Subsequent Carbothermal Reduction Research Articles

Eggplant-derived SiC aerogels with high-performance electromagnetic wave absorption and thermal insulation properties

Lightweight and strong silicon carbide (SiC) aerogels with a three-dimensional architecture and in situ grown SiC nanowires are obtained from natural eggplants by direct graphitization and subsequent carbothermal reduction. Effective synergism is achieved by decorating the SiC frameworks with one-dimensional SiC nanowires, which impart the aerogels with excellent electromagnetic (EM) wave absorption, thermal insulation, and mechanical properties. Highly porous, interconnected SiC networks facilitate the multiple reflection–absorption effects of infiltrated EM waves and extend the routes of heat transmission in the samples. SiC nanowires, which consist of numerous stacking faults and heterojunctions, play key roles in dissipating EM energy, obstructing heat transfer, and reinforcing the SiC skeleton. Given their 97.6% porosity, the SiC aerogels show a minimum reflection of −43 dB and effective bandwidth of 4 GHz at 2 mm thickness. The in situ grown SiC nanowires substantially increase the compressive stress of the SiC aerogels to 2.12 MPa, which is nearly 50-fold than that of carbon aerogels derived from eggplants. Moreover, the SiC aerogels show a very low thermal conductivity of 0.035 W/m·K. These results indicate that the developed SiC aerogels are outstanding materials with potential applications in high-performance EM absorption and thermal insulation in the aviation and aerospace fields.

Graphene-supported cubic hollow carbon shell-coated germanium particles as high-performance anode for lithium-ion batteries

Germanium-based materials are considered to be an alternative material for high energy density lithium-ion battery anodes due to their superior theoretical capacity. However, the severe volume expansion during the lithium insertion and the easily agglomerated tendency of Ge nanoparticles become the key obstacles to the stable cycle and capacity retention of Ge anodes. Herein, we designed a double-layered protective structure in which the cubic hollow [email protected] hybrids are uniformly dispersed on reduced graphene oxide sheets ([email protected]) through conventional dopamine-coated precursor and subsequent carbothermal reduction processes. In the synthesized [email protected] hybrids, the large-area rGO sheets cooperate with the amorphous carbon layer to accommodate and buffer the volume expansion of Ge particles, and to ensure that the Ge nanoparticles are in a separated state to the utmost extent. The [email protected] electrode which is employed in lithium-ion battery owns the reversible capacities of 1183 mAh·g−1 at the specific current of 100 mA g−1 and 710 mAh·g−1 at 1 A g−1 for 200 cycles. In addition, it exhibited good cycle stability, rate reversibility and electronic conductivity, and is a potential anode material with high performance and long-cycle capability.

Facile fabrication of sheet-on-sheet hierarchical nanostructured Sb/C composite with boosting sodium storage

Rational design and facile synthesis of two-dimensional (2D) materials still remain a great challenge. Herein, a facile process was proposed to construct 2D porous hybrid nanosheets, with ultrathin antimony nanoplates (with a thickness of ca. 0.5 nm) being anchored on acetone-derived graphene-like carbon porous nanosheets, by an aldol reaction and subsequent carbothermal reduction method using acetone and antimony acetate as the starting raw materials. The novel structural and compositional characteristics afford the 2D porous hybrid nanosheets with impressive boosting electrochemical sodium storage properties in terms of excellent cycling stability, high reversible specific capacity, and superior rate performance. The present work would provide significant value for the development of both synthetic methodology of 2D materials and their application as electrode active materials for energy storage and conversion.

Co nanoparticles supported on cotton-based carbon fibers: A novel broadband microwave absorbent

