Heating Stage Research Articles

Kinetics of isothermal solidification during transient liquid phase bonding of Inconel 718 superalloy by differential scanning calorimetry

In the transient liquid phase bonding of Inconel 718 alloy, the time for isothermal solidification is measured by using the cyclic differential scanning calorimetry method. The enthalpy of solidification of the remnant liquid is used in the current investigation to determine the isothermal solidification rate and time. The differential scanning calorimetry results reveal a reduction in interlayer width during the heating and melting stage of transient liquid phase bonding due to the rapid interdiffusion of elements. The result also reveals that the isothermal solidification time for a eutectic-free joint depends upon the actual width of the interlayer material. The actual width of the interlayer material prior to isothermal solidification is found to be less than the initial width of the interlayer material due to rapid diffusional solidification. The measured isothermal solidification time and rate for transient liquid phase bonding of the Inconel 718 joint are in good agreement with the experimental and theoretical results.

Effect of Latent Heat by Phase Transformation on the Thermal Behavior of Steel Billet during Heating.

The effect of latent heat via phase transformation on the thermal behavior of a billet was investigated during the heating process. The latent heat of the billet strongly affected the temperature distribution of the billet during heating, although the heating rate of the billet was not high during the process. The temperature profile of the center region of the steel billet with latent heat had a strong flat shape compared with the other regions, as the heat supply to the center region was limited during the heating process owing to the finite thermal conductivity and mass effect of the billet. The latent heat by phase transformation typically occurred in the middle stage of heating, and the latent heat increased the temperature deviation of the billet during heating owing to the delay in the temperature rise at the center region of the billet. During the phase transformation of carbon steels during heating, the gas temperature needs to be low to reduce the temperature deviation or thermal stress of the billet. Industrial hot rolling mills are required to consider the latent heat by phase transformation of the billet to properly design the heating pattern for the billet. The heating pattern in the reheating furnace should be varied with the materials to obtain a high heating quality for the billet.

Evaporation of flammable liquids droplets in an electric discharge

Evaporation of a liquid drop under the action of a high-frequency electric discharge is considered. The drops were suspended on a thermocouple and were in air at room temperature. The analysis was carried out under the assumption that the action of the discharge is thermal. It is shown that pure liquid fuel drop (ethanol and diesel fuel) evaporates according to the d2-law. At the same time, the rate of evaporation takes a maximum value depending on the distance to the electrode. Analysis of the rate of drop mass reduction made it possible to estimate the thermal power of the discharge, which also passes through a maximum when the electrode is moved away from the drop. When evaporating emulsion droplets (50%/50% fuel/water) after the heating stage, pulsations of geometric size are observed. The drop size periodically changes near some average value with a certain frequency, which decreases with the time of "evaporation". A physico-mathematical model of droplet heating under the thermal action of a discharge was constructed. The pulsations are explained by the evaporation of water globules inside the emulsion drop, the subsequent increase in the size of the vapor bubbles before the "micro-explosion" of the drop. The loss of emulsion material under the action of an electric discharge occurs mainly due to emissions during microexplosions. That is, the electric discharge leads to the dispersion of emulsions droplets with a high water content, in contrast to individual flammable liquids droplets. A decrease in the water content and the power of the electric discharge leads to an increase in the period of pulsations.

Numerical simulations of reactive cold sintering of BaTiO3

Numerical simulations of reactive cold sintering of BaTiO3 are performed under the experimental condition of Guo et al. It is suggested that amorphous BaTiO3 particles are produced first by chemical reactions and subsequent nucleation from the aqueous solution according to the Ostwald’s rule of stages. For the case of cold sintering under 300 °C and 500 MPa, the amorphous particles are transformed into crystalline particles partly during the initial heating stage by a simple thermal excitation when the particle size is less than about 5 nm and partly during cold sintering under high pressure through coalescence with other crystalline particles. For the case of 150 °C in sintering temperature, on the other hand, appreciable amounts of amorphous particles remain even after the cold sintering due to the incomplete sintering. The calculated grain sizes almost agree with the experimental data, which supports the present numerical simulations.

