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“Flash heating” that transiently generates high temperatures above 1000 °C has great potential in synthesizing new materials with unprecedently properties. Up to now, the realization of “flash heating” still relies on the external power, which requires sophisticated setups for vast energy input. In this study, a mechanochemically triggered, self‐powered flash heating approach is proposed by harnessing the enthalpy from chemical reactions themselves. Through a model reaction between Mg3N2/carbon and P2O5, it is demonstrated that this self‐powered flash heating is controllable and compatible with conventional devices. Benefit from the self‐powered flash heating, the resulting product has a nanoporous structure with a uniform distribution of phosphorus (P) nanoparticles in carbon (C) nanobowls with strong P─‐C bonds. Consequently, the P/C composite demonstrates remarkable energy storage performance in lithium‐ion batteries, including high capacity (1417 mAh g−1 at 0.2 A g−1), robust cyclic stability (935 mAh g−1 at 2 A g−1 after 800 cycles, 91.6% retention), high‐rate capability (739 mAh g−1 at 20 A g−1), high loading performance (3.6 mAh cm−2 after 100 cycles), and full cell cyclic stability (90% retention after 100 cycles). This work broadens the flash heating concept and can potentially find application in various fields. [ABSTRACT FROM AUTHOR]

To address the fundamental challenge of resource sustainability and to effectively deal with issues pertaining to supply chain resilience, cost efficiency, environmental impact, and the ability to meet specific local needs; there is an urgent need for high‐grade battery anode materials produced locally from readily available raw materials. In this work, synthesis of high‐quality graphitic carbon (GH) derived from human hair is demonstrated using an in‐house engineered reactor based on Joule's Flash heating method. The GH is characterized using various techniques to examine its chemical composition, particle morphology, crystallinity, and demonstrate its usability as an anode material for lithium‐ion batteries. Fabricated coin cell with active material exhibits a gravimetric capacity of 320 mAh g−1 at a current density of 30 mA g−1 (equivalent to a C rate of ≈0.1C) over the 100 cycles. The in situ and ex situ studies using XRD, Raman, XPS, and UPS techniques conclude that during the initial charge cycle for GH, lithium ions diffused into the electrode during the resting period are effectively removed. This not only improves the lithium inventory to start with but also mitigates subsequent solvent degradation during solid electrolyte interphase (SEI) formation. Thus, these improvements ultimately enhance the capacity of the anode to 500mAh g−1 at a current density of 20 mA g−1. The study offers the potential to initiate a new realm of research by redirecting the focus to a material once considered as mere waste. [ABSTRACT FROM AUTHOR]

