Conventional Carbothermal Reduction Research Articles

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.

Cleaner extraction of white phosphorus from phosphate rock through molten salt electrolysis

White phosphorus (P4) is an essential raw material for the production of phosphorus chemicals. The conventional carbothermal reduction process used to extract P4 from phosphate rock is known as energy intensive and environmentally polluting, posing obstacles to meeting the urgent global demands for clean production and carbon neutrality. Moreover, the low product purity restricts its application in high-value industries. This paper presents an original approach that is both simple and coke-free for extracting high-purity P4. The method involves electrolyzing dissolved phosphate rock in molten CaCl2 at a mild temperature. We undertake an in-depth investigation into the dissolution behavior of phosphate rock in molten CaCl2 and the electrolysis behavior of the melt. The experiments demonstrate the rapid dissolution of phosphate in the rock when exposed to molten CaCl2, reaching saturation within a short time (e.g., within 10 min at 850 °C). The dissolution of phosphate shows a preference over silicates present in the phosphate rock. The electrochemical reduction of PO43− in molten CaCl2 is electrochemically reversible, as observed at potential scan rates not exceeding 0.20 V s−1. The obtained P4 product through electrolysis is of higher purity compared to the industrial-grade commercial product produced via carbothermal reduction. The implementation of pre-electrolysis can further improve the purity of the product and the current efficiency of the electrolysis process. The theoretical electricity and carbon consumption in the electrolysis method are estimated to be 9.12 kWh and 0.53 kg, respectively, for every 1 kg of P4 produced. These values are lower than the conventional carbothermal reduction process. This cutting-edge electrolysis method represents a paradigm shift towards a more sustainable development of the phosphorus chemical industry, thereby showcasing its potential for revolutionizing the field.

Mechanism and experimental study on preparation of high-quality vanadium nitride by one-step vacuum carbothermal reduction nitridation method

With high hardness, high electrical conductivity, and good catalytic activity, VN is widely used in alloy materials, catalysis and electrode materials, and other fields. However, the conventional carbothermal reduction nitridation (CRN) methods are often limited by high temperatures and long reaction times. In this paper, the reaction process of vanadium trioxide one-step vacuum carbothermal reduction nitridation (VCRN) synthesis of vanadium nitride was studied by combining theoretical calculation and experimental research. The experimental results show that reducing the pressure is favorable for the V2O3-CRN reaction and high-quality VN was successfully synthesized under the conditions of 1473 K (300 Pa, 3 h) and the carbon mass ratio (mC/mV2O3) is 0.25. In addition, the reaction mechanism of V2O3-VCRN was elucidated by ab initio molecular dynamics (AIMD) simulations. The results show that carbon plays important role in the VCRN reaction process of vanadium trioxide. First, Carbon catalyzes the dissociation of nitrogen molecules on the surface of V2O3–C, which promotes the formation of the V–N bond, second is to react with O in the V2O3 lattice and reduces V2O3.

Comparison of microwave and conventional carbothermal reduction of red mud for recovery of iron values

This study investigates the recovery of iron values from Indian red mud through different routes. The conventional beneficiation was found futile to recover iron values from the red mud due to complex structure. The carbothermal reduction is carried out in both muffle and microwave furnace using statistical design. The XRD quantitative phase analysis of the magnetic concentrate indicates distinct phase transformation of hematite to ferrite as a function of temperature and in the sequence Fe2O3 → Fe3O4 → FeO → Fe. In microwave furnace, concentrate with ∼47% grade and 88% recovery at a yield of 72% is attained at optimal conditions of 1000 °C, 10 min with 11% C whereas in muffle furnace, optimal conditions of 1000 °C, 50 min reduction time with 16.5% C yields a concentrate ∼49% iron, 87% iron recovery with a yield of 56%. On comparison of carbothermal reduction in muffle and microwave routes, the microwave route provides a significant improvement in iron grade and recovery at comparatively lower levels of time and reductant dosage. Along with enhanced iron grade-recovery, significant ferrite balls of 1 ± 0.5 mm (∼92% iron content with 94% purity) are observed in the microwave route and were handpicked from the product. Nevertheless, the ferrite phase is forming in both the routes, but in microwave route, ferrite balls of appreciable size and purity accounting ∼8–10% of total iron values in the feed are also observed. In addition, the microwave assisted carbothermal reduction offers a faster reduction rate, cleaner processing and relatively economical in terms of energy and reductant consumption. The product obtained is rich in magnetite, wustite and ferrite phase which can be further used in alternate iron making units.

Low temperature synthesis of ZrB2-SiC powders by molten salt magnesiothermic reduction and their oxidation resistance

Herein, we prepare phase-pure ZrB2-SiC composite powders by molten-salt-mediated reduction of ZrSiO4/B2O3/activated carbon mixtures with Mg, showing that the phase composition and morphology of the above composites is influenced by firing temperature, B:Zr and C:Si molar ratios, and the amount of excess Mg. Notably, phase-pure ZrB2-SiC powder with a ZrB2:SiC weight ratio of ~75:25 could be obtained by 3-h firing at 1200 °C, i.e., at a temperature lower than that used for conventional carbothermal reduction by at least 200 °C. As-prepared ZrB2-SiC composites exhibited grain sizes of several microns and comprised SiC nanoparticles well distributed in the ZrB2 matrix. Finally, the oxidation activation energies of the prepared ZrB2 and ZrB2-SiC powders were determined as 326 and 381 kJ/mol, respectively, which demonstrated that the introduction of SiC improved the oxidation resistance of monolithic ZrB2.

Electrochemical Preparation of Nanostructured Silicon from Rice Husks As a Sustainable Source for High Performance Anode in Secondary Lithium Ion Battery

Silicon is one of the most promising anode material candidates for lithium ion batteries because of its high specific capacity (3579 mAh/g), which is ten times higher than existing graphite anodes. One of the most important issues toward commercialization is the high cost of nanostructured silicon related to the complex fabrication amd expansive raw materials. In this work, we demonstrate the recycling of pure silicon nanoporous particles from rice husks (RHs) directly, which is an abundant agricultural byproduct (108 tons/year) in worldwide. Besides, the massive amount of RHs has unique nanoporous structure on the RHs to preform the function as protection and ventilation. In the first step of our experiment, the metal ions in the RHs by HCl leaching were removed and then incinerate the leached RHs to produce silica with nanostructure. Next step, we convert the silica to silicon by electrochemical reduction method, which is a potential process for large scale reduction in a relative low tempareture compared with conventional carbothermal reduction. Owing to the nanoporous nature, these recovered silicon nano-particles show high performance as lithium ion battery anodes, with high reversible capacity and long cycle life. Recycling RHs as the source of silicon, this work presents a process to produce Si based Li-ion battery with cost effective, energy-efficient, green, and potential of large scale synthesis in industry. Key words: rice husk, electrochemical reduction, Li-ion battery

Synthesis of Stoichiometric Titanium Carbide by a Combination of Carbothermal Reduction and Molten Salt Method and Its Characterization

Abstract A novel method of preparing stoichiometric titanium carbide (TiC) powders was present by combining carbothermal reduction and molten salt synthesis (MSS) from raw materials of titanium oxide (anatase), C (carbon black), and sodium chloride. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser particle size analysis, energy spectrum analysis (EDS), and thermodynamic analysis were used to characterize the powders. The effects of heating temperatures and molar ratios of titania to carbon black on the preparation of TiC were discussed. Results show that the use of MSS reduces the synthesis temperatures of both stoichiometric and pure TiC from 1700 °C to 1550 °C and the time required for synthesis decreases from 10 h for conventional carbothermal reduction of TiO2 to 3 h. A dissolution-precipitation mechanism of synthesis of TiC by MSS was established based on these observed results.

Microwave-assisted Synthesis of a ZrC-SiC Nanocomposite by Carbothermal Reduction and its Effect on Mean Particle Size

ZrC-SiC nanopowders were prepared by carbothermal reduction of ZrO2 and SiO2 with carbon black in argon gas atmosphere, using microwave energy as an alternative heating source. The samples were characterized by XRD, SEM and BET surface area analysis. The results indicate that highly crystalline ZrC-SiC composites with a mean particle size of about 80 nm can be synthesized at a relatively low temperature (~1420 °C). Microwave-assisted heating to obtain the ZrC-SiC nanopowders significantly reduces the synthesis time to only 40 min when compared with the long reaction times involved in conventional carbothermal reduction, which requires about 8 hours to obtain ZrC and 2 hours to obtain SiC.