Method for Low-Temperature Vacuum-Thermal Cleaning of Surface Single Crystals Si and GaAs

The paper reports on a method of low-temperature vacuum-thermal cleaning of the surface of Si and GaAs single crystals developed by the authors, which consists in implanting Ba+ ions (or alkaline elements) into Si and GaAs crystals preliminarily cleaned by ultra-high vacuum by ion etching and subsequent annealing in two stage at 800 K - 15 minutes and at 1000 K for 30 minutes. The effect of effective cleaning is achieved due to the fact that the introduced ions of Ba+ and alkaline elements, being active, form compounds with impurity atoms (O, C, S, N, etc.) at the first stage and are removed together with impurities after the second stage of heating.

#71 : Successful IVF Procedure on SARS-CoV-2 Positive Advance Maternal Age Woman

Background and Aims: Due to the coronavirus disease-19 (COVID-19) pandemic, assisted reproductive techniqueservices across Indonesia have been suspended. With an unpredictable duration, the suspension is affecting particular groups of women who want to achieve pregnancy, including advanced aged women whose fertility has declined significantly. Here we present a 44-year-old woman with primary infertility and nulliparous with unexplained indication who underwent an in vitro fertilization procedure while confirmed positive for COVID-19. The goal of this study was to investigate SARS-CoV-2 transmission through the embryo and its effect on the embryo survival rate. Method: The IVF procedure was carried out following standard methods. Controlled ovarian stimulation was done by giving growth hormone and exogenous gonadotropin on the first day of the cycle, gonadotropin-releasing hormone antagonist on day 7 of the cycle, and human chorionic gonadotropin 36 hours before ovum pick up. Then, ovum pick up was carried out with COVID-19 standard safety procedures and the follicles were sent to the IVF laboratory with a heating stage. The oocytes were obtained from the follicular fluid analysis, following intracytoplasmic sperm injection. The zygotes were cultured for 48 hours and tested negative for SARS-CoV-2. Afterward, the entire embryos were vitrified for 30 days until the patient’s RT-PCR test confirmed negative for SARS-CoV-2 infection. Thereafter, an endometrial thickness examination was done, followed by embryo transfer on the same day. Results: Six oocytes in metaphase-II were retrieved while the patient was confirmed positive with COVID-19. After fertilization, 6 embryos were obtained, tested negative for COVID-19, and were later vitrified. Conclusion: Two of the embryos survived vitrification and both were successfully transferred. IVF with standard procedures is safe to proceed on COVID-19 positive women.

Study on the thermal reaction characteristics and kinetics of coal and coal gangue coexisting spontaneous combustion

In the hope of exploring the effect of coal gangue left in goaf on coal spontaneous combustion, the variations of thermal effects and free radical parameters during coexisting spontaneous combustion of coal and coal gangue were tested, and kinetic at different heating stages were calculated. The following beneficial findings were obtained. For the mixed samples, the heat flow curve, ignition temperature, and free radical concentration all decline with the increase of coal gangue content, and the free radical parameters exhibit periodic changes with increasing temperature. Both the experimental value of thermal effect and free radical concentration with coal and coal gangue mixture during the spontaneous combustion process are higher than the calculated value. The calculation results of kinetic show that at the endothermic stage, the activation energies of the mixed samples decline with the increase of coal gangue, and the experimental value of activation energy is greater than the calculate value; at the exothermic stage, the case is exactly the opposite. Furthermore, due to the higher reactivity of coal gangue groups and stronger thermal conductivity, the coexistence of coal and coal gangue spontaneous combustion reaction is promoted. Resultantly, coal spontaneous combustion is normally more threatening in gangue-containing goafs.

