Carbon Thermal Reduction Reaction Research Articles

Effects of SiO2-coated CNTs on the directional formation of SiC whiskers and improvement in the ablative resistance of polymer-matrix composites

As the development of hypersonic aerospace technology progresses, greater challenges are presented for solid rocket motors (SRMs) thermal protection, and the ablation performance of insulation materials needs to be further improved. Carbon nanotubes (CNTs) as a new type of reinforcing nano-filler, readily react with the oxidative components in the working gas during SRMs operation, limiting their excellent performance. In this study, we propose to coat the commonly used reinforcing filler, SiO2, on the surface of CNTs to suppress their susceptibility to oxidation and investigate the effects of adding CNTs, SiO2, and CNTs@SiO2 to the matrix on material properties. The results show that the addition of CNTs@SiO2 significantly improves the ablation resistance of the insulation material, with the linear ablation rate of M-@SiO2-2 being 56 % lower than that of M-SiO2-2. Based on the analysis of the material's antioxidation performance and the strength of the resulting char layer after ablation, the reasons for the improvement of ablation performance are discussed. By conducting high-temperature tube furnace tests, the composition and structure of the char layer at different temperatures are studied, and it is found that CNTs in the CNTs@SiO2 formulation can directly provide the carbon source required for the carbon thermal reduction reaction, promoting the directional growth of SiC whiskers. Based on these findings, an ablation mechanism is proposed.

Carbon thermal reduction of waste ternary cathode materials and wet magnetic separation based on Ni/MnO nanocomposite particles

The widespread use of lithium-ion batteries and the increase in the number of new energy electric vehicles have brought more waste batteries to be recycled. In this paper, a new combined process for in-situ recycling of wasted ternary lithium batteries using graphite for carbon thermal reduction with the cathode material under nitrogen atmosphere, after which the nanocomposite particles formed by the reduction products were separated and recovered by wet magnetic separation, has been proposed. The carbon thermal reduction products were Li2CO3, Ni, Co and MnO, respectively, and Ni and Co could form nanocomposite particles with MnO in the thermal reduction process. The reaction mechanism of the carbon thermal reduction reaction of anode materials and the effects of carbon thermal reduction temperature, wet magnetic separation time and solid-to-liquid ratio on the recovery rate were investigated. The recovery rate of Li, Ni, Co and Mn were 95.57 %, 96.44 %, 94.88 % and 94.98 %, respectively, under the optimum condition of reaction temperature of 650 °C, wet magnetic separation time of 75 min and solid-liquid ratio of 15 g/L, respectively.

Optimization of response surface methodology (RSM) for defluorination of spent carbon cathode (SCC) in fire-roasting aluminum electrolysis

• Response surface methodology can effectively remove fluoride from SCC. • Determine the optimal treatment process in a conventional muffle furnace. • When the roasting temperature is 1499 °C, the treatment time is 3.33 h, and the average particle size is 10 mm, the fluorine removal rate reaches 88%. Spent carbon cathode (SCC) is a typical toxic and hazardous solid waste generated in aluminum electrolysis. The harmless treatment of SCC is extremely important for the aluminum electrolysis industry. Herein, the response surface methodology was used to investigate the best process for removing fluoride from the SCC of aluminum electrolysis using the roasting method. A Box–Behnken design (BBD) was used to investigate the effects of three independent variables, namely, particle size, roasting temperature, and treatment time, on the fluorine removal rate of the SCC. Seventeen groups of experiments were conducted according to these three factors. Statistical analysis system software and a second-order polynomial model were used to analyze the data and predict the response. The results showed that the particle size, roasting temperature, and treatment time significantly influenced fluoride removal in the SCC. Under optimum process conditions, the system predicted a fluoride removal rate of 87% for the SCC. Validation experiments were conducted on the fluoride removal rate of the SCC under optimum process conditions. The results showed that the actual value reached 88%. The X-ray diffraction analysis before and after calcination showed that a small amount of SiO 2 was converted into SiC through a carbon thermal reduction reaction after calcination. This paper provides a theoretical basis for the best process of roasting SCC to remove fluoride. It also has a certain guiding significance for other solid waste treatments.

