Optical characterization of nanocarbon phases in detonation soot and shocked graphite

Raman spectroscopy, photoluminescence and FTIR absorption were used to characterize the carbon phases in detonation soot and shocked graphite samples. Detonation synthesized diamond and shock synthesized diamond, which were separated from the detonation soot and shocked graphite respectively, were also collected for further examination. The detonation soot was obtained under different charge conditions and environmental conditions including gas and water, and the diamond was separated from the detonation soot by different purification methods. Size-induced transformation in the Raman and photoluminescence spectra was observed. Sp² carbon is a dominant defect in both detonation synthesized diamond and shock synthesized diamond. The two dynamically synthesized diamonds have similar structure and surface properties. The properties of detonation soot and detonation synthesized diamond are influenced by charge conditions and environmental conditions. The diamond and graphite crystallites in detonation soot and shocked graphite are both in nanometer sizes. The diamond and graphite crystallites in detonation soot have a smaller size and are more disordered than those in shocked graphite.     

Surface electronic structure of detonation nanodiamonds after oxidative treatment

X-ray absorption spectroscopy has been used for comparative study of electronic structure of detonation nanodiamonds (ND) purified using different oxidative treatments. The treatment of detonation soot with a mixture of nitric and sulphuric acids followed by ion exchange and ultrafiltration of hydrosol obtained was found to result in developing of ND surface coverage consisting of oxidized carbon species, which electronic state is close to that of strongly oxidized graphite. The deeper purification of ND was demonstrated to allow cleaning of ND particles from most of the oxidized carbon contaminations.     

Detonation synthesis of nanoscale silicon carbide from elemental silicon

Direct reaction of precursors with the products of detonation remains an underexplored area in the ever-growing body of detonation synthesis literature. This study demonstrated the synthesis of silicon carbide during detonation by reaction of elemental silicon with carbon products formed from detonation of RDX/TNT mixtures. Continuum scale simulation of the detonation showed that energy transfer by the detonation wave was completed within 2–9 μs depending on location of measurement within the detonating explosive charge. The simulated environment in the detonation product flow beyond the Chapman-Jouguet condition where pressure approaches 27 GPa and temperatures reach 3300 K was thermodynamically suitable for cubic silicon carbide formation. Carbon and added elemental silicon in the detonation products remained chemically reactive up to 500 ns after the detonation wave passage, which indicated that the carbon-containing products of detonation could participate in silicon carbide synthesis provided sufficient carbon-silicon interaction. Controlled detonation of an RDX/TNT charge loaded with 3.2 wt% elemental silicon conducted in argon environment lead to formation of ～3.1 wt% β-SiC in the condensed detonation products. Other condensed detonation products included primarily amorphous silica and carbon in addition to residual silicon. These results show that the energized detonation products of conventional high explosives can be used as precursors in detonation synthesis of ceramic nanomaterials.     

An efficient purification method for detonation nanodiamonds

This article reports the purification process of detonation soot to obtain pure nanodiamond powder. Nanodiamonds are synthesized by detonation using a high explosive mixture composed of trinitrotoluene and hexogen. The detonation of the charge leads to a powder containing nanodiamonds as well as metallic impurities and sp² carbon species. Further, to remove metallic particles, an unusual acidic treatment (hydrofluoric/nitric acids; i.e. fluorinated aqua regia) was set up. To eliminate sp² carbon species such as graphite and amorphous carbon, a thermal oxidation treatment was performed at 420 °C under air in a furnace during several hours. Transmission Electronic Microscopy, Raman spectroscopy, X-ray diffraction and Thermo-Gravimetric Analysis showed that this purification process is very efficient. From TGA measurements, a model of the carbon grain combustion was developed by considering graphitic shells surrounding the nanodiamond particles, and was used to demonstrate that the selective oxidation of graphite was experimentally realistic. Moreover, another model was set up from specific area measurements to evaluate the thickness of the functional groups surrounding the nanodiamonds after the oxidation of sp² carbonaceous species. The treatment described herein was achieved on several tens of grams of product and could be easily adapted to the industrial scale.     

