Diamond Core Research Articles

Highly Conductive Diamond-Graphite Nanohybrid Films with Enhanced Electron Field Emission and Microplasma Illumination Properties.

Bias-enhanced nucleation and growth of diamond-graphite nanohybrid (DGH) films on silicon substrates by microwave plasma enhanced chemical vapor deposition using CH4/N2 gas mixture is reported herein. It is observed that by controlling the growth time, the microstructure of the DGH films and, thus, the electrical conductivity and the electron field emission (EFE) properties of the films can be manipulated. The films grown for 30 min (DGHB30) possess needle-like geometry, which comprised of a diamond core encased in a sheath of sp(2)-bonded graphitic phase. These films achieved high conductivity of σ = 900 S/cm and superior EFE properties, namely, low turn-on field of 2.9 V/μm and high EFE current density of 3.8 mA/cm(2) at an applied field of 6.0 V/μm. On increasing the growth time to 60 min (the DGHB60), the acicular grain growth ceased and formed nanographite clusters or defective diamond clusters (n-diamond). Even though DGHB60 films possess higher electrical conductivity (σ = 1549 S/cm) than the DGHB30 films, the EFE properties degraded. The implication of this result is that higher conductivity by itself does not guarantee better EFE properties. The nanosized diamond grains with needle-like geometry are the most promising ones for the electron emission, exclusively when they are encased in graphene-like layers. The salient feature of such materials with unique granular structure is that their conductivity and EFE properties can be tuned in a wide range, which makes them especially useful in practical applications.

A Heterodinuclear FeIIIZnII Complex as a Mimic for Purple Acid Phosphatase with Site‐Specific ZnII Binding

AbstractPurple acid phosphatases (PAPs) are the only dinuclear metallohydrolases for which the necessity for a heterovalent active site (FeIII–MII; M = Fe, Zn or Mn) for catalysis has been established. A major goal for the synthesis of PAP biomimetics is to design a ligand in which the two coordination sites exhibit discrimination between the trivalent and divalent metal ions. With this goal in mind the ligand 2‐{[bis(2‐methoxyethyl)amino]methyl}‐6‐{[(2‐hydroxybenzyl)(2‐pyridylmethyl)amino]methyl}‐4‐methylphenol (BMMHPH2), with two distinct coordination sites, N2O2 (α) and NO3 (β), has been prepared. Although not exactly mimicking the active site of PAP, the ligand facilitated the formation of the complex [FeIIIZnII(BMMHP)(CH3COO)2](BPh4), which exhibited regioselectivity in the two metal binding sites. The phosphoesterase‐like activity of the complex in 50:50 acetonitrile/water was investigated by using the substrate bis(2,4‐dinitrophenyl) phosphate (BDNPP) yielding kinetically relevant pKa values of 6.89, 7.37 and 9.00, a KM of 10.8 ± 2.1 mM and a kcat of 3.20 ± 0.38 × 10–3 s–1 (at pH = 7.5). Attempts to prepare a diiron analogue resulted in a centrosymmetric dimer, [FeIII2(BMMHPH)2(μ‐OH)2](BPh4)2, with one six‐coordinate FeIII atom in each of the α‐sites, connected by two μ‐hydroxido groups. In this Fe(μ‐OH)2Fe diamond core the FeIII ions are weakly antiferromagnetically coupled, with J = –1.76 ± 0.03 cm–1. The β‐sites were vacant. Attempts to replace the ZnII ion with MgII resulted in the formation of a centrosymmetric trimer, i.e. [FeIII2MgII(BMMHPH)2(CH3COO)2(CH3O)2](BPh4)2.

Structure of the key species in the enzymatic oxidation of methane to methanol.

Methane monooxygenase (MMO) catalyses the O2-dependent conversion of methane to methanol in methanotrophic bacteria, thereby preventing the atmospheric egress of approximately one billion tons of this potent greenhouse gas annually. The key reaction cycle intermediate of the soluble form of MMO (sMMO) is termed compound Q (Q). Q contains a unique dinuclear Fe(IV) cluster that reacts with methane to break an exceptionally strong 105kcalmol(-1) C-H bond and insert one oxygen atom. No other biological oxidant, except that found in the particulate form of MMO, is capable of such catalysis. The structure of Q remains controversial despite numerous spectroscopic, computational and synthetic model studies. A definitive structural assignment can be made from resonance Raman vibrational spectroscopy but, despite efforts over the past two decades, no vibrational spectrum of Q has yet been obtained. Here we report the core structures of Q and the following product complex, compound T, using time-resolved resonance Raman spectroscopy (TR(3)). TR(3) permits fingerprinting of intermediates by their unique vibrational signatures through extended signal averaging for short-lived species. We report unambiguous evidence that Q possesses a bis-μ-oxo diamond core structure and show that both bridging oxygens originate from O2. This observation strongly supports a homolytic mechanism for O-O bond cleavage. We also show that T retains a single oxygen atom from O2 as a bridging ligand, while the other oxygen atom is incorporated into the product. Capture of the extreme oxidizing potential of Q is of great contemporary interest for bioremediation and the development of synthetic approaches to methane-based alternative fuels and chemical industry feedstocks. Insight into the formation and reactivity of Q from the structure reported here is an important step towards harnessing this potential.

