CO<Subscript>2</Subscript> gas sensitivity of sputtered zinc oxide thin films

For the first time, sputtered zinc oxide (ZnO) thin films have been used as a CO₂ gas sensor. Zinc oxide thin films have been synthesized using reactive d.c. sputtering method for gas sensor applications, in the deposition temperature range from 130–153°C at a chamber pressure of 8·5 mbar for 18 h. Argon and oxygen gases were used as sputtering and reactive gases, respectively. ZnO phase could be crystallized using a pure metal target of zinc. The structure of the films determined by means of X-ray diffraction method indicates that the zinc oxide single phase can be fabricated in this substrate temperature range. The sensitivity of the film synthesized at substrate temperature of 130°C is 2·17 in the presence of CO₂ gas at a measuring temperature of 100°C.     

How is wettability of titanium surfaces influenced by their preparation and storage conditions?

The effect of two different etching procedures with inorganic acids (HSE and CSE)—one using additionally strongly oxidising conditions due to the presence of CrO₃ (CSE)—and consecutive storage conditions (dry methanol and air) for previous corundum blasted titanium surfaces is compared with respect to their wettability behaviour and the potential of the etching processes for removing remaining blasting material. The etching procedures result in distinct different surface morphologies. Whereas the HSE surface shows sub-mm to sub-μm structures but neither porosity nor undercuts, the CSE surface is extremely rugged and porous with structures protruding the more homogeneously attacked areas by several micrometers. By EDX analysis both remaining blasting material and chromium and sulphur from the etching treatment has been detected on the CSE surfaces only. Both surfaces states show super-hydrophilic behaviour immediately after etching and storage up to 28 days in dry methanol. Whereas contact with air does not change super-hydrophilicity for the CSE samples, wettings angles of the HSE samples increase within minutes and reach about angles of about 60° and 90° after one and 2 days exposure to air, respectively. The increasing hydrophobicity is discussed with respect to the formation of a surface coverage from hydrocarbons originating from aromatic compounds present in traces in air.     

Advances in sulfide phosphors for displays and lighting

For traditional applications such as cathode ray tubes and fluorescent lamps, many inorganic phosphors have been optimised during decades. For new applications in display and lighting technology, novel materials are being developed. After giving a short history of sulfide phosphors, the present paper will focus on Ca_1−x Sr _x S:Eu single crystal particle phosphors. The material is grown by solvothermal synthesis, process not needing toxic gases or high temperature processing steps. This phosphor combines a broad excitation spectrum and a broad—saturated red—emission spectrum, which makes it an ideal material for wavelength conversion in LEDs for general lighting.     

Insulation capability of the bark of trees with different fire adaptation

When exposed to a surface fire, the probability of a tree to survive widely varies, depending on its capability to protect the cambium from lethal temperatures above 60 °C. Thereby, the bark, the entirety of all tissues outside the cambium, serves as an insulation layer. In laboratory experiments, the heat production of a surface fire was simulated and the time span τ₆₀ until the temperature of 60 °C is reached in the inner bark surface was measured. Thereby, τ₆₀—as a measure of the fire resistance—was quantitatively determined for seven tree species. In addition, the influence of bark thickness and moisture content on bark heat insulation capacities was examined. Independent of the tree species and bark moisture content a power function correlation between bark thickness and τ₆₀ was found. Our results also show that fire resistance increases with decreasing bark density. The seven tree species examined can be classified in two groups differing highly significant in their bark structure: (1) tree species with a faintly structured bark, which show a low fire resistance, and (2) tree species with an intensely structured bark, showing a high fire resistance. Furthermore a mathematical model simulating heat conduction was applied to describe the experimental results, and some ideas for a transfer into biomimetic materials are presented.     

The vortex liquid piston engine and some other vortex technologies

By exploiting three unique characteristics of confined swirling incompressible flows — centrifugal acceleration, internal separation or recirculation zones near the axis, andbistability (i.e. rarefied and condensed stable states) of multi-phase flows — we developed several innovativevortex machines which will revolutionize mechanical technologies in a variety of industries. The machines utilizing these features include:Vortex Engine, Vortex Thruster, Vortex Suction Device, Vortex Chemical Reactor, Bubbling Centrifuge andVortex Mill. As a specific example, we describe here in some detail the development of a liquid piston engine, including analysis of its hydrodynamic and thermodynamic features. We have designed a laboratory ‘cold’ model and performed detailed experimental, theoretical and numerical analyses to study the role of the controlling parameters and are now ready to test a ‘hot’ model. In addition, we mention a few other vortex technologies of interest to us. A list of symbols used appears at the end of the paper.     