Calculation of Detonation Properties of Gaseous Explosives Using Generalized Reduced Gradient Nonlinear Optimization

In this paper, a study on the development of a numerical modeling of the detonation of C H N O‐based gaseous explosives is presented. In accordance with the numerical model, a FORTRAN computer code named GasPX has been developed to compute both the detonation point and the detonation properties on the basis of Chapman–Jouguet (C‐J) theory. The determination of the detonation properties in GasPX is performed in chemical equilibrium and steady‐state conditions. GasPX has two improvements over other thermodynamic equilibrium codes, which predict steady‐state detonation properties of gaseous explosives. First, GasPX employs a nonlinear optimization code based on Generalized Reduced Gradient (GRG) algorithm to compute the equilibrium composition of the detonation products. This optimization code provides a higher level of robustness of the solutions and global optimum determination efficiency. Second, GasPX can calculate the solid carbon formation in the products for gaseous explosives with high carbon content. Detonation properties such as detonation pressure, detonation temperature, detonation energy, mole fractions of species at the detonation point, etc. have been calculated by GasPX for many gaseous explosives. The comparison between the results from this study and those of CEA code by NASA and the experimental studies in the literature are in good agreement.     

Isotope studies of detonation mechanisms of TNT,RDX, and HMX

An analysis is performed of experimental data from isotopic tracer studies of the detonation mechanism and formation of the diamond phase of carbon in the detonation products of TNT, RDX, HMX, and their mixtures. Dependences of the relative yield and phase composition of carbon in the detonation products of components of composite explosives on the particle sizes of the explosives are given. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 96–103, September–October, 2007.     

凝聚相炸药爆炸火光现象的初步研究

为弄清凝聚相炸药爆炸火光现象的形成机制及影响爆炸发光现象的相关因素,对凝聚相炸药爆炸过程中存在发光现象的各阶段发光机制进行了理论分析,用文献试验结果分析了影响爆炸发光强度的因素。采用高速摄像的试验手段研究了16种凝聚相炸药的爆炸火光现象。结果表明,凝聚相炸药的爆炸发光过程由爆炸和后燃两阶段组成。凝聚相炸药的爆炸发光强度与炸药的爆压、爆温、爆速和氧平衡均有关系。而炸药的氧平衡和质量则影响爆炸火光现象持续的时间。     

Synthesis of an ultradispersed diamond phase during detonation of composites

Conclusion We have attempted to analyze the synthesis of the diamond phase during, the detonation of secondary explosives by comparing the results of an explosion experiment with data obtained by studying preserved UDD powders.These data show that during detonation the growth in the UDD particles is a strongly limited process that is essentially independent of the size of the explosive charge or the external cooling conditions. The size distributions of diamond particles formed during direct synthesis from the carbon contained in the molecular structure of the explosive and during dissociation of inert organic substances are in satisfactory agreement with a lognormal distribution. The thermodynamic conditions during synthesis determine the dispersivity of the product UDD particles and this must be taken into account in thermodynamic detonation calculations. The effect of the different constituents of the, explosive on UDD synthesis (heat and mass transfer) is strongly limited.These data may support the concept of detonation in secondary explosives as a set of relatively fast and much slower reactions [25, 26] where, in the case of composites, the coagulation of carbon released during decomposition of each component separately and diffusion processes among the components may both act as slow exothermic reactions.Novosibirsk. Translated from Fizika Goreniya i. Vzryva, Vol. 29, No. 1, pp. 120–128, January–February, 1993.     

On mixing of the products of detonation of composite explosives in the chemical reaction region

The problem of mixing of the products of detonation of composite explosives is of principal importance for the synthesis of ultrafine diamond from composite mixtures and also for chemistry of detonation processes as a whole. An analysis of mixing in the chemical reaction region due to molecular diffusion shows that this mechanism may be important only for grain sizes of several micrometers. If the grain sizes reach tens or hundreds of micrometers, only partial mixing on the grain boundaries is possible. Investigations of the hydrodynamic mechanism of mixing shows that it may occur owing to a nonuniform velocity field behind the detonation wave front in the mixture and to the development of turbulence and cumulative processes during pore implosion. In mixtures with grain sizes of the order of 30 μm, these processes can lead to appreciable mixing during the time of ≈0.5 μs and longer. Theoretical estimates are compared with the results of experiments performed at the Lavrentyev Institute of Hydrodynamics of the Siberian Branch of the Russian Academy of Sciences and at the Altai Scientific and Industrial Enterprise (Biisk) for studying the synthesis of ultrafine diamond with the use of the isotope method.     

VLW爆轰产物状态方程的发展及应用

以国际公认理论完美的维里(VIRIAL)状态方程为基础,建立了VLW炸药爆轰产物状态方程,简述了VLW炸药爆轰产物状态方程的形成背景,呈现了VLW方程的推导过程;应用VLW方程计算了军用高能炸药、民用工业炸药、凝聚相炸药、气相燃料空气炸药的爆轰性能参数,以及火箭推进燃烧性能参数,推导了爆轰产物的热力学函数(内能、熵、化学位等)。结果表明,应用VLW方程计算的参数结果准确合理;成功解决了高温下(T*>20)高级维里系数计算难题,准确表达了爆轰条件下的维里方程属性。     

Experience of using synchrotron radiation for studying detonation processes

Results of studying detonation processes in condensed high explosives, which are obtained by methods based on using synchrotron radiation, are summarized. Beam parameters are given, and elements of the station and measurement system are described. Data on the density distribution in the detonation front for several high explosives are presented, and values of parameters in the Neumann spike and at the Jouguet point are determined. A method used to reconstruct a complete set of gasdynamic characteristics (density fields, particle velocity vector, and pressure) from the experimentally measured dynamics of the x-ray shadow of the examined flow is described. Results of using this method for studying detonation of a charge of plastic-bonded TATB are presented. A method of measuring small-angle x-ray scattering in the course of detonation conversion is described. Based on results obtained by this method for a number of high explosives with an excess content of carbon, kinetics of condensation of free carbon and dynamics of the mean size of nanoparticles being formed thereby are analyzed.     

Structure and properties of Dalan detonation diamonds

This paper presents the results of an investigation of the fine crystal structure of Dalan diamonds synthesized from graphite and carbon black by detonation. The phase composition of the diamond powders was found to vary widely; the structural and structural-morphological states of diamond particles were studied. The main types and subtypes of detonation diamonds are characterized according to transmission electron microscopy data. Assumptions are made concerning diamond formation during detonation synthesis. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 108–116, January–February, 2009.     

Initial stages in the growth of polycrystalline diamond on silicon

Polycrystalline diamond films prepared in a hot filament chemical vapour deposition reactor were investigated with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) in order to identify chemically and structurally distinguishable phases during nucleation and early stages of diamond growth. This was achieved by investigating a series of films grown under identical conditions for 5 min to 4 h. In addition, the interface between a solid diamond film and its silicon substrate was studied after the film had been removed from the substrate. Carbon deposition commences initially with the simultaneous growth of diamond crystallites along scratches and a layer of microcrystalline graphite covering the remainder of the substrate. Small amounts of SiC could also be identified during the first 100 min of deposition. Once the individual diamond crystallites have grown together to form a continuous layer, the graphitic phase in the spectra is replaced by an amorphous carbon phase which we attribute to the grain boundaries between the crystals. Inspection of the film backside revealed that the amorphous carbon had merely overgrown the microcrystalline graphite which was still present as the major component. Only after prolonged growth times (24 h) did the Raman and XPS spectra exhibit the characteristic diamond features free from any other contributions. On the basis of these observations a model for the initial stages of diamond growth on Si is developed.     

Raman scattering in a new carbon material

Samples of a new carbon material, Diamonite-B, were fabricated under high pressure from a commercial carbon black — identified as mixed fullerenes. The new material is neither graphite-like nor diamond-like, but exhibits electrical properties close to graphite and mechanical properties close to diamond. The use of Raman spectroscopy to investigate the vibrational dynamics of this new carbon material and to provide structural characterization of its short-, medium- and long-range order is reported. We also provide the results of investigations of these samples by high resolution electron microscopy and X-ray diffraction. Hardness, electrical conductivity, thermal conductivity and other properties of this new material are compared with synthetic graphite-like and diamond-like materials, two other phases of synthetic bulk carbon.     

Diamond nanoparticles to carbon onions transformation: X-ray diffraction studies

Carbon onions prepared by high temperature annealing of ultradispersed diamond nanoparticles of about 5 nm in average diameter have been studied by X-ray diffraction using synchrotron radiation. The X-ray diffraction patterns show transformation of the diamond nanoparticles with sp³ bonds into spherical carbon onions containing remaining diamond-like core and then into polyhedral onions with facets on their outer part and pure sp² graphitic bonds. The prepared onions form concentric-shell particles which comprise of about ten shells with an intershell distance of 0.35-0.36 nm. The large intershell distance suggests a considerable reduction in intershell interaction when compared to perfect graphite. The X-ray data are related to the previously performed studies by electron energy-loss spectroscopy and electron spin resonance.     

Dependence of Diamond Transition on Microtexture in Graphite Starting Materials under Shock Compression

The effect of microtexture on diamond transition was examined for graphite starting materials under shock compressions of 50 to 60 GPa and 80 to 90 GPa. Each of the starting materials used in the present study possessed a fully homogeneous microtexture. To distinguish the effect of microtexture from that of other experimental parameters, the shock conditions were standardized for all specimens tested. Three graphite materials—a glassy carbon, a carbon black, and a natural graphite—were selected and shock compressed using a quenching technique to generate conditions common to all samples. Detailed characterization by transmission electron microscopy and electron energy-loss spectroscopy revealed a clear tendency: The lower the crystallinity and crystallite size of the starting graphite, the more easily the graphite transformed to diamond when the transition mechanism was reconstructive.     

The importance of an extensive elemental analysis of single-walled carbon nanotube soot

Few manufacturers provide elemental analysis information on the certificates of analysis of their single-walled carbon nanotube (SWCNT) soot products, and those who do primarily perform surface sensitive analyses that may not accurately represent the bulk properties of heterogeneous soot samples. Since the accurate elemental analysis of SWCNT soot is a requisite for exacting assessments of product quality and environmental health and safety (EH&S) risk, the purpose of this work was to develop a routine laboratory procedure for an extensive elemental analysis of SWCNT soot using bulk methods of analyses. Herein, a combination of carbon, hydrogen, nitrogen, sulfur, and oxygen (CHNS/O) combustion analyses, oxygen flask combustion/anion chromatography (OFC/AC), graphite furnace-atomic absorption spectroscopy (GF-AAS), and inductively coupled plasma-mass spectroscopy (ICP-MS) were used to generate a 77-element analysis of two as-received CoMoCAT® SWCNT soot products. Fourteen elements were detected in one product, nineteen in the other, and each data set was compared to its respective certificate of analysis. The addition of the OFC/AC results improved the accuracy of elements detected by GF-AAS and ICP-MS, and an assessment was performed on the results that concluded that the trace elemental impurities should not pose an EH&S concern if these soot products became airborne.     

Phase Diagram of Ultrafine Carbon

A three-dimensional phase diagram of carbon has been built in the coordinates pressure–temperature—dispersivity on the basis of the published data on detonation-diamond properties. Key words: three-dimensional phase diagram, detonation diamond, nanoscale diamond particles, ultrafine carbon.     

X-ray scattering and spectroscopy studies on diesel soot from oxygenated fuel under various engine load conditions

Diesel soot from reference diesel fuel and oxygenated fuel under idle and load engine conditions was investigated with X-ray scattering and X-ray carbon K-edge absorption spectroscopy. Up to five characteristic size ranges were found. Idle soot was generally found to have larger primary particles and aggregates but smaller crystallites, than load soot. Load soot has a higher degree of crystallinity than idle soot. Adding oxygenates to diesel fuel enhanced differences in the characteristics of diesel soot, or even reversed them. Aromaticity of idle soot from oxygenated diesel fuel was significantly larger than from the corresponding load soot. Carbon near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was applied to gather information about the presence of relative amounts of carbon double bonds (CC, CO) and carbon single bonds (C-H, C-OH, COOH). Using scanning X-ray transmission microspectroscopy (STXM), the relative amounts of these carbon bond states were shown to vary spatially over distances approximately 50 to 100 nm. The results from the X-ray techniques are supported by thermo-gravimetry analysis and high-resolution transmission electron microscopy.     

Influence of carbon structure of the anode on the production of graphite in single-walled carbon nanotube soot synthesized by arc discharge using a Fe–Ni–S catalyst

We investigated the production of the graphite contained in the soot of single-walled carbon nanotubes (SWCNTs) synthesized using the arc discharge method with a poorly graphitized carbon (PGC) rod in comparison to a graphite rod. A PGC rod was produced using a mixture of coal tar and carbon black and was heat treated to 1000 °C. The rod was packed with a mixture of iron (Fe), nickel (Ni), sulfur (S), and PGC and used for the production of SWCNT soot using arc discharge. From the results of X-ray diffraction and electron microscopy, the amount of graphite in the SWCNT soot synthesized by PGC rod was lower than that by graphite rod. The production of graphite in the soot was found to be dependent on the carbon structure of the anode and the current density of arc discharge.