Increasing Heat Treatment Temperature Research Articles

Radiofrequency pasteurization of Aspergillus flavus ATCC 28539 spores at cellular and molecular levels

Radio frequency (RF) heating has been used to study pasteurization technology, but its mechanism has not been thoroughly studied, especially for fungi. In this paper, pasteurization processes and potential bactericidal mechanisms of Aspergillus flavus spore using RF was investigated. The best heating and pasteurization efficiency were achieved at (Electrode gap 130 mm, conductivity of spore suspension 0.1 S/m, volume of spore suspension 40 mL). At the cellular level, with the increase of RF heating temperature to 80 °C, the number of surviving cells decreased dramatically, the degree of cellular damage deepened through observation, the absorbance values of nucleic acid and protein increased to 0.468 ± 0.016 and 0.526 ± 0.023 respectively, the conductivity reached 99.0 ± 0.5%, the fluorescence intensity of reactive oxygen content increased to 51.6 ± 1.6 AU, while adenosine triphosphate (ATP) concentration reduced to 0.57 ± 0.07 mM. At the molecular level, transcriptomics analysis showed that the number of differentially expressed genes (DEGs) increased with the temperature increased. Gene ontology (GO) annotation analysis showed that DEGs mainly existed in the molecular function. This study investigated the potential bactericidal mechanism of A. flavus using RF, provided some theoretical basis for the research of the pasteurization of fungi.

Numerical investigation of the transient fluid flow and heat transfer behavior in self-driven natural circulation cooling loop

An innovative open natural circulation system is proposed in this work, which utilizes the difference of the heat flux loaded on different parts of the pipe to form a self-circulation flow of working fluid. Via CFD simulation established by embedding self-programmed code into commercial software, the transient performance of a three-dimensional natural circulation loop is studied. The results indicate that: applying uniform heat flux on the wall of the loop, the fluid flow state successively experiences three stages, i.e., liquid expansion, partial circulation, and phase change, and finally a vapor plunger blocks the pipe, leading to local heat transfer deterioration and temperature increase; applying non-uniform heat flux, the fluid can be driven to form self-circulation flow, which can not only cool the structure via convection, but also prevent bubbles from accumulating, stabilizing the maximum temperature of the system around the boiling point; further for the loop with a more complex configuration, the self-circulation can be also started but with different start modes. Therefore, the new natural circulation system can achieve effective and adaptive cooling according to the external thermal environment, avoid fluctuation and vapor block phenomenon caused by violent phase change, and reduce the driving equipment and control unit. This work provides a reference for the design of the natural circulation system applied in a non-uniform heating environment. Through transient numerical simulation of the start-up stage, the fluid flow, phase change, and heat transfer characteristics in the natural circulation loop are studied, and the start mode and mechanism are analyzed.

An Experimental Study on the Influence of Different Cooling Methods on the Mechanical Properties of PVA Fiber-Reinforced High-Strength Concrete after High-Temperature Action

High-strength concrete (HSC) has a high compressive strength, high density, excellent durability, and seepage resistance, but its deformation ability is weak. Adding fibers can improve the physical and mechanical properties of HSC. Additionally, the HSC structure may face the threat of fire. In the process of fire extinguishing, the damage mechanism of high-temperature-resistant concrete is complicated due to the different contact conditions with water at different locations. Hence, it is essential to conduct pertinent research on the behavior of fiber-reinforced HSC with different cooling methods after high-temperature action. In this paper, polyvinyl alcohol fiber (PVA fiber) was selected to be added into the HSC to carry out high-temperature experimental research, so as to explore the apparent changes, failure pattern, and mass loss rate of the fiber-reinforced HSC using different cooling methods and analyze the influence of its residual compressive strength and flexural strength. The test results suggest that, with the increase in heating temperature, the color of the specimen’s surface transitions from dark blue-gray to white, and the quantity of surface cracks on the specimen gradually rises. The mechanical strength gradually decreases as the heating temperature increases. At a consistent heating temperature, the mechanical strength initially rises, and then falls with an increase in fiber content. The maximum compressive strength and flexural strength were achieved at PVA fiber contents of 0.2% and 0.3%, respectively. For different temperatures and fiber contents, the mechanical strength after natural cooling is generally higher than that after immersion cooling. In addition, X-ray polycrystalline diffractometry (XRD) and scanning electron microscopy (SEM) tests were conducted to analyze the compositional alterations and microstructure of the fiber-reinforced HSC following high-temperature exposure, accompanied by an explanation of the factors influencing the alterations in the physical and mechanical properties. Therefore, the findings of this study can serve as a valuable reference for the utilization of HSC in engineering structures and contribute to the advancement of HSC technology.

Austenite Growth Behavior and Prediction Modeling of Ti Microalloyed Steel.

Previous studies on the austenite grain growth were mostly based on a fixed temperature, and the relationship between the austenite grain and austenitizing parameters was fitted according to the results. However, there is a lack of quantitative research on the austenite grain growth during the heating process. In the present work, based on the diffusion principle of the controlled Ti microalloying element, the diffusion process of carbonitrides containing Ti during the heating process was analyzed. Combined with the precipitation model and the austenite growth model, the prediction model of austenite grain growth of Ti microalloyed steel during different heat treatment processes was established. The austenite grain size versus the temperature at four different heating rates of 0.5, 1, 10, 100 °C/s was calculated. The grain growth behavior of austenite during the heating process of Ti microalloyed steel was studied by optical microscope, scanning electron microscope and transmission electron microscope. The experimental data of the austenite grain size was in good agreement with the calculation by the proposed model, which provides a new idea for the prediction of austenite grain size in non-equilibrium state during the heating process. In addition, for Ti-containing microalloyed steels, the austenite grain size increased with the increasing heating temperature, while it changed little by further prolonging isothermal time after certain heating time, which was related to the equilibrium degree of the precipitation and the dissolution of Ti element. The austenite grain coarsening temperature of the tested Ti microalloyed steel was estimated within 1100~1200 °C.

The composition and flavor change mechanism of membrane-filtered sugarcane syrup during the acid hydrolysis process based on 1H NMR and GC–IMS

Nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-ion mobility spectrometry (GC-IMS) were employed to comprehensively characterize both non-volatile and volatile components present in membrane-filtrated sugarcane syrup (MS). A total of 19 non-volatile compounds and 65 volatile compounds were successfully identified within the MS sample. Among the volatile compounds, 12 were determined to be key aroma contributors based on their Relative Odor Activity Values (ROAV). Our investigation elucidated that hydrolysis and Maillard reactions serve as the primary pathways during acid hydrolysis, with reaction kinetics strengthened by increasing heating temperature and citric acid concentration, thereby enhancing the caramel and roasted aromas of MS. These findings not only contribute to a deeper understanding of the composition of sugarcane syrup but also offer valuable insights into flavor characterization and quality control within the sugarcane industry. Furthermore, this research lays a foundation for future studies aimed at optimizing processing techniques to enhance syrup flavor and overall product quality.

Influence of Cyclic Heat Treatment Temperature on Microstructure and Mechanical Properties of 18Ni(C250) Maraging Steel.

Cyclic heat treatment is an effective approach for enhancing the mechanical properties of 18Ni(C250) maraging steel, and the selection of cyclic heat treatment temperature is a key factor. In this study, a cyclic heat treatment process with a two-step solution treatment is employed to investigate the influence of cyclic heat treatment temperature, specifically the first solution treatment temperature (920 °C, 950 °C, and 980 °C), on the microstructure and mechanical properties of 18Ni(C250) maraging steel. The results indicate that with an increase in the cyclic heat treatment temperature, the average grain size of the 18Ni(C250) maraging steel decreases initially and then increases. When the cyclic heat treatment temperature reaches 950 °C, the grain size is at its minimum, exhibiting optimal grain uniformity. Additionally, the increase in cyclic heat treatment temperature results in a reduction in the size of martensitic lath with the same orientation inside the grains, along with an increase in the relative quantity of low-angle grain boundaries. Furthermore, the volume fraction and size of retained austenite show a monotonous increase with the rise in the temperature of the cyclic heat treatment, and the rate of increase becomes notably larger when the temperature is raised from 950 °C to 980 °C. Based on the observed microstructural changes, the variation in the mechanical properties of the 18Ni(C250) maraging steel was analyzed. Specifically, as the cyclic heat treatment temperature increases, the tensile strength of the 18Ni(C250) maraging steel initially increases and then stabilizes, while the elongation and fracture toughness exhibit a monotonic increase.