Effects of post-deposition annealing temperature and ambient on RF magnetron sputtered Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> gate on n-type silicon substrate

Samarium oxide (Sm₂O₃) thin films with thicknesses in the range of 15–30 nm are deposited on n-type silicon (100) substrate via radio frequency magnetron sputtering. Effects of post-deposition annealing ambient [argon and forming gas (FG) (90% N₂ + 10% H₂)] and temperatures (500, 600, 700, and 800 °C) on the structural and electrical properties of deposited films are investigated and reported. X-ray diffraction revealed that all of the annealed samples possessed polycrystalline structure with C-type cubic phase. Atomic force microscope results indicated root-mean-square surface roughness of the oxide film being annealed in argon ambient are lower than that of FG annealed samples, but they are comparable at the annealing temperature of 700 °C (Argon—0.378 nm, FG—0.395 nm). High frequency capacitance–voltage measurements are carried out to determine effective oxide charge, dielectric constant and semiconductor-oxide interface trap density of the annealed oxide films. Sm₂O₃ thin films annealed in FG have smaller amount of effective oxide charge and semiconductor-oxide interface trap density than those oxide films annealed in argon. Current–voltage measurements are conducted to obtain barrier heights of the annealed oxide films during Fowler–Nordheim tunneling.     

Thermoanalytical study of the polymorphism and melting behavior of Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

We have developed a procedure for the synthesis of phase-pure α- and β-Cu₂V₂O₇. Thermal analysis and X-ray diffraction demonstrate that the β-phase (monoclinic structure) exists at low temperatures (stability range 25–610°C), while α-Cu₂V₂O₇ (orthorhombic structure) is stable in the range 610–704°C. The α-phase observed during cooling, in particular at room temperature, is in a metastable state. The melting of the high-temperature phase γ-Cu₂V₂O₇, which forms between 704 and 716°C, has the highest rate in the range 770–785°S and is accompanied by peritectic decomposition and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9°C) is attributable to the crystallization of the peritectic melt, one (620.1°C) is due to the γ → α → β phase transformations of Cu₂V₂O₇, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing α- and β-Cu₂V₂O₇, CuVO₃, and other compounds.     

A statistical study of spots in torsional Couette flow

This article presents some results on the statistical behavior of localized structures—called “spots”—that propagate in the flow between a rotating and a stationary disk when those are very close one to the other. Under these conditions the rotating-disk flow belongs to the Couette-flow family and is called the torsional Couette flow. Some visualizations of its transition to turbulence have already revealed the propagation of these spots (Schouveiler et al., J Fluid Mech 443:329–350, 2001) from the rim of the disk towards its center. Using flow visualizations and an original image analysis, the present study aims to better describe the characteristics of the spots whose number continuously increases with the Reynolds number until they invade the whole flow. Moreover, we propose a statistical model that predicts an error-function shape for the probability to observe a spot at a given radial position. This prediction is confirmed by an image analysis of the flow and the stability curve of torsional Couette flow is deduced from these observations.     

Gasification of Belarusian oil shales in a filtration-combustion wave

The regimes of gasification of Belarusian oil shales have been analyzed based on a generalized volume-averaged filtration-combustion model. The existence of three basic regimes — those of cocurrent and countercurrent filtration waves and of low-temperature volume pyrolysis — has been established. Data on the conditions of their existence have been obtained. The heat content of a producer gas in shale gasification in a stationary cocurrent filtration-combustion wave with air and oxygen-enriched blast has been evaluated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 205–214, March–April, 2009.     

Spinel ferrites of the quaternary system Cu-Ni-Fe-O: Synthesis and characterization

The decomposition of the freeze dried Cu(II)-Ni(II)-Fe(III) formate precursors at 1000°C in air yields complex oxides Cu_xNi_1−xFe₂O_4±δ (0 ≤ x ≤ 1) with a cubic spinel structure. For x < 0.7, single phase spinels are formed at 1000°C. However, for 0.7 ≤ x ≤ 1, Copper oxide (CuO) is identified as a second phase and the formation of a pure spinel phase requires an increase of the iron content in the mixture. For example, Cu_0.81Ni_0.1Fe_2.09O₄ is a single phase at 1000°C/air. Other single spinel phases Cu_0.5+yNi_0.5−y−zFe_2+zO_4±δ, 0 ≤ (y + z) ≤ 0.5, in the phase triangle Cu_0.5Ni_0.5Fe₂O₄–CuFe₂O₄–Cu_0.5Fe_2.5O₄ have been synthesized under special p(O₂)/T—synthesis conditions. The increase of the iron content requires an increase of the reaction temperature and/or a decrease of the p(O₂) in the reaction gas stream. The oxygen exchange between Cu_0.9Fe_2.1O_4.02 and the reducing gaseous phases shows that the non stoichiometry δ of copper ferrite is only about ±0.03. Significant changes in the oxygen content lead to the separation in different phases. The electrical and magnetic properties of copper ferrite samples depend on their chemical composition and preparation conditions.     

