Fast Heating Rate Research Articles

Microstructure Evolution of Nanosecond Laser Annealed Si/Si1-XGex/Si Structures

Si1-xGex has a liquidus temperature lower than the melting point of Si [1], and the liquidus temperature decrease with the Ge concentration. Here, we investigate the possibility of selectively melting a buried Si1-xGex layer in Si during annealing. However, as Si and Ge are miscible over the entire composition range [2], Ge can diffuse into the Si matrix before such melting occurs. To avoid this effect, we used a nanosecond Laser Annealing (nLA) which allows raising the temperature at a fast heating rate (1010 K/s).Pseudomorphic Si1-xGex layers [3] of 20 nm for x = 0.3 or 0.4, and of 15 nm for x= 0.5 (corresponding to Delta Temperature = Tmelt Si – Tliq Si1-xGex of 60°C, 95°C, and 139°C respectively) were grown on 300 mm (001)-Si wafers. The Si1-xGex layers were covered with 17 nm of Si. Selected areas of the wafers were irradiated with nLA (308 nm wavelength and pulse duration of 160 ns) at different energy densities (ED). After laser annealing, the samples were characterized by X-Ray Diffraction (XRD), SP2 Haze, Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM).In Fig. 1a, we show the in-situ time-resolved reflectometry (TRR) recorded during the laser annealing. For ED lower than the ones indicated by the dotted lines, the surface reflectivity remains unchanged during annealing. For higher ED, the reflectivity increases sharply for a transient period ranging from 100 ns to 380 ns. This is typically associated with a melting process [4].In Fig. 1b, we display the (004) XRD scans for the three studied structures. For low ED, the Si1-xGex diffraction pattern may present a gradual reduction in intensity. For an ED higher than a threshold ED (different for each substrate), we report on a sharp transition of the Si1-xGex peak to a characteristic position of lower Ge concentration. This new characteristic peak increases in intensity with ED. The peak gradually shifts towards lower Ge concentrations for the higher tested EDs.In Fig. 1c, we show the measurements of the SP2 haze and AFM Root Mean Square (RMS) roughness. For ED lower than a threshold ED (zone 1), the roughness is low, characteristic of an unmodified surface. For intermediate ED (zone 2), the roughness rises abruptly. It then gradually falls with increasing ED to enter a third zone showing constant values.In Fig. 1d, we display SEM micrographs using secondary electrons (SE) and backscattered electrons (BSE). The SE provides topographic information and BSE provides additional chemical information from a higher depth range in the substrate. In the stacks with Si0.7Ge0.3 and Si0.6Ge0.4 layers, four-fold structures with symmetry along <110>-directions are observed in the images obtained using SE and BSE. For the stack with Si0.5Ge0.5, these formations are observed only with the BSE.The presented results show that using AFM, Haze, and SEM, surface modifications are detected at a lower ED compared to intensity rise obtained by TRR, providing then a higher sensitivity to identify the melt onset. By XRD, the first modifications are detected at a higher ED compared to TRR, wherein a larger modified volume is likely required to provide enough diffraction intensity. The characteristic Si1-xGex peak in the diffraction diagrams (Fig. 1b), abruptly appearing at a threshold ED for each stack, is associated with the formation of the four-fold structures in the SEM micrographs (Fig. 1d). Therefore, it is a signature of its composition/structure. The SEMs have also shown that for the Si1-xGex layers with up to 40 at% Ge, the Si1-xGex and top Si layers are both molten at the detected melt onset. In contrast, for the stack with Si0.5Ge0.5, the four-fold structure is only detected with BSE, evidencing a buried transformation. Therefore, for our experimental setup, a minimum Ge content of 50 at% or a Delta Temperature of 139°C was necessary to obtain a buried melted layer.

