface reactions in inducing surface modifications and reactivity enhancement of boron particles is discussed.

Experimental and numerical simulation study on thermal decomposition model of ammonium nitrate

High heating rates is one typical character under fire scenario and thermal decomposition behavior of ammonium nitrate (AN) under high heating rates is still unclear. In the current study, a thermal decomposition model of AN was developed to predict thermal decomposition process under high heating rates by a numerical simulation solver Thermakin2Ds based on experimental results. To be more specific, average apparent activation energy and pre-exponential factor were calculated as 75.16 kJ/mol and 3.6×103 s−1 respectively according to simultaneous thermal analyzer (STA) experimental results. Thermal decomposition products were determined as H2O, N2O, NO2, and HNO3 by thermogravimetric-Fourier transform infrared spectrometer (TG-FTIR) experiments. The obtained information was utilized for modelling and determining the most reliable thermal decomposition numerical model of AN. The simulated mass loss and mass loss rate at 10 K/min by the model were accordance with experimental data. The prediction ability was verified at heating rates of 5, 16, 25 K/min. Finally, thermal decomposition processes at higher heating rates of 100, 125, 150, and 200 K/min were predicted. This work is significantly meaningful for the storage safety of AN, providing theoretical guidance for preventing the occurrence of AN explosion from the early fire stage.

Studies on Ablative Performance of Silicone Low-Density Ablative Material

In the present studies, silicon based low-density ablative material has been studied for its ablative performance to protect flight hardware from temperature raises due to aerodynamic forces for a longer duration. The oxyacetylene flame test estimates ablative properties at 100–120 W/m2 heat flux. The time duration for the flame test is taken 200 s. The material shows low mass and linear ablation rate with high ablative effectiveness. The degradation kinetics of silicon ablator is studied by Thermo Gravimetric Analysis (TGA) method. Non-isothermal TGA is performed in the temperature range of 30 °C to 900 °C at various heating rates, viz. 5, 10, 15, and 20 °C/ min. Knowledge of the kinetic parameters of thermal decomposition is used to predict the degradation kinetics of the material at high heating rates, which the ablator faces during aerospace applications. During ablation, the silicone ablative material consists of a virgin zone, reaction zone, and char zone. These are explained by kinetic parameters determined with the help of free software called Kinetic Calculation.

Joining of dissimilar bulk metallic glasses with non-common supercooled liquid regions

We first successfully joined dissimilar bulk metallic glasses with non-common supercooled liquid regions via pulse current and obtained an amorphous structure joint, which exhibits an excellent tensile shear strength of ∼ 1.7 GPa. The joining process is derived from the Lasocka equation that the glass transition temperature and crystallization temperature of bulk metallic glasses increase with the heating rate, and the supercooled liquid region shifts toward the high-temperature region simultaneously. The difference in heating rate dependence of glass transition temperature and crystallization temperature of dissimilar bulk metallic glasses can be amplified at high heating rates and overlap the originally non-overlapped supercooled liquid phase region simultaneously. Especially, a new parameter K was introduced to screen the composition combinations of dissimilar bulk metallic glasses for this method. This method is a promising candidate for scaling up metallic glass sizes, realizing the successful joining of dissimilar BMGs, and providing a new idea for manufacturing amorphous alloy components with complex performance requirements.