Influence of Argon on the Phase Behavior and Vibrational Properties of Solid Nitrogen at High Pressure

The mixed solid N ₂–Ar has been studied at high pressure at the nitrogen–rich side of the phase diagram by Raman spectroscopy. The argon atoms dissolve into some of the nitrogen structures. Within the *–phase the Ar–-atoms are mainly located at the sphere–like disordered sites in agreement with computer simulations. The second order transition of pure N ₂ is still present in the mixed solid at 25 mole% Ar. The * – * and *–fluid transitions in the mixed solid are shifted compared to the pure system. The phase diagram of the mixture for x[N ₂]0.75 has been studied.     

Mixtures of (N2)1−x : (O2) x at High Pressures and Low Temperatures

We performed Raman measurements at 18 K and pressures up to 25 GPa in order to construct a tentative phase diagram of the (N ₂)_1–x :(O ₂)_x –system at low temperatures. We varied the composition of the mixed system over the whole concentration range. Here we focused on the systems with high nitrogen concentration and pressures above 2 GPa. It is known that at room temperature oxygen is highly solvable in the –phase of N ₂. The experimental results show that oxygen suppresses the disorder–order transition –N ₂.     

Formation of compounds by high-flux nitrogen ion implantation in titanium

Polycrystalline titanium was implanted with nitrogen ions at energies from 30 to 60 keV and with doses from 1 × 10¹⁶ to 1.5 × 10¹⁸ N⁺-ions cm^–2 at room temperature. The implanted titanium layers were investigated by high-voltage electron microscopy and transmission high-energy electron diffraction. The formation of titanium nitride, titanium carbonitride and titanium carbide phases were considered in relation to their dependence on nitrogen ion implantation dose. In the dose range from 1 × 10¹⁶ up to 1.5 × 10¹⁸ N⁺-ions cm^–2 the cubic phase -TiN _x was formed. In the dose range between 1 to 2.5 × 10¹⁷ and 1.5 × 10¹⁸N⁺-ions cm^–2 the tetragonal phase -Ti₂N was found in addition to the -TiN _x phase. The lattice structure of these titanium nitride phases is a function of the nitrogen ion implantation dose. Additionally, the presence of titanium carbonitrido TiC _y O _x and titanium carbide TiC _y phases can be proved. The analysed titanium nitride, titanium carbUnitride and titanium carbide phases are represented in a state diagram as a function of implantation dose.     

Designing and upgrading model of pre-denitrification systems

This paper reports a three-substrate steady-state integrated model, whose unknowns are expressed in explicit terms once concentrations of nitrogen compounds in the effluent flow are fixed. The model can be applied both to design and to upgrade wastewater treatment plants. The model is also able to evaluate the flexibility of existing wastewater treatment plants, which represents the capacity of the system to operate under different working conditions caused by increases in influent load or reductions in effluent quality standards. In this case the admissible variation of influent load or effluent concentration can be measured using suitable dimensionless flexibility indexes.List of symbols Q influent flow [L³ T^–1] - R₁ sludge recycle flow ratio - R₂ aerated mixed liquor recycle flow ratio - V_D denitrification reactor volume [L³] - V_N nitrification reactor volume [L³] - S biodegradable organic substrate concentration [M L^–3] - N-NH₄ ammonia nitrogen concentration [M L^–3] - N-NO₃ nitrate nitrogen concentration [M L^–3] - N_tot total nitrogen concentration [M L^–3] - O₂ oxygen concentration in the nitrification reactor [M L^–3] - X_H heterotrophic biomass concentration [M L^–3] - X_AUT autotrophic biomass concentration [M L^–3] - maximum removal rate of biodegradable organic substrate for an assigned value of temperature [T^–1] - maximum removal rate of nitrate for an assigned value of temperature [T^–1] - maximum removal rate of ammonia nitrogen for assigned values of pH and temperature [T^–1] - _S removal rate of biodegradable organic substrate [T^–1] - _D removal rate of nitrate [T^–1] - _N removal rate of ammonia nitrogen [T^–1] - K_S saturation coefficient for biodegradable organic substrate [M L^–3] - K_D saturation coefficient for nitrate [M L^–3] - K_SD saturation coefficient for organic substrate in the denitrification kinetic [M L^–3] - K_N saturation coefficient for ammonia nitrogen [M L^–3] - saturation coefficient for oxygen [M L^–3] - Y_H yield coefficient for heterotrophic microorganisms in the biodegradable organic substrate removal process - Y_D yield coefficient for heterotrophic microorganisms in the nitrate nitrogen removal process - Y_AUT yield coefficient for autotrophic microorganisms in the ammonia nitrogen removal process - (X_H)_r heterotrophic biomass concentration in the recycle sludge [M L^–3] - (X_AUT)_r autotrophic biomass concentration in the recycle sludge [M L^–3] - biodegradable organic mass consumption for unitary nitrate nitrogen mass reduction in the denitrification reactor - nitrogen consumption in the biodegradable organic oxidation process by mean of heterotrophic biomass     