The working temperature of any 3D printer has a critical effect on process feasibility as well as the final quality of the product. In this respect, thermal analysis can provide a comprehensive understanding of operation parameters and optimization potential. This most certainly also is the case for the new layer-wise additive manufacturing system, selective thermoplastic electrophotographic process (STEP). In the present paper, we propose a 3D part-scale finite element thermal model for multi-materials which is developed in the commercial software Abaqus/CAE 2021. The reduced-order method, flash heating (FH), is adopted in the model to obtain good accuracy with acceptable simulation time. A specific analysis of the trade-offs between accuracy and CPU-time is carried out by varying the amount of lumping in the meta-layers in the FH method. Furthermore, we conduct an in-house experiment in which we use IR cameras for measuring temperatures during manufacturing, and the results are applied for model validation and calibration. We specifically compare measured and numerically predicted average surface temperatures when steady state is obtained after printing of each layer. Here we obtain a mean error up to 6% depending on the thickness of the meta-layers. Moreover, parametric studies show that pulse duration and heater intensity significantly influence both the surface and bulk temperature profiles, and this provides us with an increased understanding of the thermal behavior of the recently developed STEP process which in turn could make way for further process optimization. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Flash‐weakening models typically show good agreement with the total magnitude of weakening in high‐speed rock friction experiments, however deviations during the acceleration and deceleration phases, and at low and intermediate sliding velocities, remain unresolved. Here, we incorporate inhomogeneous mm‐scale normal stress evolution into a model for flash heating and weakening to resolve outstanding transient and hysteretic friction observed in laboratory experiments and to identify unique solutions to constitutive parameters. We conduced 37 rock friction experiments on Westerly granite using a high‐speed biaxial apparatus outfitted with a high‐speed infrared camera. We initiated velocity steps from quasi‐static rates of 1 mm/s to sliding velocities ranging from 300 to 900 mm/s and conducted both constant‐ and decreasing‐velocity tests following the velocity step. Two sliding surfaces geometries were used to control mm‐scale life‐times and rest‐times. Constant‐strength sliding is achieved within 2–3 mm of initiating the velocity step in all constant‐velocity experiments. Macroscopic surface temperature is inhomogeneous and increases with slip distance, velocity, and decreasing rest‐time. Weakening increases with sliding velocity and decreasing rest‐time. We combine thermal models with measured surface temperatures to constrain the evolution of local normal stress at the mm‐scale and incorporate this evolution into a flash‐weakening model that considers weakening at both the µm‐ and mm‐scale. The flash‐weakening model improves when the effects of mm‐scale wear processes are incorporated and multi‐scale weakening is considered, however some transient friction remains undescribed. Models will be advanced by further incorporating wear processes and by considering processes at the mm‐scale and above. Plain Language Summary: Natural fault roughness results in a true contact area much smaller than the apparent area and concentrated loads at microscopic asperity contacts. Rapid slip during earthquakes dramatically increases the temperature at these asperities and reduces the frictional strength of asperity contacts, dramatically reducing the frictional strength of the surface. Theoretical models for this frictional weakening show good overall agreement with data from laboratory experiments, though models do not predict some hysteretic frictional behavior during the mechanically significant acceleration and deceleration phases of sliding, nor do they capture some transient frictional behaviors observed in experiments. Here, we conduct experiments to resolve this outstanding frictional behavior. We use an infrared camera to measure surface temperature on laboratory fault surfaces during earthquake experiments and combine measured temperature data with mechanical data and thermal models to resolve the spatial distribution of temperature and normal stress on fault surfaces during sliding. We incorporate this evolution into a frictional weakening model that considers contacts at the micrometer asperity scale and the millimeter scale and shows improved model predictions, though some frictional behavior is still not described. Further advancements can be made by considering wear processes and frictional processes occurring over mm or longer length scales. Key Points: Temperature is inhomogeneous and increases with slip. Temperature and weakening increase with sliding velocity and mm‐scale contact lifetimeIncorporating mm‐scale contact evolution along with weakening at both the µm‐ and mm‐scale improves the flash‐weakening modelDynamic weakening models will be advanced by further incorporating wear processes and considering processes at the mm‐scale and above [ABSTRACT FROM AUTHOR]

This investigation demonstrates the formation of a unique coconut-shell-type iron nugget by flash heating an off-grade iron ore–graphite composite pellet at 1200 °C. An analytical estimation showed that flash heating at 1200 °C could achieve a pellet heating rate of 150 °C/min value. This is in contrast to the maximum furnace heating rate of 25 °C/min, where the maximum pellet heating rate may, at best, equal the furnace heating rate. The factsage calculation showed that carburized iron remained in the liquid state at 1200 °C and slag in the solid state. Liquid iron oozes out to the pellet surface and forms a hard shell of iron nugget at the periphery, leaving slag at the interior. Optimum carbon (C/O = 1) and basicity (0.84) produced a higher iron yield in the nugget. [ABSTRACT FROM AUTHOR]

The present study aimed to investigate the effectiveness of a flash heating method to produce in a short time industrial-grade activated carbon with a well-developed pore structure and high adsorption capacity. Hazelnut shells, rice husk, and corn stalks were impregnated with potassium hydroxide (KOH) and activated using flash and slow heating at different temperatures. The slow heating process was conducted with a heating rate of 10 °C/min, while no heating rate was applied in flash heating during activated carbon production. Obtained products were characterized by the X-ray diffractometer, fourier transform infrared, and BET surface area. It was observed that the surface area of ACs ranged from 1650 and 2573 m2/g by using flash heating, and 1005–3257 m2/g by using slow heating. Methylene and iodine number test procedures were applied to the final product to examine the adsorption capacity of the available pores. The methylene blue adsorption capacity was 714 mg/g which is the highest value using flash heating while 630 mg/g is the best value for slow heating. Iodine numbers were over 1000 mg/g for all obtained activated carbons. Consequently, the high methylene and iodine number values were attained with the flash-activated carbons, showing their high adsorption potential as an adsorbent compared to commercial activated carbon. The results of this study show that flash-activated carbon could be used as an alternative to commercial carbon and produced in a short time with a promising heating way. [ABSTRACT FROM AUTHOR]

Controlling aspects of the μ2‐X− bridging anion in the metal–organic framework Ga‐MIL‐53 [GaX(bdc)] (X−=(OH)− or F−, bdc=1, 4‐benzenedicarboxylate) is shown to direct the temperature at which thermally induced breathing transitions of this framework occur. In situ single crystal X‐ray diffraction studies reveal that substituting 20 % of (OH)− in [Ga(OH)(bdc)] (1) for F− to produce [Ga(OH)0.8F0.2(bdc)] (2) stabilises the large pore (lp) form relative to the narrow pore (np) form, causing a well‐defined decrease in the onset of the lp to np transition at higher temperatures, and the adsorption/desorption of nitrogen at lower temperatures through np to lp to intermediate (int) pore transitions. These in situ diffraction studies have also yielded a more plausible crystal structure of the int‐[GaX(bdc)] ⋅ H2O phases and shown that increasing the heating rate to a flash heating regime can enable the int‐[GaX(bdc)] ⋅ H2O to lp‐[GaX(bdc)] transition to occur at a lower temperature than np‐[GaX(bdc)] via an unreported pathway. [ABSTRACT FROM AUTHOR]

This work presents constitutive equations and a dataset of a thermal model for the prediction of temperature fields and heating rates during the application of localized laser treatments to a Fe-C-Ni alloy. The model considers transient material properties and the coupling between temperature and microstructure, with emphasis on the phase dependence of the thermal parameters and the hysteresis in the phase change. The model can predict temperature fields that are in agreement with the experimental microstructures at the laser-affected zones. This model can be applied to other materials exhibiting solid-state transformations upon the application of laser treatments.

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.

Abstract Gold nanoparticles (Au NPs) based technology has been shown to possess enormous potential in the viral nucleic acid diagnosis. Despite significant advancement in this domain, the existing literature reveals the diversity in the conditions employed for hybridization and tagging of thiolated nucleic acid probes over the Au NPs. Here we employ the probe sequence derived from the Hepatitis C virus to identify the optimal hybridization and thiol-Au NP tagging conditions. In a typical polymerase chain reaction, the probes are initially subjected to flash heating at elevated temperatures to obtain efficient annealing. Motivated by this, in the current study, the hybridization between the target and the antisense oligonucleotide (ASO) has been studied at 65 °C with and without employing flash heating at temperatures from 75 to 95 °C. Besides, the efficiency of the thiolated ASO’s tagging over the Au NPs with and without citrate buffer has been explored. The study has revealed the beneficial role of flash heating at 95 °C for efficient hybridization and the presence of citrate buffer for rapid and effective thiol tagging over the Au NPs. The combinatorial effect of these conditions has been found to be advantageous in enhancing the sensitivity of ratiometric genosensing using Au NPs.

The realisation of sophisticated hierarchically patterned multiphase steels has the potential to enable unprecedented properties in engineering components. The present work explores the controlled creation of patterned multiphase steels in which the patterns are defined by two different crystal structures: face centre cubic or fcc (austenite) and body centre cubic or bcc (martensite). These austenite/martensite mesostructures are generated by solid–solid phase transformations during the application of localised laser heat treatments in a Fe-Ni-C alloy. In particular, four patterned configurations are analysed in this work consisting of one or two horizontal austenite line structures imprinted in a base of as-quenched or tempered martensite. Digital image correlation analysis during tensile testing of the developed materials showed that both the strength of the base martensite and the mesostructure at the gauge have a strong effect on the resulting properties. Clear differences were observed among the configurations in strain partitioning, hardening of the different constituents and failure. The uniform elongation and tensile strength are increased with respect to that of the reference martensite and austenite, respectively. Concepts explored in this work can be extended to more complex patterns and other base microstructures, opening novel strategies to engineer properties in steel and other alloys.

