Reduction of aluminum oxide in a nonequilibrium hydrogen plasma

A new method is proposed and experimental investigations are carried out aimed at reducing aluminum oxide in a nonequilibrium hydrogen plasma of a combined glow discharge (CGD) at a pressure of 1315.8–13,158 Pa, a discharge current of 5·10⁻²–3 A, and a hydrogen flow rate of 10⁻⁶–10⁻⁴ nm³/sec. A high degree of conversion of the aluminum oxide (60%) with an energy consumption of 20 kW·h/kg of Al₂O₃ is attained. Reduction of metals from oxides and other compounds in a CGD nonequilibrium hydrogen plasma can be used for producing rare-earth and high-purity metals. Translated from Inzhenerno-Fizcheskii Zhurnal, Vol. 73, No. 3, pp. 580–584, May–June, 2000.     

Surface alloying of steels in the process of mechanical pulse treatment

It is shown that intense saturation of the surface layers of a hardened metal with nickel, copper, and chromium from electroplates occurs in the course of mechanical pulse treatment in the zone of frictional contact. In this case, the mass transfer coefficients range from 0.95·10⁻⁷ to 1.1·10⁻⁷ m²/sec. It is established that the number of alloying elements is defined by the number of generated dislocations. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 3, pp. 108–110, May–June, 1998.     

Optical and electrical properties of SnO2 films prepared by chemical vapour deposition

Transparent and conducting SnO₂ films are prepared at 500°C on quartz substrates by chemical vapour deposition technique, involving oxidation of SnCl₂. The effect of oxygen gas flow rate on the properties of SnO₂ films is reported. Oxygen with a flow rate from 0·8–1·35 lmin⁻¹ was used as both carrier and oxidizing gas. Electrical and optical properties are studied for 150 nm thick films. The films obtained have a resistivity between 1·72 × 10⁻³ and 4·95 × 10⁻³ ohm cm and the average transmission in the visible region ranges 86–90%. The performance of these films was checked and the maximum figure of merit value of 2·03 × 10⁻³ ohm⁻¹ was obtained with the films deposited at the flow rate of 1·16 lmin⁻¹.     

Magnetic Anisotropy and Magneto-Transport Properties of Co–Ni–N Granular Alloys Thin Films

The effect of nitrogen addition on the morphology, magnetic anisotropy, and magnetoresistance properties of Co–Ni–N granular thin films were investigated. The films were grown by electrodeposition onto aluminum substrates at room temperature. By a complex process of cationic catalysis occurring at the cathode/electrolyte interface, nitrogen is adsorbed in the Co–Ni film. Finally, a granular film grows by a tridimensional progressive nucleation mechanism. The nature of the grains and of the interface between them influences exchange interactions between grains, which play an important role in determining the magnetic anisotropy. From the magnetic measurements, we found that the magnetic anisotropy constant varied in the range K _eff=(−21.5÷36.6)×10⁴ J⋅m⁻³ and the coercivity varied between H _c=(13÷67) kA⋅m⁻¹ depending on the sodium nitrate content in the plating bath. The Co–Ni–N granular thin films display large values (∼160%) of magnetoresistance. These large values of magnetoresistance make such structures attractive for applications as sensitive magnetic field sensors.     

Corrosion-mechanical characteristics of the materials of nonmagnetic retaining rings of turbogenerators. III. Crack formation in the course of service

We analyze reasons for failures of rotors and retaining rings of powerful turbogenerators made of traditional materials and establish that corrosion cracking in working media and alternating stresses are the main reasons for failures. Holding specimens made of new 18Mn−18Cr steel under stress in hightemperature water and a 22% NaCl solution leads to transcrystalline corrosion cracking at a rate of 0.5–40·10⁻¹¹ m/sec. In the course of dissolution of high-nitrogen chromium-manganese steels in the electrochemically active state, their corrosion ratei _cor is 0.1–4 mA/cm². Alternating stresses in chloride-containing acidic media most strongly intensify selective dissolution of manganese and then iron and chromium, which is in agreement with results of an analysis of products of corrosion on actual retaining rings. We established that a saturated solution of copper dichloride is the most aggressive medium for high-nitrogen chromium-manganese steels. Even short-term contact of the steel with this solution at room temperature leads to intense pitting, while long-term contact results in catastrophic intercrystalline cracking at a rate of 1.56·10⁻⁹ m/sec. In subsequent stages, this contact causes selective dissolution of the steel and pitting corrosion. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 115–122, March–April, 1998     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

