Behavior of coal-chlorine in chemical looping combustion

This work focuses on two aspects: (i) the behavior of coal-derived chlorine in chemical looping combustion (CLC); (ii) the potential adverse impacts of primary gaseous chlorine (i.e., HCl) on Cu-based oxygen carrier (OC). The inactivation mechanism of the sol-gel-derived CuO/Al₂O₃ OC is investigated. Systematic experiments are conducted in a batch fluidized reactor. First, in CLC of coal, chlorine distribution including HCl, Cl₂, Cl adsorbed in the outlet tube and Cl in solid phase is studied under various bed inventories, temperatures and gas atmospheres. The main gaseous Cl from coal is HCl, which shows a high reactivity towards CuO and is partially physically adsorbed by Al₂O₃. Unconverted HCl is 15.63 ± 0.20%, which could result in corrosion of the CO₂ transportation line and compression equipment. What's more, the coal ash exhibits a dechlorination function by forming KCl and CaCl₂. The CO₂ atmosphere and high temperature in fuel reactor show a promotion on the conversion of coal-Cl to HCl. Then, the corrosion of various OC components is evaluated by a mixture gas with 400 ppm HCl, i.e., Cu-Al (whole OC), CuO (active phase) and Al₂O₃ (inert support phase). It is found that a part of HCl is converted to Cl₂ via the Deacon reaction (4HCl + O₂ = 2H₂O + 2Cl₂) and oxidized by CuO (2CuO + 4HCl = 2CuCl + Cl₂ + 2H₂O). At the high concentration of HCl (400 ppm) atmosphere, CuO is partially lost from the OC, producing the gaseous copper chlorides, i.e., CuCl and (CuCl)₃, which are found to be condensed in the outlet tube. Besides, the solid-phase copper chlorides also degrade the oxygen donation capacity of the OC. Finally, the migration path of coal-chlorine during CLC is summarized. This work will contribute to the development of Cl-resistance OCs and control approaches for Cl emission.     

Investigation of the diocotron instability of an infinitely wide sheet electron beam by using the macroscopic cold-fluid model theory

This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting walls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory. Assuming low-frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency ω_c to a wider usage range, which is restricted to be much larger than the plasma frequency ω_p in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by augmenting the normalized beam thickness to a conductor gap larger than a threshold λ_b, which is greatly dependent on the parameter ω_c/ω_p. The larger ω_c/ω_p is, the smaller λ_b will be needed. Moreover, the system parameters, including the wave number k_x of the perturbations and the relativistic mass factor γ_b, will also influence the growth rate of diocotron instability obviously.     

The ion streaming effect on Weibel instability in the relativistic dense plasma

The Weibel instability plays an important role in stopping hot electrons and energy deposition mechanism in fast ignition of inertial fusion process. In this paper, the ion Weibel instability in counter propagating electron‐ion plasmas is investigate. The obtained results show that the growth rate of Weibel instability will be decreased about 40% with the anisotropy velocity as v_xe = 2v_ze = 20; the ion density ratio, b = n _{0i 1}/n _{0i 2}, and density gradient, are increasing 50 and 90% respectively. The ion streaming in density gradient of dense plasma leads to increasing the Weibel instability growth rate and its amplification through ion streaming in the large wavenumber. The maximum unstable wavenumber has been decreased with decreasing the ion beam density ratio. For fixed ion density ratio, increasing 90% of the density gradient in the near of fuel plasma corona leads to reducing growth rate and unstable wavenumber about 43 and 42% respectively.     

Formation and measurement of cluster beams at gasdynamic cooling of CF2HCl molecules

The clustering of CF₂HCl (Freon-22 refrigerant) molecules is found to take place when these molecules are dynamically cooled in a pulsed supersonic beam. A method of CF₂HCl cluster beam diagnostics is developed that combines UV multiphoton ionization, time-of-flight mass spectroscopy, and cluster IR photodissociation. The velocity of directed motion of (CH₂HCl)_n clusters, as well as the longitudinal and transverse velocities of their thermal motion, are measured at different stagnation pressures P ₀. The cluster mean size and the degree of clustering in the flow are estimated depending on supersonic flow conditions.     

Magnetic field dependence of the Peierls instability in one-dimensional conductors

We show that an applied magnetic field will suppress the Peierls instability in one-dimensional conductors. The effect is big enough to be observable. In sufficiently strong fields the transition between the metallic and insulating state is due to the condensation of a phonon with wave vectorq≠2p _F, but close to 2p _F. The role of spinorbit interactions is also discussed.     

