Thermal Behavior Research Articles

Promoting nanoprecipitates via prefabricated defects to pin dislocations and grain boundaries for trading off high-strength and low-thermal-expansion of invar alloys

Invar alloys that combine high strength with a low coefficient of thermal expansion (CTE) are urgently required for industrial applications. Based on the lower coarsening rate during aging and the CTE values of carbonitrides, a novel strategy is proposed to prepare carbonitrides by reducing carbon and increasing nitrogen to design high-strength and low-thermal-expansion invar alloys. The V(C, N) nanoprecipitate was introduced into the invar alloy, and its effects on the microstructure, thermal expansion behavior, and mechanical properties were investigated. The direct-aged alloy exhibited an enhanced tensile strength of 525 MPa and a ductility of 47.6%. The cold-deformation aging alloy achieved an enhanced tensile strength of 815 MPa while retaining 7.4% ductility and a low CTE value of 1.23×10−6 /°C. The V(C, N) nanoprecipitates effectively immobilized dislocations and grain boundaries, leading to a high dislocation density and small grain size in the alloy. The contributions of each strengthening mechanism were calculated, and the precipitation and dislocation strengthening were found to be the main mechanisms of strength enhancement. These results provide a novel approach for preparing high-strength and low-CTE invar alloys.

The effect of pressure on the thermodynamic properties of hydrogenic impurity in the GaAs semiconductor quantum well

ABSTRACT Studying the thermodynamic properties of hydrogen impurity in low-dimensional nanostructures under high-pressure environment is crucial for understanding the optical property and thermal excitation behaviour of semiconductor material. Here, we extensively explore the effect of pressure on thermodynamic properties, specifically, the average energy, free energy, entropy, and heat capacity of one-dimensional (1-D) hydrogenic impurity in GaAs semiconductor quantum well. Our findings reveal some novel phenomenon in the thermodynamic properties of hydrogenic impurity as pressure increases in the GaAs quantum well. Remarkably, at a constant temperature, both the average energy and free energy of hydrogenic impurity decrease as pressure rises, while entropy increases with increasing pressure. Intriguingly, the heat capacity shows distinct behaviour with varying pressure for different sizes of the quantum well. For very small size of the quantum well, the heat capacity increases with increasing pressure. However, for larger size of the quantum wells, the variation of heat capacity with pressure becomes irregular, showing a changeover from an increase to a decrease in response to increasing pressure. This research presents a pioneering method that employs pressure as a versatile tool for modulating the thermodynamic properties of hydrogenic impurity states in the nanostructures, and has some guidance for the preparation and synthesis of semiconductor devices.

High barrier polyesters based on 2,5-furandicarboxylic acid and disulfide bond: Smart degradation induced by low concentrations of redox reagent

Bio-based and biodegradable polymers opens up opportunities to overcome resource depletion and plastic pollution. However, the degradation mechanism based on ester bond breakage makes it difficult to achieve controllable degradation induced by external stimuli. In this work, we present a new 2,5-furandicarboxylic acid-based copolyesters (PBFDi) by partially replacing carbon–carbon backbones with disulfide bonds and discuss the influence of disulfide bonds on thermal stability, crystallization behavior, mechanical and barrier properties of polyesters. They could maintain stable for 1 h at processing temperatures of 220 °C, meeting the needs of long-term melt processing. The asymmetric structure of the furan ring and the slower free rotation of disulfide bonds help restrict the mobility of chains and obstruct gas permeation, resulting in 9.3–126.7 times increase in O2 barrier than commercial PBAT. With the introduction of small amount (≤40 %) of disulfide bond units, the hydrolysis rate is relatively slow and can maintain stable during storage and use. As expected, the copolyesters show redox dual-responsive degradation. Even at low concentrations (0.01 M and 0.1 M) of H2O2, the transition from hydrophobicity to hydrophilicity can be achieved, expected to accelerate the hydrolysis of PBFDi. The fast cleavage of disulfide bonds induced by DTT could be influenced by the copolymerized FDCA units. Lastly, the redox dual-responsive mechanism is elucidated, and how the rigid FDCA co-monomers affect the redox dual responsiveness is also clarified.

