Effect of a low-amplitude shock wave with residual pressure on hexagonal boron nitride

We have performed shock-wave loading of hexagonal boron nitride under pressures of10.8–16 GPa in the range of initial temperatures of20–500°C in flat recovery ampoules allowing one to sustain residual pressures of ∼1 GPa. To form a plane shock wave, a gas gun was used. Application of a residual pressure under the action of a shock wave with an intensity of16 GPa increased the yield of wurtzite boron nitride by4 to5 times. This explained on the basis of the assumption of wurtzite formation from the amorphous phase in high-temperature zones of adiabatic shear in the residual regime. Center of High Dynamic Pressures, Mendeleevo 141570. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 5, pp. 122–127, September–October, 1997.     

Technological aspects of heat resistance in carbon-ceramic composite refractories

A technology has been developed for making carbon-ceramic composite refractories by combining carbon fibers as reinforcing component with a mixture matrix, which allows one to make refractory components of various sizes and geometry, including thin-walled large constructions. The heat resistance of these composite refractories increases with the bulk silicization during ceramic production on a carbon-carbon substrate. The degree of silicization is determined by the volume of the open microporosity of transport type, which is formed by pyrolysis of a polymer coke-forming matrix in the initial carbon plastic. The transport micropores are produced by a modification of the phenol-formaldehyde resin additive treatment, which does not give rise to coke on pyrolysis. As a result, the content of open pores in the carbon framework attains 55%, which enables one to make a silicized composite refractory of density up to 2.7 g/cm³ with a compressive strength of 250 – 300 MPa, bending strength 120 – 140, and tensile strength 60 – 80 MPa, elastic modulus 120 – 140 GPa, linear expansion coefficient 3.5 × 10^–6 – 4.5 × 10^–6 K^–1, and thermal conductivity 6 – 8 W/(m ∙ K). These refractories are widely used in various branches of industry Translated from Novye Ogneupory, No. 4, pp. 132 – 135, April, 2009.     

Grain-size effect on the properties of materials under dynamic deformation

Some deformation features in fine-grained copper under gradient dynamic stresses are studied which provide a better understanding of the mechanism of the processes involved. The experimentally observed abrupt change in the properties of materials with grain sizes smaller than a certain critical value is shown to be related to intergranular slip during deformation. Materials with a grain size of 5–50 μm are found to exhibit properties characteristic of nanomaterials with a strain rate varying from 10⁴ to 3 · 10⁶ sec⁻¹. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 133–138, May–June, 2008.     

Improvement of Manufacturing Technology for Ultrastrong and High-Modulus Carbon Fibres

1. The quality of CF, their strength and modulus of elasticity in particular, can be increased by the following methods: reducing the porosity of the initial PAN fibres by selecting the optimum conditions for spinning, plasticization drawing, finishing, and drying; decreasing the nonuniformity of the fibre diameter due to suppression of deformation resonance during spinning by selecting the jet formation and hardening conditions; decreasing the fibril and crystallite size by reducing the precipitator and solvent concentration gradient in the precipitation zone (spinning into mild baths); creating optimum conditions for mesophase self-ordering of the material at 450–550° C during precarbonization; increasing the cohesive energy by increasing the density to 1.8–2.1 g/cm³. 2. Replacing convective tempering of PAN twists in thermooxidative treatment by conductive tempering reduces the treatment time by 3–4 times. __________ Translated from Khimicheskie Volokna, No. 5, pp. 11–15, September–October, 2005.     

Formation and growth of dispersed carbon particles during pyrolysis of ethylene,benzene, and naphthalene in a reflected shock wave

The formation and growth rates of dispersed carbon particles were determined experimentally for pyrolysis of ethylene, benzene, and naphthalene in a reflected shock wave at temperatures of 1920–2560 K and hydrocarbon concentrations in argon of 1.8–20%. The diameter of the particles formed was estimated (30–600 Å). The maximum rate of particle formation at various temperatures [(0.7–96) · 10¹⁶ cm⁻³·sec⁻¹] and the particle growth rate (0.002–0.036 cm · sec⁻¹) were determined from results of measurements of reaction (residence) times. For pyrolysis of benzene, the activation energy of the overall process of particle formation is 410 kJ/mole, and for all hydrocarbons studied, the activation energy of the overall process of particle growth is 5–50 kJ/mole. The surface average particle diameter increases with increasing concentration of the initial hydrocarbon at a constant temperature. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 82–89, July–August, 2007.     