Influence of nitriding gases on the growth of boron nitride nanotubes

Boron nitride (BN) nanotubes of different sizes and tubular structures exhibit very different mechanical and chemical properties, as well as different applications. BN nanotubes of different sizes and nanostructures have been produced in different nitriding gases in a milling and annealing process, in which elemental boron powder was first milled in NH₃ for 150 h and subsequently annealed at 1,200 °C for 6 h. The influence of nitriding gases was investigated by using N₂, NH₃, N₂–H₂ mixture gases. A relatively slow nitriding reaction in NH₃ gas leaded to a 2D growth of BN (002) basal planes and the formation of thin BN nanotubes without the help of metal catalysts. Fast nitriding reactions occurred in N₂ or N₂–H₂ mixture gases, catalyzed by metal particles, resulted in 3D crystal growth and the formation of many large cylindrical and bamboo tubes.     

A New Instrument for the Measurement of the Thermal Conductivity of Fluids

The transient hot-wire technique is at present the best technique for obtaining standard reference data for the thermal conductivity of fluids. It is an absolute technique, with a working equation and a complete set of corrections reflecting departures from the ideal model, where the principal variables are measured with a high degree of accuracy. It is possible to evaluate the uncertainty of the experimental thermal conductivity data obtained using the best metrological recommendations. The liquids proposed by IUPAC (toluene, benzene, and water) as primary standards were measured with this technique with an uncertainty of 1% or better (95% confidence level). Pure gases and gaseous mixtures were also extensively studied. It is the purpose of this paper to report on a new instrument, developed in Lisbon, for the measurement of the thermal conductivity of gases and liquids, covering temperature and pressure ranges that contain the near-critical region. The performance of the instrument for pressures up to 15 MPa was tested with gaseous argon, and measurements on dry air (Synthetic gas mixture, with molar composition certified by Linde AG, Wiesbaden, Germany, Ar – 0.00920; O₂ – 0.20966; N₂ – 0.78114), from room temperature to 473 K and pressures up to 10 MPa are also reported. The estimated uncertainty is 1%.M. L. V. Ramires: DeceasedPaper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Acid functionalization of carbon nanofibers

We have studied the effects of temperature (70–100°C), process duration (1–4 h), and the ratio of the acid mixture (concentrated HNO₃ and H₂SO₄ in the volume ratio 1: 3) volume to carbon nanofiber weight (70: 1 to 133: 1 ml/g) on the yield of functionalization products and their dispersibility in water. The results indicate that, with increasing temperature and process duration, the yield of functionalization products decreases, and their concentration (“solubility”) in the aqueous dispersion increases: from 1.2–1.3 to 11.0 mg/ml when the yield decreases from 71–89 to 30%. We present the first measurements of the gas volume evolved during functionalization and show that it increases with increasing temperature and process duration, reaching 500–600 ml/g carbon under the most severe conditions. The major component of the reaction gases is CO₂ (over 50 vol %).     

Synthesis,characterization and gas sensing performance of SnO<Subscript>2</Subscript> thin films prepared by spray pyrolysis

In this work, SnO₂ thin films were deposited onto alumina substrates at 350°C by spray pyrolysis technique. The films were studied after annealing in air at temperatures 550°C, 750°C and 950°C for 30 min. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption spectroscopy technique. The grain size was observed to increase with the increase in annealing temperature. Absorbance spectra were taken to examine the optical properties and bandgap energy was observed to decrease with the increase in annealing temperature. These films were tested in various gases at different operating temperatures ranging from 50–450°C. The film showed maximum sensitivity to H ₂S gas. The H₂S sensing properties of the SnO₂ films were investigated with different annealing temperatures and H ₂S gas concentrations. It was found that the annealing temperature significantly affects the sensitivity of the SnO₂ to the H ₂S. The sensitivity was found to be maximum for the film annealed at temperature 950°C at an operating temperature of 100°C. The quick response and fast recovery are the main features of this film. The effect of annealing temperature on the optical, structural, morphological and gas sensing properties of the films were studied and discussed.     

