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A lithium aluminium borate composite microwave dielectric ceramic with low permittivity, near-zero shrinkage, and low sintering temperature
摘要： A low temperature co-fired dielectric material with low shrinkage during the sintering process can enhance the circuit design of electronic devices. Lithium aluminium borate composite ceramic with a composition of Li2O:Al2O3:B2O3=1:1:2 (abbreviated: LAB) was prepared by a traditional solid-state reaction method. These ceramics have a low sintering temperature (675–750 °C), low permittivity, and near-zero shrinkage. When the sintering temperature was 725 °C, the LAB ceramics exhibited a small shrinkage of ~2.4% and the best microwave dielectric properties with εr = 3.9, Q × f = 35?500 GHz, and τ? = -64 ppm/°C. The LAB ceramics sintered at 700 °C have near-zero shrinkage of ~ 0.4% and good microwave dielectric properties. The ceramics transformed from (Li2B4O7 and Al2O3) to (Li2Al2B4O10 and Li4Al4B6O17) phases with increasing the sintering temperature, which may be the reason why they show marginal shrinkage. In addition, the ceramics could be co-fired with Ag, indicating that this material is a good candidate for low-temperature co-fired ceramic devices.
关键词： Low temperature co-fired ceramic,Lithium aluminium borate composite,Near-zero shrinkage
更新于2025-09-23 15:23:52
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Effect of indirect restorative material and thickness on light transmission at different wavelengths
摘要： Purpose: The aim of this study was to evaluate the influence of indirect restorative material type and thickness on the transmission of different wavelengths from a broad-banded dental curing light. Methods: Four dental indirect restorative materials for computer-aided design and computer-aided manufacturing (CAD/CAM) were evaluated: [RC] resin/ceramic hybrid material (Lava Ultimate), [FC] feldspathic ceramic (VitaBlocs), and two zirconia-based ceramics ([ZK] Katana; and [ZL] Lava). Total loss of irradiance (TL) was measured for blue (WB, 425–490 nm) and violet (WV, 350–425 nm) wavelengths. Specimens of 15 mm with varying thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were fabricated (n = 5). A plasma-arc dental light-curing unit was used (Arc Light-II). To assess TL as a function of wavelength, a software (Spectra Suite v5.1) connected to a spectroradiometer (USB2000) and an integrating sphere (CTSM-LSM-60-SF) was used. Data was subjected to statistical analysis (two-way ANOVA and post-hoc Tukey test, α = 0.05). Results: A 0.5 mm interposition resulted in TL from 50.5 to 67.2%, depending on material. Increased thickness resulted in higher TL for all materials. FC showed less TL compared to ZK. In general, WV showed higher TL than did WB, and WV/WB proportion decreased with increasing thickness. Conclusions: Indirect materials significantly reduced TL, and this effect is greater with increasing thickness. WV showed lower penetration compared to WB.
关键词： Ceramics,Photopolymerization,Irradiance,Composite,Zirconia
更新于2025-09-23 15:23:52
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An eco-friendly method to enhance optical and electrical properties of conducting polymers by means of carboxymethyl cellulose
摘要： In this work, an eco-friendly method is proposed for the electro-synthesis of conductive polymers with superior optical and electrical properties by means of CMC in aqueous media. For this purpose, an aqueous dispersion of a water-insoluble monomer namely 4-amino-N-[2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl]benzamide (TPB) has been prepared by attaching it to CMC via hydrogen bonds and the conductive composite film (PTPB–CMC) has been obtained by electropolymerization. The TPB monomer has been chosen to interact with the CMC via hydrogen bonds which ensures to obtain dispersion with the CMC and also increase the compatibility of its polymer in the composite structure. As a result of the electrochemical, spectroelectrochemical investigation and surface morphology analyses of the obtained conductive polymer, it has been found that anionic CMC makes improvements in the electrical, optical and mechanical properties of the polymer by making the plasticizing effect and acting as a dopant. Furthermore, in the presence of nanocarbon materials on electrode surface, it has been determined that the polymerization potential reduced and more stable and long-lasting polymeric films which are crucial for technological applications have been obtained.