Transient thermal response of a highly porous ventilated brake disc

The transient thermal response of a newly developed ventilated brake disc cored with a porous medium (wire-woven bulk diamond) is compared with those of a solid brake disc and a conventionally ventilated brake disc with pin fins. The best-performing brake disc vis-à-vis the operating temperature is dependent on the duration of braking: for a short braking event, T(solid) < T(pin-finned) < T(porous); however, for extended braking T(porous) < T(pin-finned) < T(solid). These experimental results are explained in terms of the governing thermophysical parameters using a classical first-order unsteady-state differential equation. The initial rate of increase in the brake disc temperature is dominated by the thermal capacity term; hence, for a short braking event, solid discs with a large thermal capacity operate at a low temperature. However, for extended braking, ventilated discs run cooler and reach lower steady-state temperatures than solid rotors do owing to the increased convective surface area and the forced convection in the ventilated channels. With the wire-woven bulk diamond core which allows a slightly lighter disc than the conventional pin-finned disc, a substantially lower steady-state temperature can be achieved, resulting from promoted flow mixing by three-dimensional wire-woven bulk diamond ligaments which enhance convection.

Multiobjective optimization and sensitivity analysis of honeycomb sandwich cylindrical columns under axial crushing loads

This paper firstly investigates the energy absorption characteristics of honeycomb sandwich cylindrical columns such as square, triangle, kagome and diamond core under axial crushing loads by nonlinear finite element analysis. The interaction effects between the honeycomb and column walls greatly improve the energy absorption efficiency. The response surface method with cubic basis functions is employed to formulate specific energy absorption and peak crushing force which reduces considerably the computational cost of crush simulations by finite element method. Both the single objective and multiobjective optimizations are performed for columns under axial crushing load with design variables inner, outer and core thickness. Models are optimized by multiobjective particle swarm optimization algorithm to achieve maximum specific energy absorption capacity and minimum peak crushing force. Furthermore, local and global sensitivity analyses are performed to assess the effect of design variable values on the specific energy absorption and peak crushing force functions in design domain.

Comparative NEXAFS, NMR, and FTIR Study of Various-Sized Nanodiamonds: As-Prepared and Fluorinated

Various 4–50 nm in size diamond nanoparticles prepared by different synthesis methods and their fluorinated derivatives were studied by NEXAFS, solid state NMR and FTIR spectroscopy. C 1s and F 1s NEXAFS spectra of as-prepared and fluorinated nanodiamonds (NDs and F-NDs) were analyzed based on a comparison with the known ones of reference compounds (graphitized carbon nanodiscs, phenol and amino acid molecules, graphite oxide and monofluoride). It has been found that all the studied diamond nanoparticles have crystalline diamond cores and their surfaces are covered with graphite-like carbon clusters. These clusters are partially amorphized and oxidized with the formation of functional groups C–OH, C═O, or O═C–OH and the properties of these surface shells depend on the synthesis method of nanodiamonds. The fluorination of diamond nanoparticles has a purely superficial character; it almost completely cleans the NDs particles from carbon clusters and saturates dangling bonds on the surface of the diamond nanoparticles with F atoms forming covalent σ(C–F) bonds. NEXAFS data are further supported by NMR and FTIR spectroscopy, leading to similar conclusions concerning the properties of various NDs and the chemical bonding between C and F atoms in F-NDs. A combination of NEXAFS, solid state NMR and FTIR spectroscopy is demonstrated to be very efficient in investigating various NDs and their functionalized derivatives.

Characterization of the structure of ultradispersed diamond using X-ray diffractometry and small-angle X-ray scattering

Two samples of detonation-synthesized ultradispersed diamond have been studied using X-ray diffractometry and small-angle X-ray scattering. It has been shown based on the X-ray diffractometry data that two samples contain regions with both the diamond and graphite-like lattices. Grain radii inside both samples are evaluated from the small-angle scattering data as 30–50 nm. The samples also contain low-dimensional components. A broad Bragg peak corresponding to a set of interplanar distances from 5 to 15 nm is revealed in the small-angle scattering curve of sample no. 1. A structural model of ultradispersed diamond particles, which represents the diamond core surrounded by concentric graphite shells similar to the onionskin, is confirmed.

