Carbonado Research Articles

Carbonado Diamonds and the Application of their Unique Properties

To this days, carbonado diamonds remain a subject of discussion, and scientists are still studying their properties to understand what else they are capable of in their applications. Carbonado diamonds are extremely rare and occur in very limited quantities, which only increases interest in them.

4D Imaging of Mineral Dissolution in Porous Carbonado Diamond: Implications for Acid Digestion and XCT Measurement of Porosity and Material Properties

Dissolution and leaching are difficult processes to observe with combined temporal and spatial context, particularly when dissolving material within a nonreactive pore network. X-ray computed tomography (XCT) is a uniquely suited technique for observing dissolution in situ, and extracting quantitative data on pore networks and the material in them in 3D. We XCT imaged two samples of porous diamond (carbonado) during a sequential acid leaching procedure designed to remove a diverse assemblage of pore-filling minerals. This experiment allowed us to not only observe mineral dissolution in 3D, but also test various approaches to measuring porosity. We found that methods based on quantitative interpretation of CT numbers as partial porosity give more accurate results than purely binary segmentation, and that attempts to segment the pore network using visual criteria were scattered and unreliable. We identified differences in mineral inclusions and pore network topology between carbonado samples based on dissimilar dissolution styles and rates. We were also able to observe the formation of insoluble fluorides during acid digestion, which can drastically affect yields for geochemical measurements of certain elements, most importantly REEs, U, Th, and Pb. We found that image quality is unexpectedly locally affected by material properties, with filled pores measurably blurrier than empty ones. Such local variation in point-spread function is important when segmenting any object in XCT for the purposes of quantification. Finally, we demonstrate that by comparing mass and X-ray attenuation loss it is possible to estimate the relative heavy-metal content of the leached material.

Carbonado Diamond: A Review of Properties and Origin

Carbonado Diamond: A Review of Properties and Origin

Manufacture of drill bits from new diamond materials at high pressures and temperatures

The manufacture of diamond drill bits (diameter up to 212 mm) at pressures up to 1.5 GPa and temperatures up to 1250°C is described. This technology includes sintering by electric heating within a thermally and electrically insulating shell in a steel high-pressure chamber, for 120 min. Such high-pressure sintering is found to be a relatively rapid process, and the equipment may be employed repeatedly. Steel highpressure chambers of cylinder–piston type with working diameters up to 280 mm are developed and produced. In bit manufacture by this means, matrix material with diamonds may be pressed onto steel housing; alternatively, it is possible to use a powder housing with diamonds or with holes for subsequent attachment of diamonds by soldering or mechanical methods. Bits with model cutting elements made of polycrystalline carbonado diamonds are manufactured, and their operational properties are verified. In drilling a marble block under loads up to 50 kN, at speeds of 355 rpm, mechanical speeds up to 20 m/h are attained. In the technology developed, the cutting properties of carbonado diamonds may be retained, but the thermal stability matches that of PCD diamond–hard-alloy composites. The bits are rugged enough for use in the most challenging drilling conditions. The metal–ceramic matrix permits the reliable attachment of cutting elements made of ASPK diamond composites. It is strong and wear-resistant. This is an energy-saving technology with little environmental impact and is fast. It may be used to produce wear- and corrosion-resistant metal–ceramic housings, with subsequent attachment of diamonds by soldering or mechanical methods, on the basis of PCD composites with varying thermal stability.

MANUFACTURING TECHNOLOGY OF DRILL BITS UNDER HIGH PRESSURE AND TEMPERATURE WITH THE APPLICATION OF NEW DIAMOND MATERIALS

An original manufacturing technology of diamind drill bits with up to 212 mm at pressures up to 1.5 GPa and temperatures up to 1250 °C was developed. The bits were produced by sintering in a heat insulating jacket, an electrical insulating casing with electri cal heaters in a steel high pressure cell for 120 min. In the manufacture of drill bits by sintering under high pressure in steel HPC it was found that the sintering process is productive and apparatus for it can be used repeatedly. It can be used steel casing for pressing the diamond matrix material on it. The whole body can be made of diamond powder or holes for fi xing of diamonds by the subsequent soldering or by mechanical method. The authors have developed and manufactured a piston-cylinder type of HPC with a working diameter up to 280 mm by a high-pressure chamber. Also they have made a bit of model cutting elements such as polycrystalline carbonado diamonds and have tested their performance properties. When drilling of marble unit at load of 50 kN and the revolutions number of 355 rev/min the mechanical speed was reached up to 20 m/h. It was found that the developed technology allows to keep cutting properties such as carbonado diamonds have, which are analogues of PCD for thermal stability. Strength bit performance allows its operation under the most intense power drilling modes; metal-ceramic matrix provides a reliable fastening of the cutting elements. Carbonado is wear resistant and has high strength. This technology is energy effi cient, environmentally friendly and productive, as the technology can be used for the manufacture of metalceramic wear-resistant, corrosion-resistant casing bit and then fi xing it in the diamond cutting elements by soldering, or mechanical fastening, using a diamond composite materials of PCD types with diff erent thermal stability.

