Low-temperature synthesis of CeB6 nanowires and nanoparticles as feasible lithium-ion anode materials

Metallic CeB₆ nanomaterials were prepared via the low-temperature solution combustion method (nanoparticles) and high-pressure solid state reaction (nanowires). X-ray diffraction patterns and High-resolution transmission electron microscopy images reveal that CeB₆ nanoparticles are highly crystalline and CeB₆ nanowires are single crystals. The X-ray photoelectron spectroscopy analysis indicates that the cerium is present in the +3 and +4 mixed-valence state in CeB₆. As lithium-ion anodes, CeB₆ nanowires (nanoparticles) electrode achieves a capacity of ~531 (338) mA h g⁻¹ in the initial cycle and keeps a reversible capacity of ~225 (185) mA h g⁻¹ after 60 cycles. CeB₆ nanowires are tested for 6000 cycles at 1000 mA g⁻¹, which shows a specific capacity approaching to the capacity at 100 mA g⁻¹ in spite of fluctuation within a narrow range, and keep ~168 mA h g⁻¹ after 6000 cycles, indicating a stable cycling performance owing to the excellent metal-like conductivity of (~5.67 × 10³ S m⁻¹). The reason of capacity rising is that the reduction and oxidation levels of CeB₆ electrodes are improved after the 2nd cycle with Li⁺ insertion/extraction. Meanwhile, kinetic analysis reveals that the Li⁺ storage mechanism is mainly controlled by a surface capacitive behavior.     

Realizing enhanced thermoelectric properties in Cu2S-alloyed SnSe based composites produced via solution synthesis and sintering

SnSe emerges as one of the most promising Te-free thermoelectric materials due to its strong anharmonic-ity and multiple valence bands structure.Recently,compositing has been proven effective in optimizing thermoelectric performance of various metal chalcogenides.Herein,a series of SnSe-xCu2S(x=0,0.5％,1％,3％,5％)materials have been fabricated via solution synthesis,particle blending,and spark plasma sinter-ing in sequence.After incorporating Cu2S,the materials become SnSe based composites with Cu doping,S substitution and Cu2SnSe3 secondary phase.We elucidate that the power factor of polycrystalline SnSe can be tuned and enhanced at varied temperature ranges through adjusting the addition amount of Cu2S.Additionally,the composites achieve suppressed lattice thermal conductivity when compared to SnSe itself,as the introduced point defects and SnSe/Cu2SnSe3 interfaces intensify phonon scattering.Conse-quently,SnSe-0.5％Cu2S and SnSe-3％Cu2S achieve a peak zT of 0.70 at 830 K(intermediate temperature range)and a highly increased zT of 0.28 at 473 K(low temperature range),respectively,which are～130％and 200％of values reached by SnSe at the corresponding temperatures.The study demonstrates that our approach,which combines compositing with elemental doping and substitution,is effective in optimizing the thermoelectric performance of SnSe at varied temperature ranges.     

Scalable synthesis of few-layered MoS2/C sandwiched nanocomposites via ionic crystal (NH4)2MoS4 assisted ball-milling method and their enhanced high-rate lithium storage property

Ball milling has been proven to be an efficient method for exfoliating and reassembling heterogeneous layered nanocomposites on a large scale. This study explores the use of ammonium tetrathiomolybdate (NH₄)₂MoS₄, an ion crystal with an octahedral structure, as both a precursor of layered molybdenum disulfide (MoS₂) and an intermediate during ball milling to assist in the exfoliation and fragilization of expandable graphite (EG). Due to its ion crystal structure and high hardness, (NH₄)₂MoS₄ can efficiently transfer and magnify the impacting and shearing forces generated during the ball milling process, accelerating the exfoliation and fragmentation efficiency of EG. Moreover, (NH₄)₂MoS₄ is nano-crystallized by the ball milling forces and uniformly distributed on the carbon nanosheets. Electrochemical performance tests indicate that the resulting nanocomposites, with a satisfactory heterogeneous structure, exhibit excellent Li-storage capacity, achieving 529 mA h g⁻¹ after 150 cycles at a high current density of 500 mA g⁻¹. The relationship between the microstructure and improved electrochemical performance, as well as the formation mechanism of the product, is discussed in detail. This study provides a new approach for conveniently constructing nanocomposites using two types of layered materials that offer satisfactory rate capability and cyclability, making them potentially suitable for application in Li-ion batteries.     