Aiming at the disadvantages of high cost, complex processes, and low yield of carbon-based microwave absorbing materials. In this study, Co/C fibers were successfully prepared by using low-cost cotton as carbon source. The synthetic route was a flexible two-step approach consisting of immersion and subsequent carbothermal reduction in N2 atmosphere. By means of controlling the Co(NO3)2·6H2O concentration and calcination temperature, Co nanoparticles with different loading amount and particle size were uniformly dispersed along the cotton-based carbon fibers. The Co loading amount, calcination temperature, and filling rate on electromagnetic parameters and microwave absorption performance were systematically studied. Among the Co/C fibers obtained at different Co(NO3)2·6H2O concentration and calcination temperatures, the Co/C fibers synthesized at 600 °C with 0.5 M Co(NO3)2·6H2O exhibited the best microwave absorption performance. The reflection loss (RL) values less than −10 dB were obtained in the frequency range of 11.3–18 GHz, which covered the entire Ku-band (from 12 to 18 GHz). Such excellent microwave absorption performance was attributed to the synergistic effect of dielectric loss, magnetic loss, and good impedance matching. Owing to the characteristics of cost-effective synthetic strategy, low density, and good microwave absorption, the Co/C fibers are highly promising as economic and broadband microwave absorbent.

Synthesis and characterization of TiC nanopowders via sol-gel and subsequent carbothermal reduction process

TiC nanocrystalline powders were synthesized by in-situ carbothermic reduction of Ti-O-C precursor under vacuum atmosphere. And the Ti-O-C precursor was formed by sol-gel method from titanium butyrate (TBOT) and sucrose. To obtain stable sol, TBOT was directly added into mixed solution which contains water, sucrose, acetic acid (AcOH) and acetylacetone (ACAC). This procedure is more convenient and economical because it avoids the use of alcohol which is used as solvent in most reports of alkoxide hydrolysis sol-gel method. TG-DSC, XRD, FTIR and SEM/TEM were employed to analyze and characterize the product during the entire process. The phase composition and crystalline structure parameters of powders with different C/Ti molar ratio were investigated by Rietveld refinement method, and elemental quantitative analysis of the samples were performed. Furthermore, the optimal parameters of carbothermal reduction were obtained and the grain growth mechanism was demonstrated. The results show that TiC nanocrystalline powders (C/Ti molar ratio is 3.5 in the precursor) were synthesized at 1300 °C for 2 h, which have near standard lattice parameter, well crystallinity and fine average grain size (~37.4 nm).

Synthesis and characterization of nano-crystalized HfC based on an aqueous solution-derived precursor.

Nano-crystalized HfC was successfully synthesized based on an aqueous solution-derived precursor using hafnium tetrachloride and sucrose as raw materials. The precursor can be converted to pure phase HfC after pyrolysis at ∼600 °C and subsequent carbothermal reduction reaction at ∼1600 °C, with a ceramic yield of around 46.3%. Reaction mechanisms of the synthesis process are revealed based on FT-IR, TG-DSC, TEM analysis and thermodynamic calculations, etc. The obtained HfC nanoparticles possess an equiaxial shape with an average particle size of ∼73 nm. Oxygen content of the as-synthesized HfC powders is as low as 0.64 wt%, which exists in the form of an amorphous Hf–O–C thin layer covering the surface of the HfC particles. This feasible and promising method for HfC particle synthesis is believed to be suitable for the fabrication of continuous fibers reinforced HfC ceramic matrix composites.

Porous Zr2SC-carbon composite microspheres: Possible radiation tolerant sorbents and transmutation hosts for technetium-99

The preparation, characteristics and adsorption properties of novel porous carbon-ceramic composite microspheres are presented. The composites were synthesised by a simple ion exchange process involving the cationic Zr tetramer and commonly-available macroporous sulphonated polystyrene-divinylbenzene cation exchange resins, with subsequent carbothermal reduction at 1350 °C. The materials were extensively characterised with respect to composition, chemical structure and porosity. Carbothermal reduction of the Zr-loaded templates resulted in formation of crystallites of the MAX phase zirconium sulphide carbide (Zr2SC) embedded within a highly microporous carbon framework with a macroporous secondary structure inherited from the resin template. Despite the high BET surface areas of the Zr2SC-carbon composite microspheres (in some cases, greater than 600 m2 g−1), they are extremely mechanically robust. The microspheres displayed high adsorption selectivity for oxoanions relative to cationic solution species, including perrhenate (ReO4−), a pertechnetate (TcO4−) surrogate. Accumulation of ReO4− on the Zr2SC particles was unequivocally demonstrated by elemental mapping. Such materials are potential candidates as combined 99Tc sorbents and reusable transmutation hosts.

