Diamond Fibers Research Articles

Diamond fibers for efficient electrocatalytic degradation of environmental pollutants

The efficient electrocatalytic degradation of environmental pollutants requires an electrode with a large surface area, high electrocatalytic activities, long-term stability, and a low cost. Herein, the diamond fibers (DFs) are synthesized by overgrowing the cost-effective carbon fibers as the core with a uniform boron dopped diamond (BDD) film as a shell. Since these fibrous core/shell-like DFs combine both features of BDD and carbon fiber, they are utilized as the electrode for the efficient electrocatalytic degradation of environmental pollutants. The DFs exhibit a 5.2-fold larger surface area and a 6.8-fold higher peak current density than those of a planar BDD electrode. Methyl orange is degraded below the limit of detection within 1.5 h using these DFs, while the degradation fraction using a planar BDD electrode is only 22%. For other various organic pollutants, these DFs exhibit excellent degradation capacity. Such a high performance of electrocatalytic degradation of these environmental pollutants originates from increased surface areas and active sites by the three-dimensional fibrous structure as well as the decreased charge-transfer resistance by the core/shell structure. These DFs are thus promising as a new electrode material or an electrocatalyst for various catalytic applications in the environmental and energy fields.

Flexible Diamond Fibers for High‐Energy‐Density Zinc‐Ion Supercapacitors

AbstractSupercapacitors supply high power densities but suffer from low energy densities and small specific capacitances. The design and implementation of unique capacitor electrodes are expected to overcome these challenges. Herein, flexible diamond fibers (a fibrous core/shell structure of diamond/carbon fibers) are produced through overgrowing conductive carbon fibers core with a thin boron‐doped diamond film as a shell using a chemical vapor deposition technique. The resultant fibers combine the properties of boron‐doped diamond with those of carbon fibers. This allows these binder‐free diamond fibers to be employed as the positive electrode in the fabrication of zinc‐ion supercapacitors. Together with a negative electrode fabricated from zinc nanosheet coated diamond fibers, this diamond supercapacitor delivers a high and stable specific capacitance. More importantly, it delivers high gravimetric and volumetric energy and power densities, even under severe bending states. The performance of this flexible supercapacitor is superior to previous diamond and carbon fiber‐based supercapacitors. Such flexible diamond supercapacitors are promising energy storage devices for various flexible electronics.

Pseudo-topotactic growth of diamond nanofibers

We report pseudo-topotactic growth of single-crystal diamond fibers by nanosecond laser melting of amorphous carbon nanofibers (CNFs) and crystalline multi-wall carbon nanotubes (MWCNTs). A rapid laser melting in a super undercooled state and subsequent quenching convert the tips of CNFs and MWCNTs into phase-pure <110> nanodiamonds along the growth directions. Subsequent laser pluses melt regions below <110> nanodiamonds that provide seeds for epitaxial growth. By repeating this process, the length of <110> nanodiamond fibers can be increased, as each pulse results in ∼50 nm nanodiamond region, depending upon the initial size of CNFs and MWCTs. This conversion process can be carried at ambient temperature and pressure in air. The epitaxial nature of <110> nanodiamond fibers has been confirmed by systematic electron-back-scatter-diffraction studies along the fiber in high-resolution scanning electron microscopy, and high-resolution TEM imaging and diffraction. The nature of C–C bonding characteristics was studied by high-resolution electron-energy-loss spectroscopy to establish the formation of diamond phase by the characteristic peak at 292 eV for sp3 bonding (σ∗), and absence of 284 eV peak for sp2 (π∗) graphitic bonding. The characteristic diamond Raman peak at 1332 cm−1 is found to downshift to 1321 cm−1 because of phonon confinement in nanodiamonds associated with nanofibers. These nanodiamond structures can be doped with both n- and p-type dopants with concentrations far higher than thermodynamic solubility limit due to solute trapping during quenching from the liquid phase. Thus, these nanodiamond structures provide ideal platform for nanosensing, computing and communication, including efficient field emitting devices.

Direct conversion of carbon nanofibers and nanotubes into diamond nanofibers and the subsequent growth of large-sized diamonds.

We report a pulsed laser annealing method to convert carbon fibers and nanotubes into diamond fibers at ambient temperature and pressure in air. The conversion of carbon nanofibers and nanotubes into diamond nanofibers involves melting in a super undercooled state using nanosecond laser pulses, and quenching rapidly to convert into phase-pure diamond. The conversion process occurs at ambient temperature and pressure, and can be carried out in air. The structure of diamond fibers has been confirmed by selected-area electron diffraction in transmission electron microscopy, electron-back-scatter-diffraction in high-resolution scanning electron microscopy, all showing characteristic diffraction lines for the diamond structure. The bonding characteristics were determined by Raman spectroscopy with a strong peak near 1332 cm-1, and high-resolution electron-energy-loss spectroscopy in transmission electron microscopy with a characteristic peak at 292 eV for σ* for sp3 bonding and the absence of π* for sp2 bonding. The Raman peak at 1332 cm-1 downshifts to 1321 cm-1 for diamond nanofibers due to the phonon confinement in nanodiamonds. These laser-treated carbon fibers with diamond seeds are used to grow larger diamond crystallites further by using standard hot-filament chemical vapor deposition (HFCVD). We compare these results with those obtained without laser treating the carbon fibers. The details of diamond conversion and HFCVD growth are presented in this paper.

