Numerical study on soot removal in partial oxidation of methane to syngas reactors

The serious carbon deposition existing in catalytic partial oxidation of methane (CPOM) to syngas process is one of the key problems that impede its industrialization. In this study, 3-dimensional unsteady numerical simulations of the soot formation and oxidation in oxidation section in a heat coupling reactor were carried out by computational fluid dynamics (CFD) approach incorporating the Moss-Brookes model for soot formation. The model has been validated and proven to be in good agreement with experiment results. Effects of nozzle type, nozzle convergence angle, channel spacing, number of channels, radius/height ratio, oxygen/carbon ratio, preheat temperature and additional introduction of steam on the soot formation were simulated. Results show that the soot formation in oxidation section of the heat coupling reactor depends on both nozzle structures and operation conditions, and the soot concentration can be greatly reduced by optimization with the maximum mass fraction of soot inside the oxidation reactor from 2.28% to 0.0501%, and so that the soot mass fraction at the exit reduces from 0.74% to 0.03%.     

Controllable synthesis,characterization,and growth mechanism of hollow Zn_x Cd_(1-x) S spheres generated by a one-step thermal evaporation method

Novel hollow ZnxCdl xS spheres that are uniform in size are synthesized through the one-step thermal evaporation of a mixture of Zn and CdS powder. From an X-ray diffraction （XRD） study, the hexagonal wurtzite phase of ZnxCdl_xS is verified, and the Zn mole fraction （x） is determined to be 0.09. According to the experimental results, we propose a mechanism for the growth of Zn0.09Cd0.91S hollow spheres. The results of the cathodoluminescence investigation indicate uniform Zn, Cd, and S distribution of alloyed Zn0.09Cd0.91S, instead of separate CdS, ZnS, or nanocrystals of a core- shell structure. To the best of our knowledge, the fabrication of ZnxCd1-xS hollow spheres of this kind by one-step thermal evaporation has never been reported. This work would present a new method of growing and applying hollow spheres on Si substrates, and the discovery of the Zn0.09Cd0.91S hollow spheres would make the investigation of ZnxCd1-xS micro/nanostructures more interesting and intriguing.     

A low-temperature X-ray diffraction study of the Cu2ZnSnSe4 thin films

Low-temperature XRD measurements were performed to confirm the phase composition and structural parameters of the electrochemically deposited Cu₂ZnSnSe₄ thin films on flexible metal substrates.     

Dispersion and deposition mechanisms of particles suspended in a turbulent plane Couette flow

Inertial particle transfer in a turbulent plane Couette flow (C flow) was studied using Direct Numerical Simulation (DNS) of the flow combined with a Lagrangian particle tracking approach for particles with Stokes numbers (St) 5, 25 and 125. The particle concentration was assumed low enough, so that the simulations were done under one-way coupling condition.     

Controllable growth and characterizations of hybrid spiral-like atomically thin molybdenum disulfide

Monolayer MoS₂ is an emerging two-dimensional semiconductor with wide-ranging potential applications in novel electronic and optoelectronic devices. Here, we reported controlled vapor phase growth of hybrid spiral-like MoS₂ crystals investigated by multiple means of X-Ray photoemission spectroscopy, scanning electron microscopy, atomic force microscopy, kelvin probe force microscopy, Raman and Photoluminescence techniques. Morphological characterizations reveal an intriguing hybrid spiral-like MoS₂ feature whose lower planes are AB Bernal stacking and upper structure is spiral. We ascribe the hybrid spiral-like structure to a screw dislocation drive growth mechanism owing to lower supersaturation and layer-by-layer growth mode. In addition, the electrostatic properties of MoS₂ microflakes with hybrid spiral structures are obvious inhomogeneous and dependent on morphology manifested by kelvin probe force microscopy. Our work deepens the understanding of growth mechanisms of CVD-grown MoS₂, which is also adoptable to other TMDC materials.     

The fabrication of ReS2 flowers at controlled locations by chemical vapor deposition

Here we report a metal induced nucleation to realize the growth of ReS₂ flowers at controlled locations. The ordered arrays of ReS₂ flowers have been successfully prepared on SiO₂/Si substrate using Pt metal dots as nucleation sites and S, NH₄ReO₄ powders as precursors by a chemical vapor depostion method. The NH₄ReO₄ powders are used as the rhenium sources. The ReS₂ flowers are grown above the pre-patterned Pt dots, Raman and transmission electron microscopy measurements indicated that the prepared ReS₂ flowers have excellent crystalline quality.     