How to manipulate the electrospinning jet with controlled properties to obtain uniform fibers with the smallest diameter?—a brief discussion of solution electrospinning process

Solutions of five different polymers, namely, polystyrene (PS), polyacrylonitrile (PAN), polyhydroxybutrate (PHB), poly(D-L-lactic acid) (PLA), and Nylon6, were used to investigate their rheological properties on the electrospinnability. In order to effectively reduce the diameter of electrospun fibers, polymers with higher molecular weights (MW) were needed to develop entangled solutions at much lower concentrations and with viscosities as low as that of a pure solvent. A minimum polymer concentration 1.0–2.0 times larger than the entanglement concentration was required to prepare the bead-free fibers. Using this strategy, uniform PS fibers with the lowest ever diameter of ∼15 nm were successfully obtained using an MW of 3 × 10⁷ g/mol at a concentration of 0.1 vol.%. For a given electrospinning solution, processing variables of low flow-rate (Q) and high voltage (V) were desirable in obtaining fibers with small diameters. However, Q and V were correlated by a power law relation: V∼Q ^a, wherein the exponent a had a value of 0.1–0.4, which was relevant with the solution types. Based on the finite element analysis (FEA), a significant measure of electric field (E) occurred around the needle tip used in the experiment, and its magnitude decayed with increasing distance from the needle end (z): E∼z ⁻ⁿ. The exponent n was 1.0–2.0, depending on the needle–plate geometry, i.e., needle length, needle diameter (D _o ), plate diameter, and tip-to-plate distance (H). According to FEA results, H exhibited negligible effects on the electric field in the region of interest, i.e., z/D _o ∼1 to 10. Due to the presence of high measures of E at the needle end, approaches to render a shorter and thinner straight jet issuing from the Taylor cone to yield thinner fibers were sought because a more significant jet stretching in the “jet whipping region” can take place. A feasible route to predict the as-spun fiber diameter produced by the manipulation of the electrified jet is provided by experimentally measuring the jet diameter and numerically calculating the electric field for the jet whipping process.     

A spectroscopic study of the interaction of nigerloxin,a fungal metabolite,with serum albumin

Nigerloxin [2-amido-3-hydroxy-6-methoxy-5-methyl-4-(prop-1′-enyl) benzoic acid], a fungal metabolite, is an inhibitor of lipoxygenase and aldose reductase with free radical-scavenging properties. The interaction of nigerloxin with bovine serum albumin (BSA) was investigated using fluorescence spectroscopy and circular dichroic measurements. The fluorescence of BSA was quenched following interaction with nigerloxin, and this property was used to generate a binding constant. The estimated association constant was 1.01±0.2×10⁶ M⁻¹. Job's method of continuous variation indicated that nigerloxin formed a 1∶1±0.1 complex with BSA. To understand the nature of the interaction, the variance in the association constant as a function of temperature in the range of 14–45°C was used to calculate the thermodynamic parameters. The thermodynamic parameters at 27°C derived from the mass action plot and van't Hoff's plot were as follows: ΔG=−8.2±0.1 kcal/mol, ΔH≈0 kcal/mol, and ΔS=27.5±0.4 cal/mol/K (where ΔG is free energy, ΔH is enthalpy, and ΔS is entropy). Increasing ionic strength did not favor interaction. Circular dichroic measurements revealed that the interaction of nigerloxin with BSA did not lead to changes in the secondary structure of the protein. The reversibility of the interaction verified by the dilution method was found to be reversible. These measurements suggest that partial hydrophobic and partial ionic bonding play a role in the interaction of nigerloxin with BSA.     

Synthesis and characterization of a novel soil stabilizer based on biodegradable poly(aspartic acid) hydrogel

A novel soil stabilizer based on poly-amino acid - polyaspartic acid (PASP) and its copolymer which modified by xanthan gum (XG) was studied to increase soil particle compressive strength and resistance to wind erosion. Due to its unique property, the stabilizer aggregated individual soil particles and formed crust. The sample compressive strength increased from 0.175 to 0.612 MPa and the wind erosion modulus reduced from 22.43 to 10.56 g·m⁻²·min⁻¹ after the 1% PASP hydrogel was applied by 1.67 Lm⁻² (1 cm of crust). The soil water content was higher than the control due to the polymer’s excellent water-retaining property. The polymer had no negative influence on seed germination and growth. The biodegradability experiment showed that PASP was easy to biodegrade and therefore it was safe to apply in the field. This work was presented at 13 ^th YABEC symposium held at Seoul, Korea, October 20–22, 2007.     