Research on the pyrolysis characteristics and mechanisms of waste printed circuit boards at fast and slow heating rates

The pyrolysis treatment of waste printed circuit boards (WPCBs) shows great potential for sustainable treatment and hazard reduction. In this work, based on thermogravimetry (TG), pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS), and density functional theory (DFT), the thermal weight loss, product distribution, and kinetics of WPCBs pyrolysis were studied by single-step and multi-step pyrolysis at fast (600 °C/min) and slow (10 °C/min) heating rates. The heating rates of TG and Py-GC/MS were the same for each group of experiments. In addition, the bond dissociation energy (BDE) of WPCBs polymer monomers was calculated by DFT method. Compared with slow pyrolysis, the final weight loss of fast pyrolysis is reduced by 0.76 wt%. The kinetic analysis indicates that the activation energies of main pyrolysis stages range from 98.29 kJ/mol to 177.59 kJ/mol. The volatile products of fast pyrolysis are mainly phenols and aromatics. With the increase of multi-step pyrolysis temperature, the order of the escaping volatiles is phenols, hydrocarbyl phenols, aromatics, and benzene (or diphenyl phenol). The pyrolysis residue of WPCBs may contains phenolics and polymers. Based on the free radical reactions, the mechanism and reaction pathways of WPCBs pyrolysis were deduced by the DFT. Moreover, a large amount of benzene is produced by pyrolysis, and its formation mechanism was elaborated.

Exploring “No Man's Land”—Arrhenius Crystallization of Thin‐Film Phase Change Material at 1 000 000 K s−1 via Nanocalorimetry

AbstractNon‐volatile phase‐change memory (PCM) devices are based on phase‐change materials such as Ge2Sb2Te5 (GST). PCM requires critically high crystallization growth velocity (CGV) for nanosecond switching speeds, which makes its material‐level kinetics investigation inaccessible for most characterization methods and remains ambiguous. In this work, nanocalorimetry enters this “no‐man's land” with scanning rate up to 1 000 000 K s−1 (fastest heating rate among all reported calorimetric studies on GST) and smaller sample‐size (10–40 nm thick) typical of PCM devices. Viscosity of supercooled liquid GST (inferred from the crystallization kinetic) exhibits Arrhenius behavior up to 290 °C, indicating its low fragility nature and thus a fragile‐to‐strong crossover at ≈410 °C. Thin‐film GST crystallization is found to be a single‐step Arrhenius process dominated by growth of interfacial nuclei with activation energy of 2.36 ± 0.14 eV. Calculated CGV is consistent with that of actual PCM cells. This addresses a 10‐year‐debate originated from the unexpected non‐Arrhenius kinetics measured by commercialized chip‐based calorimetry, which reports CGV 103−105 higher than those measured using PCM cells. Negligible thermal lag (&lt;1.5 K) and no delamination is observed in this work. Melting, solidification, and specific heat of GST are also measured and agree with conventional calorimetry of bulk samples.

Transient dynamics of the thermally induced deformation of sands

AbstractCurrently, inconclusive evidence characterizes the thermally induced deformation of sands. In this context, the role of the transient nature of heat diffusion on the thermally induced deformation of sands has remained largely disregarded. This paper presents a theoretical and computational investigation of the transient dynamics characterizing the thermally induced deformation of sands under oedometric conditions. The study shows that heating rates determined by the pore fluid pressure dissipation timescale to ensure drained conditions can cause an important temperature nonuniformity and a breakdown of quasi‐static conditions. Under these dynamic conditions, the differential expansion between the sand and the confining oedometer ring uniquely characterizes the response and is broken down into two characteristic regimes. For slow heating rates and low‐expansion ring materials, a mathematical analysis shows that expansion and only expansion can occur, regardless of relative density and stress level. For fast heating rates and high‐expansion ring materials, a parametric analysis establishes the possibility of a very small initial volumetric contraction for loose materials under high stress levels. In the light of the existing literature, the study shows that the intrinsic volumetric response to heating loads of sand, as a material, is only expansive; volumetric contraction may only be observed under transient conditions. This work supports a conceptual shift in the framework of analysis of thermally induced deformation of sands, from a temperature‐dependent material response to a rate‐dependent response of a finite volume under nonuniform conditions.

Silicon alloying enhances fast heating rate combustion of aluminum particles

Alloys and composites of aluminum (Al) have shown promise in regulating and enhancing particle combustion for energy generation applications. Recent work on aluminum-silicon (Al-Si) spherical alloy particles has shown improved combustion at low heating rates through enhanced diffusion accompanying a lower melting temperature. This study extends reactivity analysis to higher heating rates, comparing oxidation of Al-Si with Al. Flame speeds of Al-Si powder mixed with molybdenum trioxide (MoO3) powder (Al-Si+MoO3) exhibited a faster transition to steady propagation relative to Al+MoO3. Bomb calorimetry experiments revealed up to 5.8% greater early temperature rise for Al-Si powder. Rapid steady propagation for Al-Si mixture and faster temperature rise for Al-Si particles were attributed to accelerated kinetics evidenced in thermal equilibrium analysis of the mixtures using a differential scanning calorimeter (DSC). Larger DSC exotherms in the early stages of oxidation (i.e., 480–720 °C) correlated with early heat release and promoted steady flame propagation for Al-Si+MoO3 compared with Al+MoO3. Furthermore, in multiple heating rate DSC studies, Al-Si+MoO3 ignited at a lower heating rate (i.e., 15 ⁰C/min) than Al+MoO3 (i.e., 20 ⁰C/min). Both mixtures ignited at temperatures less than 625 °C which is above the melting temperature of Al-Si (574 °C) and below Al (659 °C). Thus, alloy particle fuels with enhanced diffusion-controlled kinetics promote steady flame propagation and show promise for energy generation applications. This is especially promising for technologies driven by enhanced condensed phase combustion such as some propellant additives or applications dependent on reliable burn rates such as pyrotechnic time delay formulations and primers.

Ignition and combustion of Perfluoroalkyl-functionalized aluminum nanoparticles and nanothermite

Aluminum (Al) is an excellent metal fuel for combustion applications because of its high energy density and low cost. Nano-sized Al (nAl) particles have relatively low ignition temperature and high reactivity, but their performance is limited by the presence of the native oxide (Al2O3) layer surrounding the active Al core. To overcome this problem, nAl coated or mixed with fluorocarbon species have been intensively studied recently. In this work, we demonstrate a facile method to functionalize the surface of nAl particles with perfluoroalkylsilane and investigate the thermochemical and combustion behaviors of perfluoroalkyl-functionalized nAl particles at both slow and fast heating rates. At slow heating rates, the covalently-bonded perfluoroalkylsilane molecules partially undergo debonding at low temperatures before reacting with Al2O3. The remaining perfluoroalkyl molecules slowly react with surface oxide to thicken the surface shell, which improves the thermal stability of nAl particles. Nevertheless, under fast heating conditions, the dissociated fluorine species can readily react with the oxide on the nAl surface, enhancing the ignition and combustion performance of both nAl particles in the air and Al/copper (II) oxide (CuO) nanothermite. These results advance the understanding of the thermochemical behaviors of the fluorocarbon species and their effects on the ignition and combustion of nAl particles and Al-based energetic materials.

Investigation on Performance of Various Power Control Strategies with Bifilar Coil for Induction Surface Melting Application

In recent years, induction heating applications assisted by electronic power control have been very appealing. For melting applications, induction heating is widely used as it seems to be appropriate and provides higher efficiency, zero pollutants, non-contamination of material, etc. in comparison with conventional heating. The conventional variable frequency control scheme is not sufficient for melting applications because of its high switching loss, low efficiency, and lower heat rate. A superlative control technique is required to control the output power smoothly, for a high heating rate with minimum power loss, and to lower the number of components. In this paper, a capacitorless self-resonating bifilar coil is proposed for induction surface melting applications. The performance of the system in terms of modular losses, heat rate, and efficiency is analyzed for various power methods such as pulse duty cycle control, phase shift control, pulse density modulation control, and asymmetric duty cycle control. An experimental validation is performed for the 1 kW prototype, and the heating rate, efficiency, and modular losses are calculated. The control technique is digitally validated using a PIC16F877A microcontroller with 30 kHz switching frequency. The temperature distribution is analyzed using a FLIR thermal imager. Among the tested methods, pulse density modulation-based control provides smooth and varied power control from 0% to 100% with minimum modular losses. The efficiency of the system is 89% at a rated output power and is greater than 85% for pulse density modulation control with a fast heating rate.

Evaluation of Pilot-Scale Radio Frequency Heating Uniformity for Beef Sausage Pasteurization Process.