Waveguide-dielectric resonator method for accurate measurement of parameters of materials at high frequencies

The theory is given, with an analysis and various examples, of the practical implementation of a method for measuring the relative permittivity ɛ^*=ɛ′−iɛ″ of materials in the 0.5–26-GHz frequency range. The results and experimental errors are given of measurements of ε′ in the range 2–200 and of tanδ in the range from 5·10⁻⁵ to 2·10⁻². Translated from Izmeritel'naya Tekhnika, No. 6, pp. 62–66, June, 1999.     

Measurement of the gravitational constant with a torsion balance

We present results of ten years of measurements of the gravitational constant made using an evacuated torsion balance. We obtained the valueG=(6.6729±0.0005)·10⁻¹¹ N·m²·kg⁻². We have determined the major destabilizing factors accompanying the measurement process and have estimated the contribution from different sources of error. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 3–9, October, 1996.     

Design and characteristics of HTSC SQUID magnetometer with a sensitivity of 10−13 THz−1/2

The results are presented of the experimental studies on forming weak links in yttrium ceramics by scribing and high-voltage discharge. The energy resolution of SQUIDs and the magnetic field sensitivity of magnetometers produced according to these methods were 6×10⁻²⁸ J/Hz and 10⁻²⁸ J/Hz, 5×10⁻¹³ T/Hz^1/2 and 2·5×10⁻¹³ T/Hz^1/2, respectively. Different designs of HTSC interferometers sensitive to the external magnetic field variation are described. The factors affecting the sensitivity of r.f. HTSC SQUID-magnetometers are considered.     

Highly-sensitive pressure sensor based on W-lighguides

A highly sensitive pressure sensor based on two Mach-Zender interferometers is described. The interferometer measuring and reference channels are made of single-mode W-lightguides. The measured sensitivity was shown experimentally to be 65·10⁻² dB·P⁻¹·m⁻¹. Translated from Izmeritel'naya Tekhnia, pp. 43–46, September, 1999.     

Heating of a current filament and formation of constrictions in a pulsed vacuum discharge

It is shown that a rapid current rise in a pulsed vacuum discharge is accompanied by enhanced compression of the current filament by its self-induced magnetic field. As a result, a constriction forms at a distance L≃1 mm from the cathode and the electron temperature increases to 10²–10³ eV at currents of order 1 kA. This behavior explains the observed increase in the degree of ion charge and the appearance of x-rays as the current pulse length decreases. The criterion for a rapid rise is the condition τ<L/V≃10⁻²⁷ s, where τ is the characteristic current amplification time and V≃10⁶ is the velocity of the cathode plasma. Pis’ma Zh. Tekh. Fiz. 24, 50–56 (September 26, 1998)     

Recording and Analysis of Turbine Shutdown Parameters by a Phase Method

Transient recordings are considered for the shutdown of a turbine generator functioning under the conditions of a heat and electricity generating station. Photoelectric systems are used for precision chronometric recording (absolute error 1·10⁻⁷ sec) of the rotating shaft to provide for detecting effects not accessible to the standard equipment of power stations. It is proposed using this approach in computerized forecasting of turbine generator state. __________ Translated from Izmeritel'naya Tekhnika, No. 8, pp. 24–27, August, 2005.     

Measurements of thermophysical properties of molten silicon by a high-temperature electrostatic levitator

Several thermophysical properties of molten silicon measured by the high-temperature electrostatic levitator at JPL are presented. They are density, constant-pressure specific heat capacity, hemispherical total emissivity, and surface tension. Over the temperature range investigated (1350<T _m<1825 K), the measured liquid density (in g·cm⁻³) can be expressed by a quadratic function,p(T)=p _m−1.69×10⁻⁴(T−T _m)−1.75×10⁻⁷(T−T _m)² withT _m andp _m being 1687 K and 2.56 g·cm⁻³, respectively. The hemispherical total emissivity of molten silicon at the melting temperature was determined to be 0.18, and the constant-pressure specific heat was evaluated as a function of temperature. The surface tension (in 10⁻³ N·m⁻¹) of molten silicon over a similar temperature range can be expressed by σ(T)=875–0.22(T−T _m). Invited paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Production of high-current electron beams in an explosive-emission diode at gas pressures ∼ 10− 2–10−1 torr

