Shock-wave synthesis of diamonds from fullerenes C60−C100

Shock-wave synthesis of diamond from C₆₀–C₁₀₀-fullerene powder was first accomplished by using the explosive compaction technique with plane wave loading in the pressure range of 24–40 GPa. The compacts of various initial composition comprised diamond, FCC C₆₀-fullerite, graphite, and amorphous carbon. The largest diamonds of 0.1–1.0 m were obtained under shock loading of pellets consisting of copper powder with 5 wt. % fullerite at 24 and 38 GPa, and pellets consisting of copper powder with 10 wt. % fullerite at 40 GPa. The end product consists of diamond without intermediate diamondlike phases such as n-diamond and hexagonal diamond (lonsdaleite).Central Machine-Building Technology Research Institute, 109088 Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 131–138, March–April, 1995.     

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.     

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.     

High-pressure phase equilibria for the synthesis of ionic liquids in compressed CO2 for 1-hexyl-3-methylimidazolium bromide with 1-bromohexane and 1-methylimidazole

The use of carbon dioxide in the synthesis of ionic liquids (ILs) has many advantages over conventional solvents. Here, the high-pressure phase equilibria (including CO₂ solubility, volume expansion, and mixture critical points) are measured and modeled for the system involved in the synthesis of a model imidazolium ionic liquid 1-hexyl-3-methylimidazolium bromide ([HMIm][Br]) from 1-bromohexane and 1-methylimidazole. The global phase behavior of 1-methylimidazole was investigated and found to be a Type V system (or potentially IV) from the classification of Scott and van Konynenburg with regions of vapor–liquid equilibrium, vapor–liquid–liquid equilibrium, liquid–liquid equilibrium, an upper and lower critical endpoint and mixture critical points. The solubility and volume expansion of CO₂ in 1-methylimidazole, 1-bromohexane, a 1:1 mixture of 1-methylimidazole and 1-bromohexane and [HMIm][Br] was determined at 313.15 K and 333.15 K for pressures ranging from 10 to 160 bar. The solubility of CO₂ and the volume expansion increases in the order of [HMIm][Br]  1-methylimidazole < 1:1 mixture of reactants < 1-bromohexane. The Peng–Robinson equation of state with van der Waals 2-parameter mixing rules was used with estimated critical properties to well correlate the vapor–liquid equilibrium. The results have important ramifications on the kinetics and process constraints of an actual IL synthesis with CO₂.     

Phase Diagram of Nanocarbon

In the phase diagram of carbon, the positions of the melting and thermodynamic-equilibrium curves of detonation nanodiamonds or ultrafine diamonds are found as functions of diamond particle size. The position of the set of triple points located in the ranges of pressure 13.5–16.5 GPa and temperature 2210–4470 K and determining the region of the liquid state of nanocarbon is determined. In the phase diagram of nanocarbon, the diamond region is divided into three parts according to the type of nanoparticles: nanodiamond, liquid nanocarbon (nanodrops), and amorphous nanocarbon.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 110–116, July–August, 2005.     

Electrical conductivity measurement in the detonation of gases containing aluminum suspensions

In this work measurements were taken of the conductivity during detonation of gas suspensions (H₂+O₂)–Al and O₂–Al. The expriments were performed in a shock tube at initial pressures p₀=0.2–0.6 atm and with mean volumetric powder densities =01.–0.5 kg/cm³. The high =10^–2 to 1 mho/m conductivity exists over an extensive region of the hot reaction products and has a thermal nature.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 124–127, November–December, 1991.     

