Hot-pressing Technique Research Articles

Synthesis of a gallic acid-based self-healing waterborne polyurethane with a thermo-responsive dynamic phenol-carbamate network for enhanced mechanical strength, antimicrobial activity, and shape memory properties

To expedite the advancement of multifunctional next-generation smart materials, it is imperative to create polymers derived from renewable, green bio-based resources. This paper presents a direct synthesis of thermo-responsive aqueous polyurethanes by combining gallic acid (GA) with isocyanate groups to form a dynamic phenol-carbamate crosslinked network and the incorporation of the metal-organic framework Cu-MOF-2 for synergistic effects. The resulting GA-based polyurethane (MOF-GWPU) exhibits excellent thermal stability and mechanical properties, achieving an ideal balance between mechanical strength and self-healing efficiency. The MOF-GWPU film demonstrates strong antimicrobial efficacy against Escherichia coli and Staphylococcus aureus, highlighting its exceptional antibacterial performance. The thermo-responsive dynamic covalent bonds enable the MOF-GWPU film to rapidly revert from a temporary shape back to its original form. Post-processing experiments further indicate that the crosslinked GA-PU polymer can be efficiently recycled through solution casting and hot-pressing techniques. This design offers a novel approach and valuable insights for advancing the development of multifunctional smart polymers derived from bio-based resources.

Spontaneous Cooling Enables High-Quality Perovskite Wafers for High-Sensitivity X-Ray Detectors with a Low-Detection Limit.

Developing high-quality perovskite wafers is essential for integrating perovskite technology throughout the chip industry chain. In this article, a spontaneous cooling strategy with a hot-pressing technique is presented to develop high-purity, wafer-scale, pinhole-free perovskite wafers with a reflective surface. This method can be extended to a variety of perovskite wafers, including organic-inorganic, 2D, and lead-free perovskites. Besides, the size of the wafer with diameters of 10, 15, and 20 mm can be tailored by changing the mold. Furthermore, the mechanism of spontaneous cooling for improving the quality of perovskite wafers is revealed. Finally, the high-quality lead-free Cs3Cu2I5 perovskite wafers demonstrate excellent X-ray detection performances with a high sensitivity of 3433.6 µC Gyair -1 cm-2 and a low detection limit of 33.17 nGyair s-1. Moreover, the Cs3Cu2I5 wafers exhibit outstanding environmental and operational stability even without encapsulation. These research presents a spontaneous cooling strategy to achieve wafer-scale, high-quality perovskites with mirror-like surfaces for X-ray detection, paving the way for integrating perovskites into electronic and optoelectronic devices and promoting the practical application of perovskite X-ray detectors.

Effect of Cr3+ doping concentration on the microstructure, mechanical properties and optical properties of Cr3+: SrF2 transparent ceramics

Cr3+: SrF2 nanopowders were synthesized using a chemical co-precipitation method. The nanoparticles exhibited a structure consistent with the pure SrF2 phase. Cr3+: SrF2 transparent ceramics were fabricated by hot-pressed (HP) sintering technique. The transmittance of 1 at% Cr3+: SrF2 transparent ceramics reached up to 83 % at 1054 nm, which is superior to other SrF2 transparent ceramics with different Cr3+ doping concentration. Furthermore, the mechanical properties of Cr3+: SrF2 transparent ceramics improved with increasing Cr3+ doping levels. The 1 at% Cr3+: SrF2 transparent ceramics exhibited the best mechanical properties, with a microhardness of 2.573 GPa, fracture toughness of 0.70 MPa·m1/2, and compressive strength of 38.1 MPa. The luminescence spectra and fluorescence lifetimes of the SrF2 transparent ceramics as a function of Cr3+ doping concentration were also analyzed and discussed.

