Isothermal Heat Research Articles

Peculiarities of the absorption and desorption of hydrogen by opal matrices

The absorption and desorption of hydrogen at high pressure and temperature by opal matrices formed by amorphous silica spheres with a diameter of 0.235 and 1.6 μm have been studied. The Raman spectra of hydrogen-saturated opal matrices measured at a temperature of 80 K and ambient pressure show that hydrogen molecules are adsorbed in two different ways, directly into silica spheres and mesopores between them. The kinetics of hydrogen desorption was studied in-situ from a change in the relative intensity of rotational modes in the Raman spectra under annealing at 163–213 K. The hydrogen content decreases exponentially under isothermal heating, while the exponential decay time constant τ increases with a decreasing temperature showing the activation nature of desorption. The data for various temperatures are well described by the Arrhenius dependence τ(Т) = A × exp(EA/kBT) with the activation energy EA=(162 ± 13) meV and time constant А= (1.8 ± 0.5) × 10−2 s.

Isothermal structural evolution of CL-20/HMX cocrystals under slow roasting at 190 °C.

As a new type of energetic material, cocrystal explosives demonstrate many excellent properties, such as high energy density and low sensitivity, due to the interaction between the molecules of the two components. The known decomposition temperature is 235 °C for CL-20/HMX cocrystals at a faster heating rate. CL-20 molecules could separate from the cocrystal matrix and decompose at a higher temperature, much lower than the decomposition temperature. The current work provided deep insight into the isothermal structural evolution of CL-20/HMX cocrystals with slow roasting at 190 °C. We found that the initial decomposition originates from separating CL-20 molecules from the surface along the (010) plane of the cocrystals. The gas products, such as NO2 and NO, escape from the largest exposed surface of the (010) plane and generates microbubbles and microholes. At the same time, the residual HMX molecules form δ-phase HMX crystals and shrink the volume by 72%. By increasing the time held at 190 °C, the decomposition of CL-20 molecules and recrystallization of the residual HMX molecules form a gully-like structure on the (010) plane of the CL-20/HMX cocrystal. After a long time at 190 °C, the CL-20 component completely decomposes, and all HMX molecules recrystallize in the δ-HMX form. The interaction between HMX and CL-20 molecules makes the decomposition rate of the CL-20/HMX cocrystal much slower than that of the CL-20 pure crystal with a similar decomposition activation energy during isothermal heating. This work can help to deeply understand the safety of CL-20/HMX cocrystal explosives at a temperature lower than the recognized decomposition temperature.

Gypsum binders based on ceramic industry waste

A tense situation is emerging in Uzbekistan regarding the supply of high-quality natural raw materials to the gypsum production industry. Consequently, many industrial man-made wastes containing gypsum compounds are disposed of in landfills. These wastes, which are harmful to the environment, are valuable raw materials that can be used in the production of gypsum binders in many cases. The use of man-made waste in the production allows to achieve great economic efficiency in the production of gypsum binders and various construction materials and products based on two important problems -prevention of environmental pollution. The article describes the results of scientific research on obtaining gypsum binders from waste molds used in ceramic industry enterprises producing porcelain and sanitary-technical products. Waste molds of “EKOKERAMA” LLC (Fergana city, Uzbekistan) were used in the research. Waste mold pieces were treated with isothermal heat under “thermal shock” conditions. Due to the increase in the amount of α-modification of gypsum in the resulting product, gypsum binders whose physical and mechanical properties meet the requirements of GOST 23789-2018 were obtained.

Effect of isothermal heat treatment on microstructure and wear behavior of pearlitic rail steel

Effect of isothermal heat treatment on microstructure and wear behavior of pearlitic rail steel

Additive manufacturing leveraged microfluidic setup for sample to answer colorimetric detection of pathogens.