Influence of heat treatment on nanomechanical properties of Ni-based superalloy 625 fabricated by ultrasound-assisted wire arc additive manufacturing

This investigation focused on the effect of heat treatment (HT) temperature on microstructure and nanomechanical properties of Ni-based superalloy 625 fabricated by ultrasound-assisted wire arc additive manufacturing (UA-WAAM). The homogenization of the microstructure was significantly improved due to the HT helping unwanted secondary phases to dissolve back into the matrix. The nanoindentation results showed that with an increase in HT temperature, the average nano-hardness decreased from 2.13 ± 0.20 GPa to 1.39 ± 0.15 GPa, while the average creep displacement increased from 189.12 ± 33.26 nm to 634.79 ± 48.20 nm.

Warm Air Bending of AZ31B Sheets Based on an Online Local Contact Heating Method

Abstract Warm forming holds significant potential in shaping challenging materials due to its comprehensive advantages compared to cold and hot forming. Effective heating is crucial for precise warm forming processes. This study explored an innovative warm air bending technique employing an online local contact heating method. Heat transfer during the preheating stage and the air bending of AZ31B sheets were investigated through experiments and finite element analysis at temperatures ranging from room temperature (24 °C) to 250 °C, considering the thermomechanical coupling effect. The results indicate a significant increase in the bending center angle, advancing from 69.8 deg to more than 119 deg as the heating temperature rises from room temperature to 250 °C. Fractures were effectively eliminated when the sheet heating temperatures exceeded 150 °C. Simultaneously, as the localized heating temperature increases, a corresponding decrease in the rebound angle is observed, reducing from 10.6 deg to 2.3 deg. The findings validate the feasibility of warm air bending using online local contact heating in industrial applications, with regard to forming quality and production efficiency.

Effect of heat treatment on the radial structure of coaxial polyacrylonitrile/mesophase pitch composite fiber

AbstractCoaxial composite fibers with a cortex of polyacrylonitrile (PAN) and a core layer of mesophase pitch (MP) and PAN were prepared by wet spinning, then heat‐treated in air. The effects of heat treatment on the thermal reaction characteristics, pre‐oxidation degree, radial structure, and thermal stability of coaxial composite fibers were studied by differential scanning calorometry, Raman, and thermogravimetric analysis. As the heat treatment temperature increases, the coaxial composite fibers only undergo cyclization without oxidation, the peak temperature of the thermal reaction increases from 258 to 270°C, and the enthalpy increases from 19.66 to 237.82 J g−1, the heat mainly arises from the PAN component. The Dr value of the coaxial fiber skin layer increases from 0.193 to 0.255 (330°C) and then decreases to 0.236; the core layer Dr value increases from 0.353 to 0.392 (310°C) and then decreases to 0.368. The pre‐oxidation reaction leads to an increase in sp2‐hybridized carbons and an increase in pre‐oxidation degree. When the heat treatment temperature <310°C, the pre‐oxidation degree of the composite fibers increases, leading to formation of a more stable structure compared with that at lower temperatures and an increase in the carbon residue rate.

Simulation and Experimental Study of Circulatory Flash Evaporation System for High-Salt Wastewater Treatment

