Graphite Deposits Research Articles

Manufacture of diamond-coated cutting tools for micromachining applications

Micro- and nanomachining cutting tools are currently being developed in order to extend the range of manufacturing technologies available to the micro and nano engineer. Conventional diamond tools used for grinding operations have a number of problems associated with heterogeneity of the crystallites, decreased cutting efficiency and short life. Micromachining cutting tools are manufactured by imbedding diamond particles into the tip of the microtool using a suitable binder matrix material. The use of a diamond coating may offer an improvement in microtool technology. Chemical vapour deposition (CVD) of diamond coatings onto a cemented tungsten carbide (WC-Co) substrate is difficult. Generally, the adhesion of the diamond coating to cemented carbide substrates is poor. It is reported that binder materials such as cobalt can suppress diamond growth and enhance graphitic deposits, which cause poor adhesion and low diamond nucleation density. The effects of process parameters such as filament position, filament and substrate temperature and pretreated substrate material on the coating properties have been investigated using a number of experimental techniques.

Reductive deposition of graphite at lithological margins in East Central Vermont: a Sr, C and O isotope study

AbstractO, Sr and C isotopes from east‐central Vermont are used to provide information on the timing and volume of metamorphic fluid flow. The results are then used to assess the evidence for redox transformations between C species. Oxygen profiles are homogenised on a metre scale; comparison with Sr isotopes suggest that O alteration may have occurred over a significantly larger timescale than that of Sr, possibly because O was modified during dewatering and diagenesis in addition to the high temperature alteration recorded by strontium. Sr isotope distributions are consistent with cross‐layer fluid fluxes of 104−106 moles m−2; absolute values depend on the Sr fluid‐rock distribution coefficient which is poorly known; however, reaction progress constraints suggest that fluxes were towards the lower end of this range. High δ13C values observed at lithological boundaries cannot be explained by volume loss or closed system processes and are taken to indicate reductive precipitation of graphite as a result of mixing between CO2 and CH4‐bearing fluids. Mass balance calculations indicate that redox reactions occurring under metamorphic conditions convert a minimum of 10% of the CO2 released from limestones into graphite, thus providing a potentially important control on the average residence time of C within the crust with implications for C cycling models.

Geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock, Macraes gold mine, Otago Schist, New Zealand

The Macraes gold deposit in the Otago Schist, New Zealand, formed during late metamorphic fluid flow through a lower greenschist facies shear zone. Mineralisation occurred near to the brittle–ductile transition at about 300 °C. Large volumes of host rock in a shear zone up to 120 m thick have been hydrothermally altered by this fluid activity. Most alteration is not structurally controlled apart from proximity to the shear zone. Ductile and brittle microshears traverse the most mineralised rocks and some structural control of fluid flow occurred as well. Fluid flow was slow, similar to that in metamorphic rocks (mm/year) and diffusion through interconnected fluid was a significant chemical process. Localised extensional hydrofractures (m scale) are filled with mineralised quartz. Most alteration of the host rocks was isochemical with respect to the lithophile elements, and mineralised rocks have been variably enriched in As, Au, Sb, W, Mo and Bi, but not Co or Cd. Addition of sulphur has occurred to both host rocks and mineralised rocks, up to 1 wt.% above a background of 0.1 wt.%. Host rock sulphur is mainly pyritic and is not structurally controlled. Mineralised rocks have pyrite and arsenopyrite along microshears. Pyrite, chalcopyrite, sphalerite and galena have formed from sulphidation of silicates with no addition of metals. Graphite has been added to mineralised rocks along microshears, up to 3 wt.% locally, above a background of 0.1 wt.% noncarbonate carbon. Graphite deposition may have occurred as a result of mixing of two fluids, water+methane, and water+carbon dioxide. Graphitisation and sulphidation reactions released low δ D water, which accumulated in the slow-moving mineralising fluid. Distinction between this low δ D reaction water and meteoric water incursion is difficult.

