Features of the crystal structure and electrical properties of sodium chloride at pressure 20–50 GPa

The electrical properties of polycrystalline samples of sodium chloride are studied at direct and alternating current in a wide range of frequencies at high pressure and room temperature. Graphic analysis of the experimental data [1–3] in the view of equivalent circuits allowed us to separate the contributions to conductivity caused by grains and intergrain boundaries. Features of impedance at pressure up to 37 GPa are in good agreement with earlier data and structural changes. It is shown that in the studied materials the electrical resistance of grains is much greater than the resistance of intergrain boundaries.     

Interaction of binary cuprates with oxygen and water vapor at temperatures of 200–400°C

Interaction of binary cuprates with oxygen and water vapor at T = 200–400°C has been studied. It has been established that only compounds containing oxygen vacancy chains in their structure can absorb oxygen and moisture from annealing atmosphere. Absorption of oxygen brings about decrease in the lattice parameters while embedding of OH^? groups leads to their growth. In contrast to YBa₂Cu₃O _y , binary cuprates do not undergo phase transitions in interaction with the atmosphere. Saturation with water and formation of oxyhydroxides is followed by their hydrolytic decomposition involving formation of simpler oxides and hydroxides.     

Relaxation and hysteresis internal friction in ultra-fine-grained copper at temperatures of up to 400°C

The temperature- and amplitude-dependent internal friction and elastic moduli of copper samples (99.95% Cu) subjected to deformation by equal channel angular pressing with a pass number of 1, 4, and 8 along the Bc route in the hertz range of loading frequencies at room temperature and temperatures of up to 400°C are investigated. The effect of deformation and subsequent recrystallization on the parameters of thermally activated internal friction peaks due to grain-boundary relaxation and the recrystallization of intensively deformed copper, and on amplitude-dependent internal friction due to dislocation hysteresis, is determined.     

Experimental modeling of percolation of molten iron through polycrystalline olivine matrix at 2.0–5.5 GPa and 1600°C

The present work was aimed to understand the role of light elements for the penetration of Fe melt through the olivine matrix at high P–T parameters. We studied the mechanism of Fe melt percolation through the olivine matrix, whose interstices are filled with carbon and sulfur. The experiments were performed using a ‘split-sphere’ type multi-anvil high pressure apparatus at pressures 2.0 and 5.5?GPa and a temperature of 1600°C. It was demonstrated that the Fe melt penetrated through the olivine matrix at a relatively high rates in the presence of carbon or sulfur in the interstices. The percolation occurs due to fast dissolution of the light elements into Fe melt and filling of these interstices by the melt.     

Raman Spectroscopy of Nanopolycrystalline Diamond Produced from Shungite at 15 GPa and 1600°C

JETP Letters - It has been demonstrated that the high-pressure (15 GPa) treatment of shungite samples (Karelia, Russia) at a temperature of 1600°C for 2 h transforms them to diamond. The...     

Microstructure and mechanical properties of a large-dimensional bulk nanocrystalline-based Fe–Al–Cr alloy prepared by an aluminothermic reaction casting and followed annealing at 1000 °C

A large-dimensional bulk nanocrystalline phase-based Fe–Al–Cr alloy with 10?wt.% Cr, which was about 200?mm in diameter and 10?mm in thickness, was prepared by an aluminothermic reaction casting and followed annealing at 1000?°C. Microstructures of the alloy were investigated by optical microscope, electron probe microscope, scanning electron microscope attached with electron backscattered diffraction, X-ray diffraction and transmission electron microscope. The magnetization curves of the alloy were tested by Lake Shore 7410 vibrating sample magnetometer. Compressive properties of the alloy were tested. The results show the alloy was consisted of a Fe–Al–Cr nanocrystalline matrix, Cr₇C₃ phase and contaminants in micrometre. Average grain size of the nanocrystalline matrix was 19?nm. Volume fraction of the Cr₇C₃ phase in the alloy was about 4.5%. After annealing, the saturated intensity of magnetization and the specific magnetic susceptibility of the alloy increased slightly from 99 emu/g and 0.083 emu/g?Oe to 104 emu/g and 0.113 emu/g?Oe, respectively. Compressive strength of the alloy was 1200?MPa and much higher than that of the small-scale nanocrystalline alloy and alloy with grains in micrometre.     