Comparative study of NH4OH and HCl etching behaviours on AlGaN surfaces

A controlled AlGaN surface preparation method avails to improve the performance of GaN-based HEMT devices. A comparative investigation of chemical treatments by (1:10) NH₄OH:H₂O and (1:10) HCl:H₂O solutions for AlGaN surface preparation by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) is reported. The XPS data clearly reveal that the native oxide on AlGaN was composed of Al₂O₃, Ga₂O₃ and NO compounds. These compounds were etched off partially or completely by both the chemical treatments, namely NH₄OH or HCl solutions, independently. The HCl treatment etches out Al₂O₃ completely from native oxide unlike NH₄OH treatment. The HCl treatment results in larger amount of carbon segregation on AlGaN surfaces, however it removes all oxides’ compounds faster than NH₄OH treatment. The AFM results reveal the improvement of surface morphology by both the chemical treatments leading to the surface roughness RMS values of 0.24 nm and 0.21 nm for NH₄OH and HCl treated AlGaN layers, respectively.     

Size-Dependent HCl Generation of PVC/SiO2 Micro- and Nanocomposites

In this study HCl generation of polyvinyl (chloride) (PVC)/SiO₂ composites during its combustion was investigated. SiO₂ with different particle sizes were used as HCl absorbers and their HCl uptake ability results were compared to that of CaCO₃. It was found that the amount of released HCl gas during PVC combustion decreased in the presence of SiO₂. The HCl uptake ability of SiO₂ improved with decreasing of its particle size. Although thermogravimetric analysis (TGA) results showed that SiO₂ particles decreased the first thermal degradation temperature (T _onset) of PVC by initiating dehydrochlorination of PVC at lower temperatures, SiO₂ particles had more effective HCl uptaking ability than that of CaCO₃. Scanning electron microscopy (SEM) micrographs showed that some aggregates whose size was less than 100 nm were formed when Si-25 nm was used as filler. When SiO₂ with micron size was added to PVC as filler, more uniform and better distribution of the SiO₂ on the surface was observed.     

Mössbauer Investigation of the Itinerant Magnets U(Ga0.98Sn0.02)3 and CeFe2

The theoretical predictions that UGa₃ and CeFe₂ should be regarded as itinerant magnets stimulated new investigations. In this paper we focus on Mössbauer measurements aimed to characterize their magnetic properties. We show that the analysis of the transferred hyperfine interactions at the ¹¹⁹Sn nuclei in U(Ga_0.98Sn_0.02)₃, a type II antiferromagnet, provides direct information on the f-p hybridization and allows to determine the orientation of the U moments. The study of CeFe₂ demonstrates that the intrinsic ferromagnetism coexists with short range antiferromagnetic correlations. The instability of the ferromagnetic state is illustrated by doping CeFe₂ with a small amount of Co and by application of pressure on pure CeFe₂. Our results will be discussed in connection with neutron and synchrotron experiments.     

Comment on the 4kF instability of quasi-one-dimensional systems

It will be shown that the 4k_F-instability, as observed in some TCNQ compounds, may be understood as a second-order effect of the electron gas. Moreover, the presented approach suggests a further instability at 6k_F.     

Linewidths of HCl broadened by CO2 and N2 and CO broadened by CO2

High resolution measurement of the linewidths of HCl broadened by CO₂ and N₂ and CO broadened by CO₂ have been performed in both the 1-0 and 2-0 bands of HCl and the 2-0 band of CO. The data were analyzed by the direct and the peak absorption methods. Values of the linewidths obtained by the two methods are in good agreement. For |m| ≤ 3, for the case of HCl + CO₂, the agreement is good for the values obtained in both bands of HCl. However for |m| > 3, the HCl + CO₂ linewidths in the 1-0 band are smaller than the corresponding lines in the 2-0 band by as much as 11% for |m| = 9. Lines (|m| ≤ 3) of the 1-0 and 2-0 bands of HCl broadened by CO₂ were also analyzed in terms of the super-Lorentzian line profile proposed by Varanasi, S. K. Sarangi, and G. D. T. Tejwani (J. Quan. Spectr. Radiative Transfer12, 857 (1972)) and the Lorentzian profile. The results indicate that near the line center (within 3γ), the shape of HCl + CO₂ lines are Lorentzian.     

The effect of acids on fluorescence of coumarin-6 in organic solvents

The effect of acids (HCl, HClO₄, HNO₃, and CH₃COOH) on the fluorescence of coumarin-6 in organic solvents (acetonitrile, acetone, butanol-1, and ethanol) is studied. The regions of acid (HCl, HClO₄, HNO₃) concentrations that lead to a change in the fluorescence spectra are determined for each of the solvents. It is shown that, for all the solvents studied, acetic acid with a concentration within the region 10^?1–10^?6 M causes no significant changes in the fluorescence spectrum of coumarin-6. A mechanism of the coumarin-6 protonation is proposed.     

First-principles study on the structure instability and electronic structure of cubic Ba0.5Sr0.5TiO3

We present first-principles calculations on the structure instability and the electronic structure properties of cubic Ba_0.5Sr_0.5TiO₃ (BST). The calculated total energy result shows that the Sr ions have a more important effect on the structure instability of BST system than the Ba ions. The off-center displacement of the Sr ions will lower the system energy and makes it instable. In order to understand the interaction between ions, the density of states and the charge density distribution were calculated. From the analysis of the density of states, we conclude that the hybridization between Ba p and O p is stronger than that between Sr p and O p. This is consistent with the analysis of the charge density distribution.     

The structure of shock fronts in various gases

The optical reflectivity of shock fronts in A, N₂, O₂, CO, CO₂, N₂O, CH₄, Cl₂ and HCl have been studied. The thickness of shock fronts in A up to the Mach number M = 1·55 is in agreement with the theory of Gilbarg and Paolucci. The rotational relaxation time is about 5·5 collisions in N₂ and equal to or less than that in the other gases. However, for stronger shocks N₂ does not appear to reach rotational equilibrium in the shock front and a qualitative theoretical discussion of this phenomenon is presented. In HCl there appears to be over-excitation of rotation in the shock front. There is no vibrational excitation of any of the gases.     

In situ HCl etching of Si for the elaboration of locally misorientated surfaces

We have studied the in situ HCl etching of Si active areas on patterned wafers. After some in situ HCl etching at 20 Torr of Si(1 0 0), we have locally obtained 2 μm long areas with misorientation angles around 4.5° towards 〈1 1 0〉. Furthermore, we have evidenced a recess shape transition from convex (T ≤ 865 °C) to concave (T ≥ 895 °C) as the etch temperature increases, with a nearly flat surface with no facets at T = 880 °C. The morphology of the etched structures at a given time, temperature and PHCl/PH₂ ratio will be a function of the slope lengths and the pattern dimensions. Different kinds of surfaces (rounded areas, facets) were obtained in 3.5 μm × 3.5 μm Si windows after HCl etching at 850 °C during 300 s, depending on the stress within. Thermal oxidations can indeed be used to increase by 65 MPa up to 110 MPa the compressive stress in those Si windows which are bordered by SiO₂ shallow trench isolation. An increase of the misorientation angle from 4.5° up to 6° occurred after the above-mentioned HCl etch when switching from conventional to highly strained Si windows. For the shortest etching times studied here (150 s), a selective etching of 3.5 μm × 3.5 μm Si windows edges is responsible for the misorientation. The etch is then more uniform. Stress gradients might consequently be one of the main misorientation causes. We have also probed the influence of the shallow trench isolation (STI) thickness on the misorientation. A morphological difference before HCl etching has been shown to be responsible for the transition from sloped to rounded areas. A local loading effect may prevail in this case.     

Return current instability and its effects on beam-plasma system

The return current induced in a plasma by a relativisitc electron beam generates a new electron-ion two-stream instability (return current instability). Although the effect of these currents on the beam-plasma e-e instability is negligible, there exists a range of wave numbers which is unstable only to return current (RC) instability and not to e-e instability. The electromagnetic waves propagating along the direction of the external magnetic field, in which the plasma is immersed, are stabilized by these currents but the e.m. waves with frequencies,ω ²≪Ω _e ² ≪ω _pe ² (Ω _e andω _pe being cyclotron and plasma frequency for the electrons of the plasma respectively) propagating transverse to the magnetic field get destabilized. Heuristic estimates of plasma heating, due to RC instability and due to decay of ion-acoustic turbulence generated by the return current, are made. The fastest time scale on which the return current delivers energy to the plasma due to the scattering of ion-sound waves by the electrons can be ∼ω _pi ⁻¹ (ω _pi being the plasma frequency for the ions).     

Solute distribution in KNbO3 melt-solution and its effect on dendrite growth during rapid solidification

This paper reports that the rapid solidification of mixed Li 2 B 4 O 7 and KNbO 3 melted in a Pt loop heater has been performed experimentally by the method of quenching, and various morphologies of KNbO 3 crystals have been observed in different regions of the quenched melt-solution. Dendrites were formed in the central region where mass transfer is performed by diffusion, whereas polygonal crystals with smooth surface grew in the marginal region where convection dominates mass transport. Based on measurement of KNbO 3 concentration along crystal interface by electronic probe analysis, it finds the variety of crystal morphologies, which is the result of different solute distributions: in the central region the inhomogeneity of solute concentration is much sharper and morphological instability is easier to take place; nevertheless in the marginal region the concentration homogeneity has been greatly enhanced by convection which prevents the occurrence of morphological instability. Additional solute distribution in the melt along the primary dendrite trunk axis as well as that in mushy zones has also been determined. Results show that the solute concentration in the liquid increases linearly with distance from the trunk tip and more solutes were found to be concentrated in mushy zones. The closer the mushy zone is to trunk tip, the lower the solute concentration will be there.     