Advanced GC/ICP-MS design for high-boiling analyte speciation and large volume solvent injection

A home made multifunctionary interface has been developed to connect a capillary gas chromatograph (GC) and an inductively coupled plasma mass spectrometer (ICP-MS). It can analyze high boiling analytes with a boiling point as high as that of C26 n-paraffin (412 °C) at only 140 °C temperature in the transfer line. The design performs splitless large volume solvent injection to analyze sensitively very low and high boiling analytes in one run. The thin and flexible transfer line is heated by a combination of hot argon mixed with the GC effluent before passing the transfer line using a T-joint in the GC oven, and by electrical resistance heating. The flow through the transferline can be reversed to eliminate the solvent peak and to prevent graphite deposition onto the ICP-MS cones after large volume splittless injection. The detection limits for organotin (the propyl derivatives of all methyl and n-butyl, mono- and di-n-octyl, and all phenyltin), range from 68–250 fg absolute and are in the pg l−1 range for 80 ml water samples extracted with 1 ml of solvent. The instrumental repeatablility is about 2% uncorrected and the linearity ranges to 5 ng absolute. This interface design is potentially useful for coupling more than one GC with one ICP-MS, for other plasma spectrometers (ICP-AES), for other types of large volume injection, and for high temperature (HT)-GC-ICP-MS.

Synthesis of C 3N 4+ by the combination of laser ablation of graphite and N 2 molecular beam

The gas phase analysis of carbon and carbon nitride ion clusters produced during pulsed laser deposition (PLD) of graphite under nitrogen molecular beam was studied. In this paper, we present the time of flight mass analysis of the ions produced within the plasma/gas interaction as a function of the ablating laser wavelength (1064, 532, 308 and 248 nm). The mass analysis shows the presence of C n + ( n≤31), C n N 2 + ( n≤8) and C 2 n+1 N 4 + ( n=0,1,2) clusters. Out of all laser wavelengths used C 3N 4 + cluster ions were most effectively formed using 532 nm laser light.

Iron layer formation during cementite decomposition in carburising atmospheres

In the following report cementite (Fe 3C) formation and subsequent decomposition is investigated on pure iron samples at 700 °C in CO–H 2–H 2O gas mixtures. The carbon activities of the atmospheres are a C=15.9 and 20, values higher than the value of the equilibrium α-Fe+Fe 3C. During the carburisation process cementite forms at the surface. Graphite deposition at the surface initiates cementite decomposition. An iron layer of 1–3 μm thickness forms between cementite and graphite as a result of cementite decomposition. In previous studies of metal dusting on iron it was found that at lower temperatures T⩽650 ° C the decomposition product iron is found in the coke as small particles.

Tribological and corrosion wear of graphite ring against Ti 6Al 4V disk in artificial sea water

Severe degradations result from the friction of two antagonists in sea water environment. It is proposed to evaluate materials resistance to wear with a tribocorrosion experimental set-up which is mechanically and electrochemically instrumented. The method is illustrated with graphite and Ti 6Al 4V. The deposition of graphite on Ti 6Al 4V samples is observed and modifies the contact characteristics. Processes of graphite wear due to mechanical effect are characterised. Observations clearly indicate that Ti 6Al 4V degradations depend on the electrochemical potential imposed and more precisely on the electrochemical conditions in the contact zone.

On the bonding structure of hydrogenated carbon nitrides grown by electron cyclotron resonance chemical vapour deposition: towards the synthesis of non-graphitic carbon nitrides

This work compares the composition and bonding structure of hydrogenated carbon nitride films (CNx:H) obtained by electron cyclotron resonance chemical vapour deposition (ECR-CVD) with those of hydrogen-free carbon nitrides (CNx) obtained by nitrogen ion beam assisted deposition (IBAD) of graphite. The composition and structure of the films was analysed by ion scattering techniques well suited to the detection of hydrogen, in addition to the more conventional infrared spectroscopy. The bonding structure was examined by X-ray absorption spectroscopy (XANES). The typical IBAD CNx films are graphitic with a N/C content below 0.3. However, the ECR-CVD films show a less graphitic bonding structure. The ECR-CVD films were synthesised in a conventional microwave ECR reactor (2.25 GHz, 875 Gauss, 250 W) using as precursor gases N2 and Ar in the reactor chamber, and CH4 directly in the deposition chamber.