In situ complex impedance spectroscopy of mantle minerals measured at 20 GPa and 1400°C

Electrical conductivities of mantle silicate minerals (Mg_0·9Fe_0·1)₂SiO₄ olivine, wadsleyite and ringwoodite were determined at pressures up to 20 GPa and temperatures up to 1400°C using complex impedance spectroscopy in a high pressure multianvil apparatus. All samples were polycrystalline, synthesized in separate high pressure experiments prior to the electrical measurements. Olivine conductivities up to 10 GPa are very close to values determined at ambient pressure under controlled oxygen fugacities in previous studies indicating a very small pressure dependence. The conductivities of wadsleyite at 15 GPa and ringwoodite at 20 GPa are similar, and both about 100 times greater than for olivine. When compared to conductivity models of Earth's mantle, these results suggest that the steep increase in conductivity near the transition zone is mainly due to the olivine to wadsleyite phase transformation at 410 km depth, with only minor changes in conductivity occurring over the wadsleyite to ringwoodite transformation near 520 km depth.     

Stress-assisted nucleation and growth of γ″ and γ′ precipitates in a Cu–1.2 wt%Be–0.1 wt%Co alloy aged at 320°C

An investigation by high-resolution transmission electron microscopy of the precipitation process during ageing a Cu–1.2?wt%Be–0.1?wt%Co alloy at 320°C has revealed that the transition phases follow a γ″→ γ″?+?γ′?→?γ sequence. The γ′ phase heterogeneously precipitates on the γ″ phase. The effects of an external stress on the nucleation and growth of disc-shaped γ″ and plate-shaped γ′ precipitates have been examined for the alloy aged at 320°C. A compressive stress applied in the [001] direction during ageing preferentially accelerates the nucleation and growth of the γ″ variant normal to the [001] axis among three crystallographically equivalent variants and the specific four γ′ variants formed on the γ″ variant normal to the [001] axis. A tensile stress does not significantly affect those of γ″ and γ′ precipitates. The critical diameter of the disc-shaped γ″ nucleus is estimated as about 1?nm from evaluation of the interaction energy between the applied stress and the misfit strains of γ″ precipitates. It is proposed that applied external stress does not affect the diffusion rate but the interphase boundary velocity.     

Phase relationships in the Gd–Co–Al ternary system at 500°C

The phase relationships in the Gd–Co–Al ternary system at 500°C have been investigated mainly by X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The existence of two ternary compounds GdCo_0.74Al_1.26 and Gd₂Co₂Al has been confirmed. Twenty-two single-phase regions (including solid solution regions of the binary compounds), 43 two-phase regions, and 22 three-phase regions were found to exist at this isothermal section. In this work, no new binary or ternary phase was found.     

Resistance to deformation and fracture of aluminum AD1 under shock-wave loading at temperatures of 20 and 600°C

The results of measurements of the dynamic elastic limit and spall strength under shock-wave loading of aluminum samples AD1 of thicknesses between 0.5 and 10.0 mm at room temperature and at temperature increased up to 600°C are presented. The anomalous thermal hardening of aluminum under high strain rate has been confirmed. An analysis of the decay of precursors at temperatures of 20 and 600°C has shown that the change in the main mechanism of drag of dislocations occurs at a strain rate equal approximately to 5 × 10³ s⁻¹, which agrees with the results of measurements by the Hopkinson split bar method. The results of measurements of the spall strength in a wide range of strain rates add the previously obtained data and agree with them.     

The system Na2CO3–CaCO3–MgCO3 at 6 GPa and 900–1250°C and its relation to the partial melting of carbonated mantle

