Ball-milled Graphite Research Articles

Effect of Milling Conditions on the Purity of Hydrogen Desorbed from Ball-Milled Graphite

During ball milling, graphite can absorb a relatively large amount of hydrogen (7.4 wt %). However, during subsequent heating, hydrogen is usually desorbed together with a small amount of methane. ...

Effects of ball-milled graphite in the synthesis of SnO2/graphite as an active material in lithium ion batteries

Nano-sized SnO2 particles supported on ball-milled graphite were manufactured by the in situ NaBH4 reduction method and were used as an anode active material in lithium-ion batteries. Their physical and electrochemical characteristics were investigated using various characterization techniques: Raman spectroscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM), and cyclic voltammetry (CV). From coin half-cell tests, the SnO2 particles supported on graphite that was ball-milled for 24 hr showed a reversible capacity better than that of commercial graphite and other SnO2/graphite materials for which the graphite was ball-milled for longer lengths of time.

An EPR Study on Nanographites

We present the results of an electron paramagnetic resonance study (EPR) in the range of 4–290 K on samples of nanographites obtained by ball milling graphite for different times. With a careful simulation of the spectral line shapes, we disentangled the EPR bands, providing the spectral profiles and intensities of the components on varying the temperature, their g tensors, and the homogeneous line widths of the contributing spin packets. We have been able to follow the effect of decreasing progressively the size of the flakes on the EPR bands due to mobile electrons and on Lorentzian lines due to nonbonding electrons on the zigzag edges of the crystallites. The temperature dependence of the EPR intensities shows a common trend for the signals attributed to edge electrons and to mobile electrons, showing that they belong to the same bath.

A joint Raman and EPR spectroscopic study on ball-milled nanographites

Multi-wavelength Raman and EPR spectroscopies have been used on ball-milled graphite to investigate the effect of varying crystallite size and defect concentration. A correlation between Raman ID/IG intensity ratio and EPR T1 spin lattice relaxation time of conduction electrons has been discovered which could represent an appealing characterization technique for graphitic materials.

Hydrogen storage properties of ball-milled graphite with 0.5 wt% Fe

SUMMARY Ball-milled hydrogenated graphite-iron materials have attracted interest as possible hydrogen storage media because of theoretically estimated hydrogen capacities of about 10 wt%. However, such a value needs to be experimentally verified. In this work, graphite-0.5 wt% Fe was milled under 3 bar hydrogen in a tungsten carbide milling pot. The effect of iron on the microstructure and hydrogen storage properties of milled graphite was investigated by thermal gravimetric analysis–mass spectrometry, X-ray diffraction, and transmission electron microscopy. When a 10-hour milled graphite with 0.5 wt% Fe sample was heated under argon to 990 °C, 9.6 wt% of hydrogen was released, which is almost double than that for a graphite sample with no iron (5.5 wt% hydrogen). The addition of iron also was found to reduce the onset temperature of hydrogen desorption by 50 to 350 °C. However, for a longer milling time of 40 hours, the amount of hydrogen desorbed for graphite-0.5 wt% Fe decreased, and methane also was detected. The results suggest that iron carbide produced during milling plays a catalytic role, increasing the hydrogen storage capacity and lowering the onset temperature of hydrogen desorption. Copyright © 2011 John Wiley & Sons, Ltd.

CoSn-graphite electrode material prepared by using the polyol method and high-intensity ultrasonication

Composite electrode materials containing nanoparticles of nearly amorphous CoSn and ultrathin layers of graphite are prepared here. For this purpose, Sn(II) and Co(II) ions in tetraethyleneglycol are reduced with NaBH4 in the presence of ball-milled graphite while high-intensity ultrasonication is continuously applied. The followed preparative route is a combination of the polyol and sonochemical methods. The observed capacity value for CoSn-ball milled graphite is over 400mAh/g after 40 cycles (this is superior to graphite). The good electrochemical cycling behavior is connected to the small particle size of CoSn, the low crystallinity of CoSn and the dispersion of the CoSn particles in an optimized carbon matrix. The selected binder (polyvinylidene fluoride or lithium polyacrylate) also can contribute to improve the cycling behavior. The low electrochemical efficiency, particularly in the first cycles, may be related to the spontaneous oxidation of the metallic particles surface and irreversible electrolyte consumption. The use of inert atmosphere (Ar-flow) results in a decrease of the tin oxide content, as determined by using 119Sn Mössbauer spectroscopy, an increase of the initial electrochemical efficiency up to a maximum of 90.4%, and higher capacities (507mAh/g after 40 cycles).