Fabrication, Microstructure, Thermal and Electrical Properties of Copper Heat Sink Composites

Copper as well as copper base composites reinforced with coated and uncoated 1 wt% diamond, graphite particles or short carbon fibers are prepared by powder metallurgy process. The reinforcement particles were encapsulated with silver as well as copper layer by using the electroless deposition technique to investigate the influence of the reinforcement surface coating on the microstructure, density, electrical and thermal properties of the sintered samples. The coated and the uncoated powders were cold compacted at 600 MPa, and then sintered at 1173 K (900°C) for 2 h under hydrogen atmosphere. The phase composition, morphology and microstructure of the prepared powders as well as the copper base sintered composites were investigated using X-ray diffraction analysis (XRD) and Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS) respectively. The density of the sintered composites was measured by Archimedes method. The copper base consolidated composites had a density up to 96% and the reinforcement coated particles were distributed uniformly within the copper matrix better than the uncoated one. The electrical resistivity at room temperature and the heat transfer conduction of the produced samples were measured in a temperature range between 323 K (50°C) and 393 K (120°C). The results observed that the sintered materials prepared from the coated powder have lower electrical resistivity than the sintered materials prepared from the mixed powders. On the other hand the thermal conductivity values were calculated using the heat transfer conduction values by means of the Fourier formula. The results observed that the thermal conductivity of copper is (391 W/m·K), 1 wt% diamond/Cu is (408 W/m·K), 1 wt% graphite coated silver/Cu is (393 W/m·K), 1 wt% Cu coated short carbon fiber/Cu is (393 W/m·K), graphite/Cu is (383 W/m·K) and short carbon fiber/Cu is (382 W/m·K). The obtained composites are expected to be suitable for heat sink applications. The heat transfer testing experiments were done. The forced convection of the present work was done and compared with the previous work in the literature, and satisfactory agreement was achieved.

Study on Preparation and Cutting Performance of a New Diamond Grinding Fiber

A new kind of diamond fiber with a certain length to diameter ratio and macroscopic dimensions(1mm×1mm×10mm)by powder injection molding and buried sand sintering method is designed and obtained. The new diamond fiber uses the Na2O-Al2O3-B2O3-SiO2 system ceramics adding a certain amount of iron group metal Co as the diamond abrasive ceramic-metal bond. Different from the traditional diamond grits, this new kind fiber has orderly arrangement in accordance with the requirements and can prepare ordered diamond fiber grinding wheel. Then the flexural strength, hardness and other properties of the diamond fiber are measured, and the contrast test between single diamond fiber specimen and normal ceramic wheel processed ultrahard material SiC enhanced high silicon aluminum alloy is conducted. The results shows that the new diamond fiber prepared has a certain strength and hardness; ceramic-metal bond in the new fiber gives better wet-ability and stronger holding force to the diamond abrasive particle and makes it difficult to fall off; meanwhile, the new diamond fiber has good processing performance and the workpiece has good surface quality, which can achieve precise machining SiC enhanced high silicon aluminum alloy. Effective diamond abrasive particles have a high percentage in the new diamond fibers, and the distribution is uniform. The abrasive particles have a good quality of high uniformity of protrusion height, and have a high utilization with large amount of abrasive particle participated in cutting. Diamond in the diamond fibers realizes three-dimensional arrangement, which means that the lower diamond can continue to play its cutting ability when the upper abrasive loses cutting ability or falls off due to bearing greater friction and extrusion pressure.

Research on Grinding Temperature of a New Diamond Grinding Wheel

It is aimed at developing a new diamond wheel in order to overcome the shortages of traditional grinding wheel, such as the abrasive easily fall off the grinding wheel prematurely, high grinding temperature, random grits distribution and the loading problems become more severe in grinding process. And further study on the grinding temperature of the new diamond wheel prepared in comparison with traditional resin-bonded diamond grinding wheel in machining Al2O3 ceramic. The prepared new diamond wheel has many diamond fibers involved in grinding process which are artificially ordered, diamond grits are not easily fall off, and it has big chip-pocket space and heat dissipating capability. The experimental results indicated that the grinding temperature of the new diamond wheel in comparison with the conventional diamond wheel under the same conditions was decreased by 80°C-120°C.

Machining Mechanism of Diamond Fibers Cutter

A novel diamond fibers cutter was proposed in this paper for machining of advanced materials. The fibers cutter was prepared by artificially distributing and orientating a large number of diamond fibers, which were prepared by cutting polycrystalline diamond into size of 0.4mm*0.6mm*10mm using Nd:YAG laser, and then lapped on a lapping machine to form sharpened cutting edges. To investigate the machining mechanism of the diamond fibers cutter, an experiment on machining of aluminum alloy reinforced by SiC particles and nano-structured WC/Co coating was conducted in this paper. Based on the surface observation and the cutting force analysis, it could be found that the diamond fibers cutter combined the advantages of conventional wheels and cutting tools, and was fit for machining of both brittle materials and soft materials.

