Optical transmittance and electrical conductivity of silica glass with biserial and hierarchical network structures made of carbon nanofibers

Silica glass composites, with biserial and hierarchical percolative network made of carbon nanofibers (CNFs), was fabricated using a layer-by-layer technique and spark plasma sintering to obtain high optical transmittance and electrical conductivity. Owing to the network, the critical volume fraction, V_c, for the CNF percolation in the silica glass-matrix composite (0.5–0.7 vol%), when the electrical conductivity of the composite drastically increased with change from insulator (～10^?10 S/m) to conductor (～10^?1 S/m), is smaller than theoretical V_c predicted for the three-dimensional random orientation of CNFs (2.6 vol% for the CNF aspect ratio of 30). The conductivity of the composite with above the V_c of CNFs (～10 S/m) is higher than that reported for the polymer-matrix composite (～10^?5–～10^?3 S/m). Furthermore, high optical transmittance was observed for the electrically conductive composite with V_c of CNFs.     

Hot pressed and spark plasma sintered zirconia/carbon nanofiber composites

Zirconia/carbon nanofiber composites were prepared by hot pressing and spark plasma sintering with 2.0 and 3.3 vol.% of carbon nanofibers (CNFs). The effects of the sintering route and the carbon nanofiber additions on the microstructure, fracture/mechanical and electrical properties of the CNF/3Y-TZP composites were investigated. The microstructure of the ZrO₂ and ZrO₂–CNF composites consisted of a small grain sized matrix (approximately 120 nm), with relatively well dispersed carbon nanofibers in the composite. All of the composites showed significantly higher electrical conductivity (from 391 to 985 S/m) compared to the monolithic zirconia (approximately 1 × 10⁻¹⁰ S/m). The spark plasma sintered composites exhibited higher densities, hardness and indentation toughness but lower electrical conductivity compared to the hot pressed composites. The improved electrical conductivity of the composites is caused by CNFs network and by thin disordered graphite layers at the ZrO₂/ZrO₂ boundaries.     

Synergistic effect of carbon nanofiber decorated with iron oxide in enhancing properties of styrene butadiene rubber nanocomposites

Elastomer nanocomposites reinforced with carbon nanofiber (CNF) decorated with metal nanoparticles exhibit excellent thermal, mechanical, and magnetic properties with low volume fraction of the reinforcement. Generally, metal nanoparticles are used to modify the surface of CNF, to improve their dispersion and contact resistance in the polymer matrix. In this study, Fe₂O₃ metal nanoparticles were decorated on CNF by electrostatic attraction via a green and facile solution‐based method. Interestingly, the CNF decorated with Fe₂O₃ (CNF‐Fe₂O₃)/elastomer improved both the tensile strength and the fatigue property of plain CNF/elastomer by as much as 57.2% and 27.2%, respectively. Moreover, the CNF‐Fe₂O₃/elastomer exhibited superior thermal conductivity, a twofold enhancement compared with carbon fibers. The elastomer nanocomposites consisting of CNF‐Fe₂O₃ also exhibited enhanced magnetic properties due to synergies between the Fe₂O₃ nanoparticles and the CNF. The elastomer nanocomposites prepared with CNF‐Fe₂O₃ will open significant new opportunities for preparing advanced elastomer nanocomposites for future engineering applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45376.     

Conductivity enhancement of carbon nanotube and nanofiber-based polymer nanocomposites by melt annealing

The addition of multi-walled carbon nanotubes (MWCNTs) or carbon nanofibers (CNFs) to polymeric melts offers a convenient route to obtain highly conductive plastics. However, when these materials are melt processed, their conductivity can be lost. Here, it is shown that conductivities can be recovered through melt annealing at temperatures above the polymer's glass transition temperature (T_g). We demonstrate these results for both MWCNT and CNF-based composites in polystyrene (PS). The mechanism behind the conductivity increase is elucidated through modeling. It involves a transition from aligned, unconnected particles prior to annealing to an interconnected network after annealing through viscoelastic relaxation of the polymer. Such re-arrangement is directly visualized for the case of the CNF-based composites using confocal microscopy. The annealing-induced increase in particle connectivity is also reflected in dynamic rheological measurements on both MWCNT and CNF composites as an increase in their elastic moduli at low frequencies.     