Simulation of the Processes of Formation and Dissociation of Neutral Particles in Air Plasma: Vibrational Kinetics of Ground States of Molecules

The results are given of the calculations of populations of vibrational levels of N₂(X ¹·⁺ ₈ ), ₂(X ³·^- ₈ ), and NO(X²) molecules in an air plasma whose parameters correspond to the positive column of a DC discharge at pressures of 30–300 Pa and currents of 20–110 mA. Different processes are analyzed that form the distribution of molecules over levels, including the electron impact, V–Vand V–T exchange, chemical reactions, and heterogeneous deactivation. The calculation results for N₂(X ¹·⁺ ₈ ) are compared with experiment. It is found that the values of the effective vibrational temperature characterizing the populations of N₂(X ¹·⁺ ₈ ) are close to the values realized in a nitrogen plasma, and the difference of the vibrational temperatures of ₂(X³·^- ₈ ) and NO(X²) from the gas temperatures is not significant, which is due to high frequencies of V–T relaxation of vibrational states of these molecules in collisions with (³ P) atoms.     

Spin-polarization effect on electron attachment to atomic hydrogen on liquid helium surface

No Heading Reaction rates of electron attachment to atomic hydrogen are measured as a function of magnetic field. The reaction takes place in a two-dimensional mixture of hydrogen atoms and electrons on liquid helium surface. Surface electron density, measured by using vibrating capacitor electrometer technique, decreases when H atoms are introduced. Applied high magnetic field suppresses electron attachment, H + e^– H^–, as well as hydrogen recombination, H + H H₂. Since the electronic state of negative hydrogen, H^–, is spin singlet, electron attachment is suppressed by spin-polarization. Possible microscopic mechanisms to explain the measured magnetic field dependence of the reaction kinetics are discussed.PACS numbers: 67.65.+z, 68.     

Measurement of the Surface Tension of Undercooled Liquid Ti90Al6V4 by the Oscillating Drop Technique

The surface tension of liquid Ti₉₀Al₆V₄ was measured. The samples have been processed containerlessly by electromagnetic levitation, which allows the handling of highly reactive materials and measurements in the undercooled temperature region. The use of digital image processing allows the identification of oscillation modes and calculation of the surface tension from the l = 2 and m = 0, m = 2 oscillation modes. A linear least squares fit to the data showed the following temperature dependence: = 1.389 ± 0.09 – 9.017 × 10^–4 ± 5.64 × 10^–5(T – 1660°C) [Nm^–1]     

Superconducting Density of States from the Magnetic Penetration Depth of Electron-Doped Cuprates La2−x Ce x CuO4−y and Pr2−x Ce x CuO4−y

From measurements of the magnetic penetration depth, (T), from 1.6 K to T _c in films of electron-doped cuprates La_2–x Ce _x CuO_4–y and Pr_2–x Ce _x CuO_4–y we obtain the normalized density of states, N _s(E) at T=0 by using a simple model. In this framework, the flat behavior of ^–2(T) at low T implies N _s(E) is small, possibly gapped, at low energies. The upward curvature in ^–2(T) near T _c seen in overdoped films implies that superfluid comes from an anomalously small energy band within about 3k _B T _c of the Fermi surface.     

Thermal condition in plasma flows of a coaxial-electrode hall accelerator

Results of electron temperature determination in free jets of plasma of a coaxial-electrode Hall accelerator are reported. The recombination structure for population of upper energy levels of a nitrogen ion is established and the degree of population departure of these levels from the equilibrium conditions is determined.Notation n_e electron concentration, cm^–3 - I discharge current, A - G working gas flow rate, g/sec - n_z population of the excited state, cm^–3 - u_z statistical sum over the states - T_e electron temperature, K - T_p population temperature, K - T_R distribution temperature, K - E_ex excitation energy, eV. Indices - e electron component - i excited level - z ion charge Academic Scientific Complex A. V. Lykov Heat and Mass Transfer Institute, Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 4, pp. 425–429, October, 1992.     

The hP1-type phases in alloys of cadmium,mercury, and indium with tin

The hP1-type phases in alloys of Cd, Hg, and In with Sn are stable in the valence electron concentration interval 3.80–3.95. Following a rule of Raynor, the axial ratioc/a decreases with increasing valence electron concentration,N _b ^/at . Using lattice constant measurements the rule is confirmed, and by using density measurements the absence of constitutional vacancies is verified. Thec/aN _b ^/at relation of the hP1 phases is similar toc/aN _b ^/at of InSn _m (03Sn. A bonding-type proposal, explaining the stability of these structures and the dependence of their axial ratio on valence electron concentration, is derived.     

X-ray,electrical conductivity and infrared studies of the system Zn1−x CO x Mn1−x Fe x CrO4

The system Zn_1–x Co _x Mn_1–x Fe _x CrO₄ is tetragonal in the range 0.0x0.4 and cubic in the range 0.5x1. Electrical resistivity temperature behaviour obeys Wilson's law for all the compounds and thermoelectric coefficient values vary between 135 to 226V K^–1. All compounds exhibit P-type semiconductivity and possess low mobility values (10^–9 cm² V^–1 sec^–1). The infrared spectra show the presence of two strong absorption bands around 500 and 600 cm^–1. The probable ionic configuration for the system is suggested to be Zn _1–x ²⁺ Fe _x ^–y3+ -Co _x ²⁺ [Mn _1–x ³⁺ Fe _y ³⁺ CO _x ^–y2+ Cr³⁺]O₄.     

The growth of oriented ceramic eutectics

Controlled microstructures of the two eutectics in the alumina-titania system have been grown using a special electron beam heating technique. In the aluminium titanate-titania system, the eutectic interlamallar spacing varies with the freezing rate R as =AR ^–n where n=0.5 and the value of the constant A is 8.5×10^–6 cm^3/2sec^–1/2. Primary plate-like dendrites of aluminium titanate in a matrix of discontinuous aluminium titanate-titania eutectic are formed on solidifying a composition TiO₂-20 wt % Al₂O₃. These dendrites appear to deflect cracks in this ceramic. In the alumina-aluminium titanate system, primary rod-like dendrites of alumina were grown in a ribbon-like eutectic of alumina and aluminium titanate on solidifying a composition Al₂O₃–38.5% TiO₂.     

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine –SiC–35 wt% –Si₃N₄ containing 6 wt% Al₂O₃ and 4 wt% Y₂O₃ as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si₃N₄, which were much finer than those of ordinary sintered SiC–Si₃N₄ composites. Both strength and fracture toughness of fine–grained SiC–Si₃N₄ composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (250 nm for SiC and 400 nm for Si₃N₄) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m^1/2, respectively.     

Characterizations of InzGa1?z As1?x?yN xSbyP-i-N structures grown on GaAs by molecular beam epitaxy

The GaAs-based double-heterojunction P-i-N structures using In_zGa_1–zAs_1–x–yN_xSb_y as the i-layer is investigated for the first time using solid source molecular beam epitaxy. High quality coherent bulk InGaAsN_3.45%Sb (0.5 m) with a lattice-mismatch of 2.6 × 10^–3 can be achieved due to the surfactant properties of antimony, while the bulk InGaAsN_2% at 0.5 m with 1.06× 10^–3 mismatch is fully relaxed. Rapid thermal annealing (RTA) resulted in 25 meV low temperature (LT) photoluminescence (PL) full-width half-maximums (FWHM) for the bulk InGaAsNSb layers. InGaAsNSb experiences 30% less blueshifting with subjected under the same annealing conditions as InGaAsN with similar N content. Room temperature (RT) absorption measurements are in the range of 0.9–1.4 eV. The absorption edge of 1.41 m is achieved for sample D4.     

Diffusion coefficients of tetrazolium blue in homogeneous and micellar solutions

Diffusion coefficients of the electron acceptor dye tetrazolium blue were measured by the Taylor dispersion method, with an accuracy better than 4%, in two solvents: (i) a homogeneous one-aqueous phosphate buffer, 0.1 M, pH=7.0 (medium I); and (ii) a heterogeneous one-nonionic micelles of Triton X-100, 2.0 mM (where M stands for mol·dm^–3), in the same aqueous phosphate buffer (medium II). The values obtained were D ₁₂ ^I =3.64×10^–10m²·s^–1 and D ₁₂ ^II =3.01×10^–10m²·s^–1·D ₁₂ ^II has the meaning of a macroscopird or average diffusion coefficient, in which the partition coefficient of tetrazolium blue between micelles and water, as well as the diffusion coefficients of this dye and of the micelles in the aqueous phase, are involved.     

