Carbon Thermal Reduction Research Articles

In-Situ 2p3d Resonant Inelastic X-ray Scattering Tracking Cobalt Nanoparticle Reduction.

In-situ carbon-thermal reduction of cobalt oxide nanoparticles supported on carbon nanotubes was studied by cobalt 2p3d resonant inelastic X-ray scattering (RIXS). The in-situ 2p X-ray absorption spectroscopy (XAS) and RIXS measurements were performed at 500, 600, and 700 °C, where four consistent excitation energies were used for RIXS acquisitions. After 700 °C reduction, the XAS spectrum shows a cobalt metal-like shape, while the RIXS spectra reveal the minority cobalt monoxide phase. The holistic fit on both XAS and RIXS data reveals the respective contributions from metal and monoxide. We show that the relative precision to determine the monoxide content changes from ∼5.6% in XAS results to better than 0.8% in the RIXS analysis, suggesting that RIXS is a useful tool to track the oxidation state of nanoparticles under in situ conditions. We determined a relative radiative ratio (P) factor of approximately 5, where this factor gives the ratio between the relative strengths of the radiative decay channels compared to the nonradiative channels in CoO and Co metal.

Adjustable 3-D structure with enhanced interfaces and junctions towards microwave response using FeCo/C core-shell nanocomposites

In this work, the 3-D honeycomb-like FeCo/C nanocomposites were synthesized through the carbon thermal reduction under an inert atmosphere. The enhanced microwave absorption properties of the composites were mainly attributed to the unique three dimensional structure of the FeCo/C nanocomposites, abundant interfaces and junctions, and the appropriate impedance matching. The Cole-Cole semicircles proved the sufficient dielectric relaxation process. The sample calcinated at 600°C for 4h showed the best microwave absorption properties. A maximum reflection loss of −54.6dB was achieved at 10.8GHz with a thickness of 2.3mm and the frequency bandwidth was as large as 5.3GHz. The results showed that the as-prepared FeCo/C nanocomposite could be a potential candidate for microwave absorption.

Effect of reduction time on the structure and properties of porous graphene

Porous graphene with nanoscaled pores on the sheets was prepared by a carbon thermal reduction method, in which the molybdenum oxide nanoparticles generated from the thermal decomposition of molybdate were used as the etching reagent, and the pores were formed on the surface of the reduced graphene oxide under the conditions of 650 °C and a nitrogen atmosphere. The morphology of pores on the graphene sheets may affect their potential applications in various fields, especially in the enhancement of mass transfer. Previous studies have shown that the reduction temperature and the amount of metal oxide are the key factors affecting the morphology of porous graphene, but in fact the reduction time is a more important affecting factor according to the present study. The results of SEM/TEM showed that a disordered large sheet-like structure with wrinkles was obtained at 120 min in the carbon-thermal reaction. The structural integrity of the PG was further destroyed after the reaction time of 140 min, in which the edge exhibited slightly crush and significant fold. The PG exhibited a hollow rod-like structure at the reaction time of 180 min. FTIR, Raman, XRD, and XPS studies were performed to characterize the morphology of porous graphene prepared at different reduction times.

Enhanced electrochemical performance of lithium ion battery cathode Li3V2(PO4)3/C

Li-ion battery cathode material lithium-vanadium-phosphate Li3V2(PO4)3 was synthesized by a carbon-thermal reduction method, using stearic acid, LiH2PO4, and V2O5 as raw materials. And stearic acid acted as reductant, carbon source, and surface active agent. The effect of its content on the crystal structure and electrochemical performance of Li3V2(PO4)3/C were characterized by XRD and electrochemical performance testing, respectively. The results showed that the content of carbon source has no significant effect on the crystal structure of lithium vanadium phosphate. Lihtium vanadium phosphate obtained with 12.3% stearic acid demonstrated the best electrochemical properties with a typical discharge capacity of 119.4 mAh/g at 0.1 C and capacity retention behavior of 98.5% after 50 cycles. And it has high reversible discharge capacity of 83 mAh/g at 5 C with the voltage window of 3 to 4.3 V.