Gas production decline trends for Longmaxi shale under thermally stimulated conditions

Recently, thermal treatment has emerged as a promising technology to enhance shale gas recovery efficiency by promoting gas desorption. However, the understanding of gas desorption characteristics from heterogeneous shale matrix under thermal stimulation remains inadequate, which constrains the development of thermal recovery technology. In this study, on-site canister desorption tests were employed to investigate the shale gas desorption patterns of four distinct shale cores, sourced from four various production zones, under two heating stages (50 °C and 110 °C). Additionally, low-temperature N2 adsorption experiments and infrared examination were used to study the microstructure characteristics of shale before and after thermal treatments. The canister desorption tests revealed that the gas production rates increased for all shales under heating conditions, particularly when transitioning from 50 °C to 110 °C. However, the peak gas production rates at the two heating stages exhibited different trends: nearly identical for Shale-1 and Shale-2, decreasing for Shale-3 and increasing for Shale-4. This can be attributed to the different quantities of adsorbed gas present in shale samples, with Shale-4 containing approximately 0.0088 m3, compared to the markedly lower volumes in Shale-1 (0.0053 m3), Shale-2 (0.0040 m3), and Shale-3 (0.0041 m3). Furthermore, the gas production rates followed distinct decline trends at different temperatures: exponentially at 50 °C and following a power law at 110 °C, indicating varying gas desorption dynamics under different thermal conditions. Moreover, the findings from low-temperature N2 adsorption experiments and infrared examination indicated that combustion increased the pore volume and induced thermal cracks and fractures, thereby enhancing shale permeability. These insights highlight the potential of combustion fracturing as a technology to improve gas recovery efficiency.

The Activation Energy of Viscous Flow and Liquid–Liquid Structure Transition in Co-B Alloys

The temperature dependences of the kinematic viscosity during heating and cooling have been investigated in Co-B melts with a boron content of up to 30.8 at. A liquid–liquid structural transition was found, which is accompanied by an increase in the activation energy and cluster size, as well as a significant decrease in the density of the melt. The liquid–liquid structural transition was associated with the formation of clusters with a short-range order of Co23B6 in the intermediate temperature region. At low and high temperatures, clusters of the order of an atomic size are active participants in the viscous flow. It was shown that with an increase in the cluster size, the activation energy increases and the viscosity of melts decreases. The formation of large Co23B6 clusters during the cooling of melt with low boron content leads to undercooling and the appearance of the transition temperature region with high activation energy, although this region does not exist during the heating stage.

A new approach for characterizing internal stress of fresh concrete during thermal treatment period

Addressing the scarcity of research on the residual expansion deformation of steam-cured concrete and its underlying factors, this study introduces a testing apparatus to characterize the internal stress in fresh concrete during the thermal treatment. It explores the impact of water-to-cement ratio (w/c) and paste-to-aggregate ratio (p/a) on internal stress and elucidates the developmental patterns of internal stress in concrete throughout the thermal treatment phase. The key findings are as follows: (i) During the thermal treatment, the internal stress in concrete under constraint is predominantly compressive, exhibiting a rapid increase in the heating stage, followed by a gradual decline in the constant temperature treatment stage, and a continued decrease with a decelerating trend during the cooling stage. (ii) Both w/c and p/c significantly influence internal stress in concrete, and this stress can be enhanced by reducing the initial free water content and augmenting the initial structural strength of the concrete. This paper serves as a valuable foundation and reference for further investigations into the residual expansion deformation of steam-cured concrete.

Understanding the effect of char oxidation on wood temperature profiles for varying heating and oxygen conditions

The use of mass timber framing as a sustainable material, particularly in high-rise buildings, requires detailed structural fire performance calculations. Thermal models describing only the solid phase are cost-effective alternatives to provide information to structural behavior models. Their accuracy depends on an adequate description of drying, pyrolysis, charring and eventually flaming phenomena. While in recent years there have been considerable contributions to the development of such models, there are still open questions. This work proposes a thermal model which incorporates char oxidation, describing both the kinetic- and diffusion-controlled regimes. The model was used to replicate two sets of experimental results which used standard fire calorimeters to study the ignition of thick wood specimens within a range of incident heat fluxes and oxygen concentrations, respectively. The model yields adequate temperature predictions in the early heating stages, but fails to replicate the behavior at later stages, when the effect of the surface combustion is noticeable. In terms of mass loss rates, a poorer performance is observed. To change from one oxidation regime to another, a Damköhler number is proposed, based on char oxidation reaction rates. It is found that for compartment fire conditions, char oxidation will mostly occur develop under diffusion-controlled conditions.

Seasonal Evolution of Stable Thermal Stratification in Central Area of Lake Ladoga

The complete climatic courses of the parameters of stable thermal stratification for the central part of Lake Ladoga, the largest European lake, are presented on the basis of empirical relationships, taking into account the physical processes governing water temperature variations. For the first time, the seasonal cycle of the surface water temperature, the temperature and the depth of the thermocline, and the hypolimnion temperature are calculated using the vertical profiles of the temperature obtained from the central area of Lake Ladoga. Temperature data are used for the period of in situ observations from 1897 to the present. The proposed functional forms of the temporal temperature cycle and the course of thermocline’s boundaries deepening are useful for examination and simulation of the heat vertical transport from air to water. Approximation curves for the parameters of heating and cooling periods were developed with high significant determination coefficients. Time dependencies of the climatic rates of change in water temperature and the depth of the thermocline boundaries were determined from the onset of stable stratification to its dissipation. The highest rate of water temperature change in the heating stage takes place in late June–early July, which at the water surface, is 0.32 °C/day, while in the thermocline layer, it is 0.18 °C/day. The peak velocity during the cooling stage at the surface occurs in late August–early September and is 0.14 °C/day, whereas in the thermocline, it is 0.08 °C/day and takes place between September and early October. During the period of heating, the deepening parameters of the thermocline layer do not fluctuate very much, only within the range of 0.1–0.3 m/day. During the cooling period, under the influence of free convection, rates increase drastically. The maximum rates of deepening during the period of full autumn mixing reach 1.8 m/day. When the autumn overturn occurs, the epilimnion thickness equals the bottom depth, and the bottom temperature reaches its maximum during the annual cycle. Climatic norms of the stratification parameters against which it is necessary to assess climate change are calculated.

Transformation-mediated in-situ β recrystallization in laser powder-bed fusion additively manufactured Ti-6Al-4V

Achieving equiaxed grain structure is highly sought after in metal processing for most critical structural applications but it is seldom realized in Ti-6Al-4V additively manufactured (AM) by laser powder-bed fusion (LPBF) due to its unique thermal environment in favor of columnar grain growth. To convert columnar grains into equiaxed, post heat treatment in the β phase field is often adopted to initiate recrystallization of prior-β grains. This study demonstrates the achievement of equiaxed prior-β grain structure in situ in LPBF Ti-6Al-4V via epitaxial recrystallization mediated by α → β phase transformation taking place in the rapid heating stage of LPBF thermal cycling. In this rapid reverse phase transformation process, new β nuclei of distinct variants to their parent prior-β grain nucleate directly on α matrix in accordance with Burgers orientation relationship and grow towards the surrounding α matrix while α is transforming to β within a specific prior-β grain. This hypothesis is strongly supported by the experimental evidence that a significant fraction of β/β grain boundaries are featured with misorientations near 60° in both as-built Ti-6Al-4V and those subjected to post rapid heat treatment. This essentially excludes conventional recrystallization as the mechanism responsible for the evolution of equiaxed prior-β grain structure in the as-built state. The new finding unveils the critical role of LPBF thermal cycling and associated phase transformation in microstructure evolution and paves the way for the development of high-quality AM Ti-6Al-4V with reduced performance anisotropy.

Measurement of reaction temperature distribution inside of methanol steam reforming microreactor using infrared thermography

Methanol steam reforming is a promising method for in-situ hydrogen production and greatly affected by the reaction temperature inside the microreactor, while the inside reaction temperature distribution is quite difficult to be measured. Here, we developed a visible methanol steam reforming microreactor using optical crystal as observation window and using infrared thermography to measure the real-time reaction temperatures. The method of using infrared thermography to measure the distribution of reaction temperature was presented and characterized with the accuracy of 98.4 % in the range of 300.0–575.0 K. Then, temperature heating and hydrogen production tests were conducted, and results showed that the lower oxygen to carbon (O/C) ratio leads to higher heating rate of 18.0 K/min during microreactor heating stage. The measured temperature distribution on the copper foam increases with a stable gradient of 0.91 K/mm along the reactant flow direction and the temperature difference in vertical direction is less than 10.0 K. The maximum methanol conversion is 98.0 % at the gas hourly space velocity (GHSV) of 3600 mL/(g·h) and maximum reformate flow rate is 100.8 mL/min at the GHSV of 6000 mL/(g·h). The obtained results demonstrated that the visible methanol steam reforming microreactor and reaction temperature measurement method would be beneficial for future microreactor’s design.