Effect of oxidation on Li-ion secondary battery with non-stoichiometric silicon oxide (SiOx) nanoparticles generated in cold plasma

In order to study the effect of oxidation on anode material for Li-ion secondary battery, non-stoichiometric silicon oxide nanoparticles are synthesized using inductively coupled plasma (13.56 MHz). The chemical compositions and size distribution of the generated nanoparticles are measured with EDS and SMPS (Scanning Mobility Particle Sizer). The chemical composition of the nanoparticles was very similar with that of a non-stoichiometric silicon oxide film. For Li-ion secondary battery, it is recommended that the oxygen concentration should be reduced below 18 at.%. It is also revealed that pitch coating was a good method for preventing the natural oxidation and improving capacity.     

Numerical investigation of nanoparticle synthesis in supersonic thermal plasma expansion

In this communication, we are numerically investigating the nucleation and growth of nanoparticles in the context of a supersonically expanded thermal plasma assisted process, using the Nodal General Dynamic Equations (NGDE) model. The dependence of particle size distribution on reactant injection rate and sample collection chamber pressure is investigated. The possible effect of particle charging in the plasma environment on nucleation and growth of particle sizes is also studied. Results are compared with findings from an actual experimental reactor system in the laboratory of the authors.     

Microwave-assisted synthesis and characterization of tin oxide nanoparticles

Tin oxide nanoplatelets (SnO) and nanoparticles (SnO₂) were prepared by microwave assisted technique with an operating frequency of 2.45 GHz. This technique permits to produce gram quantity of homogeneous nanoparticles in just 10 min. The crystalline size was evaluated from XRD and found to range from 26 to 34 nm. SEM and TEM analyses showed that the nanoparticles present a platelet-like shaped particle or, a pseudo spherical morphology, after calcination at moderate temperature during which the phase transformation from SnO to SnO₂ takes place. Additional FT-IR, density and resistivity measurements were also presented.     

Hot-wire synthesis of Si nanoparticles

The viability of producing silicon nanoparticles using the HWCVD process is investigated. A system is assembled and particles are produced from silane at pressures between 0.2 and 48 mbar, with hydrogen dilutions of 0-80%, at a total flow rate of 50 sccm and with a tungsten filament maintained at 1650 °C. The as-prepared powder varies in colour from yellowish to dark brown and is deposited on all surfaces inside the reaction chamber. The material is a highly porous agglomeration of nanoparticles of primary size in the order of 40 nm, with a narrow size distribution. The nanoparticles produced are mostly amorphous, hydrogenated and have a partially oxidised surface.     

High throughput production of nanocomposite SiOx powders by plasma spray physical vapor deposition for negative electrode of lithium ion batteries

Nanocomposite Si/SiO_x powders were produced by plasma spray physical vapor deposition (PS-PVD) at a material throughput of 480 g h⁻¹. The powders are fundamentally an aggregate of primary ∼20 nm particles, which are composed of a crystalline Si core and SiO_x shell structure. This is made possible by complete evaporation of raw SiO powders and subsequent rapid condensation of high temperature SiO_x vapors, followed by disproportionation reaction of nucleated SiO_x nanoparticles. When CH₄ was additionally introduced to the PS-PVD, the volume of the core Si increases while reducing potentially the SiO_x shell thickness as a result of the enhanced SiO reduction, although an unfavorable SiC phase emerges when the C/Si molar ratio is greater than 1. As a result of the increased amount of Si active material and reduced source for irreversible capacity, half-cell batteries made of PS-PVD powders with C/Si = 0.25 have exhibited improved initial efficiency and maintenance of capacity as high as 1000 mAh g⁻¹ after 100 cycles at the same time.     

