First lasers created at the Institute of High Current Electronics of the Russian Academy of Sciences (Siberian Division)

This paper presents the designs and radiation characteristics for lasers operating by self-limited transitions of nitrogen (λ=337.1 nm) and neon (λ=614.3 nm) and pumped by a pulsed longitudinal discharge, and for atmosphericCO ₂ lasers (λ=10.6 μm) pumped by a transverse electron-beam-initiated discharge or by a transverse discharge with uv preionization. These lasers were put into operation at IHCE in 1969 (the nitrogen and neon lasers), in 1971 (theCO ₂ laser pumped by an electron-beam-initiated discharge), and in 1972 (theCO ₂ laser pumped by a transverse discharge with uv preionization). Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 14–17, August, 1999.     

On the factors determining the pyrophoric stability of tungsten nanopowder obtained by plasma-chemical pyrolysis of W(CO)6

Nonpyrophoric tungsten powders with an average particle size of about 30 nm were obtained by pyrolysis of tungsten hexacarbonyl in a flow of microwave discharge nitrogen plasma. It is found that these powders are stable in air up to 300°C. The reason for such stability is that the structure of powder particles is of the core-double shell type, in which the metal core is covered with an oxide film approximately 1 nm in thickness, coated in turn with roentgenoamorphous layer consisting of carbon, oxygen, and nitrogen atoms. It is also established that the powders under investigation mainly release carbon oxides (CO and CO₂) and water into the gas phase upon heating in vacuum. Among the molecules present in the gas phase in small concentrations, nitrogen monoxide (NO) and formaldehyde (H₂CO) are worth mentioning apart from C1–C3 hydrocarbons.     

Sensors for the nitrogen oxides, NO2, NO and N2O, based on In2O3 and WO3 nanowires

Sensing characteristics of ZnO, In₂O₃ and WO₃ nanowires have been investigated for the three nitrogen oxides, NO₂, NO and N₂O. In₂O₃ nanowires of ∼20 nm diameter prepared by using porous alumina membranes are found to have a sensitivity (defined as the ratio of the sensor resistance in the gas concerned to that in air) of about 60 for 10 ppm of all the three gases at a relatively low temperature of 150 °C. The response and recovery times are around 20 s. The sensitivity of these In₂O₃ nanowires is around 40 for 0.1 ppm of NO₂ and N₂O at 150 °C. WO₃ nanowires of 5–15 nm diameter, prepared by the solvothermal process show a sensitivity of 20–25 for 10 ppm of the three nitrogen oxides at 250 °C. The response and recovery times are 10 s and 60 s, respectively. The sensitivity is around 10 for 0.1 ppm of NO₂ at 250 °C. The sensitivity of In₂O₃ and WO₃ nanowires is not affected by humidity even up to 90% relative humidity. The study also reveals that the sensing mechanism for the three nitrogen oxides have a commonality in that the desorption of oxygen is a crucial step in all the cases. PACS 07.07.Df; 85.35.-p; 82.35.Np     

New advanced in situ carbon monoxide sensor for the process application

Mixed potential solid electrolyte CO sensors with sensing electrodes based on composite with various semiconducting oxides were extensively studied in the temperature range 500–650 °C for sensitivity, stability and cross-sensitivity besides CO to other combustion components like CO₂, H₂O, O₂, and SO₂. The highest CO sensitivity was found for the CO sensor with composite electrode based on Au/Ga₂O₃ showing also good reproducibility and stability in hazardous combustion environment. CO sensor response behavior in non equilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. Mixed oxides based on doped chromites show only a little sensitivity to CO. CO sensor based on Au/Ga₂O₃ composite electrodes was showing good CO selectivity in the presence of other combustion gas species and finally was tested in combustion environment at power plant. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Catalytic and electrocatalytic activation of methane over manganese oxides deposited on YSZ

The catalytic and the electrocatalytic behavior of MnO_x oxides deposited on Yttria Stabilized Zirconia (YSZ) in the form of thin porous films, was studied during the reaction of methane activation at high methane to oxygen ratios. Experiments were carried out in a continuous flow well-mixed reactor (CSTR), at atmospheric total pressure and in a temperature range between 500–850 °C. It was found that the electrochemical pumping of oxygen anions (O²⁻) through the solid electrolyte (YSZ) affect drastically the rates of CO₂, C₂H₄ and C₂H₆ formation and consequently the C₂ selectivity. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Ethanol utilization in solid oxide fuel cells: A thermodynamic approach

