Ultrafast Heating Rates Research Articles

Estimating energy release performance of oxidizer-activated aluminum fuel particles under ultrafast stimulus

Aluminum (Al) particles are good fuel additives to improve the energy output performances of explosives. Under detonation environment, reaction delay of Al particles plays a key role in the energy release efficiency. Up to date, reaction delay of Al particles is still limited by the efficiency of mass and heat transfer from oxidizers to Al particles. To address this issue, a homogeneous fuel-oxidizer assembly has recently become a promising strategy. In this work, oxidizer-activated Al fuel particles (ALG) were prepared with glycidyl azide polymer (GAP) as the oxidizer. The ALG was in uniform spherical shape and core-shell structure with shell layer of around 5 nm which was observed by scanning electron microscope and transmission electron microscope. The localized nanoscale mid-IR measurement detected the uniform distribution of characteristic absorption bond of GAP in the shell layer which confirmed the homogenous fuel-oxidizer structure of ALG. A thermal gravimetric analysis of ALG at ultrafast heating rate of 1000 °C/min under argon atmosphere was conducted. The decomposition of GAP finished much earlier than that of GAP at heating rate of 10 °C/min. Under ultrafast high laser fluence, the reaction response of ALG was characterized and compared with that of micro-sized Al (μAl). With the increase of laser energy, the propagation distance of the shock wave increased. However, the velocity histories were nearly the same when energies were lower than 299 mJ or higher than 706 mJ. The propagation distance of the shock wave for ALG was 0.5 mm larger than that for μAl at 2.1 μs. The underwater explosion showed the peak pressure and the shock wave energy of the ALG-based explosive were both higher than those of the μAl-based explosive at 2.5 m. This study shows the feasibility to improve the energy release of Al-based explosives via using the oxidizer-activated Al fuel particles with energetic polymer as the oxidizer.

Ultrafast synthesis of hard carbon anodes for sodium-ion batteries.

Hard carbons (HCs) are a significantly promising anode material for alkali metal-ion batteries. However, long calcination time and much energy consumption are required for the traditional fabrication way, resulting in an obstacle for high-throughput synthesis and structure regulation of HCs. Herein, we report an emerging sintering method to rapidly fabricate HCs from different carbon precursors at an ultrafast heating rate (300 to 500 °C min-1) under one minute by a multifield-regulated spark plasma sintering (SPS) technology. HCs prepared via the SPS possess significantly fewer defects, lower porosity, and less oxygen content than those pyrolyzed in traditional sintering ways. The molecular dynamics simulations are employed to elucidate the mechanism of the remarkably accelerated pyrolysis from the quickly increased carbon sp2 content under the multifield effect. As a proof of concept, the SPS-derived HC exhibits an improved initial Coulombic efficiency (88.9%), a larger reversible capacity (299.4 mAh⋅g-1), and remarkably enhanced rate capacities (136.6 mAh⋅g-1 at 5 A⋅g-1) than anode materials derived from a traditional route for Na-ion batteries.

Thermally-insulated ultra-fast high temperature sintering (UHS) of zirconia: A master sintering curve analysis

A thermally-insulated Ultra-fast High temperature Sintering (UHS) has been developed to maximize the densification of 3 mol% yttria-stabilized zirconia and improve the energy efficiency of the process. Thermally-Insulated UHS (TI-UHS) employed a fibreboard insulator, which reduced the energy consumption by ≈40% compared to the reference set-up. An ultrafast heating rate, approaching ≈2000°C/min, produced dense (99% relative density) and fine-grained (178±18 nm) microstructures within 60 s. By cross-linking finite element simulations with master sintering curves a good fit between experimental and predicted density was obtained, allowing the development of predictive models for UHS densification.

Ultrafast high-temperature sintering of silicon nitride: A comparison with the state-of-the-art techniques

Ultrafast High-temperature Sintering (UHS) has been successfully applied to fabricate the silicon nitride (Si3N4) bulks, as the first attempt of ultra-rapid consolidation of a non-oxide ceramics. At a heating rate of 875 °C/min, the bulk Si3N4 ceramic with a relative density greater than 96 % and an α-β phase transformation degree above 80 % could be obtained within 300 s. The effects of ultrafast heating on the liquid phase sintering (LPS) were also comparatively studied. Results showed that, the ultrafast heating rate and high temperature under UHS might promote the LPS system evolving to a nonequilibrium state. By comparing with other pressureless sintering processes with much lower heating rates, UHS apart from reducing the processing time, and it is also an effective method to form a bimodal microstructure composed of interlocked rod-like β-Si3N4 grains.