Influence of alloy catalysts with different adhesion at carbon on the synthesis of carbonado polycrystalline diamonds

The influence of molybdenum, titanium, tantalum, boron, and carbon on the wetting of pyrographite in solutions based on Nichrome (20% Cr–80% Ni alloy) is studied. The surface tension of the melts is measured, as well as the limiting wetting angles for the melts at pyrographite. The work of adhesion of the melts at pyrographite is calculated. The Nichrome-based alloys are used as catalysts in the synthesis of polycrystalline carbonado diamonds. The synthesis of carbonado, in contrast to the synthesis of diamond single crystals and powder, proceeds deep in the region of thermodynamic stability of carbon. Therefore, the adhesive characteristics of the alloys have no significant influence on the formation of polycrystals.

New textural evidence on the origin of carbonado diamond: An example of 3-D petrography using X-ray computed tomography

Three-dimensional textural observations of inclusion and porosity patterns in a 23carat carbonado diamond using high-resolution X-ray computed tomography reveal new information bearing on the nature and origin of this enigmatic material. A prominent patinaed surface is texturally linked to a banding and grading of inclusions and pore space beneath, extending several millimeters into the specimen. In situ observation demonstrates that almost all inclusions are polymineralic and show replacement textures, corroborating previous work indicating that the pore network is fully three-dimensionally (3-D) connected, and that virtually all macroinclusions are secondary. Large metal inclusions are only found immediately adjacent to the margin of the specimen, and are thus also likely to be secondary or even tertiary. However, we also report pseudomorphs after a phase forming pristinely euhedral rhombic dodecahedra, individually and in clusters from 0.3 to 1 mm in diameter; although we could fi nd no evidence of this phase persisting, it nevertheless represents the fi rst “true” macro-inclusion reported in carbonado, which almost certainly formed syngenetically with the diamond material. The pore system is essentially trimodal, consisting of single and clustered pseudomorphs, oblate pores 0.1‐0.3 mm in length with a clear preferred orientation, and 20 µm to <1 µm pores that form the connected network. Our observations support recent work suggesting that carbonado crystallized from a carbon-supersaturated fl uid and suggest that the second stage may correspond with the creation of the pore alignment fabric. We further postulate that, although the present-day macroinclusions are certainly secondary, the bulk material that comprises them may not be, and may instead be broken-down remains of the original included phase(s). While further verifi cation is needed, a model built around this hypothesis may provide the simplest explanation to many of the unusual features of carbonado.

Hyperspectral Cathodoluminescence Examination of Defects in a Carbonado Diamond

Hyperspectral cathodoluminescence mapping is used to examine a carbonado diamond. The hyperspectral dataset is examined using a data clustering algorithm to interpret the range of spectral shapes present within the dataset, which are related to defects within the structure of the diamond. The cathodoluminescence response from this particular carbonado diamond can be attributed to a small number of defect types: N-V0, N2V, N3V, a 3.188 eV line, which is attributed to radiation damage, and two broad luminescence bands. Both the N2V and 3.188 eV defects require high-temperature annealing, which has implications for interpreting the thermal history of the diamond. In addition, bright halos observed within the diamond cathodoluminescence, from alpha decay radiation damage, can be attributed to the decay of 238U.