Colorimetric readout for the detection of infectious diseases is gaining traction at the point of care/need owing to its ease of analysis and interpretation, and integration potential with highly specific loop-mediated amplification (LAMP) assays. However, coupling colorimetric readout with LAMP is rife with challenges including, rapidity, inter-user variability, colorimetric signal quantification, and user involvement in sequential steps of the LAMP assay, hindering its application. To address these challenges, for the first time, we propose a remotely smartphone-operated automated setup consisting of (i) an additively manufactured microfluidic cartridge, (ii) a portable reflected-light imaging setup with controlled epi-illumination (PRICE) module, and (iii) a control and data analysis module. The microfluidic cartridge facilitates sample collection, lysis, mixing of amplification reagents stored on-chip, and subsequent isothermal heating for initiation of amplification in a novel way by employing tunable elastomeric chambers and auxiliary components (heaters and linear actuators). PRICE offers a new imaging setup that captures the colorimetric change of the amplification media over a plasmonic nanostructured substrate in a controlled and noise-free environment for rapid minute-scale nucleic acid detection. The control and data analysis module employs microprocessors to automate cartridge operation in tandem with the imaging module. The different device components were characterized individually and finally, as a proof of concept, SARS-CoV-2 wild-type RNA was detected with a turnaround time of 13 minutes, showing the device's clinical feasibility. The suggested automated device can be adopted in future iterations for other detection and molecular assays that require sequential fluid handling steps.

Assessment of unexplored isoconversional methods to predict epoxy-based composite curing under arbitrary thermal histories

The mass manufacturing of composite products is hindered by long curing times, and composite manufacturers demand shorter curing cycles while keeping material properties. This requires reliable methods to predict the curing kinetics of each resin formulation. Isoconversional methods are easy to implement and able to deal with complex processes. However, scientists still limit their isoconversional predictions of curing degree to isothermal or constant heating programs. In this study, we perform combined dynamic and isothermal DSC measurements for two different commercial epoxies for aerospace applications (M18 and VTC401). Based on the isoconversional kinetic analysis, we show the feasibility of predicting the evolution of an epoxy resin cure for an arbitrary and complex temperature program using two different unexplored methods for this purpose. Because of the versatility of both prediction methods, they are especially suited to deal with actual conditions in industrial processes. The proposed approach is validated experimentally by comparing predictions against the curing degree of these epoxies during a temperature program that comprises isothermal and dynamic stages. These reliable and straightforward predictions open the door to optimize curing times and increase productivity in composites.

Role of curved walls on efficient thermal convection in porous beds confined within enclosures: heatline and entropy production maps

PurposeThis study aims to elucidate the role of curved walls in the presence of identical mass of porous bed with identical heating at a wall for two heating objectives: enhancement of heat transfer to fluid saturated porous beds and reduction of entropy production for thermal and flow irreversibilities.Design/methodology/approachTwo heating configurations have been proposed: Case 1: isothermal heating at bottom straight wall with cold side curved walls and Case 2: isothermal heating at left straight wall with cold horizontal curved walls. Galerkin finite element method is used to obtain the streamfunctions and heatfunctions associated with local entropy generation terms.FindingsThe flow and thermal maps show significant variation from Case 1 to Case 2 arrangements. Case 1 configuration may be the optimal strategy as it offers larger heat transfer rates at larger values of Darcy number, Dam. However, Case 2 may be the optimal strategy as it provides moderate heat transfer rates involving savings on entropy production at larger values of Dam. On the other hand, at lower values of Dam (Dam ≤ 10−3), Case 1 or 2 exhibits almost similar heat transfer rates, while Case 1 is preferred for savings of entropy production.Originality/valueThe concave wall is found to be effective to enhance heat transfer rates to promote convection, while convex wall exhibits reduction of entropy production rate. Comparison between Case 1 and Case 2 heating strategies enlightens efficient heating strategies involving concave or convex walls for various values of Dam.