Static and dynamic mechanical properties of aluminum nitride-silicon carbide whisker composites

AlN composites reinforced with SiC whiskers and Y2O3 sintering aids were fabricated using the hot-pressing technique to investigate static and dynamic mechanical properties. Microstructure analysis revealed that increasing SiC whisker content yielded grain refinement and decreasing relative density. The Vickers hardness increased from 10.29 to 14.47 GPa, while the fracture toughness improved from 3.03 to 4.39 MPa·m1/2 with 30 wt% SiC whiskers. A numerical approach for evaluating the dynamic modulus and loss factor is presented utilizing the wave propagation characteristics. The dynamic properties showed decreasing dynamic modulus and increasing loss factor with higher SiC content, attributed to increased porosity and interphase boundaries. Thermal conductivity, however, decreased from 139.53 to 49.95 W/m·K as SiC whisker content increased, primarily due to enhanced phonon scattering at grain and interphase boundaries. These findings suggest that AlN-SiCw composites are promising candidates for heat dissipation ceramic substrates, which offer superior mechanical strength and reliable thermal management.

A comparative study of microstructure and mechanical properties for carbon fibers and carbon nanotubes reinforced copper composites doped by Zr70Cu30 particles

Carbon fibers (CFs) and carbon nanotubes (CNTs) reinforced Cu composites doped by Zr70Cu30 alloy particles were fabricated by a conventional vacuum hot-press technique and their microstructures, mechanical properties and electrical conductivities were compared. The results revealed that the CNTs/Cu composite exhibited a superior combination between mechanical properties and electrical conductivity, having the highest relative density of 94.8 %, the maximum microhardness of 85.7 HV and the maximum electrical conductivity of 84.2 % IACS among various composites. The incorporation of Zr70Cu30 alloy particles led to limited contacts with CFs (or CNTs) reinforcements but caused the decrease of relative density and consequently the deleterious mechanical and electrical properties. The dominant strengthening mechanism for the fabricated Cu matrix composites was load transfer mechanism. The CNTs reinforcements demonstrated the highest reinforcement efficiency in the Cu matrix composites, which can provide some new insights for designing novel high-strength and high-connectivity Cu matrix composites.

EVALUATION OF PROPERTIES OF WOOD PLASTIC COMPOSITES MADE FROM SEVEN TYPES OF LIGNOCELLULOSIC FIBERS

This article aims to investigate the characteristics of wood plastic composites (WPC) prepared from polyethylene (PE) reinforced with lignocellulosic fibers derived from the xylem and bark of Masson pine, fir, cypress, as well as from Moso bamboo. The surface polarity and elemental composition of fibers were determined through contact angle measurements and X-ray photoelectron spectroscopy (XPS). The lignocellulosic fiber/PE composites were manufactured through hot-pressing technique, and their water absorption, mechanical properties, and mildew resistance were evaluated. The results revealed that the surface free energy of xylem fibers was higher than that of bark fibers among the three conifer species. XPS analysis showed that the O/C ratio of bark was consistently lower than that of xylem fiber. Among the three conifers, the Masson pine bark had the lowest O/C ratio (22.25%), while its xylem fibers had the highest ratio of 41.64%. WPC made with bark fibers had better water resistance. Additionally, the composites reinforced with xylem fibers showed superior static bending strength, impact strength, and mildew-resistant properties as compared to the composites reinforced with bark fibers. WPC made from bamboo fibers exhibited the best water resistance, with a water absorption rate and thickness swelling rate of 1.83% and 1.42%, respectively. They also had the highest static bending strength, elastic modulus, and impact strength, at 41.31 MPa, 3.82 GPa, and 10.24 kJ/m2, respectively. The WPC made from fir xylem fibers showed the most effective mildew resistance, with the smallest damage (0.50).

Production of Thermoplastic Starch-Aloe Vera Gel Film Embedded with Polyethylene for Improved Tensile Strength and Water Absorption