Application of diamond coatings onto small dental tools

Small dental tools such as burs and drills are commonly used in dental practice and laboratory. Conventional diamond burs used for grinding operations have a number of problems associated with heterogeneity of the crystallites, decreased cutting efficiency, need for repeated sterilisation and short life. These burs are manufactured by imbedding diamond particles into the burs using a suitable binder matrix material. The use of a diamond coating may offer an improvement in dental bur technology. Chemical vapour deposition (CVD) of diamond coatings onto the cemented tungsten carbide WC–Co substrate is problematic. Generally the adhesion of diamond coating to cemented carbide substrate is poor. It is obvious that the binder materials such as cobalt can suppress diamond growth and enhance graphitic deposits, which cause poor adhesion and low diamond nucleation density. The effects of key process parameters such as filament position, filament and substrate temperature and pre-treated substrate material on the coating properties have been investigated using a variety of analytical techniques. Characterisations of the substrates and polycrystalline diamond film morphology were analysed by scanning electron microscopy (SEM). The chemical composition was evaluated by energy dispersive spectroscopy (EDS). Raman spectroscopy was used to assess the carbon-phase purity and give an indication of the stress levels in the as-grown polycrystalline diamond films.

Vein Graphite Deposits of the Kegalle District, Sri Lanka: Further Evidence for Post-Metamorphic, Fluid-Deposited Graphite

Vein Graphite Deposits of the Kegalle District, Sri Lanka: Further Evidence for Post-Metamorphic, Fluid-Deposited Graphite

Diamond growth reactor chemistry and film nucleation enhancement using chlorinated hydrocarbons

The chemistry of diamond film growth from chlorinated hydrocarbons has been investigated using a hot filament reactor coupled to an orifice sampling mass spectrometer. The relative concentrations of the species present near the growth surface have been determined as a function of filament temperature for dilute mixtures of CH 4, CH 3Cl, CH 2Cl 2 and CHCl 3 in H 2. Mass spectral analysis indicated that chlorinated hydrocarbons are sequentially dechlorinated in the presence of hydrogen at moderate reactor temperatures. A dark film was deposited on all surfaces of the reactor during studies of this dechlorination of CHCl 3. Raman analysis indicated that these deposits are small particle polycrystalline graphite. Pretreatment of a Si 〈111〉 substrate under conditions that create the graphite deposit is seen to produce a significant nucleation enhancement of diamond when followed by growth at a higher temperature. Chemical mechanisms for some of these processes are proposed.

Metallogeny, Minerogenic Series, and Gold Mineralization of the Qinling Orogen, China

The Qinling orogen extends 1650 km E-W and has a width of 95-255 km. It has a long evolutionary history of ∼3.02 Ga and a mineralization history of approximately 2.5 Ga. There are more than 400 mineral deposits of Au, Ag, Pb, Zn, Sb, Hg, Mo, W, Fe, Ni, Mn, rare elements, REE, U, V, P, As, Ba, Sr, Ti, Al, pyrite, gypsum, trona, halite, glauberite, mirabilite, blue asbestos, fluorite, rock crystal, mica, vermiculite, graphite, kyanite, andalusite, talc, fireclay, and K-feldspar in the Qinling orogen and adjacent areas. The deposits were formed in six tectono-minerogenic cycles and have been grouped into 21 regional minerogenic series. The metallogeny of the Qinling orogen is closely associated with the tectonic evolution of the orogen, and most of the ore deposits were formed in two important metallogenic periods: (1) Middle Proterozoic to Early Paleozoic, which was characterized by spreading and rifting-related minerogenetic processes; during this period, the minerogenic series are directly associated with basic-ultrabasic magmatism and marine volcanism resulting from spreading-rifting and deep faulting; (2) Mesozoic, when mineralization was controlled by intracontinental subduction and postorogenic relaxational taphrogenesis or extension; the minerogenetic series are associated with intermediate-acid magmatism and terrestrial volcanism. Gold is one of the most important ore-forming commodities in the Qinling orogen. Over 80% of those gold deposits were formed in the Mesozoic and Cenozoic and are related genetically to magmatism, terrestrial volcanism, and alluvial sedimentation. Most gold deposits in the Qinling orogenic belt are of hydrothermal origin. The Dashui-type gold deposits may be a new category of high-sulfi-dation epithermal gold deposits hosted by carbonate rocks of the Upper Paleozoic and Triassic in the southwestern part of the Qinling orogen. Shuangwangtype gold deposits in the middle of the Qinling orogen are characterized by low-grade (but large in terms of tonnage) ores hosted by brecciated and banded albitites, which are thought to have been formed by Yanshanian (late Mesozoic) magmatic-hydrothermal fluids injected into the Devonian sedimentary rocks. Carlin-type, quartz vein-type, and placer-type deposits also are important in this continental orogenic belt and adjacent areas.