Precipitation strengthening is an effective method to strengthen high-entropy alloys (HEAs); however, the incompatible plastic deformation caused by precipitates accelerates the initiation and development of cracks, reducing ductility. Therefore, it is necessary to spare no effort to overcome this strength–ductility trade-off. However, improving the ductility of HEAs without losing the precipitation-strengthening effect remains a daunting challenge. The strategy of this study is to increase chemical supersaturation without introducing other defects to drive the formation of high-density nanoprecipitates to share stress, reduce localization, and alleviate incompatible plastic deformation, thereby fully utilizing the strain-hardening ability to improve the ductility of HEAs without reducing their strength. Specifically, common Ni 35 (CoCrFe) 55 Al 5.5 Ti 4.5 (at.%) precipitation-strengthened HEAs were selected as the experimental object. Short-term high-temperature flash heating causes the dissolution of the initial nanoprecipitates, and the separated atoms form chemically supersaturated microregions in the matrix between the initial nanoprecipitates after insufficient short-range diffusion, resulting in the formation of high-density new nanoprecipitates. The density of the nanoprecipitates reaches 5.0 × 1024 m −3, representing a two-order increase in magnitude compared to the aging state (1.9 × 1022 m −3). By increasing the density of nanoprecipitates, multiple nanoprecipitates share stress together. Sufficient slippage of dislocations maximizes the potential excellent strain-hardening ability, considerably improving the ductility of HEAs. Moreover, the strategy of improving the ductility by increasing the density of nanoprecipitates can be applied to many other precipitation-strengthened alloy systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Copyright of Journal of Natural Sciences, Life & Applied Sciences is the property of Arab Journal of Sciences & Research Publishing (AJSRP) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Gold nanoparticles (Au NPs) based technology has been shown to possess enormous potential in the viral nucleic acid diagnosis. Despite significant advancement in this domain, the existing literature reveals the diversity in the conditions employed for hybridization and tagging of thiolated nucleic acid probes over the Au NPs. Here we employ the probe sequence derived from the Hepatitis C virus to identify the optimal hybridization and thiol-Au NP tagging conditions. In a typical polymerase chain reaction, the probes are initially subjected to flash heating at elevated temperatures to obtain efficient annealing. Motivated by this, in the current study, the hybridization between the target and the antisense oligonucleotide (ASO) has been studied at 65 °C with and without employing flash heating at temperatures from 75 to 95 °C. Besides, the efficiency of the thiolated ASO's tagging over the Au NPs with and without citrate buffer has been explored. The study has revealed the beneficial role of flash heating at 95 °C for efficient hybridization and the presence of citrate buffer for rapid and effective thiol tagging over the Au NPs. The combinatorial effect of these conditions has been found to be advantageous in enhancing the sensitivity of ratiometric genosensing using Au NPs. [ABSTRACT FROM AUTHOR]

At seismic slip rates, flash‐weakening can significantly reduce the coefficient of friction, and the magnitude of weakening increases with surface temperature. To quantify the distribution of flash temperature, high‐speed double‐direct shear experiments were conducted on Westerly granite blocks using velocity steps from 1 mm/s to 900 mm/s at 9 MPa normal stress. We employed a high‐speed infrared camera to measure surface temperatures on the moving block during sliding, and utilized a novel sliding‐surface geometry to control the mm‐scale contact history. Following the initial weakening upon the velocity step, the blocks slide at a constant coefficient of friction. Surface temperatures are inhomogeneously distributed across the sliding surface, and increase with displacement. To determine the local normal stress distribution at the mm‐scale, we combine a one‐dimensional thermal model with conventional flash‐weakening models that incorporate a surface temperature‐dependence informed by the controlled, mm‐scale contact history. Early contacts experience local normal stress exceeding 40 times the applied normal stress. As sliding progresses, the local normal stress at the hottest contacts decreases as contact area increases, leading to local normal stresses ranging from 2 to 6 times the applied normal stress on most contacts by 30 mm of slip. Increases in surface temperature, which would decrease the coefficient of friction, are buffered by wear processes that increase contact area and decrease the local normal stress. Treatments of flash heating are advanced by incorporating improved characterization of the state of the sliding surface at the mm and larger scales during sliding. Key Points: Flash surface‐temperature and local normal stress at millimeter and larger scale are inhomogeneous on rock interfaces during seismic slipMm‐scale contacts comprise ∼10% of the apparent area, flash to 200˚C–400˚C, and support local normal stress 6–20 times the macroscopic stressDynamic friction remains constant with increasing flash temperature as wear reduces local normal stress and increases contact area with slip [ABSTRACT FROM AUTHOR]