Removal of Mercury from Simulated Natural Gas by SO2 Activated Petroleum Coke

A preparation method based on the carbon-thermal reduction reaction was proposed to make petroleum coke-based mercury adsorbent. The effects of activation agent flow rate, time and inlet mercury concentration on mercury removal were investigated. Mercury adsorption experiments were carried out on a fixed-bed reactor system under simulated natural gas atmosphere. Meanwhile, the mercury removal mechanism was put forward based on the characterization results, including surface area and micropore structure, element contents and active chemical functional groups. The results show that the raw petroleum coke (RPC) has almost no mercury removal capacity while the mercury removal efficiency of the sulfur activated petroleum coke (SPC) is greatly improved. After activation, specific surface area and micropores increased significantly. The sulfur content increased as well. Meanwhile, the relative content of non-oxidative sulfur forms and oxygen functional groups of SPC are significantly higher than RPC. The optimum parameters of activation agent flow rate and time of 100 mL/min and 1.5 h are reached in this experiment, respectively.

Ultrathin-wall mesoporous surface carbon foam stabilized stearic acid as a desirable phase change material for thermal energy storage

A fluffy ultrathin-wall mesoporous surface carbon foam (UMSCF) with high thermal conductivity was prepared via carbon-thermal reduction reaction between a carbon foam and aluminium nitrate, and then used as a supporting material for stearic acid (SA) to form shape-stabilized composite phase change materials (PCMs). The UMSCF and the as-prepared SA/UMSCF composite PCMs were characterized by SEM, TEM, XRD, Raman, BET, FTIR, wettability test, compression test, TG, DSC, thermal cycling test and laser flash method, respectively. Results shows that the carbon-thermal reduction temperature greatly influences the microstructures of the UMSCF, and the UMSCF prepared at 1600°C (UMSCF-1600) possesses good lipophilicity, high thermal conductivity and superior mechanical properties. The prepared UMSCF as supporting matrix simultaneously improves thermal conductivity and shape-stabilization of PCMs, as well as retains relative high phase change enthalpy. The melting and freezing enthalpy for SA/UMSCF-1600 composite was measured as 149.3 and 151.2J/g, respectively. The thermal conductivity of the composite PCMs is as high as 1.725W/mK, which increases by about 6.791-fold compared with pristine SA. Meanwhile, the composites display good thermal reliability and chemical stability, suggesting their promising characteristics for thermal management applications.

Preparation of hollow SiC spheres with biological template and research on its wave absorption properties

In this work, SiO2 was evenly coated on dry yeast as biological template by sol-gel method, and the internal substances of yeast were removed at 700 °C to obtain hollow silicon template. Then, RF aerogel (carbon source) was used to wrap the silicon template. After carbonization treatment, carbon thermal reduction reaction was carried out at 1400 °C to obtain hollow SiC spheres (HSS). Under the coating of RF aerogel, the hollow SiO2 maintained its complete physical shape in the process of high-temperature synthesis, and the final product was hollow ellipsoidal silicon carbide with the maximum diameter of about 4.3 μm and the minimum diameter of about 3.5 μm, basically keeping the shape of yeast. The basic properties of the products were characterized by XRD, FT-IR, SEM, TEM and Tg, the absorption properties of the products were analyzed by VNA. The research found that the absorption performance of the hollow SiC with yeast morphology increased significantly in the frequency band of 2–18 GHz. When the thickness is 3.1 mm, the hollow SiC has the maximum reflection loss of −51.74 dB at 12.08 GHz. When the thickness is 4.0 mm, it has an effective absorption frequency width of 6.05 GHz, which has obvious advantages over SiC without special hollow morphology. The effect of hollow structure on the electromagnetic properties of SiC is discussed in detail.

In-situ formation of bulk and porous h-AlN/SiC-based ceramics from geopolymer technique

In this paper, bulk and porous AlN/SiC based ceramics were in-situ prepared from graphite/geopolymer composites based on the carbon thermal reduction reaction under high temperatures. Thermal evolution of graphite/geopolymer composites were systematically investigated by XRD, TG/DTA, DIL, SEM, and TEM. The results show that graphite co-exists with amorphous geopolymer below 900 °C, whereas leucite crystallizes from geopolymer matrix and thus results in graphite/leucite composites in the temperature range of 1000 °C–1400 °C. After being treated at 1500 °C, h-AlN emerges due to the carbon thermal reduction reaction. By further increasing the heating temperature to 1700 °C, h-AlN or SiC with flocculent structures dominate the resulting high-temperature products, depending on the sintering atmosphere. It has been proved that h-AlN is the predominant phase of the resulting products after being treated at 1700 °C in N2 atmosphere. Nevertheless, SiC becomes the dominant one in Ar atmosphere, ceteris paribus. Moreover, both h-AlN and SiC ceramics derived by this technique show porous features, with the porosity of 61% and 68% and considerable compressive strength of 0.76 MPa and 0.63 MPa, respectively.