Hydrothermal synthesis of multiwall carbon nanotubes

Multiwall open-end and closed carbon nanotubes with the wall thickness from several to more than 100 carbon layers were produced by a principally new method— hydrothermal synthesis—using polyethylene/water mixtures in the presence of nickel at 700–800 °C under 60–100 MPa pressure. An important feature of hydrothermal nanotubes is a small wall thickness, which is about 10% of the large inner diameter of 20–800 nm. Closed nanotubes were leak-tight by virtue of holding encapsulated water at high vacuum and can be used as test tubes for in situ experiments in transmission electron microscope (TEM). Raman microspectroscopy analysis of single nanotubes shows a well-ordered graphitic structure, in agreement with high-resolution TEM. The hydrothermal synthesis has the potential for producing multiwall nanotubes for a variety of applications. The fabrication of nanotubes under hydrothermal conditions may explain their presence in coals and carbonaceous rocks and suggests that they should be present in natural graphite deposits formed under hydrothermal conditions.

A summary of electromagnetic studies on the Abitibi-Grenville transect

Electromagnetic surveys on the Abitibi-Grenville Lithoprobe transect have elucidated a number of conductivity signatures that can be genetically linked to Precambrian tectonic processes. Some major fault zones are moderately conductive, possibly signalling graphite deposition from a mantle CO2 flux along crust-penetrating fault systems. However, conductive (graphitic) metasedimentary rocks characteristic of foreland basins are apparently absent from the transect area. A weak inverse correlation between metamorphic grade and electrical conductivity was observed by following rock units across the Grenville Front into high-grade equivalents within the parautochthonous belt. A uniformly conductive mid-crustal layer extends across the Grenville Front, apparently without change in character. The existence of this ubiquitous mid-crustal conductor has been interpreted to mean that electrical conductivity is controlled by the present-day pressure, temperature, and fluid saturation of the lower crust, independent of ancient structure, mineralogy, or metamorphic grade. Lower crustal (upper mantle?) electrical anisotropy is pervasive across the transect area. An apparent spatial correlation of conductivity anisotropy with Archean tectonic deformation patterns has been interpreted to indicate that the lithosphere has remained intact since the Neoarchean.

Accreted terranes and mineral deposits of Indochina

Indochina is an amalgamation of the Sino–Vietnam, Viet–Lao, Uttaradit, and Khorat–Kontum terranes. Mineral deposits are distributed as follows: In the Sino–Vietnam terranes, gold, iron, copper, lead–zinc, ruby, pagodite, and Permian bauxite deposits are known. Gold, tin, tungsten, phosphate, lead–zinc, skarn type iron, rare-earth minerals, pagodite, and graphite deposits are found in the Viet–Lao terrane. Gold, Tertiary bauxite, lead–zinc, copper, ruby, sapphire, tin, pagodite, phosphate, potash, and halite deposits are present in the Khorat–Kontum terrane, whereas chromium, gold, tin, and tungsten deposits occur in the Uttaradit terrane. The tectonic evolution of these terranes provides information on the distribution and origin of these deposits.

Mesoproterozoic graphite deposits, New Jersey Highlands: geologic and stable isotopic evidence for possible algal origins

Graphite deposits of Mesoproterozoic age are locally abundant in the eastern New Jersey Highlands, where they are hosted by sulphidic biotite–quartz–feldspar gneiss, metaquartzite, and anatectic pegmatite. Gneiss and metaquartzite represent a shallow marine shelf sequence of locally organic-rich sand and mud. Graphite from massive deposits within metaquartzite yielded δ13C values of –26 ± 2‰ (1σ), and graphite from massive deposits within biotite-quartz-feldspar gneiss yielded δ13C values of –23 ± 4‰. Disseminated graphite from biotite–quartz–feldspar gneiss country rock was –22 ± 3‰, indistinguishable from the massive deposits hosted by the same lithology. Anatectic pegmatite is graphitic only where generated from graphite-bearing host rocks; one sample gave a δ13C value of –15‰. The δ34S values of trace pyrrhotite are uniform within individual deposits, but vary from 0 to 9‰ from one deposit to another. Apart from pegmatitic occurrences, evidence is lacking for long-range mobilization of carbon during Grenvillian orogenesis or post-Grenvillian tectonism. The field, petrographic, and isotope data suggest that massive graphite was formed by granulite-facies metamorphism of Proterozoic accumulations of sedimentary organic matter, possibly algal mats. Preservation of these accumulations in the sedimentary environment requires anoxic basin waters or rapid burial. Anoxia would also favour the accumulation of dissolved ferrous iron in basin waters, which may explain some of the metasediment-hosted massive magnetite deposits in the New Jersey Highlands.

