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Silicone elastomers filled with rare earth oxides
摘要： Silicones which possess, amongst others, remarkable mechanical properties, thermal stability over a wide range of temperatures and processability, and rare earth oxides (REO), known for their unique optic, magnetic and catalytic properties can be coupled into multifunctional composite materials (S-REOs). In addition, the intrinsic hydrophobicity of REO and polysiloxanes makes them easily compatible without the need for surface treatments of the former. Thus, europium oxide (Eu2O3), gadolinium oxide (Gd2O3) and dysprosium oxide (Dy2O3) in amounts of 20 pph are incorporated as ?llers into silicone matrices, followed by processing mixture as thin ?lms and crosslinking at room temperature. The analysis of the obtained ?lms reveals the changes induced by these ?llers in the thermal, mechanical, dielectric and optical properties, as well as the hydrophobicity of the silicones. The luminescence properties of S-REO composites were investigated by ?uorescence spectra and lifetime - resolved measurements with a multiemission peaks from blue to greenish register. The thermogravimetrical analysis indicates an increasing of thermal stability of the composites that contain REO, compared to pure silicone. As expected, the dielectric permittivity signi?cantly increased due to nature of the ?llers, while the dielectric loss values are relatively low for all samples, indicating a minimal conversion of electrical energy in the form of heat within bulk composites. The presence of rare earth oxides into the silicone matrix facilitates the motions of long-range charge carriers through the network resulting in higher values of conductivity of the composite ?lms. The stress-strain measurements revealed the reinforcing effect of the rare earth metal oxides on a silicone matrix, leading to a signi?cant increase of Young modulus. The known hydrophobicity of silicones is further enhanced by the presence of REO.
关键词： silicone,rare earth oxides,active ?llers,hydrophobicity,composites
更新于2025-09-19 17:13:59
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Optical properties of hydrothermally synthesised and thermally annealed ZnO/ZnO <sub/>2</sub> composites
摘要： ZnO/ZnO2 composites grown by hydrothermal synthesis at low temperature (180 °C) and thermally annealed at 300 °C were fully analysed by morphological, structural and optical techniques. X-ray diffraction patterns (XRD) and Raman spectroscopy clearly evidences the presence of both crystalline phases in the ZnO/ZnO2 sample. The differential scanning calorimetry analysis and thermogravimetric profiles indicate an exothermic event with a peak temperature ca. 225 °C, which is accompanied by a 8.5 % weight loss, being attributed to the crystallization of ZnO from ZnO2. Upon a thermal annealing treatment at 300 °C in the ZnO2 phase was completely converted into ZnO as measured by XRD and Raman spectroscopy. Photoluminescence investigations reveal that the emission is dominated by a broad band recombination in both samples, which are due to the overlapping of different emitting centres, and that the peak position of the PL emission is dependent on the excitation density. The ZnO/ZnO2 sample exhibits a widening of the bandgap when compared to the one only containing ZnO, likely related with the presence of the additional ZnO2 phase and suggesting a bandgap energy of 3.42 eV for this compound. Surface analysis revealed that sample exhibits a surface area of 90 m2/g, which decreases to 30 m2/g after the thermal annealing and the full conversion into ZnO. This difference in the surface area showed a particular relevance in the stability of the measured optical properties. Particularly, the intensity of the photoluminescence signal was seen to be higher in the ZnO/ZnO2 sample and strongly dependent on the measurement atmosphere, highlighting their potential to be employed in the fabrication of optical-based sensing systems for environmental applications, namely in gas sensors.
关键词： photoluminescence,gas sensors,ZnO/ZnO2 composites,hydrothermal synthesis,optical properties
更新于2025-09-19 17:13:59
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Evaluating the interfacial properties of wrinkled graphene fiber through single-fiber fragmentation tests
摘要： Graphene ?ber has attracted much attention due to its potential applications in supercapacitors, dye-sensitized solar cells, actuators, motors, stretchable circuits and functional composites, owing to its high electrical conductivity, tensile strength and good ?exibility. The high tensile strength of graphene ?ber renders it promising candidate as the reinforcement in the composites. The interface is the key element for the ?ber-reinforced composites; however, there is no study about the interfacial evaluation about the graphene ?ber reinforcement composites. Herein, in this study, we fabricate the high-strength graphene ?bers (up to 890.1 MPa) through the wet spinning and thermal annealing method, make the graphene ?ber-reinforced single-?ber composite, and develop a novel and facile fragmentation test to quantitatively evaluate the interfacial performance of graphene ?ber. Graphene ?ber has the interfacial shear stress (IFSS) of 60.6 MPa, exhibiting one of the highest IFSS among the carbon nanotube yarns and commercial carbon ?bers composites. The superior interfacial performance of graphene ?ber is attributed to the surface wrinkles and grooves, which establishes strong physical interlocking between graphene ?ber and resin, favoring for the stress transfer. This work will pave the way for the development of graphene ?ber-reinforced composites.