Influence of concentrations of copper,levelling agents and temperature on the diffusion coefficient of cupric ions in industrial electro-refining electrolytes

Few data are available for diffusion coefficients measured in industrial copper electrolytes. In the present work the influence of copper concentration (19.9–58.1 g dm⁻³), temperature (20–60°C) and concentrations levelling agents i.e. animal glue (0–5 mg dm⁻³) and thiourea (0–5 mg dm⁻³) on diffusion coefficients of copper was studied in industrial copper refinery electrolytes. Chronoamperometry at ultramicroelectrodes was used as an electrochemical technique. Apparent bulk diffusion coefficients were calculated on the basis of the theory of electrochemical nucleation on disc-shaped ultramicroelectrodes. Increasing copper concentration decreased the apparent bulk diffusion coefficient of copper and diffusion coefficients followed the Arrhenius temperature relationship. The experimental activation energy was 26.8 kJ mol⁻¹. The influence of levelling agents on diffusion coefficients was not strong in the studied concentration range of animal glue and thiourea.     

Effect of shock-wave loading on the internal microstructure and mechanical properties of fine-grained copper

It is shown that preloading of fine-grained copper with a the grain size of 0.5 m by a shock wave of intensity ≈25–50 GPa does not lead to changes in its internal microstructure and mechanical properties, and the dislocation density increases only slightly from 1.8 · 10¹¹ cm^s-2 in the initial state to (3.1–3.6) · 1011 cm^s-2 after shockwave loading. An increase in shock wave intensity to pressures > 55 GPa leads to a decrease in the dislocation density to 2.5 · 10⁹ cm^s-2, an increase in the grain size to ≈19 fum, the occurrence of microtwins inside the grains, and a reduction in the mechanical properties of fine-grained copper to the level of coarse-crystalline copper.     

Electrical signals in shock compression of the Sn+S system

Experimental data are presented supporting the validity of using the electrical response of a semiconductor to shock compression as a method of studying chemical interactions in heterogeneous systems behind a shock-wave front. The method is tested on theSn+S system at dynamic pressures above 20GPa. Institute of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 2, pp. 139–142, March–April, 1997.     

Electrodeposition and corrosion behaviour of a Ni–W–B amorphous alloy

Electrodeposition of Ni–W–B alloys from plating baths containing ammonia and citrate is reported. Optimum conditions for plating including current density, temperature, mechanical agitation and pH were studied. The corrosion resistance and amorphous character were also evaluated. The operational conditions for depositing the alloy with good corrosion resistance were: current density 35 mA cm⁻², bath temperature 40 °C, pH 9.0 and cathode rotation at 90 rpm. The alloy was deposited at 38% current efficiency, with an average composition of 73 wt% Ni, 27 wt% W and traces of boron and with E _corr −0.300 V and R _p 3.369×10⁴ Ω. The deposit obtained under these conditions had an amorphous character with the presence of some microcracks on its surface reaching down to the copper substrate. Electrochemical corrosion tests verified that the Ni–W–B alloy had better corrosion resistance than Co–W–B.     

Study of compaction of high-alumina ceramoconcretes. 4. The effect of firing temperature on the properties of a matrix system and on ceramoconcrete

The effect of firing temperature on variations of the linear sizes, open porosity, apparent density, and mechanical strength both of the matrix system and of industrially produced ceramoconcretes based on a high-concentrated ceramic binding suspension (HCBS) containing 90% bauxite and 10% quartz glass is investigated. Experimental materials based on HCBS of density 2.62–2.77 g/cm³ (C _V = 0.65–0.70) with the content of particles of size below 1 μm varying from 4 to 15% encompass the whole spectrum of quantitative parameters of initial suspensions that are prescribed or possible in industrial production. Samples based on a bauxite HCBS with 10% highly disperse quartz glass, as well as samples of ceramoconcrete consisting of the same HCBS (35%) and a bauxite-based refractory filler, were obtained by compaction, heat-treated and fired in the interval of 100–1420°C. Perceptible sintering accompanied by shrinkage and significant strengthening of the material is registered in the interval of 1000–1250°C. A certain expansion and loosening of the material is observed in the range of 1300–1400°C due to intense mullite formation. Significant sintering and strengthening is achieved by protracted firing at 1400–1420°C. Comparative analysis of the properties of the matrix system and ceramoconcrete has established that, other terms being equal, σ_comp of ceramoconcrete amounts to 40–50% σ_comp of the matrix system. __________ Translated from Novye Ogneupory, No. 10, pp. 29–37, October, 2006.     