Mesoproterozoic graphite deposits, New Jersey Highlands: geologic and stable isotopic evidence for possible algal origins

Mesoproterozoic graphite deposits, New Jersey Highlands: geologic and stable isotopic evidence for possible algal origins

Experimental confirmation of thermal plasma CVD of diamond with liquid feedstock injection model

Abstract A three-dimensional model of diamond chemical vapor deposition in a thermal plasma system has been compared with experimental results to confirm the validity of the model in simulating reactor flow patterns and deposit characteristics. Model and experimental cases were tested with the same boundary and operating conditions. Several sets of operating conditions were analyzed to confirm the validity of the model. Trends in the diamond chemical vapor deposition system based on the effects of droplet size, injection probe to substrate offset, the addition of an inert carrier gas, and the differences associated with the use of liquid or gaseous precursor feedstock were investigated. To test the validity of flow patterns predicted by the model, a laser strobe video system was used to map droplet trajectories in the reactor. Experimental results were found to support the calculated droplet trajectories and flowlines in the reactor. Deposition characteristics such as the mass deposition rate and the area of deposit were examined in the model and experimental cases. General trends, with respect to deposition characteristics, produced by altering the operating conditions in the experiment, and respectively the boundary conditions in the model were found to be similar. Differences between model and experimental results are probably due to the use of an overly simplified surface chemistry model, which does not take into account graphite deposition. In addition, modeling of radial droplet injection does not take into account non-radial perturbations.

Diamond growth by hollow cathode arc chemical vapor deposition at low pressure range of 0.02–2 mbar

Abstract An attempt was made to synthesize diamond films on (001) silicon substrates by means of a graphite or tungsten hollow cathode arc chemical vapor deposition at a lower pressure range of 0.02–2 mbar. The hollow cathode arc provides the advantage of the generation of a large area, high-flux electron beam, a very high-density plasma, and the high kinetic reaction species due to relatively low pressure operation. Diamond films have been characterized by scanning electron microscopy and Raman spectroscopy. The quality of diamond films deposited using the graphite hollow cathode was better than that using the tungsten hollow cathode at 2 mbar pressure. With further decreasing the deposition pressure, the evaporation and sputtering of the graphite hollow cathode are increased and the film quality was deteriorated. The growth rate of diamond films decreased and the nucleation density increased with decreasing deposition pressure.

Causes of the uniformly high crystallinity of graphite in large epigenetic deposits

In low‐pressure environments, precipitation of graphite is hindered at low to moderate temperatures by the high solubility of carbon in C‐O‐H fluids and by kinetic barriers to nucleation. Those low‐temperature fluids that do attain saturation tend to precipitate graphite continuously during flow and cooling, thereby producing widely dispersed films of low‐crystallinity graphite. In contrast, at high temperatures, particularly when combined with high pressures, the precipitation of graphite is enhanced by decreased solubility of carbon in C‐O‐H fluids and by improved nucleation under those conditions. The longevity of fluid systems in high‐temperature, high‐pressure terranes permits efficient, long‐term scavenging of dispersed carbon from the crust. The latter may be redistributed in a much more concentrated form as fluids rise, cool and decompress, and as the carbon is finally precipitated as highly crystalline graphite in fracture systems. The combined effects of the thermochemical controls on carbon solubility and the geological controls on fluid generation, movement and P–T pathways are the reason that large, epigenetic graphite deposits form dominantly at high temperatures and pressures. Those high‐temperature, high‐pressure conditions, in turn, account for the uniformly high crystallinity of the fluid‐deposited graphite.