Search Results (127)

To enhance the thermal performance of a Stirling air conditioner, this study applies Schmidt-based dimensionless analysis to systematically investigate the influence of key structural parameters on its cooling and heating characteristics. A dimensionless thermodynamic framework is established under the ideal isothermal assumptions of the Schmidt model to investigate the effects of temperature ratio, swept volume ratio, dead volume ratio, and phase angle on a Stirling system. The results indicate that increasing the temperature ratio enhances the thermodynamic driving potential; however, excessive temperature ratios introduce stronger irreversibilities, resulting in saturation or even degradation of effective cooling performance. The dimensionless cooling capacity increases significantly with phase angle, rising from 0.25 at α = 50° to 0.65 at α = 120°, while heating capacity peaks at α ≈ 71.6° with ε_e = 0.18. The p–v diagram analysis reveals optimal work output at α ≈ 75°, where the cycle area reaches 20.8, representing a 44.4% increase from the value at 15°. Performance saturation occurs at τ > 3 and κ > 6 for cooling and beyond κ > 4 for heating. Within the assumptions of the ideal Schmidt model, the results suggest that medium-to-high temperature ratios (τ ≈ 3–4) combined with moderate swept volume ratios (κ ≈ 6–8) provide the optimal balance between thermodynamic performance and structural compactness; these parameter combinations should be regarded as theoretical design references for ideal operating conditions rather than directly applicable engineering optimization guidelines. Full article

The macroscopic mechanical properties of near-β titanium alloys depend inherently on their complex microstructural morphologies and phase transformation kinetics. This study investigates the deformation behavior of a lamellar Ti-55531 alloy during isothermal compression and in situ tensile testing. Pronounced strain rate sensitivity dictates the deformation of the lamellar microstructure. Low strain rate deformation (0.001 s⁻¹) induces dynamic recovery and recrystallization, which in turn drive α-lamellae fragmentation and the nucleation of new α phase during compression. The α precipitation is governed by a strict Burgers orientation relationship (BOR), but extensive plastic deformation may lead to the breakdown of the BOR. During tension, continuous slip transfer between adjacent phases is critically restricted by α/β interfacial thickness. As plastic strain accumulates, lath-like, V-shaped, and acicular α phases precipitate concurrently within β grains, creating a complex α microstructure. Full article

Polydiacetylene (PDA) nanovesicles are widely recognized as versatile chromatic sensing platforms, exhibiting a visible blue-to-red colorimetric transition in response to external stimuli such as temperature, pH, and molecular recognition events. In contrast to the conventional goal of amplifying this chromatic response, this work presents a supramolecular approach to inhibit the α-cyclodextrin (α-CD)-induced colorimetric transition in PDA systems. α-CD is known to interact with PDA vesicles through host–guest inclusion at the vesicle interface, triggering the characteristic chromatic change. Here, we show that the incorporation of an EO–PO–EO triblock copolymer (L64) into PDA suspensions enables controlled modulation of the α-CD-induced chromatic response, leading to a progressive attenuation of the blue-to-red transition as the L64 concentration increases. Isothermal titration calorimetry reveals a stronger affinity of α-CD for L64 (K = 11,300) than for PDA vesicles (K = 4000), with both interactions being spontaneous (ΔG° ≈ −21 kJ mol⁻¹) and predominantly entropy-driven. Copolymer aggregation and phase separation occur without compromising the PDA vesicles, indicating that the observed chromatic modulation arises from supramolecular competition. This study introduces a strategy to regulate PDA affinity chromism using biocompatible triblock copolymers, offering a tunable and robust pathway for the design of responsive and safe chromatic sensing platforms. Full article

Understanding the rapid non-isothermal crystallization behavior of polymers is crucial for tailoring and optimizing their performance. However, conventional techniques are limited in achieving rapid heating and cooling rates, which hinders in-depth investigation of the crystallization kinetics of fast-crystallizing polymers. In this study, a high-scan-rate MEMS thermopile DSC chip is employed to systematically investigate the non-isothermal crystallization kinetics of polyamide 66 (PA66) under rapid temperature variations. The results show that PA66 forms a lamellar α phase under slow cooling (1 °C/s) and a cauliflower-like γ phase under rapid cooling (300 °C/s), and becomes completely amorphous under ultrafast cooling (quenching). Furthermore, the technique enables quantitative analysis of the cold crystallization kinetics of fully amorphous PA66 during rapid heating. The results indicate that PA66 exhibits a higher apparent activation energy for homogeneous nucleation cold crystallization at low heating rates (≤10 °C/s), reaching 172.3 kJ·mol⁻¹, which is approximately 3.2 times that at high heating rates (≥25 °C/s). The results of this study demonstrate that the developed fast-scanning chip-based DSC provides a powerful tool for analyzing the processing heating and cooling rate conditions of rapidly crystallizing polymers. Full article

