Rapid Heating Process Research Articles

Real-time laser ultrasonic monitoring of laser-induced thermal processes

Intra- and inter-layer integrity of components fabricated with advanced manufacturing techniques, such as laser powder bed fusion, is dependent upon rapid heating, melting, and solidification processes. There is a need for new techniques to provide in situ feedback of these processes. Here a laser-based ultrasonic technique to probe thermal effects induced by a high-power continuous wave laser in titanium samples is described. Numerical simulations were performed to show that, for a spatially uniform heating beam, laser-induced surface acoustic waves are strongly influenced by surface heating conditions, are dispersive in the case of rapid heating, and that an abrupt velocity reduction happens upon the onset of surface melting. Furthermore, laser-based ultrasound experimental results which monitor the transient change of surface wave travel time associated with high power laser surface heating are provided. A pulsed laser is used to generate high frequency surface acoustic waves that propagate through the laser-heated region and are detected using a photorefractive crystal-based interferometer. Qualitative agreement is observed between theory and experiment with both showing a rapid reduction in the surface wave velocity at the onset of illumination and further decrease in surface wave velocity associated with melting. It is demonstrated that changes in the surface wave velocity can be used to track local heating and detect the onset of surface melting in real time.

Microstructure and Composition Comparison of Ti‐ and Ta‐Doped Nb3Al Superconducting Wires Fabricated by RHQT Process

Herein, the microstructure and composition of the Ti‐ and Ta‐doped Nb3Al superconductor fabricated by rapid heating, quenching, and transformation (RHQT) process are compared. After rapid heating and quenching (RHQ) process, body‐centered cubic (bcc) phase is formed in all the wires, showing dark stripe and bright contrast morphology in the backscattered electron (BSE) images. After transformation heat‐treatment, all wires consist of A15 phase and show the same morphology as that of the quenched samples. Near‐stoichiometric composition is shown in 3 at% Ti‐ and Ta‐doped Nb3Al samples, but when doping amount is 10 at%, Ti‐doped sample has constant Nb content of 67 at% and Ta‐doped sample has Al + Ta content of 25 at%. Superconducting properties of both 3 at% Ti‐ and Ta‐doped Nb3Al samples are comparable and much superior than that of 10 at% doped samples, including critical temperature (Tc), critical current density (Jc), and irreversible field (Birr). Though 10 at% Ta‐doped Nb3Al has higher Tc than 10 at% Ti‐doped sample, it presents wider ΔTc value and lower Jc performance. When increasing the measurement temperature from 8 to 10 K, the decay ratio of Birr value for Ti‐doped Nb3Al superconductor follows the scaling law; however, the Ta‐doped samples are not the case.

Experimental investigation on the effect of open fire on the tensile properties and damage evolution behavior of granite

The stability of rock mass after fire is a concern of many engineering projects. In this paper, the effects of open fire and different cooling methods on granites were investigated. The static Brazilian test, dynamic Brazilian test, and P-wave velocity test were carried out to evaluate the mechanical properties and damage evolution behavior. A high-speed camera is employed to monitor the failure process of rock. The microstructures of the treated granites were observed by scanning electron microscope (SEM). The results showed that the fire duration and cooling treatment have a significant effect on the P-wave velocity, static nominal tensile strength, and dynamic nominal tensile strength of granite. These characteristics decrease rapidly during 0 to 10 min, and slowly decrease after 20 min. Compared to the air-cooling treatment, the water-cooling treatment has greater damage to the heated granite. To better understand the results, the rapid heating process of open fire heating was simulated using Abaqus software. The results reveal that there is a thinner compressive stress zone at the bottom of the specimen, and there is a large zone in the middle of the sample with higher tensile stress. The crack extension would be expanded due to high tensile stress, leading to the reduction of the tensile strength of the rock. This paper aims to better predict the degree of damage of rock materials after actual fire, as well as preliminarily explore the effect of the fire exposure duration and fire extinguishing method on the tensile properties of rock.

Prediction of the Non-Isothermal Austenitization Kinetics of Fe-C-Cr Low Alloy Steels with Lamellar Pearlite Microstructure.

