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.     

Synthesis and characterization of HDA/NaMMT organoclay

In this study, the rheologic and colloidal characterizations of sodium montmorillonite (NaMMT) were examined. Hexadecylamine (CH₃(CH₂)₁₅NH₂, HDA) was added to the bentonite water dispersion (2%, w/w) in different concentrations in the range 5.6 × 10⁻⁴−9.4 × 10⁻³ mmol/l. The rheological and electrokinetic behaviour of aqueous montmorillonite dispersions was investigated as a function of solid content and HDA concentration. The basal spacings of the HDA/NaMMT composites were studied by X-ray diffraction. The FTIR spectra were obtained from the modified bentonite products, which revealed the characteristic absorbances after treatment with HDA.     

Gas chromatography/mass spectrometry analysis of arsine of high purity

The procedure of gas chromatography/mass spectrometry determination in arsine of high purity was described for impurities of permanent gases, carbon dioxide, C₁–C₅ hydrocarbons, and hydrides of groups 4–6 of Mendeleev’s periodic table of elements. The detection limits of impurities took values from 2 × 10⁻⁵ to 2 × 10⁻⁷ mol %.     

Effect of temperature and α-irradiation on gas permeability for polymeric membrane

In the present study the polyethersulphone (PES) membranes of thickness (35 ±2) μm were prepared by solution cast method. The permeability of these membranes was calculated by varying the temperature and by irradiation of α ions. For the variation of temperature, the gas permeation cell was dipped in a constant temperature water bath in the temperature range from 303–373 K, which is well below the glass transition temperature (498 K). The permeability of H₂ and CO₂ increased with increasing temperature. The PES membrane was exposed by a-source (₉₅Am₂₄₁) of strength (1 μ Ci) in vacuum of the order of 10⁻⁶ torr, with fluence 2.7 × 10⁷ ions/cm². The permeability of H₂ and CO₂ has been observed for irradiated membrane with increasing etching time. The permeability increases with increasing etching time for both gases. There was a sudden change in permeability for both the gases when observed at 18 min etching. At this stage the tracks are visible with optical instrument, which confirms that the pores are generated. Most of pores seen in the micrograph are circular cross-section ones.     

Identification and characterization of diffusion barriers for Cu/SiC systems

The promise of CuSiC metal matrix composites (MMCs) as a thermal management material is to provide increased power density and high reliability for advanced electronic systems. CuSiC will offer high thermal conductivity between 250 and 325 W/mK with corresponding adjustable thermal expansion coefficient between 8.0 and 12.5 ppm/^∘C. The major challenge in development of these materials is control of the interface interactions. Cu and SiC react at high temperatures between 850 and 1150^∘C, needed for fabrication of the CuSiC material, with an expected decrease in thermal conductivity of the CuSiC MMCs as the Si product of reaction dissolves into the Cu. The application of barrier coatings onto SiC was observed to control chemical reaction of Cu and SiC. In the current study, the effectiveness of four barriers to prevent Cu diffusion and reaction with SiC were evaluated between 850 to 1150^∘C. Immersion experiments were conducted at 1150^∘C to understand the reaction between copper and silicon carbide. Reaction products were identified with transmission electron microscopy (TEM) and electron diffraction. Laser flash thermal diffusivity measurements confirmed thermal conductivity to decrease with increasing silicon content of the copper as determined by induction coupled plasma mass spectrometry (ICPMS) and glow discharge mass spectrometry (GDMS). An erratum to this article is available at .     

Charge and mass transfer in the cathode plasma jet of a low-inductance vacuum spark

The contributions of fast and slow ion components to the average mass transfer rate in the cathode plasma jet of a low-inductance vacuum spark have been determined using time-of-flight measurements. The total mechanical momentum of the cathode plasma jet has been found using the ballistic pendulum technique. The coefficient γ of ion erosion of a cathode material was evaluated in the range of discharge current amplitudes 3–13 kA and the discharge current buildup rates 4 × 10⁹ − 1.5 × 10¹⁰ A/s. The γ value exhibits small variations in the indicated range of discharge parameters and is close to the values known for vacuum arcs.     

Determination of impurities in aluminum isopropoxide by inductively coupled plasma atomic emission spectrometry

A procedure has been developed for the determination of impurities in aluminum isopropoxide by inductively coupled plasma atomic emission spectrometry. The matrix effect has been compensated by adding a Bi internal standard. The detection limits of impurities are 10⁻⁷ to 10⁻⁵ wt %.     