等离子原位合成TiC颗粒增强Ni基复合涂层

采用等离子熔覆技术,选择合适的工艺参数,在碳钢表面原位合成了TiC/Ni基复合材料涂层.借助金相显微镜、扫描电镜、X射线仪、透射电镜对复合涂层的组织、结构进行了测试,并利用热力学原理对TiC形成进行了分析.结果表明:熔覆层的组织由γ-Ni、M23C6、CrB及原位合成的TiC组成,TiC以颗粒状为主,少量呈块状,尺寸为1～2μm,弥散分布于熔覆层中;TiC的形成遵循形核与长大方式进行,等离子快速加热、快速冷却的特点决定了原位合成的TiC颗粒尺寸细小;TiC的不同形态可由共晶过程得到解释.     

A facile synthesis of monodisperse Au nanoparticles and their catalysis of CO oxidation

Monodisperse Au nanoparticles (NPs) have been synthesized at room temperature via a burst nucleation of Au upon injection of the reducing agent t-butylamine-borane complex into a 1, 2, 3, 4-tetrahydronaphthalene solution of HAuCl₄·3H₂O in the presence of oleylamine. The as-synthesized Au NPs show size-dependent surface plasmonic properties between 520 and 530 nm. They adopt an icosahedral shape and are polycrystalline with multiple-twinned structures. When deposited on a graphitized porous carbon support, the NPs are highly active for CO oxidation, showing 100% CO conversion at −45 °C. This article is published with open access at Springerlink.com     

Investigation of gas-liquid interface in atmospheric-pressure micro plasma with solution

An atmospheric-pressure glow-discharge micro plasma in contact with liquid paraffin is stably generated by using a capacitively coupled plasma method with a mesh electrode. When characteristics of the plasma are measured in the boundary between the micro plasma (gas-phase) and liquid paraffin (liquid-phase) using optical emission spectroscopy, spectrum peaks of the emission of CH and C₂ which dissociate from paraffin are observed. The result indicates that solution can feed particles to the plasma at gas-liquid interface and this plasma is accordingly expected to promote an attractive plasma process for creating materials consisting of elements in various solutions.     

高频热等离子体制备形状可控的一维结构纳米材料

介绍了采用高频热等离子体宏量制备ZnO、ZnS和A1N等一维结构纳米材料。研究了不同工艺条件对形貌的影响；采用锌粉为原料，成功制备了不同长径比的氧化锌纳米棒；同样，采用锌粉和硫粉混合物为原料，获得了均匀的棒状和四角状等不同形貌的一维结构纳米ZnS；采用铝粉与氨气在等离子体中的反应，获得了一维结构纳米A1N。通过控制不同的参数可以调控合成产物的大小、长径比和形貌等。在等离子体合成过程中，合成产物可以达到50g／min，而且，产物的大小和形貌均匀。XRD、SEM、HRTEM和拉曼光谱等表征了合成产物的结构和形貌。在高频常压热等离子体合成过程中，一维结构纳米材料的生长过程只有数秒，而合成的一维纳米材料的长度甚至可以达到几十微米。通过分析发现，在等离子体合成过程中，一维纳米材料的生长符合VS机制，而且，生长过程是双向进行的。     

A controllable and byproduct-free synthesis method of carbon-coated silicon nanoparticles by induction thermal plasma for lithium ion battery