The water absorption characteristics of thermoplastic starch (TPS) reveal its ability to interact with and absorb water, influencing its overall performance in various applications. The introduction of aloe vera (AV) gel into the TPS polymeric matrix film has proven beneficial in enhancing tensile strength but a notable deficiency is observed in lowering water absorption percentage. Therefore, this paper aims to reduce the water absorption of the TPS30AV polymer matrix film by utilizing polyethylene (PE) without reducing the tensile strength performance of the TPS30AV film. The TPS30AV film was produced using melt-blending and hot-press techniques. Six samples were presented consisting of a control film (TPS30AV) and TPS30AV film with different concentrations of PE resins (5%, 10%, 20%, 30%, and 40%). The film's performance was assessed by examining its mechanical properties, water absorption, and water solubility. The finding shows that TPS30AV with 40% PE has the highest improvement in water absorption percentage which reduces from 309.86% to 34.16% but a tremendous decrement in tensile strength performance. However, TPS30AV with 10% PE has the highest tensile strength, 9.65 MPa with a 20.99% improvement in water absorption reduction. The properties obtained for TPS30AV10PE were also good inYoung's modulus and water solubility percentage. It shows that the film formulated is comparable with previous studies, and improvement has been achieved. As a conclusion, adding PE improved the polymeric structure of TPS30AV and can be used as a biodegradable food-packaging film.

Fine-grained BCZT piezoelectric ceramics by combining high-energy mechanochemical synthesis and hot-press sintering

Different stoichiometries of lead-free BaZr0.2Ti0.8O3–Ba0.7Ca0.3TiO3 (BCZT) prepared by mechanosynthesis and sintered by either conventional sintering (CS) or hot pressing (HP) techniques were studied to establish the dependence of piezoelectric and dielectric properties on sintering parameters and microstructure. All synthesized stoichiometries showed a pseudocubic perovskite phase with homogeneously distributed A- and B-cations in the structure. The BCZT retained the pseudocubic symmetry after sintering and an average grain size <1.8 µm was obtained in all cases. HP sintering hindered the secondary phase segregation observed in the CS ceramics and increased the relative density. Piezoelectric coefficients (d33) ranging from 5.1 to 21 pC/N and from 10.0 to 88.0 pC/N were obtained for CS and HP ceramics, respectively, despite the pseudocubic symmetry and the fine grain size. The higher d33 values for the HP ceramics are a consequence of the higher density, better chemical homogeneity and lower sintering temperature and time required for the mechanosynthesized BCZT powders with high sintering activity.

An investigation of the thermal performance of functionally graded annular fins on a horizontal cylinder under natural convection

ABSTRACT In industrial applications, annular fins are commonly made of homogeneous materials such as aluminum, struggling to provide uniform temperature distribution along their length. Recognizing the potential of Functionally Graded Materials (FGMs) to enhance thermal performance by combining two different materials with a gradual variation, this study proposes their use as fin materials to achieve optimum performance. The study consists of three major components: (1) numerical analyses to determine the optimum volume composition of FG fins, (2) the fabrication process of aluminum and FG fins utilizing powder metallurgy and the hot-pressing technique, and (3) experiments to evaluate the thermal performance of FG and aluminum fin arrays attached to a horizontal cylinder of 250 mm length under natural convection. Heat ranging from 25 W to 150 W is applied to the cylinder during these experiments. Based on the experiments, the thermal performances of fins are evaluated in terms of net free convection heat transfer rate, the Nusselt number, and fin effectiveness. Overall, experimental results demonstrate that the net convection heat transfer rate depends on fin spacing, material, and the base-to-ambient temperature difference. Specifically, FG fin arrays enhance the net heat transfer rate by 59%, while aluminum fin arrays increase it by 33% compared to finless cylinders. Moreover, FG fins outperform aluminum fin arrays by 40% in convective heat transfer coefficient h. Due to being the first experimental study, this study sets itself apart.

Optimizing structural anisotropy and thermal properties of hexagonal boron nitride ceramics through bimodal particle size distribution

Hexagonal boron nitride (h-BN) ceramics exhibit exceptional thermal conductivity, yet integrating their anisotropic thermal properties into bulk ceramics remains challenging. This study investigates the impact of bimodal particle size distribution on the structure, thermal and mechanical properties of h-BN ceramics. Through DEM simulations and hot-pressing techniques, we demonstrate that incorporating large particles into fine ones significantly enhances the packing density, structural anisotropy and thermal properties of h-BN ceramics. The resulting high-purity h-BN ceramic prepared with 10 vol% large particles (10LBN) exhibits an Index of Orientation Preference (IOP) of −2780.57, surpassing that of ceramics without large particles (0LBN) at −1168.61. By regulating the structure, 10LBN h-BN ceramic show a notable increase of the in-plane thermal conductivity from 81.78 for 0LBN ceramics to 153.20 W/(m·K), along with a flexural strength of 58.21 MPa. Additionally, structural characterization and performance testing show that, compared to adding sintering additives, incorporating large plate-like h-BN particles offers greater benefits in optimizing the orientation structure and thermal conductivity of h-BN ceramics. These findings offer new insights for powder compaction using dual-sized plate-like particles and into the sintering of h-BN ceramics with tailored structural and thermal properties.