Electrospun carbon nanofiber-based flexible films for electric heating elements with adjustable resistance, ultrafast heating rate, and high infrared emissivity

Electrospun carbon nanofiber-based flexible films for electric heating elements with adjustable resistance, ultrafast heating rate, and high infrared emissivity

Effects of CO2 and H2O on coal pyrolysis with the ultrafast heating rate in a concentrating photothermal reactor

A novel concentrating photothermal reactor with the ultrafast heating rate at around 1800 °C/min was developed to study the effects of CO2 and H2O on coal pyrolysis for oxy-fuel combustion. The mass loss rate with the ultrafast heating rate increased by several decuples than that with the slow heating rate. Coal pyrolysis process with the ultrafast heating rate was promoted by CO2 within 50% concentration but inhibited for a further higher concentration (70%). The addition of H2O into 30% CO2 exhibited a continuous positive role in coal pyrolysis with the ultrafast heating rate. Different from the satisfied prediction of chemical reaction models with the slow heating rates, diffusion models were of higher correlation coefficients for the ultrafast-heating pyrolysis process. The correction factors for CO2 and H2O were determined accordingly, and the modified three-dimensional diffusion mechanism model based on Jander equation (D3 model) well described the ultrafast-heating coal pyrolysis process.

IMPROVING THE SURFACE STRUCTURE OF MASSIVE PARTS BY THE PLASMA METHOD

An increase in the reliability of the operation of large-sized and massive parts by plasma hardening of their surfaces is substantiated. It has been established that the formation of several structural zones of different microhardness is observed in detail along the depth of hardening, indicating the formation of a gradient-layered structure. It has been proved that at ultrafast heating rates, which occur during surface plasma hardening, phase and structural changes move to the high temperature region, changing the kinetics of the appearance and growth of new phase nuclei. In this case, fine-grained austenite is formed, which is transformed into a highly dispersed martensitic structure, which increases the strength and reliability of the surfaces of the parts.

Fast fabrication of Al3Ti/Al composites using combustion synthesis and melt dilution

A simple method combined combustion synthesis (CS) and melt dilution was utilized to fast fabricate Al3Ti/Al composites. This paper mainly focuses on analyzing the effect of heat source temperature (Ths) on combustion behaviors and reaction products in the 5Al-Ti system. The ultrafast heating rate induced by Ths could activate liquid-solid combustion in powder compacts. Due to the presence of Al3Ti layer acted as a diffusion barrier, it is suggested that reaction kinetics is mainly Ti-diffusion-controlled. Increasing the heating rate remarkably enhances the Ti flux across Al3Ti layer into the Al melt, which in turn releases a higher reaction exothermicity and finally promotes reaction to completion. Based on the above experimental results, a dissolution-precipitation mechanism for Al3Ti formation during CS was established.

Approaching the melting temperature: There regimes in the non-isothermal crystallization of Ce68Al10Cu20Co2 bulk metallic glass revealed by nanocalorimetry

Nanocalorimetry is an ideal candidate for revealing the crystallization of metallic glass in a wide temperature range attributing to its ultrafast heating rate and ultrahigh sensitivity. In this study, in situ preparation of Ce68Al10Cu20Co2 (at.%) metallic glass was realized by the nanocalorimetry. By the subsequent reheating at the rates from 500 to 40,000 K/s, the crystallization in a wide temperature range was demonstrated. The crystallization activation energy and Avrami exponent are calculated with the aid of the Kissinger and Johnson-Mehl-Avrami (JMA) equations to reveal the temperature-dependent nucleation and crystal growth behavior in the undercooled liquid, where three crystallization regimes are identified. At low temperature, the crystallization occurs with constant activation energy. In an intermediate temperature range, the crystallization is controlled by crystal growth with a reduction of activation energy. At temperatures approaching Tm, an increased activation energy resulting from the thermodynamic driving force dominates the nucleation-controlled crystallization. This study provides a novel strategy to reveal the crystallization behavior in the undercooled liquid from Tg to Tm and to demonstrate the transition from growth-controlled crystallization to nucleation-controlled one with the decrease of undercooling.