Ionized nitrogen mono‐hydride bands are identified in the presolar and carbonado diamond spectra

Abstract– None of the well‐established nitrogen‐related IR absorption bands, common in synthetic and terrestrial diamonds, have been identified in the presolar diamond spectra. In the carbonado diamond spectra, only the single nitrogen impurity (C center) is identified and the assignments of the rest of the nitrogen‐related bands are still debated. It is speculated that the unidentified bands in the nitrogen absorption region are not induced by nitrogen, but rather by nitrogen‐hydrides because in the interstellar environment, nitrogen reacts with hydrogen and forms NH+; NH; NH2; NH3. Among these hydrides, the electronic configuration of NH+ is the closest to carbon. Thus, this ionized nitrogen‐mono‐hydride is the best candidate to substitute carbon in the diamond structure. The bands of the substitutional NH+ defect are deduced by redshifting the irradiation‐induced N+ bands due to the mass of the additional hydrogen. The six bands of the NH+ defects are identified in both the presolar and the carbonado diamond spectra. The new assignments identify all of the nitrogen‐related bands in the spectra, indicating that presolar and carbonado diamonds contain only single nitrogen impurities.

Hydrogen isotope compositions in carbonado diamond: constraints on terrestrial formation

Abstract In this study we report the first hydrogen isotope composition analyses on carbonado diamond along with cathodoluminescence and scanning electron microscopic imaging, electron microprobe analyses, and stable (H and C) and radiogenic (Sr) isotope measurements. The hydrogen of bulk carbonado (consisting diamond and pore-filling minerals) yielded ∼ −4‰, consistent with usual crustal or mantle-derived fluids. The diamond-related hydrogen component is about 70 ± 30 ppm and shows a D-depletion down to −200‰. Determined H isotope values — together with C isotope compositions — overlap the ranges for mantle-derived hydrocarbons. Textural characteristics and Sr isotope ratios of pore-filling florencite indicate that the carbonado was formed in a fluid-rich environment, underwent a significant high-temperature influence and finally suffered thorough alteration. Based on these observations, a terrestrial formation during interaction of mantle rocks/melts or subducted crustal materials and reduced C-H fluids...

INTRAGRAIN VARIATION IN 13C AND NITROGEN CONCENTRATION ASSOCIATED WITH TEXTURAL HETEROGENEITIES OF CARBONADO

We have investigated the textural diversity in four Brazilian samples of carbonado diamond by cathodoluminescence petrography and spectroscopy, coupled with carbon, nitrogen and argon isotope analyses. Three types of textures were observed: homogeneous, porphyritic and flow textures. In these last two textural varieties, carbon isotopic composition and nitrogen contents covary in different ways. The complex texture and δ 13 C–[N] variability in our two heterogeneous samples are analogous to those in igneous rocks. All four grains yielded similar cathodoluminescence spectra with respect to peak, positions and shapes, but relative intensities exhibit great differences. The main band at 575 nm represents the N + V center, which can involve (i) an irradiation followed by annealing, (ii) a plastic deformation during sintering of Ib-type microcrystals of diamond, or (iii) a growth of diamond crystals by a chemical vapor deposition (CVD) mechanism. Both cathodoluminescence spectra and N 2 / 40 Ar values of carbonado are distinct from those of impact-generated diamond. The relatively low concentration of Ar also does not support a CVD origin of carbonado diamond.

Infrared and Raman spectroscopic observations of Central African carbonado and implications for its origin

Carbonado diamonds from the Central African Republic (CAR) were investigated using spectroscopic observations. Raman spectra for a polished section of carbonado showed the average Raman frequency as 1333.0 cm −1 ; measurements 10 μm below the sample surface showed a bimodal distribution of the Raman frequency with the average at 1333.5 cm −1 . These contrasting results indicate that the carbonado interior retains considerable residual pressure. The maximum residual pressure detected in this study from the 10 μm subsurface was 0.49 GPa. From infrared (IR) absorption spectra for crushed carbonado samples, no absorption attributable to diamond was observed because absorption bands of mineral and fluid inclusions were too strongly observed. Acid leaching treatment of the crushed grains elicited IR bands assignable to intrinsic diamond vibration and nitrogen impurity in the diamonds. Nitrogen atoms in the CAR carbonado were not much aggregated and the degree of aggregation was intermediate between type Ib and type IaA. In the chemically treated samples, IR absorption bands from liquid water and carbonate were ubiquitous suggesting that the CAR carbonado samples contain fluid inclusions and are similar to diamonds containing mantle-derived fluids. The experimental results of this study suggest that the CAR carbonado originated from rapid heating event with a presence of fluid in the mantle and subsequent rapid cooling before aggregation of nitrogen impurity in the diamond lattice.