Fe–Fe3C/C Fibers as a Highly Efficient Microwave Absorbent

As electromagnetic pollution is becoming more and more serious, novel composite microwave absorbents are gaining much attention. In this work, Fe–Fe3C/C fibers were successfully synthesized by using low-cost cotton as carbon source. The synthetic route was an easy and flexible two-step approach consisting of immersion and subsequent carbothermal reduction in N2 atmosphere. The results showed that the Fe–Fe3C nanoparticles were uniformly loaded on the cotton-based carbon fibers. Resulting from the synergistic effect of magnetic loss from Fe–Fe3C nanoparticles and dielectric loss from cotton-based carbon fibers, a wide region of microwave absorption was achieved. When the thickness is 1.5 mm, the minimum reflection loss (RL) is −28.3 dB, and the effective bandwidth of RL less than −10 dB could reach up to 4.2 GHz. Owing to the characteristics of cost-effective synthetic route, low density, low filling rate and good microwave absorption with thin thickness, the Fe–Fe3C/C fibers could be used as a practical microwave absorbent.

Mechanical properties of (TixW1−x)C–Co cermet prepared by carbothermal reduction of high energy ball milled TiO2–WO3–C

A series of solid–solution carbides, (TixW1−x)C (x=0.9, 0.8, 0.7, 0.6), was prepared by the high-energy milling of TiO2–WO3–C mixtures via subsequent carbothermal reduction. With high-energy milling, only the size reduction of the constituent powders was apparent without any chemical reaction. The milled mixture powder was transformed to a single–phase (TixW1−x)C solid solution by heat treatment in a vacuum at 1200°C. (TixW1−x)C–Co cermets were consolidated by isothermal sintering at 1300, 1400, and 1500°C. The powders were fully densified by liquid-phase sintering at 1500°C because the Co melted at 1430°C. The mechanical properties of the (TixW1−x)C–Co cermet (Hv: ~24GPa) were significantly better than those of the conventional WC–Co (Hv: ~13GPa) or TiC–Co cermets (Hv: ~16GPa). The use of a solid–solution carbide instead of conventional WC almost doubled its hardness values without a loss of toughness. It is indicated that the improved hardness of the (TixW1−x)C–Co cermet originates from the high hardness of (TixW1−x)C, and the solid–solution carbide would be a valuable substitute for conventional carbide cermets.

Creation of Titanium and Zirconium Carbide Fibers with the Forcespinning Technique

The forcespinning (FS) technique is used here to produce titanium dioxide and carbon composite fibers, as well as zirconium dioxide and carbon composite fibers. Subsequent carbothermal reduction of these fibers facilitated the creation of titanium carbide and zirconium carbide fibers respectably. The role of FS parameters such as the revolutions per minute (RPM) and the collector distance employed is examined. Sol‐gel chemistry is used to produce the solutions for the initial FS, and the control of sol‐gel chemistry and its effect on the end fiber products is also investigated. The effect of these variables is examined using X‐ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The results confirm that titanium and zirconium carbide fibers can be produced using the sol‐gel and FS techniques.

Fe-, Co-, and Ni-Loaded Porous Activated Carbon Balls as Lightweight Microwave Absorbents.

Porous activated carbon ball (PACB) composites impregnated with iron, cobalt, nickel and/or their oxides were synthesized through a wet chemistry method involving PACBs as the carrier to load Fe(3+), Co(2+), and Ni(2+) ions and a subsequent carbothermal reduction at different annealing temperatures. The results show that the pyrolysis products of nitrates and/or the products from the carbothermal reduction are embedded in the pores of the PACBs, with different distributions, resulting in different crystalline phases. The as-prepared PACB composites possessed high specific surface areas of 791.2-901.5 m(2) g(-1) and low densities of 1.1-1.3 g cm(-3). Minimum reflection loss (RL) values of -50.1, -20.6, and -20.4 dB were achieved for Fe-PACB (annealed at 500 °C), Co-PACB (annealed at 800 °C), and Ni-PACB (annealed at 800 °C) composites, respectively. Moreover, the influence of the amount of the magnetic components in the PACB composites on the microwave-absorbing performances was investigated, further confirming that the dielectric loss was the primary contributor to microwave absorption.