关键词： Wet spinning,Thermal annealing,Graphene ?ber,Composites,Interfacial properties,Fragmentation test
更新于2025-09-19 17:13:59
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Ablation behavior of SiCp/AA2024 composites irradiated by a single-pulse nanosecond laser
摘要： In this study, homogenous Al alloy and SiC materials and SiCp/AA2024 composites with mean particle diameters of 5 μm and 30 μm were irradiated by a single-pulse nanosecond fiber laser with a 200 ns pulse width and 1064 nm wavelength. Using a laser pulse, regular circular heat-affected zones (HAZ) were formed in the homogenous materials. For the composites, an Al allloy matrix was melted and sputtered, and the SiC particles bulged when irradiated by the laser pulse. According to the measured results, the HAZ increased with the pulse energy density in a logarithmic pattern. Nonlinear fitting results demonstrated that the damage thresholds of the composites and SiC homogenous materials were the lowest and highest, respectively. SiCp/AA2024 composites with different mean particle diameters exhibited similar damage thresholds. The measured etching depths of the SiC particles and Al alloy matrix were smaller than the respective values of the homogenous materials. Thermal simulation results revealed that thermal-mechanical coupling occurred between the SiC particles and Al alloy matrix. The SiC particles in the composite heated more rapidly under a nanosecond laser, and the heat was then transferred to the matrix. Large SiC particles constrained the matrix’s molten pool, which accelerated its gasification but hindered further etching.
关键词： Composites materials,Phase transitions,Ablation mechanism,Nanosecond laser irradiating,Interface effect
更新于2025-09-19 17:13:59
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Effects of initial density during laser machining assisted CVI process and its influence on strength of C/SiC composites
摘要： Novel laser-assisted chemical vapor infiltration (LA-CVI) technique has been used to improve the density and strength of carbon fiber reinforced SiC composites (C/SiC). Initial density of C/SiC before laser machining played an important role in determining the final density and strength of composites. Results show that final density and bending strength of lower initial density composites were better than that of higher initial density samples after LA-CVI process, while the porosity exhibited opposite behavior. Micro-CT and COMSEL simulation results verify that after LA-CVI process, dense band width of C/SiC with initial density of 1.5 g/cm3 was twice as that of C/SiC with initial density of 1.8 g/cm3. This led to crack propagation bypassing the micro-hole. In conclusion, low initial density when laser machining was carried out resulted in better properties of final composites.
关键词： Bending strength,LA-CVI,C/SiC composites,Micro-structure
更新于2025-09-19 17:13:59
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Preparation and Characterization of UV-LED Curable Acrylic Films Containing Biochar and/or Multiwalled Carbon Nanotubes: Effect of the Filler Loading on the Rheological, Thermal and Optical Properties
摘要： UV-LED curable coatings represent an up-to-date attractive field due to the high curing efficiency even in the presence of high filler loadings, as well as to the absence of infrared wavelengths that may negatively impact on heat-sensitive substrates. The addition of carbonaceous materials, such as biochar (BC) and/or multiwalled carbon nanotubes (MWCNTs) could positively improve both the rheological and thermal properties. In this study we report on the synthesis and characterization of carbon-reinforced films containing nanometric (MWCNTs) and micrometric (BC) carbon-based materials. We analyze the rheological properties of the UV-LED curable dispersions, as well as the thermal and optical properties of the resulting films, establishing some correlations between filler dispersion/loading with the main observed properties.
关键词： composites,epoxy-acrylate resin,biochar,multiwalled carbon nanotubes,UV-LED curing
更新于2025-09-19 17:13:59
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Transparent Cellulose Nanofibrils Composites with Two-layer Delignified Rotary-cutting Poplar Veneers (0?°-layer and 90?°-layer) for Light Acquisition of Solar Cell
摘要： Our transparent cellulose nanofibrils composites (TCNC) directly from rotary-cutting poplar veneer (RPV) whose lignin can be easily stripped by our treatment. This TCNC is prepared by stripping lignin of original RPV and infiltrating epoxy resin (ER) into delignified RPV. This TCNC with two-layer delignified RPVs whose grains perpendicular (0/90°) to each other, which were solidified on solar cell while infiltrating ER. This TCNC with high transmittance (~90%), high haze (~90%), and equal refractive index fluctuation. Comparing with epoxy resin (ER), this TCNC can enhance open circuit voltage (VOC) from 1.16 to ~1.36 and short circuit density (JSC) from 30 to ~34 for the solar cell, and can enhance test fore from 0.155 kN to ~0.185 kN and displacement from 43.6 mm to ~52.5 mm.