The austenitization of low alloy steels during rapid heating processes was involved in many kinds of advanced heat treatment technologies. Most of the previous research on the austenitization kinetics was focused on the spherical pearlite microstructures, which were different from the lamellar pearlite microstructures. In the present research, to predict the non-isothermal austenitization process of an Fe-C-Cr steel with lamellar pearlite, a novel 3-dimensional (3D) cellular automata model, which considered the influences of the coupling diffusion of Cr and C, and the interfacial diffusion between pearlite lamellae and the pearlite lamellar orientation, was established based on the thermodynamic equilibrium data obtained from the Thermo-Calc software and the simulation results of the DICTRA module. To clarify the influences of the heating rate on the austenitization kinetics and validate the simulation results, the austenitization processes of a Fe-1C-1.41Cr steel for different heating rates were studied with a series of dilatometric experiments. The good agreements between the cellular automata simulation results and the experimental results showed that the newly proposed cellular automata model is reasonable. The experimental results show an obvious change of the transition activity energies from the low to high heating rates. The transition from partitioning local equilibrium (PLE) to non-partitioning local equilibrium (NPLE) mechanisms was proved with DICTRA simulations. Basing on the simulation results, the influences of the pearlite lamellae orientation on the austenitization kinetics and the topological aspects of austenite grains were evaluated. In addition, the topological aspects of the rapidly austenitized grains were also compared to the normal grains.

The study on rock thermal fractures at sliding surface of Jiweishan landslide

High temperatures lead to thermal fracture in the rock, which can greatly impair the rock's mechanical properties. During Jiweishan landslide, rocks on the sliding surface generate high temperatures due to frictional heating. Studies on thermal fracture during landslides and its influence on the sliding process are unclear. Here we use thermogravimetry and dilatometry to study the thermal expansion and thermal fracture of the rocks at the base of the 2009 Jiweishan landslide. Experimental results show that rocks generate a large number of thermal fractures and thermal expansion while reaching temperatures of up to 827.3 °C. The generation of CO2 gas also significantly produces and promotes thermal fractures. This indicates that the rapid heating process during the Jiweishan landslide could have caused thermal fractures on the sliding surface during the landslide, which could have then weakened the mechanical properties of the rock, making the sliding surface more susceptible to entrainment. As a result, the sliding surface lost frictional resistance during the landslide, resulting in a faster sliding velocity and a longer sliding distance. In addition, we infer that thermal fracture is beneficial for CO2 gas to be released from the rock and enter the sliding zone, which may produce pore pressure, reduce the effective normal stress on the sliding surface, and which also contributes to the lubrication.

Noble metal alloy thin films by atomic layer deposition and rapid Joule heating

Metal alloys are usually fabricated by melting constituent metals together or sintering metal alloy particles made by high energy ball milling (mechanical alloying). All these methods only allow for bulk alloys to be formed. This manuscript details a new method of fabricating Rhodium–Iridium (Rh–Ir) metal alloy films using atomic layer deposition (ALD) and rapid Joule heating induced alloying that gives functional thin film alloys, enabling conformal thin films with high aspect ratios on 3D nanostructured substrate. In this work, ALD was used to deposit Rh thin film on an Al2O3 substrate, followed by an Ir overlayer on top of the Rh film. The multilayered structure was then alloyed/sintered using rapid Joule heating. We can precisely control the thickness of the resultant alloy films down to the atomic scale. The Rh–Ir alloy thin films were characterized using scanning and transmission electron microscopy (SEM/TEM) and energy dispersive spectroscopy (EDS) to study their microstructural characteristics which showed the morphology difference before and after rapid Joule heating and confirmed the interdiffusion between Rh and Ir during rapid Joule heating. The diffraction peak shift was observed by Grazing-incidence X-ray diffraction (GIXRD) indicating the formation of Rh–Ir thin film alloys after rapid Joule heating. X-ray photoelectron spectroscopy (XPS) was also carried out and implied the formation of Rh–Ir alloy. Molecular dynamics simulation experiments of Rh–Ir alloys using Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) were performed to elucidate the alloying mechanism during the rapid heating process, corroborating the experimental results.

