Graphite Suspension Research Articles

Electrical Conductivity and Micro Hardness of Synthetic and Natural Graphite Epoxy Composite

This study investigates the electrical conductivity and micro hardness of synthetic and natural graphite epoxy composite. Graphite used on this study is synthetic graphite (SG) and natural graphite (NG) with particle size 44m and 30m, respectively. Different graphite concentrations (50 ~ 80 wt.%) were added into the epoxy resin. The dispersion of graphite in epoxy resin was conducted by high speed mixer through mechanical shearing mechanism, its graphite epoxy suspension was poured into the mold and compression molding was conducted for fabrication of graphite epoxy composites. Electrical conductivity was measured by the four point probe. Microscopic analyses conducted on fracture surface use scanning electron microscopic. Results reveal that non conductive epoxy polymer becomes conductor as addition of graphite. Electrical conductivity of NG higher than SG at the same weight percentage (Wt. %) of conducting filler loading. The highest loading concentration, it exhibited values 12.6 S/cm and 7 S/cm at (80 Wt. %). Hardness property of epoxy composites of both type of graphite increase continuously and reached peak at 60 wt% for NG and 70 wt % for SG, while more addition decreased it.

Foamability of aqueous suspensions of fine graphite and quartz particles with a triblock copolymer

The foamability of a triblock copolymer solution was strongly influenced by the presence of particles. The stability of the foam was evaluated by measuring the foam volume, the drainage of water and particles, and the bubble size as a function of time. The higher stability of foams produced with hydrophilic quartz particles, compared with hydrophobic graphite particles, was related to the presence of quartz aggregates in the lamellae and Plateau borders reducing water drainage, and therefore thin film rupture and bubble coalescence. The copolymer adsorbed slightly more on the hydrophobic graphite, causing the particles to disperse and drain, with the water out of the foam, whereas the hydrophilic quartz aggregated and remain in the lamellar and Plateau borders of the foam.

Mathematical simulation of anodic intercalation of graphite in dilute nitric acid

The article suggests a mathematical model for the process of anodic intercalation of the dense graphite suspension in dilute nitric acid, where the spontaneous intercalation is absent. The model is based on the idea of electric neutrality of a graphite particle, due to which the anion current NO 3 − entering the particle is precisely equal to the quantity of electrons, which are diverted from a particle to a current lead according to the mechanism of electronic conductivity provided by the outer constriction of the suspension. The anodic polarization is conditioned by the mass transfer of anions NO 3 − inside the equipotential graphite particle. The computational solution of the problem showed that even at a small suspension layer height (2 cm), there is a significant nonuniformity of intercalation, which corresponds to the data provided in the literature. A method for the estimation of an intercalation nonuniformity and a method for its reduction by using a multistep process were suggested. The results of the computation can be used for an estimation of the technical characteristics of the final product.

Nanocrystalline Diamond Synthesized in Graphite Suspension by Pulsed Laser Irradiation

Cycled water suspension of fine graphite powders was irradiated by a Nd:YAG pulsed laser with low energy density and long pulse width. Transmission Electron Microscopy (TEM) results indicated diamond particles with cubic structure were obtained, and the size of the diamond particles was about 5 nm. The mechanism of the diamond formation was investigated; it was found that graphite powders were molten by laser irradiation and diamond formed through a nucleation‐growth process.

The effect of high power ultrasound on an aqueous suspension of graphite

Ultrasound treatment was used to study the decrease of the granulometry of graphite, due to the cavitation, which allows the erosion by separating grains. At a smaller scale, cavitation bubble implosion tears apart graphite sheets as shown by HRTEM, while HO and H radicals produced from water sonolysis, generate oxidative and reductive reactions on these sheet fragments. Such reactions form smaller species, e.g. dissolved organic matter. The methodology proposed is very sensitive to unambiguously identifying the in situ composition of organic compounds in water. The use of the atmospheric pressure chemical ionization (APCI) Fourier transform mass spectrometry (FTMS) technique minimizes the perturbation of the organic composition and does not require chemical treatment for analysis. The structural features observed in the narrow range ( m/ z < 300) were mainly aromatic compounds (phenol, benzene, toluene, xylene, benzenediazonium, etc.), C 4–C 6 alkenes and C 2–C 10 carboxylic acids. Synthesis of small compounds from graphite sonication has never been reported and will probably be helpful to understand the mechanisms involved in high energy radical reactions.

