The study of structure and work function of barium oxide films and the BaO double system on the (0001) face of rhenium: I. Barium oxide on rhenium (0001) face

The structure of barium oxide films on the (0001) face of rhenium has been investigated by the techniques of low energy electron diffraction (LEED) and contact potential difference method in a wide range of coverages. The changes in surface structure of the BaO films have been observed after annealing at various temperatures. It was shown that the structure and orientation of the films depended essentially on the interaction of barium oxide with the substrate. The result of this interaction was equivalent to the oxidation of the (0001) face of rhenium. This fact was confirmed by experiments with the adsorption of BaO films on an oxidized substrate. The structures observed after heating to high temperatures (900°–1000°C) seem to be formed by the products of chemical interaction of barium oxide with rhenium (rhenates).     

Synthesizing of ZnO Micro/Nanostructures at Low Temperature with New Reducing Agents

Instead of the conventional graphite, new additional reducing agents （diamond, silicon, metal elements, etc.） have been mixed with zinc oxide （ZnO） powder to fabricate ZnO micro/nanostructures by a thermal vapour transport method. Due to the strong reducibility for those additions, the corresponding heating temperature is decreased by 100 500℃ compared to the case of graphite, which subsequently decreases the corresponding growth temperature for the products. Being placed separately for the powder sources of ZnO and addition, a vapour-vapour reduction-oxidation reaction mechanism between the sources is proposed as an important channel to fabricate ZnO. Photoluminescence and magnetic examinations indicate that the ZnO products synthesized have strong ultraviolet （visible） emissions and are room-temperature ferromagnetic, meaning that the products are available for applications.     

Thermal conductivity of the amorphous and nanocrystalline phases of the beech wood biocarbon nanocomposite

Natural composites (biocarbons) obtained by carbonization of beech wood at different carbonization temperatures T _carb in the range of 800–2400°C have been studied using X-ray diffraction. The composites consist of an amorphous matrix and nanocrystallites of graphite and graphene. The volume fractions of the amorphous and nanocrystalline phases as functions of T _carb have been determined. Temperature dependences of the phonon thermal conductivity κ(T) of the biocarbons with different temperatures T _carb (1000 and 2400°C) have been analyzed in the range of 5–300 K. It has been shown that the behavior of κ(T) of the biocarbon with T _carb = 1000°C is controlled by the amorphous phase in the range of 5–50 K and by the nanocrystalline phase in the range of 100–300 K. The character of κ(T) of the biocarbon with T _carb = 2400°C is determined by the heat transfer (scattering) in the nanocrystalline phase over the entire temperature range of 5–300 K.     

Trace analyses of gaseous products formed during heat treatment of high stage H2SO4-GICs and expanded graphite

H₂SO₄-GICs samples prepared by different methods were heated to 1000 °C under flow of air using heating rates of 2, 10 and 20 K/min Gaseous products of decomposition were analysed using FTIR spectra recorded during the thermal process. It was detected that S–O species started evolving from graphite gallery above 500 °C, not depending on the method of GIC preparation. High expansion of H₂SO₄-GIC was observed when the intercalate evolved from the intercalated graphite before its abrupt oxidation to CO₂. The disordered structure of graphite layers in H₂SO₄-GIC leads to easy release of S–O species without exfoliation effect. It was observed that using 2 K/min heating rate the time needed for intercalate to release from graphite gallery is shorter than that needed for its exfoliation. Therefore, the exfoliation process should be conducted using high heating rate.     

Distribution of light alkanes in the reaction of graphite hydrogenation at pressure of 0.1–7.8 GPa and temperatures of 1000–1350°C

ABSTRACT

We studied the effect of pressure and temperature on the hydrocarbon (HC) chain length distribution and total amount of HCs in the reaction of direct graphite hydrogenation at pressures of 0.1–7.8?GPa and temperatures of 1000–1350°C. An increase in pressure was found to lead both to an increase in the absolute yield of HCs due to direct graphite hydrogenation and to chain elongation of HC products. Light alkanes predominate among HCs in the entire studied range of P–T parameters. However, their concentration in quenched fluids increases as pressure is elevated, from less than 10?rel.% at 0.1?GPa to more than 40–50?rel.% at P?≥?3.8?GPa. Methane is actually the only light alkane among reaction products at 0.1?GPa and 1000°C, while it is a minor component at 7.8?GPa and 1350°C. The most stable alkane at pressures above 3.8?GPa is ethane (C₂H₆).     

Graphite–boron composite heater in a Kawai-type apparatus: the inhibitory effect of boron oxide and countermeasures

We have investigated the performance of a graphite–boron composite (GBC) with 3?wt % boron as a precursor for a boron-doped diamond heater in a Kawai-type apparatus at 15?GPa. We first tested a machinable cylinder of GBC sintered at 1000°C in Ar/H₂ gas (99:1 molar ratio). Boron oxide (B₂O₃) formed during sintering frequently hindered the GBC heater from stable operation at temperatures higher than 1400°C by producing melt throughout the heater together with oxide and/or silicates. We then rinsed the GBC heater in hydrochloric acid to remove B₂O₃. After rinsing, we succeeded in stably generating temperatures higher than 2000°C. We also improved a molding process of different-sized GBC tubes for convenient use and tested the molded GBC heater. It was free from the B₂O₃ problem. The electromotive force of the W/Re thermocouple was successfully monitored up to 2400°C.     

Kinetics of the oxidation of an electroexplosion iron nanopowder during heating in air

The regularities of the oxidation of electroexplosion iron nanopowder, produced by the wire electric explosion, heated in air under conditions of linearly increasing temperature and in the isothermal mode are examined. The oxidation process under conditions of linear heating is demonstrated to occur stepwise due to the combined influence of the fractional composition of the powder, its phase composition, and the structure of the oxide layer formed on the surface of the particles. It is shown that, under isothermal conditions (250–600°C), the oxidation of the nanopowder, as opposed to micron-sized powders, obeys a linear law and proceeds in the kinetic regime with E _a = 100 ± 7 kJ/mol. The conditions of thermogravimetry analysis at which the thermal self-ignition of the nanopowder occurs are determined. Based on the numerical evaluation of the sample surface heating parameter, the experimentally measured critical temperature is verified.     

A new method for deaggregation of nanodiamond from explosive detonation: Graphitization-oxidation method

In this communication, a new method for the deaggregation of detonation nanodiamond (ND) and some preliminary results using this method are presented. ND is firstly graphitized in nitrogen at 1000°C and then oxidized by air at 450°C to remove the surface graphite layer formed. The sample after such treatment was suspended in water by ultrasonics, and the particle-size distributions were measured. It has been found that the diameters of more than 50% of the ND particles can be reduced to less than 50 nm.     

The role of chemical reactions in the Chernobyl accident

It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80–110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000°C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.     

Phase Transitions in a Mixture of Amorphous C<Subscript>60</Subscript> and C<Subscript>70</Subscript> Fullerene Phases at High Temperatures and Pressures

Phase transitions in two types of amorphous fullerene phases (C₆₀–C₇₀ (50/50) mixtures and an amorpous C₇₀ fullerene phase) are studied via neutron diffraction at pressures of 2–8 GPa and temperatures of 200–1100°C. Fullerenes are amorphized by grinding in a ball mill and sintered under quasi-hydrostatic pressure in a toroidal-type chamber. Diffraction studies are performed ex situ. It is shown that the amorphous phase of fullerenes retains its structure at temperatures of 200–500°C, and amorphous graphite is formed at 800–1100°C with a subsequent transition to crystalline graphite. This process is slow in a mixture of fullerenes, compared to C₇₀ fullerene. According to neutron diffraction data, the amorphous graphite formed from amorphous fullerene phases has anisotropy that is much weaker in a fullerene mixture.     

Optical characteristics of particles produced using electroerosion dispersion of titanium in hydrogen peroxide

Titanium oxide particles are produced using electric-discharge dispersion of titanium in aqueous solution of hydrogen peroxide. Electron vacuum microscopy, X-ray diffraction, and diffuse reflection spectroscopy are used to study the morphology, composition, and optical characteristics of the erosion particles. It has been demonstrated that the particles consist of titanium and titanium oxides with different valences. The edge of the optical absorption is located in the UV spectral range. The band gap is 3.35 eV for indirect transitions and 3.87 eV for direct allowed transitions. The band gap decreases due to the relatively long heating in air at a temperature of 480–550°C, so that powder oxide compositions can be obtained, the optical characteristics of which are similar to optical characteristics of anatase. The erosion products are completely oxidized to rutile after annealing in air at a temperature of 1000°C.     