Effect of ball-milling on the rate and cycle-life performance of graphite as negative electrodes in lithium-ion capacitors

A commercial graphite is ball-milled and the pristine and ball-milled graphites are characterised for use as negative electrodes in lithium-ion capacitors (LICs). Ball milling graphite results in a decrease in discharge capacity when the charge rate is relatively slow, whereas, it leads to an increase in discharge capacity when the charge rate is high. When charged at 0.1C, the discharge capacities of pristine, 3h, 10h and 30h-milled materials at 6C are 75, 69, 67 and 66% of theoretical capacity, respectively; however, when charged at 60C, the discharge capacities of pristine, 3h, 10h and 30h-milled materials, at 60C, fall to 0.9, 13, 23 and 24% of theoretical capacity, respectively (theoretical capacity: 372mAhg−1, for LiC6 stoichiometry). This difference in the discharge rate capability behaviour of the pristine and ball-milled graphites with charge rate is attributed to the interplay of two different charge storage mechanisms: Li-ion intercalation and Li-ion adsorption that co-exist; but the later becomes more significant for milled samples. In terms of cycle-life performance, pristine and ball-milled graphites follow similar trends observed for their rate capability behaviour.

The synthesis of peculiar structure of spring-like multiwalled carbon nanotubes via mechanothermal method

A simple, economical and convenient mechanothermal process for the synthesis of spring-like multiwalled carbon nanotubes (S-MWCNTs) with advantages of large-quantity production and low cost is described. Interestingly, many peculiar morphologies are reported for the first time as an extraordinary structure from family carbons that could represent unique building blocks for nanoengineering as a result of their special electronic and mechanical properties. As the matter of fact, this special structure guarantees its usage in the world of composites as reinforcement material for good flexible structures. Here, we report the synthesis of S-MWCNTs by annealing amorphous carbon powders at 1380 °C in an Ar atmosphere. The amorphous powders were obtained after ball-milling graphite for times longer than 150 h. The characterization of S-MWCNTs by high resolution transmission electron microscope, scanning electron microscope indicated that S-MWCNTs had uniform tubular hollow structures with openings, a length of about several millimeters, and a diameter of 80 ± 30 nm at the open and closed end. Also, Brunauer–Emmett–Teller indicated surface area as high as ∼210 m 2/g. Finally, the magical structure introduced an intermediate structure between two well-known structures as may be of particular interest from both fundamental and applied points of view.

The effects of graphite on the reversible hydrogen storage of nanostructured lithium amide and lithium hydride (LiNH 2 + 1.2LiH) system

The addition of 5 wt.% of graphite was incorporated into the (LiNH 2 + 1.2LiH) hydride system in order to study its effect on the prevention of LiH from hydrolysis/oxidation which leads to the escape of NH 3. The composite hydride system was processed by ball milling for 25 h. Thermal behavior in DSC up to 500 °C and isothermal desorption in a Sieverts-type apparatus were carried out. XRD was used to obtain information about phase changes. It is found that after ball milling graphite becomes amorphous. DSC analysis shows that for the mixture ((LiNH 2 + 1.2LiH) + 5 wt.% graphite) graphite can prevent or at least substantially reduce the oxidation/hydrolysis of LiH since no melting peak of retained LiNH 2 is observed. Both the DSC and Sieverts-type tests show that the addition of graphite increases the apparent activation energy of desorption from the ∼57–58 to ∼85–90 kJ/mol range. On the other hand, the graphite additive increases measurably the desorbed/absorbed capacity of hydrogen at 275, 300 and 325 °C. The ((LiNH 2 + 1.2LiH) + 5 wt.% graphite) system is fully reversible desorbing/absorbing ∼5 wt.% H 2 at 325 °C in the following reaction: (LiNH 2 + LiH ↔ Li 2NH + H 2). Step-wise pressure–composition–temperature (PCT) tests show that the enthalpy and entropy change of this reversible reaction is −62.4 and −61.0 kJ/mol H 2 and 117.8 and 115.8 J/mol K for undoped and 5 wt.% G doped (LiNH 2 + 1.2LiH) system, respectively. It shows that within an experimental error there is no measurable effect of graphite additive on the thermodynamic properties. The Van’t Hoff analysis of the obtained thermodynamic data shows that the equilibrium temperature at atmospheric pressure of hydrogen (1 bar H 2) is 256.8 and 253.9 °C for the undoped and 5 wt.% G doped (LiNH 2 + 1.2 LiH) system ball milled for 25 h, respectively. Such high equilibrium temperatures render it rather obvious that both of these hydride systems cannot be employed for hydrogen desorption/absorption below 100 °C as required by the DOE targets for the automotive hydrogen storage materials.

