Rapid Heating Rate Research Articles

Development of cube recrystallization textures in high-purity Al

Abstract High-purity (99.99 wt.%) Al containing 50 wt. ppm Cu was cold rolled to 98% reduction in thickness and annealed by varying the heating rate of annealing and annealing cycles. Textures developed at various stages of annealing were investigated with the orientation distribution function analysis. The observed results were compared with those obtained on standard high purity (99.99 wt.%) Al without Cu addition. In slow heating rate annealing, it was found that in high purity Al the addition of 50 wt.ppm Cu significantly enhanced the development of {100}<001> recrystallization textures. Intensities of {100}<001> developed in high purity Al with 50 wt. ppm Cu were about twice as high as those observed in high purity Al without Cu addition. {123}<634> R orientations were completely eliminated by the addition of 50 wt. ppm Cu. In rapid heating annealing, on the other hand, annealing at temperatures above 325 °C resulted in the formation of very coarse recrystallized grains with weak {100}<001> recrystallization textures irrespective of Cu content. Such grain coarsening could be suppressed by pre-annealing at temperatures between 225 and 300 °C. In the specimens subjected to this pre-annealing, strong {100}<001> recrystallization textures could be obtained, even if they were annealed with a rapid heating rate in final annealing.

Thermal stress-assisted annealing to improve the crystalline quality of an epitaxial YSZ buffer layer on Si

A rapid heating rate (∼110 °C s−1) allows strain energy to maximally build up in the YSZ layer at the annealing temperature, and the defects are effectively annihilated during annealing.

Oxygen Kinetic Isotope Effects in the Thermal Decomposition and Reduction of Ammonium Diuranate.

Oxygen stable isotopes in uranium oxides processed through the nuclear fuel cycle may have the potential to provide information about a material’s origin and processing history. However, a more thorough understanding of the fractionating processes governing the formation of signatures in real-world samples is still needed. In this study, laboratory synthesis of uranium oxides modeled after industrial nuclear fuel fabrication was performed to follow the isotope fractionation during thermal decomposition and reduction of ammonium diuranate (ADU). Synthesis of ADU occurred using a gaseous NH3 route, followed by thermal decomposition in a dry nitrogen atmosphere at 400, 600, and 800 °C. The kinetic impact of heating ramp rates on isotope effects was explored by ramping to each decomposition temperature at 2, 20, and 200 °C min–1. In addition, ADU was reduced using direct (ramped to 600 °C in a hydrogen atmosphere) and indirect (thermally decomposed to U3O8 at 600 °C, then exposed to a hydrogen atmosphere) routes. The bulk oxygen isotope composition of ADU (δ18O = −16 ± 1‰) was very closely related to precipitation water (δ18O = −15.6‰). The solid products of thermal decomposition using ramp rates of 2 and 20 °C min–1 had statistically indistinguishable oxygen isotope compositions at each decomposition temperature, with increasing δ18O values in the transition from ADU to UO3 at 400 °C (δ18OUO3 – δ18OADU = 12.3‰) and the transition from UO3 to U3O8 at 600 °C (δ18OU3O8 – δ18OUO3 = 2.8‰). An enrichment of 18O attributable to water volatilization was observed in the low temperature (400 °C) product of thermal decomposition using a 200 °C min–1 ramp rate (δ18OUO3 – δ18OADU = 9.2‰). Above 400 °C, no additional fractionation was observed as UO3 decomposed to U3O8 with the rapid heating rate. Indirect reduction of ADU produced UO2 with a δ18O value 19.1‰ greater than the precipitate and 4.0‰ greater than the intermediate U3O8. Direct reduction of ADU at 600 °C in a hydrogen atmosphere resulted in the production of U4O9 with a δ18O value 17.1‰ greater than the precipitate. Except when a 200 °C min–1 ramp rate is employed, the results of both thermal decomposition and reduction show a consistent preferential enrichment of 18O as oxygen is removed from the original precipitate. Hence, the calcination and reduction reactions leading to the production of UO2 will yield unique oxygen isotope fractionations based on process parameters including heating rate and decomposition temperature.

Evolution mechanism of dynamic thermal parameters of shale

In situ conversion is a process that converts organic matter into light oil and gas via underground in situ heating, which leads to changes in shale material composition and dynamic changes in thermal field parameters. At present, there is a lack of understanding of the evolution behavior and mechanism associated with dynamic thermal field parameters of shale. The dynamic thermal field parameters of shale with different organic matter abundances at various temperatures, orientation, heating rates, and pressures are obtained using an improved surface thermal source method and the laser flash method. The results show that the changes in dynamic thermal field parameters of shale are mainly controlled by organic matter abundance. The thermal diffusivity of shale decreases with the increase in temperature, and the thermal conductivity presents an “M-shaped” dynamic evolution with temperature. The thermal conductivity and thermal diffusivity of shale parallel to bedding are higher than those shale that are perpendicular to bedding. The rapid heating rate decreases thermal diffusivity above 200 °C, which is believed to be due to the instantaneous weight loss rate at high temperatures. The thermal conductivity and thermal diffusivity of shale parallel and perpendicular to bedding show the following two-stage evolution characteristics with the increase in pressure. Through matrix analysis, the bi-directional thermal conductivity model of shale with different organic matter abundances under different temperature and pressure conditions is constructed, which provides accurate parameters for studying dynamic thermal field evolution and efficient heat transfer during in situ conversion.

A novel approach for processing CaAlSiON glass-ceramics by spark plasma sintering: Mechanical and electrical properties

Lithium containing glassy materials can be used as solid electrolytes or electrode materials for lithium-ion batteries due to their high energy density. Conventional melt-quenched Ca11Al14Si16O49N10 glass powder containing 24 e/o N, doped with Li-ions (1, 3, and 6 wt. %) and sintered by spark plasma sintering technique (SPS) was studied. The benefits of using SPS to produce glass-ceramics are rapid heating rates compared to conventional consolidation techniques and tuning of properties, adjusting the temperature, holding time (closed to Tg temperature), heating rate (solidification), and pressure (densification) profile during the heat treatment using SPS. Pure glass and glass-ceramic were obtained under identical SPS conditions and compared with pristine oxynitride and soda-lime-silicate (float) glasses. XRD and SEM analysis confirmed that increasing the amount of Li increases the crystallinity in the glass matrix. Nano-indentation analysis showed a decreased hardness and reduced elastic modulus values with the addition of Li-ions. The direct current conductivity increases with the addition of Li due to the high mobility of Li-ions. However, the float glass sample doped with 6 wt.% of Li exhibits even higher values of D.C. conductivity, than the analogously doped Ca11Al14Si16O49N10 glass. The magnitude of activation energy (more than 1 eV) is typical for an ion hopping mechanism and the D.C. conduction mechanism is dominated by Li+ hopping.

Mechanistic and Machine Learning Modeling of Microwave Heating Process in Domestic Ovens: A Review.

The domestic microwave oven has been popularly used at home in heating foods for its rapid heating rate and high power efficiency. However, non-uniform heating by microwave is the major drawback that can lead to severe food safety and quality issues. In order to alleviate this problem, modeling of microwave heating process in domestic ovens has been employed to simulate and understand the complicated interactions between microwaves and food products. This paper extensively reviews the mechanistic models with different geometric dimensions and physics/kinetics that simulated the microwave heating process. The model implementation and validation strategies related to the model accuracy and efficiency are also discussed. With the emergence of the machine learning technique, this paper also discusses the recent development of hybrid models that integrate machine learning with mechanistic models in improving microwave heating performance. Besides, pure machine learning models using only experimental data as input are also covered. Further research is needed to improve the model accuracy, efficiency, and ease of use to enable the industrial application of the models in the development of microwave systems and food products.