Suppression of the sausaging effect in (Ba,Na)Fe2As2 round wires by using Ag1−zSnz/Cu double sheath

We report the fabrication of (Ba,Na)Fe2As2 round wires that are processed using the hot isostatic pressing (HIP) technique. We employed double sheaths composed of Cu and Ag1−zSnz alloy because they offer superior mechanical strength compared to pure Ag. The cross-sectional area of the wire core was measured using X-ray computed tomography. The findings of this study demonstrate that utilizing Ag1−zSnz alloy as the inner sheath material helps reduce the degree of the sausaging effect in the wire, resulting in a more uniform cross-sectional area of the wire core. However, transport critical current density (Jc) of the wires with the Ag1−zSnz alloy decreased gradually as the Sn content, z, increased, which may be attributed to the nonoptimized sintering temperatures during the HIP process. These results suggest that when heat-treated at an appropriate temperature during the HIP process, the use of Ag1−zSnz alloy holds great potential for use in high-performance applications.

Influences of binder phase and post-HIP treatment on tribological behavior of WC-based composite

In this study, WC-12Co and WC-12CoCrMo cemented carbides were prepared by the hot press sintering technique and subsequently post-treated by applying the hot isostatic pressing (HIP) technique. The effects of the binder phase and post-HIP treatment on the microstructures and mechanical and tribological properties of the two cemented carbides were investigated for ambient temperature use. The hardness and wear resistance of WC-12CoCrMo were increased by 87 % and two orders of magnitude compared to WC-12Co, respectively. The post-HIP did not affect the wear mechanism of cemented carbide. The binder phase was the fundamental factor in changing the wear mechanism. Post-HIP is a more viable option to enhance mechanical properties for complex carbide systems, as it promotes solid-state chemical reactions and results in an increased precipitation of secondary phases.

Comprehensive analysis of the effects of the traditional stir-fry process on the dynamic changes of volatile metabolites in Hainan camellia oil

The traditional stir-fry process before pressing is crucial to manufacture Hainan camellia oil. To assess the effects of the stir-fry process on Hainan camellia oil, six samples across different stir-fry stages were analyzed. The stir-fry process modified odors, volatile metabolite profiles, and human health-promoting functions of Hainan camellia oil. Totally, 350 volatile metabolites were detected, and heterocyclic compounds were revealed as the main contributors of strong aroma. Potential indicators for monitoring the stir-fry degree were established. Eight key aroma volatile metabolites were identified, including three new ones (1-octen-3-one, 2,3-butanedione, and vanillin). Lipids degradation and the Millard reaction are probably the main pathways for aroma generation. Over-stir-fry treatment diminished the contents of some important volatile metabolites but increased the risk of arising burnt odor. Our work offered insights into the effects of the stir-fry process and over-stir-fry treatment on Hainan camellia oil, which is meaningful for improving the hot-pressing technique.

AC conductivity, dielectric and thermal properties of hybrid composite: bagasse cellulose carbon nanofibers composite

AbstractThis study investigates the impact of incorporating carbon nanofibers (CNFs) into sugar cane cellulose at a high weight ratio (6 wt.%). Composite samples were prepared using a hot hydraulic press technique, and their thermal stability was analyzed through thermal gravitational analysis in a nitrogen environment. The results indicate that the cellulose-CNF composite exhibits a simplified single-stage decomposition compared to the more complex behavior observed in pure cellulose. FTIR analysis reveals the presence of –OH bonds, indicating enhanced hydrophilic properties in the composite. Dielectric spectroscopy, conducted over a frequency range of 100 Hz to 1 MHz, explores the effects of CNFs on the relaxation and conduction mechanisms at different temperatures. Parameters such as dielectric permittivity, AC conductivity, electrical modulus, and complex impedance were studied, incorporating Jonscher’s equation, and the Havriliak–Negami model. The interplay between interfacial charge and cellulose crystallinity emerged as a crucial factor in the observed dielectric behavior. Overall, this research provides insights into the thermal and dielectric properties of cellulose/CNF composites, offering potential applications in diverse fields.