Preparation of graphitic carbon nitride with large specific surface area and outstanding N2 photofixation ability via a dissolve-regrowth process

Nitrogen fixation is the second most important chemical process in nature next to photosynthesis. Here, we report a convenient dissolve-regrowth method for synthesizing graphitic carbon nitride (g-C₃N₄) with a large surface area and nitrogen vacancies by HCl treatment. XRD, N₂adsorption, SEM, TEM, UV–Vis spectroscopy, EPR, N₂-TPD, Photoluminescence and Photocurrent were used to characterize the prepared catalysts. The results indicate that HCl treatment does not influence the crystal phase of g-C₃N₄ but change the morphology and optical property, leading to the smaller particle size, larger surface area and increased bang gap energy. It is deduced by N₂-TPD, Photoluminescence, Photocurrent and DFT simulations that the nitrogen vacancies formed by the HCl treatment not only serve as active sites to adsorb and activate N₂ molecules but also promote interfacial charge transfer from g-C₃N₄to N₂ molecules. The HCl treated g-C₃N₄ catalyst exhibits outstanding nitrogen photofixation ability under visible light, which is 13.4-fold higher than that of bulk g-C₃N₄ without nitrogen vacancy. The possible reaction mechanism is proposed.     

Ultraviolet photoemission spectroscopy of HCl on Si(111) surfaces

Chemisorption of HCl on thermally cleaned Si(111) surfaces has been studied by ultraviolet photoemission spectroscopy. HCl chemisorption, both at 300K and 850 K, induces two main peaks in the photoemission spectrum which are attributed to Cl lone pair p_x, p_y orbitals and Si: sp³?Cl:p_z bonding orbital, respectively. This strongly suggests that HCl molecules dissociate on Si(111) surfaces already at room temperature.     

On the fast-time oscillatory instabilities of Liñán's diffusion-flame regime

Fast-time instability for diffusion flames, with Lewis numbers set equal for fuel and oxidizer but greater than unity, is numerically analysed by the activation energy asymptotics and Evans function method. The time and length scales being chosen to be those of the inner reactive–diffusive layer, the problem corresponds to the instability problem for the Liñán's diffusion-flame regime. The instability is primarily oscillatory and emerges prior to reaching the turning point of the characteristic C-curve, usually known as the Liñán's extinction condition. A critical Lewis number, L _c , is also found, across which the instability changes its qualitative character. Below L _c , the instability possesses primarily a pulsating nature in that the two real branches of the dispersion relation existing for small wave numbers merge at a finite wave number, from which a pair of complex conjugate branches bifurcate. The maximum growth rate is found at the zero wave number. For Lewis numbers greater than L _c , the eigensolution branch for small reactant leakages is found to be purely complex with the maximum growth rate found at a finite wave number, thereby exhibiting a travelling nature. As the reactant-leakage parameter is further increased, the instability characteristics turns into a pulsating type, similar to that for 1 < L < L _c . The switching between different instability characters is found to correspond to the Bogdanov-Takens bifurcation.     

Comparative Studies on the Development of a 188W-188Re Generator

A comparative study on the sorption behaviour of tungsten and rhenium between anion exchange resin, charcoal and alumina and aqueous media of HNO₃, HCl and NaCl were carried out. The equilibrium distribution coefficient obtained for the different systems were evaluated and discussed in terms of the separation factor between W and Re. It is found that the systems based on alumina and HCl or NaCl are the most promising systems to be used for development of ¹⁸⁸W-¹⁸⁸Re generator. The capacity of a chromatographic column loaded with alumina for ¹⁸⁸W from 0.01 M HCl, 0.7% NaCl and 1.2% NaCl was found to equals 75.3, 91.0 and 126.0 mg/cm, respectively. A recommended procedure was adopted for ¹⁸⁸W-¹⁸⁸Re generator.

Es wurde eine Vergleichsuntersuchung zum Sorptionsverhalten von W und Re zwischen einem Anionenaustauscherharz einer Aktivkohle und einer Tonerde und den wüβirigen Lösungen von HN0₃, HCl and NaCl ausgeführt. Die Gleichgeiwichlsverteilungskoeffizienten der unterschiedlichen Systeme wurden bestimmt und als Trennfaktoren zwischen W und Re diskutiert. Es wurde gefunden, daβ sich das System Tonerde/HCl oder NaCl sehr als Trennsystem für die Entuwicklung eines ¹⁸⁸W¹⁸⁸Re-Generators eignet. Die Kapazitäten einer mit Tonerde gefüllten Säule für ¹⁸⁸W mit 0.01 M HCl, 0.7% NaCl und 1.2% NaCl betrugen entsprechend 75.3, 90.0 und 126.0 mg/cm. Es wird eine geeignete Trennmethode für einen ¹⁸⁸.¹⁸⁸ Re-Generator empfohlen.