Effect of non-isothermal creep aging on the microstructure, mechanical properties and stress corrosion cracking resistance of 7075 alloy

The effect of non-isothermal creep aging (NICA) on the microstructure, mechanical properties, and stress corrosion cracking (SCC) resistance of 7075 alloy was investigated. The results showed that the tensile strength of the alloy increased to 565 MPa when the alloy was heated to 210 °C (CH210) and reached 580 MPa when it was subsequently cooled to 120 °C (CC120). Simultaneously, the SCC susceptibility of rtf increased from 50.8 % to 98.4 %. As compared with traditional creep aging process [1], a large strength increment with excellent stress corrosion resistance have been obtained by NICA. The microstructure revealed that a lot of dislocations have been introduced by creep during the heating stage which could improve the precipitates volume fraction and accelerate the diffusion of solutes; while during the cooling stage, η′ was greatly refined, and GPI and GPⅡ were re-precipitated from the matrix due to the decreased solid solubility and increased critical radius R*; both of them are responsible for the continuous strength increase during NICA. Moreover, the width of the precipitate free zone (PFZ) was narrowed from 46.1 nm (CH210) to 28.6 nm (CC120). The microchemical analysis reveals that solutes were more homogenously distributed in grain boundary precipitates (GB-ppts), matrix precipitates, the PFZ, and the matrix with the help of creep. The narrower PFZ and homogeneous solute distribution are responsible for improving the SCC susceptibility in the CC120 alloy.

Desorption – sorption – desorption profile of clinoptilolite in different air media: a DSC-TG study

Desorption–sorption processes of clinoptilolite sample from Beli Plast deposit, Bulgaria, were studied in a simultaneous DSC-TG experiment, applying a temperature profile including successive stages of heating up to 300 °C, holding, cooling to 40 °C, holding, and reheating up to 600 °C. Two experiments were provided: in humid static air and dynamic dry air. Thus, in a single experiment, quantitative information was obtained about the behavior of the sample in a complicated temperature profile and specific gas media. The first heating processes took place with almost the same dehydrated amount regardless of air media. In the humid air media, a possible sorbate is H2O molecules, while in the dry air are N2 molecules. In both air media, rapid sorption was observed already with the first steps of cooling, while a corresponding exothermic effect is manifested specifically for both experiments. Different sorption amount of H2O and N2 molecules was explained by their role as dipole or quadrupole and their different way of internal filling into the dehydrated zeolite structure. The desorption of newly sorbed molecules proceeds during the second heating, and after 300 °C the dehydration completes. The presented complicated approach gives information about the behavior of the clinoptilolite at each thermal stage that is of importance for various practical applications.

PHYSICOCHEMICAL AND BIOSPECIFIC PROPERTIES OF A POROUS CARBON SORBENT MODIFIED WITH SULPHOSALICYLIC ACID

A mesoporous carbon sorbent modified with sulphosalicylic acid by adsorption from aqueous solutions has been synthesized. The optimal modification parameters were selected: the ratio, concentration, the duration of impregnation and heat treatment stages, and pH. The physicochemical properties of the samples have been studied: textural characteristics, qualitative and quantitative composition of surface functional groups, the amount of applied modifier, adsorption and desorption properties. The adsorption characteristics of the studied samples with respect to organic dyes methylene blue and methanyl yellow are determined. It has been established that during desorption for 48 h, ~ 68% and ~ 82% of the initial concentration of sulphosalicylic acid applied to the sample pass into the aqueous solution, modelling the intestinal medium and into ethanol, respectively. In this case, a decrease in the pH of the initial solutions by 6 units is observed. High antibacterial properties of the modified carbon sorbent towards Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae have been established in vitro.