DFT study on the effect of relative positions of methyl-, nitro- and N→oxide groups on the molecular structure,thermal/kinetic stability,crystal density,heat of decomposition and performance characteristics of triazolones

Methyl-, nitro- and N→oxide substituted triazolones are of interest in the contest of high-energy density compounds and have been found to have true local energy minima at the B3LYP/aug-cc-pVDZ level. The optimised structures, harmonic frequencies and thermodynamic values for all the model molecules have been obtained in their ground state. The velocity of detonation (D) and detonation pressure (P) have been evaluated by the Kamlet–Jacob equations using the crystal density and the heat of explosion. The estimated performance properties are higher (D = 9.92–10.27 km/s, P = 48.10–52.52 GPa) compared with 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D = 9.20 km/s, P = 42.0 Gpa). The higher densities are possibly due to the intramolecular hydrogen bonds and the layered structures in the crystal lattice. We speculate that the calculated heat of explosion and the density are for the gas phase compounds and in the reality they should be for the solid phase which would diminish the magnitude of the calculated values. The –N→O and –NO₂ group leads to the desirable consequences of higher heat of explosion and diminished sensitivities. The substituting of N–H hydrogen atom(s) of triazolones for a –CH₃ group decreases melting point, heat of formation and density; however, the methyl group increases the thermal stability.     

Micromechanism of sulfurizing activated carbon and its ability to adsorb mercury

The effect of ambient environment (dry or wet) and overlapping laser pulses on the laser ablation performance of brass has been investigated. For this purpose, a Q-switched, frequency doubled Nd:YAG laser with a wavelength of 532 nm, pulse energy of 150 mJ, pulse width of 6 ns and repetition rate of 10 Hz is employed. In order to explore the effect of ambient environments, brass targets have been exposed in deionized water, methanol and air. The targets are exposed for 1000, 2000, 3000 and 4000 succeeding pulses in each atmosphere. The surface morphology and chemical composition of ablated targets have been characterized by using Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Attenuated Total Reflection (ATR) techniques. In case of liquid environment, various features like nano- and micro-scale laser-induced periodic surface structures with periodicity 500 nm–1 μm, cavities of size few micrometers with multiple ablative layers and phenomenon of thermal stress cracking are observed. These features are originated by various chemical and thermal phenomena induced by laser heating at the liquid–solid interfaces. The convective bubble motion, explosive boiling, pressure gradients, cluster and colloid formation due to confinement effects of liquids are possible cause for such kind of features. The metal oxides and alcohol formed on irradiated surface are also playing the significant role for the formation of these kinds of structure. In case of air one huge crater is formed along with the redeposition of sputtered material and is ascribed to laser-induced evaporation and oxide formation.     

Activation and cleaning of oxide surfaces by a cw CO2 laser

Silica, alumina, and zinc oxide surfaces have been dehydroxylated by a cw CO₂ laser. Three to seven W/cm² produce the same surfaces spectroscopically as does heating at 400–1000°C. Varying the laser power while keeping the total number of photons constant shows that this is not a linear photochemical process and may be purely thermal desorption. Laser heating has a number of practical advantages over traditional heating methods which have been used for surface cleaning and activation.     

Forming mechanism of nitrogen doped graphene prepared by thermal solid-state reaction of graphite oxide and urea

Nitrogen doped graphene was synthesized from graphite oxide and urea by thermal solid-state reaction. The samples were characterized by transmission electron microscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, element analysis, and electrical conductivity measurement. The results reveal that there is a gradual thermal transformation of nitrogen bonding configurations from amide form nitrogen to pyrrolic, then to pyridinic, and finally to “graphitic” nitrogen in graphene sheets with increasing annealing temperature from 200 to 700 °C. The products prepared at 600 °C and 700 °C show that the quantity of nitrogen incorporated into graphene lattice is ∼10 at.% with simultaneous reduction of graphite oxide. Oxygen-containing functional groups in graphite oxide are responsible for the doping reaction to produce nitrogen doped graphene.     

Behavior of Volatile Elements in the Graphite Furnace in the Presence of Silver as Matrix Modifier

The effect of silver, as an aqueous solution of AgNO₃, on the pretreatment and atomization behaviour of As, Cd, Bi, Hg, Pb, Sb, Se, Sn and Tl during electrothermal atomic absorption spectrometry has been investigated. The presence of silver in the graphite furnace leads to thermal stabilisation of all investigated volatile elements to allow higher pyrolysis temperatures. The maximum, loss‐free, pretreatment temperatures (°C) in the presence of 100 µg Ag by atomization from the wall or from a platform are respectively: As (1500°C, –); Cd (800°C, 800°C); Bi (700°C, 700°C); Hg (250°C, –); Pb (600°C, 900°C); Sb (1200°C, 1200°C); Se (1400°C, 1400°C); Sn (1100°C, 1100°C) and Tl (1000°C, 1100°C). Also, silver facilitates a relatively low atomization temperature (°C) from the wall for Cd (1300°C), Bi (1700°C), Pb (1400°C), Se (1900°C) and Tl (1400°C). In addition, silver enhances the measurement sensitivity by a factor of 1.2–1.8.     

Modeling and simulation of planar SOFC to study the electrochemical properties

In this paper, modeling and simulations are carried out using COMSOL Multiphysics. A three-dimensional model is developed for a planar intermediate temperature (IT) solid oxide fuel cell (SOFC). A parametric study has been carried out to analyze the performance of SOFC.Simulations reveal some promising features and enhanced performance of SOFC. It is shown that the maximum value of power (4–3.3) kW/m² still remains higher with significant rise of temperature (600 °C–1000 °C), nearly 0.15 kW/m² is the very small loss of power per 100 °C rise of temperature. Results have shown that the electrolytic current density is (6700–5500) A/m² for peak value of power (4–3.3) kW/m² with increase of temperature (600 °C–1000 °C). For model validation we have plotted a comparison of average current density.     

Investigating Thin Ti–O–N Films Deposited via Reactive Magnetron Sputtering

Infrared spectroscopy and atomic emission analysis help establish the corrosion resistance of Ti?O–N films deposited on steel substrates via reactive magnetron sputtering, along with potential biological activity by detecting nitric oxide in model solutions after contact with Ti–O–N coatings. Differential thermal analysis and scanning electron microscopy allow the thermal stability of the films to be judged at temperatures of up to 1300°C.     

In situ Mössbauer spectroscopic study of iron III chloride intercalated in graphite under reaction conditions

In situ⁵⁷Mössbauer spectroscopy has been used to study the process of reduction and Fischer-Tropsch reactions on FeCl₃ intercalated in graphite layers. It is found that on flowing H₂ on graphite intercalated by FeCl₃ at 400° C, FeCl₃ converts to FeCl₂ and partly to small particles of α-Fe. The Mössbauer spectra of the reduced sample are superposition of a sextuplet and two quadrupole doublets indicative of metallic iron and two species of FeCl₂. However, at room temperature and at 400° C for a short period of reduction the magnetic hyperfine splittings (ca. 295 kOe and 262 kOe respectively) are smaller than the corresponding parameters for bulk metallic iron. The differences have been attributed to the interaction between the monolayers of iron atoms and the carbon nets of the graphite support. When the reduction was carried out for a longer period, α-Fe was formed. When a sample reduced for a short period of time is heated at 400°C in the presence of the synthesis gas, part of the iron particles sinter, and α-iron is observed. On heating the above sample once again at 400°C in the presence of the synthesis gas, the remaining small particles of iron are totally converted to the bulk phase (α-Fe). Experimental observations indicate that α-Fe and FeCl₂ are present on the surface as well as inbetween the intercalated graphite layers.     

Rearrangement of the Ultrasmooth Surface of La3Ga5SiO14 Crystals at Heating

The morphology and phase composition of the surface of La₃Ga₅SiO₁₄ (langasite) crystals at annealing in a temperature range 1000–1200°C have been studied using electron and atomic force microscopy. It has been shown that trigonal lanthanum oxide (La₂O₃) crystals with sizes to 3–4 μm, as well as a microstructure with sizes to 50 μm with gallium excess, with the approximate composition of 15 mol % La₂O₃, 65 mol % Ga₂O₃, and 20 mol % SiO₂ are formed on the surface of langasite crystals annealed in air at temperatures above 1100°C. Possible reasons for thermal destruction of the compound can be a significant rearrangement of the disordered crystal structure of langasite caused by the interaction with air oxygen and under the intense surface diffusion of atoms of the crystal, as well as the incongruent character of melting of the La₃Ga₅SiO₁₄ compound. The revealed thermal destruction of the surface of langasite crystals should be taken into account when using this material to fabricate piezoelectric elements for operation at high temperatures.