Carbothermal Reduction Of SiO2 Research Articles

Carbothermal Reduction of SiO2 Using Different Coal

Carbothermal Reduction of SiO2 Using Different Coal

Synthesize and crystallization behavior of SiOC/SiC nanocomposites derived from organosilane slurry residue

AbstractA route preparing SiOC/SiC nanocomposites directly by pyrolysis of organosilane slurry residue was investigated. Organosilane slurry residue's unique composition, containing both silicon and carbon, offers an intriguing platform for developing advanced ceramic materials. The pyrolysis process is examined comprehensively, revealing the chemical reactions and structural changes leading to SiC crystals formation. The phase evolution at various annealing temperatures was revealed. