Electrostatic potentials in gas–solid fluidized beds influenced by the injection of charge inducing agents

Accumulation of electrostatic charges in gas–solid fluidized beds can lead to particle adhesions, electrostatic discharges, wall sheeting and even explosion. Therefore, it is of vital importance to reduce the electrostatic level in industrial fluidized beds. Adding chemical static agents was reported as one of the most promising ways to control fluidized bed electrostatic potentials. In this study, the electrostatic potential distributions were measured in a three-dimensional column gas–solid fluidized bed with the LLDPE particles for fluidization and the introduction of chemical static agents. Seven charge inducing agents including TiO₂, Al₂O₃, MgO, H₂O, C₂H₅OH, ZnO, and Fe₂O₃ were employed to investigate their influence on electrostatic potentials distribution respectively. Additionally, Al(Et)₃, which is normally used as the cocatalyst for olefin polymerization, was also studied for comparison. It was found that the adding of negative charge inducing agent such as TiO₂ made the positive electrostatic potentials shift to higher values and the negative electrostatic potentials shift to lower values. The injection of positive charge inducing agent such as Al₂O₃ and MgO caused the positive electrostatic potentials dropping to lower values and the negative electrostatic potentials shifting to the values near zero at low injection amount. Affecting mechanism of charge inducing agents was discussed based on the experimental results and the electronegativity of corresponding compounds. It was found that the electronegativity (χ_i) of the metal ion played an important role in determining the charge polarity on the LLDPE particles and the change in the electrostatic potentials after contact and separation with the charge inducing agent particles.     

用光刺激放电法研究纳米粉末掺杂低密度聚乙烯中陷阱能级

通过光刺激放电(PSD)技术研究了纳米粉末掺杂低密度聚乙烯(LDPE)中的陷阱能级.利用连续扫描法得到了不同掺杂比例的Al₂O₃,MgO纳米粉末掺杂试样以及相同掺杂比例的多种纳米粉末掺杂试样的PSD电流谱,定性地得出了试样陷阱能级的深浅变化.分步扫描法定量地描述了LDPE试样在Al₂O₃纳米掺杂前后陷阱能量分布的变化.结果表明,掺杂比例大于0.2%的Al₂O₃纳米粉末掺杂、大于0.5%的MgO纳米粉末掺杂能够显著地使得LDPE陷阱能级变深.结合纳米掺杂对LDPE空间电荷注入影响的相关报道,可推测纳米掺杂对空间电荷注入的抑制与试样中陷阱能级变深存在密切的关联.     

Molecular orbital interpretation of X-ray emission and esca spectral shifts in silicates

An approximate molecular orbital theory is presented, tested, and applied to silicon and aluminum oxyanions. The orbital structure of SiO₄^?4 is calculated and is used to assign the X-ray emission spectra. Calculations are performed at several internuclear distances and semiquantitative agreement is found with experimentally observed trends in A1Kα and SiKβ spectra. Calculations on Si₂O₇^?6 and AlSiO₇^?7 yield fair agreement with experimental trends relating to degree of SiO₄ polymerization and to Al/Si ratio. Charges for bridging and non-bridging oxygens in Si₂O₇^?6, combined with point charge potentials from metal ions in the orthopyroxene structure yield Ols binding energies in agreement with ESCA results.     

Electronic structure of crystal-forming fullerenes C2n,fulsicenes Si n C n,and their crystals—Fulsicenites

A number of crystal-forming polyhedral clusters X _n Y _n from which zeolite-like covalent crystals can be constructed and synthesized through copolymerization by faces are proposed. A series of the smallest sized crystal-forming carbon clusters C_2n (where n = 10, 12, 14, 16, 18, 24, 36, 60) and silicon carbide clusters Si _n C _n (where n = 12, 16, 18, 24, 36, 60) are constructed. Their optimized geometries, electronic structures, charge transfers, band gaps, cohesive energies, and electron density maps are calculated using the spinrestricted Hartree-Fock method in the 6–31G(d) basis set. The Si₁₂C₁₂ and Si₂₄C₂₄ clusters, referred to as the fulsicenes, are used to construct possible crystals with rock salt (Si₁₂C₁₂), simple cubic (Si₂₄C₂₄), body-centered cubic (Si₁₂C₁₂), face-centered cubic (Si₂₄C₂₄), and hyperdiamond (Si₁₂C₁₂) lattices, which are termed fulsicenites. Their X-ray diffraction patterns are calculated.     

Electronic structure and the infrared absorption and Raman spectra of the semiconductor clusters C24, B12N12, Si12C12, Zn12O12, and Ga12N12

The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, electron density maps, infrared absorption spectra, Raman spectra, and relevant modes of natural acoustic vibrations for the semiconductor clusters C₂₄, B₁₂N₁₂, Si₁₂C₁₂, Zn₁₂O₁₂, and Ga₁₂N₁₂ are calculated using the ab initio Hartree-Fock method in the 6–31G basis set. Original Russian Text ? V.V. Pokropivny, L.I. Ovsyannikova, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 3, pp. 535–542.     

A method for the experimental determination of the net atomic charge via X-ray photoemission spectroscopy

A method for the experimental determination of the net charge distribution over the atoms in a large class of compounds is described. The method is based on X-ray photoemission spectroscopy and requires the determination of two core-level energies per constituting atomic species. Two special cases of large conceptual and practical interest are discussed: the silicon charge in CoSi₂, Si_1-xGe_x (0≤x≤0.3), SiC, Si₃N₄ and SiO₂, and the aluminum charge in aluminum-doped zeolites. Received: 20 March 2000 / Accepted: 28 March 2000 / Published online: 21 March 2001     

Interstitial oxide positions in oxygen-excess oxy-apatites

Several oxy-apatites materials, La_8.65Sr_1.35(Si₆O₂₄)O_2.32, La_8.65Sr_1.35(Ge₆O₂₄)O_2.32, La₉Sr₁(Si_5.5Al_0.5O₂₄)O_2.25, La_9.67□_0.33(Si_5.5Al_0.5O₂₄)O_2.25, La_8.5Sr_1.5(Si_5.5Al_0.5O₂₄)O₂ and La_9.5□_0.5(Si_5.5Al_0.5O₂₄)O₂ have been prepared as crystalline phases. The impedance study showed that all samples are oxide ion conductors and their conductivities are similar to those previously reported for related oxy-apatites. A thorough study on the oxygen sublattices for oxygen excess samples has been carried out using neutron powder diffraction data by the Rietveld method. The structural study shows the presence of interstitial oxide anions close to the periphery apatite channels. However, the interstitial oxide position in cation stoichiometric silicates, f. i. La_8.65Sr_1.35(Si₆O₂₄)O_2.32, is different from that in germanates, f. i. La_8.65Sr_1.35(Ge₆O₂₄)O_2.32. This is likely due to the different structural flexibility of the two tetrahedral groups and it explains the previously reported evidence of higher oxygen contents for germanates oxy-apatites. The structural characteristics of these oxide anion conductors are discussed.     

Effect of ultrasound on the synthesis of low-modulus zeolites from a metakaolin

It was studied the effect of ultrasonic processing (22 kHz) of the aqueous suspension of metakaolin, sodium hydroxide and alumina with a molar ratio 2Al₂Si₂O₇:12NaOH:2Al₂O₃ on the low-modulus zeolite synthesis processes. To investigate the XRD, SEM, IR, EDS had been used. It was shown that after ultrasonic processing, sodium aluminates are formed, what leads to a change in process of further synthesis. It was found that without ultrasonic processing on the stage of thermal treatment at 650 °C, SOD zeolite (|Na₆|[Al₆Si₆O₂₄]) and sodium aluminosilicate (Na₆Al₄Si₄O₁₇) are synthesized. In the sample after ultrasound during thermal treatment, only sodium aluminosilicates of cubic syngony (Na₆Al₄Si₄O₁₇ and Na₈Al₄Si₄O₁₈) are formed. It was demonstrated that sodium aluminosilicates are precursors for the formation of LTA zeolite (|Na₁₂|[Al₁₂Si₁₂O₄₈]). As a result zeolitization of sodium aluminosilicates after the hydrothermal crystallization in alkaline solution, the sonicated sample contained 97 wt% LTA. Without ultrasonic processing, the product of synthesis contained 50 wt% SOD and 40 wt% LTA.     