Effect of Backbone Rigidity on the Glass Transition of Polymers of Intrinsic Microporosity Probed by Fast Scanning Calorimetry.

Polymers of Intrinsic Microporosity (PIMs) of high performance have developed as materials with a wide application range in gas separation and other energy-related fields. Further optimization and long-term behavior of devices with PIMs require an understanding of the structure-property relationships, including physical aging. In this context, the glass transition plays a central role, but with conventional thermal analysis a glass transition is usually not detectable for PIMs before their thermal decomposition. Fast scanning calorimetry provides evidence of the glass transition for a series of PIMs, as the time scales responsible for thermal degradation and for the glass transition are decoupled by employing ultrafast heating rates of tens of thousands K s-1. The investigated PIMs were chosen considering the chain rigidity. The estimated glass transition temperatures follow the order of the rigidity of the backbone of the PIMs.

Fundamentals of isothermal austenite reversion in a Ti-stabilized 12Cr – 6 Ni – 2 Mo super martensitic stainless steel: Thermodynamics versus experimental assessments

This work addresses the fundamentals of inter-critical austenite reversion in a Ti-stabilized 12Cr-6Ni-2Mo (at.%) supermartensitic stainless steel, combining thermodynamic and experimental assessments. The calculation of the temperature and composition at which ferrite and austenite phases have the same free energy, i.e. T0 and C0(T), respectively, is discussed as a methodology to understand the austenite reversion and stabilization mechanisms. An ultra-fast heating rate of 500 °C s−1 provided isothermal austenite nucleation and growth from a fully solubilized martensite, allowing direct comparison with the compositional tie-lines and the transformation paths described by the free energy calculations. Isothermal transformation temperatures below and above T0 (625 °C) were used. Below T0, massive reversion was suppressed since it would imply a free energy increase. The opposite occurred above T0, since the critical Ni concentration for austenite reversion was lower than for the solubilized case. Transmission electron microscopy and atom probe tomography evidenced that, in all cases, lath growth occurred by local equilibrium partitioning of Ni, along with co-segregation of ferrite-stabilizing elements (Cr and Mo) at the advancing interface. The complex interaction between Cr, Ni and Mo on the energy gain upon nucleation of austenite revealed that Cr segregation can be beneficial while the adverse effect of Mo can be quickly outbalanced by Ni. The most stable reverted laths were obtained for transformation temperatures at least 15 °C below T0 with average austenite/martensite Ni partitioning factors higher than 2.0.

Insight into the induction hardening behavior of a new 0.40% C microalloyed steel: Effects of initial microstructure and thermal cycles

The induction hardening behavior of a new, hot-rolled 0.4 wt% carbon steel with the two different starting microstructures of upper and lower bainite has been simulated using a Gleeble 3800. The effect of heating rate in the range 1–500 °C/s on austenite grain size distribution has been rationalized. Dilatometry together with Scanning Electron Microscopy combined with Electron Backscatter Diffraction analyses and thermodynamic simulations provide insight into the austenite formation mechanisms that operate at different heating rates. Two main mechanisms of austenite formation during re-austenitization were identified: diffusional and diffusionless (massive). At conventional (1–5 °C/s) and fast (10–50 °C/s) heating rates the austenite formation mechanism and kinetics are controlled by diffusion, whereas at ultrafast heating rates (100–500 °C/s) the formation of austenite starts by diffusion control, but is later overtaken by a massive transformation mechanism. Comprehensive thermodynamic descriptions of the influence of cementite on austenite formation are discussed. The finest austenite grain size and the highest final hardness are achieved with a lower bainite starting microstructure processed with a heating rate of 50 °C/s to an austenitization temperature of 850 °C followed by cooling at 60 °C/s.