Radio frequency (RF) heating has the advantages of a much faster heating rate as well as the great potential for sterilization of food compared to traditional thermal sterilization. A new kettle was designed for sterilization experiments applying RF energy (27.12 MHz, 6 kW). In this research, beef sausages were pasteurized by RF heating alone, the dielectric properties (DPs) of which were determined, and heating uniformity and heating rate were evaluated under different conditions. The results indicate that the DPs of samples were significantly influenced (p < 0.01) by the temperature and frequency. The electrode gap, sample height and NaCl content had significant effects (p < 0.01) on the heating uniformity when using RF energy alone. The best heating uniformity was obtained under an electrode gap of 180 mm, a sample height of 80 mm and NaCl content of 3%. The cold points and hot spots were located at the edge of the upper section and geometric center of the sample, respectively. This study reveals the great potential in solid food for pasteurization using RF energy alone. Future studies should focus on sterilization applying RF energy and SW simultaneously using the newly designed kettle.

Fast successive self‐nucleation and annealing (SSA) thermal fractionation protocol for the characterization of polyolefin blends from mechanical recycling

AbstractThe sorting stage of mechanical recycling of post‐consumer polyolefins has severe challenges. Polypropylene (PP) is often contaminated with polyethylene (PE) and vice versa. To meet quality requirements, characterization of the recycled pellets is needed. To address this problem, fast characterization generating a statistical assessment of the content of the various batches from recycling is required. This investigation shows that the use of fast scanning rates (in a conventional Differential Scanning Calorimeter) in the successive self‐nucleation and annealing (SSA) protocol can reduce the thermal fractionation time, without losing resolution power, as long as the increase in heating/cooling rate is compensated by reducing sample mass. Using a “coupled SSA protocol” for polypropylene and polyethylene fractions at a rate of 10 °C/min, the measurement time is approximately 420 min. Implementing mass compensation, faster heating rates (i.e., 30 °C/min) and using a single‐fraction protocol, sufficient to determine the content of PP and high‐density PE, reduced the time of the measurement to 75 min. Examples of fractionations of commercial post‐consumer and post‐industrial recycled polyolefin blends conducted at a faster rate are provided. The derived polyolefin content is compared with the standard temperature rising elution fractionation analysis to assess the validity of the proposed method.

Characterization of charcoals produced from Acacia, Albizia and Leucaena for application in ironmaking

Fossil coal can be replaced with renewable charcoal to reduce CO2 emissions from ironmaking processes. Charcoals produced from three hardwood species, Acacia nilotica (W1), Albizia lebbeck (W2) and Leucaena leucocephala (W3), were evaluated as a reductant in ironmaking. Charcoals were produced with slow (5 °C/min) and fast heating rates (50 °C/min) at 600, 800 and 1100 °C. Charcoals were characterized using proximate, ultimate analysis, volume shrinkage, compressive loading, scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy for their chemical, mechanical and physical properties. It was found that among the selected biomass species, fixed and total carbon content is higher in W1 (83–97; 84–91%) and W2 (83–96; 86–92%) than W3 (76–89; 78–84%) and increases with increase in carbonization temperature and heating rate. Charcoal yield in W1 (22–28%), W2 (22–26%) and W3 (23–28%) decreases with an increase in carbonization temperature and heating rate. Charcoals produced at various carbonization conditions have at most 10% ash content. Values from different tests indicate that W2 and W3 charcoal are potentially better reductant than W1.

Effects of inorganic sodium on the combustion characteristics of Zhundong coal with fast-heating rate