The Effect of Heat Treatment and Different Degrees of Deformation on the Microstructure and Mechanical Properties of Pure Mo Sheets

Molybdenum has a broad application and good prospect in the field of nuclear energy, aerospace, electronics, etc., due to its high melting point, high hardness, corrosion resistance and other excellent performances. In this paper, an isothermal and isochronous annealing heat treatment, at the temperature of 800–1300 °C for 0.5–2 h, was applied to pure molybdenum (PM) sheets with deformation of 70%, 80%, 90%, and 95%. The initial deformation of the PM sheet was increased from 70% to 95%. After annealing at 900–1200 °C for 1 h, the recrystallized grain size gradually decreased. The Goss texture ({110}<001>) was always present in the pure molybdenum sheet with 95% deformation during heat treatment, but its strength decreased with the increase of the temperature. The copper texture ({112}<110>) deflected to a cubic texture, and its orientation changed from {001}<110> to that of cube texture {110}<100>. With the increase of the temperature, the cubic texture was obtained more easily in the pure molybdenum sheet. The recrystallization nucleation mechanism of the pure molybdenum sheet with 95% deformation was mainly in situ nucleation and orientation nucleation. The Avrami index of the pure molybdenum sheet with 95% deformation was calculated by the JMAK equation and found to be 3.6.

Enhanced alite dissolution by CAH10 addition

The influence of varying Al addition in the form of CAH10 on the hydration of alite was studied to gain further insights into the alite hydration mechanisms in the presence of increased Al concentration in pore solution. Therefore, pure alite and mixtures of alite and CAH10 were investigated by means of isothermal heat flow calorimetry, XRD and pore solution chemistry analysis. The two occurring hydration events can be attributed to the precipitation of two different silicate-bearing hydrate phases, C2ASH8 and C-(A)-S-H. In this case, the consumption and removal of Al in pore solution initiated the change to C-(A)-S-H-forming hydration. Furthermore, the formation of C2ASH8 and the alite reaction rate and reaction were directly influenced by the amount of Al provided by CAH10 addition, leading to an alite reaction turnover of up to 68–86 % within 48 h.

The effect of Cu2+ doping in β-tricalcium phosphate on the hydration mechanism of a brushite cement

Brushite cements show excellent biocompatibility and are therefore an often-used material for bone repair. However, methods to prevent inflammations after surgery are needed. As Cu2+ was proven to provide antibacterial properties, as well as other application relevant features, it is a promising additive. Concerning these factors, a brushite cement containing Cu2+-doped β-tricalcium phosphate, monocalcium phosphate monohydrate, and phytic acid as setting retarder was investigated with powder and in situ X-ray diffraction, isothermal heat flow calorimetry, in situ 1H-time domain – nuclear magnet resonance, and pore solution analysis. The influence of Cu2+ ions on the hydration kinetics of the brushite cement and the locations of the Cu2+ ions after completion of the hydration were the main questions of interest. Heat flow calorimetry showed a significant retardation and deceleration of the hydration with increasing Cu2+ content in β-tricalcium phosphate. This effect can be directly correlated to the Cu2+ ions, as it was also shown for cements without phytic acid. X-ray diffraction showed brushite as main hydrate phase. Additionally, Cu2+-doped cements formed a hydrate phase not assignable by X-ray diffraction, which is assumed to be Cu2+ containing. Furthermore, Cu2+ was detected in the pore solution after the hydration, and no signs of Cu2+ incorporation in the crystal structure of brushite were found.

Isothermal decomposition of austenite in presence of martensite in advanced high strength steels: A review

