Search Results (9)

Fluidized bed-chemical vapor deposition (FB-CVD) technology stands as a cross-cutting achievement of fluidized bed technology in chemical engineering and chemical vapor deposition (CVD) in materials science, finding applications in particle coating, granulation, and material preparation. As compared to conventional CVD technology, FB-CVD distinguishes itself through enhanced heat/mass transfer efficiency, achieving a uniform coating layer while maintaining low production costs. Given the related research on FB-CVD micro-nano particle coating, the mechanism of particle fluidization and chemical vapor deposition, and the difficulty of micro-nano particle agglomeration were summarized. The process intensification of micro-nano particle fluidization assisted by particle design and external force field, such as vibration field, magnetic field, and sound field, and micro-nano particle chemical vapor deposition coating were summarized. In particular, applications of FB-CVD micro-nano particle coating are introduced. Finally, the opportunities and challenges faced by FB-CVD micro-nano particle coating technology are discussed, and the development prospect of this technology is prospected. This review is beneficial for the researchers of the fluidization field, and also the particle coating technology. Full article

Three−dimensional (3D) graphene with novel nano−architectures exhibits many excellent properties and is promising for energy storage and conversion applications. Herein, a new strategy based on the fluidized bed chemical vapor deposition (FB−CVD) process was proposed to prepare 3D graphene networks (3DGNs) with various nano−architectures. Specially designed SiC−C@graphene core/shell nanoparticles were prepared taking the advantages of the FB−CVD system, and 3DGNs with hierarchical nanostructures were obtained after removing the SiC core. The 3DGNs performed well as electrodes of lithium–sulfur batteries. The C–S cathode showed good rate performance at the current density of 0.1–2.0 C, and an initial discharge capacity of 790 mAhg⁻¹ cathode was achieved at a current density of 0.2 C. The Li−S batteries showed stabilized coulombic efficiency as high as 94% and excellent cyclic performance with an ultra low cyclic fading rate of 0.075% for the initial 280 cycles at a current density of 1.0 C. The improved electrochemical performance was ascribed to the enhanced conductivity by the connective graphene networks and the weakened shuttle effect by the special outer graphene layers. Mass production of the products was realized by the continuous FB−CVD process, which opens up new perspectives for large scale application of 3D graphene materials. Full article

Fine particles are widely used in many industrial fields, and there are many techniques applied for these particles, like electroplating, and chemical and physical vapor deposition. However, in the food and pharmaceutical industries, most coating processes conducted with fluidized bed use core particles with a diameter larger than 200 μm, otherwise agglomerates are formed. This study contributes to the development of a new coating process for fine particles with diameters of around 50 μm. The innovation lies in the combined use of a Wurster fluidized bed and a novel aerosol atomizer. The feasibility of the operation is based on the application of the aerosol atomizer, which generates droplets smaller than 1 μm in diameter. A series of experiments with different coating solutions and glass beads in a 150 mm fluidized bed fed with droplet aerosol supplied from the cone chamber bottom is presented. The quality of the coating product is analyzed by scanning electron microscopy and CAMSIZER^®. In this way, the influence of different conditions and core material properties on the product quality were determined. Experimental results showed the coating layer quality getting worse as coating solution viscosity became lower, meanwhile moderate process temperature was found to enhance coating layer formation and quality of that. It was also observed that lower aerosol feed rates help improve the yield of the process. Full article

As electromagnetic functional materials, soft magnetic composites (SMCs) have great potential for applications in high-energy electromagnetic conversion devices. The most effective way to optimize the performance of an SMC is to incorporate it into insulated ferromagnetic core-shell particles with high structural uniformity and integrity. Fluidized bed chemical vapor deposition (FBCVD) is a facile and efficient technique for the synthesis of ferromagnetic/SiO₂ core-shell particles. However, the formation mechanism and conditions of integrated ferromagnetic/SiO₂ core-shell structures during the FBCVD process are not fully understood. On this basis, the formation process and the deposition time required for transformation of the Fe-6.5wt.%Si substrate into the Fe-6.5wt.%Si/SiO₂ composite, and finally into the Fe-6.5wt.%Si/SiO₂ core-shell structure, were investigated. Deposition of the insulative SiO₂ coating onto the Fe-6.5wt.%Si particles was described by the three-dimensional island nucleation theory. The SiO₂ islands were initially concentrated in rough areas on the Fe-6.5wt.%Si particle substrates owing to the lower heterogeneous nucleation energy. Deposition for at least 960 s was necessary to obtain the integrated ferromagnetic/SiO₂ core-shell structure. The uniformity, integrity, and thickness of the insulative SiO₂ coating increased with the increasing deposition time. The results in this study may provide a foundation for future kinetics investigations and the application of FBCVD technology. Full article

