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Preparation, composition, and mechanical properties of CVD polycrystalline ZnS
摘要： Polycrystalline ZnS samples with a slight composition fluctuation are grown by chemical vapor deposition (CVD) method, and their optical and mechanical properties and microstructure were investigated in detail. The CVD samples present a maximum transmittance of ~73 % in the 7-10 μm region. By changing the sulfur content, a maximum Knoop hardness of 2.375 GPa was found in the Zn50.06S49.94 sample, while Zn46.84S53.16 presents a high flexural strength of 133.8 MPa. The microstructural origin of this abnormal changing of mechanical properties was discussed according to the results of micrographs, XRD patterns and Raman spectra. The results suggest that beside the main phase of zincblende, a small amount of wurtzite is existed. This composited microstructure is responsible for the higher hardness and strength of CVD ZnS.
关键词： CVD,mechanical properties,ZnS,Raman spectra,microstructure
更新于2025-09-09 09:28:46
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Mechanical, Electronic and Optical Properties of Two Phases of NbB4: First-Principles Calculations
摘要： As transition metal borides have been successfully synthesised, the study of the combination of transition metal and boron is another effective way to investigate the properties of boride. We have predicted the novel phase Amm2-NbB4. Using the Cambridge Serial Total Energy Package (CASTEP) code, we further researched on the mechanical, electronic and optical properties of C2/c- and Amm2-NbB4. It is found that both the phases of NbB4 are dynamically and mechanically stable at 0 and 100 GPa. Their Vickers hardness values are both 34 GPa, which indicate that they are hard materials. The band gap of C2/c-NbB4 is 0.145 eV, which indicates that it is a semiconductor (or metalloid) at 0 GPa. For the Amm2-NbB4, the band structure without band gap indicates it is a metal at 0 GPa. The optical properties of these two structures are similar. At 0 eV, the real part of dielectric function is 28.8 for C2/c-NbB4, and the real part value for Amm2-NbB4 is 43. We hope our work will provide some help to the experimental work about the technology of the material.
关键词： Mechanical Properties,Optical Properties,First-Principles Calculations,Electronic Properties,NbB4
更新于2025-09-04 15:30:14
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Nonparasitic behavior of embedded triboluminescent sensor in multifunctional composites
摘要： Bio-inspired In situ Triboluminescent Optical Fiber (ITOF) sensors are embedded into the composites for real-time distributed damage monitoring. Real-time damage sensing in large composite structures is imperative to allow for necessary actions before catastrophic failure occurs. This article investigates how embedded ITOF sensors affect the tensile and flexural properties of composite laminates. ITOF sensors with diameters of 275, 570, and 1500 μm, were embedded into the carbon fibers/vinyl ester composite laminates. The ultimate tensile strength and the shear strength of composites with embedded 275 μm reduce by about 0.15% and 1.41%, respectively when embedded in 0° direction. Small-sized sensors have a moderate adverse effect on tensile properties of composite, particularly in the direction perpendicular to the ITOF sensor. Additionally, the ability of the varying ITOF sensors to monitor the low velocity impact damage in composites was assessed. Small-sized sensors demonstrate nonparasitic behavior in multifunctional composites when embedded in 0° direction.
关键词： A. Multifunctional composites,E. Vacuum infusion,B. Mechanical properties,D. Mechanical testing
更新于2025-09-04 15:30:14
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Moisture absorption and hydrothermal aging of phenylethynyl-terminated pyromellitic dianhydride-type asymmetric polyimide and composites
摘要： The effects of moisture on a polymerized monomeric reactant (PMR)-type polyimide (TriA X) and associated composites were investigated. Water uptake tests were performed on the polyimide at various temperatures and relative humidity levels to investigate moisture absorption behavior. Two-stage moisture absorption was observed, in which the first stage was diffusion controlled, whereas the second stage was moisture plasticization controlled. As exposure temperature increased, the equilibrium moisture content of the polyimide decreased, indicating an exothermic absorption process. The Arrhenius temperature dependence and moisture saturation as functions of temperature and humidity in the neat polymer were determined using curve fitting based on the published mathematical models. Long-term hydrothermal aging at 95°C was conducted on the neat polyimide and associated carbon fiber composites. Reversible hydrolytic reactions and a trace of irreversible hydrolysis were observed in the long-term exposure. The tensile ductility of the neat polyimide and the short-beam shear strength of the composites decreased with increasing aging time, while the tensile strength and modulus and thermal properties of the polyimide exhibited little change after 2000-h aging, demonstrating hydrothermal stability. The decrease in the ductility of the neat polymer after long-term moisture exposure was attributed to the network structure change, driven by hydrolysis and moisture plasticization.