Quadrupole-based glow discharge mass spectrometer: Design and results compared to secondary ion mass spectrometry analyses

A design of quadrupole-based glow discharge mass spectrometer is briefly presented. A glow discharge occurs when a DC voltage (up to 3 kV) is applied between two electrodes in a cell filled with Ar at ∼1 hPa pressure. In this configuration, the sample acts as the cathode, and its surface (∼12 mm²) is sputtered by impacting Ar ions. The sputtered neutral atoms are ionised downstream in the plasma, and are extracted through a diaphragm to an energy filter and quadrupole spectrometer (6 mm rods) in high vacuum. The processes of sputtering and ionisation are separated, therefore reducing matrix effects.Preliminary results of elemental analysis of stainless steel, chromium-vanadium steel, Al-Mg-Cu and Armco alloys are presented. These results are compared to secondary ion mass spectrometry (SIMS) results obtained for the same set of samples using a 5 keV Ar⁺ ion beam and a quadrupole mass analyser (16 mm rods). The glow discharge mass spectrometry (GDMS) results allowed us to find SIMS relative sensitivity factors (RSF) for the analysed materials. Simple design and quick analysis time makes the new GDMS analyser an attractive tool in material technology.     

Analysis of microstress in neutron irradiated polyester fibre by X-ray diffraction technique

Microstresses developed in the crystallites of polymeric material due to irradiation of high-energy particle causes peak broadening and shifting of X-ray diffraction lines to lower angle. Neutron irradiation significantly changes the material properties by displacement of lattice atoms and the generation of helium and hydrogen by nuclear transmutation. Another important aspect of neutron irradiation is that the fast neutron can produce dense ionization at deep levels in the materials. The polyethylene terephthalate (PET) fibre of raw denier value, 78.2, were irradiated by fast neutron of energy, 4.44 MeV, at different fluences ranging from 1×10⁹ n/cm² to 1 × 10¹² n/cm². In the present work, the radiation heating microstresses developed in PET micro-crystallites was investigated applying X’Pert-MPD Philips Analytical X-ray diffractometer and the effects of microstresses in tensile strength of fibre measured by Instron have also been reported. The shift of 0.45 cm⁻¹ in the Raman peak position of 1614.65 cm{−1} to a higher value confirmed the development of microstresses due to neutron irradiation using micro-Raman technique. The defects due to irradiation were observed by SEM micrographs of single fibre for virgin and all irradiated samples.     

Direct atomic-absorption determination of platinum,palladium, and rhodium in dead ceramic-based autocatalysts

The data on the effect of different concentrations of components of dead automobile catalysts on determination of platinum, palladium, and rhodium using the method of ETAAS are obtained and systematized. The conditions for direct atomic-absorption determination of Pt, Pd, and Rh are optimized. The technique of atomic-absorption determination of PM in secondary raw and technogenic materials is developed (n × 10⁻⁴−n × 10⁻¹ wt %, s _r = 0.12–0.07).     

Synthesis, characterization and conductivity studies of polypyrrole-fly ash composites

In situ polymerization of pyrrole was carried out in the presence of fly ash (FA) to synthesize polypyrrole-fly ash composites (PPy/FA) by chemical oxidation method. The PPy/FA composites have been synthesized with various compositions (10, 20, 30, 40 and 50 wt%) of fly ash in pyrrole. The surface morphology of these composites was studied with scanning electron micrograph (SEM). The polypyrrole-fly ash composites were also characterized by employing X-ray diffractometry (XRD) and infrared spectroscopy (IR). The a.c. conductivity behaviour has been investigated in the frequency range 10²–10⁶ Hz. The d.c. conductivity was studied in the temperature range from 40–200°C. The dimensions of fly ash in the matrix have a greater influence on the observed conductivity values. The results obtained for these composites are of greater scientific and technological interest.     

Structure and Features of the Motion of a Cathode Spot on a Continuous Titanium Cathode

High-speed video filming by the VS-FAST-NG CCD-array-based video camera from the firm of Videoskan with speeds of 1000 and 5000 frames per second and exposure time of 1·10⁻³ and 2·10⁻⁴ sec, respectively, is conducted. It is established that the arc burns from two or three cathode spots for (1–1.2)·10⁻³ sec. The mean and local speeds of the group of cathode spots are determined. If there is no external magnetic field present, the mean speed is equal to 5–6 m/sec. If there is a magnetic field B = 0.005 T present, the mean speed is equal to 15–16 m/sec. __________ Translated from Izmeritel'naya Tekhnika, No. 10, pp. 42–44, October, 2005.     