In order to constrain the Na₂CO₃–CaCO₃–MgCO₃ T–X diagram at 6?GPa in addition to the binary and pseudo-binary systems we conducted experiments along the Na₂CO₃–Ca_0.5Mg_0.5CO₃ join. At 900–1000°C, melting does not occur and isothermal sections are presented by one-, two- and three-phase regions containing Ca-bearing magnesite, aragonite, Na₂CO₃ (Na₂) and Na₂(Ca_1–0.9Mg_0-0.1)_3-4(CO₃)_4-5 (Na₂Ca_3-4), Na₄(Ca_1–0.6Mg_0–0.4)(CO₃)₃ (Na₄Ca), Na₂(Ca_0-0.08Mg_1–0.92)(CO₃)₂ (Na₂Mg) phases with intermediate compositions. The minimum melting point locates between 1000°C and 1100°C. This point would resemble that of three eutectics: Mgs–Na₂Ca₃–Na₂Mg, Na₂Mg–Na₂Ca₃–Na₄Ca or Na₂Mg–Na₄Ca–Na₂, in the compositional interval of [45Na₂CO₃·55(Ca_0.6Mg_0.4)CO₃]–[60Na₂CO₃·40Ca_0.6Mg_0.4CO₃]. The liquidus projection has seven primary solidification phase regions for Mgs, Dol, Arg, Na₂Ca₃, Na₄Ca, Na₂ and Na₂Mg. The results suggest that extraction of Na and Ca from silicate to carbonate components has to decrease minimum melting temperature of carbonated mantle rocks to 1000–1100°C at 6?GPa and yields Na-rich dolomitic melt with a Na# (Na₂O/(Na₂O?+?CaO?+?MgO))?≥?28?mol%.     

Hydrogen CARS thermometry in H2–N2 mixtures at high pressure and medium temperatures: influence of linewidths models

In order to improve the accuracy of H₂ CARS thermometry, H₂ Q-branch CARS spectra have been recorded for various H₂-N₂ mixtures in a high-pressure cell at different pressures and temperatures (up to 40 bar and 875 K). Due to the low spectral resolution of broadband CARS experiments, the relevant spectral lineshape factor is the linewidth ratio &(Q(3))/&(Q(1)), since Q(1) and Q(3) are the most intense lines of the Q-branch spectrum in this temperature range. For the first time, the speed-inhomogeneous effects are accounted for in the simulation of the CARS profiles. The evaluated temperatures are in good agreement with reference values obtained by thermocouples. The specific role on the accuracy of H₂ CARS thermometry of the speed inhomogeneity is carefully analyzed, in connection with the influence of the nitrogen concentration.     

The absorption of sulfur dioxide in the terahertz range at temperatures of 300–1200 K

The rotational spectrum of the absorption of the main isotope of sulfur dioxide (³²S¹⁶O₂), which corresponds to the terahertz range of electromagnetic waves, namely 1–250 cm^?1 (0.1–10 THz), is studied. The consideration covers rotational transitions within all vibrational states whose Hamiltonian parameters are known from the literature: (000-000), (010-010), (100-100), (001-001), (020-020), (110-110), (011-011), (030-030), (120-120), (200-200), (002-002), (130-130), (103-103), (301-301), (101-101), (021-021), (210-210), (111-111), (201-201), (003-003), and (131-131). As a result, the absorption coefficient of ³²S¹⁶O₂ is calculated for a broad temperature range (300–1200 K) and the contribution of the rotational band of each vibrational state to the total absorption coefficient is evaluated.     

Phase transformations in the TiO2–SiO2 system at high pressures and temperatures

In situ X-ray diffraction study of a sol–gel-produced SiO₂–TiO₂ glass and intimately mixed ultrafine powders of SiO₂ and TiO₂ was used to investigate the effect of TiO₂ on the high-pressure phase transformations of SiO₂ and specifically on the change in the p,T-conditions of the formation of coesite and stishovite. Our findings have shown that at pressures to 7.5?GPa and temperatures up to 1300?K the presence of TiO₂ does not favor the formation of stishovite.     

Collision-induced emission of singlet oxygen in the visible spectral region at temperatures of 90–315 K

Collision-induced emission of singlet oxygen molecules is studied using spectrometers calibrated for absolute spectral sensitivity. The collision-induced emission-rate constants at wavelengths of 479, 514, 577, 634, and 703 nm are determined within the temperature range 90–315 K. It is found that the intensities of the emission bands increase with decreasing temperature below 100 K. The interrelation between the collision-induced emission-rate constants and the intensities of the collision-induced absorption bands is discussed. The Einstein coefficients for spontaneous emission of excited free O₂: O₂ complexes are estimated.     

