Synthesis of ultrafine SiC from rice hulls (husks): A plasma process

Heat-treated rice hulls have been used as precursor material for synthesis of ultrafne SiC in a RF plasma reactor. Rice hulls containing finely distributed silica and active carbon act as a source for SiC formation. The plasma-synthesized powder contained ultrafnc -SiC with excess carbon and some unreacted silica. Post-treatment processes such as oxidation and acid (HF) treatment appear to be effective in removing the excess carbon and silica.     

Polarography of oxyanions in molten salts

A review of the polarography of oxyanions in molten salts is presented.     

Directly conversion the biomass-waste to Si/C composite anode materials for advanced lithium ion batteries

The necessity to explore high-efficiency and high-value utilization strategy for biomass-waste is desirable.Herein,the strategy for direct conversion biomass-waste(rice husks) to Si/C composite structure anode was built.The Si/C composite materials were successfully obtained via the typical thermal reduction with magnesium,and the Si nanopa rticle was uniformly embedded in carbon frame,as revealed by Raman,X-ray diffraction(XRD) and transmission electron microscope(TEM) measurement.The carbon structure among rice husks was effectively used as a protective layer to accommodate the volume variation of Si anode during the repeated lithiation/delithiation process.Benefitting from the structure design,the batteries show a superior electrochemical stability with the capacity retention rate above 90% after 150 cycles at the charge/discha rge rate of 0.5 C(1 C=600 mAh/g),and hold a high charge capacity of 420.7 mAh/g at the rate of 3 C.Therefore,our finding not only provides a promising design strategy for directly conversion biomass-waste to electrochemical storage materials but broadens the high-efficiency utilization method for other biomass by-products.     

Ablation properties of C/C–SiC composites tested on an arc heater

Carbon fiber-reinforced carbon and silicon carbide (C/C–SiC) composites were fabricated by a combination of chemical vapor infiltration and liquid silicon infiltration. Ablation properties of C/C–SiC composites and C/C composites with similar technique were tested on a high-pressure arc heater. The results show that ablation properties of C/C–SiC composites are more severe than those of C/C composites. Ablation of C/C–SiC composites includes oxidation, sublimation of SiC (Si), and mechanical denudation. Oxidation and sublimation of SiC (Si) lead to the enlarged ablation rates between carbon fibers and matrices, which finally cause serious ablation of C/C–SiC composites.     

Anodic reactions of sulphate in molten salts

Electrochemical behaviour of sulphate under anodic polarization in molten sodium chloride, cryolite and sodium fluoride was investigated by cyclic voltammetry and chronopotentiometry at the temperatures of 820°C, 1010°C, and 1000°C, respectively. Using a platinum working electrode, two waves were observed on the chronopotentiograms in the systems: NaCl-Na₂SO₄ and Na₃AlF₆-Na₂SO₄. The first wave was attributed to the formation of oxygen. The second wave probably originated from the reaction of oxygen with platinum, or from oxidation of SO₃ decomposition products. Three waves were observed for the anodic process of sulphate ions dissolved in molten sodium fluoride. The first wave was attributed to the formation of oxygen. The second and the third wave were attributed to the formation of PtO and PtO₂. This conclusion was supported by cyclic voltammetry experiments of the in-situ formed sulphide in molten NaCl at 820°C and by chronopotentiometry on a gold working electrode in the system NaCl-Na₂SO₄, where no anodic wave was observed.     

Electrochemical synthesis of ammonia in molten salts

Ammonia is important feedstock for both fertilizer production and carbon-free liquid fuel.Many techniques for ammonia formation have been developed,hoping to replace the industrial energy-intensive Haber-Bosch route.Electrochemical synthesis of ammonia in molten salts is one promising alternative method due to the strong solubility of N~(3-) ions,a wide potential window of molten salt electrolytes and tunable electrode reactions.Generally,electrochemical synthesis of ammonia in molten salts begins with the electro-cleavage of N_2/hydrogen sources on electrode surfaces,followed by diffusion of N~(3-)/H~+-containing ions towards each other for NH_3 formation.Therefore,the hydrogen sources and molten salt composition will greatly affect the reactions on electrodes and ions diffusion in electrolytes,being critical factors determining the faradaic efficiency and formation rate for ammonia synthesis.This report summarizes the selection criteria for hydrogen sources,the reaction characteristics in various molten salt systems,and the preliminary explorations on the scaling-up synthesis of ammonia in molten salt.The formation rate and faradaic efficiency for ammonia synthesis are discussed in detail based on different hydrogen sources,various molten salt systems,changed electrolysis conditions as well as diverse catalysts.Electrochemical synthesis of ammonia might be further enhanced by optimizing the molten salt composition,using electrocatalysts with well-defined composition and microstructure,and innovation of novel reaction mechanism.     

Coordination chemistry of actinides in molten salts

The problems of actinide molten salt coordination chemistry are considered in terms of spectroscopic parameters as functions of melt composition and temperature. Parameters connected with energy, intensity and fine structure of 5f-5f transitions have been obtained for molten alkali metal chlorides, fluorides and chloride-fluoride mixtures. The regularities of variation of both actinide-chlorine distances and actinide fluorocomplex stability have been studied.     