Fundamentals of Isothermal Austenite Reversion in a Ti-Stabilized 12cr - 6 Ni - 2 Mo Super Martensitic Stainless Steels: Thermodynamics Versus Experimental Assessments

This work addresses the fundamentals of inter-critical austenite reversion in a 12Cr-6Ni-2Mo supermartensitic stainless steel, combining thermodynamic and experimental assessments. The calculation of the temperature and composition at which ferrite and austenite phases have the same free energy, i.e. T0 and C0, is discussed as a methodology to understand the austenite reversion and stabilization mechanisms. An ultra-fast heating rate of 500 °C.s-1 provided isothermal nucleation and growth from a fully solubilized martensite, allowing direct comparison with the compositional tie-lines and the transformation paths described by the free energy calculations. Isothermal transformation temperatures below and above T0 (625 °C) were used. Below T0, massive reversion was suppressed since it would imply a free energy increase. The opposite occurred above T0, since the critical Ni concentration for austenite reversion (C0-Ni) was lower than the solubilized case. Nevertheless, transmission electron microscopy and Atom Probe Tomography evidenced that, in all cases, lath growth occurred by local equilibrium partitioning of Ni, along with co-segregation of ferrite-stabilizing elements (Cr and Mo) at the advancing interface. The complex interaction between Cr, Ni and Mo on the energy gain upon nucleation of austenite revealed that Cr segregation can be beneficial while the adverse effect of Mo can be quickly outbalanced by Ni. The concentration of Ni along the reverted laths was rather inhomogeneous due to isothermal coalescence and lack of redistribution. However, the most stable laths were obtained for transformations at least 15 °C below T0, with average austenite/martensite Ni partitioning factors higher than 2.0.

Exploring the microstructure and tensile properties of cold-rolled low and medium carbon steels after ultrafast heating and quenching

The aim of the present study is to evaluate the impact of heating rate on the microstructure and tensile properties of cold-rolled low and medium carbon steels. For this purpose, cold-rolled low and medium carbon steels were subjected to short peak-annealing experiments at 900 and 1100 °C under three heating rates (10, 450 and 1500 °C/s). The microstructure reveals a mixture of phases and microconstituents (ferrite, bainite, and as-quenched martensite) which are related to the carbon heterogeneities in austenite. The microstructural characterization suggests that the grain refinement achieved after ultrafast heating has a minor effect on the yield and ultimate tensile strength, compared to the relative microstructural distribution. It is suggested that the interplay of various strengthening mechanisms in samples subjected to ultrafast heating rates are responsible for the observed increase in strength and ductility.

Ultrafast, Reversible Transition of Superwettability of Graphene Network and Controllable Underwater Oil Adhesion for Oil Microdroplet Transportation

AbstractRecently, reversible surface superwettability has attracted enormous interest, and methods to shorten the cycle time of transition have also garnered the attention of researchers. Herein, a superhydrophobic, open‐cell graphene network (OCGN) is fabricated via self‐assembly of graphene oxide and vapor ejection. Owing to the special open‐cell microstructure, the OCGNs can be transformed to be superhydrophilic rapidly within only 1 s by air plasma treatment. Moreover, the OCGNs with pure graphene composition have a high conductivity and show an ultrafast Joule heating rate of up to 20 °C s−1 at a voltage of 20 V. By means of this property, for the first time an ultrafast recovery of the superhydrophobicity for OCGNs by self‐induced Joule heating with the shortest time of 1 min is reported. The mechanism of ultrafast, reversible transition is also explored specifically in this study. In addition, the superhydrophilic OCGNs show superoleophobicity in water and their underwater adhesion for oil droplets can be controlled by plasma treatment. Finally, the OCGNs with different oil adhesion properties are fabricated and the underwater oil microdroplet transportation is realized using OCGNs. Therefore, the OCGNs with smart surface can be an excellent candidate for achieving multifunctional superwettability of surfaces.

Reflection and refraction of a thermal wave at an ideal interface

Thermal waves are of great significance as non-Fourier effects arise with ultrafast heating rates and small system length. This study analytically and numerically investigated the behavior of thermal waves based on the Cattaneo-Vernotte model at an ideal interface. A stable, fast algorithm based on the alternative direction implicit method is introduced to solve the two-dimensional heat conduction problem. When thermal waves meet with an ideal interface, some energy is reflected back while the rest is conveyed across the interface, which are called the reflection and refraction of thermal waves. The changes of the profile and direction and the energy distribution between the reflection and refraction of the thermal waves are studied both analytically and numerically. Regardless of the boundary conditions imposed on the interface, the reflection angle is always identical to the incident angle, and the ratio of the sine of the refraction angle of the thermal waves to that of the incident angle is equal to the ratio of the thermal wave speeds in the two material layers. A theoretical equation to describe the relationships between the energy distribution and the material thermal properties shows that the thermal wave speeds in the materials, the specific heat and the incident angle determine the thermal energy transmittance ratio. Total reflection can occur for some conditions, and the nature of the energy conveyed by thermal waves is interesting and instructive.