TiCxNy and TiCx-TiN films obtained by CVD in an ultrasonic field

TiC _x N _y mono- and TiC_x-TiN double-layer films with a thickness of 30 to 100 m were prepared on a carbon steel (C: 0.6 to 0.7%) substrate by CVD in an ultrasonic field (ultrasound frequency: 19kHz; power: 10 to 20Wcm^–2). The moderate deposition conditions for obtaining an adherent and thick film of TiC _x N _y were: substrate temperature: 1050° C; H₂, N₂, TiCl₄ and CH₄ flow rates: 6.2, 4.0, 0.9 and 0.26 to 2.0 ml sec^–1, respectively. The growth rate, grain size and degree of 2 2 0 preferred orientation were found to decrease with increase in CH₄ concentration. TiC _x N _y film on carbon steel had a Vickers microhardness of 1800 to 2600 and an adhesion strength to the substrate of more than 120 kg cm^–2. A TiC _x -TiN (x0.5) double-layer film was obtained at 1050° C by a controlled alternative deposition of TiC _x or TiN. Quasiepitaxial growth of crystallites in the double layers was found to prevail in both coatings of TiC _x (220)/TiN (220)/steel and TiN (200)/TiC_x (200)/steel.     

Preparation and electrical properties of ITO thin films by dip-coating process

Indium tin oxide (ITO) thin films were prepared on quartz glass substrates by a dip-coating process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. The ITO thin films containing 0 20 mol% SnO₂ were successfully prepared by heat-treatment at above 400 °C. Chemical stability of sol were investigated by using a FTIR spectrometer. The electrical resistivity of the thin films decreased with increasing heat-treatment temperature, that is carrier concentration increased, and mobility decreased with increasing SnO₂ content. The ITO thin films containing 12 mol% SnO₂ showed the minimum resistivity of =1.2 × 10^–3 ( cm). It also showed high carrier concentration of N=1.2 × 10²⁰(cm^–3) and mobility _H=7.0(cm² V^–1 s^–1).     

Transverse Magnetoresistive Effects in a Quasi-One-Dimensional Electron System Over Superfluid Helium

No Heading The transverse magnetoresistive effects in a nondegenerate quasi-one-dimensional (Q1D) electron system over superfluid helium have been investigated experimentally. The longitudinal magnetoresistance _xx have been measured in magnetic fields B up to 2.5 T in the temperature range 0.48 – 2 K. The width of conducting channels was 90 nm and 35 m, the mean electron density varied from 10⁹ m^–2 to 1.5 × 10¹² m^–2. It has been shown that the value of _xx practically does not depend on B at low B and _xx B in the quantum regime. The effective mobility of electrons in narrow channels increases under decreasing temperature and is determined by electron scattering by gas atoms, ripplons, and non-uniformities of the substrate. The mobility of electrons in wide channels increases with decreasing temperature and, below some temperature T_m, decreases. The negative magnetoresistance has been observed in the gas- and ripplon-scattering region. This effect has been explained by weak localization of carriers caused by the interaction of electrons with gas atoms in vapor at high temperatures and with ripplons or with non-uniformities of the substrate at low temperatures.PACS numbers: 73.20.Dx; 73.90.+     

Supercooling of In2Bi and InBi Melts

The effect of melt overheating T ⁺ on the critical supercooling T ^– of liquid In₂Bi and InBi is studied by cyclic thermal analysis. It is shown that, the T ^– for In₂Bi is 2.0 K, independent of the melt preheating temperature. In contrast, the T ^– for InBi varies jumpwise with T ⁺: T ^– 1.0–1.6 K at T ⁺ < 5 K, and T ^– 16 K at T ⁺ = 5–300 K, independent of the cooling rate (varied from 0.002 to 8.0 K/s). The solidification behaviors of In₂Bi and InBi are shown to correlate with the structures of their liquid and solid phases.     

The effect of particles on the critical strain associated with the Portevin-LeChatelier effect in aluminium alloys

The effect of particles on the critical strain, _c, associated with the Portevin-LeChatelier (PL) effect of aluminium alloys is studied using Al-Mg-Ni and Al-Si alloys. Al-Mg-Ni and Al-Si alloy matrixes are composed of Al₃Ni and Si particles, respectively. Tensile tests were performed in the temperature range 223–273 K in which the critical strain decreases with increasing temperature, and strain rates between 10^–5 and 10^–2 s^–1 were chosen. According to the apparent activation energies, Q, Mg and Si solute atoms are responsible for the flow instability in Al-Mg-Ni and Al-Si alloys, respectively. The experimental results also show that the critical strain decreases with decreasing particle spacing, d _p. Since the particle spacing is small compared to the corresponding grain size, the decrease in critical strain should be ascribed to the effect of particles. Considering that the dislocation density is increased by the particles, a modified model showing the critical strain, _c, as a function of particle spacing, d _p, is proposed as T ^–1 exp (–Q/kT), in which , T and k are the strain rate, temperature and Boltzmann constant, respectively. Linear fit of the plots of In _c versus In d _p and In _c versus In d _p indicates that this equation is appropriate to rationalize the particle effect on the critical strain.