Characterization of carbon nanofiber composites synthesized by shaping process

Catalytically grown carbon nanofibers (CNFs) are shaped into pellets in desired size and configuration by a conventional molding process so as to extend the potential applications of CNFs in industrial heterogeneous catalysis. After shaping, a novel carbon nanofiber composite with sufficient mechanical strength is produced, in which isolated CNFs are connected by a carbon network formed through polymer binder carbonization. Characterization of the synthesized CNF composite is performed by using HRTEM, XRD, Raman, N₂ physisorption, TPD and TGA. A comparison of the textural and structural properties, as well as the surface chemistry is made amongst the CNFs, the CNF composite, and a commercial coal-based activated carbon, in order to attain a comprehensive understanding of the CNF composite. The results show that the CNF composite preserves the mesoporous texture of the CNFs which will be beneficial to those reactions of mass transfer control. The modification effect of oxidative treatments on physico-chemical properties of the CNF composite is also investigated. More surface oxygen-containing groups are introduced to the composite by treating the material either in boiling HNO₃ solution or in static air at 400 °C.     

Controlling the yield and structure of carbon nanofibers grown on a nickel/activated carbon catalyst

Carbon nanofibers (CNFs) were grown via the chemical vapor deposition of C₂H₄ on an activated carbon (AC)-supported Ni catalyst. The texture of the CNF/AC composites can be tuned by varying the growth temperature and by treatment in reducing atmosphere prior to C₂H₄/H₂ exposure. The Ni-catalyzed gasification of the AC support increases the microporosity of the composite and shown to be dominant throughout the composite synthesis especially during reduction, subsequent treatment in reducing atmosphere, and CNF growth at low temperatures. N₂ isotherm and scanning electron microscope were used to characterize the texture and morphology of the composites. Subsequent treatment in reducing atmosphere were shown to increase the Ni catalyst activity to grow CNFs. High resolution transmission electron microscope however did not reveal any microstructural difference for Ni catalyst with and without the subsequent reduction treatment. We propose in this paper that the carbon dissolutions during treatment of the catalyst might have an implication on the CNF growth.     

Synthesis and characterization of LiFePO4–carbon nanofiber–carbon nanotube composites prepared by electrospinning and thermal treatment as a cathode material for lithium‐ion batteries

Binder‐free LiFePO₄–carbon nanofiber (CNF)–multiwalled carbon nanotube (MWCNT) composites were prepared by electrospinning and thermal treatment to form a freestanding conductive web that could be used directly as a battery cathode without addition of a conductive material and polymer binder. The thermal decomposition behavior of the electrospun LiFePO₄ precursor–polyacrylonitrile (PAN) and LiFePO₄ precursor–PAN–MWCNT composites before and after stabilization were studied with thermogravimetric analysis (TGA)/differential scanning calorimetry and TGA/differential thermal analysis, respectively. The structure, morphology, and carbon content of the LiFePO₄–CNF and LiFePO₄–CNF–MWCNT composites were determined by X‐ray diffraction, high‐resolution transmission electron microscopy, Raman spectroscopy, scanning electron microscopy, and elemental analysis. The electrochemical properties of the LiFePO₄–CNF and LiFePO₄–CNF–MWCNT composite cathodes were measured by charge–discharge tests and electrochemical impedance spectroscopy. The synthesized composites with MWCNTs exhibited better rate performances and more stable cycle performances than the LiFePO₄–CNF composites; this was due to the increase in electron transfer and lithium‐ion diffusion within the composites loaded with MWCNTs. The composites containing 0.15 wt % MWCNTs delivered a proper initial discharge capacity of 156.7 mA h g^?1 at 0.5 C rate and a stable cycle ability on the basis of the weight of the active material, LiFePO₄. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43001.     

Multifunctional carbon nanofiber-reinforced Ge25Sb10S65 chalcogenide glassy composites

Carbon nanomaterials have wide applications in sensors, batteries, electromagnetic shielding, and mechanical reinforcement. Here, carbon nanofiber (CNF)-reinforced Ge₂₅Sb₁₀S₆₅ chalcogenide glassy composites with excellent mechanical and electrical properties were obtained. These glassy composites maintained the amorphous properties of glass. Thermodynamic parameters, microscopic morphology, and structural characteristics were further studied. Benefiting from the remarkable high strength and conductivity of CNFs, as well as the great interface connection between CNFs and glass, the electrical and mechanical properties of glassy composites were greatly enhanced. The Vickers hardness improved by 36% (from 200 kg/mm² to 272 kg/mm²), the tensile modulus increased from 45.9 GPa to 57 GPa, and the shear modulus increased from 22.2 GPa to 23.7 GPa when the CNF concentration increased from 0 wt% to 3.0 wt%. Furthermore, DC conductivity was raised by several orders of magnitude compared with bulk glass at 293 K (from 4.55 × 10⁻¹⁰ S/cm to 3.15 × 10⁻⁴ S/cm) owing to the formation of a continuous conductive network. Thus, these CNF-reinforced glassy composites provide a new way for realizing multifunctional composites.     

Electromagnetic properties of electrospun Fe3O4/carbon composite nanofibers

In order to develop multifunctional nanofibers, the electrical conductivity and magnetic properties of Fe₃O₄/carbon composite nanofibers have been examined. Polyacrylonitrile (PAN) is used as a matrix to produce magnetic composite nanofibers containing different amounts of magnetite (Fe₃O₄) nanoparticles. Electrospun composite nanofibers were thermally treated to produce electrically conductive and magnetically permeable composite carbon nanofibers. The composite nanofibers were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), Raman spectroscopy, four-point probe and Superconducting Quantum Interference Device (SQUID). Uniform nanofibers were obtained with successful transferring of magnetic properties of Fe₃O₄ into the as-spun composite nanofibers. The electromagnetic properties were tuned by adjusting the amount of Fe₃O₄ in the matrix and carbonization process. The electrical conductivity, magnetic moment and also magnetic hysteresis rise up by adding Fe₃O₄ and increasing carbonization temperature. The high surface area provided by the ultrafine fibrous structures, the flexibility and tuneable electromagnetic properties are expected to enable the expansion of the design options for a wide rage of electronic devices.     

Magnetically aligning multilayer graphene to enhance thermal conductivity of silicone rubber composites

The increasing demand for packaging materials calls for new technologies to achieve excellent thermal conductivity of polymer composites with low content of thermal conductive filler. This article prepared a kind of magnetically functionalized multilayer graphene (Fe₃O₄@MG) via electrostatic interactions, which efficiently enhanced the thermal conductivity of silicone rubber (SR) composites by the alignment of Fe₃O₄@MG in an external magnetic field. The morphology and structure of the Fe₃O₄@MG together with the thermal conductivity of corresponding Fe₃O₄@MG/SR composites were systematically investigated by SEM, TEM, XRD, elemental mapping, and thermal conductivity tester. The obtained results showed that Fe₃O₄@MG was induced to form chain-like bundles in silicone rubber matrix under the applied magnetic field, which enhanced the MG–MG interaction, and formed effective thermal pathways in the alignment direction. Furthermore, as coating mass ratio of Fe₃O₄@MG increased, the thermal conductivity of randomly oriented Fe₃O₄@MG/silicone rubber composites (R-Fe₃O₄@MG/SR) decreased gradually, whereas the through-plane thermal conductivity of vertically aligned Fe₃O₄@MG/silicone rubber composites (V-Fe₃O₄@MG/SR) increased even filled with same contents of thermal conductive filler. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47951.     

Biomimetic synthesis and characterization of carbon nanofiber/hydroxyapatite composite scaffolds

Three dimensional electrospun carbon nanofiber (CNF)/hydroxyapatite (HAp) composites were biomimetically synthesized in simulated body fluid (SBF). The CNFs with diameter of ∼250 nm were first fabricated from electrospun polyacrylonitrile precursor nanofibers by stabilization at 280 °C for 2 h, followed by carbonization at 1200 °C. The morphology, structure and water contact angle (WCA) of the CNFs and CNF/HAp composites were characterized. The pristine CNFs were hydrophobic with a WCA of 139.6°, resulting in the HAp growth only on the very outer layer fibers of the CNF mat. Treatment in NaOH aq. solutions introduced carboxylic groups onto the CNFs surfaces, and hence making the CNFs hydrophilic. In the SBF, the surface activated CNFs bonded with Ca²⁺ to form nuclei, which then easily induced the growth of HAp crystals on the CNFs throughout the CNF mat. The fracture strength of the CNF/HAp composite with a CNF content of 41.3% reached 67.3 MPa. Such CNF/HAp composites with strong interfacial bondings and high mechanical strength can be potentially useful in the field of bone tissue engineering.     