Dioxygen activation by siloxide complexes of chromium(II) and chromium(IV).

The reaction of a tripodal trisilanol with n-butyllithium and CrCl2 results in a dinuclear Cr(II) complex (1), which is capable of cleaving O2 to yield in a unique complex (2) with an asymmetric diamond core composed of two Cr(IV) O units. Magnetic susceptibility data reveal significant exchange coupling of Cr(II) (S=2) in 1 and large zero-field splitting for Cr(IV) (S=1) in 2 owing to strong spin-orbit coupling of the ground state. The Cr(IV) O compound can also be generated using PhIO, and evidence was gathered that although it is the stable product isolated after excessive O2 treatment, it further activates O2 to yield an intermediate species that oxidizes THF or Me-THF. By extensive (18) O labeling studies we were able to show, that in the course of this process (18) O2 exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands.

Dioxygen Activation by Siloxide Complexes of Chromium(II) and Chromium(IV)

The reaction of a tripodal trisilanol with n-butyllithium and CrCl2 results in a dinuclear CrII complex (1), which is capable of cleaving O2 to yield in a unique complex (2) with an asymmetric diamond core composed of two CrIVO units. Magnetic susceptibility data reveal significant exchange coupling of CrII (S=2) in 1 and large zero-field splitting for CrIV (S=1) in 2 owing to strong spin–orbit coupling of the ground state. The CrIVO compound can also be generated using PhIO, and evidence was gathered that although it is the stable product isolated after excessive O2 treatment, it further activates O2 to yield an intermediate species that oxidizes THF or Me-THF. By extensive 18O labeling studies we were able to show, that in the course of this process 18O2 exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands.

Fabrication of Nitrogen-Modified Annealed Nanodiamond with Improved Catalytic Activity

Annealed ultradispersed nanodiamond (ADD) with sp(2) curved concentric graphitic shells is an interesting hybrid material consisting of the remarkable surface properties of graphene-based nanomaterials and the intrinsic properties of a diamond core. In this case, based on its specific properties and surface oxygen functional groups, nitrogen-modified ADD powders have been tunably synthesized via three different preparation methods in a calcination treatment process. The detailed formation and dynamic behaviors of the nitrogen species on the modified ADD during the preparation process are revealed by elemental analysis, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption. Moreover, we study the catalytic performance on the metal-free nitrogen-modified ADD catalysts by means of selective oxidation of benzylic alcohols as a probe reaction. The results indicate that the modified ADD catalysts exhibit a higher catalytic activity than pristine ADD. By correlating XPS data with catalytic measurements, we conclude that the pyridinic nitrogen species plays a pivotal role in the catalytic reaction. Our work provides valuable information on the design of modified carbon materials with more excellent properties.

Experimental studies on drilling tool load and machining quality of C/SiC composites in rotary ultrasonic machining

Carbon fiber reinforced silicon carbide matrix (C/SiC) composites have great potential in space applications because of their excellent properties such as low density, superior wear resistance and high temperature resistance. However, the use of C/SiC has been hindered seriously because of its poor machining characteristics. With an objective to improve the machining process of C/SiC composites, rotary ultrasonic machining (RUM) and conventional drilling (CD) tests with a diamond core drill were conducted. The effects of ultrasonic vibration on mechanical load and machining quality were studied by comparing the drilling force, torque, quality of holes exit and surface roughness of drilled holes between the two processes. The results showed that the drilling force and torque for RUM were reduced by 23% and 47.6%, respectively of those for CD. In addition, the reduction in drilling force and torque decreased gradually with increasing spindle speed, while they changed slightly with increasing feed rate. Under identical conditions, RUM gave better holes exit than CD. Moreover, because of the lower lamellar brittle fracture and pit originating from carbon fibers fracture, the roughness of surface of drilled holes obtained with RUM was lower than CD and the maximum reduction was 23%.

Molecular and electronic structure of dinuclear uranium bis-μ-oxo complexes with diamond core structural motifs.

