Carbon Thermal Reduction Process Research Articles

Synthesis and field emission characterization of La-doped SiC nanowires using graphite powder as carbon source

Lanthanum (La)-doped SiC nanowires (NMs) were synthesized via a carbon thermal reduction process using different graphite powders, while milled Si-SiO2 mixed powders were employed as the silicon source. The identification of the products as β-SiC were supported by Select-area electron diffraction (SAED) and X-ray diffraction (XRD) analysis. The field emission results demonstrated that the turn-on field reached a minimum value of approximately 2.3 V/μm when the graphite content ranged from 2.5 g–3 g. The product exhibited higher density at this stage, accompanied by an increase in nanowire diameter and a tendency toward straightness. The energy spectrum analysis revealed a significant increase in the lanthanum content within the nanowires, with the atomic percentage rising from 0.05 to 0.26–0.27. The synergistic effect of morphology and La improved the field emission performance of the product. The findings may offer valuable insights for enhancing the field emission performance of one-dimensional nanomaterials.

Controlled synthesis of tantalum-based solid solution and exploration of electrochemical properties as soluble anode for molten salt electrolysis

Metal oxycarbide solid solution possesses an extensive potential applications due to its remarkable physical features. In this paper, TaCxO1-x solid solution is successively and controllably synthesized by carbothermal reduction of Ta2O5. Based on the thermodynamic calculation, the possible reactions under different conditions in the carbothermal reduction process were analyzed, which provides theoretical guidance for controllable regulation and optimization of carbon thermal reduction process. The effects of carbon content, sintering temperature, and holding time on the synthesis of TaCxO1-x solid solution were investigated and the ideal process parameters for the synthesis of single-phase solid solution were identified. A single-phase solid solution with a carbon‑oxygen ratio close to 1:1 can be created as a soluble anode if the synthesis temperature is 1500 °C, the holding period is 6 h, and the molar ratio of C/Ta is 3.42. Moreover, the process feasibility of preparing metal tantalum by electrolysis of tantalum-based soluble anode is discussed, which provides a new method for metal tantalum preparation.

Kinetics of microwave carbothermal reduction of Sb2O3: Isothermal and non‐isothermal microwave thermogravimetric analysis

AbstractKinetics of antimony production via carbothermal reduction of Sb2O3–carbon powder–NaCl mixture using microwave and conventional heating was investigated to identify the dominant controlling mechanism. Results of conventional heating revealed the temperature range of conventional carbothermal reduction reaction is 500°C to 800°C, with the average activation energy of each stage being 81.97 kJ/mol (α = 0.1–0.5), 65.17 kJ/mol (α = 0.5–0.75), and 69.86 kJ/mol (α = 0.75–1.0), respectively. In the microwave field, the carbothermal reduction reaction of raw materials can be completed at 600°C to obtain antimony, and the weight loss data of the carbothermal reduction process were recorded for the first time. The above results show that the microwave field enhanced the interfacial chemical effect, accelerated the interfacial diffusion from the metal phase to the oxide phase, and reduced the activation energy of the carbon thermal reduction process to 6.85 kJ/mol. The growth index of antimony grain growth process is estimated to be 4.33, controlled by the surface diffusion. These data provide a reliable theoretical basis for studying the reduction reactions of minerals in microwave fields.

Preparation of Silicon Carbide Powder from Amorphous Silica and Investigation of Synthesis Mechanism

An innovative process for preparing silicon carbide (SiC) from acid leaching residue of ferronickel slag through a carbon–thermal reduction process was proposed in this study. The results indicate that the acid leaching residue is an ideal silicon source for SiC preparation according to its high amorphous silica content of 84.20% and fine particle size of d50 = 29.16 μm. Compared with carbon black, activated carbon, and graphite, coke is the more appropriate carbon source for SiC preparation. A micron-size SiC powder with grade of 88.90% and an average particle size (d50) of 44.68 μm can be obtained under the following conditions: the mass ratio of coke to leaching residue as 1.2:1, in an air atmosphere, reducing at 1600 °C for 3 h, following by decarbonizing at 700 °C for 4 h. The XRD, SEM and FTIR analyses show that the prepared powder is 3C-SiC and belongs to the β-SiC crystal type. Based on thermodynamic analysis and micromorphology observation, it can be concluded that with amorphous silica as the silicon source, the carbon–thermal synthesis of SiC powder follows both the solid–solid reaction mechanism and the gas–solid mechanism. The SiC created through solid–solid reaction is primarily nucleated in situ on amorphous SiO2, with a size close to that of the original acid-leaching slag, while the SiC generated according to the gas–solid mechanism mainly nucleates heterogeneously on the surface of carbon particles, resulting in a smaller particle size and mostly adhering to the surface of solid–solid nucleated SiC particles. This study provides a feasible method for the effective utilization of amorphous silica, which is also significant for the efficient consumption of the vast acid leaching residue.