The microstructure of advanced high-strength steels (AHSSs) is usually designed via adjusting austenite decomposition behavior upon cooling, while relatively less attention was paid to austenite formation upon heating. Here we explore the potentials of flash heating in tuning the microstructure and mechanical behavior of Quenching & Partitioning (Q&P) steels with an emphasis on the role of chemical heterogeneity. Besides substantially refining intercritical austenite grains (e.g. austenite formed during intercritical annealing), it was interestingly found that flash heating can also allow intercritical austenite to inherit Mn heterogeneity in the original pearlite-ferrite microstructure due to the kinetic mismatch between the sluggish diffusion of Mn and the rapid austenite formation. Chemical heterogeneity can to a large extent alter the decomposition of intercritical austenite and carbon partitioning upon cooling, and plays a notable role in enhancing thermal stability of austenite. The role of chemical heterogeneity in austenite decomposition and carbon partitioning behavior was explained via phase field simulations. The flash treated Q&P (FQP) steels have a broad range of tensile strength (from 980 MPa to 1180 MPa) and good ductility, which outperforms the conventional Q&P (CQP) steels. The current study demonstrates that flash heating opens alternative routes to create unique microstructures and improve the mechanical performance of AHSSs. [ABSTRACT FROM AUTHOR]

Evolution of fault strength during the initial stages of seismic slip plays an important role in the onset of velocity‐induced weakening, which in turn, leads to larger earthquake events. A key dynamic weakening mechanism during the early stages of slip is flash heating, where stress concentrations at contacts on the interface lead to the rapid generation of heat. Although potential weakening from flash heating has been extensively modeled, there is little recorded microstructural evidence of its physical manifestations. We present results of a series of triaxial experiments on synthetic faults in quartz sandstone. Samples were subjected to a variety of normal stresses and ambient temperatures, to induce a range of slip event sizes and sliding velocities. We show the microstructural evolution of asperity interactions from the onset of flash heating through to the formation of grain‐scale areas of sheared melt. Using microstructural observations and mechanical data from the experiments, we model temperature and the viscoelastic behavior of the glass. Results suggest that, in the earliest stages of slip asperity contacts melt, but temperatures remain too low for viscous shear to occur within the melt layer. Instead melted asperities behave as glassy solids, facilitating continued frictional heating. With further slip, increased asperity temperatures allow the transition to viscous shear within the melt layer, facilitating weakening. These results highlight the dynamic evolution of the viscoelastic properties of the melt and resulting effects on asperity strength. Such complexity has, to‐date, not been fully addressed in modeling of flash heating. Key Points: A microstructural evolution of asperity interactions is documented from the onset of flash heating to the formation of sheared meltHigh strain rates and long relaxation times cause melted asperity tips to behave as glassy solidsMelt rheology is essential for understanding asperity behavior and strength during the early stages of earthquake slip [ABSTRACT FROM AUTHOR]

Retained austenite (RA) is especially valued in advanced high strength steels for its transformation-induced plasticity (TRIP) effect during deformation. However, the stabilization of RA in lean steels (C < 0.2, Mn < 2 wt%) is challenging due to the lack of austenite stabilization elements. In this study, a flash austenitization heat treatment approach was used to shorten the low-carbon TRIP steel processing time. This achieved a dual-phase microstructure composed of mass retained austenite and fine-grained ferrite in place of traditional bainite. Blocky, lamellar, and granular RAs were observed in the microstructure. Mn heterogeneity in the initial pearlitic cementite and ferrite was found to prevail in the retained austenite. Following the designed annealing route, phase-field simulations revealed that the ferrite transition kinetics accelerated in the Mn-depleted region which induced efficient carbon enrichment in austenite. The pronounced chemical heterogeneity of C and Mn co-resulted in the nonuniformity of the phase transition driving force from austenite to bainite and martensite, thus aiding the stabilization of austenite. • A Fe-0.2C-1.8Mn-1.4Si steel achieved a dual-phase microstructure by flash heating. • The microstructure composed of mass retained austenite (over 20 vol%) and fine-grained ferrite. • Mn heterogeneity in the initial pearlitic cementite and ferrite was found to prevail in the retained austenite. • The pronounced chemical heterogeneity of C and Mn co-aiding the stabilization of austenite. • The cooling and soaking process was simulated by Micress software. [ABSTRACT FROM AUTHOR]