Study on the mechanism of the effect of biomass ash on the erosion and adhesion behavior of Al2O3 ceramic particles

Biomass coupled with photothermal gasification technology is a new type of technology using heat carriers to transfer the solar energy to supply heat, and directs the solar energy absorbed by the heat carrier to provide a continuous heat source for biomass gasification. To investigate the erosion and adhesion mechanism of cornstalk ash (CSA) on heat carriers (Al2O3 ceramic spheres) during heat transfer, ash fusion temperature analyzer (AFTA) and FactSage thermodynamics software were used to analyze the effect of alumina addition over CSA sintering from the perspective of melting point, high-temperature heating stage coupled with optical microscope system (HTSOM) was used to observe of the adhesion behavior of CSA on the surface of ceramic spheres, X-ray diffractometry (XRD) and Laser-induced breakdown spectroscopy (LIBS) as well as SEM-EDS (Scanning electron microscope - Energy dispersive spectrometer) were used to detect the mineral evolution from both matter and elements. The results showed that the sintering stage (FT-DT) of CSA extended by adding more than 5 wt% of Al2O3 to CSA. Furthermore, it was found that as the temperature increased, Al-containing minerals such as pyroxene and chalcocite were formed, which indicated the CSA began to erode the heat carrier by mineral evolution on the surface of ceramic spheres. At high temperatures (>1200 ℃), CSA completely melted to form a liquid phase that wrapped around the surface of the ceramic spheres, which played a role in insulation layer during the cooling process to reduce the cooling rate of the surface of the ceramic sphere, resulting in more evident slagging problem. At the same time, the K and Ca element in the CSA was captured by ceramic spheres. The mineral transformation between the ceramic spheres and CSA was simulated by FactSage thermodynamic software, and it was found that the addition of Al2O3 resulted in the increase of the ash melting temperature and the formation of Al-containing mineral matters such as nepheline and augite.

Effects of Multistage Aging Treatment on the Microstructure and Mechanical Properties of α + β-Type Ti-6Al-7Nb Alloy

The influence of multistage heat treatments on the microstructure and mechanical properties of Ti-6Al-7Nb alloy used for functional structures was systematically studied. Cast Ti-6Al-7Nb alloy samples were subjected to hot forging, annealing, and multiple stages of heat treatments. The relationship between volume fraction of α-phase and the mechanical properties was investigated. Herein, multiple heat treatment steps were selected based on the dilatometric analysis, at the end of the beta transformation and the start of the beta transformation, followed by aging at low temperature, i.e., 500 °C. A higher volume fraction of α-phase leads to higher strength but lower ductility. The yield, ultimate tensile strengths, and ductility of the annealed alloy are 822 MPa, 1019 MPa, and 10%, respectively. The corresponding values for the alloy treated at 900 °C followed by WQ are 777 MPa, 932 MPa, and 16%, while the aged alloy has 879 MPa, 967 MPa, and 12%, respectively. A trade-off between strength and ductility was attained. Besides, the microstructural evolution of the studied conditions was also covered in depth.Graphical

Artificial intelligence classification and amylose content prediction of rice flour varieties from their pasting features

The pasting features of eight varieties of rice flour with varying amylose content were characterized and then subjected to machine learning analysis in order to classify the rice varieties and predict their amylose content. The waxy rice flour with the least amylose showed a peak viscosity in the early stage of heating, and the high amylose rice flours had the highest final viscosity. Principal component analysis showed that 87.2% of the total variability was explained by the two principal components, which were mainly related to peak temperature and final viscosity. When the pasting features were used as a machine learning dataset for classification, the support vector machine classifier was the most effective in correctly classifying the rice flour varieties by showing a high accuracy and F1-score, followed by the decision tree and stochastic gradient descent. In addition, the integration of pasting features with machine learning analysis showed the potential to predict the amylose content of rice flours. These prediction performances were confirmed by validating the models with independent datasets.