In situ high-valued transformation of nonmetals in waste printed circuit boards into supercapacitor electrodes with excellent performance.

Nonmetals in waste printed circuit boards after metal separation containing brominated resin and fiberglass are considered hazardous and low-recoveryvalue e-waste. However, if these nonmetals are not treated or are improperly treated, they can cause serious environmental pollution. Therefore, there is an urgent and significant need to develop an efficient recycling process for these nonmetals. Based on the concept of high-valued recycling of waste, this study in situ utilized such nonmetals to prepare a porous supercapacitor electrode through a facile carbonization, activation, and carbon thermal reduction process. The results indicated that the activation was a key role in constructing a porous structure. The optimal parameters for activation were a temperature of 800 °C, mass ratio of KOH to pyrolytic residues of 2, and an activation time of 1 h. The electrode materials exhibited a surface area of 589 m2 g-1 and hierarchical porous structures. In addition, the supercapacitors exhibited a capacitance of 77.14 mF cm-2 (62.5 mF cm-2) at 0.5 mA cm-2 (100 mV s-1). Moreover, the supercapacitors had excellent temperature resistance and adaptability. The capacitance retention was 89.36% and 90% at -50 °C and 100 °C after 10 000 cycles, respectively. This study provides a high-valued recycling strategy to utilize the nonmetals in e-waste as energy materials.

Leaching Li from mixed cathode materials of spent lithium-ion batteries via carbon thermal reduction.

The use of a carbon thermal reduction roasting method to recover lithium resources from spent lithium-ion batteries (S-LIBs) provides an important opportunity for recycling S-LIBs. The preferential extraction of Li via reduction roasting has been widely studied; however, the extraction of Li from mixed cathode materials has been rarely reported. Herein, we propose a method based on carbon thermal reduction to preferentially extract Li from mixed cathode materials. It was confirmed that there are differences in carbon thermal reduction products at 700 °C-850 °C by the thermodynamic analysis of the carbon thermal reduction process. At the same time, the effects of factors such as roasting temperature, roasting time, and material ratio on Li leaching efficiency were investigated. The Li recovery rate reached 98.86% under the optimal conditions of holding at 750 °C for 4 h with a molar ratio of mixed cathode materials to graphite of 1 : 0.25. Recovered Li2CO3 can be directly used as a lithium source for the regeneration of cathode materials. This study will provide new opportunities for the efficient recycling of spent lithium-ion batteries (S-LIB) mixtures.

Microbial mechanism underlying the effect of biochar supported nano zero-valent iron on the anaerobic digestion of food waste

Anaerobic digestion (AD) is one of the effective methods to treat the food waste (FW). In this study, biochar supported nano zero-valent iron (BC-nZVI) was prepared by carbon thermal reduction process. The effects of concentrations (1, 2 and 3 g/L) of BC-nZVI on methane production, microorganisms and metabolic mechanism during the AD of food waste were investigated. The results showed that 1 g/L of BC-nZVI was the best concentration for methane production. The cumulative methane production was enhanced by 29.54% at BC-nZVI 1 g/L. Microbial community analysis showed that BC-nZVI mainly increased the abundances of hydrolytic bacteria (including Bacteroidetes_vadinHA17, Proteiniphilum, Syntrophobacter) and acetoclast (Methanosaeta). Further exploration of the mechanism using PICRUSt2 version based on 16 S rRNA gene sequence analysis indicated that the addition of BC-nZVI promoted the abundances of enzymes related to methane metabolism such as the phosphate acetyltransferase and the methyl-coenzyme M reductase alpha subunit, which made the AD system stable.

Systematic thermodynamic and experimental studies for recovering indium and tin from indium tin oxide waste target with hydrogen

Resource utilization of waste indium tin oxide (ITO) can not only avoid the hazards of electronic waste, but also realize the recycling of dispersed metal indium (In). However, the current carbon thermal reduction process has the problems of high energy consumption and large carbon emissions. In this study, the feasibility and specific advantages of hydrogen reduction of waste ITO were explored by using high energy density and non-polluting H2 as reducing agent. The reduction process was thermodynamically analyzed by isothermal equation and molecular interaction volume model (MIVM), and the thermodynamic analysis results were verified by systematic experimental study. Experimental results showed that the reduction ratio of waste ITO can reach 99.43% under optimal conditions of 1173 K, 120 min, and 0.3 mol/L H2 flow rate, which indicated that the reduction process is feasible and efficient. Compared with vacuum carbothermal reduction process, hydrogen reduction process can reduce carbon emissions from the source, and theoretical energy consumption can be reduced by 70.12%. This work proposes a new method for recycling waste ITO that can reduce energy consumption and carbon emissions, providing further opportunities for the recycling of indium resources and the green economy of the electronics industry.