关键词： Electrochemical polymerization,Composite materials,Conducting polymers,Carboxymethyl cellulose
更新于2025-09-23 15:23:52
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Ultra-broadband metamaterial absorber with graphene composites fabricated by 3D printing
摘要： An ultra-broadband electromagnetic (EM) absorber composed of composite metamaterials was designed, fabricated and characterized. Polylactic-acid/reduced graphene oxide (PLA/RGO) composites with different amounts of RGO were prepared as a primary material collection. To provide good impedance matching and efficient wave attenuation, the multilayer absorbers were designed with a gradient index (GRIN) of characteristic impedance by manipulating the RGO content and the geometric parameters of the unit cell. The absorbers with different numbers of layers were fabricated by a material extrusion process, and then the reflection loss (RL) of the prepared samples was measured. Results showed that the methodology for designing a metamaterial absorber with gradient impedance and fabricating through a 3D printing process was effective in producing ultra-broadband absorbers. The seven-layer absorber achieved an absorption above 90% in a broad bandwidth of 4.5–40 GHz. This work could provide inspiration for upgrading the performance of some conventional absorbing composites through a rational design of the composite proportion and structure.
关键词： Microwave absorption,Multilayer structure,3D printing,Composite materials,Metamaterials
更新于2025-09-23 15:23:52
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Effect of phototherapy on dentin bond strength and microleakage when bonded to resin with different conditioning regimes
摘要： Aim To assess the efficacy of phototherapy on bond strength and microleakage of bulk fill composites in comparison to conventional dentin surface treatments. Materials and Methods Ninety human third molars were divided into 3 groups (n=30 each) according to surface conditioning treatment. Group 1 (Etch and Bond) EB, group 2 was treated with Er,Cr: YSGG (ECL) and group 3 was treated with a diode laser (DL). Based on the type of bulk fill resin composite, samples were divided into six sub-groups. In sub-group 1, 2 and 3 (n=15) build-up was done using ZirconCore (ZC) and these subgroups were named as EB-ZC, ECL-ZC and DL-ZC. In subgroup 4,5,6 (n=15) MulticCore Flow (MC) was used for core build-up and these subgroups were named as EB-MC, ECL-MC, DL-MC. For shear bond strength (SBS) all the samples were exposed to loads using a universal testing machine. Five samples each from all subgroups were immersed in methylene blue dye for 24hours prior to microleakage testing. Data were assessed using analysis of variance and Tukey multiple comparisons test. Results: Among all the groups the lowest bond strength was achieved in DL-ZC [10.45(0.459)]. Similarly, the highest bond strength was attained in EB-MC[17.84(0.925)]. The highest microleakage scores amongst different group was exhibited in DL-ZC [82.45(39.459)] whereas, the lowest microleakage scores were displayed in EB-MC [31.21(15.92)]. Conclusion: Phototherapy in the form of Er,Cr:YSGG laser showed comparable adhesive bond outcomes to conventional etch and bond dentin conditioning techniques. Moreover, Multicore bulk fill material showed better bond strength and microleakage scores than zirconium particle infiltrated bulk fill composite in the presence of dentin phototherapy.