DC electric field‐assisted hot pressing of zirconia: Methodology, phenomenology, and sintering mechanism

AbstractFlash sintering (FS) is an important technique in the field of ceramic sintering. Nevertheless, conventional FS is less attractive for practical applications because of the complex shapes and small sizes of the specimens. In this study, using the novel electric field‐assisted hot pressing (FAHP) technique, we successfully achieved FS during the net‐shape hot pressing (HP) process for the first time. It was found that the 3 mol% yttria‐stabilized zirconia (3YSZ) can be flash sintered at 909°C using a fairly low DC field of 33 V/cm under 30 MPa pressure. The grain sizes of the FAHP‐sintered samples were 20% smaller than that of the HP‐sintered sample. When the current density limit is ≥240 mA/mm2, 3YSZ can be fully densified during the flash events. Careful analysis of the sintering curves suggests that although the carrier type or concentration is changed during flash events, it cannot explain the ultrafast densification. Additionally, we devised a qualitative method to analyze the densification mechanism. The results indicated that the ultrafast densification observed during flash events resulted from the synergistic effects of the rapid heating rate and peak sample temperature. Finally, the atomic force microscopy confirmed the lower grain boundary energy for the FAHP‐sintered samples, which accounts for the smaller grain sizes than the HP‐sintered sample. We believe that the FAHP technique could create new possibilities for theoretical and applied research on field‐assisted sintering techniques.

Single-Step Synthesis Process for High-Entropy Transition Metal Boride Powders Using Microwave Plasma

A novel approach is demonstrated for the synthesis of the high entropy transition metal boride (Ta, Mo, Hf, Zr, Ti)B2 using a single heating step enabled by microwave-induced plasma. The argon-rich plasma allows rapid boro-carbothermal reduction of a consolidated powder mixture containing the five metal oxides, blended with graphite and boron carbide (B4C) as reducing agents. For plasma exposure as low as 1800 °C for 1 h, a single-phase hexagonal AlB2-type structure forms, with an average particle size of 165 nm and with uniform distribution of the five metal cations in the microstructure. In contrast to primarily convection-based (e.g., vacuum furnace) methods that typically require a thermal reduction step followed by conversion to the single high-entropy phase at elevated temperature, the microwave approach enables rapid heating rates and reduced processing time in a single heating step. The high-entropy phase purity improves significantly with the increasing of the ball milling time of the oxide precursors from two to eight hours. However, further improvement in phase purity was not observed as a result of increasing the microwave processing temperature from 1800 to 2000 °C (for fixed ball milling time). The benefits of microwave plasma heating, in terms of allowing the combination of boro-carbothermal reduction and high entropy single-phase formation in a single heating step, are expected to accelerate progress in the field of high entropy ceramic materials.

Probing boron thermite energy release at rapid heating rates

Boron (B) is a promising fuel for energetic materials due to its high gravimetric and volumetric energy density. The enhanced ignition and combustion of B in a thermite with CuO and Bi2O3 and their mixtures compared to single metal oxides was recently demonstrated. In this study, we compared the early-time reaction B-thermite mixtures using the laser-induced air shock from energetic materials (LASEM) technique, bomb calorimetry, and differential scanning calorimetry (DSC). The application of LASEM to B/metal oxide samples has enabled the quantification of their microsecond-timescale energy release and excitation temperatures under extremely high heating rates, and the elucidation of their chemistry differences on both the microsecond and millisecond timescales. The time to peak combustion determined by LASEM follows the trend B/CuO/Bi2O3 < B/Bi2O3 < B/CuO. The energy release measured by LASEM on both the microsecond- (laser-induced shock velocities) and millisecond- (combustion reactions) timescales was the highest for B/CuO/Bi2O3. These relative measurements are in agreement with the heat of reaction as measured by the bomb calorimetry and onset of DSC traces, which follow similar ordering and suggests that enhanced ignition of these composites is contributing to the early-time energy release. Finally, our morphology characterization revealed that CuO has a strong affinity for both B and Bi2O3; we suggest the CuO pulls the Bi2O3 into closer contact with the B particles in the binary metal oxide mixture, resulting in a synergetic enhancement effect compared to the single metal oxide.

Microwave-Assisted Preparation of Luminescent Inorganic Materials: A Fast Route to Light Conversion and Storage Phosphors.