Highly dispersed and electrically conductive polycarbonate/oxidized carbon nanofiber composites for electrostatic dissipation applications

The influence of low cost, commercially oxidized carbon nanofibers (ox-CNFs) on the morphological, thermal, mechanical and electrical properties of polycarbonate (PC) composites was examined. Using a simple solution mixing process leads to good dispersion and high packing density of CNFs in the resultant composites. The composite materials exhibit a dramatic improvement in the DC conductivity; for example, increasing from 2.36 × 10⁻¹⁴ S/m for PC to ca. 10⁻² S/m for the composite at only 3.0 wt.% of CNFs, and exhibits a very fast static charge dissipation rate. Dynamic mechanical analysis showed a remarkable increase in storage modulus (282%) at 165 °C, compared to pure PC. Thermogravimetric analysis showed that thermal stability of the composites increased by 54 °C compared to the pure PC. To our knowledge, the measured electrical conductivity and thermal properties for PC/CNF are the highest values yet reported for PC/CNF composites at comparable loadings. The AC/DC conductivity is shown to play an important role to predict the state of dispersion.     

Effects of VGCF pretreatment on the characteristics of Fe2O3/VGCF composites as anode materials for Li-ion batteries

Two main topics were handled in this study: loss minimization in the irreversible capacity of vapor-grown carbon fibers (VGCFs) by pretreatment techniques and reversible capacity increase in pretreated VGCFs by the deposition of nano-sized Fe₂O₃. VGCFs were ball-milled and acid-treated, and nano-sized Fe₂O₃ particles were supported on the pretreated VGCFs. Their performance as anodes in lithium-ion batteries was characterized using a variety of techniques. Compared to the electrode containing pristine VGCF only, electrodes composed of the pretreated-VGCFs enhanced both charge transfer and discharge capacities due to an increase in lithium-ion mobility. Moreover, the Fe₂O₃ nanoparticles supported on the pretreated VGCFs could eliminate defects and functional groups on the surface of VGCFs generated by the pretreatment, such that the composite of Fe₂O₃ and pretreated VGCF showed higher reversible capacity at any rate of charge/discharge than the composite of Fe₂O₃ and the pristine VGCF. Therefore, the Fe₂O₃/pretreated VGCF composites could be a good candidate for high capacity anodes.     

Differential scanning calorimetry analysis of an enhanced LiNi0.8Co0.2O2 cathode with single wall carbon nanotube conductive additives

The replacement of traditional conductive carbon additives with single wall carbon nanotubes (SWCNTs) in lithium metal oxide cathode composites has been shown to enhance thermal stability as well as power capability and electrode energy density. The dispersion of 1 wt% high purity laser-produced SWCNTs in a LiNi_0.8Co_0.2O₂ electrode created an improved percolation network over an equivalent composite electrode using 4 wt% Super C65 carbon black; evidenced by additive connectivity in SEM images and an order of magnitude increase in electrode electrical conductivity. The cathode with 1 wt% SWCNT additives showed comparable active material capacity (185–188 mAh g⁻¹), at a low rate, and Coulombic efficiency to the cathode composite with 4 wt% Super C65. At increased cycling rates, the cathode with SWCNT additives had higher capacity retention with more than three times the capacity at 10C (16.4 mA cm⁻²). The thermal stability of the electrodes was evaluated by differential scanning calorimetry after charging to 4.3 V and float charging for 12 h. A 40% reduction of the cathode exothermic energy released was measured when using 1 wt% SWCNTs as the additive. Thus, the results demonstrate that replacing traditional conductive carbon additives with a lower weight loading of SWCNTs is a simple way to improve the thermal transport, safety, power, and energy characteristics of cathode composites for lithium ion batteries.     

Multi-contact hybrid thermal conductive filler Al2O3@AgNPs optimized three-dimensional thermal network for flexible thermal interface materials