The development of the quenching and partitioning (Q&P) process has prompted an interest in the process of isothermal transformation in presence of a pre-existing phase such as martensite. The presence of prior martensite is known to accelerate the overall kinetics of bainite formation, both in the 1-step and 2-step Q&P process. The underlying mechanisms behind this phenomenon are not fully understood. Also, the nature of the isothermal product (isothermal martensite and/or bainite) formed in presence of prior martensite seems to differ according to the thermodynamic and kinetic conditions. For certain thermodynamic conditions, depending on alloying, isothermal martensite may also form in the temperature range just above and below M s . In the event that both bainite and isothermal martensite formation are thermodynamically allowed, the competition in kinetics determines the observed transformation product. The effect of martensite on the subsequent isothermal transformation is reviewed with a focus on the nature of the transformation products and kinetics. In that context, the kinetics of the isothermal transformation in presence of other prior phases such as polygonal ferrite and bainite are also compared and discussed, together with the possible mechanisms behind the acceleration of the transformation kinetics. Guidelines for further investigation are also proposed. − Formation of both bainite and isothermal martensite is possible during isothermal heat treatment of austenite in presence of martensite. − Bainite formation kinetics is accelerated in presence of martensite, potentially due to an increase in the nucleation site density. − Opinions are differed whether bainite formed at or near the interface. Therefore the primary mechanism is not established yet. − Complexities in identifying the primary mechanism are discussed and possible research guidelines are proposed.

Effect of distribution characters of ferrite/bainite on deformation compatibility in dual-phase pipeline steel: Experimental and numerical study

The morphology distribution of microstructure has an important influence on the match of the strength and plasticity of dual-phase pipeline steel. Bainite and PF dual-phase steels with layered and network morphology were obtained by combining the Thermomechanical Control Process (TMCP) and inter-critical isothermal heat treatment. A novel experimental-numerical methodology studied the effect of phase distribution characters on the deformability of PF and bainite dual-phase pipeline steel. The plastic damage features and microscopic strain and stress distribution in both network and layered microstructure were clarified. The obvious differences in the microstructure evolution for both samples were captured by a quasi-situ tensile test. The PF phase in the network morphology sample was believed the main deformation phase, but the deformation of the PF phase in the layered morphology sample was restrained. Two three-dimensional (3D) crystal plasticity finite element models (CPFEMs) were established based on the electron backscatter diffraction (EBSD) data. The simulation results indicated that the strain field in layered microstructure was more uniform than that in network microstructure, and the continuous internal stress relaxation (ISR) in the bainite phase led to plastic damage at low tensile strain level; The strain field in network microstructure mainly existed in the PF phase, the deformation of the PF phase can be fully utilized. When changing the tensile x-direction of the layered microstructure to the z-direction, the strain field showed an obvious anisotropy, and loading in the z-direction increased the risk of interlaminar crack formation. • Quasi-situ tensile test was used to study the deformation behavior • Strain/stress distribution characteristics were clarified using CPFEM method • Uniform strain distribution and ISR in layered microstructure decreased its plasticity • z-axis loading increased the risk of interlaminar crack for layered microstructure

Modeling the influence of heat sinks on the structure of the temperature field of a profile heat pipe

Within the framework of a computer experiment using the finite element method, a technique has been developed graphical representation the structure of the temperature field of a heat pipe with active-type defects - heat energy sink, localized in the body between the ribs. It is shown that when the pipe start-up mode is implemented and certain heat energy sink power, a typical isotherm shape with a concave front is formed. The passage by the isotherm heat energy sink of a round form is accompanied by the formation of a local isothermal circuit. Significant variability of the shape of the isotherms is noted.

Dispersion Mechanism of Styrene–Butadiene Rubber Powder Modified by Itaconic Acid and Its Toughening Effect on Oil Well Cement

Styrene-butadiene rubber (SBR) has been extensively applied to enhance the toughness of hardened cement. The instability of existing liquid latex leads to difficulties in storage and transportation, and even performance regression. Thus, the well-dispersed carboxylated butylbenzene (SISBR) latex powders were fabricated through the seed emulsion polymerization of liquid polybutadiene (LPB), styrene (St), itaconic acid (IA), and sodium p-styrenesulfonate (SSS) to overcome the difficulties. The dispersion performance of latex powders with various IA amounts was quantitatively evaluated using particle size distribution, zeta potential, and ultraviolet-visible spectrophotometry. Results showed that the carboxylic ionic (COO-) from IA enhanced the dispersing abilities of SISBR latex powders, which ensured the uniform distribution in water. Based on this, the influence of latex powder on cement was assessed mainly by fluidity, isothermal heat flow calorimetry, X-ray diffraction (XRD), and triaxial mechanical testing. Results showed the fluidity and dispersion performance of cement were improved with more IA in latex, while the hydration of cement was retarded due to excessive adsorption of carboxyl (-COOH) groups in IA. Triaxial mechanical testing showed that cement with SISBR-3 (latex containing 3% IA) exhibited the minimal elastic modulus of 3.16 GPa, which was lower than that of plain cement (8.34 GPa).