Freestanding Flexible Li2S Paper Electrode with High Mass and Capacity Loading for High‐Energy Li–S Batteries

Lithium–sulfur (Li–S) batteries are a very appealing power source with extremely high energy density. But the use of a metallic‐Li anode causes serious safety hazards, such as short‐circuiting and explosion of the cells. Replacing a sulfur cathode with a fully‐lithiated lithium sulfide (Li2S) to pair with metallic‐Li‐free high‐capacity anodes paves a feasible way to address this issue. However, the practical utility of Li2S cathodes faces the challenges of poor conductivity, sluggish activation process, and high sensitivity to moisture and oxygen that make electrode production more difficult than dealing with sulfur cathodes. Here, an efficient but low‐cost strategy for easy production of freestanding flexible Li2S‐based paper electrodes with very high mass and capacity loading in terms of in situ carbonthermal reduction of Li2SO4 by electrospinning carbon is reported. This chemistry enables high loading but strong affinity of ultrafine Li2S nanoparticles in a freestanding conductive carbon‐nanofiber network, meanwhile greatly reducing the manufacturing complexity and cost of Li2S cathodes. Benefiting from enhanced structural stability and reaction kinetics, the areal specific capacities of such cathodes can be significantly boosted with less sacrificing of high‐rate and cycling capability. This unique Li2S‐cathode design can be directly applied for constructing metallic‐Li‐free or flexible Li–S batteries with high‐energy density.

Low content of Pt supported on Ni-MoCx/carbon black as a highly durable and active electrocatalyst for methanol oxidation, oxygen reduction and hydrogen evolution reactions in acidic condition

Nickel and molybdenum carbide modified carbon black (Ni-MoCx/C) was synthesized by a two-step microwave-assisted deposition/carbonthermal reduction method and characterized by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The as-prepared Ni-MoCx/C supported Pt (10wt%) electrocatalyst (10Pt/Ni-MoCx/C) was synthesized through a microwave-assisted reduction method and 10Pt/Ni-MoCx/C exhibited high electrocatalytic activity for methanol oxidation, oxygen reduction and hydrogen evolution reactions. Results showed that 10Pt/Ni-MoCx/C electrocatalyst had better electrocatalytic activity and stability performance than 20wt% Pt/C (20Pt/C) electrocatalyst. Among them, the electrochemical surface area of 10Pt/Ni-MoCx/C reached 68.4m2g−1, which was higher than that of 20Pt/C (63.2m2g−1). The enhanced stability and activity of 10Pt/Ni-MoCx/C electrocatalyst were attributed to: (1) an anchoring effect of Ni and MoCx formed during carbonthermal reduction process; (2) a synergistic effect among Pt, Ni, MoOx and MoCx. These findings indicated that 10Pt/Ni-MoCx/C was a promising electrocatalyst for direct methanol fuel cells.

Removal of Fe from fly ash by carbon thermal reduction

Main chemical compositions of fly ash is SiO2 and Al2O3, which are also main chemical components of zeolite. Therefore, fly ash can be used to prepare zeolite after removing impurities such as Fe. Previous studies have only used the methods of magnetic separation and acid leaching to remove impurities, which can not wipe out the impurities thoroughly, especially Fe impurities. In the paper, carbon thermal method is used to reduce hematite, and then low valence Fe is removed by magnetic separation and acid leaching. The experimental results derived from XRF, XRD, SEM/EDS analysis show that the total iron content of the fly ash is reduced to be 0.49% from 4.62%, the CaO content is reduced to be 2.08% from 9.61% after 1 pretreatment cycle. The raw material requirements for the preparation of zeolite are preliminarily achieved.

Enhanced electrochemical performance of LiFePO4 cathode with synergistic modification of Na3V2(PO4)3 and carbon network

A high performance 9LiFePO4–Na3V2(PO4)3/C composite is successfully prepared by a sol–gel technique followed by subsequent carbonthermal reduction process. The structure and performance of 9LiFePO4–Na3V2(PO4)3/C composite have been investigated by XRD, SEM, TEM, EDS, CV and EIS. The result shows that the Na3V2(PO4)3 acting as ionic conductor improves the lithium ion transmission rate, while a thin amorphous carbon layer on the surface of nanoparticles and interfacial structure between the two phase enhances the electronic transmission rate of the composite. The synergistic effect of continual conductive carbon network and Na3V2(PO4)3 phase facilitates the diffusion of lithium ion and electron, ensures the stability of the LiFePO4 nanoparticles by limiting the direct contact of LiFePO4 particle with the electrolyte and ultimately improve the rate capability and long-cycling life of the material. The 9LiFePO4–Na3V2(PO4)3/C composite delivers discharge capacities of 151.2, 144.9 and 118.1mAhg−1 at 1.0, 2.0, 5.0 C, respectively, with high capacity retention up to 88.2% after 2000cycles at 2.0 C, exhibiting good electrochemical performance compared with that of the pristine one.

Tailoring the input impedance of FeCo/C composites with efficient broadband absorption.