Luminescent inorganic materials are used in several technological applications such as light-emitting displays, white LEDs for illumination, bioimaging, and photodynamic therapy. Usually, inorganic phosphors (e.g., complex oxides, silicates) need high temperatures and, in some cases, specific atmospheres to be formed or to obtain a homogeneous composition. Low ionic diffusion and high melting points of the precursors lead to long processing times in these solid-state syntheses with a cost in energy consumption when conventional heating methods are applied. Microwave-assisted synthesis relies on selective, volumetric heating attributed to the electromagnetic radiation interaction with the matter. The microwave heating allows for rapid heating rates and small temperature gradients yielding homogeneous, well-formed materials swiftly. Luminescent inorganic materials can benefit significantly from the microwave-assisted synthesis for high homogeneity, diverse morphology, and rapid screening of different compositions. The rapid screening allows for fast material investigation, whereas the benefits of enhanced homogeneity include improvement in the optical properties such as quantum yields and storage capacity.

Spark plasma sintering of CNT-NiAl nanocomposites – Process parameter, densification mechanism, and grain analysis

The densification process and grain analysis of consolidated NiAl-CNT composites at 1000 °C, and at varied heating rates from 50 °C/min to 150 °C/min was investigated. The results revealed the effect of heating rate on the densification behaviour of the samples. The displacement of the composites decreased from 3.39 mm to 2.63 mm with increasing heating rate, while the porosity increased by 69% at rapid heating rate. The grain analysis of the sintered samples through the electron backscattered (EBSD) technique indicates the evolution of bigger grains as the heating rate proceeds higher. Furthermore, the mean grain size of the consolidated composites increased from 3.93 μm, to 8.05 μm due to the concentration of defects. Interestingly, there was no texture or predominance of any color evolution in the sintered materials.

Investigation on the structural feature and gasification reactivity of bio-char derived from energy crop

A kind of energy crops (Arundo donax) was selected to investigate effects of pyrolysis heating rate (PHR) on char structure and CO2 gasification reactivity. The gasification reactivity and microstructure of char obtained at various PHR were explored. Besides, the surface morphology, microcrystalline and aromatic structure of bio-chars were analyzed via scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The results reveal that the main thermal decomposition of Arundo donax occurs in the range of 180 °C - 570 °C. The surface of chars obtained at rapid pyrolysis appears to be rougher than that under slow pyrolysis. Rapid pyrolysis results in high temperature gradient inside and outside the particles, leading to condensation of free radical fragments in a short time. The bio-char obtained at rapid heating rate has more structural defects and imperfections of the carbon crystallites. Besides, the crystallization size, graphitization and aromatization degree decrease of bio-char were inhibited as the PHR increased. In addition, some H2O-soluble K was volatilized with the increase of heating rate, and a small part was converted to NH4Ac-soluble K during pyrolysis. Therefore, the gasification reactivity of chars obtained from rapid pyrolysis rate was higher than that from the low pyrolysis rate, which was associated with the formation of alkali metal distribution and micro-areas structure evolution in the bio-chars.

Applications of Concentrating Photothermal Reactor in Coal Combustion Research

High temperature, rapid heating rate and application potential of special reaction conditions (high pressure, high humidity, corrosive atmosphere) made the concentrating photothermal reactor (CPR) become a hot spot in the thermal experimental research. By the 1930s, the concepts of radical reactions and thermal equilibrium concepts had contributed to the formation of theoretical basis of coal combustion. The application of concentrating photothermal reactor in coal combustion research had provided a new perspective for this traditional subject. This paper introduced the structure and characteristics of concentrating photothermal reactor, and summarized the latest research results on the influence of heating rate, oxygen concentration and biomass addition on coal combustion. A potential frontier research direction - pressurized combustion based on concentrating photothermal reactor was also proposed.