Theoretical study on the mono and multiply oxygenated Si60H60 fullerene

We have applied density functional theory (DFT) calculations to study the structures, stabilities, electronic and magnetic properties of mono and multiply oxygenated Si₆₀H₆₀ fullerenes (Si₆₀H_60–2nO_n, n = 1, 3, 6, 9, 10, 12, 18, 20, 21, 27 and 30). DFT results show that rearrangement between the closed [6,6] and [5,6] isomers of Si₆₀H₅₈O follows a two-step pathway involving an intermediate and two transition states. Preserving the C₃ symmetry in the cage structure, extra epoxidation of Si₆₀H₆₀ has been accomplished. Based on our results, formation energies per oxygen atom for the multiple additions of oxygen atoms on Si₆₀H₆₀ cage are positive (endothermic character), and increase with the increasing of the number of oxygen atoms. In general, the oxygenation of Si₆₀H₆₀ cage leads to an increase in the electrophilicity of the Si₆₀H_60–2nO_n oxides. The oxygenation of Si–Si bonds not only introduces a substantial broadening of the NMR pattern but also yield individual peaks, indicating different electrostatic environments of silicon nuclei in the Si₆₀H_60–2nO_n oxides.     

Charge state measurements of 23 MeV Cl ions traversing a liquid target

The charge distribution of 23 MeV Cl ions traversing a cloud of silicon oil ((C₆H₅)₄Si₃O₂(CH₃)₄) droplets was measured and was found to extend to very high charge states (17⁺), higher than those obtained for similar stripping in carbon foils.     

Oxidation of silicon surface with atomic oxygen radical anions

The surface oxidation of silicon （Si） wafers by atomic oxygen radical anions （O- anions） and the preparation of metal-oxide-semiconductor （MOS） capacitors on the O-oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al2sO64]^4＋·4O^- （Cl2A7-O^- for short）. After it has been irradiated by an O- anion bean： （0.5 μA/cm^2） at 300℃ for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy （XPS） results reveal that the oxide layer is of a mixture of SiO2, Si2 O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of 〈Al electrode/SiOx/Si〉 are investigated by measuring capacitance-voltage （C - V） and current-voltage （I - V） curves. The oxide charge density is about 6.0 × 10^1 cm^-2 derived from the （C - V curves. The leakage current density is in the order of 10^-6 A/cm^2 below 4 MV/cm, obtained from the I - V curves. The O- anions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.     

Density-functional theory study of structures,stabilities, and electronic properties of the Cu2-doped silicon clusters: Comparison with pure silicon clusters

Equilibrium geometric structures, stabilities, and electronic properties of Si_nCu₂ (n=1–8) clusters and pure silicon Si_n (n=3–10) clusters are investigated systematically by exchange-correlation density functional (B3LYP). The optimized geometries show that the most stable isomers have 3D structure for n=2, 4–8, and Cu-substituted Si_n+2 clusters is dominating growth pattern for the Si_nCu₂ clusters. The calculated averaged binding energies, fragmentation energies, second-order difference of energies, and the HOMO–LUMO gaps show that Si₂Cu₂ and Si₅Cu₂ clusters have enhanced relative stabilities and chemical stability than their neighboring clusters. Electronic properties of Si_nCu₂ (n=1–8) clusters are studied by calculating the natural population analysis and electrostatic potential, where the results show that the two copper atoms always possess positive charge and positive potential surround them. In addition, the VIP, VEA and the chemical hardness (η) are also analyzed and compared.     

Atomic transport in ionic solid solutions

Summary This paper examines certain aspects of the relation of tracer diffusion coefficients to the corresponding so-called intrinsic diffusion coefficients arising in chemical interdiffusion in binary solid solutions. Although no exact general relation between these quantities is to be expected, the existence of such a relation for the solute species is to be anticipated in dilute solid solutions. In metallic alloys they become equal in the dilute limit, but in solid solutions of ionic conductors the ratio depends on details of the system (in particular on the solute and solvent ion charges and the degree of association between solute ions and charge compensating defects). Both the macroscopic and microscopic theories of these ionic solutions are described. A rather clear conflict exists between the theoretical predictions and some existing experimental results on the system Cr₂O₃ in MgO. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