Nitriding of technical-purity titanium in hollow-cathode glow discharge

The process of nitriding at low pressures and temperatures (≤550°C) in hollow-cathode glow discharge plasma was studied for technical-purity titanium of the VT1-0 commercial grade. The diffusion saturation of titanium with nitrogen in plasma with a concentration of n = 10¹⁰–10¹¹ cm⁻³ takes place at an ion current density on the cathode within 1.6–4.0 mA/cm². It is established that a key role in the process of metal saturation is played by atomic nitrogen. The experiments revealed the formation of a layer of gradient structure with a high microhardness (∼14 GPa) on the surface of nitrided titanium.     

Conductometric Study of Some Metal Halides in Glycerol + Water Mixtures

Electrolytic conductivities of potassium halides, KX (X = Cl⁻, Br⁻, I⁻) have been investigated in 10, 20, and 30 mass% glycerol + H₂O mixtures at 298.0, 308.0, and 318.0 K. The conductance data have been analyzed by the Fuoss-conductance–concentration equation in terms of the limiting molar conductance (Λ⁰), the association constant (K _A ), and the distance of closest approach of ion (R). The association constant (K _A ) tends to increase in the order: 10 mass% < 20 mass% < 30 mass% glycerol + water mixtures, while it decreases with temperature. Thermodynamic parameters ΔH ⁰, ΔG ⁰, and ΔS ⁰ are obtained and discussed. Also, Walden products (Λ⁰η) are reported. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents.     

Optical properties of lead-bismuth cuprous glasses

The optical transmission and absorption spectra in UV- VIS were recorded in the wavelength range 350–800 nm for different glass compositions in the system (CuO) _x (PbO) ₅₀−x(Bi₂O₃)₅₀ (x = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (α), optical energy gap (E_opt), refractive index (n_D), optical dielectric constant (ε′_∞), measure of extent of band tailing (ΔE), constant (β) and ratio of carrier concentration to the effective mass (N/m*) have been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear behaviour. The optical parameters were found to be almost the same for different glasses in the same family.     

High resistivity In-doped ZnTe: electrical and optical properties

Semi-insulating <111> ZnTe prepared by In doping during Bridgman growth was found to have a resistivity of 5.74 × 10⁷ ohm-cm, the highest reported so far in ZnTe, with hole concentration of 2.4 × 10⁹/cm³ and hole mobility of 46 cm² /V.s at 300 K. The optical band gap was 2.06 eV at 293 K compared with 2.26 eV for undoped semiconducting ZnTe. Thermally stimulated current (TSC) studies revealed 2 trap levels at depths of 202–222 meV and 412–419 meV, respectively. Photoluminescence (PL) studies at 10 K showed strong peaks at 1.37 eV and 1.03 eV with a weak shoulder at 1.43 eV. Short anneal for 3 min at 250°C led to conversion to a p-type material with resistivity, 14.5 ohm-cm, indicating metastable behaviour. Raman studies carried out on undoped and In-doped samples showed small but significant differences. Possible models for semi-insulating behaviour and meta-stability are proposed.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions in ZnO implanted with group V ions

n-Type ZnO〈Ga〉 films were implanted with 150-keV N⁺ (As⁺) ions to a dose of 7 × 10¹⁵ cm⁻² and then annealed in atomic oxygen at different temperatures. p-Type conductivity was obtained at annealing temperatures in the range 770–870 K. The parameters of the p-type layers were determined by photoluminescence spectroscopy, secondary ion mass spectrometry, and Hall effect measurements. According to the Hall data, the p-type layers had a resistivity of ∼30 Ω cm, carrier mobility of ∼2 cm²/(V s), and carrier concentration of ∼10¹⁸ cm⁻³. The electroluminescence spectra of the p-n junctions produced by ion implantation showed a band at 440 nm, due to recombination via donor-acceptor pairs.     

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)     

Diamond-like a-C:H coatings deposited in a non-self-sustained discharge with plasma cathode

Hydrogenated amorphous carbon (a-C:H) coatings have been obtained by means of acetylene decomposition in a non-self-sustained periodic pulse discharge (2A, 50 kHz, 10 μs) with hollow cathode. The discharge operation was maintained by plasma cathode emission with grid stabilization based on dc glow discharge. Using the proposed method, it is possible to control the deposition conditions (total pressure of the Ar + C₂H₂ mixture, partial pressure of C₂H₂, ion current density, carbon ion energy) within broad limits, to apply a-C:H coatings onto large-area articles, and to perform deposition in one technological cycle with ion etching and ion implantation treatments aimed at improving the adhesion of coatings to substrates (Ti, Al, stainless steel, VK8 hard alloy) at temperatures below 150°C. Results of determining the deposition rate (1–8 μm), the nanohardness of coatings (up to 70 GPa), and the fraction of sp ³ bonds (25–70%) in the diamond-like coating material are presented.     

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)