关键词： dentine,bond strength,Cr: YSGG,microleakage,Er,bulk fill composite
更新于2025-09-23 15:23:52
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Improvement of nickel nanocomposite coatings by combining zinc-doped TiO2 nanoparticles
摘要： Pure nickel and compound of nickel coatings (Ni-TiO2 and Ni-Zn/TiO2) were coated on the steel material using Watts bath with the electrodeposition conditions. Effect of the nanoparticle type and current density on the coating structure, surface morphology of the coating, hardness of the coating, and the corrosion properties of the coatings are presented. Phase and elemental analysis of the coatings were carried out by XRD and EDS techniques, respectively. SEM was used to investigate the surface morphology of the coatings, and Vickers microhardness values were measured to determine the hardness variation of the coatings. NaCl solution (3.5 wt%) was used to evaluate the corrosion properties of the coatings by the potentiodynamic polarization tests. Corrosion current density of 2.890 μA/cm2 for pure nickel coating was improved to 0.379 μA/cm2 by the coating of Zn-doped TiO2 nanoparticles at the 7A/dm2 current density. Microhardness of the Zn-doped TiO2 coating was improved compared to the pure Ni coating.
关键词： Sol-gel processes,Metal matrix composites,Nanoparticles,Composite coatings
更新于2025-09-23 15:23:52
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Hydrophilic Poly(vinylidene Fluoride) Film with Enhanced Inner Channels for Both Water- and Ionic Liquid-Driven Ion-Exchange Polymer Metal Composite Actuators
摘要： This study presents a novel and facile strategy to fabricate a hydrophilic poly(vinylidene fluoride) (PVDF) electrolyte film with enhanced inner channels for a high-performance and cost-effective ion-exchange polymer metal composite (IPMC) actuator. The resultant PVDF composite film is composed of hierarchical micro/nanoscale structures: well-defined polymer grains with a diameter of ～20 μm and much finer particles with a diameter of ～390 nm, producing three-dimensional interconnected, hierarchical inner channels to facilitate ion migration of the electrolyte matrix film has a high porosity of 15.8% and yields a high water uptake of 44.2% and an ionic liquid (IL, [EMIm]·[BF4]) uptake of 38.1% to make both water-driven and IL-driven IPMC actuators because of the introduction of polar polyvinyl pyrrolidone. Compared to the conventional PVDF/IL-based IPMC, both water-driven and IL-driven PVDF-based IPMCs exhibit high ion migration rates, thus effectively improving the actuation frequency and producing remarkably higher levels of actuation force and displacement. Specifically, the force outputs are increased by 13.4 and 3.0 folds, and the displacement outputs are increased by 2.2 and 1.9 folds. Using an identical electrolyte matrix, water-driven IPMC exhibits stronger electromechanical performance, benefiting to make IPMC actuator with high levels of force and power outputs, whereas IL-driven IPMC exhibits a more stable electromechanical performance, benefiting to make long lifetime IPMC actuator in air. Thus, the resultant IPMCs are promising in the design of artificial muscles with tunable electromechanical performance for flexible actuators or displacement/vibration sensors at low cost.
关键词： ionic exchange polymer metal composite (IPMC),ionic liquid (IL),poly(vinylidene fluoride) (PVDF),inner channel,electromechanical response,polyvinyl pyrrolidone (PVP)
更新于2025-09-23 15:23:52
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Mitigating the electromagnetic radiation by coupling use of waste cathode-ray tube glass and graphene oxide on cement composites
摘要： With technological development, the rapid growing numbers of electronic devices generate severe electromagnetic interference (EMI) and radiation to human environment. In this study, the coupling effect of graphene oxide (GO) addition (up to 0.10 wt.% of cement) and waste cathode-ray tube (CRT) glass replacement for fine aggregates (30 and 60 wt.%) in cement-based composites on mitigating EMI was studied. The electric permittivity obtained using a decoupling method was applied for evaluating the EMI shielding capacity of cement-based composites, while direct current (DC) electrical resistance measurement is conducted using four-probe method. The DC electrical resistivity of specimens increases insignificantly with increasing in GO content, but remarkably with increasing CRT glass content from 30 to 60 wt.%. The 60 wt.% replacement of waste CRT glass with 0.1 wt.% GO addition increases the relative permittivity by about 50% and 200% when the frequency is in the ranges of 104–5 × 106 Hz and 101–103 Hz, respectively. It is concluded that a significant increase in the permittivity can be obtained owing to the synergetic interaction between waste CRT glass and GO. The improvement in the EMI shielding ability of cement-based composites not only enables the applications of these composites in mitigating electromagnetic pollution, but also promotes large-volume recycling of toxic waste CRT glass.