The Ash-Forming Element Migration and Mineral Transformation during the Bamboo Combustion Process.

To investigate the effect of combustion temperatures on element transformation of ash, bamboo was fired using a muffle furnace at 550, 600, 700, 800, 900, and 1000 °C. Chemical compositions, micromorphology, and mineral and thermal behavior of ash were characterized. The main components included K2O, SiO2, P2O5, MgO, and CaO at a temperature of 550 °C. The high temperature decreased the content of K2O from 63.03 to 35.71% to improve the fusion characteristics of bamboo ash. 700 °C was a key temperature for designing a combustion system of bamboo, where bamboo ash had a maximum volatility. The mineral phases were chlorides, carbonates, and sulfates below a temperature of 700 °C, which transformed to complex silicates, aluminosilicates, and phosphates above a temperature of 700 °C. The temperature ranges of the three main stages were 550-980, 980-1190, and 1190-1500 °C, corresponding to mass losses of 11.52, 6.13, and 17.17%, respectively.

Mechanical and Thermal Behavior of Semiconducting Cadmium Oxide at High-Pressure

Abstract The effect of high pressures on the mechanical and thermal properties up to phase transition pressure for cubic rock-salt cadmium oxide (CdO) semiconducting compound is presented in this research. The calculations are based on the equation of state (EOS) parameters measured at ambient conditions reported in the literature. The approach used here was previously applied successfully for other materials. Our study shows that the parameters reflect the rigidity of the semiconductor and the melting temperature increases with increasing pressure, while some other parameters decrease gradually for our material of interest. A comparative analysis of some quantities for CdO compound under high pressure was done. Similar behaviors were observed in the literature for particular materials with particular structures. Furthermore, we calculated both the fracture toughness and the fracture surface energy, which are at around 1.23 MPa.m1/2 and 5.14 J.m−2, respectively.

MODELLING AND ANALYSIS OF HEAT EXCHANGER

Shell and tube heat exchangers in their various construction modifications are probably the most widespread and commonly used basic heat exchanger configuration in the process industries. The modelling of the heat exchanger has done by using the advanced design software CATIA. In this project the Heat Exchanger is modelled and assembled with the help of CATIA and the component is meshed and analysis is done in ANSYS software and the thermal and static behaviour is studied and the results are tabulated. The various stresses acting on the Heat Exchanger under various loading conditions has been studied. In the preset work has been taken up on the following aspects to cover the research gaps and to present the results based on the systematic studies. Temperature distribution and heat flow through the Heat Exchanger. FEA analysis of the Heat Exchanger to measure temperature at the points where it is not possible to find out practically and to observe the heat flow inside the Heat Exchanger. Key Words: Shell and Tube Heat Exchanger, Catia,and Ansys Softwares, Static and Thermal behavior, and FEA Analysis.

Unveiling the potential of cellulose, chitosan and polylactic acid as precursors for the production of green carbon nanofibers with controlled morphology and diameter

Carbon nanofibers (CNFs) are very promising materials with application in many fields, such as sensors, filtration systems, and energy storage devices. This study aims to explore the use of eco-friendly biopolymers for CNF production, finding novel, suitable and sustainable precursors and thus prioritising environmentally conscious processes and ecological compatibility.Polymeric nanofibers (PNFs) using cellulose acetate, polylactic acid, and chitosan as precursors were successfully prepared via electrospinning. Rheological testing was performed to determine suitable solution concentrations for the production of PNFs with controlled diameter and appropriate morphology. Their dimensions and structure were found to be significantly influenced by the solution concentration and electrospinning flow rate. Subsequently, the electrospun green nanofibers were subject to stabilisation and carbonisation to convert them into CNFs. Thermal behaviour and chemical/structural changes of the nanofibers during stabilisation were investigated by means of thermogravimetric analysis and Fourier-transform infrared spectroscopy, while the final morphology of the fibers after stabilisation and carbonisation was examined through scanning electron microscopy to determine the optimal stabilisation parameters. The optimal fabrication parameters for cellulose and chitosan-based CNFs with excellent morphology and thermal stability were successfully established, providing valuable insight and methods for the sustainable and environmentally friendly synthesis of these promising materials.