The combustion characteristics of raw (RAW), acid-washed (AW) and inorganic sodium impregnated (NaCl-loaded) Zhundong (ZD) coals were researched in a fast-heating rate combustion system and thermal gravimetric (TG) analyzer, aiming to exhibit the effect of inorganic sodium on coal combustion processes under different heating rates. The results showed that the ignition delay time decreased in the order: NaCl-loaded coal > AW coal > RAW coal in the early stage with fast-heating rate. The surface temperature of NaCl-loaded coal increased the slowest, while with the highest Tis, reflecting that the ignition and combustion behavior became more difficult after adding NaCl in the early stage. However, in the later stage, the fastest increase in temperature and the shortest tb, together with the shorter extinction time of volatile flame, were observed on NaCl-loaded coal. The size of NaCl-loaded coal decreased faster than that of AW coal. Thus, it can be concluded that inorganic sodium will inhibit coal combustion in the early stage, while promotes coal combustion in the later stage under fast-heating rate. In the TG experiment, the Ti-TG and Tb-TG of NaCl-loaded coal were lower than that of AW coal, and the Tm-TG of NaCl-loaded coal moved to the low temperature area, revealing that inorganic sodium can promote coal combustion with low-heating rate during the whole combustion process. The quantum chemistry calculation at M06-2X/6-31G(d,p)//CBS-QB3 level reveals that inorganic sodium can catalyze the addition and cyclization reactions of small chain molecules in the early stage with fast-heating rate, thereby inhibiting coal combustion in the early stage, which was different from that in the later stage. Inorganic sodium will promote the formation of OH radical, and the organic sodium obtained from sodium-containing surface compounds of the char can be beneficial for the oxidation reaction of the carbon residue, thereby promoting coal combustion in the later stage with fast-heating rate, which was consistent with the references.

Regeneration of graphite anode from spent lithium-ion batteries via microwave calcination

• Microwave calcination is applied to regenerate spent anode graphite. • Microwave calcination consumes less energy than conventional calcination. • The charge specific capacity of regenerated graphite is 354.1 mAh·g −1 at 0.1 C. • The capacity retention rate of regenerated graphite is 98.3% after 60 cycles at 0.1 C. An efficient and economical recycling method for spent anode graphite via microwave has been proposed in this study. The spent graphite (SG) was firstly treated by sulfuric acid curing-acid leaching, and then regenerated by microwave calcination. The effects of microwave calcination temperature and time on electrochemical performance were systematically studied. The morphology and structure of graphite were analyzed by SEM, FT-IR and XRD. The results show that compared with the SG, regenerated graphite (RG) obtained by microwave calcination has a neat graphite surface and a significantly improved electrochemical performance, such as the initial coulombic efficiency and the charge specific capacity at 0.1 C are 83.4% and 354.1 mAh·g −1 , and the capacity retention rate after 60 cycles at 0.1 C increases to 98.3%. In addition, microwave calcination has the advantages of selective heating and fast heating rate. Therefore, this method can realize efficient regeneration of spent anode graphite with low-energy consumption, which provides new light on the recycling of spent graphite.

Preparation of large-area, high-performance single-walled carbon nanotube (SWCNT)-based heater films by roll-to-roll gravure printing

In this work, we have developed an eco-friendly and fast method for the preparation of large-area high-performance single-walled-carbon-nanotube (SWCNT)-based conductive thin films on polyethylene terephthalate substrates by roll-to-roll (R2R) gravure printing technology. Large-area (16 cm × 32 cm) conductive films, consisting of SWCNT or SWCNT/silver nanowire (AgNW) films, were fabricated for the first time by R2R gravure printing technique. The conductivity, transmittance, mechanical flexibility and heating ability were evaluated in detail. For example, the square resistances of the SWCNT thin film and SWCNT/AgNW composite film were 69.92 and 17.44 Ω/□ and the optical transmittance at a wavelength of 550 nm were 50.70% and 66.77%, respectively. Meanwhile, the prepared SWCNT and SWCNT/AgNW composite films exhibit excellent heating stability, temperature uniformity and resistance to bending. The composite films can withstand 6000 bending cycles at a curvature radius of 3.5 mm and obtain a temperature of up to 100 °C with a low driving voltage (6 V), a fast heating response (within 15 s) and heating rate (about 4.933 °C s−1). These properties reflect the potential of SWCNTs in improving the mechanical and heating properties of composite films, which are promising for low power, large area, flexible and customizable electronic devices.