Electrically Conductive Thin Films Prepared from Layer‐by‐Layer Assembly of Graphite Platelets

AbstractLayer‐by‐layer (LBL) assembly of carbon nanoparticles for low electrical contact resistance thin film applications is demonstrated. The nanoparticles consist of irregularly shaped graphite platelets, with acrylamide/ββ‐methacryl‐oxyethyl‐trimethyl‐ammonium copolymer as the cationic binder. Nanoparticle zeta (ζζ) potential and thereby electrostatic interactions are varied by altering the pH of graphite suspension as well as that of the binder suspension. Film thickness as a function of zeta potential, immersion time, and the number of layers deposited is obtained using Monte Carlo simulation of the energy dispersive spectroscopy measurements. Multilayer film surface morphology is visualized via field‐emission scanning electron microscopy and atomic‐force microscopy. Thin film electrical properties are characterized using electrical contact resistance measurements. Graphite nanoparticles are found to self‐assemble onto gold substrates through two distinct yet overlapping mechanisms. The first mechanism is characterized by logarithmic carbon uptake with respect to the number of deposition cycles and slow clustering of nanoparticles on the gold surface. The second mechanism results from more rapid LBL nanoparticle assembly and is characterized by linear weight uptake with respect to the number of deposition cycles and a constant bilayer thickness of 15 to 21 nm. Thin‐film electrical contact resistance is found to be proportional to the thickness after equilibration of the bilayer structure. Measured values range from 1.6 mΩ cm−2 at 173 nm to 3.5 mΩ cm−2 at 276 nm. Coating volume resistivity is reduced when electrostatic interactions are enhanced during LBL assembly.

Microstructure and mechanical properties of silicon carbide fiber-reinforced silicon carbide composite fabricated by electrophoretic deposition and hot-pressing

Colloidal graphite aqueous solution was used as the suspension for carbon coating on the fiber, and carbon layer was formed on SiC fiber by electrophoretic method, and SiC/SiC composite was fabricated by sheet stacking method and hot-pressing. The effect of the concentration of colloidal graphite on mechanical properties of SiC/SiC composite was investigated. Bulk density and open porosity of the composites fabricated in this study were nearly the same, and these values were independent of the concentration of colloidal graphite suspension. The carbon coating on SiC fibers was successfully formed by the electrophoretic deposition method using colloidal graphite suspension. In the case of coating with 0.10mass% of colloidal graphite suspension on SiC fibers, relatively uniform carbon coating on the fibers was observed and large fiber pullout occurred effectively during fracture.

Formation of carbon coating on SiC fiber for two-dimensional SiC f/SiC composites by electrophoretic deposition

Carbon coating was formed on SiC fibers in the cloth by electrophoretic deposition method using commercial colloidal graphite suspension, and mechanical properties of SiC f/SiC composites fabricated by sheet stacking method and hot-pressing were investigated. Furthermore, the effectiveness of carbon coating on SiC fiber for SiC f/SiC composite was investigated. Graphite particles partially existed on the SiC fibers after dip-coating or vacuum infiltration, and carbon coating was non-uniform on SiC fibers. In the case of electrophoretic deposition, the surface of SiC fibers was wholly coated with flaky graphite particles, and graphite particles were infiltrated into fiber bundle by electrical force, and relatively homogeneous carbon coating was also formed on not only SiC fibers at the surface of the bundle but also fibers at the center of the bundle. This homogeneous carbon coating provided the optimum interface between fiber and the matrix, and promoted large amount of fiber pullout during fracture.

Graphite-to-diamond transformation induced by ultrasound cavitation

Diamond microcrystals have been synthesized using ultrasonic cavitation of a suspension of hexagonal graphite in various organic liquid media, at an average bulk temperature of the liquid up to 120°C and at atmospheric pressure. The yield of diamond is up to 10% by mass. The diamonds were characterized by scanning electron microscopy, X-ray diffraction and laser Raman spectroscopy. Analysis of the crystallite size distribution showed that the diamonds were nearly mono-dispersed, having a size 6 or 9μm ± 0.5μm, with cubic, crystalline morphology.

A Water Evaporation Based Model for Lubricant Dryoff on Die Surfaces Heated Beyond the Leidenfrost Point

Lubricants in hot forging are applied to the heated die surface by spraying dilute water based graphite suspensions through high-pressure nozzles. To avoid undesirable steam formation, these lubricant droplets need to completely dry before deformation begins. This paper presents an analytical model to estimate evaporation time for the impacting drops at surface temperatures above Leidenfrost, 300–450°C. It is based on the suspension of deformed droplet on a vapor cushion sustained by a continuous supply of water from the drying droplet. Model predictions are validated by single droplet experiments with different surface temperatures, dilution ratios, and impacting speeds.

The effect of carboxymethyl cellulose swelling on the stability of natural graphite particulates in an aqueous medium for lithium ion battery anodes

The effect of carboxymethyl cellulose (CMC) swelling on the stability and chemical properties of a natural graphite suspension in an aqueous medium was investigated. Suspensions prepared at different pH were characterized according to swelling behavior, rheology, green microstructural observation, and measurement of the pore size. A correlation was found between dispersion stability and electrochemical performance. It was found that the swelling of CMC was a critical factor influencing the stability of graphite suspensions. This was evidenced by observations of the green microstructures and changes noted in sedimentation behaviors. Electrochemical experiments using a Li/organic electrolyte/natural graphite anode half-cell and 750 mAh-class lithium ion cells exhibited an initial discharge capacity above 340 mAh g−1 and an improved charge-discharge efficiency.

Ultrafine diamond synthesized by long-pulse-width laser

Nanodiamonds with sizes of 3–6nm were prepared by irradiating graphite suspension using a long-pulse-width (1.2ms) laser at room temperature and normal pressure. The low power density and long pulse laser generated a lower temperature and a lower pressure, which determine the stable size of nanodiamonds. On the other hand, the low degree of supercooling allows a rather low growth velocity, and a disordered structure formed at the diamond surface retards the epitaxy growth. The above two factors dynamically limit the final size of nanodiamonds. Our results suggest that the growth of nanodiamonds follows the Wilson-Frenkel law, and the long pulse laser is propitious to producing fine nanodiamonds.

Gravimetric and electric conductivity studies of settling in binary graphite and kaolin suspensions

This work is devoted to the investigation of the settling process and electric conductivity in binary aqueous colloidal suspensions of graphite and kaolin. The combination of conductometric and gravimetric methods allows to analyze kinetics of both deposit formation and reorganization. Dependences of the characteristic times of mass and conductivity kinetic curves of settling versus pH and surfactant concentration are discussed.

Effect of Carboxymethyl Cellulose on Aqueous Processing of Natural Graphite Negative Electrodes and their Electrochemical Performance for Lithium Batteries

Suspensions of natural graphite particles were prepared in an aqueous medium using carboxymethyl cellulose (CMC) and emulsified styrene-butadiene copolymer latex as part of an environmentally friendly fabrication process for graphite anodes (negative electrodes) intended for application in Li-ion batteries. Suspensions were characterized by adsorption isotherms, electroacoustic measurements, rheology and sedimentation tests, at two different degrees of carboxymethyl substitution (DS) on CMC. A lower DS value (0.7) resulted in greater uptake of CMC on graphite compared with a higher DS value (1.28). This was attributed to attractive hydrophobic interactions associated with the lower carboxymethyl substitution. The greater adsorption for correlates with lower relative viscosity in concentrated graphite suspensions, a higher adhesion strength with a copper substrate, and a greater retention of discharge capacity after cycling. The effect of DS is attributed to differences in the aqueous dispersion properties and stability of graphite suspensions. Based on these results, we fabricated high-capacity graphite negative electrodes characterized by gravimetric and volumetric energy densities of greater than and , respectively. This formulation also led to improved adhesion strength, giving the as-fabricated cell an attractive cycle life greater than 90% of initial discharge capacity after .

Aqueous processing of natural graphite particulates for lithium-ion battery anodes and their electrochemical performance

Aqueous-based natural graphite particulates for fabrication of lithium-ion battery anodes are investigated with emphasis on chemical control of suspension component interactions among graphite particulates, sodium carboxymethyl cellulose (CMC), and emulsified styrene butadiene rubber (SBR). The chemical stability and dispersion properties of the natural graphite particles are characterized using electroacoustic, flow behaviour and green microstructural observations, as well as by measurement of pore size. Correlation is made between the dispersion characteristics and the electrochemical performance of the particles. The dispersion stability of the graphite suspension is improved by charge development when both SBR and CMC are incorporated into the graphite suspension, compared with an unstable graphite suspension prepared with CMC alone. A method to improve the dispersion and homogeneity of the suspension component based on the use of SBR and CMC is proposed. Electrochemical experiments using a Li–organic electrolyte–as-cast natural graphite half-cell and 750-mAh lithium-ion cells show an initial discharge capacity above 340 mAh g −1, improved charge–discharge efficiency, and excellent rate capability.