Multi-cations doped LiVPO4F cathode for lithium-ion batteries

The multi-cations doped LiVPO 4 F , nominally Li 0.97 Cr 0.01 V 0.95 Al 0.01 Nb 0.02 PO 4 F 0.97, is prepared by Chromium ( Cr ) doping on lithium site and Al – Nb co-doping on vanadium site via a conventional carbothermal reduction (CTR) route. The crystallographic lattice volume, particle size and morphology are not obviously changed comparing with un-doped LiVPO 4 F . However, the high rate and lifetime cycling performances are noticeably improved although the capacities at very low currents are slightly decreased. The reversible capacity at 1/10 C, 1 C, 2 C and 4 C of the pristine LiVPO 4 F is 143 mA h g-1, 99 mA h g-1, 86 mA h g-1 and 70 mA h g-1, respectively, while that of the doped counterpart is 138 mA h g-1, 102 mA h g-1, 95 mA h g-1 and 82 mA h g-1, respectively. The capacity retention after 100 galvanostatic cycles at 1.5 C is enhanced from 85.4% to 90.9% by such multi-cations doping. Moreover, the initial coulombic efficiency is significantly increased from 81.8% to 90.3% as well.

Synthesis of ultrafine (Ti,W,Nb)C solid solution powders by microwave-assisted carbothermal reduction

(Ti,W,Nb)C solid solution was obtained via microwave-assisted carbothermal reduction (MWCR) which was more cost-effective and timesaving than conventional carbothermal reduction (CR). Oxide–graphite mixtures were used as starting materials in the procedures. The phase evolution during MWCR has been discussed and compared with conventional CR in terms of the X-ray diffractometry. Microwave irradiation accelerated the formation of individual carbides (WC and NbC) as well as the formation of the final complete solid solution. The monolithic (Ti,W,Nb)C solid solution was synthesized at 1250°C for 30min. The agglomerates sizes of the final product were in the range of 100–350nm.

Using a cobalt activator to synthesize titanium carbide (TiC) nanopowders

Titanium carbide (TiC) nanopowders were successfully synthesized by in-situ reduction and carbonization using a precursor comprising elemental titanium, carbon, and cobalt. The samples prepared at different conditions were characterized by X-ray diffraction and transmission electron microscopy techniques. The thermolysis process of the precursor was investigated by themogravimetric analysis and differential thermal analysis. The experimental results show that the samples have average sizes ranging within 30–40nm. In addition, the experimental temperature is 100–900°C lower and the reaction time is 2–90h shorter than those used in the conventional carbothermal reduction method.

A novel method with low-cost Fe2O3 to synthesize small size LiFePO4 by carbothermal reduction method

The phase-pure LiFePO4/C cathode materials have been successfully fabricated by precursor containing Fe2O3 coated with polyaniline through carbothermal reduction method. The polyaniline coating at Fe2O3 could restrict the growth of crystal and subsequently become electric carbon at higher synthesis temperature. Compared with conventional carbothermal reduction method, the sample showed a better capacity and less than 3% capacity fading after 30 cycles at various charge and discharge rate.

New manufacturing process for nanometric SiC

Abstract Nanometric β-SiC powder was prepared by carbothermal reduction of freeze-dried gel. Initially, the gel was obtained by polycondensation of sol consisting of resorcinol and formaldehyde as a source of C and tetraethoxysilane as a source of silicon. The effect of temperature and time of heat treatment (carbothermal reduction) as well as the effect of C/Si ratio on SiC powder properties was studied. It was possible to obtain nanosized (∼20 nm) β-SiC powder after one-hour heat treatment at relatively low temperature of 1200 °C. The powder was successfully synthesised without the need for excess carbon which is typical for conventional carbothermal reduction using some other sources of graphite. The increase in temperature of heat treatment to 1400 °C caused considerable growth of SiC particles up to 400 nm. It was found that prolonged heat treatment at 1200 °C is an effective way to obtain well crystallized SiC and keep the size of SiC particles below 50 nm at the same time.