Hydrogen bond‐reinforced double‐network hydrogels with enhanced mechanical strength: Preparation, characterization and swelling behavior

AbstractRecently, double network (DN) gels with dynamic non‐covalent interaction such as hydrogen bonds has drawn much attention as an innovative material having both high water content and high mechanical strength. Research efforts have identified DN gels as a promising class of materials due to their unique network architecture. These gels comprise two interpenetrating networks formed by different types of polymer. Herein, we report a tough DN hydrogel with high mechanical strength and high swelling ability. The DN gel is synthesized via a two‐step network formation. The first network gel was synthesized via frontal polymerization. Then, the first gel is immersed in an aqueous solution of a second monomer and carrying out a second polymerization in the presence of first network. The spectroscopic analysis and thermal behavior with differential scanning calorimeter measurements corroborated the existence of hydrogen bonds. The mechanical test and microscopic morphology were further explored to explain the strength and high imbibing characteristics. We expect that this facile strategy may explore a dynamic and tunable hydrogel to expand its potential applications in biomedical field.

Scaling analysis of nuclear power plant (APR1400) utilizing ATLAS integral effect test result of A5.1 (Counterpart test for LSTF 1% cold-leg break LOCA)

ATLAS is the thermal hydraulic integral effect test loop that can simulate the same pressure and temperature condition with nuclear power plant. It was designed with a height ratio of 1/2 and a volume ratio of 1/288 with reference to APR1400. The counterpart test against LSTF which was named as A5.1 test was performed within the OECD/NEA ATLAS international joint research project to compare major thermal hydraulic phenomena between two test facilities. The main scenario for the A5.1 test is the LSTF SB-CL-32 test. The SB-CL-32 test is a 1% horizontal small break loss of coolant accident (SBLOCA) at the cold leg with cold leg injection of the emergency core cooling system (ECCS) and accident management (AM) action.From the counterpart test results, the significant differences were found in the viewpoint of the thermal–hydraulic phenomena. It was concluded that the different result were caused by the different design characteristic of each test facility because they referred the different nuclear power plant. Thus, the applicability of the ATLAS test results to its reference nuclear power plant was evaluated by utilizing ATLAS A5.1 test results which was the counterpart test with the LSTF.The transient scenario and initial and boundary conditions of the A5.1 test were adopted to APR1400 after applying scaling ratios of ATLAS. The MARS-KS code was utilized to analyzed thermal hydraulic behaviors of APR1400 and the analysis results were compared with the scaled A5.1 test result. From the result of comparison, it was concluded that the ATLAS test results predicted the thermal hydraulic behavior of the nuclear power plant well. Thus, it was confirmed that ATLAS is a well-designed integral effect test facility which is designed with an appropriate scaling method.

Interface bonding characteristics and thermal damage behavior of brazed diamond with Nb-added Ni[sbnd]Cr filler alloys

NiCr alloy is one of the important filler for brazed diamond tools because of its high hardness, high wear resistance and good wettability to diamond. However, the high brazing temperature and catalytic action of Ni element contained in alloy tend to cause the thermal damage of diamond and interface failure of brazed samples. In this work, the noval NiCr filler alloys added with different contents of Nb are prepared, and the microstructures, mechanical and wear resistance properties of brazed layers used these alloys are investigated. On this basis, the interfacial bonding characteristics and thermal damage behaviors of diamond brazed with Nb-added NiCr filler alloys are further studied. The results show that the addition of Nb element improves the hardness and wear resistance of NiCr filler layer, and the filler alloys exhibit good wettability and climbing effect to diamond. The refined Cr3C2 and Cr7C3 carbides are formed on the surface of diamond, which effectively enhances the interface bonding strength between filler alloy and diamond. Meanwhile, the addition of Nb element consumes some Ni and generates NbNi compound, which weakens, to some extent, the graphitization catalysis and chemical erosion of Ni to diamond. When the addition amounts of Nb are 1–1.2 wt%, the brazed diamond samples present excellent interfacial bonding strength and mechanical properties.

Fenugreek seed mucilage-based active edible films for extending fresh fruit shelf life: Antimicrobial and physicochemical properties

Trigonella foenum-graecum, known as fenugreek, belongs to the leguminous family of wild growth in Western Asia, Europe, the Mediterranean, and Asia; its ripe seeds contain a pool of bioactive substances with great potential in the food industry and medicine. In this study, fenugreek seed mucilage (FSM) was extracted and characterized in its structural properties by X-ray diffraction, nuclear magnetic resonance, and high-performance liquid chromatography. Then, the applicability of FSM as an antimicrobial agent was demonstrated via the development of novel, active, edible FSM-based biofilms containing carboxymethyl cellulose and rosemary essential oil (REO). Incorporating REO in the biofilms brought about specific changes in Fourier-transform infrared spectra, affecting thermal degradation behavior. Scanning electron microscopy and atomic force microscopy morphography showed an even distribution of REO and smoother surfaces in the loaded films. Besides, the solubility tests evidenced a reduction in water solubility with increasing REO concentration from 1 to 3 wt%. The biological assay evidenced the antimicrobial activity of REO-loaded biofilms against Staphylococcus aureus and Escherichia coli. Finally, whole apples were dip-coated with FSM-based solutions to showcase future edible systems. The REO-loaded biofilms extended the shelf life of apples to 30 days, demonstrating their potential for sustainable and active coatings.

Origin of the surface facet dependence in the thermal degradation of the diamond (111) and (100) surfaces in vacuum investigated by machine learning molecular dynamics simulations

We perform machine learning molecular dynamics simulations to gain an atomic-level understanding of the dependence of the graphitization and thermal degradation behavior of diamond to the (111) and (100) surface facets. The interatomic potential is constructed using graph neural network model, trained using energies and forces from spin-polarized van der Walls-corrected density functional theory calculations. Our results show that the C(111) surface is more susceptible to thermal degradation, which occurs from 2850 K through synchronized bilayer exfoliation mechanism. In comparison, the C(100) surface thermally degrade from a higher temperature of 3680 K through the formation of sp1 carbon chains and amorphous sp2-sp3 carbon network. Due to the dangling bonds at the step edges, the stepped surfaces are more susceptible to thermal degradation compared to the corresponding flat surfaces, with the stepped C(111) and C(100) surfaces thermally degrading from 1810 K and 3070 K, respectively. We propose potential applications of this study in diamond tool wear suppression, diamond polishing, and production of graphene directly from the diamond surface.

Preparation of wheat straw-based aerogel and the research of it’s flame retardancy

Using waste biomass resources wheat straw(WS) as raw material, sodium alginate(SA) as basic skeleton and phytic acid(PA) solution as flame retardant, WS based composite aerogel(CA) was prepared in this research. Single factor experimental variables were used to optimize the preparation process conditions, and the relevant properties of CA were determined by FT-IR, limiting oxygen index, Raman test, etc. The experimental results show that the preparation conditions with better performance: the mass ratio of SA to WS was 1:1, the concentration of PA was 75%, the mass ratio of PA to SA was 1:4, and the mass ratio of PA to WS was 1:4. The obtained CAs have low density characteristics, the lowest density is 0.0122 g/cm3, the limiting oxygen index(LOI) attains a high level of 30.2%, while the vertical burning test(UL-94) demonstrates an impressive V-0 grade. FT-IR analysis showed that WS, SA and PA were physically cross-linked. The results of thermogravimetry analysis(TGA) showed that WS based CA had similar thermal degradation behavior，and raman analysis showed that the mixture of SA/WS/PA CA greatly improved the graphitization degree of the CA material, which helped to improve the stability of residual carbon ratio. WS produces no additional carbon dioxide throughout its life cycle, and the use of waste biomass WS in whole components does not need to be separated in advance, which is good for the environment, and reduces a lot of manpower, material and financial resources, and has more economic and application prospects. It is meaningful for the high-value utilization of waste resources, turning waste into treasure.

