Flexible Graphite Research Articles

General Solution Growth of Mesoporous NiCo2O4 Nanosheets on Various Conductive Substrates as High‐Performance Electrodes for Supercapacitors

Mesoporous NiCo(2) O(4) nanosheets can be directly grown on various conductive substrates, such as Ni foam, Ti foil, stainless-steel foil and flexible graphite paper, through a general template-free solution method combined with a simple post annealing treatment. As a highly integrated binder- and conductive-agent-free electrode for supercapacitors, the mesoporous NiCo(2) O(4) nanosheets supported on Ni foam deliver ultrahigh capacitance and excellent high-rate cycling stability.

Alkali-metal-graphite intercalation compounds prepared from flexible graphite sheets exhibiting high air stability and electrical conductivity

The practical use of graphite intercalation compounds (GICs) as industrial materials has been considered to be unfeasible because their air stability is fairly low, notwithstanding their high electrical conductivities and low densities. On the other hand, some air-stable GICs that exhibit p-type conduction have been reported. In this study, air-stable and electrically conductive GICs that exhibited n-type conduction were prepared from commercially available flexible graphite sheets (PGS graphite sheets). We observed that K-GIC and Cs-GIC were air-stable enough to be used in practical applications and were highly electrically conductive. The air stability of Cs-GIC was slightly higher than that of K-GIC. In addition, the stage-2 structure of Cs-GIC was more stable in that it maintained ten times higher electrical conductivity than that of the host graphite after 10years of exposure to air. Moreover, Cs-ethylene-GIC was the most stable and exhibited a blue colored surface after 10years of exposure to air. We assumed that the significantly improved air stability of the alkali-metal-GICs prepared from PGS graphite sheets is caused by the large crystalline size and the bending graphite layer structure of the host PGS graphite.

Synthesis and characterization of pulsed polymerized poly(3,4-ethylenedioxythiophene) electrodes for high-performance electrochemical capacitors

Poly(3,4-ethylenedioxythiophene) (PEDOT) is electrochemically prepared as a film on flexible thin graphite substrate by short galvanic pulse method in organic media. For comparative studies, PEDOT films are also prepared by potentiostatic polymerization method. The nucleation and growth mechanism for PEDOT film polymerized by short current pulses is presented with morphological and structural studies. The growth of PEDOT is continuous during the pulse off period as confirmed by the deposited mass of PEDOT by these two different methods. The SEM studies of pulse polymerized PEDOT films with different pulse on time show the features of highly porous and ridge like structures which help in rapid migration of dopant ClO4− ions during the charge and discharge processes. The X-ray photoelectron spectroscopy (XPS) studies confirm that in the pulse polymerized PEDOT films polymer chains are fully conjugated with the dopant ClO4− ions. The electrochemical characterization of PEDOT films show that pulse polymerized PEDOT films exhibited high specific capacitance (126.5Fg−1) with an improved energy density and rate kinetics as comparison to the potentiostatically deposited PEDOT films (100Fg−1) in aqueous electrolyte.

Electrophoretic deposition of MnO2-coated carbon nanotubes on a graphite sheet as a flexible electrode for supercapacitors

A flexible electrode was prepared by microwave heating deposition of manganese oxide (MnO2) on carbon nanotubes (CNTs) followed by electrophoretic deposition of the MnO2-coated CNTs on a flexible graphite sheet (FGS). The prepared MnO2-coated CNTs were characterized by scanning and transmission electron microscopy, and X-ray diffraction. A uniformly thin nano-scale MnO2 coating was formed on the surface of the CNTs. The MnO2-coated CNTs–FGS electrode showed highly capacitive behaviour in the 0.5M Na2SO4 aqueous solution, with a specific capacitance of 442.9F/g based on MnO2 at 2mV/s. It exhibited an excellent cycling stability with no more than 1.1% capacitance loss after 1000cycles at 50mV/s.

