Synthesis of ultrafine 3C–SiC powder by sol–gel and carbothermal reduction processing

A novel low-temperature chlorination process of nitrided ilmenite (TiOxCyNz) for efficient and economical production of titanium is investigated. Knowledge and understanding of the mechanism and influential factors affecting chlorination are required to establish an effective low-chlorination process with higher production of Fe-free TiCl4. In this study, the chlorination of nitrided ilmenite using statistical design of experiments was investigated. Malaysian ilmenite was carbothermally reduced at 1250°C for 180 minutes in the presence of a 50-50 vol.% mixture of H2−N2 gas. The three carbon sources used for carbothermal reduction (CTR) process are graphite, activated carbon (AC) and carbon nanotubes (CNT). Nitrided ilmenite obtained from the CTR process were chlorinated based on the factorial design (2k) for a temperature range of 400-500°C, chlorination duration of 1-3 hours and different carbon reactants. Ilmenite was reduced to titanium oxycarbonitride (TiOxCyNz) through simultaneous carbothermal reduction and nitridation process for further chlorination into titanium tetrachloride. Microstructural characterization and phase analysis of raw materials and reduced samples were conducted. DOE analysis suggested that the type of carbon reactant was the most influential factor in the chlorination of nitrided ilmenite. The highest extent of chlorination i.e., 72 % was obtained for a chlorination temperature of 500°C, chlorination time of 3 hours and carbon nanotube as a carbon reactant in the CTR process.

Bamboo charcoal was expected to be a renewable carbon source for carbide materials in carbothermal reduction because of its superior characteristics. SiC powders with characteristic shapes were fabricated by carbothermal reduction with industrial silica sol and bamboo charcoal particles as silicon and carbon sources respectively, and the effects of reacting temperature and time on shape evolutions and properties of the as-prepared SiC powders were investigated. The silica sol/bamboo charcoal system was firstly transformed into SiO2/C system by the transition of silica sol and graphitization of bamboo charcoal, and the carbothermal reduction between SiO2 and C occurred at/above 1600°C. The characteristic shapes of SiC particles were transformed from string-beads-like to dumbbell-like and rod-like with the increase of reacting temperature. The prepared SiC powders are expected to become new raw material for silicon carbide ceramic composites.

Red mud is a hazardous waste of alumina production. Currently, the total accumulated amount of red mud is over 4 billion tons. The promising method of red mud processing is a carbothermic reduction of iron at 1000–1400 °C into metallic form followed by magnetic separation. In this study, the mechanism of carbothermic solid-phase reduction of red mud was investigated. Based on the experimental data, the two-step mechanism of the first rapid stage of the process was proposed, which leads to almost full iron reduction. The estimated value of activation energy has indicated that solid-phase diffusion is a rate-controlling step for this stage. However, an almost full reduction is necessary, but insufficient factor for successful magnetic separation. The second crucial factor of the process is enlargement of iron grain size, which leads to gangue-grain release during grinding and increases efficiency of the magnetic separation. The prediction model of iron grain growth process during the carbothermic reduction process was suggested. The calculation of average size of iron grains formed during the reduction process that was performed according to the assumption of diffusion-controlled process showed their correlation with experimental data. Various methods were proposed to promote the process of iron grain growth during carbothermic reduction of red mud.

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.

Silicon assistant carbothermal reduction for SiC powders

Nano sized SiC powder was successfully synthesized by the carbothermal reduction in SiO2. Precursor for SiC was prepared by using phenolic resin as a carbon source and ethylsilicate as a silicon source. After mixing, hydrolysis, drying and pyrolysis at 1000°C, SiC precursor consisted of C and SiO2 was obtained. The precursor was heat treated at 1500-1800°C in Ar to synthesize SiC by the carbothermal reduction. The carbothermal redction reaction was almost completed at 1700°C and then SiC particle with suitable size was obtained at this temperature. Nano-sized SiC particles could be achieved at 1600 °C, and unreacted SiO2 and C remained in the sample. Pure SiC particles were obtained by oxidation and acid treatment. Nano-sized SiC powder had the diameter of 10-20 nm and BET surface area of 156 m²/g.

Nanometer silicon carbide powders are synthesized by sol-gel and carbothermal reduction processing with TEOS( tetraethoxysilane, (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> ) ) and saccharose (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> ) as starting materials. Silica sol is prepared by hydrolyzed TEOS with deionized water, ethanol (CH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> CH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> OH) as cosolvent and hydrochloric acid as catalyst. It further dehydrated to make colorless and transparent gel and dried to obtain drying gel at 40°C. Carbothermal reduction of the prepared silica/ saccharose composites is carried out in argon atmosphere of 500 Pa in a high vacuum furnace at temperatures ranging from 1200°C to 1500°C to form powders. The surface morphology and crystal structure of nanometer SiC powders have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and Raman spectrum. Experimental results show that the samples have better crystalline state and its typical diameters reach nanometer magnitude.

Silicon carbide (SiC) precursor was obtained by sol–gel used tetraethoxysilane as silicon source and saccharose as carbon source, and then the precursor was used to prepare SiC by carbothermal reduction under dynamic vacuum condition. The samples were characterized by X-ray diffraction, scanning electron microscope, and low-temperature nitrogen adsorption–desorption measurement. The results showed that the carbothermal temperature for synthesizing SiC needed to be at 1,100 °C under dynamic vacuum. At this temperature, the obtained sample is composed of agglomerated regular grains with size ranging from 20 to 40 nm and has a high surface area of 167 m2/g and the main pore size center at 5.3 nm.