An experimental and kinetic modeling study of the auto-ignition of natural gas blends containing C1–C7 alkanes

Ignition delay time measurements for multi-component natural gas mixtures were carried out using a rapid compression machine at conditions relevant to gas turbine operation, at equivalence ratios of 0.5–2.0 in ‘air’ in the temperature range 650–1050 K, at pressures of 10–30 bar. Natural gas mixtures comprising C₁–C₇ n-alkanes with methane as the major component (volume fraction: 0.35–0.98) were considered. A design of experiments was employed to minimize the number of experiments needed to cover the wide range of pressures, temperatures and equivalence ratios. The new experimental data, together with available literature data, were used to develop and assess a comprehensive chemical kinetic model. Replacing 1.875% methane with 1.25% n-hexane and 0.625% n-heptane in a mixture containing C₁–C₅ components leads to a significant increase in a mixture's reactivity. The mixtures containing heavier hydrocarbons also tend to show a strong negative temperature coefficient and two-stage ignition behavior. Sensitivity analyses of the C₁–C₇ blends have been performed to highlight the key reactions controlling their ignition behavior.     

Pressure broadening of ammonia lines in the 6475åband at room and low temperatures

Measurements of pressure broadened half-widths have been performed for four ammonia vibration-rotation lines in the 6475Åband. Self-, hydrogen- and helium-broadening have been measured over a temperature range of 175–295 K. Pressure broadening coefficients and temperature dependence indices have been obtained for each line and broadening gas. A rotational quantum number dependence for the line width has been observed for all broadening gases studied.     

Thermal stability of a freestanding EUV filter under long-term vacuum annealing at 700–1000°C

Freestanding absorption filters based on Mo/Si and Mo/ZrSi₂ are tested under conditions of long-term heating in vacuum in the temperature range 700?C1000°C. The effect of high temperatures on the optical and structural characteristics of the films is studied. The critical thermal loads at which filters maintain their properties during many hours of testing are estimated. The mechanisms for the degradation of filter characteristics upon annealing are determined by means of secondary ion mass spectrometry (SIMS) data and optical measurements.     

The room-temperature decomposition of metastable phases precipitated in the Al-Zn alloys at 200 °C

The room-temperature decomposition of metastable phases in the Al-Zn alloys (from 25 to 50 wt. % Zn) was studied by the transmission electron microscopy and X-ray diffraction. Metastable phases, i.e. G.-P. zones, _R-and -phases, were grown at 200 °C and their decomposition into equilibrium -phase at 20 °C was investigated. Ageing times comprised 1 to 999 days.Both the decomposition mechanism and the rate of decomposition of coherent phases were found to be dependent on the particle sizes and their density reached at 200 °C. The local vacancy supersaturation around the -nucleus in a dense system of G.-P. zones leads to an enhanced growth rate of such nucleus and thus to the formation of one large -precipitate at the expense of several neighbouring G.-P. zones. The elastic stress field around this -particle promotes the further nucleation and growth of -precipitates and leads to their gradual spread throughout the matrix. The decomposition of intermediately sized _Rprecipitates results in the development of -precipitates of comparable sizes nucleated on the array of misfit dislocations at the periphery of _R-precipitates. The cooperative effect between neighbouring particles does not influence the decomposition of large _R-precipitated which split then into several smaller -particles. The rate of G.-P. zones or _R to -decomposition increases with the increasing sizes of transition precipitates and with the zinc content of the alloy. The kinetics of to -decomposition was found to be independent both on the annealing time at 200 °C and on the investigated alloy composition. This can be attributed to the constant density of misfit dislocations as nucleation sites for -precipitates along the -matrix interface and to the large mutual separation of -precipitates in all these alloys.In conclusion we would like to express our thanks to Doc. Dr. V.Syneek, CSc. for his valuable discussions and to Ing. V.íma for the preparation of Al-Zn alloys. Our thanks are also due to Mr. Z.iký for his help in the X-ray diffraction measurement and to P.Vyhlídka for the careful chemical analyses of the investigated alloys.     

Pressure broadening of methane lines in the 6190Åand 6825Åbands at room and low temperatures

Measurements of pressure broadened half-widths have been performed for one vibration-rotation line in the 6190Åmethane band and one vibration-rotation line in the 6825Åmethane band. Self-, nitrogen-, hydrogen- and helium-broadening have been measured over a temperature range of 77–295 K. Pressure broadening coefficients and temperature dependence indices have been obtained for each line and broadening gas.