Proper impedance matching and strong attenuation capabilities are crucial factors for an excellent microwave absorbent. Significant attention and effort have been focused on the attenuation capabilities, whereas little attention has been paid to impedance matching, which is particularly important to design broadband absorbing materials. In this study, coin-like porous FeCo/C composites were successfully prepared by a simple carbon thermal reduction method. The Zin/Zo values of the FeCo/C composites were calculated to investigate the effects of the Fe/Co molar ratio and structure on the impedance matching. The results show that the coin-like porous samples were equipped with optimal impedance matching (Zin/Zo ≈ 1) and broad frequency bandwidth. The coin-like porous structure can induce multiple scattering and extend the travel path of the waves, which is in favour of electromagnetic loss. In this way, the effective frequency bandwidth (RL < -10 dB) as large as 6 GHz (from 11.36 to 17.36 GHz) has been achieved at a thickness of 2 mm when the Fe/Co molar ratio is 4 : 6. In addition, the average frequency broadband reached 5.57 GHz in the thickness range of 2-2.6 mm. We believe that this study may provide a new strategy for tuning the impedance matching for optimal broadband absorbers.

High Energy Density LiFePO4/C Cathode Material Synthesized by Wet Ball Milling Combined with Spray Drying Method

Lithium iron phosphate with high energy density was synthesized by a combination of wet ball milling, spray drying and carbon thermal reduction technology using inexpensive FePO4 as starting material. The effect of morphology on structure and electrochemical properties of LiFePO4/C cathode material was systematically investigated. The as-obtained LiFePO4/C composite has ordered olivine structure and micro-spherical morphology assembled with nanosized primary particles. The lithium iron phosphate microsphere has a core-shell structure, not only does the surface of nanoparticles have a homogeneous and complete carbon coating but also does the surface of secondary particles form a carbon shell, which results in its uniform particle size distribution and enhanced electronic conductivity. All above-mentioned factors lead to its excellent room-temperature and low-temperature electrochemical performance in LiFePO4/Li half-cell, as well as good processabilty in 14500 cylindrical full-cell. More importantly, its high tap density and pole piece compaction density can effectively improve the volumetric specific energy of the battery.

DEVELOPMENT OF RESOURCE-SAVING TECHNOLOGIES OF STEEL DIRECT ALLOYING ON THE BASIS OF THERMODYNAMIC MODELING OF METALS RECOVERY PROCESSES IN ELEMENTARY SYSTEMS

One of the promising trends of the perfection of the existing technologies is the development of the technologies of alloying and modification of steel oxide, including natural materials. Such materials are the bariumstrontiumcontaining carbonate ores, the nickel concentrates and converter vanadium slag, whose use makes it possible to obtain metal with the improved properties, at the same time from the process is excluded the stage of obtaining ferroalloys and masteralloys, which is characterized by significant expenditures. For improving the existing metallurgical processes the significant studies are required, which can be accomplished with the use of methods of thermodynamic simulation. In the article the results of thermodynamic simulation in the elementary systems of the reduction processes of barium, strontium, vanadium and nickel from their oxides from different restorers are given. The obtained results made it possible to explain the possibility in principle of the realization of the processes of microalloying and modification of steel by inexpensive materials and to determine type and optimum expenditures of restorer. As the tool with the thermodynamic simulation was used the program set “TERRA”, which allows on the basis of the principle of the entropy maximum defining equilibrium classification of multicomponent heterogeneous system for the high-temperature conditions. As the restorers were examined carbon, silicon and aluminum. Studies of the effect of temperature and expenditures of restorers for conditions and regimes of the reduction processes of metals were carried out. The results of investigating the reduction processes of barium and strontium have shown that as the restorer during the application of the oxide barium-containing materials for the treatment of steels is more preferably to use silicon or aluminum. The optimum expenditures of restorers were determined, which ensure the maximum degree of the reduction of barium and strontium. The studies were carried out and the possibility of nickel restoring by carbon was confirmed. The results of investigating the process of vanadium reduction confirmed the realizability of process both separately by silicon and by carbon and by the joint carbon-thermal reduction, during which carbon is the predominant restorer. The use of obtained results will make it possible to develop the new resource-saving technologies with the use of oxide materials for the alloying, microalloying and modifications of the fusions of the system Fe – C.

Biomass-Derived Porous Fe3C/Tungsten Carbide/Graphitic Carbon Nanocomposite for Efficient Electrocatalysis of Oxygen Reduction.