Discoveries in Detonation of Molecular Condensed Explosives in the 20th Century

A number of experimental results that could not be satisfactorily explained within the framework of the Grib—Zel'dovich—Neumann—Döring detonation theory are reviewed, namely, the oscillating detonation of some liquid high explosives (HE), the weak dependence of the time of detonation transformation of heterogeneous charges on their structure (particle size, liquid or solid state, etc.) with a strong dependence of the critical diameter of detonation on the structure, and the extremely weak dependence of the detonation rate of liquid HE on the charge diameter with a significant value of the critical diameter of detonation. These studies yielded the following results: 1) for each heterogeneous HE, a typical shock–wave pressure p ^* and a typical initial density ₀ ^* were found, such that, for their low values, HE transformation follows the mechanism of hot points (depends on the charge structure), and for high values of these parameters, HE transformation obeys the homogeneous mechanism (does not depend on the charge structure); 2) two new theoretical notions were discovered and used in the detonation theory: the phenomenon of breakdown of the chemical reaction in the shock–wave front by rarefaction waves and the notion of a shock jump, which reflects the specific character of action of shock waves on complex multiatomic molecules of condensed HE. It was also shown that the discovery of the parameters p ^* and ₀ ^* and the breakdown and shock jump phenomena allowed one to confirm experimentally the explanations of the above observations, which are incompatible with the Grib—Zel'dovich—Neumann—Döring detonation theory, to propose the structure of the front of detonation waves both in homogeneous (stable and oscillating) and heterogeneous HE whose basic property is HE transformation (partial or complete depending on the HE power and initial density) already in the shock–wave front, and to proposed principally new ideas on the nature of the critical diameter of detonation of homogeneous and heterogeneous HE.     

Attrition studies with precipitated iron Fischer–Tropsch catalysts under reaction conditions

Iron Fischer–Tropsch (F–T) catalyst particles break-up during reaction in slurry phase reactors by physical attrition, and due to chemical stresses caused by phase transformations. Although chemical attrition is known to be important with iron (Fe) F–T catalysts, there have been no studies of attrition properties of precipitated Fe catalysts under reaction conditions. Here we report on attrition properties of three precipitated Fe catalysts (100 Fe/3–5 Cu/4–6 K/16–25 SiO₂) during F–T synthesis in a stirred tank slurry reactor (STSR). Our results show that after 295–497 h of F–T synthesis with these three catalysts in the STSR, the particle size reduction by fracture was moderate, whereas erosion (generation of particles smaller than 10 m) was small (2.3–2.7). The attrition strength of these catalysts is adequate for use in Slurry bubble column reactors (SBCRs) for F–T synthesis.     

Properties of massive Ag/YBCO contacts obtained by explosive compaction with subsequent heat treatment

Axisymmetric explosive compaction with a shock-wave pressure of 2 GPa was used to obtain low-resistance Ag/YBCO (YBa₂Cu₃O_7–x) contacts. Measurements were made of compressive strength at 300 K and microhardness and electrical resistivity within the temperature interval 300–77 K for annealed specimens of Ag/YBCO. Ultimate compressive strength was 0.12 GPa. The microhardness of the ceramic near the Ag/YBCO interface was 3.1 GPa. Contact resistance at the temperature of liquid nitrogen <1·10^–8 ·cm² (contact area 1.0 cm²).IGiL, Siberian Branch of the Russian Academy of Sciences, 630090, Novosibirsk. Translated from Fizika Goreniya i Vzryva, No. 1, pp. 130–134, January–February, 1995.     

Dynamics of Phase Transitions in the SHS of a 3Cu–Al Powder Mixture in the Regime of Thermal Explosion

The paper reports results of dynamic xray photography of selfpropagating hightemperature synthesis of a 3Cu–Al powder mixture in the regime of thermal explosion. The stages of formation of the final product are considered, beginning with the heating of the starting mixture and interaction of its components and ending with phase transitions during cooling of the product — intermetallides Cu₉Al₄ and Cu₃Al, which are the main components of Cu based tribotechnical materials. It is shown that upon heating in the temperature range of 550 – 590°C, the intensity of diffraction lines of Al drops to the background level. The exothermicreaction of synthesis of the intermetallide is initiated at a temperature of 610 – 630°C. In the period of sharp increase in temperature to 1040°C, the presence of the starting copper and the newly formed hightemperature phase with the Cu₉Al₄ tructure are detected simultaneously in the combustion wave. When cooled to 300$°C, the material contains two cubic phases — Cu₉Al₄ and an solid solution of Al in Cu. Further cooling is accompanied by formation and increase of peaks of the Cu₃Al phase with an orthorhombic lattice. The phase composition of aluminum bronze produced by SHS with combustion in the regime of thermal explosion is not in equilibrium.     