Automotive steels with ultra-high strength and low alloy content under different heating and cooling processes were investigated. It was shown that those processes exhibited a great influence on the performance of the investigated steels due to the different auto-tempering effects. Compared with the steels under water quenching, there was approximately a 70% increase in the strength and elongation of steels under air cooling, in which the martensite was well-tempered. Although the elongation of the steel with a microstructure composed of ferrite, well-tempered martensite and less-tempered martensite could exceed 15%, the hole expansion ratio was still lower because of the undesirable hardness distribution between the hard phases and the soft phases. It followed from the calculation results based on SEM, TEM and XRD analyses, that for the steel under air cooling, the strengthening mechanism was dominated by the solid solution strengthening and the elongation was determined by the auto-tempering of martensite. Experiments and analyses aimed to explore the strengthening and plasticity mechanisms of auto-tempering steels under the special process of flash heating.

Abstract Heteroatom doping can enhance the electrochemical properties of graphene. However, unstable C N bonding at high temperature limits the concentration of nitrogen dopants. Intense pulsed light (IPL) was used to prepare heavily nitrogen-doped reduced graphene oxide (NrGO). Unlike general heating methods like thermal annealing, IPL provides ultrafast direct heating and cooling in the graphene layers because they serve as the heating source after light absorption. As this heat originates from the photothermal effect of surface plasmons on the graphene layers, nitrogen precursors are effectively decomposed. The fast cooling also generates a corrugated graphene structure with high specific surface area owing to thermal quenching. The electronic and structural properties of flash-heated NrGO (FH-NrGO) were investigated by X-ray photoelectron spectroscopy, Raman spectroscopy, and ultraviolet photoelectron spectroscopy, which revealed a high total nitrogen content of 26 at.% after flash heating at 1500 °C. Moreover, the nitrogen content could be varied by controlling the irradiation energy, and the electrochemical performance of FH-NrGO was better than that of NrGO prepared by general heating. Therefore, flash heating by IPL can be used to produce heavily nitrogen-doped graphene with superior electrochemical performance as an anode material for energy-storage devices. Graphical abstract Flash heating method was used to prepare heavily nitrogen-doped reduced graphene oxide (NrGO). Unlike general heating methods like thermal annealing, this method provides ultrafast direct heating and cooling in the graphene layers because they serve as the heating source after light absorption. This easy and straightforward method offered doping of graphene layers with a high concentration of about 26 at.% of nitrogen in a few milliseconds. Image 1 [ABSTRACT FROM AUTHOR]

Real contacts on the scale of ~10 μm support gigapascal shear tractions and normal tractions on rapidly sliding faults. At sliding velocities above ~0.1 m/s, the asperity tips of the contacts become hot and weak. The macroscopic friction depends on the average strength of the asperity tips during their lifetimes of contact. The strength of the asperity tips does not go essentially to zero once they become weak because frictional heating would then cease and the tips would cool and strengthen. Rather, the contact retains finite strength so that frictional heating balances the heat lost from the asperity tip by conduction. Crudely, the macroscopic coefficient of friction at high sliding velocities decreases with the inverse of the square root of velocity rather than the inverse of the velocity in the widely used model of Rice (2006, https://doi.org/10.1029/2005/JB004006). Numerical thermal‐mechanical models support this inference. The finite strength of the asperity tips retards lateral extrusion of weakened material from the tips. Otherwise, extrusion would allow the sliding surfaces to converge establishing new contacts, which would renew the strength of the surface. The macroscopic coefficient of friction with somewhat weakened asperity tips remains high enough that the fault surface becomes hot on a millimeter scale in large crustal earthquakes. Fluid pressurization and eventually millimeter‐scale melting then reduce the macroscopic shear traction to lower values than does asperity tip weakening acting alone. Plain Language Summary: Real contacts support macroscopic stresses on the sliding surfaces of crustal faults. The tips of the asperities of contacts become hot and weaken at the sliding velocities of crustal earthquakes. The strength of the asperity tips does not decrease to zero. Rather a balance is achieved between the heat generated by friction on the asperity tip and the heat lost by conduction. This balance allows the formulation of analytic and numerical models of the strength of crustal faults versus sliding velocity. Key Points: Thermal weakening of asperity tips of real contact reduces coefficient of friction above about 0.1 m/s sliding velocityThe fault retains enough strength that thermal pressurization or millimeter‐scale melt still occurs in large eventsThe asperity tips retain enough strength that they do not collapse and extrude under normal traction [ABSTRACT FROM AUTHOR]