Effect of neutron dose on the tritium release behavior of Li2TiO3–0.5Li4SiO4 biphasic ceramic

Neutron irradiation with different fluence and flux on the Li2TiO3-0.5Li4SiO4 biphasic ceramic powders was conducted. The tritium release behavior was studied by thermal desorption spectroscopy (TDS) with different heating rates and isothermal heating at various temperatures. It was found that the tritium TDS spectra were shifted toward the higher temperature side as the neutron fluence was reduced. The tritium migration in the biphasic ceramic was governed by diffusion and de-trapping processes with the activation energies of 0.29–0.50 eV and 1.00–1.13 eV for the neutron-irradiated samples with the fluence of 8.25 × 1015 and 3.96 × 1016 n cm−2. For isothermal heating, there is another tritium desorption peak when the sample was continually heated to higher temperatures after isothermally heating at 690 K and 800 K, indicating that tritium still remained in the ceramic under isothermal heating conditions. The intensity of the second peak was decreased at the higher isothermal heating temperatures. The diffusion model with detrapping reaction can fit the experimental data, suggesting that both the detrapping and diffusion processes should be considered to estimate tritium release characteristics for the tritium breeding biphasic ceramics.

Natural Convection From an Isothermally Heated Hollow Vertical Cylinder Submerged in Quiescent Power-Law Fluids

Abstract An attempt has been made to study the natural convection around a hollow vertical cylinder numerically which is suspended in motionless power-law fluids in the laminar range. The influence of various non-dimensional pertinent parameters, such as Grashof number (10 ≤ Gr ≤ 105), Prandtl number (0.71 ≤ Pr ≤ 100), and power-law index (0.2 ≤ n ≤ 1.8) on thermofluid characteristics around the hollow cylinder, is predicted computationally. Simulations are performed by varying the cylindrical aspect ratio (L/D) over the range of 1 ≤ L/D ≤ 20. It is reported that the average Nusselt number appreciably grows with the rise of Gr or/and Pr for a constant L/D. Moreover, the rate of rising of Nusselt number (Nu) with Gr or/and Pr strongly depends upon the power-law index (n); i.e., Nu finds a stronger dependence on Gr than that of Pr with a lower value of n (shear-thinning fluids, (n < 1)) and a completely different pattern has been noticed in shear-thickening fluids (n > 1). Furthermore, the average Nu on the outer wall (Nuouter) grows approximately in a linear way with an increase in aspect ratio for a particular Gr, Pr, and n. In contrast, Nuinner drops drastically and almost attains the asymptotic trend at a greater value of aspect ratio for lower Gr or/and Pr. The decreasing pattern of Nuinner is found to be remarkably steep for n < 1 (shear-thinning fluids) in comparison to n > 1 (shear-thickening fluids). Correlations are developed for Nuouter and Nuinner in terms of Gr, Pr, n, and L/D, which operate extremely well within ± 6% of the computational data.

An Opposite Tendency of Mechanical Properties and Corrosion Resistance of a High-Strength Al-5024 Alloy Processed by Laser Powder Bed Fusion