关键词： Permittivity,Waste CRT glass,Cement composite,Graphene oxide,Electromagnetic interference
更新于2025-09-23 15:23:52
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Modified dielectric and ferroelectric properties in the composite of ferrimagnetic Co1.75Fe1.25O4 ferrite and ferroelectric BaTiO3 perovskite in comparison to Co1.75Fe1.25O4 ferrite
摘要： The ferrimagnetic Co1.75Fe1.25O4 ferrite with cubic spinel structure (space group Fd3m) was made into composite by mixing with ferroelectric BaTiO3 perovskite with tetragonal structure (space group P4mm) at the mass ratio 50:50. Disc shaped composite powder was finally heated at 1000 °C to study the structure, dielectric and ferroelectric properties. The electrical conductivity, dielectric response and ferroelectric properties of the composite samples are remarkably modified in comparison to their ferrite counterparts before making the composite. The composite system has shown improvement of dielectric constant with reduced dielectric loss factor and electrical conductivity in comparison to the ferrite samples. The mechanism of modified dielectric properties was understood by analyzing ac conductivity data using Jonscher's power law, complex impedance spectra in Cole-Cole plots using equivalent circuit model, and complex electrical modulus spectra using Kohlrausch, Williams and Watts (KWW) proposed model. Electrical conductivity in the composite material was determined by small polaron hoping (SPH) up to measurement temperature 400 K (close to ferroelectric transition of BaTiO3) and overlapping large polaron hopping conductivity at higher temperatures. In contrast, SPH dominates throughout the measurement temperature range for ferrite samples. The space charge polarization, which was largely effective at low frequencies and high measurement temperatures, is significantly reduced in composite samples. High capacitive response in composite samples and its extension up to high measurement temperature is confirmed from the temperature dependence of phase shift and well defined ferroelectric polarization loop and associated electrical parameters.
关键词： Composite dielectric,Polaron hopping,Ferroelectric polarization,Co rich spinel oxide
更新于2025-09-23 15:23:52
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2D reentrant micro-honeycomb structure of graphene-CNT in polyurethane: High stretchability, superior electrical/thermal conductivity, and improved shape memory properties
摘要： The recent rapid development of soft electronics and wearable technology has demanded materials with the function of combining mechanical deformation and electronics. Particularly, materials simultaneously having memory shape characteristics in which mechanical deformation repeatedly occurs in response to stimulus, high stretchability and excellent electric/heat transfer characteristics are interesting actuator materials in future applications. As a stretchable and conductive platform, we fabricated a reentrant micro-honeycomb structure from graphene-CNT, which had structural stretchability due to the accordion-like reentrant structure and continuous conductive paths in the vertical and horizontal directions. To impart shape memory properties, we fabricated composites by simply infiltrating shape memory polyurethane (SMPU) into a stable graphene/CNT framework. Our resulting reentrant micro-honeycomb graphene-CNT/SMPU composites simultaneously exhibited a relatively low resistivity of 5 Ω cm, a change in resistance of less than 10% in the 50% stretching/releasing states, long term stability, and superior tensile shape memory properties, including 95.6% shape fixity and a 90.6% recovery ratio. Regularly distributed graphene-CNT structures offer heterogeneous nucleation sites and undisturbed crystal growth in neat SMPU pillars, resulting in superior shape memory properties. We also constructed a circuit with portable batteries to demonstrate that our reentrant graphene-CNT/SMPU composite offers potential applications as an emergency circuit breaker.
关键词： Shape memory,Polyurethane,Reentrant graphene-CNT,Composite,Ice-templated self-assembly
更新于2025-09-23 15:23:52