Coseismic fault displacement is quite large at shallow depths in some earthquakes, and it implies that fault gouges and sediments have extremely low dynamic friction during seismic slip. However, the dynamic weakening mechanisms of gouges under wet conditions are still not well constrained. Here we present direct evidence for the occurrence of flash heating and local fluid pressurization in water‐saturated gouges, by performing low‐ to high‐velocity (V = 10 μm/s to 1 m/s) friction experiments in a pressure vessel, under conditions specially designed to suppress weakening effects of bulk thermal and compaction‐induced pressurization. The tested gouges exhibit transition from velocity strengthening to drastic velocity weakening as slip rates increase. Strong dynamic weakening starts to occur at V ≥ 0.04 m/s at the initiation of sliding (<~0.1 m), which is much more efficient than previously reported in terms of the weakening velocity and distance. Furthermore, the onset of weakening is always accompanied by an instantaneous dilatancy (10–25 μm), which is much larger than that observed in dry tests and in contrast with gradual changes displayed in the wet tests without dynamic weakening. Numerical modeling integrated with microstructural observation reveals that bulk thermal pressurization cannot explain the experimental results, while flash weakening triggered by vaporization of water layers on/around asperity contacts and the resultant local fluid pressurization may be responsible for the observed rapid weakening concomitant with instantaneous dilatancy. Given high efficiency of such weakening process, fluid‐infiltrated faults could be weakened more rapidly than previously recognized during seismic slip. Key Points: Dynamic weakening of wet gouges occurs at slip rates ≥40 mm/s at the onset of slip under conditions suppressing bulk fluid pressurizationThe onset of dynamic weakening is always contemporaneous with instantaneous dilatancyFlash weakening triggered by water vaporization around asperities and the resultant local pressurization may cause rapid dynamic weakening [ABSTRACT FROM AUTHOR]

The experimental shearing of granitic faults revealed complex evolution of strength and microstructure. We use a rotary shear apparatus to shear three types of granitic rocks at moderate slip velocity of 0.01-0.11 m/s, normal stress of 1.0-6.8 MPa, and slip distance up to 60 m. Three stages of strength evolution with slip distance were systematically observed. In Stage I, faults exhibited initial weakening in which the friction coefficient dropped to a steady state level of μ ≈ 0.3. This weakening is associated with powder lubrication and the development of cohesive gouge layers. Stage II included strengthening to μ ≈ 0.5 associated with volumetric expansion, melting of fault patches, and viscous braking at these patches. In Stage III, fault weakening is due to melt lubrication when the melted patches reach a critical fraction of the fault surface area. We show that this complex weakening-strengthening-weakening evolution is controlled by thermally activated deformation processes that can explain the friction behavior of igneous rocks at seismic velocity range. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mesostructure of α'/ γ steel was tailored by varying laser parameters. • Gradient microstructures resulted from steep temperature and heating rate gradients. • Formulated model predictions are in agreement with observed microstructures. • Specimen thickness and absorptivity determine laser heat penetration. • High heating rates produced pseudo-displacive α' → γ and recrystallization. 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. [ABSTRACT FROM AUTHOR]

Coseismic faulting may activate complicated physicochemical processes in the fault zone through both mechanical deformation and frictional heating. While plenty of work emphasizes the great importance of thermal effects on dynamic fault weakening, less attention has been paid to the mechanochemical effects. We study the effects of mechanochemical changes of chlorite on its dynamic weakening process via low- and high-velocity friction experiments, simultaneous thermal analysis, X-ray diffraction, microstructural observation, and numerical modeling in this work. With higher degrees of deformation, the experimentally sheared chlorite samples generally show more pronounced reductions in the onset temperature of thermal decomposition (T d 0 ; from 561 °C to 189 °C in the extreme case) and more striking increases in the reaction rate. The exponential-decay formula can well describe the relation between T d 0 and the mechanical work (integral of shear stress with respect to displacement) in the shear deformation. Moreover, the presence of pore water and the variation in chlorite content could significantly affect the mechanochemical changes of the sheared chlorite-bearing samples. Taking the markedly lowered T d 0 as the characteristic temperature leading to thermal softening of asperity contacts, numerical modeling shows that flash weakening of chlorite-rich samples can be significantly promoted, dwarfing the thermochemical pressurization that is also enhanced by mechanochemical effects though. This is largely supported by high-velocity experiments (∼m/s) performed on the pre-deformed chlorite samples, which show both lower peak friction and fracture energy, and earlier activation of dynamic weakening. Clearly, shear deformation plays a key role in aiding thermally-activated mechanisms in weakening faults and facilitating rupture propagation during earthquakes. • Shear deformation markedly reduces thermal decomposition temperature of chlorite. • Pre-deformed chlorite shows lower fracture energy and quicker dynamic weakening. • Shear deformation may significantly promote flash weakening in clay-rich faults. • Shear-enhanced thermochemical pressurization aids dynamic fault weakening. [ABSTRACT FROM AUTHOR]