Data on production of electron beams with ∼200 keV electrons and above ∼100 A beam current in a diode with an explosive-emission cathode at background gas pressures ∼10⁻²−10⁻¹ torr are presented. Discharge regimes with high-voltage stage duration up to 500–800 ns at 10⁻² torr and 80 ns at 10⁻¹ torr have been obtained. The duration of the electron beam behind a 50 μm thick titanium foil was equal to 200 and 400 ns, respectively, and was limited by the transmittance of the foil. Pis’ma Zh. Tekh. Fiz. 24, 88–92 (January 26, 1998)     

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

Measurement of the hydrodynamic characteristics of artificial heart valves by photochromic visualization

We propose using photochromic visualization to measure the hydrodynamic characteristics of artificial heart valves under simulated physiological flow conditions. The photochromic visualization method is based on generation of colored markers in the flow behind the artificial heart valve in a time equal to 10⁻⁶ to 10⁻⁹ sec. We use high-power laser radiation as the source for generating the colored markers. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 65–68, October, 1998.     

Thermal Conductivity of a Simulated Fuel with Dissolved Fission Products

The thermal diffusivity of a simulated fuel with fission products forming a solid solution was measured using the laser-flash method in the temperature range from room temperature to 1673 K. The density and the grain size of the simulated fuel with the solid solutions used in the measurement were 10.49 g · cm⁻³ (96.9% of theoretical density) at room temperature and 9.5 μm, respectively. The diameter and thickness of the specimens were 10 and 1 mm, respectively. The thermal diffusivity decreased from 2.108 m² · s⁻¹ at room temperature to 0.626 m² · s⁻¹ at 1673 K. The thermal conductivity was calculated by combining the thermal diffusivity with the specific heat and density. The thermal conductivity of the simulated fuel with the dissolved fission products decreased from 4.973 W · m⁻¹ · K⁻¹ at 300 K to 2.02 W · m⁻¹ · K⁻¹ at 1673 K. The thermal conductivity of the simulated fuel was lower than that of UO₂ by 34.36% at 300 K and by 15.05% at 1673 K. The difference in the thermal conductivity between the simulated fuel and UO₂ was large at room temperature, and decreased with an increase in temperature. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Li-storage and cycling properties of spinel,CdFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as an anode for lithium ion batteries

Cadmium ferrite, CdFe₂O₄, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe₂O₄ shows a first cycle reversible capacity of 870 (± 10) mAhg⁻¹ at 0·07C-rate, but the capacity degrades at 4 mAhg⁻¹ per cycle and retains only 680 (± 10) mAhg⁻¹ after 50 cycles. Heat-treated electrode of CdFe₂O₄ (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg⁻¹ corresponding to 8·7 moles of Li per mole of CdFe₂O₄ (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe₂O₄ is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg⁻¹ at 0·5 C and 1·4 C (1 C = 840 mAg⁻¹) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted. Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years     

Diffusion of erbium in silicon

Diffusion of erbium in silicon has been investigated by the electric method. The erbium diffusion coefficient in the temperature range 1150–1250 °C increases from 1.4×10⁻¹³ to 6.2×10^{− 13} cm²·s⁻¹. The values obtained for the diffusion coefficient of erbium in silicon are in good agreement with data obtained by the method of tagged atoms. Pis’ma Zh. Tekh. Fiz. 24, 68–71 (January 26, 1998)     

Deep level transient spectroscopy of anisotropic semiconductor GaTe

Deep level transient spectroscopy (DLTS) was carried out on single crystals of the layered chalcogenide p-GaTe using Schottky barriers parallel and perpendicular to the layer planes to study the possible anisotropy of the defect levels. Deep levels with the same energies (0·28 eV and 0·42–0·45eV) have been found in both directions with concentrations ranging from 10¹³cm⁻³ to 10¹⁴ cm⁻³ and capture cross-sections from 10⁻¹⁵cm² to 10⁻¹⁷cm². The difference in the spectra obtained from the two planes and the possible reason for the deep level energies being independent of crystal orientation are discussed.