Treatment methods for high-salt wastewater mainly consist of physical methods, chemical methods and biological methods. However, there are some problems, such as slow treatment speed, high investment costs and low treatment efficiency. To address NaCl solutions, in this study, a circulatory flash system was designed based on gas–liquid equilibrium, mass conservation equation and energy conservation equation. A circulatory flash evaporation simulation and a static flash evaporation experiment were conducted on NaCl solutions under various operating conditions to investigate the effects of heating temperature, flash pressure and initial NaCl concentration on the circulatory flash evaporation system. The significance of each factor’s influence on the evaporation fraction and energy consumption was examined through static flash experiments. The simulation results demonstrated that increasing the heating temperature, decreasing the flash pressure and having a higher initial NaCl concentration could enhance the treatment capacity of high-salt wastewater. The flow rate of vapor outlets increased with higher heating temperature but decreased as the flash pressure rose. The experimental results demonstrated that flash evaporation pressure was the primary factor influencing both the evaporation fraction and the energy consumption per unit mass of vapor produced. It was observed that with an increase in heating temperature, the flash pressure decreased and there was a corresponding decrease in energy consumption per unit mass of vapor produced. The optimal experimental conditions were achieved at a heating temperature of 99 °C, a flash pressure of 15 kPa, and an initial NaCl concentration of 20%.

Effect of heat treatment on interface failure behavior in SiCf/PyC/SiC composites reinforced with Cansas-3 fibers

The influence of heat treatment on the correlation between interfacial mechanical properties and microstructure in CVI-SiCf/PyC/SiC composites was systematically investigated. The results reveal a progressive reduction in the average interfacial bond strength, interfacial shear stress, and interfacial debonding energy within the composites as the heat treatment temperature increases, especially beyond 1350 °C. This decline can be attributed to the attenuation of the SiCf/PyC interfacial bond strength arising from the contraction in fiber volume induced by the precipitation of Cansas-3 fibers. After push-in testing, SiCf/PyC/SiC composites heat-treated at or below 1350 °C displayed fibers in a compressed state. Conversely, composites exposed to extended heat treatment at 1400 °C or higher maintained fibers in an ejected state after push-in testing. Moreover, the composites heat-treated at 1450 °C and 1500 °C demonstrated fibers that were spontaneously ejected subsequent to cross-section polishing.

Tritium release performance of biphasic Li2TiO3–Li4SiO4 ceramic pebbles fabricated by centrifugal granulation method

At present, the biphasic Li2TiO3–Li4SiO4 ceramic pebbles with high lithium content and crushing load have been viewed as promising tritium breeders for maintaining the safety-state operation of the D-T fusion reactor. The tritium release behavior of Li2TiO3–Li4SiO4 ceramic pebbles fabricated by centrifugal granulation method was investigated by using the Thermal Desorption Spectroscopy apparatus at Shizuoka University. It can be found that the Li2TiO3–Li4SiO4 ceramic pebbles show three tritium release peaks, and most of the tritium was released as HTO observed from T-TDS spectra, and the peaks at 581 K and 734 K are mainly due to tritium release from Li2TiO3 in core and shell. The peak at 813 K is mainly deemed as tritium release derived from the Li4SiO4 shell. The content of tritium release from biphasic Li2TiO3–Li4SiO4 ceramic is up to 11.5 MBq g−1, but the amount of gas species (HT) is only 0.126 MBq g−1. Besides, the isothermal heating experiment showed that the tritium release behavior was subject to diffusion process and de-trapping in defect sites. At the same time, the irradiation defects of E′-center, O-related center, and Ti3+ for breeding material can be found by using an ESR device, and the isochronous heating experiments have manifested that the amount of irradiated defect decreases as heating temperature increases, which indicates that the tritium release behavior is closely related to defect annihilation process. Therefore, the advanced Li2TiO3–Li4SiO4 ceramic breeder can be fabricated based on tritium release result, which will be conducive to meet the practical application of breeder in the future.

Uniaxial compressive stress-strain model of Molybdenum tailings concrete after high-temperature exposure