Nitrogen-doped hierarchical porous carbon for supercapacitors with high rate performance

Abstract Nitrogen-doped, hierarchical porous carbons with high surface area are synthesized using sucrose as carbon precursors, and nitrogen-containing organic salt, i.e. ethylenediamine tetraacetic acid disodium zinc salt (EDTANa2Zn), as hard template, activation agent and nitrogen source simultaneously. During pyrolysis of the EDTANa2Zn/sucrose composites, the nano-ZnO and Na2CO3 particles produced from EDTANa2Zn are evenly dispersed in the nitrogen-doped carbon, which can act as hard templates to create mesopores. Furthermore, the nano-ZnO can etch carbon as an activation agent when the pyrolysis temperature further increases. The carbon thermal reduction reaction and the subsequent evaporation of the Zn form many micropores and small mesopores. Due to the hierarchical porous architecture, large surface area (2160 m2 g−1) and nitrogen doping, the carbon prepared at 950 °C exhibits a high specific capacitance (229 F g−1 at 0.1 A g−1), excellent rate capability (191 F g−1 at 300 A g−1) and superior cycle durability (capacitance retention of 95.3% after 20,000 cycles at 10 A g−1) in 6 M KOH aqueous electrolytes, showing promise as an outstanding supercapacitor electrode material.

Effect of Pre-oxidation and SO2 Modification on Mercury Removal Performance of High Sulfur Petroleum Coke in Simulated Natural Gas

A high sulfur petroleum coke (RPC) was selected as the raw material to make mercury adsorbent used in the simulated natural gas. The effect of pre-oxidation with air at set temperature and set time and sulfurization with 20% SO2 on mercury removal in simulated natural gas was studied. The experiments were carried out on a fixed-bed experimental device. The physicochemical properties of the sorbents were characterized by surface area and porosity analysis, elemental analysis and X-ray photoelectron spectroscopy (XPS). The results show that the mercury removal performance of the sulfur-loaded petroleum coke is greatly improved through carbonthermal reduction reaction. The optimum oxidation temperature of the SO2 activated petroleum coke is 300°C, and the Hg0 removal efficiency decreases with increase of the pre-oxidation time. The three main factors such as non-oxidative sulfur functional groups, carbonyl and ester sulfur functional groups, and pore structure greatly influence the mercury removal characteristics. The pre-oxidation time and temperature play an adjustable role for getting better performance of mercury removal.

Optimizing the particle-size distribution and tap density of LiFePO4/C composites containing excess lithium

LiFePO4 is a promising cathode material for lithium-ion batteries, but its inferior tap density leads to low-volumetric energy density of Li-ion batteries. This work reports that lithium amount can tune the particle-size distribution and tap density of the Li1 + xFePO4/C (x = 0–0.16) composites prepared via a wet chemistry method followed by carbon thermal reduction reaction. Excess lithium effectively prevents the agglomeration of primary particles, tunes the particle-size distribution, and thus improves the tap density of Li1 + xFePO4/C composite. The charge transfer resistance of the Li1 + xFePO4/C composite decreases with the increase of lithium amount. The Li1 + xFePO4/C composite with x = 0.12 exhibits a high tap density of 1.55 g cm−3 and a discharge capacity of 156 mAh g−1 at 0.1 C. Therefore, the tap density and electrochemical performance of LiFePO4/C composite could be conveniently tuned by lithium amount, indicating a facile and promising technique for LiFePO4/C composite preparation.

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.

Synthesis and Electrochemical Performance of the Na3V2(PO4)3 Cathode for Sodium-Ion Batteries

Rhombohedral Na3V2(PO4)3 with a Na+ superionic conductor structure was synthesized using a solid-state reaction method. Citric acid was used as a carbon resource for carbon-thermal reduction reaction to reduce the oxidation state of vanadium. The shape of Na3V2(PO4)3 particles is irregular and its average diameter is in the range 30–50 nm. The Na3V2(PO4)3 exhibits a superior cycling ability and rate capability. The discharge capacity retains 74.3% of the discharge capacity of its first cycle with coulombic efficiency of 99.3% after 100 cycles. The discharge capacity of Na3V2(PO4)3 at 10 C is 48.87 mAh g−1, which is 58.4% of the cell cycled at 0.1 C. Furthermore, the structure of Na3V2(PO4)3 is stable for a considerable amount of Na+ ions (2 mol of Na+ ions) insertion and extraction with only 0.42% difference of unit-cell volume between fully charged and discharged states. Na3V2(PO4)3 is a potential cathode material for sodium-ion battery applications.