The effect of the pre-heating stage on the microstructure and texture of a cold rolled FeCMnAlSi steel under conventional and ultrafast heating

This work focuses on the effect of a pre-heating stage on the microstructure evolution during continuous heating of 50% and 75% cold-rolled low carbon steel under conventional and ultrafast heating rates. Peak annealing experiments under two heating rates (10°C/s and 400°C/s) are applied to the samples after a pre-heating stage of 10s. The selected pre-heating temperatures (300°C and 400°C) show an influence on the phase fraction of austenite formed after a short holding time in the intercritical (α+γ) phase field, and an effect on the intensity of recrystallized ferrite texture components. A refinement of ferritic average grain diameter is observed after increasing the heating rate from 10°C/s to 400°C/s. It is concluded that a pre-heating stage has a negligible impact on the microstructure and texture of cold-rolled low carbon steel. Therefore, a suitable technological window for the application of ultrafast heating rates in steel processing is enabled.

The Effect of Ultrafast Heating on Cold-Rolled Low Carbon Steel: Formation and Decomposition of Austenite

The effect of heating rate on the formation and decomposition of austenite was investigated on cold-rolled low carbon steel. Experiments were performed at two heating rates, 150 °C/s and 1500 °C/s, respectively. The microstructures were characterized by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Experimental evidence of nucleation of austenite in α/θ, as well as in α/α boundaries is analyzed from the thermodynamic point of view. The increase in the heating rates from 150 °C/s to 1500 °C/s has an impact on the morphology of austenite in the intercritical range. The effect of heating rate on the austenite formation mechanism is analyzed combining thermodynamic calculations and experimental data. The results provide indirect evidence of a transition in the mechanism of austenite formation, from carbon diffusion control to interface control mode. The resulting microstructure after the application of ultrafast heating rates is complex and consists of a mixture of ferrite with different morphologies, undissolved cementite, martensite, and retained austenite.

Austenite formation in 0.2% C and 0.45% C steels under conventional and ultrafast heating

The austenite formation in 0.2% C and 0.45% C steels with the initial microstructure of ferrite and pearlite has been studied. The effect of conventional (10°C/s), fast (50°C/s–100°C/s) and ultrafast heating rates (>100°C/s) on the austenite nucleation and growth mechanisms is rationalized. Scanning Electron Microscopy (SEM), and Electron BackScatter Diffraction (EBSD) analyses provide novel experimental evidence of the austenite nucleation and growth mechanisms operating at ultrafast heating rates. Two mechanisms of austenite formation are identified: diffusional and massive. It is demonstrated that at conventional heating rates the austenite formation kinetics are determined by carbon diffusion, whereas at ultrafast heating rates formation of austenite starts by carbon diffusion control, which is later overtaken by a massive mechanism. Comprehensive thermodynamic and kinetic descriptions of austenite nucleation and growth are developed based on experimental results.

Three-Dimensional Printable High-Temperature and High-Rate Heaters.

High temperature heaters are ubiquitously used in materials synthesis and device processing. In this work, we developed three-dimensional (3D) printed reduced graphene oxide (RGO)-based heaters to function as high-performance thermal supply with high temperature and ultrafast heating rate. Compared with other heating sources, such as furnace, laser, and infrared radiation, the 3D printed heaters demonstrated in this work have the following distinct advantages: (1) the RGO based heater can operate at high temperature up to 3000 K because of using the high temperature-sustainable carbon material; (2) the heater temperature can be ramped up and down with extremely fast rates, up to ∼20 000 K/second; (3) heaters with different shapes can be directly printed with small sizes and onto different substrates to enable heating anywhere. The 3D printable RGO heaters can be applied to a wide range of nanomanufacturing when precise temperature control in time, placement, and the ramping rate are important.