The Use of Utilizable Explosives to Increase the Efficiency of an Explosion

The possibility of using the utilizable explosives to increase the efficiency of an explosion of industrial high–explosive (HE) charges is studied under laboratory and working conditions. To do this, the explosive charges were used as linear initiators of the elongated charges of industrial HE. It is shown that the placing of an NB–40 ballistite powder rod of diameter 10 mm in a bulk–density TNT charge of diameter 40 mm increases the velocity of acceleration of an aluminum shell by 14% (the ratio between the detonation velocities of the powder and TNT is 1.8 : 1.0). The use of ShZ–1 TNT–based and ShZ–2 RDX–based hose charges in well charges of industrial HE, such as 79/21 Grammonit (79% granular ammonium nitrate/21% scale–shaped TNT), 30/70 Grammonit (30% granular ammonium nitrate/70% granular TNT), and ammonium nitrate, as linear initiators leads to a decrease in the output of bulky rock by 15—20% and allows one to increase the grid of the wells of diameters 160 and 220 mm by 20—25% with preservation of the rock output. The ratio of the detonation velocities of ShZ–1 and ShZ–2 and industrial HE charges is within 1.5—1.7 in the case of 79/21 Grammonit and 2.2—2.6 in the case of ammonium nitrate. The results obtained are explained by the fact that the detonation of a linear initiator from utilizable materials changes the form of the detonation wave front of the basic charge; as a result, it arrives at the surface of an ambient medium at a large angle and a more intense shock wave enters the medium compared to the case without a linear initiator.     

Attenuation of Blast Overpressures from Liquid in an Elastic Shell

Parameters of air blast waves produced by a ground explosion of explosive charges of mass G=0.1 – 1 kg placed in a liquid bounded by an elastic shell were measured experimentally. Encapsulation of the liquid in the elastic shell leads to an increase in the compressibility of the medium which transfers the energy of explosion products to the air and contributes to a significant decrease in airblast amplitude at a reduced distance R/G ^1/3 = 0.63 – 6.8 m/kg^1/3. The efficiency of attenuation of overpressures by immersing an explosive in a liquid bounded by an elastic shell is comparable to efficiency of damping blast waves by gasfilled twophase systems. It is shown that the main parameter of blastwave attenuation is the ratio of the mass of the liquid to the mass of the explosive charge rather than the viscosity and density of the liquid.     

Liquid Immiscibility Phenomena in Melts of the ZrO2–FeO–Fe2O3 System

The ZrO₂–FeO _x melts prepared by induction melting in a cold crucible in air are investigated experimentally. It is found that the immiscibility region exists in the liquid phase. The theoretical fusibility curves (calculated according to the authors' DIATRIS 1.2 program) for the ZrO₂–FeO–Fe₂O₃ system are compared with the experimental temperatures of the formation of the secondary phase, liquidus and solidus lines, and X-ray microprobe spectroscopic and X-ray powder diffraction data for quenched and slowly cooled samples. It is demonstrated that the immiscibility region in the liquid phase in an air atmosphere is observed in the temperature range 1870–2230°C and the concentration range 34–82 wt % ZrO₂.     

Direct synthesis of graphitic carbon nanostructures from saccharides and their use as electrocatalytic supports

An easy method is described for fabricating graphitic carbon nanostructures (GCNs) from a variety of saccharides; i.e., a monosaccharide (glucose), a disaccharide (sucrose) and a polysaccharide (starch). The synthesis scheme consists of: (a) impregnation of saccharide with Ni or Fe nitrates, (b) heat treatment under inert atmosphere (N₂) up to 900 °C or 1000 °C and (c) oxidation in liquid phase to selectively recover the graphitic carbon. This procedure leads to GCNs with a variety of morphologies: nanopipes nanocoils and nanocapsules. Such GCNs have a high crystallinity, as shown by TEM/SAED, XRD and Raman analysis. The GCNs were used as supports for platinum nanoparticles, which were well dispersed (Mean Pt size  2–3 nm). Electrocatalysts thus prepared have electrocatalytic surface areas in the 70–95 m² g⁻¹ Pt range and exhibit high catalytic activities towards methanol electrooxidation.     