A thermodynamic analysis of electrical power generation in ethanol fueled solid oxide fuel cells (SOFCs) was made in the temperature range between 800–1200 K at atmospheric total pressure. A SOFC was considered being fed with the thermodynamic equilibrium products of ethanol a) steam reforming b) CO₂ reforming and c) partial oxidation. In each case, ethanol, steam, carbon oxides, methane and hydrogen were considered coexisting in the equilibrium mixture produced by different ethanol to oxidant (H₂O, CO₂ and O₂) initial ratios. The boundary conditions for carbonization were also examined. The theoretically derived values of the molar fractions of the species in equilibrium were used for the evaluation of the thermodynamic value of the electromotive force (emf) established in the cell under the equilibrium conditions. Finally, the maximum electrical power obtainable in SOFC was calculated in each case under consideration. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Characterization of a Br(2P1/2)–CO2(1001-1000) transfer laser driven by photolysis of iodine monobromide

2 laser operating on the 10⁰1-10⁰0 transition at λ=4.3 μm and pumped by E –V energy transfer from Br(²P_1/2) has been demonstrated. The dynamics and performance of this device were characterized by observing the time-resolved stimulated emission and the steady-state spontaneous side fluorescence after photolysis of IBr or Br₂ by a frequency-doubled Nd:YAG laser or Ar⁺ laser, respectively. Although the E –V excitation kinetics are favorable, rapid vibrational relaxation limits laser action to CO₂ pressures of less than 1 Torr. Numerical modeling of laser pulse shapes and the dependence on IBr and CO₂ pressure and photolysis energy establish a relatively high gain of 0.33%/cm, a CO₂-pressure-dependent optical loss of 0.04–0.06%/cm, and an efficiency of 2×10^-5 4.3-μm-laser photons per incident photolysis photon. The CO₂ fluorescence after photolysis of a fixed Br₂/CO₂ gas mixture decreases as a function of photolysis time by about 30%/h, indicating the photolytic production of an important quencher. Received: 23 June 1997/Revised version: 23 September 1997     

Physical and electrical characteristics of metal-organic decomposed CeO<Subscript>2</Subscript> gate spin-coated on 4H-SiC

The effects of post-deposition annealing temperatures (600–1150°C) in 95%N₂–5%H₂ ambient on the electrical and physical properties of metal-organic decomposed CeO₂ spin-coated on n-type 4H-SiC were investigated. As the annealing temperature increased, oxides changed from polycrystalline to preferred oriented structures and, eventually, to silicate structures. The oxides also showed an incremental increase in surface roughness as annealing temperature increased. The Lorentz-Lorenz law was utilized to determine the density of the oxides. The highest density was obtained by a sample annealed at the highest temperature. Electrical results showed that this sample obtained the lowest leakage current density. Parameters affecting this observation were also investigated.     

Comparison of selected optical properties of oxyfluoride glass fibers doped with Er3+ and co-doped with Er3+ Yb3+

The method of manufacturing and spectroscopic evaluation of the Er³⁺ ions doped and Er³⁺–Yb³⁺co-doped SiO₂–Al₂O₃–Na₂CO₃–CaO–PbO–PbF₂ oxyfluoride glass fibers is presented in the paper. Both optically active elements erbium and ytterbium were introduced into the batch in the form of fluorides. The X-ray diffraction (XRD) technique was applied at each stage of fibers manufacturing in order to control an amorphous structure of the preforms and fibers. Optical studies of glass preforms and fibers (reflection/transmission, absorption, emission, and excited state absorption (ESA)) were directed to examine their suitability as fiber amplifiers at 1.55 μm band.     

Remote detection of sulfur dioxide by means of a CO2 laser

The possibility of remote detection of SO₂ in the 9-μm region of the spectrum by means of a TEA CO₂ laser was theoretically and experimentally investigated with regard to the real state of the atmosphere and the contribution of background concentrations of H₂O, CO₂ and NH₃ to absorption. For sounding along short paths (2L=2 km), the method of detection of small concentrations of SO₂ (at the MPC level) with the use of the lines of the CO₂-molecule regular transitions (00^o1–02^o0 band) has been devised and experimentally tested. It is shown that in sounding along longer paths (2L=6 km), a noticeable increase in sensitivity can be achieved by the generation lines of the CO₂-molecule sequential 00^o2–02^o1 band. B. I. Stepanov Institute of Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 508–515, July–August, 1998.     