Coke-assisted microwave ignition and combustion behaviors of anthracite in a switching atmosphere

Low volatile coal has a large reserve but faces significant challenges in industrial applications. Due to the rapid and selective heating process, microwave-based technology is generally applied in various studies of carbonaceous materials. This work verified a novel non-contact microwave ignition of anthracite mixed with coke, where typical events of ignition or combustion were recorded by a digital camera. Video image analysis showed that the weakening of O2 to the tiny spark discharges between coke particles failed microwave heating. Hence a switching atmosphere (100% N2 firstly, then O2 at a certain proportion added) was used to ensure rapid microwave heating and subsequent ignition. Ignition of mixed anthracite & coke took place in the middle of the sample once the volatile flame appeared, which following the sample locally turned red-hot. The time for the flame burning was prolonged by the microwave power and especially the increase of O2 proportion. Gas products analysis showed a large amount of CO and CO2 instead of CH4 and H2O during the flame burning, which suggested that extra gasification reaction, where CO as product, supported the existence of flame. Moreover, the plasma generated by the violent discharge further expanded the range of the flame, with clear spectral peaks at 589 nm, 766 nm, and 770 nm. In addition, the distribution of coke in the mixture for effective ignition was also discussed. This study may provide a new idea for the application of low volatile coals.

Microstructure Evolution of Powder in Tube Nb3al Wires During Rapid Heating Process and Properties of the Transformed Superconducting Wires

Microstructure Evolution of Powder in Tube Nb3al Wires During Rapid Heating Process and Properties of the Transformed Superconducting Wires

Microstructure Evolution of Powder in Tube Nb3al Wires During Rapid Heating Process and Properties of the Transformed Superconducting Wires

Microstructure Evolution of Powder in Tube Nb3al Wires During Rapid Heating Process and Properties of the Transformed Superconducting Wires

One-shot high-resolution melting curve analysis for KRAS point-mutation discrimination on a digital microfluidics platform.

Single-nucleotide polymorphism (SNP) plays a critical role in personalized medicine, forensics, pharmacogenetics, and disease diagnostics. Among different existing SNP genotyping techniques, melting curve analysis (MCA) becomes increasingly popular due to its high accuracy and straightforward procedures in extracting the melting temperature (Tm). Yet, its study on existing digital microfluidic (DMF) platforms has intrinsic limitations due to the temperature inhomogeneity within a thickened droplet during the on-chip rapid heating process. Although the utilization of an on-chip thermostat can regulate and monitor the dynamic melting process in real time, the limited Tm accuracy resulting from the insufficient system response time to accommodate the fast-melting evolution still poses a great challenge for precise MCA with high throughput. This work proposes a one-shot MCA on a DMF platform. The tailoring of a functional substrate with hierarchical micro/nano structure enables high-resolution patterning of pL-scale droplets. Specifically, the hydrothermal and photocatalysis treatment allows the functional substrate to exhibit a superwettability contrast of >170°, facilitating passive isolation of the pL-scale DNA sample into highly-resolved pL droplets above the 200 μm superhydrophilic patterns. This high-resolution MCA technique can successfully discriminate KRAS gene targets with single-nucleotide mutations in 3 seconds. The high accuracy and consistency in the acquired Tm when compared with off-chip results demonstrate its opportunities for near-patient diagnostics, precision medicines, genetic counseling, and prevention strategies on DMF platforms.

Rapid sintering of 3 mol % Y<sub>2</sub>O<sub>3</sub>-doped ZrO<sub>2</sub> by a combined rapid furnace heating and shrinkage-controlled flash sintering protocol

Flash sintering has attracted much attention as a useful sintering technique that is able to lower the sintering furnace temperature and shorten the sintering time. To further improve this original flash sintering technique, we have developed a technique to facilitate shrinkage at a constant shrinkage rate by controlling the power dissipation during a flash state, which is termed as shrinkage-controlled flash (SCF) sintering. Here, we combine this SCF sintering method with a rapid furnace heating process to shorten the entire sintering process time. Accordingly, we succeed in sintering 3 mol % Y2O3-doped ZrO2 (3YSZ) polycrystals with a high density of 6.05 g/cm3 and a uniform grain size of approximately 0.47 µm with a short sintering time of approximately 40 min. The obtained 3YSZ polycrystals are confirmed to exhibit a Vickers hardness and fracture toughness [by an indentation fracture method] of approximately 1295 HV and 5.3 MPa m1/2, respectively.