Highly efficient separation of titanium minerals from a modified bauxite residue through direct reduction: A comparison study

Bauxite residue, which is a solid waste generated during the production of alumina, contains significant amounts of iron (Fe) and titanium (Ti) resources. The large-scale utilization of bauxite residue has become an urgent concern from both an environmental and resource perspective. In this study, a calculation of phase diagram (Calphad) was conducted to analyze the changes in mineral phases during the direct reduction process of both the current and reductive Bayer bauxite residue. Additionally, a comparison experiment was performed to investigate the enrichment and separation characteristics of iron and titanium minerals. The results indicated that during the carbon thermal reduction process, titanium existed as CaTiO3 and Na-Al-Si-Ti molten phase slag in the current and reductive Bayer bauxite residue, respectively. Furthermore, NaFeO2 was observed in the latter slag phase, which facilitated the migration and reduction of iron-containing minerals. The reductive Bayer bauxite residue was carbon thermal reduced for 1 h at a temperature of 1200 °C, with the addition of 7.5% Na2CO3. Following grinding and separation under a magnetic field strength of 0.08 T, the iron grade of the concentrate, iron recovery, and TiO2 grade in the tailing increased to 95.30%, 98.40%, and 50.50%, respectively. This was in comparison to the bauxite residue from current Bayer digestion, which showed values of 78.90%, 87.18%, and 14.87% under the same conditions. The findings of this work contribute to the potential utilization of iron and titanium present in bauxite residue from a modified Bayer digestion process.

Structure control and growth mechanism of beaded SiC nanowires with microwave absorption properties

Large-scale SiC nanowires (SiCnws) were successfully synthesized on graphite substrates by a catalyst-free carbon thermal reduction process using low-cost silicone oil, silica powder, and activated carbon. The control of different nanowire structures was achieved by parameter regulation. An in-depth discussion of their growth mechanisms is provided. Beaded SiCnws consisting of amorphous SiO2 beads and SiC strings were synthesized at 1400 °C. The formation of beads is mainly due to the supersaturation of SiO vapor, which leads to the reaction of excess SiO to form SiO2 at the defects of the SiCnws. The dielectric parameters of beaded SiCnws were analyzed, and it was found that the beaded SiCnws have a maximum effective absorption width of 1.84 GHz and a maximum reflection loss of −16.03 dB. The exploration of the growth mechanism of beaded SiCnws in this study provides a useful reference for the preparation of one-dimensional nanomaterials.

One-step preparation of Fe/N co-doped porous biochar for chromium(VI) and bisphenol a decontamination in water: Insights to co-activation and adsorption mechanisms

Herein, magnetic nitrogen doped porous biochar (Fe/N-PBC) was prepared by mixing KHCO3, K2FeO4 and CO(NH2)2 through one-step pyrolysis, and was employed for adsorbing Cr(VI) and BPA in water. The whole co-activated process was accompanied with pore-forming, carbon thermal reduction and element doping. Specifically, the developed microporous structures and high surface area of Fe/N-PBC (1093.68 m2/g) were achieved under synergistic activation of KHCO3 and K2FeO4. Meanwhile, carbon thermal reduction process successfully converted K2FeO4 to Fe0 with introduction of heterocyclic-N (pyrrolic N and pyridinic N) structures by CO(NH2)2 doping. Fe/N-PBC exhibited outstanding uptake for Cr(VI) (340.96 mg/g) and BPA (355.14 mg/g), and possessed favorable regeneration properties after three cycles. Notably, the high-performance Cr(VI) removal was associated to reduction, electrostatic interaction, complexation, pore filling and ion exchange, while pore filling, hydrogen-bonding interaction and π-π stacking were responsible for BPA binding. This work presents reasonable design of Fe/N-carbon materials for Cr(VI)/BPA polluted water remediation.

Reduction Behavior and Direct Reduction Kinetics of Red Mud-Biomass Composite Pellets

A large amount of red mud is discharged in the aluminum oxide production process, which contains a variety of valuable metals and is considered as a secondary resource. In order to reveal the mechanism of red mud carbon thermal reduction process, isothermal reduction experiments on carbon-bearing pellets of red mud were investigated with biomass carbon as a reducing agent. In this study, the reduction temperatures were conducted using a microwave stove in the temperature range from 850 to 1250 ℃, and the C/O molar ratio was 1.1. The results show that the reduction process of red mud is governed by a carbon gasification reaction, and the apparent activation energy is 88.44 kJ/mol. The optimum reduction process conditions were established to be 1150 ℃ for 13 min.