To investigate the effect of high-temperature exposure on the mechanical properties of molybdenum tailings concrete, 75 cubes and 150 prisms of molybdenum tailings concrete were tested, by considering five heating temperatures (20, 200, 400, 600, and 800 ℃) and five replacement ratios (0, 25, 50, 75, 100%). The failure modes, mass loss rate, and mechanical properties of the specimens were analyzed in detail. The experimental results indicate that with an increasing heating temperature, the color of the blocks became lighter, accompanied by gradually intensifying phenomena such as skin peeling and crack propagation. At 800 ℃, many small cracks at the fracture site of the blocks after splitting failure, and obvious fracture zones in the block under axial compression failure were observed. With an increasing temperature, the mass loss rate and peak strain of the molybdenum tailings concrete show a linear growth trend, reaching the maximum amplitude at 800 ℃ (7.85% and 192.5%), whilst the molybdenum tailings concrete splitting tensile strength, peak stress, and elastic modulus showed a decreasing trend, reaching the maximum amplitude (404%, 61.7%, and 84.9%). By increasing replacement ratios, the mass loss rate of the molybdenum tailings concrete shows a linear growth trend, with a maximum increase of 1.07%. The mechanical properties of the concrete at all temperatures show a trend of first increasing and then decreasing. A 25% replacement ratio can improve the deterioration of the molybdenum tailings concrete after high-temperature exposure, with the maximum amplitude increase of the peak stress, peak strain, and elastic modulus being 24.3%, 12.4%, and 21%, respectively. Based on the test data, the prediction formulas of the mechanical properties of molybdenum tailings under different high-temperature and molybdenum tailings replacement ratios are fitted. The existing constitutive equations are modified to establish the stress-strain constitutive model of molybdenum tailings concrete after high-temperature exposure, of which results are in good agreement with the test data.

Creep deformation behavior and microstructure of α-Mg/long-period stacking ordered (LPSO) duplex Mg-Y-Zn alloy prepared by hot extrusion and heat treatment

There exists a great demand for improving the creep resistance of α-Mg/long-period stacking ordered (LPSO) duplex alloys. In this study, microstructure control through hot extrusion and heat treatment was employed on Mg-Y-Zn duplex alloys with the aim of achieving superior creep resistance. The extruded Mg-Y-Zn alloy exhibited an enhancement in the creep resistance with increasing heat treatment temperature. Furthermore, the heat-treated samples demonstrated outstanding creep resistance even under high stress. Their creep behavior is characterized by a low minimum creep rate and a relatively small stress exponent (n ∼ 5) even at high stress. Microstructural observations revealed that heat treatment induces grain coarsening and an increase in solute concentration within the recrystallized grains. Additionally, during creep deformation, a plate-like LPSO phase and kink bands formed within the recrystallized grains. Therefore, it is affirmed that the exceptional creep resistance observed in the Mg-Y-Zn alloys in this study can be attributed to the microstructure evolution induced by heat treatment and creep deformation.

Encapsulation of roast beef flavor by soy protein isolate/chitosan complex Pickering emulsions to improve its releasing properties during the processing of plant-based meat analogues

During the production of plant-based meat analogues (PBMA), a significant loss of flavor characteristic compounds in meat-flavor essences could be observed. Pickering emulsion-based encapsulation is an effective method to improve their stability. Therefore, a soy protein isolate (SPI)/chitosan (CS) complex Pickering emulsion was fabricated to encapsulate roast beef flavor (RBF) and further applied in the processing of PBMA. Our results indicated that the network structure of emulsions was dominated by elasticity, while hydrogen and covalent bonding interactions played important roles in the encapsulation process. The release rate of flavor compounds gradually increased with the increase of pH value, glutamine transaminase, NaCl content, heating temperature or heating time, while encapsulation significantly reduced the loss of characteristic aroma compounds. In addition, the releasing characteristics of aroma compounds and textural properties of PBMA were greatly improved by treating with RBF-loaded emulsions. Consequently, the emulsions were promising to improve the flavor quality of PBMA.

Phase transformation sequence of amorphous nickel-molybdenum electrodeposit

In this paper, the amorphous Ni-Mo alloy with cauliflower-like morphology is successfully prepared by electrodeposition, and the effects of heat treatment on its morphology, element content and structure are studied. The results of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) show that, when the temperature is higher than 600 ℃, the fine grains gradually appear and then cover the entire surface of Ni-Mo alloy. The Ni-Mo alloy occurs simultaneously the segregation phenomenon and the Mo content increases on the surface. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis illustrate that the Ni-Mo alloy gradually transfers from amorphous into crystalline structure, and the first phase MoNi4 and the second phase MoNi precipitate near 633℃ and 707℃ respectively. The apparent activation energy is 234.1 kJ/mol (ΔEa1) for the first phase crystallization and 819.9 kJ/mol (ΔEa2) for the second phase crystallization. The HER catalytic activity of Ni-Mo alloy increases first and then decreases with the increase of heat treatment temperature.