Carbon coated silicon nanoparticle is regarded as a promising anode material for the next generation of lithium ion batteries, while the development of a cost-effective and environmental-friendly preparation method is still difficult and hinders the practical implementation. In this research, a controllable and byproduct-free synthesis method is proposed for the preparation of silicon nanoparticles with amorphous hydrogenated carbon coating. The current apparatus is operated based on the application of induction thermal plasma. Plasma properties are tunable by adjusting the ratio of tangential and radial gas flow rates (T/R), which compose the plasma sheath gas. Obtained results reveal the plasma shape is shrunk with higher T/R values, which will lead to a steeper temperature gradient and lower temperature distributions in reaction chamber. Consequently, the compositions and properties of synthesized particles can be modified with T/R values. The formation of SiC, which was an intractable issue before, can be vanished at higher tangential gas flow rates in current research and the capacity of silicon anode for batteries will be improved in predict. This research is significant for a deep understanding of plasma synthesis processing and design of batteries with excellent performance.     

Direct synthesis of monodispersed ZnO nanoparticles in an aqueous solution

Monodispersed ZnO nanoparticles with mesopores were successfully prepared via a simple route through the transformation of Zn(NH₃)₄²⁺ precursor in the presence of sodium oleate and hydrazine at 80 °C with the pH of 8.5. Hydrazine and sodium oleate were used to control the size at 30-60 nm and to improve dispersion properties of ZnO nanoparticles. The samples were characterized by TEM, XRD, IR and TG-DTA, and the results suggest that the grains are composed of ZnO and a small quantity of oleate. The oleate plays an important role in preventing the ZnO nanoparticles from aggregating.     

Large-scale preparation of powder composites xNiO/(1-x)Al2O3 in reactions of solution combustion synthesis

The conditions for the production of composites by Solution Combustion Synthesis (SCS) from reaction solutions of aluminum and nickel nitrates of various concentrations with glycine have been studied. The concentration of reaction solutions increases the product yield and the productivity of SCS process. The effect of the presence of Al³⁺ cations in reaction solutions on the combustion reaction intensity reduction has been established. The SCS precursors contained metallic nickel, nickel oxide and amorphous alumina. The phase composition of the samples changed in the process of annealing: nickel oxidation, crystallization of γ-Al₂O₃ (600 °C) and formation of NiAl₂O₄ spinel (600–800 °C) were observed. The maximal specific surface area value recorded after annealing at 800 °C was 59–63 m²/g. In samples obtained with a lower fuel content, γ-Al₂O₃ or a mixture of γ-Al₂O₃ and NiAl₂O₄ crystallize on the surface of composite particles. The concentration of NiO on the surface of composites obtained from precursors synthesized from concentrated solutions at φ = 1.4 is close to the nominal composition.     

Formation phenomena of iron oxide-silica composite in microwave plasma and DC thermal plasma

Iron oxide-silica composite was synthesized using atmospheric microwave plasma and DC thermal plasma. There has recently been increasing interest in predicting the final product during vapor phase synthesis using plasma because of difficulty obtaining desirable product. In this study, vapor phase synthesis of iron oxide-silica composite from iron pentacarbonyl (Fe(CO)₅) and tetraethyl orthosilicate (SiC₈H₂₀O₄, TEOS) was conducted using various Fe/Si ratios and different types of plasma to identify the formation mechanism in the Fe-Si-O multi-component system. The morphologies and phase compositions of the synthesized particles were analyzed and compared. The results showed that the Fe/Si ratio and the type of plasma influenced the morphologies and the phase composition. A thermodynamic consideration was introduced to investigate the particle formation phenomena, which could explain the differences induced by varying the Fe/Si ratio and type of plasma. The particle formation mechanism was divided into a condensation step and a diffusion step. At the condensation step, the Fe/Si ratio determined the condensation temperature, which is related to the morphology. At the diffusion step, the quenching rate of the plasma determined the degree of diffusion, which was related to the phase composition and formation of the external layer.     