Structural and electrical measurements of CdZnSe composite

TheI—Vcharacterization and the electrical resistivity of selenium rich Se₈₅Cd_15-xZn_x (x = 0, 3, 7, 11 and 15) system at room temperature have been studied. Samples were obtained using melt cooling technique. So prepared samples were then characterized in terms of their crystal structure and lattice parameter using X-ray diffraction method. The materials were found to be poly crystalline in nature, having zinc blend structure over the whole range of zinc concentration. The measurements ofI—V bdcharacteristics have been carried out at different temperatures from room to 140°C. The electrical resistivity of the samples with composition at room temperature has been found to vary between maximum 2.7 x 10⁸ Ωm and minimum 7.3 x 10⁵ Ωm and shows a maximum at 3 at. wt.% of Zn. The carrier activation energy of the samples with composition has also been determined and found to vary from 0.026 eV to 0.111 eV.     

Deflagration-to-detonation transition in gases in tubes with cavities

The existence of a supersonic second combustion mode — detonation — discovered by Mallard and Le Chatelier and by Berthélot and Vieille in 1881 posed the question of mechanisms for transition from one mode to the other. In the period 1959–1969, experiments by Salamandra, Soloukhin, Oppenheim, and their coworkers provided insights into this complex phenomenon. Since then, among all the phenomena related to combustion processes, deflagration-to-detonation transition is, undoubtedly, the most intriguing one. Deflagration-to-detonation transition (DDT) in gases is connected with gas and vapor explosion safety issues. Knowing mechanisms of detonation onset control is of major importance for creating effective mitigation measures addressing two major goals: to prevent DDT in the case of mixture ignition, or to arrest the detonation wave in the case where it has been initiated. A new impetus to the increase in interest in deflagration-to-detonation transition processes was given by the recent development of pulse detonation devices.     

Producing clean diesel fuel by co-hydrogenation of vegetable oil with gas oil

The goal of our investigation was the production of partially bio-derived fuels in the gas oil boiling point range. Our aim was the production of diesel fuel blending components by co-hydrogenation of mixtures of high-sulphur gas oil (about 1.0%) and vegetable oil raw materials with different vegetable oil contents (0, 5, 15, 25 and 100%). The experiments were carried out on a NiMo/Al₂O₃ catalyst with a targeted composition (T = 300–380°C, P = 60–80 bar, LHSV = 1.0/h and H₂/HC = 600 Nm³/m³). We obtained that both the vegetable oil conversion reactions and the gas oil quality improvement reactions took place. Under the favourable operational conditions (360–380°C, P = 80 bar, LHSV = 1.0/h and H₂/HC = 600 Nm³/m³ and up to 15% vegetable oil content of the feed), the main properties of the high-yield (>90%) products except for the Cold Filter Plugging Point (CFPP) value satisfied the requirements of the standard of diesel fuels (EN 590:2009). The amount of vegetable oil higher than 15% reduced the desulphurization efficiency, because of the intake of large quantities of oxygen with the triglyceride molecules of the vegetable oil. The products—depending on the vegetable oil content of the feedstocks—have an increased n- and i-paraffin content, so their combustion properties are very favourable, and the emission of particles is lower.     

Laser induced plasma in the formation of surface-microstructured silicon

The plasma induced by femtosecond laser pulses irradiated on silicon surface has been investigated by optical emission spectroscopy. The plasma emission spectra show strong dependence on the structuring ambient gas species and pressure. Among the four ambient gases (SF₆, N₂, air and vacuum), the plasma obtained in sulfur hexafluoride (SF₆) shows the strongest signals. The emission intensities increase initially with the gas pressure, and achieve strongest at the pressure of about 70 kPa, then decrease as the pressure further increases. The stronger plasma emission signals indicate stronger reactions, resulting in sharper sample morphology, which provides an insight into the reaction process.     

High-temperature heat and mass transfer in a layer of coke of heat-shielding materials

The model including the structure inhomogeneity of the coke of a typical “charring” heat-shielding material (HSM) is used to investigate the process of high-temperature heat and mass transfer in a layer of HSM coke. The scales are determined of temperature nonequilibrium between condensed and gaseous products of thermal decomposition of HSM under conditions of high (above 1000 K) temperatures of the environment. It is demonstrated that, in solving numerous problems associated with heat shielding, it is appropriate to employ models including the temperature nonequilibrium of the gas and condensed phases of HSM coke.     

Fast pyrolysis of an ensemble of biomass particles in a fluidized bed

A combined approach to the modeling of fast pyrolysis of biomass particles in a fluidized bed has been used. We used models of different levels: two models of pyrolysis of a single particle — with lumped and distributed parameters — and a model of pyrolysis of an ensemble of biomass particles based on the continuum equations for the gas blown through the bed and the equations of motion for individual particles. We have determined optimal (in terms of the biofuel yield) temperatures of the process for various particle sizes of wood biomass and various values of its moisture.