The Interface Thermal Resistance Evolution between Carbide-Bonded Graphene Coating and Polymer in Rapid Molding for Microlens Array.

Surface rapid heating process is an efficient and green method for large-volume production of polymer optics by adopting 3D graphene network coated silicon molds with high thermal conductivity. Nevertheless, the heat transfer mechanism including the interface thermal resistance evolution between 3D graphene network coating and polymer has not been thoroughly revealed. In this study, the interface thermal resistance model was established by simplifying the contact situation between the coating and polymethylmethacrylate (PMMA), and then embedding into the finite element method (FEM) model to study the temperature variations of PMMA in surface rapid heating process. Heating experiments for graphene network were then carried out under different currents to provide the initial heat for heat transfer model. In addition, residual stress of the PMMA lens undergoing the non-uniform thermal history during molding was presented by the simulation model together. Finally, the optimal molding parameters including heating time and pressure will be determined according to calculation results of the interface thermal resistance model and microlens array molding experiment was conducted to illustrate that the interface thermal resistance model can predict the temperature of the polymer to achieve a better filling of microlens array with smooth surface and satisfactory optical performance.

Crystallization mechanism of Zr55Cu30Al10Ni5 metallic glass in an extended range of heating rates

The crystallization mechanisms of Zr55Cu30Al10Ni5 (Zr55) amorphous alloys from slow continuous heating to rapid laser heating are investigated. The multiphase nanocrystalline structures such as CuZr2-type, NiZr2-type and Al2Zr3-type phases with various compositions are observed at heating rates lower than 50 K/s, while the CuZr2-type/ZrCu-type eutectic dendrites are produced at heating rates higher than 50 K/s. A numerical model is established to calculate the onset crystallization temperatures as a function of the heating rates. This model indicates that in addition to rapid dendritic growth from a certain number of quenched-in nuclei, the non-Arrhenius behavior of high diffusion coefficient in the supercooled liquid region contribute to the serious crystallization during rapid heating process. The activation energy of dendritic crystallization is obviously smaller than that of multiphase nanocrystallization, which is due to a much smaller scale of diffusion distance and larger atomic diffusivity during dendritic growth.

In Situ Ultrafast and Patterned Growth of Transition Metal Dichalcogenides from Inkjet-Printed Aqueous Precursors.

Chemical vapor deposition (CVD) has been widely used to synthesize high-quality 2D transition-metal dichalcogenides (TMDCs) from different precursors. At present, quantitative control of the precursor with high precision and good repeatability is still challenging. Moreover, the process to synthesize TMDCs with designed patterns is complicated. Here, by using an industrial inkjet-printer, an in situ aqueous precursor with robust usage control at the picogram (10-12 g) level is achieved, and by precisely tuning the inkjet-printing parameters, followed by a rapid heating process, large-area patterned TMDC films with centimeter size and good thickness controllability, as well as heterostructures of the TMDCs, are achieved facilely, and high-quality single-domain monolayer TMDCs with millimeter-size can be easily synthesized within 30 s (corresponding to a growth rate up to 36.4 µm s-1 ). The resulting monolayer MoS2 and MoSe2 exhibits excellent electronic properties with carrier mobility up to 21 and 54 cm2 V-1 s-1 , respectively. The study paves a simple and robust way for the in situ ultrafast and patterned growth of high-quality TMDCs and heterostructures with promising industrialization prospects. Moreover, this ultrafast and green method can be easily used for synthesis of other 2D materials with slight modification.

Effect of Cu doping on properties of RHQT processed powder in tube Nb3Al wires

Powder-in-tube (PIT) Nb3(Al1-xCux)(x = 0–0.04) superconducting wires were fabricated by rapid heating, quenching and transformation (RHQT) process. With the addition of Cu, disordered Nb3Al A15 phase with stoichiometric composition was formed in the quenched wires and atomic long range ordering occurred during the low temperature annealing process, resulting in improvement of Tc, Jc and Birr performance compared to the pure Nb3Al sample. The highest Tc of 18.0 K, narrowest ΔTc of 0.6 K and best layer Jc of about 30481 A/cm2 @12 K, 4T was found in the Nb3(Al0·97Cu0.03) wire, which is nearly four times of pure Nb3Al sample. The Nb3(Al0·97Cu0.03) wire also shows the highest Birr value of 25.7T at 8 K and 12.9T at 12 K, respectively. The formed A15 phase exhibit uniform microstructure and composition. Flux pinning of the Nb3(Al1-xCux) wires follows the surface pinning mechanism, where grain boundary and stacking faults were considered as pinning centers.