Hollow reduced graphene oxide microspheres as a high-performance anode material for Li-ion batteries

Hollow reduced graphene oxide (RGO) microspheres are successfully synthesized in large quantities through spray-drying suspension of graphene oxide (GO) nanosheets and subsequent carbothermal reduction. With this new procedure, blighted-microspherical GO precursor is synthesized through the process of spray drying, afterwards the GO precursor is subsequently calcined at 800°C for 5h to obtain hollow RGO microspheres. A series of analyses, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR) are performed to characterize the structure and morphology of intermediates and as-obtained product. The as-obtained hollow RGO microspheres provide a high specific surface area (175.5 m2g−1) and excellent electronic conductivity (6.3 S cm−1), and facilitated high electrochemical performance as anode material for Li-ion batteries (LIBs). Compared with the RGO nanosheets, the as-obtained hollow RGO microspheres exhibit superior specific capacity and outstanding cyclability. In addition, this spray drying and carbothermal reduction (SDCTR) method provided a facile route to prepare hollow RGO microspheres in large quantities.

Evaluation of Palladium-based electrocatalyst for oxygen reduction and hydrogen oxidation in intermediate temperature polymer electrolyte fuel cells

A carbon-supported Palladium electrocatalyst was investigated for oxygen reduction and hydrogen oxidation in a polymer electrolyte fuel cell operating at intermediate temperatures (80–110 °C) and with low relative humidity (33%). A 30% Pd/C was synthesized by a colloidal method and subsequent carbothermal reduction. A mean particle size of 4.0 nm and a homogeneous dispersion of Pd particles on the support were obtained. The performance of the Pd catalyst was compared to those obtained with a 50% Pt/C catalyst and a 50% Pt3Co1/C as anode and cathode, respectively. The Pd/C catalyst showed low overpotential for hydrogen oxidation whereas its performance as cathode was significantly lower than the benchmark Pt3Co1 catalyst. The main limiting effects for the Pd-based electrocatalyst appeared to be associated to a larger mean particle size compared to the benchmark Pt catalysts and to the modification of the carbon support during the synthesis procedure. These effects led to a stronger activation control, a slight increase of the series resistance and some diffusion constraints.

(Ti,W)C–Ni cermet prepared by high-energy ball milling and subsequent carbothermal reduction of TiO2–Ti–WO3–C mixture

A single-phase (Ti,W)C solid solution was prepared by high-energy ball milling of TiO2–Ti–WO3–C powder mixtures with various TiO2/Ti ratios and subsequent carbothermal reduction. Thermodynamic calculations suggest that the reaction pathways would follow the sequences WO3→WC, TiO2→Ti2O3, Ti(CO)→TiC, Ti2O3→TiC, and TiC+WC→(Ti,W)C. The reaction pathways were substantiated by measuring CO gas evolution and heat flow using QMS and DSC, respectively. The 80(Ti,W)C–20Ni powders were sintered in vacuum at 1510°C and their mechanical properties were evaluated. The toughness values of (Ti,W)C–Ni cermet were significantly higher than those of TiC–Ni cermet owing to the alloying effect of W in TiC. The composition of raw powder mixture also affected the mechanical properties of (Ti,W)C–Ni after sintering. The toughness was improved when TiO2/Ti ratio was 2 in the raw powder mixture than when pure Ti or TiO2 was used. The enhanced toughness is attributed to larger (Ti,W)C grain size.

Carbothermal Synthesis of Aerosol-Based Adsorptive-Reactive Iron–Carbon Particles for the Remediation of Chlorinated Hydrocarbons

Spherical iron–carbon nanocomposites were synthesized through a facile aerosol-based process and a subsequent carbothermal reduction. The distribution and immobilization of iron particles throughou...