Non-stoichiometric silicon nitride for future gravitational wave detectors

Silicon nitride thin films were deposited at room temperature employing a custom ion beam deposition (IBD) system. The stoichiometry of these films was tuned by controlling the nitrogen gas flow through the ion source and a process gas ring. A correlation is established between the process parameters, such as ion beam voltage and ion current, and the optical and mechanical properties of the films based on post-deposition heat treatment. The results show that with increasing heat treatment temperature, the mechanical loss of these materials as well as their optical absorption decreases producing films with an extinction coefficient as low as k=6.2(±0.5)×10−7 at 1064 nm for samples annealed at 900 ∘C. This presents the lowest value for IBD SiN x within the context of gravitational wave detector applications. The mechanical loss of the films was measured to be ϕ=2.1(±0.6)×10−4 once annealed post deposition to 900 ∘C.

Effects of shell mold heating temperature on microstructures and freckle formation of single crystal superalloys

To study the effects of shell mold heating temperature on the microstructure and freckle formation of single crystal superalloys, the directional solidification experiment and simulation were conducted with designed stepwise specimens. The temperature field and morphology of mushy zone were analyzed. The results show that the primary and secondary dendrite arm spacings both decrease with the rise of shell mold heating temperature. This reduces the permeability of the liquid in the mushy zone and the width of the thermal-solutal convection channel, which reduces the formation tendency of freckles, the width of freckles and the number of dendritic fragments in freckled areas. In addition, with the increase of shell mold heating temperature, the cooling rate of liquid in the mushy zone increases, which reduces the cooling time of the melt in the mushy zone, weakens the breaking capability of liquid flow to the dendrite, and further reduces the tendency of freckle formation in single crystal superalloy castings.

The effect of time and heat exposure on the wettability and glossiness of CAA and FPL coatings for aluminum substrates

The use of anodized coatings as a substrate for adhesive bonding of aluminum is widespread and generally accepted. However, with time and exposure to heat, the coating’s behavior changes and its wettability decrease. We examine the coating’s wettability by measuring the contact angle. Aluminum sheets are coated with two types of anodizing and FPL coatings for this study. The results indicate that the wettability of all coatings remains stable for 16 h post application. However, there is a significant decrease in wettability over extended time periods, with the anodized coating exhibiting more pronounced changes after 30 days compared to the FPL coating. Also, in both types of coatings, as the heating temperature increases, the wettability decreases and the contact angle increases. The changes in the anodized coatings are more pronounced than in FPL coatings. Measuring the glossiness of the coating before and after heating shows that the gloss and the surface roughness of the coating remain unchanged.

CALPHAD simulation and experimental study on heat treatment process of Al-Cu-Mn-Mg-Sc cast alloys

Because different heat treatment parameters have different effects on the microstructure and mechanical properties, it is necessary to optimize the heat treatment parameters to obtain alloys with better properties. In this study, the heat treatment parameters of Al-Cu-Mn-Mg-Sc cast alloys were optimized by using thermal simulation and experimental methods. The results show that the phase transformation temperature of the low melting point eutectic phase Al2Cu is 542.9 ℃, and the time for element homogenization distribution of the alloy during solid solution at 525 ℃, 535 ℃ and 550 ℃ is 8 h, 7 h and 4.5 h, respectively. With the rise of solid solution temperature, the microhardness increase at first and then decrease, and the microhardness reaches to 96.4 HV at 535 ℃. When solid solution heat treatment is carried out at 535 ℃ for different times, the microhardness increase at first and then decrease with time, and the microhardness reaches to 118.4 HV at 5 h. It is known that the number of metastable phase decreases gradually with the increase of aging heat treatment temperature by using the calculation of thermodynamic software. The optimal aging heat treatment process parameter for the alloy is 170 ℃ for 10 h, and the microhardness at this time reaches to 142.3 HV.