Generation history of carbonado inferred from photoluminescence spectra, cathodoluminescence imaging, and carbon-isotopic composition

Carbonado diamonds from the Central African Republic were investigated using spectroscopic observations and C-isotopic analysis. Based on photoluminescence (PL) spectra, carbonado samples were classified into two groups: Group-A, which exhibits an intense PL band at 504 nm; and Group- B, which exhibits PL bands at 504, 575, and 638 nm at room temperature. PL spectra measured at 120 K gave well-resolved side-band structures of 504 nm bands. Consequently, the 504 nm band of Group-A can be assigned to the 3H center attributable to self interstitials in diamond, whereas the 504 nm band from Group-B can be assigned to the H3 center attributable to a vacancy (□) trapped at nearest-neighbor substitutional nitrogen (N) pairs. The PL band at 575 nm, which is attributable to neutral N-□ pairs, is known to increase its width with increasing residual stress in diamond aggregates. The average FWHM of the 575 nm band and the standard deviations were 3.80 and 0.54 nm for Group-A carbonado, and 2.80 and 0.38 nm for Group-B carbonado. These values suggest that Group-A carbonado samples have higher residual stress than the Group-B samples. The presence of an H3 center and the lower residual stress in Group-B carbonado both suggest that they originated from higher temperatures compared to Group-A. Radiation halos were observed in cathodoluminescence (CL) images of both Group-A and Group-B samples. The CL halos are traces of radiation damage from radioactive nuclides. The texture of the haloes suggests that the radiation damage was a secondary event after formation of the carbonado diamonds. The average C-isotopic composition of Group-A is -23.6 ± 0.52. in δ 13 C PDB and that of Group-B is -26.3 ± 0.65‰. Group-A carbonado was enriched systematically in 13 C compared with Group-B carbonado. Isotopic fractionation might occur as a result of the different thermal history of carbonado.

Computer simulation of the mechanism for the synthesis of carbonado diamond

The synthesis mechanism associated with the formation of carbonado type polycrystalline diamond has been analyzed. This analysis was performed by computer simulation of the field of temperature developed at the moment of graphite transformation into polycrystalline diamond. It was found that during the synthesis of this carbonado diamond, a strong non-steady thermal condition occurs, leading to changes in the thermodynamic equilibrium. As a consequence, a region comprising non-transformed graphite and carbonado with different characteristics is established. An experimental comparison was carried out between the carbonado hardness profile and the field of temperatures. The results show that the higher the temperature attained at local points inside the high-pressure chamber, the higher the hardness of the diamond. The simulation and experimental results indicated that concurrent mechanisms are acting during the carbonado synthesis.

Effect of dispersion strengthening of a catalyst on the properties of polycrystalline carbonado diamonds

Polycrystalline carbonado diamonds are synthesized from a carbon material in the presence of a nickel alloy catalyst. A polycrystal is a composite material that consists of a diamond phase and a binder (up to 20%) whose composition is close to the catalyst. The properties of the binder significantly affect the properties of the composite material as a whole. The strengthening properties of nickel alloys can be improved by doping them with disperse particles. In this study, we determined the conditions for forming the dispersion-strengthened binder in a polycrystalline diamond. Carbonado samples were synthesized in a high-pressure toroid-type chamber at an initial pressure of 8.0 GPa and a temperature of 1800‐ 2000 K in 12 s. The mass of the resulting polycrystal was 0.8 carat. We used MGOSCh graphite as the carbon material. In this study, we also used ultrafine powders (UDPs) that were obtained by the plasmochemical method and had the following characteristics: nickel and molybdenum (MIKhM) with an average particle size of 100 nm and an oxygen content of 3 and 5%, respectively;

Synthesis of Polycrystalline Carbonado Diamonds from Pyrographite

Synthesis of Polycrystalline Carbonado Diamonds from Pyrographite

The radial distribution of implanted and trapped [formula omitted] in single diamond crystals and implications for the origin of carbonado

We have investigated variations of 4 He content in the different zones of single natural diamond crystals using a step combustion technique. The results indicate that some diamonds may be strongly irradiated during their residence in the earth's crust, since concentrations of 4 He in the 30- μm outer layer were found to be as high as 0.014 cm 3/g. The observation leads to a conclusion that similarly high 4 He concentrations in carbonado diamonds do not necessary demand an exotic origin. Previous theoretical estimations of the magnitude of He implantation in diamonds, which use normal U–Th concentrations of ca. 30 ppm in the surrounding rocks, do not agree with experimentally-obtained results. The He concentrations actually found in the `skins' (outer ≈30- μm layer of the crystals) of the samples we studied, require concentrations of U and Th in the host rock from 160 ppm to 1000 ppm. The interiors of the samples have also been analysed and exhibited 4 He concentrations from 3×10 −7 cm 3/g to 2×10 −5 cm 3/g, indicating heterogeneity even within single diamond crystals and arguing for the changes in the growth environment. From 4 He zoning within a diamond from the Finsch kimberlite, a maximum 4 He diffusion coefficient was estimated to be ≈4×10 −21 cm 2/s, lower than previous estimates, indicating that diamond may retain indigenous 4 He in the structure during its residence under mantle PT conditions.