关键词： light acquisition,rotary-cutting poplar veneer,delignification,epoxy resin,solar cell,transparent cellulose nanofibrils composites
更新于2025-09-19 17:13:59
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Ultrahigh Resolution Pulsed Laser-Induced Photoacoustic Detection of Multi-Scale Damage in CFRP Composites
摘要： This paper presents a photoacoustic non-destructive evaluation (pNDE) system with an ultrahigh resolution for the detection of multi-scale damage in carbon fiber-reinforced plastic (CFRP) composites. The pNDE system consists of three main components: a picosecond pulsed laser-based ultrasonic actuator, an ultrasound receiver, and a data acquisition/computing subsystem. During the operation, high-frequency ultrasound is generated by pulsed laser and recorded by an ultrasound receiver. By implementing a two-dimensional back projection algorithm, pNDE images can be reconstructed from the recorded ultrasound signals to represent the embedded damage. Both potential macroscopic and microscopic damages, such as surface notches and delamination in CFRP, can be identified by examining the reconstructed pNDE images. Three ultrasonic presentation modes including A-scan, B-scan, and C-scan are employed to analyze the recorded signals for the representation of the detected micro-scale damage in two-dimensional and three-dimensional images with a high spatial resolution of up to 60 μm. Macro-scale delamination and transverse ply cracks are clearly visualized, identifying the edges of the damaged area. The results of the study demonstrate that the developed pNDE system provides a non-destructive and robust approach for multi-scale damage detection in composite materials.
关键词： composites,non-destructive testing,photoacoustic,multi-scale,ultrasonic representation,embedded damage
更新于2025-09-19 17:13:59
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Direct effects of UV irradiation on graphene-based nanocomposite films revealed by electrical resistance tomography
摘要： The integration of surface sensing elements providing an in situ monitoring of the UV-induced degradation effects in composite materials and structures is crucial for their applications in hostile environments characterized by high levels of radiation, such as space. In this work, the electrical response of a novel UV-sensitive nanocomposite film was investigated using electrical resistance tomography (ERT). The conductivity changes measured at the irradiated surfaces were compared with results from morphology analysis by scanning electron microscopy (SEM) and surface analytical techniques, such as Raman microscopy. Highly conductive and UV-sensitive nanocomposite coatings were prepared by embedding the graphene and deoxyribonucleic acid (DNA) component in a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) matrix. The coatings were deposited onto carbon-reinforced laminated structures fabricated by resin transfer molding process using an aerospace-grade epoxy resin. Two different irradiation conditions were tested by exposing the nanocomposite surfaces to UV-C irradiances of 2.6 and 4.0 mW/cm2. Results show that the ERT technique has great potential for the in situ health monitoring of carbon-based materials and structures for aerospace applications, which are subject to degradation by UV-C radiation: it allows mapping of the conductivity changes occurring at the surface of the graphene/DNA/PEDOT:PSS coatings during irradiation.
关键词： Electrical resistance tomography,B. Electrical properties,A. Functional composites,A. Nano composites
更新于2025-09-16 10:30:52
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High ammonia sensitive ability of novel Cu12Sb4S13 quantum dots@reduced graphene oxide nanosheet composites at room temperature
摘要： In the work, rGO nanosheet is synthesized using the typical Hummer’s method, then Cu12Sb4S13 quantum dots@rGO composites are prepared by solvent thermal method, and Cu12Sb4S13 quantum dots with the average size of 5 nm are densely distributed on the surface of rGO sheet. NH3 gas response of Cu12Sb4S13 quantum dots@rGO nanosheet composites at room temperature of 25 oC is enhanced compared with the pure Cu12Sb4S13 quantum dots and rGO nanosheet, and the composites possess an excellent stability during the humidity range of 45%-80% with a low detection limit of 1 ppm, which is related with the intrinsic hydrophobicity characteristic of Cu12Sb4S13 quantum dots. It also proves that Cu12Sb4S13 quantum dots@rGO nanosheet composites have a quite high selectivity towards ammonia compared with ethanol, methanol, acetone and toluene at room temperature. The gas sensing mechanism of the composites is discussed primarily
关键词： Gas response,Room temperature,Cu12Sb4S13 quantum dots@rGO nanosheet composites,NH3
更新于2025-09-16 10:30:52