Electronic structure of F,-center in MgO

The embedded-cluster numerical variational method has been developed to calculate the electronic structure of perfect MgO, F and F⁺-centers in MgO. The energy band, bulk density of states has been calculated by cluster Mg₁₄O₁₃, Mg₁₄O₁₂F⁺ and Mg₁₄O₁₂F. The calculated absorption energy for F⁺ and F centers is in good agreement with experimental data. In our calculated defect energy levels, that the first excited state of F⁺-center is at CB-3.46 eV, indicates the necessity of a large photoelectron yielding energy. We also calculate the radius of color center electron, and plot the map of charge-density distribution of valence electrons in which the structure of the color center is shown directly. Received 22 May 1998     

Investigation of orientation and packing of H8Si8O12 arrays on graphite by scanning tunneling microscopy

The layer structures of H₈Si₈O₁₂ molecules on highly oriented pyrolitic graphite have been investigated by scanning tunneling microscopy. Two kinds of ordered assemblies of H₈Si₈O₁₂ monolayers are observed, with a unit cell of 6.5 Å × 6.5 Å and 7.2 Å × 9.4 Å, respectively. On the basis of the shapes and sizes of the H₈Si₈O₁₂ STM images and the heights of the H₈Si₈O₁₂ monolayers, H₈Si₈O₁₂ can be adsorbed with one face of its cage structure in contact with the substrate surface or with a tilted orientation.     

Secondary ion emission under the bombardment of Si by multiply charged Si q+ ions

The spectra of secondary ion emission under the bombardment of a B-doped Si target by multiply charged Si ^q+ ions (q = 1?C5) have been studied in the energy range of 1 to 10 keV per unit of charge. A multifold increase in the yield of secondary cluster Sk _n ⁺ ions, multiply charged Si ^q/+ ion (q = 1?C3), and H⁺, C⁺, B⁺, Si₂N⁺, Si₂O⁺ is observed as the charge of the multiply charged ions increases. The increase in the yield of secondary ions with increasing charge of the multiply charged-ion charge is most significant for ions with relatively high ionization potentials.     

Structural, electronic and vibrational properties of indium oxide clusters

Geometric, electronic and vibrational properties of the most stable and energetically favourable configurations of indium oxide clusters In_mO_n (1≤m, n≤4) are investigated using density functional theory. The lowest energy geometries prefer the planar arrangement of the constituent atoms with a trend to maximize the number of ionic In-O bonds. Due to the charge transfer from In to O atoms, the electrostatic repulsion occurs between the atoms with the same kind of charge. The minimization of electrostatic repulsion and the maximization of In-O bond number compete between each other and determine the location of the isometric total energy. The most stable linear In-O-In-O structure of In₂O₂ cluster is attributed to the reduced electrostatic repulsive energy at the expense of In-O bond number, while the lowest energy rhombus-like structure of In₂O₃ cluster reflects the maximized number of In-O bonds. Furthermore, the vibrational frequencies of the lowest energy clusters are calculated and compared with the available experimental results. The energy gap and the charge density distribution for clusters with varying oxygen/indium ratio are also discussed.     

Luminescence of Ce3+ in lanthanum silicon oxynitride

The luminescence properties of lanthanum silicon oxynitride(La-Si-O-N) series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications.Four compound hosts of LaSiO2N,La4Si2O7N2,La5Si3O12 N,and La2Si6O3N8 were synthesized and examined in this work.Crystallographic examination for the equal amount of Ce 3+ substitution indicated that the covalency degree decreased in a sequence LaSiO2 N > La2Si6O3N8 > La4Si2O7N2 > La5Si3O12 N,not simply in correlation to the ratio of N3/O2.Excitation and emission spectrum measurements showed the main features of Ce3+ luminescence in the series:the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce-N bonding;nephelauxetic effect could not be observed clearly for the investigated series;to some extent Stokes shift was dominated by crystal-field splitting rather than Ce-N covalency degree.     

Charge effects in silicon-doped heterofullerenes

We provide information on the modification induced on the structural and electronic properties by the inclusion of an extra positive and negative charge on C₃₀Si₃₀. The calculations are performed based on the framework of Car–Parrinello molecular dynamics within the spin density version of density functional theory. Adding or extracting an electron from the C₃₀Si₃₀ does not dramatically alter the topology of the neutral network either structurally or electronically. However, negative C₃₀Si₃₀ is characterized by an accumulation of negative charge on the inner part of the Si region, while the distribution of charge in positive C₃₀Si₃₀ is closer to the neutral case. PACS 61.48.+c; 71.20.Tx