Effect of shear on the electrical conductivity of suspensions of graphite in an unsaturated polyester resin

The effect of shear on the electrical conductivity of suspensions of conductive graphite particles in a nonconductive unsaturated polyester resin was investigated. At graphite loadings near 30 wt% the electrical conductivity was higher when the suspension was undergoing shear than when shearing stopped. Moreover, shearing caused a large permanent increase in the electrical conductivity of the suspension. When shear was restarted after a period of rest the transient response of the electrical conductivity depended on the direction of previous shear, indicating that the suspension acquires an anisotropic structure under shear. The transition upon shear reversal was strain-dependent. Surprisingly, at graphite loadings near 50 wt% the effect of shear on the electrical conductivity was the opposite of that at loadings near 30 wt%. At intermediate loadings the effect of shear on the electrical conductivity was less clear. The results may have applications in the manufacture of composite bipolar plates for fuel cells and of various other parts made from conductive polymers. POLYM. ENG. SCI., 45:1540–1545, 2005. © 2005 Society of Plastics Engineers

Low Friction Stainless Steel Coatings Graphite Doped Elaborated by Air Plasma Sprayed

A new process has been developed to incorporate graphite particles into a stainless steel coating during its formation. Four means have been tested to inject the graphite particles outside the plasma jet and its plume: graphite suspension, a graphite rod rubbed on the rotating sample, powder injection close to the substrate with an injector, or a specially designed guide. The last process has been shown to be the most versatile and the most easily controllable. It allows the incorporation of between 2 and 12 vol.% of graphite particles (2–15 µm) within the plasma sprayed stainless steel coatings. A volume fraction of 2% seems to give the best results with a slight decrease (6%) of the coating hardness. This volume fraction also gave the best results in dry friction on the pin-on-disk apparatus. Depending on the sliding velocity (0.1–0.5 m/s) and loads (3.7–28 N), the dry friction coefficient against a 100C6 pin is reduced by between 1.5 and 4 compared with that obtained with plasma sprayed stainless steel.

Investigation of the Stability of Graphite Particle Dispersion and the Hemimicelle Formation Process at Graphite/Solution Interfaces Using Atomic Force Microscopy

The correlation between the dispersion stability of graphite particles suspended in aqueous solutions of dodecyldimethylhydroxylammonium chloride (C12DMAOH·Cl) and the structure of the adsorption layer on the graphite surface was investigated by a combination of data from AFM images, measurements of interaction forces, an adsorption isotherm, and turbidity measurements of graphite suspensions. A model for the two-step adsorption mechanism was successfully applied to describe the adsorption isotherm. (The first step was the formation of the horizontal adsorbed monolayer, and the second step was the formation of the hemicylindrical aggregate.) It was suggested that there is a transition regime where the horizontal adsorbed monolayer coexists with the hemicylindrical aggregate. A dispersion of graphite particles is unstable in the presence of the horizontal adsorbed monolayer. Surface force measurements suggest that the surface charges of the horizontal adsorbed monolayer are mostly neutralized by the bound counterions. The critical hemimicelle concentration (hmc) was about 0.8 mM, which was about 1/10 of the bulk critical micelle concentration (cmc ≈ 6 mM). The hmc value was close to the critical concentration at which the suspension stability started to increase dramatically with the surfactant concentration. We found that a stable dispersion of graphite particles can only be achieved once the hemicylindrical aggregates have formed on the surface at full surface coverage, leading to the development of the electric double layer forces from the positively charged aggregate.

Thin-layer chromatography combined with diode laser desorption/atmospheric pressure chemical ionization mass spectrometry.

The desorption of an analyte by a continuous wave diode laser from a porous surface of a thin-layer plate covered with a graphite suspension is presented. The thermally desorbed analyte molecules are ionized in the gas phase by a corona discharge at atmospheric pressure. Therefore, both essential processes--the desorption and the ionization of analyte molecules, which are often performed in one step--are separated. The target preparation is easy and fast since no additional extraction process is required. The mass spectrometric background signal was mostly limited to the low mass range showing no interference with typical compounds of interest. In this study, the calmative and antihypertensive drug reserpine was chosen as model analyte, which is often used for specification of mass spectrometers. No fragmentation was observed because of efficient collisional cooling under atmospheric pressure. The influence of diode laser power and the composition of the graphite suspension were investigated, and a primary optimization was performed.

Structural transitions in aqueous suspensions of natural graphite

The electric conductivity σ and viscosity η of aqueous suspensions at different volume fraction of graphite ϕ and concentration of nonionic surfactant (Triton X-305) are investigated. The correlations between conductivity and rheological properties are discussed. A model of structural transitions in aqueous graphite suspensions is discussed. Two structural transitions, corresponding to changes in electrical and rheomechanical properties, are identified as electrical connectivity and rigidity (or sol–gel) percolation transitions, respectively. An unusual initial decrease of the bulk electrical conductivity with graphite volume fraction ϕ increase was observed in the surfactant solution. This fact is explained as a result of an isolating coating formation around the graphite particles.