Effect of Internal AC Heating on the Temperature Homogeneity of Different Size Battery Cells

Rapidly warming up batteries is an important challenge both for conventional lithium-ion batteries, which operate best over 15 °C, and for most solid-state batteries, which currently require operating temperatures over 60 °C. Internal heating using an alternating current (AC) has been proposed as a possible solution in automotive applications, with faster heating rates possible than conventional external heating methods. This paper investigates the performance of internal AC heating on cells of different sizes, for both cylindrical and pouch formats. A novel experimental arrangement is used in which two cells are tested in series while connected with opposing polarity to create a zero-voltage string, allowing the use of less expensive testing equipment. The results show that larger cells exhibit a considerably greater distribution of surface temperature than smaller format cells during internal heating. This is likely due to the more extreme spatial variation in current density in the current collectors, causing an uneven distribution of internal heat generation. This highlights a significant difference compared to external heating methods, which are not affected by this, and has important implications for temperature measurement and battery management if this type of internal heating is to be used, since temperature sensors must be placed in hot spots or supplemented by validated models to ensure all parts of the battery stay within safe temperature limits.

In Situ Grazing-Incidence SAXS Investigation of Thermal-Induced Self-Assembly Process of PS-b-PMMA Films Deposited on Surface-Modified Substrate.

Directed self-assembly of block copolymers (BCPs) is widely investigated for its potential application in surface patterning. The self-assembly kinetics of BCP based on modified layers is the key to realizing structural control for obtaining highly ordered lamellar grains. In this study, morphological evolution of PS-b-PMMA films during the thermal-induced self-assembly process was investigated via the in situ grazing-incidence small-angle X-ray scattering (GISAXS) technique. In the first heating stage, reorientation of lamellar grains occurred as the temperature increased above the glass transition temperature. Then, a fast increase in the lamellar repeat period L0 was observed, which is considered as a phase separation process. Whereas the size of the lamellar grain ξ was observed to have rapidly increased in the stage wherein the temperature was held at 230 °C, the L0 was almost constant. This result indicates that the formation of ordered structure in PS-b-PMMA films was mainly determined by two periods: phase separation of block molecules followed by growth of grains in the nanodomain. In addition, it was interesting that the better-order nanodomains were obtained with thermal annealing at a faster heating rate. These findings suggest that accomplishing ordered structure control in a large area could be realized via the design of a proper heating profile.

Microwave-induced self-ignition: An efficient approach for high purity graphite digestion and multitechnique halogen determination

In this work, high purity graphite, a high chemically stable material, was effectively digested using a single method allowing compatible solutions for the further multitechnique determination of halogens by: ion chromatography (F and Cl), inductively coupled plasma mass spectrometry (Cl, Br and I) and by ion selective electrode (only for F). The recent system using microwave-induced self-ignition (MISI) is based on the strong interaction between microwave radiation and graphite in a closed system pressurized with oxygen (Maxwell-Wagner effect). Carbon-based materials present intense and specific interfacial polarization when exposed to microwave electromagnetic field resulting in a fast heating rate. This effect associated to a pressurized oxygen system, provides a quick self-ignition of carbon-based materials and consequent combustion/digestion of organic matrices. Under optimized conditions, sample masses up to 600 mg were fully digested in a quartz vessel under 20 bar of oxygen pressure and using just a diluted solution (100 mmol L−1 NH4OH) for the quantitative absorption of all the analytes. MISI method was validated, and the accuracy (better than 94%) was evaluated by comparison of results obtained by pyrohydrolysis for two coal certified reference materials as well as with subsequent analytes determination by the three techniques: IC, ICP-MS and ISE. It is important to point out that no filter paper disks, electrical connections or other ignition aids are required as in the case of previous or classical combustion methods. Moreover, just a diluted absorbing solution was used resulting in negligible blanks and relatively low limits of detection. The digestion efficiency was higher than 99%, making the proposed method a suitable and powerful alternative for the quasi complete digestion of graphite and determination of halogens virtually free of interferences.

Interaction Between Ferrite Recrystallization and Austenite Formation in Dual-Phase Steel Manufacture

In this publication, the effect of heating rate on microstructural evolution of manganese segregated cold reduced dual phase steels is systematically studied for different inter-critical temperatures and holding times. At slow heating rate, completion of ferrite recrystallization before austenite formation led to the preferential formation of austenite on the ferrite grain boundaries leading to a necklace austenite (now martensite) morphology. The slower austenite formation kinetics has been attributed to longer diffusion paths dictated by larger ferrite grain sizes. In medium heating rate condition, microstructure before austenite formation had partially recrystallized ferrite and partially spheroidized cementite. Rapid austenite growth occurred along the rolling direction in carbon-rich cementite regions and dislocation-rich recovered ferrite regions. The presence of partially recrystallized ferrite grains restricted the austenite growth in the normal direction and therefore enabled the formation of thin martensite bands parallel to the rolling direction. At fast heating rate, the microstructure before austenite formation predominately contained un-recrystallized ferrite and un-spheroidized cementite and therefore enabled faster austenite formation kinetics. Thicker martensite bands are formed at fast heating rates due to the absence of recrystallized grains, thereby, enabling the growth of austenite in all directions with a higher preference to the rolling direction.

