High Heating Rates Research Articles

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.

Advanced Fitting Method for the Kinetic Analysis of Thermogravimetric Data.

The article considered the solution of the inverse problem of chemical kinetics of the analysis of experimental data of a thermogravimetric experiment at a constant sample heating rate. The fitting method for identifying the parameters of a kinetic triplet using the integral method for a model of a solid-state reaction based on the modified Arrhenius equation is described. The effectiveness of the proposed approach was confirmed by solving test cases for low, medium, and high rates of material conversion. Unlike other methods, setting the parameters of the reaction mechanism is not required, as they are determined by the solution. Solutions for real data of TGA studies with high and low sample heating rates were compared with the results obtained by other authors and experimental data. A description of the full cycle of calculations used to identify kinetic parameters from thermogravimetric experimental data is given, from the derivation of calculated relationships to the implementation of a short (three to five formulas) program code for MS Excel spreadsheets. The presented code is easy to verify and reproduce and can be modified to solve various problems.

Molecular dynamics simulation of converting waste polyethylene (PE) to chemicals and fuels under non-isothermal and isothermal conditions

Pyrolysis, one method of chemical recycling, has been an effective and clean way for processing plastic solid waste (PSW), which is a heavy burden for sustainable development. Series of molecular dynamic simulations are carried out for detailed pyrolysis of polyethylene (PE) waste using reactive force field (ReaxFF) for both non-isothermal and isothermal conditions. The results show that the PE pyrolysis at non-isothermal conditions can be divided into four stages. The last stage (post pyrolysis) is analyzed in depth, which shows decreasing of short-chain products and increasing of relatively long-chain components at high temperatures. Pyrolysis of PE at high heating rates reduces oil cracking and results in high yield of oil. The effect of reaction time depends on the pyrolysis temperature. In addition, under isothermal pyrolysis conditions, the simulated temperature range of 2500–2750 K is optimal for more recovery of C2H4 and C3H6 due to its high yield and mild influence of reaction time. Finally, detailed mechanisms of generation and consumption of C2H4 and C3H6 of PE pyrolysis are demonstrated. The regeneration of long-chain oil in the late stage of PE pyrolysis and the corresponding mechanisms are illustrated. The results in this study can be used to guide the design of systems for PSW processing with recovery of chemicals and fuels.

Introduction of a constitutive material model considering variable carbon content for cutting simulation

Carbon steels show complex strain hardening and dynamic strain aging effects under high plastic strains, high strain rates, high temperatures and high heating rates, and thus a sufficiently complex constitutive model is needed to capture this behavior. Carbon content in such steels (e.g., AISI 1018, 1045, 1075) influences strength and hardening as well. A recently-developed material model for 1045 steels was therefore modified to capture the effect of carbon content on the material response. The model can also capture time-dependent plastic response associated with interrupted austenite transformation under short (sub-second) heating times, for the simulation of machining operations.

A new high temperature, high heating rate, low axial gradient capillary heater

A new heater design, capable of fast heating and cooling to and from >1000°C, has been developed at the Swiss-Norwegian Beamlines, European Synchrotron Radiation Facility, France. The design uses a SiC head to distribute heat, and resistive Si3N4 heat cartridges to provide heat.

The selective heating effect of microwave irradiation on a binary mixture of water and polyethylene oxide: a molecular dynamics simulation approach.

In this study, we investigate the molecular mechanisms of a microwave-driven selective heating process by performing molecular dynamics simulations for three different systems including pure water, pure polyethylene oxide (PEO), and water-PEO mixed systems in the presence of a microwave with two different intensities of electric field such as 0.001 V Å-1 and 0.01 V Å-1 at a frequency of 100 GHz. First, from performing molecular dynamics simulations of CO and CO2 in the presence of the microwave, it is confirmed that the molecular dipole moment is responsible for the rotational motion induced by the oscillating electric field. Second, by analyzing the MD simulations of the pure water system, we discover that the dipole moment of water exhibits a time lag with respect to the microwave. During the heating process, however, the temperature, kinetic, and potential energies increase synchronously with the oscillating electric field of the microwave, showing that the heating of the water system is caused by the molecular reaction of water to the microwave. Comparing the water-PEO mixed system to the pure water and pure PEO systems, the water-PEO mixed system has a higher heating rate than the pure PEO system but a lower heating rate than the pure water system. Therefore, we conclude that heating the water-PEO mixed system is driven by water molecules selectively activated by microwave irradiation. We also calculate the diffusion coefficients of water molecules and PEO chains by describing their mean square displacements, demonstrating that the diffusion coefficients are increased in the presence of microwaves for both water and PEO in pure and mixed systems. Lastly, during the microwave heating process, the structures of the water-PEO mixed system are altered as a function of the intensity of electric field, which is mainly driven by the response of water molecules.

Thermogravimetric analysis of face mask waste: Kinetic analysis via iso-conversional methods

The surge of face mask waste in response to the global pandemic has proven to be a liability to the environment. Microfibers from plastic constituents of the face mask would cause microplastic pollution in the water bodies. Fortunately, these waste could be converted into renewable source of energy via thermochemical method, i.e. pyrolysis. However, the studies on the thermal decomposition of face masks and their kinetic mechanisms are not well-established. The aim of this paper focuses on the prospects of pyrolysis at low to high heating rates ranging from 10 °C min -1 to 100 °C min -1 , to cater for the slow pyrolysis and fast pyrolysis modes. Following this, the thermal degradation behaviour of the face mask waste was studied via thermogravimetric analysis which determined the single peak temperature degradation range at 218 to 424 °C at 10 °C min -1 , and maximum degradation rate was determined at 172.51 wt.% min -1 at 520 °C, with heating rate of 100 °C min -1 . Flynn-Wall-Ozawa (FWO) and Starink method was employed to determine the average activation energy and average pre-exponential factor of the pyrolysis process of face mask waste. i.e., 41.31 kJ mol -1 and 0.9965, 10.43 kJ mol -1 and 0.9901 for FWO and Starink method, respectively.

Formation mechanisms of Ti 3(Si,Al)C 2/Al 2O 3 composites from Ti 3AlC 2 and SiO via low-temperature sintering

Ti₃SiC₂/Al₂O₃ composites have attracted attention due to their excellent mechanical and electromagnetic properties, but the high temperatures (≥ 1400 ℃) required for the densification of aluminum oxide (Al₂O₃) leads to the decomposition of Ti₃SiC₂. To address this issue, Ti₃(Si_<i>x</i>Al_1−<i>x</i>)C₂/Al₂O₃ (<i>x</i> represents the Si content) composites were synthesized for the first time via hot-pressing (HP) sintering and current-assisted sintering (CAS) of mixed Ti₃AlC₂ and silicon monoxide (SiO) powders at 1300 and 1200 ℃, respectively. Both approaches produced composites with <i>x</i> values greater than 0.9, indicating that the compositions of the prepared composites were similar to those of Ti₃SiC₂/Al₂O₃ composites. The synthetic mechanism involved substitution and continuous interdiffusion of Al and Si atoms. The composite prepared by CAS at 1200 ℃ was compacted, whereas the composite prepared by HP had a low density. The low-temperature densification mechanism is attributed to the combined effects of amorphous SiO, liquid Al, and the high heating rates for CAS. The flexural strength and hardness of the composite prepared by CAS were also comparable to those of compacted Ti₃SiC₂/Al₂O₃ composites.