Degassing mechanisms of noble gases from carbonado diamonds

Two carbonado diamonds were studied for helium diffusion by employing incremental stepwise-heating for temperature ranges from 350 to 1800°C. Arrhenius plots of experimental data demonstrate that there exist two degassing mechanisms of helium from diamond; the lower temperature degassing ( T < 1600°C) is volume diffusion and the higher temperature degassing ( T > 1600°C) is essentially governed by graphitization of diamond. Diffusivity calculated from the observed release rates of the lower temperature range assuming spherical grains and initially homogeneous helium distributions defines Arrhenius relations with an activation energy of 103.5 ± 4.8 kJ/mol and a pre-exponential factor, D 0 = 10 −13.2±0.2 cm 2/s in carbonado diamond. Using these values, we can estimate the diffusion coefficient of He to be 3 × 10 −17 cm 2/s at 1300°C.

Chemical properties of Central African carbonado and its genetic implications

Carbonado diamonds from Central African Republic exhibit very intense laser-induced photoluminescence due to the presence of the radiation damages. From the spectral profiles of photoluminescence obtained for these samples, the carbonado stones were grouped into three groups depending on a variation in the structure of radiation-damage products; Group-A carbonado with 504 nm band (3H band), Group-B carbonado with 575 nm band in addition to weak background peaks centered at 512 and 580 nm, and the Group-AB carbonado with features intermediate between Group-A and Group-B. When heating Group-A carbonado, Group-A was found to transform to Group-B at temperatures higher than 400°C. Thermogravimetry and Differential Thermal Analysis (TG-DTA) clarified the difference in thermal properties between Group-A and Group-B. While Group-A carbonado yields one intense and narrow exothermic peak at 800°C, Group-B carbonado exhibits a broad exothermic peak at 785°C. The distinct difference in the oxidation rate could be attributed to the difference in the density of micropores in carbonado. Chondrite-normalized rare earth element (REE) patterns for the bulk carbonado samples show negative Eu anomalies, and the inclinations of the patterns are similar to those of kimberlites and much steeper than that of continental crust as represented by continental shales. In the chondrite-normalized value, La/Lu ratios were of the order of 10 2 and the light REE abundances were as high as 10 3 relative to chondrite. Further, 1384 cm −1 absorption band was observed in IR (infrared) spectra of both Group-A and Group-B, which suggests the presence of nitrogen platelet in carbonado. These REE and IR results imply that the seed crystal of carbonado was formed at high pressure and high temperature and was subjected to the annealing process to generate nitrogen platelets. The genesis of Central African carbonado is discussed as a reconciliation of these experimental results.

Constraints from noble-gas contents on the origin of carbonado diamonds

CARBONADOS are porous aggregates of micrometre-size diamond crystals1,2. Although they are not rare, they have not been found in kimberlites3, and they contain inclusion minerals typical of the Earth's crust, rather than the upper-mantle assemblages commonly found in kimberlite diamonds. Carbonados also have lower 13C/12C ratios than kimberlite diamonds1,2,4. Although these observations strongly suggest that carbonados were formed in the crust, crustal conditions are generally unlikely to provide pressures and temperatures in the diamond stability field (but see ref. 5 for a possible exception). Other suggestions for the origin of carbonado include the transformation of subducted carbon in the mantle6, impact metamorphism of crustal rocks containing organic carbon7, and (for very fine-grained carbonado) the irradiation of organic matter by decaying uranium and thorium in uranium-rich phases8–10. Here we present further evidence for a crustal connection, in the form of noble-gas data for four carbonados from Brazil and Africa. We find that all four contain large amounts of implanted xenon and krypton from 238U fission, nucleogenic neon and 4He, and tightly trapped atmospheric noble gases, from which we conclude that these carbonados formed in a uranium-rich crustal environment.