Emission and Transmission Mössbauer Spectroscopic (EMS and TMS) Study of Perovskite Oxides, (Ba, Ca)(Fe, Co)O3-δ, Absorbed with CO2

Perovskite oxides, (Ba_0.95,Ca_0.05) (Co_1-x,Fe_x) O_3-δ, are prominent materials for CO₂ absorption at high temperature. The substitution of Ba sites with Ca ion, and the mixed valence states of Fe and Co ions due to the formation of oxygen vacancies at high temperatures are effective for CO₂ absorption. Especially Co ions are more active for CO absorption than Fe ions. These oxides were analyzed by EMS and TMS before and after treatment in CO₂ atmospheres. The difference between EMS and TMS spectra is found to be observed not only due to the oxygen affinity, but also to the different reactivity of Co and Fe ions in the B site towards CO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanooptical investigations of polyimide films exposed to electrons,mechanical loads,and temperatures

Joint effect of high-energy electrons, mechanical loads, and temperature on polyimide films of thicknesses in the range 30–130 μm is investigated. The films were preliminary irradiated by electrons in air using an éLU-6 linear accelerator with energy of 2 MeV and doses D = 1, 5, 10, 20, 30, 40, and 100 MGy and then subjected to uniaxial mechanical tension at temperatures (T) from 293 to 593 K. It is established that at T = 293–450 K and D = 20–40 MGy, the mechanical load causes almost the same deformations (ε_{l max}) of nonirradiated and irradiated samples; at T = 450–550 K, deformations of films sharply increase, and the character of their dependence changes. The ε_{l max} value of the initial sample increases almost linearly with temperature by a factor of 10, whereas the character of changing ε_{l max}(T) of the irradiated films is more complex, and its value increases approximately by a factor of 4. For T > 500 K, the deformation reaches limiting values. Irradiation increases the intensity of IR-spectra by 2–6 times and essentially increases the widths of absorption bands at 720, 1380, and 1775 cm⁻¹, which is caused by the formation of hydrogen bonds and cycles with nitrogen as well as by the formation of nitrogen oxides. External loading applied to film rupture causes an increase in the EPR signal amplitude from 3·10³ to 5·10³, which is connected with an increased concentration of radicals =N-H and-NH ₂. The electron irradiation of the polyimide films with their subsequent mechanical loading causes the spectrum lines to displace from 3475.0 to 3512.5 cm⁻¹ with simultaneous reduction of the signal amplitude from 6·10³ to 4·10³. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 52–58, February, 2007.     

Synthesis of boron nitride nanotubes by an oxide-assisted chemical method

We report a new method for the synthesis of boron nitride (BN) nanotubes employing a two-step process in which some oxides have found to catalyze the growth of BN nanotubes. In the first step, a precursor containing B–N–O–Fe/Mg was prepared by ball milling a mixture of B, B₂O₃, Fe₂O₃ and MgO (1:7:2:1 mass ratio) in NH₃ for 3 h. BN nanotubes (diameter: 20–100 nm) were grown in the second step from this precursor by isothermal annealing at 1,350 °C in NH₃ for about 4 h. XRD, SEM and HR-TEM studies elucidated the spindle-like morphology of these nanotubes of hexagonal crystal structure. The Raman spectrum showed the peak broadening and shifts to higher frequency. The present method showed that some oxides assisted the growth of BN nanotubes. A possible reaction mechanism on the formation of BN nanotubes in the presence of these oxides is discussed.     

Photoacoustic detection of NO2 and N2O using quantum cascade lasers

Pulsed quantum cascade lasers (QCLs) with 6.2-μm and 8-μm wavelengths and a differential photoacoustic (PA) detector were used to measure concentrations of NO₂ and N₂O in the sub-ppmv range at ambient pressure. The QCL temperatures were tuned between -40 °C and 30 °C. Good agreement was found between measured PA vibrational spectra and simulated HITRAN spectra of both nitrogen oxides. The PA signals showed a linear dependence on the concentration in the investigated 0.5–50 ppmv region in both cases. The results for N₂O are compared with a PA measurement of N₂O at 2.9 μm using a grazing-incidence optical parametric oscillator. PACS 42.62.Fi; 82.80.Kq; 82.80.Gk; 92.60.Sz     

High-temperature NO or NO2 sensor using stabilized zirconia and tungsten oxide electrode

Stabilized zirconia-based electrochemical devices for which the sensing electrode was provided with a single-metal oxide were tested for NO and NO₂ sensing properties at high temperature. Among the many single-metal oxides examined, WO₃ was found to give the best sensing properties to NO and NO₂ at 500–700°C. The EMF response of the WO₃-attached device was linear to the logarithm of NO or NO₂ concentration. The response and recovery kinetics were speedy. The device gave very small cross-sensitivities to H₂, CO, CH₄, CO₂ and water vapor. The sensing mechanism involving mixed-potential was confirmed from the measurements of polarization curves.     