关键词： β-relaxation,hydrothermal aging,moisture absorption,thermal properties,hydrolysis,Polyimide,composite,mechanical properties,plasticization
更新于2025-09-04 15:30:14
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Effect of Forestry Management and Veneer Defects Identified by X-ray Analysis on Mechanical Properties of Laminated Veneer Lumber Beams Made of Beech
摘要： Interest in the use of beech as a raw material in engineered wood products for structural purpose has increased in Europe, in particular laminated veneer lumber (LVL). Indeed, this kind of product has exhibited superior mechanical properties with a lower variability compared to solid wood. This study investigated the influence of the forestry management system (e.g., high forest versus coppice) and of the veneer defects (e.g., knots and joints) on the mechanical properties of beech laminated veneer lumber (LVL) beams. The research included the measurement of modulus of elasticity and bending strength of 40 LVL beams (50 x 50 x 1200 mm3). Bending strength and modulus of elasticity of beam made from high forest wood compared to coppice wood were respectively higher by 20% and 12%. The impact of natural and manufacturing-process defects on the bending strength was studied using an X-ray imaging system. Defects in the inner layer of LVL beams were detected via X-ray. The defects produced by the manufacturing process itself had an effect on the bending strength similar to the natural defects of wood.
关键词： LVL,Mechanical properties,Beech,Coppice,X-ray,High forest
更新于2025-09-04 15:30:14
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Full-Field Optical Coherence Tomography as a Diagnosis Tool: Recent Progress with Multimodal Imaging
摘要： Full-?eld optical coherence tomography (FF-OCT) is a variant of OCT that is able to register 2D en face views of scattering samples at a given depth. Thanks to its superior resolution, it can quickly reveal information similar to histology without the need to physically section the sample. Sensitivity and speci?city levels of diagnosis performed with FF-OCT are 80% to 95% of the equivalent histological diagnosis performances and could therefore bene?t from improvement. Therefore, multimodal systems have been designed to increase the diagnostic performance of FF-OCT. In this paper, we will discuss which contrasts can be measured with such multimodal systems in the context of ex vivo biological tissue examination. We will particularly emphasize three multimodal combinations to measure the tissue mechanics, dynamics, and molecular content respectively.
关键词： dynamics,multimodality,cellular metabolism,?uorescence microscopy,biomechanics,mechanical properties,full-?eld optical coherence tomography
更新于2025-09-04 15:30:14
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Conformal Coating of Metallic Shells on Carbon Nanotube Turfs
摘要： A synthesis method to form conformal core-shell foams of metals and alloys on a carbon nanotube (CNT) scaffold by electroplating from a single bath electrolyte is demonstrated in this work. A triple cyclic pulse electrodeposition technique was used to deposit Ni and Cu layers on the CNT scaffold, and electron microscopy was then used to identify conditions amenable to conformal and island growth morphologies. Nanoindentation of the resulting metallic foam structure, using a flat punch/compression geometry, demonstrates that adding conformal metallic shells to the CNT turf to create a metal coated low density foam increases both the hardness and elastic modulus; however, once island growth initiates there is no significant subsequent increase in mechanical properties with increases in deposited metals.