Formation mechanism of spinel LiTi2O4 prepared by carbon thermal reduction reaction

The formation mechanism of LiTi2O4 is investigated by in situ variable temperature X-ray diffraction and thermal gravimetric analysis/differential scanning calorimetry system.

Glucose-assisted synthesis of Na3V2(PO4)3/C composite as an electrode material for high-performance sodium-ion batteries

A novel electrode material for sodium-ion batteries (NIBs), Na3V2(PO4)3 with a rhombohedral, Na+ superionic conductor (NASICON)-type structure, was synthesised via a solid-state carbon-thermal reduction reaction assisted by mechanochemical activation. Electron microscopy analysis showed that the synthesised Na3V2(PO4)3 particles had an average size of 300 nm, being coated with a uniform layer of carbon 3 nm in thickness. As a cathode material, Na3V2(PO4)3/C exhibited an initial specific discharge capacity of 98.17 mAh g−1 at 0.1C for potentials ranging from 2.5 to 3.8 V. This was owing to the V3+/V4+ redox couple, which corresponded to the two-phase transition between Na3V2(PO4)3 and NaV2(PO4)3. The cathode lost 4.92% of its discharge specific capacity after 50 cycles. As an anode material, Na3V2(PO4)3/C exhibited an initial specific discharge capacity of 63.2 mAh g−1 at 0.1C for potentials ranging from 1.0 to 2.5 V. This was owing to the V2+/V3+ redox couple, which corresponded to the two-phase transition between Na3V2(PO4)3 and Na4V2(PO4)3. The anode lost approximately 5.41% of its discharge specific capacity after 50 cycles. The three-dimensional channel structure of NaV2(PO4)3 and the changes induced in its lattice parameters during the charge/discharge processes were simulated on the basis of density functional theory.

Sol–gel preparation and characterization of black titanium oxides Ti2O3 and Ti3O5

Sub-micron black titanium oxides powders Ti2O3 and Ti3O5 were synthesized via a facile and economical sol–gel method in this paper. Relatively pure Ti3O5 and Ti2O3 can be obtained by annealing the as-prepared PEG600-based gel with a heating rate of 10 °C min−1 and maintaining the temperature at 1,000 and 1,200 °C, respectively, under high pure (99.999 %) argon atmosphere for 4 h. The FESEM images reveal that the morphologies of the as-prepared Ti3O5 and Ti2O3 are sphere-like and plate-like mixed type structures. The particle size of Ti3O5 sample is in the range of 50–200 nm. However, the appearance of Ti2O3 is 200–500 nm irregular flake structures covered with 20–50 nm spherical particles. This PEG600-based sol–gel approach has a low reaction temperature of 1,000 °C herein for the preparation of Ti3O5, which is ascribed to that, the molecular PEG-600 was distributed well in the homogeneous gel through secondary cross-linking of the organic molecules, and with the increasing of heating temperature, molecular PEG-600 was carbonized. These nanoscaled and homogeneous mixtures of carbon and TiO2 made the carbon thermal reduction reaction occur subsequently at 1,000 °C. The Raman vibrational wavenumbers of as-prepared Ti3O5 and Ti2O3 are perfectly coincident with those of calculated results of pure Ti3O5 and Ti2O3. Besides, the Fourier transform infrared spectra of Ti3O5 and Ti2O3 were also investigated in this article. Finally, the powder electrical resistivity of Ti3O5 and Ti2O3 is 4.7 × 10−3 and 2.5 × 10−3 Ω m, respectively.