Electrothermal parameters and useful life of carbon fibre fabricated from viscose fibre by heat treatment at 2200°C under electric load

The electrothermal behavior of carbon fibre fabricated from viscose fibre by heat treatment at 2200°C was investigated. The analytical expressions correlating the linear density with the electrical resistance, heat capacity, thermal conductivity, temperature of the surface of the fibre, predicted useful life, and electric load were obtained. A method was developed for conducting and mathematically interpreting the experiments on determination of the lifetime before combustion of conducting carbon fibre of different linear density as a function of the strength of the electrical current passed through it. The lifetime of the carbon fibre in air with no electric load was equal to 6.3·10¹⁰ sec and decreased exponentially with an increase in the current strength. The specific resistance is approximately 5.2·10⁻⁵ Ω·m at 20°C, the specific heat capacity varied from 0.64 to 0.93 J/(g·K), and thermal conductivity of 83 to 120 W/(m·K) in the 0–100°C temperature range. UVIKOM, Mytishchi. Translated fromKhimicheskie Volokna, No. 1, pp. 55–58, January–February, 2000.     

Photoelectrochemical characterization of the synthetic crednerite CuMnO<Subscript>2</Subscript>

High quality crednerite CuMnO₂ was prepared by solid state reaction at 950 °C under argon flow. The oxide crystallizes in a monoclinically distorted delafossite structure associated to the static Jahn–Teller (J–T) effect of Mn³⁺ ion. Thermal analysis showed that it converts reversibly to spinel Cu _x Mn_3−x O₄ at ~420 °C in air and further heating reform the crednerite above 940 °C. CuMnO₂ is p-type, narrow semiconductor band gap with a direct optical gap of 1.31 eV. It exhibits a long-term chemical stability in basic medium (KOH 0.5 M), the semi logarithmic plot gave an exchange current density of 0.2 μA cm⁻² and a corrosion potential of ~−0.1 V_SCE. The electrochemical oxygen insertion/desinsertion is evidenced from the intensity–potential characteristics. The flat band potential (V _fb = −0.26 V_SCE) and the holes density (N _A  = 5.12 × 10¹⁸ cm⁻³) were determined, respectively, by extrapolating the curve C ⁻² versus the potential to the intersection with C ⁻²  = 0 and from the slope of the Mott–Schottky plot. From photoelectrochemical measurements, the valence band formed from Cu-3d wave function is positioned at 5.24 ± 0.02 eV below vacuum. The Nyquist representation shows straight line in the high frequency range with an angle of 65° ascribed to Warburg impedance originating from oxygen intercalation and compatible with a system under mass transfer control. The electrochemical junction is modeled by an equivalent electrical circuit thanks to the Randles model.     

Ligand-to-Metal Charge Transfer Resulting in Metalloaromaticity of [<Emphasis Type="Italic">R,R</Emphasis>-Cyclohexyl-1,2-bis(2-Oxidonaphthylideneiminato-<Emphasis Type="Italic">N,N′,O,O′</Emphasis>)]Cu(II): A Scrutinized Structural Investigation

Molecular and crystal structure analysis of a tetradentate ligand-to-metal charge transfer (LMCT) complex, [R,R-cyclohexyl-1,2-bis(2-oxidonaphthylideneiminato-N,N′,O,O′)]Cu(II), are described and characterized by X-ray crystallography and FTIR spectroscopy. The Cu(II) centers are coordinated by four atoms of the donor set [N₂O₂] in a distorted square-planar fashion, which can be attributed to an active electronic delocalization within metallacycles and polychelating property of the pro-ligand. Bond valences of copper centers in four crystallographically independent monomers are slightly distinguished from each other, which is associated with differences in charge delocalization levels of the pro-ligands. Total valence of the copper center is increased with increasing π-electron donation from naphthalene fragments to metallacycles. This charge transfer leads to π···π interactions between metallacycles including imine bridges. In addition, decreases in the centroid–centroid distances of π···π interactions are associated with increased aromatic character of metallacycles. Molecules of the complex are stacked as dimers in the crystal structure formed by π···π interactions and aggregations of these dimeric formations along a-axis are strengthened by C–H···O type H-bonds and C–H···π interactions.     

Explosive compaction of nano-alumina particle-reinforced copper alloy

This paper is intended to describe manufacturing of a nano-alumina particle-reinforced copper alloy with better strength and high-temperature properties than those of pure copper. A new preparation technique is proposed, which includes three processes: mechanical alloying, hydrogen sintering, and explosive compaction. Cu/α-Al₂O₃ bulk samples with a density of 97.86% of the theoretical density and hardness of H _V = 112 are obtained. The microstructure study indicates that α-Al₂O₃ particles are dispersed in the copper matrix and still keep the nanometer scale. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 133–135, January–February, 2008.     