Green composites for sustainable food packaging: Exploring the influence of lignin-TiO2 nanoparticles on poly(butylene adipate-co-terephthalate)

Titanium dioxide (TiO2) is a common pigment used in food packaging to provide a transparent appearance to plastic packaging materials. In the present study, poly(butylene adipate-co-terephthalate) (PBAT) incorporated with lignin-TiO2 nanoparticles (L-TiO2) eco-friendly composite films was prepared by employing an inexpensive melting and hot-pressing technique. The P-L-TiO2 composite films have been studied using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), Thermogravimetric analysis (TGA), and Differential scanning calorimetry (DSC) analysis. The FTIR results and homogeneous, dense SEM images confirm the interaction of L-TiO2 with the PBAT matrix. It has also been found that the addition of L-TiO2 nanoparticles can increase the crystallinity, tensile strength, and thermal stability of PBAT. The addition of L-TiO2 increased the tensile strength and decreased the elongation at break of films. The maximum tensile strength of the film, achieved with 5 wt% L-TiO2, was 47.0 MPa, compared with 24.3 MPa for pure PBAT film. The composite film with 5 wt% L-TiO2 has outstanding oxygen and water vapor barrier properties. As the content of lignin-TiO2 increases, the antimicrobial activity of the composite films also increases; the percentage of growth of all the tested bacteria Staphylococcus aureus (S. aureus), and Escherichia coli (E. coli) is significantly reduced. Strawberries were packed to evaluate the suitability of produced composite films as packaging materials, as they effectively preserved pigments from accumulation and extended the shelf-life as compared to commercial polyethylene packaging film.

Investigation on the mechanical properties of wood-plastic composites for the application of ceiling panels

Wood-plastic composites are relatively novel composite materials that consist of a blend of wood flour waste with high-density polyethylene and polypropylene plastic waste, designed for use in ceiling applications. Various samples were produced using different ratios from the total weight, including 20:80, 30:70, and 40:60, with sieve sizes of 0.425 mm, 1.18 mm, and 2 mm. The composites were created by melting plastics and sawdust at a temperature of 1800c utilizing the hot-press moldings technique employing diverse formulations. The properties of sample composites were analyzed experimentally based on ASTM standards to investigate water absorption levels as well as flexural strength, impact resistance hardness along with surface morphology via the design of experiments. This research study indicates that nine composite formulations consisting of HDPE and PP plastics combined with wood flour can produce favorable physio-mechanical properties. Among these various combination specimens tested in this study FS3/FC30N exhibited excellent physio-mechanical properties; including desirable values such as water absorption level at 5.5103%, flexural strength at 61.12 Mpa, impact resistance measuring 33.45 J cm−2, and hardness rating up to 80 RHB. Thus it is highly recommended for use in chipboard ceiling panel applications due to its potential benefits.

Formation mechanism of TiC twin during densification of SiCf/Ti2AlNb composites

SiCf/Ti2AlNb composites were fabricated using the magnetron sputtering precursor wires method in conjunction with the hot isostatic pressing (HIP) technique. The morphology, elemental distribution, and structural characteristics of the interfacial reaction layer (RL) were examined through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and wavelength dispersive spectroscopy (WDS). The results showed that the interface between SiC fibers and Ti2AlNb reacted to form TiC and α2. Due to the interdiffusion of elements at the interface, a small amount of Al atoms existed in the TiC layer. These Al atoms reduced the stacking fault energy (SFE) of TiC, which is beneficial for the formation and stability of Σ3{111} twin boundaries.

Thermal Conductivity of AlSi12/Al2O3-Graded Composites Consolidated by Hot Pressing and Spark Plasma Sintering: Experimental Evaluation and Numerical Modeling

Functionally graded metal matrix composites have attracted the attention of various industries as materials with tailorable properties due to spatially varying composition of constituents. This research work was inspired by an application, such as automotive brake disks, which requires advanced materials with improved wear resistance on the outer surface as combined with effective heat flux dissipation of the graded system. To this end, graded AlSi12/Al2O3 composites (FGMs) with a stepwise gradient in the volume fraction of alumina reinforcement were produced by hot pressing and spark plasma sintering techniques. The thermal conductivities of the individual composite layers and the FGMs were evaluated experimentally and simulated numerically using 3D finite element (FE) models based on micro-computed X-ray tomography (micro-XCT) images of actual AlSi12/Al2O3 microstructures. The numerical models incorporated the effects of porosity of the fabricated AlSi12/Al2O3 composites, thermal resistance, and imperfect interfaces between the AlSi12 matrix and the alumina particles. The obtained experimental data and the results of the numerical models are in good agreement, the relative error being in the range of 4 to 6 pct for different compositions and FGM structure. The predictive capability of the proposed micro-XCT-based FE model suggests that this model can be applied to similar types of composites and different composition gradients.

Unraveling Lattice-Distortion Hardening Mechanisms in High-Entropy Carbides.

Uncovering the hardening mechanisms is of great importance to accelerate the design of superhard high-entropy carbides (HECs). Herein, the hardening mechanisms of HECs by a combination of experiments and first-principles calculations are systematically explored. The equiatomic single-phase 4- to 8-cation HECs (4-8HECs) are successfully fabricated by the two-step approach involving ultrafast high-temperature synthesis and hot-press sintering techniques. The as-fabricated 4-8HEC samples possess fully dense microstructures (relative densities of up to ≈99%), similar grain sizes, clean grain boundaries, and uniform compositions. With the elimination of these morphological properties, the monotonic enhancement of Vickers hardness and nanohardness of the as-fabricated 4-8HEC samples is found to be driven by the aggravation of lattice distortion. Further studies show no evident association between the enhanced hardness of the as-fabricated 4-8HEC samples and other potential indicators, including bond strength, valence electron concentration, electronegativity mismatch, and metallic states. The work unveils the underlying hardening mechanisms of HECs and offers an effective strategy for designing superhard HECs.

Preparation and Performance Study of SiC-Reinforced Fe-Based Wear-Resistant Composite Grinding Media.

During industrial and laboratory processes involving material grinding, the grinding media endure prolonged high-collision and friction environments, resulting in substantial wear. Consequently, this study adopts the hot-pressing sintering technique in powder metallurgy to prepare SiC-reinforced Fe-based wear-resistant composite grinding media, aiming to increase wear performance. For this purpose, Fe with 10 wt% SiC powders were milled for the fabrication of the composite. Then, sintering was performed by hot press at 1100 °C in a furnace. Scanning electron microscopy (SEM) and X-ray diffraction were employed to investigate the microstructures and phase of SiC-reinforced Fe-based matrix composite. Subsequently, comparative performance evaluations of the newly developed grinding media and traditional chromium-based media were conducted in terms of wear rate and grinding efficiency. The wear resistance tests revealed that the SiC-reinforced composite media displayed significantly superior wear resistance across various abrasives compared to the chromium-containing alternatives. Specifically, the composite media achieved a wear rate reduction of 2.9 times against standard sand over 1 h, and 2.3 and 2.4 times against sandstone and iron slag, respectively. Moreover, extended grinding for 3 hours further enhanced these reductions to 3.1, 2.4, and 2.7 times, respectively. Additionally, efficiency assessments indicated that at a 1:1 material ratio, the composite media outperformed the chromium-containing media in grinding efficiency by 7.5%, 12.5%, and 10.3% for standard sand, sandstone, and iron slag, respectively. Further increasing the material ratio to 3:1 resulted in efficiency improvements of 7.4%, 17.5%, and 11.3%, correspondingly.