Abstract Laser Powder Bed Fusion (LPBF) manufactured Al-5024 alloy has gained worldwide interest due to its ability to fabricate high-performance complex components. This work focuses on quantitative characterization and synergic optimization of the microhardness, tensile strength, and corrosion resistance of an LPBF manufactured Al-5024 alloy by optimization of heat treatment parameters. The effect of the isothermal heat treatment (IHT) process on the microstructure evolution, mechanical properties, and electrochemical properties of an LPBF-processed Al–4.2Mg–0.4Sc-0.2Zr alloy was systematically revealed. Results showed that superior tensile strength of 506.7 ± 10.4 MPa combined with inferior corrosion resistance was simultaneously obtained at a peak-aging condition. Based on microstructure observations by electron microscopy in backscattered mode (BSE) and transmission electron microscopy (TEM), the enhanced mechanical properties were attributed to the generation of a high number density (3.8 × 109/mm2) of grain interior precipitates, while the reduced corrosion resistance was related to the massive Al3(Sc,Zr) precipitates generated along grain boundaries. As aging time further increased, the size and spacing of the precipitates were increased, which blocked the corrosion path along grain boundaries and led to a reduction of mechanical properties and an enhancement of corrosion resistance. Unlike the expected synergistic improvement in mechanical properties and corrosion resistance, an opposite evolution tendency of mechanical properties and corrosion resistance of LPBF-processed Al-5024 alloy during heat treatment was revealed in this paper, and its intrinsic mechanism is further analyzed based on microstructure characterization.

Wear resistance of austempered grey iron under dry and wet conditions

In this paper, a grey iron was submitted to low temperature isothermal heat treatment, austempering, in order to obtain austempered grey iron (AGI). Tensile strength, Brinell hardness and tribological properties were determined for the as-cast condition and for two austempering conditions. The tribological properties were evaluated by pin-on-disk testing in dry and wet environments. The results show that AGI exhibit better mechanical properties than the as-cast grey iron. Also, the mechanical properties of AGI improve as the isothermal heat treatment temperature decreases. The wear resistance of AGI is better than the wear resistance of as-cast grey iron in both dry and wet conditions. In dry conditions the wear resistance of AGI increases as the isothermal heat treatment temperature decreases. On the other hand, the wear resistance of AGI in wet conditions increases as the isothermal heat treatment temperature increased. The results are explained in terms of the microstructural differences found between the materials under evaluation.

Microstructure and mechanical behavior of Ti—Cu alloys produced by semisolid processing

The mechanical properties of Ti—Cu alloys processed via thixoforming were evaluated. Ti—Cu (25, 27, and 29 wt.% Cu) ingots were produced via arc melting, homogenization at 950 °C for 24 h, and hot-forging at 900 °C, followed by thixoforming at a speed of 8 mm/s after isothermal heat treatment at 1035 °C for 300 s. The thixoformed alloys exhibited good mechanical strength, limited plasticity under tensile loading, and reasonable plasticity under compressive loading. The mechanical strength and plasticity decreased as the Cu content increased as a result of the increasing volume fraction of the peritectic Ti2Cu phase (transformed liquid), which exhibited a lower strength and plasticity than the α + Ti2Cu regions (transformed solid). These findings indicated that the trade-off between the mechanical properties and semisolid processability is largely governed by the Cu content.

Investigation on microstructures and properties of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high-entropy alloy during isothermal heat treatment process

The Al80Mg5Li5Zn5Cu5 light-weight high-entropy alloy with globular microstructure was fabricated by isothermal heat treatment. The effects of isothermal temperatures and holding times on the semi-solid microstructure evolution were investigated. The results indicate that, with increase of the isothermal temperature, the average grain size increases and the spheroidization time shortens. With prolongation of holding time, the shape factor increases firstly and then decreases, and the average grain size decreases at first and then increases when the isothermal temperature is below 520 °C, however it increases gradually at 540 °C. The optimal semi-solid microstructure is obtained at 520 °C for 30 min, whose shape factor and average grain size are 0.90 and 56.4 µm, respectively. Compared with as-cast Al80Mg5Li5Zn5Cu5 light-weight high-entropy alloy, the compressive strength and plasticity of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high-entropy alloy are increased by 36% and 108%, respectively. The formation of semi-solid microstructures includes three stages: melting separation, spheroidization, and coarsening growth. The sluggish diffusion effect of Al80Mg5Li5Zn5Cu5 light-weight high-entropy alloy leads to a low coarsening rate, resulting in slow grain growth.