In Situ Synthesis of ZnMn2O4–ZnO–C and ZnMn2O4–C Nanohybrids as High Performance Lithium‐Ion Battery Anodes

AbstractZnMn2O4–ZnO–C nanohybrids have been synthesized by means of a simple carbonthermal reduction reaction between ZnMnO3 and acetylene black. ZnMn2O4–C nanohybrids are obtained by further washing with NaOH solution. The reversible discharge capacity of the ZnMn2O4–ZnO–C nanohybrids can reach 620 mA h g–1 at a current density of 100 mA g–1 and 520 mA h g–1 at 800 mA g–1 after 100 cycles. More importantly, ZnMn2O4–C shows better conductivity along with better rate performance after the removal of ZnO. The as‐prepared ZnMn2O4–C nanohybrids show a high specific capacity of approximately 750 mA h g–1 at a current density of 100 mA g–1 after 100 cycles and excellent rate performance. The reaction involved in the discharge/charge processes are discussed on the basis of ex situ high‐resolution transmission of the electrode materials. The conclusions will be of benefit in the design and exploration of future binary transition‐metal oxide anode materials for lithium‐ion batteries.

A biomimetic nest-like ZnO: Controllable synthesis and enhanced ethanol response

We reported a facile and controllable route to prepare nest-like ZnO without any complicate experimental equipments, pressure and gas control procedures. The nest-like ZnO was made within a muffle furnace in air atmosphere under normal pressure through a simple carbon thermal reduction reaction. The product was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), field emission scanning electron microscope (FESEM) and photoluminescence (PL). The results showed that the product was wurtzite ZnO and had an interesting hollow nest-like microstructure with a prickly porous shell. The shell consisted of ZnO nanospheres, and a few ZnO nanorods grew on the shell surface. The gas sensing test indicated that the nest-like ZnO had an excellent gas sensing behavior toward ethanol. The response of the sensor to 50ppm ethanol was about 100, which was at least four times more than other gases. Moreover, even down to 1ppm ethanol, the response still reached 3.8. Both the response time and recovery time of the sensor were short. All of these proved that the nest-like ZnO is a promising gas sensing material for ethanol detecting.

Study on Preparation of Nano-SiC Fibers by Template Method Based on Waste Cotton Linter

Waste cotton linters from textile industry were used as templates to be transformed as cotton fiber/SiO complex after sol impregnation, carbonization, carbon thermal reduction reaction, to prepare nanoSiC fibers and nanoparticles. The phase of final products were identified by XRD as β-SiC, and the diameter size of nanoSiC fiber was ranged as 20~100mm analyzed by SEM and TEM. Based on the thermodynamic analysis of each step in the thermal reduction on carbon / SiO composite to generate nanoSiC fibers, the nanoSiC fibers were generated by the vapor reaction between SiO and CO, and its growth mechanism was deduced as vapor-solid. For the reuse of cotton linter, thus the research provides a new solution.

Suppression of visible light emission of ZnO nanostructures by Ga-doping

Ga-doped ZnO nanostructures with various doping concentrations are prepared by using carbon thermal reduction reaction and in situ doping method. X-ray diffraction measurement reveals only wurzite structures existing in Ga-doped ZnO nanostructures. Scaning electron microscopy observations show that with the increase of Ga doping concentration, the morphology of ZnO nanstrucuture varies gradually from nanorods to nanocones. From the photoluminescence, we find that the visible light emission of ZnO nanostructures can be suppressed obviously and even disappears with the increase of Ga doping concentration. Moreover, the suppression of visible light emission is correlated well with the behavior, and X-ray photoelectron spectroscopy measurement reveals that the vacancy oxygen in ZnO nanostructure decreases drastically with the increase of Ga doping concentration. This result offers a new strong evidence for the mechanism that the visible light emission of ZnO nanostructures is caused by the oxygen vacancy defects. This work also demonstrates that a little Ga incorporation into ZnO nanostructures can effectively reduce the oxygen vacancy defects occurring.

Study on Magnesium Metal Preparing by Serpentine Carbon-Thermal Reduction Reaction

Metallic magnesium is prepared with serpentine breeze in vacuum induction furnace by adding calcium fluoride. In the furnace, the vacuum degree should be controlled at 500Pa, while the temperature needs to be heated to 700°C and keep the temperature for 60min in order to dewater the crystal water; And then continue to rise the temperature to 1500°C and keep the temperature for 60min which can deoxidize the element Fe and Ni in the serpentine breeze to metallic iron and metallic nickel, while metallic magnesium become vapor magnesium and then crystal to metallic magnesium at the condenser. Metallic iron and nickel in the furnace slag can be recovered through magnetic concentration and the furnace slag after magnetic concentration can be inverted to silicon carbide through carbothermic method.