Carbothermic reduction of spent Lithium-Ion batteries using CO2 as reaction medium

Long silicon carbide (SiC) microwhiskers with a necklace‐like morphology have been successfully synthesized by a carbothermal reduction process without using any catalyst. In the process, the wood flour/silica (SiO2)/phenolic composite was chosen as both silicon and carbon sources. The morphology and structure were investigated by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), field‐emission scanning electron microscopy (FESEM), and high‐resolution transmission electron microscopy (HRTEM). Studies found that the as‐synthesized whiskers were grown as single crystalline β‐SiC along the (111) direction with the length up to hundreds of micrometers. The whiskers consisted of β‐SiC strings with diameters of 1–2 μm and periodic β‐SiC beads with diameters of 3–5 μm. On the basis of characterization results, a growth mechanism is proposed to clarify the formation of necklace‐like whiskers.

Characterization of nanocrystalline porous SiC powder by electrospinning and carbothermal reduction

Iron removal from ultra-fine silicon carbide powders with ultrasound-assisted and its kinetics

Silicon carbide has excellent mechanical strength, thermal stability and chemical inertness, and avoids several of the problems inherent in the performance of commercial supports, such as alumina, silicon oxide and carbon-based materials [1]. SiC supported catalyst exhibit high performance in automotive exhaust treatment, selective isomerization of paraffinic hydrocarbons, and H2S removal by direct oxidation into elemental sulfur [1]. SiC is also a wide band gap semiconductor for high temperature, high frequency and high voltage power application and optical sensors in the ultraviolet region [2]. These unique properties of SiC are of great interest to material scientists. Several routes have been used to synthesize SiC, for instance, carbothermal reduction of silica [3], sol–gel process [4, 5], decomposition of organic silicon compounds [6], chemical vapor deposition [7], and direct combustion synthesis [8]. Pure SiC was obtained by removal of the impurities through calcination to burn away residual carbon and acid treatment to remove SiO2 and/or catalyst [5, 7]. In the above-mentioned studies, many efforts have been done on the synthesis of high surface area SiC. For instance, SiC, synthesized with activated carbon granulates loaded with small amounts of nickel through fluidized bed chemical vapor deposition, exhibits surface areas ranging between 25 and 80 m2/g [9]. SiC synthesized by SiO vapors and activated charcoal reaches a surface area of 50 m2/g by a reaction at 1200 ◦C for 15 hr and a high (Si + SiO2)/C weight ratio [10]. Recently, porous SiC has been synthesized with a surface area from 112 to 120 m2/g by a modified sol– gel method [5], chemical vapor infiltration and a carbothermal reduction process [3]. In the latter process, MCM-48 silica was filled with pyrolytic carbon using propylene as carbon precursor and treated up to 1250– 1450 ◦C in inert atmosphere leading to the formation of SiC [3].

β-silicon carbide (SiC) powders were synthesized by the carbothermal reduction of methyl-modified silica aerogel/carbon mixtures. The correlations between the phase evolution and morphologies of the SiC powders and the C/SiO2 ratio were investigated. At a C/SiO2 ratio of 3, β-SiC formed at 1425 °C and single-phase SiC powders were obtained at 1525 °C. The methyl groups (-CH3) on the silica aerogel surfaces played important roles in the formation of SiC during the carbothermal reduction. SiC could be synthesized from the silica aerogel/carbon mixtures under lower temperature and C/SiO2 ratios than those needed for quartz or hydrophilic silica. The morphology of the SiC powder depended on the C/SiO2 ratio. A low C/SiO2 ratio resulted in β-SiC powder with spherical morphology, while agglomerates consisting of fine SiC particles were obtained at the C/SiO2 ratio of 3. High-purity SiC powder (99.95%) could be obtained with C/SiO2 = 0.5 and 3 at 1525 °C for 5 h.

An inexpensive sol–gel combustion method using citric acid as fuel has been used to synthesize bismuth titanate, Bi4Ti3O12 nanopowders. Thermogravimetric analysis proved that a calcination temperature of 900 °C is sufficient for the preparation of single-phase bismuth titanate. X-ray diffraction and Fourier transform infrared spectroscopy are used to examine the influence of calcination temperature on the structural growth of the Bi4Ti3O12 nanopowder. The average crystallite size estimated by using the Scherrer method and the Williamson–Hall method was found to increase with calcination temperature. Photoluminescence behavior as a function of calcination temperature was observed at two different excitation wavelengths of 300 nm and 420 nm. The morphology of the particles analyzed using images obtained from field emission scanning electron microscopy displayed irregular, random sized, and spherical-shaped structures. The stoichiometry and purity of the nanopowder are confirmed by energy-dispersive spectroscopy. The broadband dielectric results established the highest dielectric constant (∊r = 450) for a frequency of 100 Hz achieved with a potential capacitance of 138 pF m−2. This establishes Bi4Ti3O12 as a promising dielectric material for achieving high energy density capacitors for the next-generation passive devices.