This work presents a study of oxide-scale development on a B2 FeAl-based alloy (Fe40Al5Cr0.2TiB) during long-term isothermal oxidation at 700 °C in air, with particular emphasis on the effect of plastic processing. Oxidation tests were conducted for 300, 1000, and 2000 h. Surface morphology and chemical composition were examined using SEM/EDS, phase composition was identified by XRD, and local oxide thickness was measured by TEM. Surface topography was quantified by optical profilometry using Ra and Rz parameters. In both material states (as-cast and plastically processed), the alloy formed a continuous α-Al₂O₃-based scale. Plastic processing significantly affected oxidation kinetics, resulting in higher mass gain compared to the as-cast condition. Despite differences in mass gain, the average oxide-scale thickness after 2000 h remained in the submicrometric range (~340 nm) for both states. Surface topography analysis revealed differences in roughness and morphology associated with the material condition. The results demonstrate that plastic processing influences oxidation behavior primarily through microstructural modification, while the protective character of the alumina scale remains preserved. These findings provide data relevant to FeAl-based materials considered for high-temperature energy applications. Full article

The water thermodynamics is characterized by polydispersity, which determines its structural and dynamic properties. This is due to the specifics of its characteristic bond: the hydrogen bond (HB). The isobars of the two fundamental thermodynamic functions, the isothermal compressibility ($K_T(P.T)$) and the isobaric expansivity (${\alpha }_P(P,T)$), show the presence of a temperature $T^{*}\simeq 315\pm 5$ K where both have a singular behavior. In this work, by carefully considering the thermal properties of the isobars of density $\rho$, specific heat $C_P$ and the self-diffusion $D_S$, we suggest the universality characteristics of this temperature. In addition, by analyzing the average intermolecular distance $d_{OO}$, in the same area of the P-T phase diagram, we demonstrate that such realities are due in the supercooled liquid state to the ratio between its two characteristic phases: the low-density liquid (LDL due to HB) and the HDL (which entirely characterizes the remaining parts of the phase diagram). Full article

The microstructural evolution and phase stability in Fe–Mn–Al alloys play a decisive role in determining their mechanical performance and potential applications. This study investigates the precipitation behavior and crystallography of the β-Mn phase in an Fe–28.6 Mn–10.9 Al (wt.%) alloy subjected to annealing at 1100 °C, followed by water quenching and subsequent isothermal holding at temperatures between 500 °C and 900 °C for 20 h. Microstructural analysis using X-ray diffraction, optical and electron microscopy revealed a single body-centered cubic (BCC) ferritic matrix above 850 °C and the formation of β-Mn precipitates with Widmanstätten side-plate morphology at lower temperatures. The β-Mn phase was thermally stable between ~500 °C and 850 °C, with the volume fraction increasing with temperature and reaching a maximum near 650 °C. The β-Mn precipitates coarsened progressively with increasing temperature and were found to be richer in Mn than the surrounding Fe-rich BCC matrix. Crystallographic analysis established an orientation relationship (OR) of ($02\overline{1}$)_β // (100)_α and [$\overline{1}12$]_β // [012]α, where // denotes nearly parallel alignment, signifying a semi-coherent interface between the two structures. These findings clarify β-Mn precipitation, its interfacial relationship with ferrite, and its thermal stability in high-Mn Fe–Mn–Al alloys, offering guidance for microstructural design in next-generation lightweight steels. Full article

This work presents a facile mechano-thermal route for the synthesis of carbon-decorated, hollow, mesoporous α-Fe₂O₃ microspheres. Comprehensive characterization (XRD, XPS, FT-IR, SEM/EDX, TGA, zeta-potential) confirmed the formation of phase-pure hematite with nanoscale crystallites (~19 nm), substantial residual surface carbon (~40 wt%) consistent with Fe–O–C linkages, and a positive surface charge (+15.9 mV). The hierarchical hollow/mesoporous architecture enables fast ion transport and provides extensive interior binding sites, resulting in rapid Pb(II) uptake that reaches 92% removal in ≈15 min at pH 5.0. The adsorption follows a Langmuir isotherm (q_max ≈ 70.6 mg/g) and pseudo-second-order kinetics, indicative of chemisorption coupled to efficient mass transfer into internal sites. The composite also exhibits antibacterial activity against Escherichia coli and Staphylococcus aureus, demonstrating its potential for simultaneous mitigation of heavy metal contaminants and pathogens. Full article