Study of mesomorphism behavior and protonation-induced emission of symmetrical benzalazines

Rod-shaped and polycatenar symmetric benzalazines with protonation-induced emission were synthesized, characterized, and studied for their thermal and optical behavior. Benzalazines lacking hydroxy groups at the ortho position did not show luminescence in the solid state or solution. In the presence of HCl (either in solution or vapor form) these compounds became good emitters. The protonation of azine nitrogen that may hinder the NN bond rotation by intermolecular interactions toward aggregates provided an explanation for the emission characteristics observed. The protonation-induced emission was thermally reversible. A benzalazine derived from 4-alkoxysalicylaldehyde with AIE property was prepared. For this compound with ortho-OH groups, the optical properties were not affected by the presence of acidic media. It exhibited a stable SmC phase characterized by POM, DSC, and XRD. The luminescence capability of the molecular arrangement within the smectic phase was investigated. The intense yellow-green emission in the crystals decreased significantly at the phase transition due to the non-radiative decay that occurs with increasing temperature, and loss of intermolecular H-bonding which prevents molecular rotations in the crystal.

Coupled thermomechanical analysis using isoparametric curved shell elements

This study focuses on the coupled thermo-mechanical formulation in isoparametric shell elements and its implementation in curved laminar structures. The formulation is based on the direct isoparametric formulation, specifically designed for flat and curved shell elements, and relies on the theory of degenerated solids. The research provides a comprehensive description of the coupled thermo-mechanical analysis, including the mechanical equilibrium equations, the interrelations between stress, temperature, displacement, deformation, and the conservation of thermal energy. It adopts a simultaneous approach to addressing the impacts of temperature and mechanical loads. The paper elaborates on various numerical examples that substantiate the formulation. These examples include simulations that encompass linear scenarios, which are then compared to analytical solutions and results derived from other numerical software. The examples highlighted include one-dimensional temperature diffusion, radial diffusion, and the thermal behavior of a cylindrical cover and a pipe under a linear temperature gradient. These simulations demonstrate the formulation's capacity to accurately capture the interactions between temperature variations and structural displacements. They also confirm the alignment of the proposed model with existing analytical and numerical solutions. In conclusion, the research provides a good framework for coupled thermo-mechanical analysis. The flexibility of the formulation is evidenced across different configurations and scenarios, accommodating various types of boundary conditions such as constant and linear temperature fields, distributed loads, and constraints on displacements and rotations. It effectively manages temperature flows across one, two, and three dimensions, highlighting its extensive applicability in the realm of structural analysis. This versatility underscores its broad applicability in the field of structural analysis.

Analysis of exergy and heat transfer in a tube fitted with flapped V-baffles

Vortex generator is a device that shows promise in generating streamwise vortices that can be utilized for boosting the rate of heat transmission inside a cooling/heating system with a relatively smaller penalty in terms of friction loss. The primary goal of the current research is to maximize the comparative Nusselt number ratio (Nu/Nu0) to be as large as possible to lower the size of the system while keeping thermal performance as high as feasible to save more energy. Thus, in the current study, the impacts of inserting the flapped V-baffle vortex generator (FBVG) on the thermal effectiveness improvement of a round tube were experimentally investigated. At a fixed attack angle (α = 60°) and baffle blockage ratio (BR = b/D = 0.3), the geometrical behaviors of FBVGs placed periodically along two edges of a straight tape were six different flap angles (θ = 0°, 25°, 35°, 45°, 65° and 90°) and three ratios of baffle pitches (P/D = PR = 2.0, 1.5, and 1.0). The current V-baffles, which were positioned on both tape edges, were designed to reduce friction loss caused by interrupting the central core flow when placed on both tape sides. The measurement results focused on the friction loss and thermal behaviors, including exergy and entropy analyses for Reynolds number from 4750 to 29,270. In the findings, the Nusselt number and friction factor of FBVG at θ = 0° and PR = 1 are, respectively, up to 5.6 and 35.24 times larger than those of the smooth tube. The entropy generation (S˙gen′) seems to decline as θ and PR increase, with the smallest S˙gen′ found at θ = 0° and PR = 1 for lower Re. The FBVG has the greatest exergy efficiency (ηEx) at θ = 0° and PR = 1. To find the true benefits of FBVG, its thermal performance is estimated and seen to reach a maximum at about 2.44 with NuR = 4.65 at θ = 45° and PR = 1. The optimal scenario at θ = 25° and PR = 1 was preferred, however, since it yielded the largest NuR = 5.42 at TEF = 2.39.