Performance of Isotropic and Anisotropic Heat Spreaders

Anisotropic heat spreaders (flexible graphite and continuous carbon fiber polymer-matrix composite) and isotropic heat spreaders (copper and aluminum) have been evaluated numerically in terms of thermal resistance. Anisotropic ones are attractive for their through-thickness thermal insulation ability. Flexible graphite is superior to carbon fiber composite in providing lower thermal resistance. Carbon fiber composite is advantageous in its superior through-thickness thermal insulation ability and its smaller critical thickness (the optimal thickness for maximizing heat spreading while minimizing thickness). The isotropic heat spreaders are superior to the anisotropic ones in providing low thermal resistance, provided that the thickness is large, but they do not have the through-thickness thermal insulation ability. A higher value of the in-plane thermal conductivity enhances the effectiveness of flexible graphite. As the heat source area decreases, the thermal resistance increases while the critical thickness decreases. For the same heat source area, a greater in-plane dimension of the heat source perpendicular to the intended heat spreading direction decreases the thermal resistance and critical thickness. Flexible graphite is comparatively more advantageous when the thickness is smaller and when the heat source area is larger. For the same thickness below 2 mm, flexible graphite with in-plane conductivity of 1500 W/(m K) is superior to copper and that with in-plane conductivity of 600 W/(m K) is superior to aluminum. The highest thermal conductance obtained is 6.1 × 104 W/(m2 K) when the thermal interfacial resistance is neglected and 5.1 × 104 W/(m2 K) when this resistance is included. The conductance increases with decreasing heat source area and with decreasing heat spreader length.

Three-dimensional evaluation of the compression and recovery behavior in a flexible graphite sheet by synchrotron radiation microtomography

The compression and unloading behavior of flexible graphite sheets was investigated using synchrotron radiation microtomography with 1 μm voxel size. The recovery ratio of the flexible graphite sheet was measured accurately by in-situ observation. The three-dimensional strain distribution in the interior of the specimen was obtained using the microstructural tracking method. The inner strain distribution with micrometer scale indicated inhomogeneous deformation. The microstructural tracking analysis revealed that deformation units exist in the flexible graphite sheet. The units seem to deform, affecting the neighboring units with each other. The units had a similar size and shape with compacted exfoliated graphite worms that constitute the flexible graphite sheet. Microscopic deformations during compression and unloading are surely affected by the microstructure of the sheet.

Improvement of the oxidation stability and the mechanical properties of flexible graphite foil by boron oxide impregnation

Improvement of the oxidation stability and the mechanical properties of flexible graphite foil by boron oxide impregnation

Low-temperature growth of well-aligned ZnO nanorods/nanowires on flexible graphite sheet and their photoluminescence properties

We have grown large-scale well-aligned ZnO nanorods/nanowires on commercial flexible graphite sheet (FGS) at low temperature via chemical vapor deposition method. The products were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The effects of the growth temperature and oxygen flow rate on the morphology of ZnO nanostructures have been investigated. The growth mechanism of ZnO is found to be a self-catalytic vapor–solid process assisted by the immiscibility of ZnO with graphite. The as-grown ZnO/FGS products show strong green emission and their photoluminescence properties can be tuned by changing growth condition or annealing treatment.

Superconductive CaC6 prepared from flexible graphite sheets

The host graphite material of choice for most CaC6 studies is highly oriented pyrolytic graphite (HOPG), which can affect the resulting properties of prepared graphite intercalation compounds (GICs). In order to gain a better understanding of the superconductivity of CaC6, we examined CaC6 prepared from Grafoil and PGS. To confirm their superconductivity, the dependences of the magnetic moment on temperature under a constant magnetic field were measured over 2–20 K. The resulting CaC6 transitioned to a superconducting state at around 11 K, independent of purity and homogeneity, while slight differences that depended on the host materials were observed. The transition to a superconducting state at 11.5 K occurred provided that a small amount of CaC6 was present. The co-existence of LiC6 and other GICs, and the residual Li atoms in the CaC6 had little effect on the transition temperature. The transition temperature of the CaC6 prepared from PGS was slightly lower than that of the CaC6 prepared from HOPG and Grafoil.

Improvement of the oxidation stability and the mechanical properties of flexible graphite foil by boron oxide impregnation

Flexible graphite foil produced by rolling expanded graphite impregnated with boron oxide was analyzed by laser mass spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and thermogravimetry. It was shown that the modification of the graphite foil by boron oxide increases the onset temperature of oxidation by ∼ 150 °C. Impregnation of less than 2 mass% boron oxide also increased the tensile strength of the materials. The observed improvement was attributed to the blocking of active sites by boron oxide, which is probably chemically bonded to the edges of graphene sheets in expanded graphite particles.