Synthesis and Field Emission Properties of Ultra-Nanocrystalline Diamond Fibers and Helices

We propose a novel template method for large scale synthesis of Ultra-Nanocrystalline Diamond (UNCD) fibres and helices with lengths of thousands of microns and diameters ranging from 0.5 to 5 microm: (i) Large quantities of submicrometer- or nanometer-diameter silica (a-SiO2) nanostructures, with lengths in the order of 2 to 4 mm, were synthesized by Vapor-Liquid-Solid (VLS) method; (ii) UNCD coating of as-synthesized a-SiO2 micro- or nanonanostructures by Microwave Plasma Chemical Vapour Deposition (MPCVD) technique in hydrogen-deficient condition. Electron Field Emission (EFE) of as-synthesized UNCD structures was observed with a threshold field of 3.4 V/microm. These micro- or nanostructures may find potential applications in high power electronics, vertical field-effect transistors in vacuum electronics, heat sinks in microelectronics and structural materials in Micro- and Nano-Electro-Mechanical Systems (MEMS/NEMS). The successful preparation of various types of UNCD structures suggests that this templating process can be used for a wide range of materials.

Microstructure and electron field emission study of diamond nanorod decorated a-SiO 2 nanowires by microwave Ar–CH 4/H 2 plasma chemical vapor deposition with addition of N 2

In our recent paper [M. K. Singh et al., Chem. Mater. 20 (2008) 1725], we reported the fabrication of Nanocrystalline diamond (NCD) fibers by template ( a-SiO 2 nanowires) technique. Our present work demonstrate that the addition of nitrogen of 20% by volume in the reaction gas during synthesis induce the formation of feather-like morphology of NCD on a-SiO 2 nanowires. The feather-like morphology consists oriented diamond nanorods surrounded by an sp 2-bonded carbon sheath. These have been characterized by Scanning Electron Microscopy, Transmission Electron Microscopy (high-resolution mode) and Micro-Raman spectroscopy. Electron field emission (EFE) of as-synthesized NCD fibers (with 20% N 2 addition) was observed with a threshold field of 3.5 V/µm which is quite less in comparison to previous grown NCD fibers and the current density at 10 V/µm increases around 20 times with 20% nitrogen doping in the gas source during synthesis. This may be because each diamond nanorod is enveloped in a sheath of sp 2-bonded nanocarbons which provides a conducting path for electron emission.

Novel Two-Step Method for Synthesis of High-Density Nanocrystalline Diamond Fibers

We report a novel two-step method for the fabrication of high-density nanocrystalline diamond (NCD) fibers with lengths of 50–100 µm and diameters of 1–5 µm. This method includes the synthesis of t...

Field emission from cleaved diamond fibers

Diamond fibers 100–200 μm in diameter were investigated as electron emitters. Uniform, straight boron doped fibers were grown on tungsten and sapphire fiber cores. The field emitting surface was created by mechanically cleaving the polycrystalline fiber perpendicular to the fiber axis, a procedure in which it was assumed the necessary morphology would be present for field emission. Other than cleaving, no other special surface or bulk treatments were employed. Voltage dependence and noise power spectral density (PSD) measurements were carried out on the field emission current. A subset of the diamond coated sapphire fibers exhibited electron emission at a factor of 5 reduction in the applied field as compared to the tungsten core fibers. Within experimental error, the PSD exhibited a f −1.5 dependence on frequency.

Diamond tubes and fibers

Diamond-coated fibers, diamond tubes, and diamond fibers were produced using a hot-filament-assisted chemical vapor deposition process. Diamond coatings were deposited on prepared fiber substrates of silicon carbide, copper, tungsten, and copper-coated graphite. Diamond tubes were produced in situ as a result of the removal of the substrate by atomic hydrogen or after deposition by dissolving the substrate using a chemical etch. Diamond fibers in the shape of a half-cylinder were produced by masking a portion of the substrate fiber and removing the diamond after deposition. The diamond tubes and fibers that have been produced are typically 2–3 cm in length and are self-supporting structures.

Diamond fibers for thermal energy management

Properties of paramount importance in thermal management are thermal conductivity and the coefficient of thermal expansion (CTE). The use of carbon fibers has led to significant improvements in the properties of composites of various polymeric, metal and ceramic matrices, but anisotropy of the thermal conductivity and CTE in high thermal conductivity graphitic fibers is a limiting factor. In order to tailor the thermophysical properties of composites, new fibers with isotropic thermophysical properties are required. This research addresses the development of diamond fibers, which have the highest thermal conductivity of any material found in nature, a near-isotropic thermal conductivity and a CTE nearly matching that of semiconductor materials. Both single- crystal and polycrystalline diamond fibers were attempted. For the polycrystalline diamond fibers, Raman and scanning electron microscopy analyses show that diamond coatings were successfully applied toa graphitic fiber substrate. Also, some evidence supports the feasibility of single-crystal diamond fiber formation.