Application of ohmic heating for the inactivation of microbiological hazards in food products

AbstractOhmic heating has long been used to inactivate pathogens in food products. Several research investigations on the use of ohmic heating technology in the inactivation of microbial hazards in food products are discussed in this review. These studies are discussed under the following sub‐headings: (a) inactivation of microbiological hazards, (b) in combination treatments with other sanitizing technologies, and (c) mathematical modeling, all of which are of long‐standing interest. In this review, we evaluate ohmic heating as a rapid and volumetric heating process that inactivates microbiological hazards in food products. We also examine ohmic heating‐based combination treatments as promising methods to maximize microbial inactivation efficacy and minimize the quality deterioration of food products. We first highlight the fact that most researchers had an interest in the inactivation of vegetative pathogens, whereas only a few focused on the inactivation of bacterial spores. In general, significantly higher treatment conditions were needed to inactivate bacterial spores (>95°C) than vegetative pathogens (>50°C). Studies on the inactivation of viral pathogens by ohmic heating are limited, and further research is needed in this field. In the first part of this review, the nonthermal effects of ohmic heating are also discussed, which is a popular topic in the food industry. Cumulatively, research suggests that that these nonthermal effects are dependent on the treatment conditions and the electrical conductivity of different food samples. Therefore, we suggest that focus should be on the thermal rather than the nonthermal effects of ohmic heating when considering the application of this technology to inactivate pathogens. Finally, we introduced combination technology based on ohmic heating and mathematical modeling, which are of interest recently.

Effects of electromagnetic induction hardening on the microstructure and mechanical properties of B1500HS steel

The effects of electromagnetic induction hardening process on the microstructure, original austenite grain sizes and mechanical properties of B1500HS steel are investigated in this paper. The results indicate that the electromagnetic induction hardening samples can obtain completely martensite with fine lath bundle size, and high tensile strength, which is up to 1626 MPa, and the original austenite grain size is fine and uniform when the heating temperature reaches 900°C. Compares with that of the resistance furnace heating quenching process, the samples treat by rapid heating process can obtain finer lath martensite structure and better mechanical properties after quenching.

Improving the Crystallinity and Purity of Monodisperse Ag Fine Particles by Heating Colloidal Sprays In-Flight

This work demonstrated the production of highly crystalline, monodisperse fine metal particles with high density and purity using a simple, facile rapid spray heating process. In this technique, a ...

Analysis and mitigation of defective circular structures in HPCVD-grown MgB2 thin films

In MgB2 films synthesized via hybrid physical-chemical vapor deposition, circular structures containing Mg microparticles were detected, with diameters ranging from 17 to 25 μm. The thinning of MgB2 film was observed inside these circular structures, which formation was found to be induced by rapid heating process and intense evaporation of Mg slugs. Tiny Mg droplets sputtering onto the substrates during rapid heating process influence the growth of MgB2 film and tend to form circular structures around Mg particles, which problem can be mitigated by slowing down the heating process. As a result, MgB2 films with smooth surfaces were obtained, which is instrumental in the fabrication of MgB2 film electronic devices.

Drastic Microwave Heating of Percolated Pt Metal Nanoparticles Supported on Al2O3 Substrate

Microwave (MW) heating of supported metal nanoparticles (NPs) presents attractive effects on catalysis such as the rapid heating processes and the enhancement of the reaction rate. Improving the heating property of the NPs, which act as the catalytic active sites, the MW effects will become more significant. Here we show a systematic study about the supported Pt NPs structure to improve the MW heating property. We found that the drastic heating was induced by a percolated Pt NPs structure, where the conduction electrons move around in the two-dimensional network. On the other hand, no heating was observed in an isolated Pt NPs system with the confined electrons. We conclude that the percolation of the Pt NPs giving the network structure is one of the important key factors for the efficient MW heating. The optimized Pt NPs catalyst leads to the dramatic MW effects on catalytic reactions.