Carbon materials for structural self-sensing, electromagnetic shielding and thermal interfacing

This paper reviews carbon materials for significant emerging applications that relate to structural self-sensing (a structural material sensing its own condition), electromagnetic interference shielding (blocking radio wave) and thermal interfacing (improving thermal contacts by using thermal interface materials). These applications pertain to electronics, lighting (light emitting diodes), communication, security, aircraft, spacecraft and civil infrastructure. High-performance and cost-effective materials in various forms of carbon have been developed for these applications. The forms of carbon materials include carbon fiber, carbon nanofiber, exfoliated graphite, carbon black and composite materials. Short carbon fiber cement-matrix composites and continuous carbon fiber polymer-matrix composites are particularly effective for structural self-sensing, with the attributes sensed including strain, stress, damage and temperature. Flexible graphite as a monolithic material and nickel-coated carbon nanofiber as a filler are particularly effective for electromagnetic shielding. Carbon black paste, graphite nanoplatelet paste and flexible graphite (filled with carbon black paste) are particularly effective for thermal interfacing; carbon nanotube arrays are less effective than these pastes. The associated science pertains to the relationship among processing, structure and properties in relation to the abovementioned applications. The criteria behind the design of materials for these applications and the mechanisms of the associated phenomena are also addressed.

Professor Wanci Shen and his research activity in carbon materials

Professor Wanci Shen was born in 1940 in Hubei Province.He studied metallic materials in Tsinghua University from 1957 to 1963.After that,he became a faculty member in Tsinghua University. He was one of the earliest Chinese scientists to investigate natural graphite and its processing,graphite intercalation compounds,flexible graphite,isotropic graphite and graphite materials as electrodes for batteries.He was awarded the National Invention Award in 1993 and the China Building Materials Award in 2006.He has published more than 100 academic papers.Prof.Shen was awarded the Carbon Outstanding Achievement award of China in 2011 by the Selection Committee for the Carbon Outstanding Achievement award.

Dynamic mechanical behavior of flexible graphite made from exfoliated graphite

The low-frequency dynamic mechanical properties of low density flexible graphite (0.027–0.089 g/cm 3, obtained by compressing exfoliated graphite at 0.3–1.7 MPa without a binder) are different in flexure and compression. The storage and loss moduli and the loss tangent are higher under flexure than compression. Under flexure, the storage modulus is essentially unaffected by increasing the static strain while the loss tangent and loss modulus decrease. Under compression, both storage and loss moduli increase with increasing static strain, while the loss tangent slightly decreases. The storage and loss moduli are higher and the loss tangent is lower for out-of-plane compression than for in-plane compression. The storage and loss moduli increase with increasing fabrication pressure, while the loss tangent decreases. Energy dissipation is much more effective under flexure than compression. Flexure appears to provide more sliding of the graphite layers than compression. For the highest energy dissipation under flexure, a low static strain is recommended; for high energy dissipation under compression, a high static strain is recommended.

Preparation of Flexible Graphite Sheet with Fine Flake Graphite

Flexible graphite was prepared using the fine flake graphite that could go straight through 149-85μm mesh as raw material, using sulfate acid and nitrate acid as inserting agent and Potassium permanganate as oxidant. The best oxidation reaction conditions are as follows: VSulfate acid/VNitrate acid=5:1, m (fine graphite)/m (Potassium permanganate)=1/0.12, the limited temperature is about 1100-1200°C. Under such condition, the expansion volume of the fine flake graphite with 250-149μm can be reached to 341ml/g. The graphite with 149-85μm can be reached to 230ml/g, the qualities of flexible graphite sheet when intensity is 1.20 g/cm3 are as follows: tensile strength is 4.09 Mpa; ash ratio is 2.19%; recovery rate is 7.8%; compression ratio is 44.0%, TG at 450°C is 0.32%; TG at 600°C is 18.97%; Stress relaxation rate is 3.1%.

Development of a lightweight deployable/stowable radiator for interplanetary exploration

This paper experimentally and analytically evaluates the heat rejection/retention performance of a lightweight 100 W-class re-deployable radiator with environment-adaptive functions. This radiator, reversible thermal panel (RTP), which consists of flexible high thermal conductive graphite sheets and a single crystal shape memory alloy as a passive reversible actuator, changes its function from a radiator to a solar absorber by deploying/stowing the reversible fin upon changes in the heat dissipation and thermal environment. The RTP was considered as a candidate methodology for thermal control of Venus mission, PLANET-C, in order to save survival heater power. An RTP prototype was tested and evaluated. An analytical thermal model of the RTP was also developed, and basic performances of the RTP were evaluated. Thermal performance of the RTP when applied to the longwave infrared camera of the PLANET-C was evaluated with an analytical thermal model as functions of fin deployment directions and rear surface properties of the RTP’s fin. The analytical results showed that the RTP can save survival heater power in comparison to a conventional radiator. ► New thermal control device for spacecraft with high-thermal-conductivity graphite sheets. ► Heat rejection performance can be changed based on its temperature. ► Thermal vacuum test demonstrates autonomous thermal control performance. ► A case study was conducted, and effectiveness was analytically evaluated.