The oxygen-reduction reaction (ORR) draws an extensive attention in many applications, and there is a growing interest to develop effective ORR electrocatalysts. Iron carbide (Fe3C) is a promising alternative to noble metals (e.g., platinum), but its performances need further improvement, and the real role of the Fe3C phase remains unclear. In this study, we synthesize Fe3C/tungsten carbide/graphitic carbon (Fe3C/WC/GC) nanocomposites, with waste biomass (i.e., pomelo peel) serving as carbon source, using a facile, one-step carbon thermal-reduction method. The nanocomposite is characterized by a porous structure consisting of uniform Fe3C nanoparticles encased by graphitic carbon (GC) layers with highly dispersed nanosized WC. The Fe3C provides the active sites for ORR, while the graphitic layers and WC nanoparticles can stibilize the Fe3C surface, preventing it from dissociation in the electrolyte. The Fe3C/WC/GC nanocomposite is highly active, selective, and stable toward four-electron ORR in pH-neutral electrolyte, which results in a 67.82% higher power density than that of commercial Pt/C and negligible voltage decay during a long-term phase of a 33 cycle (2200 h) operation of a microbial fuel cell (MFC). The density functional theory (DFT) calculations suggest high activity for splitting the O-O bond of molecular oxygen on the surface of Fe3C.

Lead recovery and high silica glass powder synthesis from waste CRT funnel glasses through carbon thermal reduction enhanced glass phase separation process

In this study, a novel process for the removal of toxic lead from the CRT funnel glass and synchronous preparation of high silica glass powder was developed by a carbon-thermal reduction enhanced glass phase separation process. CRT funnel glass was remelted with B2O3 in reducing atmosphere. In the thermal process, a part of PbO contained in the funnel glass was reduced into metallic Pb and detached from the glass phase. The rest of PbO and other metal oxides (including Na2O, K2O, Al2O3, BaO and CaO) were mainly concentrated in the boric oxide phase. The metallic Pb phase and boric oxide phase were completely leached out by 5mol/L HNO3. The lead removal rate was 99.80% and high silica glass powder (SiO2 purity >95wt%) was obtained by setting the temperature, B2O3 added amount and holding time at 1000°C, 20% and 30mins, respectively. The prepared high silicate glass powders can be used as catalyst carrier, semipermeable membranes, adsorbents or be remelted into high silicate glass as an ideal substitute for quartz glass. Thus this study proposed an eco-friendly and economical process for recycling Pb-rich electronic glass waste.

Nanostructured Carbon/Antimony Composites as Anode Materials for Lithium-Ion Batteries with Long Life.

A series of nanostructured carbon/antimony composites have been successfully synthesized by a simple sol-gel, high-temperature carbon thermal reduction process. In the carbon/antimony composites, antimony nanoparticles are homogeneously dispersed in the pyrolyzed nanoporous carbon matrix. As an anode material for lithium-ion batteries, the C/Sb10 composite displays a high initial discharge capacity of 1214.6 mAh g(-1) and a reversible charge capacity of 595.5 mAh g(-1) with a corresponding coulombic efficiency of 49 % in the first cycle. In addition, it exhibits a high reversible discharge capacity of 466.2 mAh g(-1) at a current density of 100 mA g(-1) after 200 cycles and a high rate discharge capacity of 354.4 mAh g(-1) at a current density of 1000 mA g(-1) . The excellent cycling stability and rate discharge performance of the C/Sb10 composite could be due to the uniform dispersion of antimony nanoparticles in the porous carbon matrix, which can buffer the volume expansion and maintain the integrity of the electrode during the charge-discharge cycles.

Preparation of Zirconium Diboride Powder by Carbon Thermal Reduction Method

Zirconium diboride (ZrB2) powders with no impurities were prepared using zirconium oxide (ZrO2), boron carbide (B4C) and carbon black as raw material by carbon thermal reduction. The phase composition of ZrB2 powders was characterized by X-ray diffraction (XRD) and the micro-morphology was observed by scanning electron microscope (SEM). The effects of B4C content, calcination temperature and holding time were studied on the formation of ZrB2 powders. The results indicated that ZrB2 powders could be successfully synthesized while holding for 1.5 h at 1600 °C in Ar atmosphere. When the content of B4C was 17.7 wt% , there existed the crystal phase of ZrB2 only. The impurities could be easily led in with the increase of content of B4C. ZrB2 powders with the size from 1-5 μm could be obtained eventually and the particle size grew obviously with increase of the holding time.