In a multiple-bond metathesis reaction, the triazacyclononane (tacn)-anchored methyl- and neopentyl (nP)-substituted tris(aryloxide) U(III) complex [(((nP,Me)ArO)3tacn)U(III)] (1) reacts with mesityl azide and CO2 to form mesityl isocyanate and the dinuclear bis(μ-oxo)-bridged U(V)/U(V) complex [{(((nP,Me)ArO)3tacn)U(V)}2(μ-O)2] (3). This reaction proceeds via the mononuclear U(V) imido intermediate [(((nP,Me)ArO)3tacn)U(V)(NMes)] (2), which has been synthesized and fully characterized independently. The dimeric U(V) oxo species shows rich redox behavior: complex 3 can be reduced by one and two electrons, respectively, yielding the mixed-valent U(IV)/U(V) bis(μ-oxo) complex [K(crypt)][{(((nP,Me)ArO)3tacn)U(IV/V)}2(μ-O)2] (7) and the U(IV)/U(IV) bis(μ-oxo) complex K2[{(((nP,Me)ArO)3tacn)U(IV)}2(μ-O)2] (6). In addition, complex 3 can be oxidized to provide the mononuclear uranium(VI) oxo complexes [(((nP,Me)ArO)3tacn)U(VI)(O)eq(OTf)ax] (8) and [(((nP,Me)ArO)3tacn)U(VI)(O)eq]SbF6 (9). The unique series of bis(μ-oxo) complexes also shows notable magnetic behavior, which was investigated in detail by UV/vis/NIR and EPR spectroscopy as well as SQUID magnetization studies. In order to understand possible magnetic exchange phenomena, the mononuclear terminal oxo complexes [(((nP,Me)ArO)3tacn)U(V)(O)(O-pyridine)] (4) and [(((nP,Me)ArO)3tacn)U(V)(O)(O-NMe3)] (5) were synthesized and fully characterized. The magnetic study revealed an unusually strong antiferromagnetic exchange coupling between the two U(V) ions in 3. Examination of the (18)O-labeled bis(μ-oxo)-bridged dinuclear complexes 3, 6, and 7 allowed for the first time the unambiguous assignment of the vibrational signature of the [U(μ-O)2U] diamond core structural motif.

Experimental Research on Temperature of Drilling CFRP with Brazed Diamond Core Drill

During the drilling process of CFRP laminate with brazed diamond core drill, drilling temperature is very important to the drilling CFRP with brazed diamond core drill, which will influence the tolerance, defects of CFRP. In drilling experiments of CFRP laminate, the temperatures under different cutting parameters were measured by an infrared camera, and the effects of drilling parameters on drilling temperature were analyzed and the influence of grits distribution on temperatures were also studied. The results shown the drilling temperatures rise while increasing density of grits, grinding speed, and decreasing feeding speed.

Design of a Downhole Motor Drilling Experimental System

In order to research the technology of impregnated diamond core bit and turbodrill which can be applied to the oil and geological field, this paper here designed a set of downhole motor drilling experimental system. We built a virtual prototype simulation model by using Solid Works which can help us dynamically design and optimize the key components and the overall structure of the whole system. In this paper, virtual assembly is available to assess the feasibility of the overall design. While the model simplification and the simulation check of the key components were carried out. Finally, we will be able to verify the correctness of the virtual prototype simulation analysis by setting up a physical prototype.

Development of a Rotary Drilling Mechanism for Impregnated Diamond Bits

Impregnated diamond core bits are often used in core drilling for geological surveys. A tri-state theory is proposed to describe the three states in drilling processes for a diamond particle or a bit. These states are contacting state, cutting state, and ploughing state. Furthermore, the relations among thrust and other mechanical parameters are also summarized. The optimal value of the specific energy is in the cutting state. Several experiment results verified the proposed model. This mechanism is useful for selecting operation parameters in core drilling using impregnated diamond core bits.

Hybrid Nanocarbon as a Catalyst for Direct Dehydrogenation of Propane: Formation of an Active and Selective Core–Shell sp2/sp3Nanocomposite Structure

Hybrid nanocarbon, comprised of a diamond core and a graphitic shell with a variable sp(2)-/sp(3)-carbon ratio, is controllably obtained through sequential annealing treatment (550-1300 °C) of nanodiamond. The formation of sp(2) carbon increases with annealing temperature and the nanodiamond surface is reconstructed from amorphous into a well-ordered, onion-like carbon structure via an intermediate composite structure--a diamond core covered by a defective, curved graphene outer shell. Direct dehydrogenation of propane shows that the sp(2)-/sp(3)-nanocomposite exhibits superior catalytic performance to that of individual nanodiamond and graphitic nanocarbon. The optimum catalytic activity of the diamond/graphene composite depends on the maximum structural defectiveness and high chemical reactivity of the ketone groups. Ketone-type functional groups anchored on the defects/vacancies are active for propene formation; nevertheless, once the oxygen functional groups are desorbed, the defects/vacancies alone might be active sites responsible for the C-H bond activation of propane.