Numerical Modeling of the Performance of Thermal Interface Materials in the Form of Paste-Coated Sheets

The performance of thermal interface materials in the form of core sheets coated on both sides with a thermal paste is numerically modeled by finiteelement analysis. The paste is polyol-ester-based carbon black paste and serves to improve the conformability. Good agreement is found between modeling and experimental results that involve copper proximate surfaces sandwiching the thermal interface material. The core sheets are copper, aluminum, indium, and flexible graphite. Flexible graphite (made from exfoliated graphite) is advantageous in its low elastic modulus, whereas copper and aluminum foils are advantageous in their high thermal conductivity. Indium is advantageous in its low elastic modulus compared with copper or aluminum and in its high thermal conductivity compared with flexible graphite. Among the four types of core sheet with identical thickness, coated indium foil gives the best performance for the range of foil thickness of 6 l mt o 112lm for the case of smooth (0.01 lm roughness) proximate surfaces and 117 lm to 320 lm for the case of rough (15 lm roughness) proximate surfaces. Aluminum foil gives the best performance for the thickness range of 112 lm to 2000 l mi n the case of smooth proximate surfaces. For thicknesses below these ranges, flexible graphite performs the best. For thicknesses above these ranges, copper foil performs the best.

OS05-3-4 Characterization of inhomogeneous deformation behavior in a flexible graphite sheet by synchrotron radiation microtomography

OS05-3-4 Characterization of inhomogeneous deformation behavior in a flexible graphite sheet by synchrotron radiation microtomography

OS05F049 Characterization of inhomogeneous deformation behavior in a flexible graphite sheet by synchrotron radiation microtomography

OS05F049 Characterization of inhomogeneous deformation behavior in a flexible graphite sheet by synchrotron radiation microtomography

An Experimental-Numerical Procedure for Stuffing Box Packing Characterization and Leak Tests

The sealing of valve stems is ensured by the traditional systems of packed stuffing boxes. The performance of this type of sealing system, which is also used in rotating equipment, is dependent on the radial contact pressures generated by the packing axial compression. The mechanical behavior of a packing seal is characterized by the transmission ratio of the radial stress over the axial stress known as the lateral pressure coefficient, which is one of the required parameters used to select packing seals. However, the modeling of the packed stuffing box requires the knowledge of other packing seal mechanical characteristics such as compression modulus and Poisson’s ratio. In this paper, the mechanical characteristics of packing seals are obtained using a hybrid experimental-numerical procedure. The experimental study is carried out on an instrumented stuffing box packing test bench. The tests results of the experiments are coupled to the ones obtained by a finite element simulation of the test rig to determine the packing seal mechanical characteristics. Two packing types are used: one based on Teflon and the other one based on flexible graphite. In addition, leak rates are measured for different axial compressive stresses and gas pressures in order to estimate the tightness performance of such seals.

Flexible graphite modified by carbon black paste for use as a thermal interface material

Polyol-ester-based carbon black pastes are used to either coat or penetrate flexible graphite, thereby increasing the thermal contact conductance of flexible graphite between copper surfaces. Paste penetration by up to an effective paste thickness (the volume of the penetrated paste divided by the geometric area of the flexible graphite) of 5 μm increases the conductance by up to 350%, 98% and 36% for thicknesses of 50, 130 and 300 μm, respectively. Paste coating up to 10 μm increases the conductance by up to 200%, 120% and 65% for thicknesses of 50, 130 and 300 μm, respectively. The paste penetration is more effective than the paste coating in enhancing the conductance, when the thickness is below 130 μm. At thickness ⩾130 μm, paste penetration and paste coating are similarly effective. These results stem from the relatively low interfacial thermal resistivity provided by paste penetration and the relatively high through-thickness thermal conductivity provided by paste coating. Paste penetration decreases the thermal conductivity of flexible graphite, but paste coating does not affect the conductivity. Both penetration and coating decrease the interfacial resistivity. The highest thermal contact conductance is 1.4 × 10 5 W/m 2 K, as provided by paste-penetrated flexible graphite of thickness 26 μm.