A novel coated-particle design and fluidized-bed chemical vapor deposition preparation method for fuel-element identification in a nuclear reactor

Particle coating is an important method that can be used to expand particle-technology applications. Coated-particle design and preparation for nuclear fuel-element trajectory tracing were focused on in this paper. Particles that contain elemental cobalt were selected because of the characteristic gamma ray spectra of ⁶⁰Co. A novel particle-structure design was proposed by coating particles that contain elemental cobalt with a high-density silicon-carbide (SiC) layer. During the coating process with the high-density SiC layer, cobalt metal was formed and diffused towards the coating, so an inner SiC–Co_xSi layer was designed and obtained by fluidized-bed chemical vapor deposition coupled with in-situ chemical reaction. The coating layers were studied by X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy techniques. The chemical composition was also determined by inductively coupled plasma optical emission spectrometry. The novel particle design can reduce the formation of metallic cobalt and prevent cobalt diffusion in the coating process, which can maintain safety in a nuclear reactor for an extended period. The experimental results also validated that coated particles maintain their structural integrity at extremely high temperatures (∼1950 °C), which meets the requirements of next-generation nuclear reactors.     

Effect of Al incorporation on the structural,morphological, optoelectronic and transport properties of PbS thin films

Doping of PbS thin films with different metal atoms produce considerable changes in structural and material properties that make them useful in the technology of thin film devices. The goal of this work is to study the effects of doping on the structural, morphological, optoelectronic and transport properties of PbS thin films as a function of Al³⁺ concentration. Thin films of pure and Al doped PbS nanoparticles are prepared on soda lime glass substrates by chemical bath deposition technique. The Al content in aqueous solution is varied from 0 to 20 mg. XRD analysis of the films revealed significant enhancement in crystallinity and crystallite size up to an optimum concentration of doping. Films are polycrystalline with crystallite size 19–32 nm, having face centered cubic structure. The optical band gap energy exhibits a decreasing trend and is shifted from 2.41 to 1.34 eV with increasing Al content. The room temperature conductivity of the as-deposited PbS films is in the range of 0.78×10⁻⁸ to 0.67×10⁻⁶(Ω cm)⁻¹ with a maximum for optimum Al content. The Al doped PbS thin film, which we synthesize with optimum Al concentration of 15 mg is found to be a most suitable material for solar control coating applications.     

Shadow-casted ultrathin surface coatings of titanium and titanium/silicon oxide sol particles via ultrasound-assisted deposition

Ultrasound-assisted deposition (USAD) of sol nanoparticles enables the formation of uniform and inherently stable thin films. However, the technique still suffers in coating hard substrates and the use of fast-reacting sol–gel precursors still remains challenging. Here, we report on the deposition of ultrathin titanium and titanium/silicon hybrid oxide coatings using hydroxylated silicon wafers as a model hard substrate. We use acetic acid as the catalyst which also suppresses the reactivity of titanium tetraisopropoxide while increasing the reactivity of tetraethyl orthosilicate through chemical modifications. Taking the advantage of this peculiar behavior, we successfully prepared titanium and titanium/silicon hybrid oxide coatings by USAD. Varying the amount of acetic acid in the reaction media, we managed to modulate thickness and surface roughness of the coatings in nanoscale. Field-emission scanning electron microscopy and atomic force microscopy studies showed the formation of conformal coatings having nanoroughness. Quantitative chemical state maps obtained by x-ray photoelectron spectroscopy (XPS) suggested the formation of ultrathin (<10 nm) coatings and thickness measurements by rotating analyzer ellipsometry supported this observation. For the first time, XPS chemical maps revealed the transport effect of ultrasonic waves since coatings were directly cast on rectangular substrates as circular shadows of the horn with clear thickness gradient from the center to the edges. In addition to the progress made in coating hard substrates, employing fast-reacting precursors and achieving hybrid coatings; this report provides the first visual evidence on previously suggested “acceleration and smashing” mechanism as the main driving force of USAD.