Chemical vapor deposition of C on SiO 2 and subsequent carbothermal reduction for the synthesis of nanocrystalline SiC particles/whiskers

This study investigates chemical vapor deposition of C from CH 4 on particulate SiO 2 and subsequent carbothermal conversion of the resultant composite particles to SiC powders. Mass measurements, HR-TEM, SEM and XRD were used to characterize the products at various stages of the processes. It was found that oxide particles gained mass rapidly at 1300 K under CH 4 atmosphere owing to enhanced C uptake. Pyrolytic carbon layers 5–8 nm thick were deposited on SiO 2 particles. The coated powders with high C loadings (40–42.6 wt.% C) were converted to SiC under Ar flow in a temperature range of 1700–1800 K. Almost pure SiC powders containing a mixture of particles and whiskers of ~ 100 nm were synthesized at 1750 K for 45 min and at 1800 K for 30 min using the starting powder with 40 wt.% C. Whisker diameter increased with the C content of the coated powder. It was proposed that SiC whisker was grown by a vapor–solid mechanism. Equilibrium thermodynamic analysis by the method of minimization of Gibbs’ free energy predicted the reaction pathways to SiC and to the product species in the Si–O–C–Ar system. This study demonstrated that either C shell-SiO 2 core powders or SiC powders could be synthesized rapidly in the same reactor.

Chemical vapor deposition of carbon on particulate TiO2 from CH4 and subsequent carbothermal reduction for the synthesis of nanocrystalline TiC powders

The present study aims to investigate chemical vapor deposition of carbon from CH4 on TiO2 particles and to establish optimal conditions for the synthesis of nanocrystalline TiC powders. Mass measurements, XRD, HR-TEM and SEM were used to characterize the products at various stages of the reactions. Oxide particles gained mass rapidly at 1300K under CH4 atmosphere and were coated with thin pyrolytic carbon layers of 10–20nm. XRD analysis showed that the coated powders consisted of C, TiO2 and titanium sub-oxides. The powders containing ∼33±2wt% carbon were used for the carbothermal reduction of TiO2 to TiC at 1600–1800K under Ar flow. Lattice constant and mass loss of the samples increased to the levels of TiC with temperature and time. Nearly pure TiC powders with a mean particle size of ∼125nm were synthesized at 1750–1800K within 30min.

Characterization of nanocrystalline porous SiC powder by electrospinning and carbothermal reduction

Nanocrystalline porous silicon carbide (SiC) powder was prepared from various ratios with SiO 2 as silicon source and carbon black as carbon source by electrospinning method and subsequent carbothermal reduction. Their microstructure, thermal stability and porosity of prepared porous silicon carbide (SiC) powder were evaluated as function of Si to C ratios in precursor. 3C/Si could not often maintain the spherical form against oxygen–carbon reaction during calcination owing to relatively low carbon content. On the other hand, the uniformed spherical forms were presented with deep wrinkles in the other prepared samples. They were believed that the wrinkled surfaces were formed by vaporization of carbonaceous gas made from carbon and oxygen. When the carbon ratio to silicon (C/Si) was 5, the β-SiC was observed without remained silica and silicon metal. Further increase in the carbon content in the precursor led to sharp and high intensity of SiC peak. Initial decomposition temperature of prepared sample was increased with decreasing C/Si ratio. We confirmed that whereas 3C/Si and 4C/Si had higher big macropore, 5C/Si and 6C/Si had much large pore volume in the range of mesopore diameter (2–50 nm) and small macropore (50–100 nm).

Synthesis of nanostructured silicon carbide spheres from mesoporous C–SiO2nanocomposites

Nanostructured porous silicon carbide hollow spheres have been synthesized by phase separation in mesoporous silica-carbon nanocomposites at high temperatures and subsequent carbothermal reduction and crystallization.

Synthesis of nano Ti(C,N) powder by mechanical activation and subsequent carbothermal reduction–nitridation reaction

Abstract Nano Ti(C,N) powder with average particle size of below 100 nm was synthesized from nano anatase/carbon black mixtures employing mechanical milling activation and subsequent carbothermal reduction–nitridation (CRN) reaction. The activated and heat-treated powders have been characterized by X-ray diffraction (XRD), reaction dynamics of activated powders has been studied by thermogravimetry-differential scanning calorimetry (TGA-DSC), and Ti(C,N) products were evaluated by transmission electron microscope (TEM). The results show that CRN reaction of anatase was enhanced by pre-milling the starting powders. Thus, onset formation temperature and holding time of Ti(C,N) decreased from 1300 °C to 1150 °C and from 4 h to 2 h, respectively. However, mechanical activation did not alter phase evolution sequences of TiO2 CRN reaction.