Space-borne remote sensing of CO2, CH4, and N2O by integrated path differential absorption lidar: a sensitivity analysis

CO₂, CH₄, and N₂O are recognised as the most important greenhouse gases, the concentrations of which increase rapidly through human activities. Space-borne integrated path differential absorption lidar allows global observations at day and night over land and water surfaces in all climates. In this study we investigate potential sources of measurement errors and compare them with the scientific requirements. Our simulations reveal that moderate-size instruments in terms of telescope aperture (0.5–1.5 m) and laser average power (0.4–4 W) potentially have a low random error of the greenhouse gas column which is 0.2% for CO₂ and 0.4% for CH₄ for soundings at 1.6 μm, 0.4% for CO₂ at 2.1 μm, 0.6% for CH₄ at 2.3 μm, and 0.3% for N₂O at 3.9 μm. Coherent detection instruments are generally limited by speckle noise, while direct detection instruments suffer from high detector noise using current technology. The wavelength selection in the vicinity of the absorption line is critical as it controls the height region of highest sensitivity, the temperature cross-sensitivity, and the demands on frequency stability. For CO₂, an error budget of 0.08% is derived from our analysis of the sources of systematic errors. Among them, the frequency stability of ± 0.3 MHz for the laser transmitter and spectral purity of 99.9% in conjunction with a narrow-band spectral filter of 1 GHz (FWHM) are identified to be challenging instrument requirements for a direct detection CO₂ system operating at 1.6 μm. PACS 42.68.Wt; 95.75.Qr     

Production of collimated positronium by positron scattering from CO<Subscript>2</Subscript>, N<Subscript>2</Subscript> and Xe

The efficiency for collimated positronium production by charge-exchange in positron collisions with gaseous targets has been investigated in the range 20–396 eV. At 250 and 396 eV, CO₂ has been found to be approximately twice as efficient as N₂, the previous best neutralising gas at high energies. The efficiency from Xe, whilst lower at low energies, becomes comparable to that from H₂ at around 100–120 eV; at ∼250 eV, it is an order of magnitude lower.     

Kinetics of the Excited States of Helium in an Atmospheric-Pressure Glow Discharge in a Helium-Nitrogen Mixture

Using an atomic-absorption spectral analysis technique, we determined the concentrations of helium atoms in states 2¹S, 2¹P, 2³S, and 2³P in an atmospheric-pressure glow discharge in helium (99.98%) and in a mixture of helium with nitrogen (99.5%He+0.5%N₂). It is shown that the population of the lower excited levels of helium atoms (n = 2) in its mixture with nitrogen is almost an order of magnitude smaller than in the case of a discharge in helium. The maximum of the concentration of excited atoms in a discharge both in helium and in its mixture with nitrogen is in the cathode region at a distance of about 0.1 mm from the cathode. The reaction of quenching of excited helium atoms by nitrogen molecules is responsible for the sharp decrease in the concentration of He(n = 2) on addition of nitrogen into helium. Presented at the 5th Symposium on Physics and Diagnostics of Laboratory and Astrophysical Plasmas, Belarus, Serbia and Montenegro, Minsk, Belarus, September 20–23, 2004; 12th International Congress on Plasma Physics, October 25–29, 2004, Nice, France. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 530–537, July–August, 2005.     

Photoacoustic analysis of CO2 content in annual tree rings

We have used laser photoacoustic gas analysis to study the CO₂ content sorbed by the capillary porous system of annual rings in cross-sectional disks of some conifers. The measurement results showed that in most cases, the CO₂ content in gas samples extracted by the vacuum method from annual rings in the disks is higher than the CO₂ content in atmospheric air. In the disks, we observe an annual trend in the CO₂ concentration, correlating in a number of cases with a rise in atmospheric CO₂. The annual trend in the average value of the CO₂ concentration change sign from positive to negative. We hypothesize that the observed pattern for the annual distribution of CO₂ in the disks is connected with a rise in atmospheric CO₂ and a change in the concentration gradient between stem and atmospheric CO₂. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 477–480, May–June, 2009.     

Determination of binary diffusion coefficients of gases using photothermal deflection technique

A photothermal deflection (PD) technique was applied to measure the binary diffusion coefficients of various gases (CO₂–N₂, CO₂–O₂, N₂–He, O₂–He, and CO₂–He). With an in-house-made Loschmidt diffusion cell, a transverse PD system was employed to measure the time-resolved PD signal associated with the variation of the thermal diffusivity and the temperature coefficient of the refractive index of the gas mixture during the diffusion. The concentration evolution of the gas mixture was deduced from the PD amplitude and phase signals based on our diffraction PD model and was processed using two mass-diffusion models explored in this work for both short- and long-time diffusions to find the diffusion coefficient. An optical fiber oxygen sensor was also used to measure the concentration changes of the mixtures with oxygen. Experimental results demonstrated that the binary diffusion coefficients precisely measured with the PD technique were in agreement with the literature values. Moreover, the PD technique can measure the diffusion coefficients of various gas mixtures with both short- and long-time diffusions. In contrast, the oxygen sensor is only suitable for the long-time diffusion measurements of the gas mixtures with oxygen. PACS 78.20.Nv; 51.20.+d