In this work, a multi-contact Al₂O₃@AgNPs hybrid thermal conductive filler was synthesized by in-situ growth method to fill high thermal conductivity polydimethylsiloxane (PDMS)-based composites to prepare TIMs. And the thermal conductivity, electrical conductivity, and mechanical properties of the composite materials were studied. During the synthesis process of the multi-contact hybrid filler, different concentrations of silver ions were reduced to generate silver nanoparticles and attached to the surface of Al₂O₃. Al₂O₃@AgNPs/PDMS thermally conductive composites were prepared by changing the filler addition. Using SEM, XPS, and XRD is used to characterize the morphology and chemical composition of Al₂O₃@AgNPs hybrid filler. The thermal conductivity of PDMS-based composites with different AgNPs content under 70 wt% filler loading was studied. The results show that the thermal conductivity of PDMS-based composites filled with 7owt%Al₂O₃@3AgNPs/PDMS multi-contact hybrid filler is 0.67 W/m·K, which is 3.72 times that of pure PDMS, and is higher than that of unmodified Al₂O₃ with the same addition amount. /PDMS composite material has a high thermal conductivity of 24%. This work provides a new idea for the design and manufacture of high thermal conductivity hybrid fillers for TIMs.     

Improvement of electrical conductivity of silicon nitride/carbon nano-fibers composite using magnesium silicon nitride and ytterbium oxide as sintering additives

In order to find out the influence of sintering additives on the electrical conductivity of Si₃N₄-based ceramics composites with dispersed carbon nano-fibers (CNFs) two different mixtures of sintering additives were tested – Al₂O₃/Yb₂O₃ and MgSiN₂/Yb₂O₃, respectively. Optimization of hot-pressing conditions was performed for each mixture. The results show that the electrical conductivity can be effectively increased up to 1315 S/m by replacement of traditional sintering aid – alumina, with magnesium silicon nitride, while the mechanical properties remained on the same level. Other advantages of using MgSiN₂ instead of alumina are the preservation of higher amounts of CNFs in the ceramic composite and lower densification temperature (1500 °C) compared to samples sintered with alumina-based sintering aids (1550 °C).     

Effect of iron oxide on the vulcanization and electrical properties of conductive butyl rubber composites

Rubber ceramic composite, negative temperature coefficient of conductivity (NTCC) thermistors, are widely used in industry because of the high dependence of their electrical conductivity on temperature. The effect of iron oxide (Fe₃O₄) on the vulcanization process, DC conductivity, thermoelectric power, dielectric constant and I–V characteristics have been measured. Also the conduction mechanism is discussed. A hot‐pressing technique has been used to enhance the microstructure core of rubber composites. It has been found that Fe₃O₄ acts as a catalyst during vulcanization process and the characteristic time constant during vulcanization decreases as the content of Fe₃O₄ increases. © 2000 Society of Chemical Industry     

The preparation of a novel Si–CNF composite as an effective anodic material for lithium–ion batteries

The suggested pyrolytic carbon (PC) coated Si-carbon nanofiber (CNF) composites can be a solution to provide higher discharge capacity and cycle-ability facilitating the 1st cycle coulombic efficiency of cheap metallic Si particles as an appropriate anodic material for Li-ion battery. The CNFs on the surface of Si particle can provide flexible space to relieve volumetric expansion during charge. Well-controlled PC coating on the surface of Si particle can improve the coherence of CNFs on the Si particle, thereby to enhance the role of CNF as all the more effective electrode material. The additional PC coating on the Si–CNF composite can accomplish the lower surface area and afford the improvement of the 1st cycle coulombic efficiency. Ingenious combinations of PC coating and CNF compositeness successfully made the novel type Si–CNF composite to achieve a remarkable discharge capacity (1115 mA h g⁻¹), an excellent cycle-ability (77% retention rate after 20th cycle), and a good 1st cycle coulombic efficiency (79%) for the effective application as an anode material.     

Preparation and characterization of conductive and magnetic PPy/Fe3O4/Ag nanocomposites

In this article, conductive and magnetic nanocomposites composed of polypyrrole (PPy), magnetite (Fe₃O₄) nanoparticles (NPs), silver (Ag) NPs, have been successfully synthesized with a two step process. First, the PPy/Fe₃O₄ was prepared by the ultrasonic in situ polymerization. Next, the PPy/Fe₃O₄/Ag was synthesized through the electrostatic adsorption. The products were characterized by fourier‐transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), Thermogravimetric (TG), conductivity and magnetization analysis, and the results showed that the Ag NPs with the good conductivity coated uniformly on the surface of PPy/Fe₃O₄ and improved the conductivity of PPy/Fe₃O₄/Ag composites. In addition, as compared with PPy/Fe₃O₄, PPy/Fe₃O₄/Ag composites also have the excellent electro‐magnetic property and enhanced thermostability. POLYM. COMPOS., 35:450–455, 2014. © 2013 Society of Plastics Engineers