关键词： Nanoindentation,Conformal coating,Electrodeposition,Mechanical properties,Carbon nanotube
更新于2025-09-04 15:30:14
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Novel polyimide nanocomposites enhanced by covalent modified graphene nanosheets based on Friedel–Crafts reaction
摘要： We report a new approach to fabricate novel polyimide (PI) nanocomposites using amine-functionalized graphene nanosheets (AGNS). AGNS was successfully prepared by Friedel–Crafts (F–C) reaction and nitroreduction. The PI nanocomposites with outstanding strength and high tribological performance were obtained though in situ polymerization in the presence of different contents of AGNS. The thermal stability, mechanical performance, and the tribological properties of PI/AGNS nanocomposites were significantly enhanced compared with that of pristine PI and PI/graphene nanosheets (GNS) blends, resulting from the strong covalent bonds between AGNS with PI matrix. Particularly, given that the friction coefficient and wear rate were reduced separately by 20.5% and 90.5% under dry sliding condition, the PI/AGNS nanocomposite with 0.5 wt% AGNS manifested the optative friction performance. The combined exclusive friction resistance and mechanical performance were the paramount factors which illustrate the applications of the resultant PI/AGNS nanocomposites in the wear-resistant field or another high-performance material.
关键词： graphene nanosheets,mechanical properties,polyimide nanocomposites,tribological performance,Friedel–Crafts reaction
更新于2025-09-04 15:30:14
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Studies on growth and characterization of (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate: a nonlinear optical material
摘要： Hydrazone compound (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate (DMABHBH) was synthesized and single crystals of DMABHBH were grown by solvent evaporation method at room temperature. Molecular structure of DMABHBH compound was confirmed by 1H and 13C nuclear magnetic resonance techniques. The presence of functional groups was confirmed by Fourier transform infrared and FT Raman spectral analyses. The X-ray crystal structure was elucidated at 173 K by single crystal X-ray diffraction and the results were compared with the corresponding values obtained at 298 K. The compound crystallizes in the chiral monoclinic space group P21. Mechanical stability of the grown crystals was estimated from the Vicker’s microhardness test. Powder second harmonic generation efficiency of DMABHBH is about 1.1 times that of potassium dihydrogen phosphate. DMABHBH is found to show optical limiting behavior at high input light intensities, the third order nonlinear optical absorption coefficient measured using open aperture Z-scan studies, is 0.95 × 10?11 m/W. Anti-bacterial activity was studied using the well and disc diffusion methods.
关键词： X-ray diffraction,Mechanical properties,Nonlinear optical material,Thermal analysis,Antibacterial activity,Hydrazone,Crystal growth
更新于2025-09-04 15:30:14
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High-Performance PEDOT:PSS/Hexamethylene Diisocyanate-Functionalized Graphene Oxide Nanocomposites: Preparation and Properties
摘要： Graphene oxide (GO) has emerged as an ideal ?ller to reinforce polymeric matrices owing to its large speci?c surface area, transparency, ?exibility, and very high mechanical strength. Nonetheless, functionalization is required to improve its solubility in common solvents and expand its practical uses. In this work, hexamethylene diisocyanate (HDI)-functionalized GO (HDI-GO) has been used as ?ller of a conductive polymer matrix, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The nanocomposites have been prepared via a simple solution casting method, and have been characterized by scanning electron microscopy (SEM), UV–Vis and Raman spectroscopies, X-ray diffraction (XRD), thermogravimetric analysis (TGA), tensile tests, and four-point probe measurements to get information about how the HDI-GO functionalization degree (FD) and the HDI-GO concentration in the nanocomposite in?uence the ?nal properties. SEM analysis showed a very homogenous dispersion of the HDI-GO nanosheets with the highest FD within the matrix, and the Raman spectra revealed the existence of very strong HDI-GO-PEDOT:PSS interactions. A gradual improvement in thermal stability was found with increasing HDI-GO concentration, with only a small loss in transparency. A reduction in the sheet resistance of PEDOT:PSS was found at low HDI-GO contents, whilst increasing moderately at the highest loading tested. The nanocomposites showed a good combination of stiffness, strength, ductility, and toughness. The optimum balance of properties was attained for samples incorporating 2 and 5 wt % HDI-GO with the highest FD. These solution-processed nanocomposites show considerably improved performance compared to conventional PEDOT:PSS nanocomposites ?lled with raw GO, and are highly suitable for applications in various ?elds, including ?exible electronics, thermoelectric devices, and solar energy applications.
关键词： hexamethylene diisocyanate,PEDOT:PSS,functionalization degree,nanocomposite,optical transmittance,sheet resistance,graphene oxide,mechanical properties
更新于2025-09-04 15:30:14