One-pot mechanical synthesis of the nanocomposite granule of LiCoO2 nanoparticles

The layered rock-salt LiCoO₂ granules consisted of the primary nanoparticles were successfully synthesized by one-pot mechanical method without external heating. The sizes of the primary nanoparticle and the granule observed using electron microscopy were 50–200 nm and 20 μm, respectively. The surface property of the primary nanoparticle was evaluated by STEM-EELS, which revealed that the primary particle possesses the lithium defective part at the surface. The penetration behavior of an electrolyte into the granule was also evaluated by STEM-EDX, which indicated that the electrolyte could not fully penetrate into the granule. The first charge and discharge capacities of Li-ion cell assembled with the synthesized LiCoO₂ granules were 140 and 120 mA h/g, respectively. The relationship between the particle structures of the synthesized LiCoO₂ granules and the electrochemical properties were discussed.     

Control of the hydrophobicity of rare earth oxide coatings deposited by solution precursor plasma spray by hydrocarbon adsorption

The basis of the hydrophobicity of lanthanide rare earth oxides(REOs)has been the subject of considerable debate.To explore this question,the wetting behaviors and surface compositions of hierarchicallystructured Yb₂o₃(one of the REOs)coatings and non-REO Al₂o₃coatings deposited via solution precursor plasma spray process were investigated in this work.The Yb₂o₃coatings were subjected to a number of post-deposition treatments including vacuum(1-15 Pa)treatment,Ar-plasma treatment,heat treatment(400℃),long-time air exposure and ultra-high vacuum(1×10^-7Pa)treatment.Subsequent characterization showed that different post-deposition treatments resulted in different wetting behavior for the Yb₂o₃coatings which correlated with the content of hydrocarbon on the surface.Yb₂o₃coatings exhibited reversible transitions between superhydrophobicity after vacuum treatment and superhydrophilicity after Ar-plasma or heat treatment,linked to hydrocarbon adsorption onto and desorption from the surface.Yb₂o₃coatings after long-time air exposure and ultra-high vacuum treatment both remained hydrophilic and showed a smaller hydrocarbon content than coatings after vacuum treatment.Al₂o₃coatings with hierarchical surface structures similar to the Yb₂o₃coatings showed an increase in WCA to only-170 after the same vacuum treatment,indicating the REO has a much higher affinity for hydrocarbon adsorption than Al₂o₃,and that the content of hydrocarbon adsorbed on the surface of the REO determined the wetting behavior.     

Controlled synthesis of alumina nanoparticles using inductively coupled thermal plasma with enhanced quenching

Synthesis of alumina nanoparticles in an Ar-O₂ inductively coupled radio frequency (rf) plasma controlled by axial quench gas injection was investigated. The flow and temperature fields for various quench gas flow rates in the plasma reactor, as well as the corresponding quench rates, were predicted using a renormalization group (RNG) k-ε turbulence model. Nanosize alumina particles were synthesized from the vapor phase by oxidation of aluminum in the plasma. The collected products were characterized by means of field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), and BET surface area analysis. The dependences of particle size and shape on the injection position and the flow rate of the quench gas were discussed.     

Electron energy-loss spectroscopy investigation of dopant homogeneity in Tb-doped Y2O3 nanoparticles prepared by solution combustion synthesis

The emergence of nanotechnology imposes a new level of control in the synthesis of materials, one in which the structure and chemistry have to be controlled and characterized at the nanoscale. The solution combustion synthesis method has been used to synthesize many different oxides, including luminescent ones. However, a systematic investigation of the dopant homogeneity at the nanoscale in materials produced by this method is lacking. This is of particular relevance in nanophosphors due to the possibility of concentration quenching. In this work, 5 at.% Tb-doped Y₂O₃ was prepared by the solution combustion synthesis method and investigated on its structure and chemical composition homogeneity at the nanoscale by means of electron energy-loss spectroscopy (EELS) scanning transmission electron microscopy (STEM), high resolution TEM, X-ray diffraction and photoluminescence measurements. The results show that it is possible to prepare luminescent materials by the solution combustion synthesis method where the dopant is homogeneously distributed within each nanoparticle.