Exogenous polyserine fibrils change membrane properties of phosphatidylcholine-liposome and red blood cells

The causative genes for neurodegenerative polyglutamine (polyQ) diseases produce homopolymeric polyglutamine (polyQ), polyserine (polyS), polyalanine (polyA), polycysteine (polyC), and polyleucine (polyL) sequences by repeat-associated non-AUG (RAN) translation. The cytotoxicity of the intracellular polyQ and RAN products has been extensively investigated. However, little is known about the toxicity of the extracellular polyQ and RAN products on the membranes of viable cells. Because polyQ aggregates induce a deflated morphology of a model membrane, we hypothesized that extracellular polyQ and RAN products might affect the membrane properties of viable cells. In this study, we demonstrated that exogenous polyS fibrils but not polyS or polyQ non-fibril aggregates altered the thermal phase transition behavior of a model membrane composed of a phosphatidylcholine bilayer using differential scanning calorimetry. PolyS fibrils induced morphological changes in viable red blood cells (RBCs). However, both polyS and polyQ non-fibril aggregates had no effects on RBCs. These results highlight the possibility that extracellular fibrils generated from RAN products may alter the properties of neuronal cell membranes, which may contribute to changes in the brain pathology.

Advancing Light Scattering Control Through the Exploration of Temperature‐Sensitive Optical Modifiers

Advancing Light Scattering Control Through the Exploration of Temperature‐Sensitive Optical Modifiers

Experimental investigation on the thermal behavior of two typical stainless steel roof systems

Experimental investigation on the thermal behavior of two typical stainless steel roof systems

Reedmergnerite and stillwellite-(Ce) from the Dara-i-Pioz alkaline massif: insights into high-temperature behavior of borosilicates

Research subject. Reedmergnerite and stillwellite-(Ce) were obtained from the rocks of the Dara-i-Pioz alkaline massif located on the southern slope of the Alai Range in Tajikistan, which is characterized by the presence of rare mineral species including borosilicates and lithium minerals. Aim. To investigate the thermal behavior of reedmergnerite and stillwellite-(Ce) using high-temperature X-ray diffraction, including the determination of phase transition temperatures and expansion/compression of the unit cell parameters, as well as the calculation of thermal expansion coefficients. Materials and methods. Chemical analysis was performed using a TESCAN MIRA 3 microscope (EDS mode) and a JEOL JXA-8230 electron probe microanalyzer (WDS mode). High-temperature powder X-ray diffraction data were collected using a D8 ADVANCE Bruker diffractometer with an HTK16 heating chamber, covering temperatures from 30°C to 750°C in ambient air. Results. The thermal expansion coefficients of reedmergnerite and stillwellite-(Ce) were determined. Heating reedmergnerite resulted in slight changes in the unit cell parameters, with the parameter c experiencing the smallest change and the parameter a showing the greatest increase. The unit cell volume increased by 1.8% when heated to 750°C and returned to its initial value upon cooling. When stillwellite-(Ce) is heated in the temperature range of 400–450°C, a phase transition occurs, which is confirmed by previously recorded temperature values. The conducted heating and subsequent cooling experiments revealed that the volume and unit cell parameters of stillwellite-(Ce) did not fully revert to their original values. Conclusions. The coefficients of thermal expansion tensor (αij) of rhodmerdgnertite and stillwellite-(Ce) were investigated as a function of temperature using high-temperature in-situ experiments. The phases exhibited relatively low values of thermal expansion parameters compared to the general data for feldspars and borosilicates obtained from literature. These findings contribute to the understanding of the thermoelastic behavior of this group of minerals and their potential applications in various fields.