FeCoNiCrAl and FeCoNiCrAlScY high-entropy coatings were fabricated via electron beam physical vapor deposition. The microstructure and short-term isothermal oxidation behavior of the coatings were compared. Sc and Y inhibited coating element diffusion to the superalloy substrate and formed co-precipitated phases during coating manufacturing. The Sc/Y co-doped coating exhibited accelerated phase transformation from θ- to α-Al₂O₃ as compared to the undoped one. The effect mechanism associated with the nucleation of α-Al₂O₃ was discussed. The preferential formation of Sc/Y-rich oxides promoted the nucleation of α-Al₂O₃ beneath them, and the θ-α phase evolution process was directly skipped, which suppressed the rapid growth of θ-Al₂O₃ and the initial formation of cracks in the alumina film and provided the FeCoNiCrAl high-entropy coating with an improved oxidation property in the early oxidation stage. Full article

Phase transformations significantly influence the mechanical properties of Fe-based alloys, making their understanding essential for the design of high-performance alloy materials. This study investigates microstructural evolution and martensitic transformations induced by B2 phase precipitation in an Fe-20Ni-4.5Al-1.0C (wt.%) alloy. The alloy was solution-treated at 1100 °C, followed by isothermal holding between 750 °C and 1000 °C, and water quenching. Microstructural analysis revealed that the as-quenched alloy consisted of a single-phase austenite (γ). Isothermal holding led to the precipitation of a (Ni,Al)-rich B2 phase within the grains and along grain boundaries. An α′-martensitic phase was also observed within γ-grains adjacent to the B2 precipitates in the isothermally held samples. Martensitic transformation is attributed to localized nickel depletion in the matrix surrounding B2, which reduced γ-phase stability and raised the martensite start temperature (Ms), promoting γ-to-α′ transformation during cooling. The co-existence of B2 and α′ phases significantly increased the hardness of the alloy, with a maximum observed at an 850 °C holding temperature. At higher temperatures, coarsening and partial dissolution of B2, as well reduced martensite formation, led to a decline in hardness. These findings highlight the role of B2 precipitation in promoting martensitic transformation and optimizing mechanical properties through controlled heat treatment. Full article

The Ti-6242 titanium alloy samples were forged at 1020 °C (slightly above the β-transus) and subjected to ultra-short isothermal holding (0–320 s) prior to quenching to investigate the rapid microstructural evolution in the parent β phase. Electron backscatter diffraction (EBSD) with parent β-phase reconstruction reveals that within only 1–3 s of holding, a pronounced <111> fiber texture develops along the forging axis, superseding the original <100> deformation fiber. This ultrafast texture change is attributed to metadynamic recrystallization (MDRX)—the post-deformation growth of nuclei formed during dynamic deformation. The newly formed <111>-oriented β grains still contain residual substructure, indicating incomplete strain release consistent with MDRX. Longer holds (tens of seconds) lead to more extensive static recrystallization and normal grain growth, which dilute the strong <111> fiber as grains of other orientations form and coarsen. These findings demonstrate that even a brief pause after forging can markedly alter the prior β texture via a MDRX mechanism. This insight highlights a novel approach to microtexture control in Ti-6242: by leveraging MDRX during short holds, one can potentially disrupt the formation of aligned α colony microtextured regions (MTRs, or “macrozones”) upon subsequent cooling, thereby mitigating dwell-fatigue susceptibility. The study revises the interpretation of the recrystallization mechanism in short-term holds and provides guidance for optimizing β-phase processing to improve fatigue performance. Full article

Aluminum alloys based on the eutectic Al–Ni system are a promising class of lightweight materials for applications at elevated temperatures owing to the thermal stability of the eutectic Al₃Ni phase. In this study, the eutectic Al–Ni alloy was modified by the addition of 0.6 wt.% Zr to enhance the α_Al matrix by precipitation strengthening. The alloys were cast and subjected to T5 heat treatment followed by long-term isothermal aging at 350 °C. A comprehensive study was carried out to evaluate the evolution of microstructure, microhardness and mechanical performance over time. The formation of fine, coherent L1₂-Al₃Zr precipitates contributed to significant strengthening, as reflected by a ~60% increase in microhardness and an approximately twofold improvement in room temperature (RT) yield strength. A TEM analysis of the L1₂-Al₃Zr precipitates showed relatively good thermal stability after 30 days. Despite the improved mechanical properties at room temperature, the alloy did not retain this improvement when tested at 300 °C. Nevertheless, these results provide a comprehensive insight into the aging and thermal stability of Al–Ni–Zr alloys. Full article