Synthesis of SiC/SiO2 nanochains by carbonthermal reduction process and its optimization

SiC/SiO2 nanochains have been successfully synthesized by carbonthermal reduction process with economical Silicon sources and Carbon sources in crucible furnace, which can largely promote the industrialization of the SiC synthesis process. The important effect of Si/SiO2 ratio, catalysts, gas atmosphere, Carbon source, reduction temperature on growth and morphology of the nanochains has been analyzed to optimize the synthesizing conditions, and so on. The characterization and performance of nanochains have been studied by IR, XRD, SEM, and TEM. The results indicate that the evenly dispersed SiC/SiO2 nanochains with uniform surface morphology and better crystallization can be obtained by calcination at 1500°C in N2 with activated carbon as Carbon sources, Si/SiO2=4 and Fe2O3 as catalyst. The synthesis mechanism of the nanochains has also been studied by TG and TEM, which verifies that the growth process obeys the VLS mechanism. The SiC nanochains are grown out from the Si–Fe–O systems and SiO vapors play an important role in the development of the reduction process.

Flotation behaviour of Ti2CO from simulated carbon-thermal reduced titanium ores by oleic acid

Extraction of titanium from its ores by carbon-thermal reduction followed with hydrometallurgical treatment is a traditional process that is costly due to the huge consumption of acid for the complete dissolving of oxide slag. In this work, a new proposal was put forward to separate the slag by flotation process. The feasibility of selective separation of titanium oxycarbide (Ti2CO) by flotation process from the MOx (M = Ca, Mg, Si, Al) was investigated by using the simulated slag with single and mixed components. The flotation products were analysed by X-ray diffraction, chemical analysis, scanning electron microscopy and Fourier transform infrared spectrum. It was found that in the case of single Ti2CO or its mixing sample with MOx, the Ti2CO will float up effectively at the pH range of 1–5 to separate from the slag with oleic acid as the main floating reagent, and the results are beneficial to the design of a new process for titanium extraction from the complex ore at much lower cost.

Cycling stability of Li3V2 (PO4)3/C cathode in a broad electrochemical window

In this paper, Li3V2(PO4)3/C was synthesized using the carbon thermal reduction method. The electrochemical performance of Li3V2(PO4)3/C in a broad electrochemical window was studied. The fine structure of Li3V2(PO4)3/C after cycling in different charge and discharge ranges was investigated by X-ray powder diffraction (XRD) refinement, X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that the cycling stability of this material decreases with the increase of charge cut-off voltages. After cycling, the unit cell volume of Li3V2(PO4)3/C expanded irreversibly, in which the lengths of the Li(3)–O and V–O bonds became longer while those of Li(2)–O and Li(1)–O bonds became shorter. In the meantime, the amount of V5+ in the material increased and the carbon layer coated on the surface of the material was destroyed as the charge cut-off voltage was increased from 4.3 to 4.8V. It is therefore reasonable to infer that the changes in the crystal structure of Li3V2(PO4)3/C cause the poor cycling performance of Li3V2(PO4)3/C. This result provides a research idea for improving the cyclic performance of Li3V2(PO4)3/C in the future.

Synthesis and characterization of chromium carbide nanopowders processed by mechanical alloying assisted microwave heating route

Chromium carbide nanopowders were synthesized via mechanical alloying assisted microwave heating route using micron-sized chromic oxide (Cr2O3) and nano-sized carbon black as raw materials. The samples were characterized by X-ray diffractometry (XRD), thermogravimetric and differential scanning calorimetry (TG-DSC), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results show that the ultimate weight loss revealed by TG curve is 47.6wt%. The transformation temperature (1030°C) of the mixture after mechanical alloying is much lower than that of the traditional mixing method (1122°C). Chromium carbide nanopowders have been successfully synthesized at 1000°C for 1h. The powders show good dispersion and are mainly composed of spherical or near-spherical particles with a mean diameter of about 50nm. Compared with the traditional carbon thermal reduction method, the reaction temperature and time synthesized by mechanical alloying assisted microwave heating method can be reduced and shortened by 400°C and 3h, respectively.

Investigation of nano-silicon nitride ceramics containing an yttria sintering additive and the carbon thermal reduction reaction

Carbothermal reduction treatment (CRT) and spark plasma sintering (SPS) were employed to prepare nano-silicon nitride ceramics from an amorphous silicon nitride powder containing yttria (Y2O3) as an additive, and the effects of the Y2O3 contents and reducing agent additives on the ceramic densification and phase transformation behavior were examined. The results showed that specimens with 6wt% Y2O3 generated dense sintered bodies with sufficient liquid-phase contents. Specimens with 3wt% and 4wt% carbon black produced single-phase silicon nitride after the CRT and SPS processes. In addition, increasing the quantity of carbon black enabled the effective removal of the second phase of silicon oxynitride and allowed the grain size of the sintered body to be maintained at a nanoscale level. An excess of the carbon black additive resulted in insufficient liquid phase production, hindering the complete conversion of α-phase silicon nitride into β-phase silicon nitride, which in turn affects the density of the sintered bodies.