Mechanochemical synthesis of nano-structured TiC from TiO 2 powders

Nano-structured TiC was successfully synthesized from mixtures of TiO 2 and graphite through high-energy mechanical milling and subsequent heat treatment at a temperature that was considerably lower than that used in conventional carbothermal reduction synthesis of TiC. TiO 2 powders mixed with graphite were milled in a planetary ball mill for 30–90 h. The milled mixtures were then heat treated at 1200 °C and 1300 °C for 60 min. The as-milled and heat treated powders were characterized using SEM-EDAX, DTA, and XRD techniques. As revealed in SEM, agglomeration was found to be more pronounced after 30 h milling. Even though the formation of TiC was not detected in as-milled powders milled for durations between 30 h and 90 h, TiC appeared in the powder mass after heat treatment as revealed by the XRD patterns. The crystallite size of TiC as a function of milling time was estimated from the XRD data using Scherrer equation and it was found to be increased with increasing milling time after heat treatment.

Preparation of Sr2Si5N8:Eu2+ phosphors using various novel reducing agents and their luminescent properties

Divalent europium-doped metal nitride phosphors, Sr2Si5N8:Eu2+, were synthesized using three novel reducing agents, C3H6N6, C2H4N4, and Sr(CH3COO)2. The samples obtained showed higher emission intensity and lower residual oxygen/carbon content as compared with the sample prepared by the conventional carbothermal reduction and nitridation (CRN) method. A maximum emission intensity of 155% relative to that of the commercially available YAG:Ce3+ (P46-Y3) standard phosphor was achieved using the Sr(CH3COO)2 route. White LEDs fabricated using synthesized phosphors emitted white light with a correlated color temperature in the range 2900–6300 K. Moreover, a general color rendering index (Ra) of 80 was obtained. The reducing methods in this study were shown to be more effective than the conventional CRN route; these phosphors can be used to compensate for a red color deficiency of the current white LED.

Preparation of titanium carbide powders by sol–gel and microwave carbothermal reduction methods at low temperature

Titanium carbide ultrafine powders were prepared from tetrabutyl titanate and sucrose by sol–gel and microwave carbothermal reduction. The influences of reaction temperature and molar ratio of Ti to C on the synthesis of titanium carbide were studied. The results show that excess amount of carbon plays a positive effect on the carbothermal reduction of TiO2 at low temperature. The inceptive carbothermal reduction temperature of TiO2 and formation of titanium oxycarbide was below 900 °C, and pure TiC can be prepared at 1,200 °C, which was considerably lower compared to that by conventional carbothermal reduction using a mixture of TiO2 and carbon powders as raw materials. The morphology and particle size of synthesized TiC powder were examined by field emission-scanning electron microscopy (FE-SEM) and the quantities of the phases of the powders were analyzed by Rietveld refinement method, the particle sizes of the TiC powders synthesized at 1,300 °C distribute over 0.1–0.5 μm.

Synthesis of titanium carbide from a composite of TiO 2 nanoparticles/methyl cellulose by carbothermal reduction

Titanium carbide (TiC) was synthesized from a composite constituted of nano-sized TiO 2 particles (ca. 5 nm in diameter) and methyl cellulose (MC) via carbothermal reduction in an Ar flow. The composite was converted into titanium oxycarbide by heating at 1050°C. With the increase of heating temperature, the lattice parameter of the titanium oxycarbide phase increased while the oxygen content in the specimen decreased, especially above 1300°C. That is, low oxygen content (0.60–2.32 wt%) TiC could be prepared from the composite by heating above 1300°C, which was a considerably lower temperature compared to that employed in the conventional carbothermal reduction methods that use a mixture of TiO 2 and carbon powders.

Al 2O 3/mullite/SiC powders synthesized by microwave-assisted carbothermal reduction of kaolin

Al 2O 3/mullite/SiC powders have been synthesized by microwave-assisted carbothermal reduction of kaolin. Kaolin, a low cost aluminosilicate, was mixed to carbon black to achieve the precursor blend which was dried, broken in mortar, sieved then reacted in a kitchen microwave oven for 45 min under reducing atmosphere. In order to compare the characteristics of the powders, conventional carbothermal reduction reaction was performed at 1450°C for 2 h. The as-reacted powders were characterized by X-ray diffraction and scanning electron microscopy to confirm the phase formation. Results obtained show Al 2O 3/mullite/SiC phase in XRD for both reaction routes, products which can be achieved only in temperature ranges of about 1450°C.