Synthesis,characterization and catalytic properties of mesoporous Al-FSM-16 materials

Al-substituted mesoporous FSM-16 materials with different SiO₂/Al₂O₃ (28–452) ratios have been synthesized by intercalating kanemite using cetyltrimethylammonium bromide (CTMABr) as the intercalating agent and sodium aluminate as the aluminium source, and characterized by different physico-chemical characterization techniques. The XRD measurements revealed a slightly disordered hexagonal packing of channels in the Al-FSM-16 samples. The thermal stability of Al-FSM-16 samples was confirmed by DTA analysis, where no structural changes were observed in the temperature range of 600–900°C. No significant changes were observed in the morphology of kanemite and the Al-FSM-16 sample obtained from kanemite as revealed by the SEM analysis. This result clearly indicated that the Al-FSM-16 sample is formed via a folded sheet mechanism. Moreover, TEM measurements confirmed the presence of a slightly disordered hexagonal array of channels in Al-FSM-16 in agreement with the XRD results. The BET surface areas (638–788 m² g⁻¹) and pore volumes (0.57–0.87 cm³ g⁻¹) were indicative of the high porosity of the Al-FSM-16 samples. The Al-FSM-16 (SiO₂/Al₂O₃ = 49) sample exhibited excellent hydrothermal stability at 150°C. The Al-FSM-16 samples were found to catalyze the isomerization of m-xylene to p- and o-xylenes.     

Nature of glowing generated by irradiation of pentaerythrite tetranitrate by an electron beam

Results of studying the nature of glowing generated by pentaerythrite tetranitrate (PETN) excitation by an electron beam with a mean electron energy of ≈250 keV and a current-pulse duration of 15 nsec are presented. The pulse-averaged power density of the beam is varied within 10⁶ ≤ P ≤ 10¹⁰ W/cm². For 10⁶ ≤ P ≤ 10⁸ W/cm², the main type of glowing is demonstrated to be pulsed cathodoluminescence of PETN. In the pre-detonation mode (P ≈ 10⁹ W/cm²), more inertial glowing is formed on the rear front of the luminescence peak, which is identified as the glowing of products of explosive transformation of PETN formed in the region of electron-beam travel. For P ≥ 5 · 10⁹ W/cm², an additional glowing pulse is formed, which is associated with formation and spreading of a dense plasma emerging owing to detonation of the entire mass of the sample. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 87–89, September–October, 2007.     

Kinetic Study of the Prooxidant Effect of α-Tocopherol. Hydrogen Abstraction from Lipids by α-Tocopheroxyl Radical

A kinetic study of the prooxidant effect of α-tocopherol was performed. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) by α-tocopheroxyl radical in toluene were determined, using a double-mixing stopped-flow spectrophotometer. The second-order rate constants (k _p) obtained are <1 × 10⁻² M⁻¹ s⁻¹ for 1, 1.90 × 10⁻² M⁻¹ s⁻¹ for 2, 8.33 × 10⁻² M⁻¹ s⁻¹ for 3, 1.92 × 10⁻¹ M⁻¹ s⁻¹ for 4, and 2.43 × 10⁻¹ M⁻¹ s⁻¹ for 5 at 25.0 °C. Fatty acid esters 3, 4, and 5 contain two, four, and six –CH₂– hydrogen atoms activated by two π-electron systems (–C=C–CH₂–C=C–). On the other hand, fatty acid ester 2 has four –CH₂– hydrogen atoms activated by a single π-electron system (–CH₂–C=C–CH₂–). Thus, the rate constants, k _abstr/H, given on an available hydrogen basis are k _p/4 = 4.75 × 10⁻³ M⁻¹ s⁻¹ for 2, k _p/2 = 4.16 × 10⁻² M⁻¹ s⁻¹ for 3, k _p/4 = 4.79 × 10⁻² M⁻¹ s⁻¹ for 4, and k _p/6 = 4.05 × 10⁻² M⁻¹ s⁻¹ for 5. The k _abstr/H values obtained for 3, 4, and 5 are similar to each other, and are by about one order of magnitude higher than that for 2. From these results, it is suggested that the prooxidant effect of α-tocopherol in edible oils, fats, and low-density lipoproteins may be induced by the above hydrogen abstraction reaction.