Acoustic emission analysis for rock–bit interactions in impregnated diamond core drilling

Our goal was to determine the relationship between acoustic emission (AE) signals and diamond drill bit wear in order to gather and interpret data to allow overall improvement of drilling performance. Achieving improved performance required investigating various drilling parameters to understand the characteristics of the AE signals in terms of their interaction with the operational parameters of the drilling apparatus. Echidna drill apparatus that simulates field exploration diamond drilling on a small scale was used to monitor AEs during rock–bit interaction. AE sensors were attached to both the drill and the rock in question to record acoustic signals being emitted during the process of drilling. Two different types of tests were conducted – step tests and wear tests. Step tests on the Echidna drill included stepping down the depth of cut from 130µm to 0µm, while the cutting speed remained constant. Wear tests, again using the Echidna drill, involved accelerating the wear rate of the drill bit by using it to cut highly abrasive rock in two different ways. Based on the step test results, a series of linear relationships were developed. These relationships make it possible to estimate the depth of cut, weight on the bit (WOB) and torque on the bit (TOB) by simply using the time spectrum of the AE signals. Wear tests also showed that AE amplitudes start to trend down as wear begins to accelerate.

Critical analysis of successful gold exploration methods

To assess common factors and the key exploration methods in gold discovery we analyse 154 case studies of successful gold exploration. Our aim is to highlight what may help find gold in the future. The case studies used here are only those documented in the consistent series of biennial volumes of New Generation Gold from 1995 to 2013. Surface and near surface sampling dominate early phases of exploration. Subsequently, as a second and third priority drilling, initially rotary air blast or air-core and then reverse circulation and diamond core drilling dominate exploration. The priority order of methods is more or less the order of access from surface. However, some discoveries document reverse circulation or diamond core drilling as the first and primary method suggesting success by bold targeting and early drilling. Gold has no direct recognisable geophysical signature but geophysics is used as an indirect tool to model the geology and weathering. Geophysical methods, be they magnetic or electrical methods, maintain a similar level of interest throughout programmes. Alteration science is recorded as a method in only 13% of discoveries, a comment that may seem at odds with the modern focus on hyperspectral mapping and logging. Similarly and despite being unambiguously the principal control on gold mineralisation, structure is recorded as of use in only 53% of discoveries, usually a 3rd or 4th priority. Of the case studies, 16% make no mention of structure at all. It is surprising that when surface outcrop is available, structural geology is rarely documented as an exploration method. The low levels of reporting of the intellectual activities of alteration and structural geology (and to a lesser extent mapping and geophysics) suggests they are (i) under-reported or, (ii) that current science is inadequate (this is unlikely) or, (iii) they are under-utilised. If under-reported, are the senior managers and directors who wrote these papers aware of the intellectual effort of their teams? Alternatively if under-used, alteration and structure may represent a significant opportunity for the next generation of exploration.

Flexible electron field emitters fabricated using conducting ultrananocrystalline diamond pyramidal microtips on polynorbornene films

High performance flexible field emitters made of aligned pyramidal shaped conducting ultrananocrystalline diamond (C-UNCD) microtips on polynorbornene substrates is demonstrated. Flexible C-UNCD pyramidal microtips show a low turn-on field of 1.80 V/μm with a field enhancement factor of 4580 and a high emission current density of 5.8 mA/cm2 (at an applied field of 4.20 V/μm) with life-time stability of 210 min. Such an enhancement in the field emission is due to the presence of sp2-graphitic sheath with a nanowire-like diamond core. This high performance flexible C-UNCD field emitter is potentially useful for the fabrication of diverse, flexible electronic devices.

Comparison of drill wear mechanism between rotary ultrasonic elliptical machining and conventional drilling of CFRP

Carbon fiber-reinforced plastic (CFRP) is widely used as aircraft structural components for its superior mechanical and physical properties. Meanwhile, the rotary ultrasonic elliptical machining (RUEM), as a new drilling method in which an elliptical ultrasonic vibration is imposed on the end of the drill, can reduce tool wear effectively. In this paper, we firstly presented an investigation on the wear mechanism of diamond core drill in RUEM of CFRP in comparison with the conventional drilling (CD). A series of drilling experiments were performed including the drilling force measurement, the observation of drill topographies, and machined hole surface. The experiment results indicated that the drill performance in RUEM of CFRP was improved significantly in comparison with that in CD. Because the length of steady region rised by 39% and the tool life increased by 28% in RUEM than those in CD, respectively. With the observation of drill surface under a microscope, it was validated that less chip adhesion and more grain micro-fracture appeared in RUEM, which had a positive effect on the better drilling performance, such as lower drilling force, smoother hole surface.