Microwave vacuum evaporation as a potential technology to concentrate sugar solutions: A study based on dielectric spectroscopy

Traditional vacuum evaporation in the sugar industry generally relies on steam and is characterized by low energy efficiency. Microwaves may be an alternative heat source to steam. In this study, three sugar solutions (glucose, maltose, and trehalose) were concentrated by lab-scale microwave vacuum evaporation (MVE). The dielectric spectroscopy in the frequency range of 0.1-6.5 GHz and the temperature range of 5-90 °C was determined and analyzed. Results showed that the dielectric loss factor increased with concentration and decreased with temperature at 2.45 GHz. The maltose solution had a lower microwave absorption and conversion capacity than glucose or trehalose solution. Meanwhile, the hydrogen bond interactions of trehalose solution were stronger, contributing to higher intermolecular interactions. These results may account for the distinct evaporation efficiencies of MVE on the three sugar solutions. Due to the rapid heating rate (up to 2.86 ± 0.08 °C/s) and massive water loss (closer to 2/3 total mass of the feed solution) over a short period of time (10 min at a microwave power density of 40 W/g and a vacuum pressure of 50 kPa), MVE may be a substitute for conventional methods. Furthermore, the dielectric spectroscopy can be an effective tool to help guide MVE to obtain sugars with high quality. • Dielectric spectroscopy of three sugar solutions was determined and analyzed. • Maltose solution had weaker microwave absorption and conversion ability. • Strong intermolecular interactions in trehalose solution impeded evaporation. • Rapid heating and massive water loss occurred during microwave vacuum evaporation. • Microwave vacuum evaporation may be a substitute for conventional evaporation.

Rapid pressure-less and spark plasma sintering of (Ba0.85Ca0.15Zr0.1T0.9)O3 lead-free piezoelectric ceramics

This work shows for the first time the possibility to sinter BCZT powder compacts by rapid heating rates within one hour of sintering, while achieving good piezoelectric properties. The sintering was performed by rapid (heating rates 100 and 200 °C/min) pressure-less sintering (PLS) at 1550 °C/5-60 min and by SPS sintering (100 °C/min, 1450 °C/5−60 min and 1500 °C/15−45 min). The rapid PLS samples reached a relative density up to 94 % and grain sizes of 17–36 μm acquiring d33 up to 414 pC/N. Although the SPS samples reached full density at 1450 °C, their piezoelectric properties worsened due to smaller grains (10−15 μm) as well as formation of cracks at dwell times > 30 min. At elevated SPS temperature of 1500 °C/30 min, the d33 increased to 360 pC/N sustaining full density. Even higher increase in d33 (424 pC/N) of SPS samples was achieved by post-rapid PLS at 1550 °C/60 min resulting from further expansion in grain size.

Melt-Spun SiGe Nano-Alloys: Microstructural Engineering Towards High Thermoelectric Efficiency

Silicon-germanium (SiGe) alloys are prominent high-temperature thermoelectric (TE) materials used as a powering source for deep space applications. In this work, we employed rapid cooling rates for solidification by melt-spinning and rapid heating rates for bulk consolidation employing spark plasma sintering to synthesize high-performance p-type SiGe nano-alloys. The current methodology exhibited a TE figure-of-merit (ZT) ≈ 0.94 at 1123 K for a higher cooling rate of ∼3.0 × 107 K/s. This corresponds to ≈ 88% enhancement in ZT when compared with currently used radioisotope thermoelectric generators (RTGs) in space flight missions, ≈ 45% higher than pressure-sintered p-type alloys, which results in a higher output power density, and TE conversion efficiency (η) ≈ 8% of synthesized SiGe nano-alloys estimated using a cumulative temperature dependence (CTD) model. The ZT enhancement is driven by selective scattering of phonons rather than of charge carriers by the high density of grain boundaries with random orientations and induced lattice-scale defects, resulting in a substantial reduction of lattice thermal conductivity and high power factor. The TE characteristics of synthesized alloys presented using the constant property model (CPM) and CTD model display their high TE performance in high-temperature regimes along with wide suitability of segmentation with different mid-temperature TE materials.