Commercial aluminum powders, part II: Energy release rates induced by rapid heating via pulsed laser excitation

We used nanosecond laser pulses to excite various aluminum (Al) powders under an extremely fast heating rate (1013 K/s). Our interest lies in three timescales: early (1–10 μs), middle (10–500 μs), and late (tens of milliseconds). We used several spectroscopic methods to monitor AlO emission to track the Al oxidation on all timescales. The characteristic laser-induced air shock velocity determined relative energy release from each Al powder on the early timescale. We found that the Al nanopowders had higher laser-induced shock velocities than the micron-sized powders, indicating faster energy release. The AlO emission monitored in the early time regime correlated with the laser-induced shock velocities, confirming that the increases in laser-induced shock velocities observed resulted from earlier oxidation of the Al. The heterogeneous nature of the Al samples and the strong influence of their properties on fast energy release demonstrated the importance of well-characterized samples for interpreting detonation experiment results.

Pyrolysis reaction mechanism of typical Chinese agriculture and forest waste pellets at high heating rates based on the photo-thermal TGA

To investigate gas generation characteristics and the kinetics mechanism of biomass pyrolysis process at fast heating rates, a concentrated Photo-thermal TGA reactor (Pt-TGA) was set up. The reactor was reliable for the study of thermochemical kinetics because the average difference between the commercial TGA and Pt-TGA curves for the cellulose pyrolysis process was only 2.1%. Four kinds of typical Chinese forest and agriculture wastes were selected to study the pyrolysis process in Pt-TGA. At higher heating rates, the volatiles from pyrolysis eventually formed more non-condensable gases because of inner-particle secondary reactions. In the range of 450–850 °C, with the temperature rising, the production of H2 increased, and the highest H2 yield reached 279 mL/g. Combined with kinetic analysis, with the increase of heating rate, heat and mass transfer had a more prominent effect on the pyrolysis of biomass particles, and the reactions were controlled by three-dimensional diffusion model.

Understanding the impact of diffusion of CO in the astrochemical models

Abstract The mobility of lighter species on the surface of interstellar dust grains plays a crucial role in forming simple through complex molecules. Carbon monoxide is one of the most abundant molecules, its surface diffusion on the grain surface is essential to forming many molecules. Recent laboratory experiments found a diverse range of diffusion barriers for CO on the grain surface, their use can significantly impact the abundance of several molecules. The impact of different diffusion barriers of CO, in the astrochemical models, is studied to understand its effect on the abundance of solid CO and the species for which it is a reactant partner. A gas-grain network is used for three different physical conditions; cold core and warm-up models with slow and fast heating rates. Two different ratios (0.3 and 0.5) between diffusion and desorption barrier are utilised for all the species. For each physical condition and ratio, six different models are run by varying diffusion barriers of CO. Solid CO abundance for the models with the lowest diffusion barrier yields less than 0.1% of water ice for cold clouds and a maximum of 0.4% for slow and fast warm-up models. Also, solid $\textrm{CO}_2$ in dense clouds is significantly overproduced ( ${\sim}140\%$ of water). The abundance of H2CO and $\textrm{CH}_3\textrm{OH}$ showed an opposite trend, and HCOOH, $\textrm{CH}_3\textrm{CHO}$ , $\textrm{NH}_2\textrm{CO}$ , and $\textrm{CH}_3\textrm{COCH}_3$ are produced in lower quantities for models with low diffusion barriers for CO. Considerable variation in abundance is observed between models with the high and low diffusion barrier. Models with higher diffusion barriers provide a relatively better agreement with the observed abundances when compared with the models having lower diffusion barriers.