Mechanical properties and fracture behaviors of C/C composites with PyC/TaC/PyC,PyC/SiC/TaC/PyC multi-interlayers

Carbon/carbon (C/C) composites with PyC/TaC/PyC or PyC/SiC/TaC/PyC multi-interlayers were prepared by isothermal chemical vapor infiltration, followed by Furan resin impregnation and carbonization. Microstructures, mechanical properties including flexural strength, ductile displacement, and fracture behaviors of composites were studied. Furthermore, composites were heat treated at 2000 °C to study the effects of heat treatment on mechanical properties and fracture behaviors. PyC/TaC/PyC and PyC/SiC/TaC/PyC multi-interlayers have been deposited uniformly in C/C composites. With the introduction of PyC/TaC/PyC multi-interlayers in C/C composites, the flexural strength decreases; however, the ductile displacement increases. The fracture behavior changes from brittleness (0% TaC) to pseudo-ductility (5% TaC) and high toughness (10% TaC). When PyC/SiC/TaC/PyC multi-interlayers are introduced in C/C composites, the flexural strength is improved remarkably from 270 MPa to 522 MPa, but the ductile displacement decreases obviously from 0.49 mm to 0.24 mm, and the fracture behavior becomes brittle again. After heat treatment at 2000 °C, the flexural strength decreases, but the ductile displacement increases and pseudo-ductility or high toughness can be obtained.     

Electrodeposition of hafnium and hafnium-based coatings in molten salts

At present, coatings are mostly produced by CVD, PVD methods, plasma, and detonation spraying. Molten salts for coatings deposition are also becoming highly attractive. They provide wide possibilities for coating production of hafnium by electrodeposition, electrochemical synthesis, and precise surface alloying. Consideration is given to all these methods. The production of heat-resistant coatings from hafnium and niobium-hafnium alloys, and the electrochemical syntheses of copperhafnium solder and HfB₂ coatings are also discussed.     

Yolk-shell Si/C composites with multiple Si nanoparticles encapsulated into double carbon shells as lithium-ion battery anodes

The conceptual design of yolk-shell structured Si/C composites is considered to be an effective way to improve the recyclability and conductivity of Si-based anode materials. Herein, a new type of yolk-shell structured Si/C composite(denoted as TSC-PDA-B) has been intelligently designed by rational engineering and precise control. In the novel structure, the multiple Si nanoparticles with small size are successfully encapsulated into the porous carbon shells with double layers benefiting from the strong etching effect of HF. The TSC-PDA-B product prepared is evaluated as anode materials for lithium-ion batteries(LIBs).The TSC-PDA-B product exhibits an excellent lithium storage performance with a high initial capacity of 2108 mAh g~(-1) at a current density of 100 mA g~(-1) and superior cycling performance of 1113 mAh g~(-1) over 200 cycles. The enhancement of lithium storage performance may be attributed to the construction of hybrid structure including small Si nanoparticles, high surface area, and double carbon shells, which can not only increase electrical conductivity and intimate electrical contact with Si nanoparticles, but also provide built-in buffer voids for Si nanoparticles to expand freely without damaging the carbon layer.The present findings can provide some scientific insights into the design and the application of advanced Si-based anode materials in energy storage fields.     

熔融盐对生物质粗燃气的组分调整实验研究

在固定床装置中进行了熔融盐对生物质粗燃气组分调整实验,考察了反应温度、静液高度和表观气速对熔融盐中出口气体组分、NaOH消耗率、熔融盐饱和吸收时间的影响。结果表明,400!600℃下,熔融盐中NaOH消耗率随温度的升高由59%升至83%,且单位质量熔融盐处理粗合成气量随温度的升高由0.42 m3/kg升至0.48 m3/kg;气体中CO转化率和出口气体平均H2/CO体积比均随反应温度、静液高度的提高而升高,随表观气速的增加而降低。     

A theory of transport properties in molten salts

Expressions for diffusion constants in molten salts have been obtained in terms of the inter-ionic pair potentials and the pair distribution functions. Numerical attempts for diffusion constants in molten alkali halides are carried out and results agreed fairly with those obtained by molecular-dynamics simulation and with some experimental data. Based on the coupling of generalized Langevin equation and damped Einstein oscillator equation, ions' velocity autocorrelation functions have also been described and are numerically applied for molten potassium fluoride. The deviation from the Nernst-Einstein relation was also discussed in detail. In Appendixes A x B x C, the short-time expansion of velocity correlation functions in relation to the partial conductivities and the diffusion constants were obtained up to the term of t(4) and these were compared with a model function described by the form of cos(omegat)sech(ttau).     

XRD-Studies of SiC/Si layers on carbon substrates

Structural investigations of thin films of SiC, SiC with free silicon and various titanium suicides (TiSi₂, TiSi and Ti₅Si₃) are described. The crystal phases have been identified using X-ray diffractometry. The growth of reaction products from surface reactions between silicon and deposited titanium can be observed.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Preparation and characterization of rice husk/ferrite composites

<正>A novel ferrite composite using rice husk as substrate has been prepared via high temperature treatment under nitrogen atmosphere.The rice husk substrate consists of porous activated carbon and silica,where spinel ferrite particles with average diameter of 59 nm are distributed.The surface area of the composite is greater than 170 m~2 g~(-1) and the bulk density is less than 0.6 g cm~(-3).Inert atmosphere is indispensable for the synthesis of pure ferrite composites,while different preparation temperatures of above 600℃result in composites with similar structures and morphologies.Due to the presence of ferrite particles,this novel composite shows enhanced adsorption ability for acid orangeⅡ.     

The cohesive energy of molten salts and its density

The cohesive energies ces of uni-univalent molten salts and the corresponding cohesive energy densities ceds and solubility parameters δ were calculated from literature data. The ceds are much larger than the internal pressures, P_i, as expected for highly structured liquids. The solubility parameters δ are too large to be significant for the solubility of the solutes, except gases, in these molten salts.