Comprehensive study on intrinsic combustion behavior of non-premixed coal-biomass pellet at rapid heating rate

Non-premixed pelletization was proposed in low-cost coal-biomass pellet production for Circulating Fluidized Bed combustors. A novel non-premixed pelletization structure C-B-C (coal-biomass-coal) was proposed according to simulation results. Comprehensive study on the combustion behaviour of non-premixed coal-biomass pellet with such structure was carried out at heating rate over 200 ℃/s in a concentrating photothermal reactor. The result showed that the addition of biomass in non-premixed coal-biomass pellet could promote the combustion process but also cause slagging. The addition of biomass significantly increased the reaction index of the whole combustion process while the activation energies during devolatilization to ignition decreased linearly from 47.44 kJ/mol to 23.18 kJ/mol. Biomass promoted CO generation, increased NO emission (due to higher N content and lower chamber temperature) and decreased SO2 emission, during the combustion of non-premixed coal-biomass pellets. The feasibility of coal-biomass non-premixed pelletization method was verified.

Effective cure cycle development via flow optimization and advanced cure environments

Out-time and moisture absorption in prepregs are generally unavoidable in an industrial setting, where prepreg layup can take weeks. The resin cross-linking and viscosity increase that occurs during out-time can reduce resin flow during a specified cure cycle, causing porosity. In this study, a flow-optimized cure cycle was developed, leveraging both flow level and time during out-of-autoclave (OoA) processing. First, predictive cure kinetics and viscosity models were used to model viscosity evolution under selected cure conditions, accounting for initial out-times and humidity conditioning. To quantify resin flow, an ‘effective flow number’ metric was defined as the integration of inverse viscosity evolution until the resin gelation point. The method described revealed that a rapid heating rate achieved by use of advanced tooling was essential to achieve a high effective flow number. The experimental results showed that the effective flow number is a useful criterion to limit flow-induced defects. The method presented also extends the boundary (by 175%) of the manufacturer’s specified out-life for OoA prepreg materials.

Effect of heating rate during solution treatment on microstructure, mechanical property and corrosion resistance of high-strength AA 7075 alloy

The heating rate during solution treatment exerted great influence on the final grain structure of AA 7075 alloy processed by thermo-mechanical treatment (TMT). In case of rapid heating rate, particle-stimulated nucleation (PSN) of recrystallization occurred and fine equi-axed structure with an average grain size of ~9 μm was obtained. On the contrary, when a slow heating rate was adopted, the resulting recrystallized grains were rather coarse and elongated (average grain length > 100 μm). After peak-ageing treatment, the mechanical property and corrosion resistance of 7075 sheets were closely associated with those grain structures. Specifically, two kinds of sheets exhibited equivalent strength while the ductility of fine-grained sample is considerably increased to 18.5%, 49% higher than that (12.4%) of coarse-grained sheet. Meanwhile, inter-granular corrosion (IGC) and exfoliation corrosion (EXCO) tests certify that the fine-grained sheet exhibited significantly enhanced corrosion resistance. Effective grain refinement induced by rapid solution treatment accounts for the notable increment in both ductility and corrosion resistance. Our results demonstrate that the comprehensive properties of 7000 alloys might be tailored by adopting proper heating rate when the alloys are subjected to solution treatment.

Effects of total pressure and CO2 partial pressure on the physicochemical properties and reactivity of pressurized coal char produced at rapid heating rate

Abstract The effects of the total pressure (0.1–1.3 MPa) and the CO2 partial pressure (0–0.45 MPa) on the physical structural properties, chemical structural properties and reactivity of Shenhua coal pressurized char at 1273 K were investigated in a pressurized drop tube furnace (PDTF). There were reverse-direction effects on char yield between total pressure and CO2 partial pressure for char preparation. Porosity characteristics were performed using an ASAP2020 instrument. It was found that same-direction increment effects on BET surface and porosity between total pressure and CO2 partial pressure for char preparation. Carbon structure and surface structure were performed by Raman and XPS methods. The results showed that both total pressure and CO2 partial pressure can promote the transformation of small aromatic structures to large aromatic structures and increase the graphitization degree of the char. With increasing total pressure and CO2 partial pressure, the unstable N-5 content decreased, while the N-6 and N-Q content increased.