In this study, flash heating was applied for activated carbon (AC) preparation to shorten the long production period as a new heating method. Activated carbons were prepared from agricultural residues of hazelnut shell (HS), rice husk (RH), and corn stalk (CS) by KOH activation in a short time below 15 min. Surface areas were 1650, 2573, and 2304 m2/g for activated carbons prepared from hazelnut shell, rice husk, and corn stalk, respectively. Obtained products were evaluated in metronidazole removal from an aqueous solution to determine the adsorption capacities of the as-prepared ACs. The adsorption data of metronidazole (MNZ) was analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherm models. Adsorption data for both HS-AC and RH-AC were best fitted by Langmuir isotherm, and the maximum adsorption capacities were 526 and 588 mg/g, respectively. The best suitable correlation for CS-AC was fitted with the Freundlich isotherm with a maximum capacity of 833 mg/g. Among the related kinetic models, pseudo-second-order was the best fitted for MNZ adsorption. The thermodynamic parameters were calculated by using the Von't Hoff equation and revealed that MNZ adsorption is an exothermic character and spontaneous nature. Experimental results showed that the applied flash heating method not only shortened the activated carbon production time but also enabled to prepare activated carbons with well-developed porous structure and excellent adsorption performance. [Display omitted] • Activated carbons were prepared from agricultural residues by flash heating method. • Carbonization and activation steps took approximately 20 min. • High surface area of 2573.45 m2/g was achieved via flash heating. • Maximum metronidazole adsorption capacity (q m) of 833 mg/g was reported. • Flash heating method proved a simple and innovative preparation route for low-cost activated carbon production. [ABSTRACT FROM AUTHOR]

This work presents constitutive equations and a dataset of a thermal model for the prediction of temperature fields and heating rates during the application of localized laser treatments to a Fe-C-Ni alloy. The model considers transient material properties and the coupling between temperature and microstructure, with emphasis on the phase dependence of the thermal parameters and the hysteresis in the phase change. The model can predict temperature fields that are in agreement with the experimental microstructures at the laser-affected zones. This model can be applied to other materials exhibiting solid-state transformations upon the application of laser treatments., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Author(s).)

Following the single-fuel initiative, the US Army is transitioning its power plants from running on various fuels to a single fuel—JP-8. Due to its low vapor pressure, JP-8 could not be used to cold start or run gasoline engines without extensive retrofit. The feasibility of running a low compression ratio, spark ignition engine with direct injection of heated JP-8 was investigated. A preliminary study found that a small piston-type spark ignition engine would not start or run on JP-8 unless JP-8 was heated to certain temperature. JP-8’s thermal decomposition, or coking, was found to be a serious issue that must be addressed if fuel heating method would be used. A flash heater concept was proposed to solve problems of JP-8’s low vapor pressure on running low compression ratio spark ignition engines, as well as JP-8’s coking issue at high temperature. A flash vapor fuel injector was designed and tested to be capable of heating up JP-8 from 26.7 °C to its vaporization temperature of >154.4 °C under one-tenth of a second at the required flow rate. The longest duration heating test (>1 million injections) did not show any coking sign with flash heating. Ignition test results show equivalent or superior ignition characteristics of pre-heated JP-8 (with heater temperature at 260.0 °C or above) provided by the developed flash vapor fuel injector, compared with non-heated aviation gasoline. [ABSTRACT FROM AUTHOR]