Few-layer graphenes from ball-milling of graphite with melamine

We report a simple, practical scalable procedure to produce few-layer graphene sheets using ball-milling. Commercially available melamine can be efficiently used to exfoliate graphite and generate concentrated water or DMF dispersions.

In-plane defects produced by ball-milling of expanded graphite

Expanded graphite (EG) was ball-milled in a high-energy planetary-type mill under air atmosphere. The products were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). During the milling process (up to 100 h), the crystallite size ( L c ) of EG decreases gradually from 15.4 to 11.3 nm. Compared with most of natural graphite, this L c decrease degree of EG is far lower. In the EG after ball-milling for 100 h, plenty of in-plane defects are produced, which rarely occur in most of ball-milled natural graphite.

Preparation and Characterization of Spherical Carbon Composite for Use as Anode Material for Lithium Ion Batteries

oC in an argon flow. The ballmilled graphite consists of distorted nanocrystallites and amorphous phases. In the composite particle, nanosized flakes are uniformly distributed in a soft carbon matrix, as revealed by X-ray diffractometer (XRD) and transmission electron microscopy (TEM) experiments. The composite is compatible with a pure propylene carbonate (PC) electrolyte and shows high rate capability and excellent cycling performance. The electrochemical properties are comparable to those of hard carbon.

Unoccupied electronic structure of ball-milled graphite

Changes in electronic and vibrational structure of well characterised macrocrystalline graphite milled by a planetary ball-mill are investigated by Raman spectroscopy and Near Edge X-ray Absorption Fine structure (NEXAFS) measurements at the C K-edge. The electronic structure changes at the surface and in the sub-surface of the particles are examined by comparing two-different NEXAFS detection modes: total fluorescence yield (TFY) and partial electron yield (PEY) respectively. When the in-plane crystallite sizes of graphite are decreased to nanosized (from approximately 160 nm to approximately 9 nm), a new spectral structure appears in TFY at 284.1 eV which is not present in the macrocrystalline graphite. This feature is assigned to electronic states associated with zigzag edges. Further the TFY shows a shift of the main graphite pi* band from 285.5 to 285.9 eV, attributed to breaking the conjugation and hence the electron localization effect during milling, The TFY spectra also show strong spectral features at 287.5 and 288.6 eV, which suggest that the local environment of carbon atoms changes from sp(2) to more sp(3) due to physical damage of the graphite sheets and formation of structures other than aromatic hexagons. Complementary Raman spectroscopic measurements demonstrate an up-shift of the graphite G band from 1575 to 1583 cm(-1)en route to nanosize. The changes in TFY NEXAFS and Raman spectra are attributed to modification of the sub-surface electronic structure due to the presence of defects in the graphite crystal produced during milling. The discovery of the strong spectral feature at 284.1 eV in nanographite and the 0.4 eV up-shift of the pi* band may open up possibilities to influence the electronic transport properties of graphite by manipulation of defects during the preparation of the nanographite.

The reaction process of hydrogen absorption and desorption on the nanocomposite ofhydrogenated graphite and lithium hydride

The lithium–carbon–hydrogen (Li–C–H) system is composed of hydrogenated nanostructural graphite (CnanoHx) and lithiumhydride (LiH). CnanoHx is synthesized by ball-milling of graphite under a hydrogen atmosphere. In this work, the reactionprocess of hydrogen absorption and desorption on the Li–C–H system is investigated. TheCnanoHx–LiH composite can desorb about 5.0 mass% of hydrogen at350 °C with theformation of Li2C2 until the second cycle. However, the hydrogen desorption amount significantly decreasesfrom the third cycle. Furthermore, it is shown by using gas chromatography that aconsiderable amount of hydrocarbons is desorbed during the rehydrogenation process.These results indicate that the amount of reaction between the polarized C–H groups inCnanoHx and LiH is reduced due to a decrease in the C–H groups by losing carbon atoms under thehydrogen absorption and desorption cycles.

Curing characteristics of an epoxy resin in the presence of ball-milled graphite particles

The effects of simply-made graphite particles (GPs, 1 wt%) on curing kinetics of an epoxy resin were investigated by means of differential scanning calorimetry (DSC). Two approaches based on constant and variable activation energy were applied to analyze the DSC curves. Results from the constant energy method showed that addition of the GPs increased the activation energy Ec and the overall order of reaction m + n. With the variable energy method, the activation energy varied with curing conversion substantially in the GP/epoxy system; in contrast, the variation in the pure epoxy was very limited. The GPs also decreased the heat of reaction (ΔH) and increased the glass transition temperature (Tg) for the epoxy. Comprehensive analyses indicated that the GPs did not significantly impede the curing reaction, which can enable improvement of the composite functionalities without creating processing penalties. The information obtained from this study provides an understanding of multiple factors involved in the complex relationship of structure and properties of the composites.

Electron Spin Resonance Investigation of Hydrogen Absorption in Ball-Milled Graphite

Nanostructured hydrogenated graphite (CnanoHx) was synthesized here from graphite by ball-milling under a hydrogen (H2) atmosphere. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and ...

Electrochemical Properties of Carbon Composites Prepared by Using Graphite Ball-milled in Argon and Air Atmosphere

A carbon composite was synthesized by mechanical mixing of ball-milled graphite and PVC powders, followed by pyrolysis reaction of PVC. Natural graphite ball milled under atmosphere of argon or air leads to a disordered structure. It appears that the electrochemical lithium intercalation reaction is dependent on the atmosphere in which the graphite is ball milled. The carbon composite obtained using air-milled graphite shows a high reversible capacity and high initial coulombic efficiency compared to argon-milled graphite. This is attributed to the enhanced thermal stability of a disordered structure in the air milled sample. For the one with air-milled graphite, the disordered structure is maintained during heat treatment, while argon-milled graphite is partially crystallized.

Publisher’s Note: Fe-Based Electrocatalysts for Oxygen Reduction in PEMFCs Using Ballmilled Graphite Powder as a Carbon Support [ J. Electrochem. Soc. , 155 , B340 (2008)

not Available.

Fe-Based Electrocatalysts for Oxygen Reduction in PEMFCs Using Ballmilled Graphite Powder as a Carbon Support

Active Fe-based electrocatalysts were prepared using ballmilled graphite powder as a carbon support. The best performing catalysts were achieved by acid-washing, iron-loading, and pyrolyzing the ballmilled graphite powders. Only of ballmilling was required to produce optimal catalytic activity. High-energy ballmilling of pristine graphite powder under nitrogen was shown to reduce crystallite size, increase nitrogen content, increase surface area, increase degree of disorder, and inevitably introduce metallic impurities. Acid-washing treatment of ballmilled graphite powders reduced, but did not completely eliminate, metallic impurities. Iron enrichment and pyrolysis of acid-washed, ballmilled graphite powder was shown to increase catalytic activity, have little effect on crystallite size, increase surface area, and decrease degree of disorder. It was found that catalytic activity increases as crystallite size decreases, degree of disorder and nitrogen content increase, and micropore specific surface area increases. Fuel cell test results have shown that the order of increasing maximum power density follows the order of increasing catalytic activity. Interestingly, the optimal crystallite size parameter and maximum activity for catalysts made with either ballmilled graphite powder or carbon black is almost the same.

Hydrogen storage in carbon/Mg nanocomposites synthesized by ball milling

Carbon nanocomposites obtained by ball milling of graphite and magnesium with organic additives (benzene or cyclohexane) under different conditions have been studied with the aim of preparing novel hydrogen storage materials. It has been proved by thermal desorption spectrometry (TDS) and neutron diffraction measurements that the hydrogen taken up by the nanocomposites exists in at least two states; the one is the hydrogen strongly associated with the carbon component and the other the hydride in the magnesium component. The ball milling resulted in the generation of large amounts of dangling carbon bonds in graphite, which acted as active sites to take up the hydrogen. When D 2 gas was brought into contact with such composites, the isotope exchange reaction with the hydrogen in the magnesium hydride occurred at 453 K, and not with the hydrogen associated with the carbon. The properties of such hydrogen taken up were also discussed from the standpoint of isotope effects.