Carbon dioxide is one of the major greenhouse gases and a leading source of global warming. Several adsorbent materials are being tested for removal of carbon dioxide (CO₂) from the atmosphere. The use of multiwalled carbon nanotubes (MWCNTs) as a CO₂ adsorbent material is a relatively new research avenue. In this study, Fe₂O₃/Al₂O₃ composite catalyst was used to synthesize MWCNTs by cracking ethylene gas molecules in a fluidized bed chemical vapor deposition (CVD) chamber. These nanotubes were treated with H₂SO₄/HNO₃ solution and functionalized with 3-aminopropyl-triethoxysilane (APTS). Chemical modification of nanotubes removed the endcaps and introduced some functional groups along the sidewalls at defected sites. The functionalization of nanotubes with amine introduced carboxylic groups on the tube surface. These functional groups significantly enhance the surface wettability, hydrophilicity and CO₂ adsorption capacity of MWCNTs. The CO₂ adsorption capacity of as-grown and amine-functionalized CNTs was computed by generating their breakthrough curves. BELSORP-mini equipment was used to generate CO₂ breakthrough curves. The oxidation and functionalization of MWCNTs revealed significant improvement in their adsorption capacity. The highest CO₂ adsorption of 129 cm³/g was achieved with amine-functionalized MWCNTs among all the tested samples. Full article

This work presents a new insight into the potential of a Ni/CeZrO₂ catalyst in two separate processes: (i) Chemical Vapor Deposition (CVD) using methane as a feedstock to obtain carbon nanotubes (CNTs) and H₂, and (ii) catalyst regeneration with H₂O that yields H₂. The direct reaction of methane with H₂O (steam methane reforming (SMR)) leads to H₂ and CO (and CO₂), whereas carbon deposition—regardless of its type—is an unwanted reaction. The concept presented in this work assumes dividing that process into two reactors, which allows one to obtain two valuable products, i.e., CNTs and H₂. The literature data on CNT production via CVD ignores the issue of H₂ formation. Moreover, there is no data concerning CNT production in fluidized bed reactors over ceria-zirconia supported metal catalysts. The results presented in this work show that CNTs can be formed on Ni/CeZrO₂ during CH₄ decomposition, and that the catalyst can be easily regenerated with H₂O, which is accompanied by a high production of H₂. The ability of Ni/CeZrO2 to be regenerated is its main advantage over the Ni-MgO catalyst that is popular for CNT production. This paper also shows that the Ni/CeZrO₂ catalyst has the potential to be used for CNT and H₂ production in a larger scale process, e.g., in a fluidized bed reactor. Full article

Fluidized bed reactors have been increasingly applied for mass production of Carbon Nanotube (CNT) using catalytic chemical vapor deposition technology. Effect of particle size (d_p = 131 μm and 220 μm) on fluidization characteristics and aggregation behavior of the CNT particles have been determined in a fluidized bed for its design and scale-up. The CNT aggregation properties such as size and shape were measured in the dilute phase of a fluidized bed (0.15 m-ID × 2.6 m high) by the laser sheet technique for the visualization. Two CNT particle beds showed different tendency in variations of the aggregates factors with gas velocity due to differences in factors contributing to the aggregate formation. The CNT particles with a larger mean size presented as relatively larger in the aggregate size than the smaller CNT particles at given gas velocities. The aggregates from the large CNT particles showed a sharp increase in the aspect ratio and rapid decrease in the roundness and the solidity with gas velocity. A possible mechanism of aggregates formation was proposed based on the variations of aggregates properties with gas velocity. The obtained Heywood diameters of aggregates have been firstly correlated with the experimental parameter. Full article

With regard to the catalysis of oxidation reactions by noble metals, the addition of FeO_x to an Al₂O₃-supported Pt catalyst is known to be energetically more favorable compared to only Pt. In this work, different process routes for the preparation of such Fe-promoted Pt/Al₂O₃ catalysts via atmospheric chemical vapor deposition (CVD) in a fluidized bed were explored. Specifically, the question of whether it would be advantageous to deposit the Fe before, along with, or after the Pt was addressed, and new information was obtained about the optimum FeO_x–Pt interface and mixing ratio. Vapors of Trimethyl(methylcyclopentadienyl)platinum(IV) and/or Ethyl-ferrocene were injected into the bed from the top, permitting a quasi-lossless precursor operation and a very good control of the deposited metal, and hence of the catalyst structure. Samples could be extracted from the top while CVD was ongoing to obtain time-resolved data. The catalytic activity was determined through CO oxidation. The Fe-Pt mixing ratio was then varied for the most active deposition sequence, in order to identify an activity optimum generated by the minimum amount of Pt catalyst. When compared to pure Pt/Al₂O₃, the optimum catalyst consistently showed superior performance even after thermal stress. Full article

In this study, multi-walled carbon nanotubes (MW-CNT) were successfully synthesized using a chemical vapor deposition-fluidized bed (CVD-FB), with 10% hydrogen and 90% argon by volume, and a reaction temperature between 750 and 850 °C in a specially designed three-stage reactor. A solid state of polyethylene (PE) was used as a carbon source and iron(III) nitrate, iron(III) chloride, and nickel(II) chloride were used as catalysts. Scanning and transmission electron microscopy and Raman spectrum analysis were used to analyze and examine the morphology and characteristics of the CNTs. A thermogravimetric analyzer was used to determine the purification temperature for the CNTs. Experimental results showed that the synthesis with iron-based catalysts produced more carbon filaments. Nickel(II) chloride catalysis resulted in the synthesis of symmetrical MW-CNTs with diameters between 30 and 40 nanometers. This catalyst produced the best graphitization level (I_D/I_G) with a value of 0.89. Excessively large particle size catalysts do not cluster carbon effectively enough to grow CNTs and this is the main reason for the appearance of carbon filaments. Full article