Synthesis and in situ growth mechanism of SiO2@SiC core–shell nanocomposite

With the aim at modifying SiC and simplifying the manufacturing process, many kinds of SiC matrix composites have been designed. In this work, the SiO2@SiC core–shell composites were synthesized via carbon thermal reduction process. The precursors were prepared from polyvinylpyrrolidone (PVP) and SiO2 spheres with different particle sizes. The viscosity of PVP solution plays a significant role in the formation of core–shell structure. After calcining at 1350 °C, the SiC layer was in situ formed on amorphous SiO2. An extensible liquid–solid–vapor growth mechanism is proposed basing on the characterization results as well as the possible reactions among the solid phases, liquid phases with a certain viscosity and intermediate gas phases. Moreover, this kind of nanocomposites was believed to have a great potential in the electromagnetic wave absorbing material and photocatalytic reactor application.

Synthesis and microwave absorbing properties of SiC nanowires

SiC nanowires with high microwave absorbing performance have been prepared by one step carbon thermal reduction process with economical activated carbon, silicon and silicon dioxide as raw materials. The characterization and performance of nanowires have been studied by IR, XRD, SEM and VNA analysis. The results indicate that the obtained SiC nanowires are samples with diameter about 40 nm and the length up to several micrometers. The large length-to-diameter ratio heightened the microwave absorbing properties. Electromagnetic parameters were tested with 50% of the titled materials and 50% of paraffin wax composites using HP8722ES vector network analyzer. In addition, the reflection loss property has been obtained on the basis of the transmission line theory. The results indicate that the SiC nanomaterials exhibit a maximum reflection loss of − 18.02 dB with the bandwidth below − 10dB over 1.7 GHz, and two sharp absorbing peaks appear at 4 mm thickness.

Preparation of nanocrystalline MoSi2 with enhanced lithium storage by sol–gel and carbonthermal reduction method

Herein nanocrystalline MoSi2 with enhanced lithium storage was successfully synthesized via a sol-gel and carbonthermal reduction method. Reduction of the gel mixture of Mo precursor and Si precursor by carbon at a desired temperature resulted in the formation of MoSi2 nanoparticles. The gel mixture was obtained through the hydrolysis of TEOS and ammonium molybdate and the polymerization of hydrolysis products of TEOS. The reducing agent carbon was produced via decarburition of sucrose's hydrolysis products, which have been wrapped in the gel during its formation process. Addition of HCl to the mixed solution controlled the hydrolysis and polymerization rate, and enabled the formation of a gel mixture with homogeneously distributed hydrolysis products of ammonium molybdate, TEOS and sucrose. This achievement likely generates a novel route to synthesize non-oxide compounds such as silicide, carbide through the sol–gel and carbonthermal reduction process. In addition, the as-received MoSi2 nanoparticles showed considerable activities in the reversible lithiation and delithiation process. When using as an anode for Li-ion batteries, MoSi2 nanoparticles delivered a specific capacity of 325 mAh g−1 at C/12 and showed an increasing capacity with cycling.

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.

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.

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.

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.

Novel synergistic 0.9LiMn0.9Fe0.1PO4·0.1Na3V2(PO4)2F3/C nano-hybrid cathode with enhanced electrochemical performance for lithium-ion batteries

The nanostructured 0.9LiMn0.9Fe0.1PO4·0.1Na3V2(PO4)2F3/C composites are successfully synthesized by a facile solvothermal method followed by mechanical activation and subsequent carbonthermal reduction process. Behaviours of bi-phase co-existence and element mutual-substitution have been investigated by XRD, TEM/EDX and FTIR. The result shows that the composites have dual phase boundaries including the semi-coherent phase interface and incoherent phase interface, as well as the advantage of Na3V2(PO4)2F3 acting as ionic conductor. Due to the multifunctional phase and (Mn,Fe)-V mutual doping as well as nano-carbon continual conducting network, enhanced Li+ migration and charge transfer of nano-hybrid is obtained. Compared with pristine one, the 0.9LiMn0.9Fe0.1PO4·0.1Na3V2(PO4)2F3/C composites exhibit high rate capability and cycling ability, showing 125.5, 106.4 mAh g−1 at 1.0 C, 3.0 C at room temperature, respectively, with high capacity retention up to 93.9% after 600th at 2 C.