Infrared Spectra and Structure of Si3N4, Si2ON2, and Sialons

Sialon powders are prepared from Kyshtymskoe kaolin with 12 – 28 wt.% carbon mixtures by the carbothermal reduction-nitridation method. The infrared spectra of -, O-, C- and 15R-phases in the Si – Al – O – N system are recorded and compared with the IR spectra of Si₃N₄, Si₂ON₂, and kaolin. The IR data are shown to correlate with the chemical composition of sialons and provide information supplementary to x-ray phase analysis data. The spectra of sialon powders differ from each other and from the spectrum of silicon nitride.     

Partial oxidation of methane to synthesis gas over α-Al2O3-supported bimetallic Pt–Co catalysts

The partial oxidation of methane to synthesis gas was studied at atmospheric pressure and in the temperature range of 550–800°C over -Al₂O₃-supported bimetallic Pt–Co, and monometallic Pt and Co catalysts, respectively. Both methane conversion and CO selectivity over a bimetallic Pt_0.5Co₁ catalyst were higher than those over monometallic Pt_0.5 and Co₁ catalysts. Furthermore, the addition of platinum in Pt–Co bimetallic catalysts effectively improved their resistance to carbon deposition with no coking occurring on Pt_0.5Co₁ during 80 h reaction. The FTIR study of CO adsorption observed only linearly bonded CO on bimetallic Pt–Co catalysts. TPR and XPS showed enhanced formation of a cobalt surface phase (CSP) in bimetallic Pt–Co catalysts. The origins of the good coking resistivity of bimetallic Pt–Co catalysts were discussed.     

Action of explosive loads on a metastable zirconium-dioxide structure

The influence of nonuniformity of the initial zirconium dioxide on the polymorphic and structural transformations in explosive loading is investigated. In the highly disperse quenched structure t-ZrO₂, there is further reduction in domain size if their boundaries are not stabilized by an Al₂O₃ glass phase. In preliminarily annealed equilibrium t-ZrO₂, as a result of loading, the structure becomes increasingly fragmentary and prone to t m transformation. In repeated explosive loading, the structural changes in quenched t-ZrO₂ and annealed t-ZrO₂ are similar.M. A. Lav'rentev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 3, pp. 72–75, May–June, 1995.     

Homoepitaxial CVD diamond: Raman and time-resolved PL characterization

In this work, we report on the structural characterization of homoepitaxial Microwave Plasma Enhanced CVD diamond grown onto Ib diamond substrates by varying systematically the methane to hydrogen ratio in the gas mixture (1–7% CH₄). X-ray diffraction, Raman spectroscopy and photoluminescence (PL) have been used to characterize the diamond samples. Raman measurements pointed out the excellent crystalline quality and phase purity of the specimens. PL measurements in the 1.7–2.7 eV energy range have shown completely flat spectra, excluding the presence of nitrogen-related optical centers. Such results show that the homoepitaxial CVD diamond can be grown, at moderate microwave power (720 W), and at growth rates not too low ( 1 μm/h) preserving a good quality. Moreover, the homoepitaxial crystals exhibited a strong free-exciton recombination radiation at room temperature even at the highest methane concentration used (7%). Preliminary measurements of the lifetime of the free exciton at room temperature have been also performed. The excitation was produced by a 5 ns pulsed laser irradiation at energies above the diamond band gap. The results have been compared with the structural properties of the samples and correlated with the growth conditions.     

Synthesis and mesomorphic behavior of poly[(2S, 3S)-(+)-2-chloro-3-methylpentyl 4′-(ω-vinyloxyalkyloxy)biphenyl-4-carboxylate]s with ethyl and propyl alkyl groups

Summary The synthesis and cationic polymerization of (2S, 3S)-(+)-2-chloro-3-methylpentyl 4-(2-vinyloxyethyloxy)biphenyl-4-carboxylate (15–2) and (2S, 3S)-(+)-2-chloro-3-methylpentyl 4-(3-vinyloxypropyloxy)biphenyl-4-carboxylate (15–3) are described. The mesomorphic behavior of the resulting polymers is discussed as a function of the molecular weight and spacer length. Based on the second and subsequent heating and cooling scans, poly(15–2)s exhibit an enantiotropic S_X (unidentified smectic) phase. Poly(15–2) with DP=4 is only crystalline. Poly(15–3)s show an enantiotropic cholesteric phase and an inverse monotropic S_X phase.