High-temperature adsorption is a promising technology for carbon mitigation, and it can be applied in direct carbon capture and the integration with utilization. Lithium-based adsorbents, known for their high CO₂ uptake and rapid kinetics, have garnered significant interest. However, adsorption performance, cycling stability, and degradation behavior of this type of adsorbent are rarely reported and compared under comparable conditions. In this work, nine lithium-based adsorbents were synthesized and characterized for their physicochemical properties. Dynamic and isothermal thermogravimetric analysis were conducted to determine adsorption/desorption equilibrium temperatures, evaluate CO₂ adsorption characteristics under varying thermal conditions, and assess cycling stability over 20 adsorption–desorption cycles. The results reveal exceptional initial CO₂ capacities for α-Li₅AlO₄, Li₅GaO₄, Li₅FeO₄, and Li₆ZnO₄; however, these values decline to 30.2 wt.%, 24.3 wt.%, 41.6 wt.%, and 44.2 wt.% after cycling. In contrast, Li₂CuO₂ and Li₄SiO₄ exhibit lower initial capacities but possess superior cycling stability with final values of 21 wt.% and 21.6 wt.%. Phase composition and microstructural analysis identify lithium carbonate and metal oxides as primary products, and microstructural sintering was observed during cycling. This study could provide insights into the trade-offs between the initial capacity and cycling stability of lithium-based adsorbents, offering guidelines for adsorbent optimization through doping or pore engineering to advance high-temperature CO₂ capture technologies. Full article

Ti-2Al-9.2Mo-2Fe (2A2F) alloy is a low-cost β-Ti alloy in which the expensive β-stabilizing elements (Ta, Nb, W, Ni) are replaced with relatively inexpensive Mo and Fe for use in low-cost applications in various industries. The 2A2F alloy exhibits excellent mechanical properties such as high specific strength and low elastic modulus compared to conventional steel alloys but is prone to brittleness owing to the formation of the ω phase when heat-treated at relatively low temperatures. Therefore, an appropriate aging treatment should be performed to control the precipitation of the isothermal ω phase and secondary α phase. This study aims to derive the appropriate aging-treatment conditions following a solution treatment at 790 °C for 1 h, which is below the β-transus temperature of 815 °C. The aging treatments are conducted at holding temperatures in the range of 450–600 °C and holding times between 1 and 18 h. At relatively low aging temperatures of 450 °C and 500 °C, the precipitation of the isothermal ω phase resulted in significantly high hardness and compressive strength. As the aging temperature and holding time increased, the ω phase gradually transformed into the secondary α phase, leading to a balanced combination of strength and ductility. However, at excessively high aging temperatures and prolonged durations, excessive precipitation and growth of secondary α phases occurred, which caused a reduction in hardness and compressive strength, accompanied by an increase in ductility. In this study, the effects of precipitation evolution on mechanical properties such as tensile strength and hardness under various heat treatment conditions were comparatively analyzed. Full article

In this study, the phase transformation mechanism during the decomposition of undercooled austenite and its effect on the deformation behavior of a high-strength medium Mn steel were studied. The results indicate that the austenite formation during heating (α → γ) is a relatively fast reaction. However, the transformation of undercooled prior austenite above the martensite start (M_s) temperature (γ → α) is difficult due to its high thermal stability. Only martensite transformation occurred during the final air-cooling stage following a 120-h isothermal treatment at 360 °C (slightly above M_s). The growth of martensite laths was limited by the boundaries of prior austenite grains and martensite packets. High-strength tensile properties were achieved, with a yield strength of 955 MPa, ultimate tensile strength of 1228 MPa, and total elongation of 11.6%. These properties result from the synergistic hardening effects of grain refinement, high-density lattice distortion, and an increased boundary length per unit area. The composition design with medium Mn content increased the processing window for high-strength martensite transformation, providing a theoretical basis for an energy-saving approach that depends on the decomposition transformation of undercooled austenite. Full article