Nanoscale Carbon Particles Research Articles

Predicting the Number of Graphene-Like Layers on Surface for Commercial Fumed Nanodiamonds with Raman Spectra and Model Calculations.

Nanoscale carbon materials have a broad range of applications in the field of surface and material sciences. Each vibration mode of a Raman and Fourier transform infrared (FT-IR) spectra corresponds to a specific frequency of a bond in the core and surface of the crystal, thus it is highly sensitive to morphology, implying that every band is sensitive to the orientation of the bonds and the atomic weight at either end of the bond. Accordingly, in this study we apply transmission electron microscope (TEM), Raman spectroscopies, and model calculations to study the relative content of carbon-carbon (C-C) bonds to the anhydrous and weakly aggregated elementary nanoscale carbon particles of detonation nanodiamonds. One point of the Raman bands at approximately 1300 cm-1 established that there are highly uniform C-C bonds in a tetrahedral crystal field environment not unlike that of diamonds. Another point at approximately 1600 cm-1 would be a hexagonal graphene-like sheet. By analyzing the relative content of carbon bonds using the area of intensity of the Raman peaks and a simulation of crystal morphology, we suggest that the number of graphene surface layers would be monolayers in nanodiamonds, comprising two kinds of C-C bonds, one being sp₃ bonds of diamond in the core and the other being sp₂ bonds of graphene on the surface.

Characterization of oil based nanofluid for quench medium

The choice of quench medium depends on the hardenability of the metal alloy, the thickness of the component, and the geometry of the component. Some of these will determine the cooling rate required to obtain the desired microstructure and material properties. Improper quench media will cause the material to become brittle, suffers from geometric distortion, or having a high undesirable residual stresses in the components. In heat treatment industries, oil and water are frequently used as the quench media. Recently, nanofluid as a quench medium has also been studied using several different fluids as the solvent. Examples of frequently used solvents include polymers, vegetable oils, and mineral oil. In this research, laboratory-grade carbon powder were used as nanoparticle. Oil was used as the fluid base in this research as the main observation focus. To obtain nanoscale carbon particles, planetary ball mill was used to ground laboratory grade carbon powder to decrease the particle size. This method was used to lower the cost for nanoparticle synthesis. Milling speed and duration were set at 500 rpm and 15 hours. Field Emission Scanning Electron Microscope (FE-SEM), and Energy Dispersive X-Ray (EDX) measurement were carried out to determine the particle size, material identification, particle morphology, and surface change of samples. The carbon nanoparticle content in nanofluid quench mediums for this research were varied at 0.1%, 0.2%, 0.3%, 0.4, and 0.5 % volume. Furthermore, these mediums were used to quench JIS S45C or AISI 1045 carbon steel samples which annealed at 1000°C. Hardness testing and metallography observation were then conducted to further examine the effect of different quench medium in steel samples.

Macro-structured carbon clusters for developing waterproof, breathable conductive cotton fabric

Unique macro-structured carbon clusters are used to develop cost effective conductive cotton fabric. Nanoscale carbon particles are stabilized into macro-structured carbon black/polymer composite with the help of an aqueous solution of natural rubber latex, polyvinyl alcohol and other auxiliary additives. The ‘knife-over-roll’ technique is used to apply structured carbon black composite on the plain woven cotton fabric. The lowest resistivity level achieved by this process is less than 60 ± 5.4 Ohm/cm2, which is very much promising for developing cost-effective, waterproof, and breathable conductive fabric. Waterproofness up to 95 cm water head column and breathability up to 4400 g/m2/24 h is achieved simultaneously. The major ingredients of the blend composition are optimized to achieve the lowest level of the surface resistivity for modern smart textile applications. The surface topography is characterized by FESEM & AFM, and the tomography of the composite is realized by the micro-CT scan. The two-dimensional topography reveals that single as well as aggregates of 2–9 carbon black particles are bounded by the blended matrix to form the macro-structured carbon composite. The lowest impedance of 0.5 Ohm is observed to remain stable up to the frequency of 105 Hz of AC supply voltage.

Structural transformation of carbon/carbon composites for aircraft brake pairs in the braking process

Amorphous structure discovered from both the wear debris and the friction layer of the carbon/carbon composites after the braking tests was attributed to the breakdown of crystallites in the graphitized bulk material. Graphite layers produced through interlayer shear deformation were found to be the basic units of the pyrocarbon during sliding while carbon fiber tended to be worn into small fragments along the fiber axis in the primary stage of rubbing. The transition of graphitic pyrocarbon in the friction process was described as four stages. Nano-scale carbon particles of onion-like structure were found in the fiction layer, which were likely to participate in the formation of friction layer and lubricate the friction process.

Nanodiamond gels in nonpolar media: Colloidal and rheological properties

Nanodiamonds (ND), i.e., sp3-hybridized nanoscale carbon particles, are being widely explored for biomedical applications, such as drug delivery and medical imaging, because of their biocompatibility, nontoxic nature, and ease of surface functionalization. However, little is known about the colloidal and rheological properties of ND dispersions. Here, we report a systematic study on NDs dispersed in a nonpolar liquid, mineral oil. We find that our smallest entities in dispersion are tightly bound aggregates (∼400 nm) of individual primary (∼5 nm) particles. These aggregates form colloidal gels (with frequency-independent moduli) at low particle concentrations (∼5 wt. %). Gelation is likely due to attractive interparticle forces composed of both van der Waals and hydrogen-bonding interactions. The elastic modulus (G′), yield stress (σy), and yield strain (γ0) of these colloidal gels all show scaling relationships with ND concentration, with G′ and σy exhibiting positive power-law exponents and γ0 showing a negative one. These results suggest a sample-spanning network of interconnected flocs, each of which is composed of several ND aggregates. Functionalization of ND surfaces with methacrylate groups eliminates gelation and gives a stable, low-viscosity dispersion. Much like other particulate gels, ND gels show thixotropic behavior, i.e., the gel network is disrupted by large deformations (steady or oscillatory shear) and is reformed upon cessation of shear. However, after oscillatory shear at a large strain-amplitude (1000%), the recovery is incomplete and the modulus of the recovered gel is only half its original value. In contrast, near-complete recovery of the modulus is observed after steady shear.

Carbon dots of different composition and surface functionalization: cytotoxicity issues relevant to fluorescence cell imaging

Nanoscale carbon particles have emerged as versatile precursors for a new class of highly fluorescent nanomaterials that resemble semiconductor quantum dots. The surface-passivated fluorescent carbon nanoparticles, dubbed 'carbon dots', were already demonstrated for their potential optical bioimaging applications in vitro and in vivo. In this study, we conducted a systematic cytotoxicity evaluation on the carbon dots prepared by various combinations of precursor carbon nanoparticles and molecules for the particle surface functionalization. The results suggested that the cytotoxicity of carbon dots was dependent on the selection of surface passivation molecules. Those dots showing more significant cytotoxicity at higher concentrations were also evaluated for their effects on the fluorescence imaging of live cells. The implications of the results on the eventual use of carbon dots as cell imaging agents are discussed.

Structural transformation of graphite by arc-discharge

The formation of novel structures by the passage of an electric current through graphite is described. These structures apparently consist of hollow three-dimensional graphitic shells bounded by curved and faceted planes, typically made up of two graphene layers. The curved structures were frequently decorated with nano-scale carbon particles, or short nanotubes. In some cases, nanotubes were found to be seamlessly connected to the thin shells, indicating that the formation of the shells and the nanotubes is intimately connected. Small nanotubes or nanoparticles were also sometimes found encapsulated inside the hollow structures, while fullerene-like particles were often seen attached to the outside surfaces. With their high surface areas and structural perfection, the new carbon structures may have applications as anodes of lithium ion batteries or as components of composite materials.

Nanoscale carbon particles and the stability of lipid bilayers

The transfer of various nano-scale fullerenes into lipid bilayers has been studied using all-atom (AA) and coarse-grained (CG) molecular dynamics (MD) simulations. The free energy change, when C60, C180, and C540 fullerenes are transferred from water to the interior of a lipid [dioleoylphosphatidylcholine (DOPC)] bilayer, has been calculated. Upon entering the lipid bilayer, the largest (2.4 nm diameter) fullerene causes local distortions in the bilayer surface, which were previously observed in carbon nanotube simulations. These local distortions, however, do not lead to any free energy barriers to bilayer entry. The free energy profiles confirm spontaneous absorption of all three fullerenes. Qualitative agreement was observed when comparing fullerene partitioning in water/bilayer systems to water–hexane systems. In contrast to these nonspecific single fullerene properties, extensive CG-MD simulations of fullerene rich lipid bilayers reveal substantial impact of fullerene-size on the bilayer stability. While previous CG-MD simulations indicated that bilayer bound C60 aggregates have little effect on the bilayer structure, the present MD simulations indicate that C540 aggregation has drastic effects. Specifically, the observed destabilization likely has implications for understanding the cytotoxic mechanisms of nano-carbon particles upon uptake by biological cells.

Research on the Nanoscale Additives to the Ni(OH)<sub>2</sub> Electrodes for High Power Ni/MH Batteries

As the positive electrodes of Ni/MH batteries, the Ni(OH)2 Electrodes needs some additives to enhance their high power performance. In this paper, two kinds of nanoscale additives were synthesized and added to the Ni(OH)2 electrodes respectively and the high rate discharge capabilities of both electrodes were investigated. Compared with the Ni(OH)2 electrodes with usual CoO, the electrodes with carbon nanotubes and with nanoscale carbon particles modified onto the surface of Ni(OH)2 spheres both presented much better cycling stability and higher specific capacity when discharged at high current rate. It is suggested that when the nanoscale additives were added to the electrodes, more sufficient conductive networks formed among Ni(OH)2 spheres. The results indicate that the nanoscale materials such as carbon nanotubes and nanoscale carbon particles are desirable additives for high power Ni/MH batteries in addition to usual CoO.

Bandgap‐Like Strong Fluorescence in Functionalized Carbon Nanoparticles

Quantum of solace: Fluorescent carbon dots (surface-passivated carbon nanoparticles) are developed as an alternative to classical semiconductor quantum dots. Gel column chromatography afforded carbon dots with emission yields close to 60 %. Their optical properties resemble band-gap transitions found in nanoscale semiconductors, thus suggesting that nanoscale carbon particles acquire essentially semiconductorlike characteristics.

The growth of single-walled carbon nanotubes on a silica substrate without using a metal catalyst

Single-walled carbon nanotubes (SWCNTs) have been directly grown on a SiO 2 substrate using the chemical vapor deposition (CVD) of ethanol without a catalyst. Care was taken to exclude the possibility that the SWCNT growth was induced by conventional metal catalysts such as Fe, Co and Ni resulting from the contamination. Pretreatment of the SiO 2 at 950 °C or a higher temperature in H 2 before CVD was critical for the synthesis of SWCNTs. After CVD process, nano-scale carbon particles were produced besides SWCNTs. Based on these results, we propose that the annealing of SiO 2 substrates in H 2 at high temperature generates defects on their surfaces, and these defects provide nucleation sites for the formation of carbon nanoparticles and assist the formation of carbon nanocaps, thus leading to the SWCNT growth.

Ultrathin graphitic structures and carbon nanotubes in a purified synthetic graphite

A new class of carbon structure is reported, which consists of microscale graphitic shellsbounded by curved and faceted planes containing two to five layers. These structures wereoriginally found in a commercial graphite produced by the Acheson process, followedby a purification treatment. The particles, which could be several hundreds ofnanometres in size, were frequently decorated with nanoscale carbon particles, or shortnanotubes. In some cases, nanotubes were found to be seamlessly connected to the thinshells, indicating that the formation of the shells and that of the nanotubes areintimately connected. The structures are believed to form during a purificationprocess which involves passing an electric current through the graphite in thepresence of a reactive gas. In support of this, it is shown that similar particlescan be produced in a standard carbon arc apparatus. With their extremely thingraphene walls and high surface areas, the new structures may have a range of usefulproperties.

Quantum-Sized Carbon Dots for Bright and Colorful Photoluminescence

We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.

Effect of mechanical grinding in argon and hydrogen atmosphere on microstructure of graphite

Structural transformations and amorphization of graphite upon high-energy ball-milling under argon and hydrogen atmosphere are studied. Nano-scale carbon particles were characterized by nitrogen adsorption measurements (BET surface area) and high-resolution transmission electron microscopy (HRTEM). The pore size distribution (PSD) was determined by the Dollimore-Heal analysis. Maxima on PSD curves can be attributed to nanoscale structures formed by exfoliated graphite sheets or stacks of graphite sheets. The pore volume for each kind of pores strongly depends on the milling atmosphere. In contrast to that the maximal contribution of ultra micropores to the total porosity reaches about 40 vol.% independently of the milling atmosphere.

Effect of mechanical grinding in argon and hydrogen atmosphere on microstructure of graphite

Structural transformations and amorphization of graphite upon high-energy ball-milling under argon and hydrogen atmosphere are studied. Nano-scale carbon particles were characterized by nitrogen adsorption measurements (BET surface area) and high-resolution transmission electron microscopy (HRTEM). The pore size distribution (PSD) was determined by the Dollimore–Heal analysis. Maxima on PSD curves can be attributed to nanoscale structures formed by exfoliated graphite sheets or stacks of graphite sheets. The pore volume for each kind of pores strongly depends on the milling atmosphere. In contrast to that the maximal contribution of ultra micropores to the total porosity reaches about 40 vol.% independently of the milling atmosphere.

Carbon solubility in nanostructured copper

A copper 10 at% carbon alloy was synthesised with mechanical alloying. In order to investigate the existence of a true solid solution several characterisation techniques were used, namely, X-ray diffraction, scanning electron microscopy (SEM-FEG), Raman spectroscopy and microhardness. The results obtained indicate the presence of nanoscale carbon particles, not a true solid solution.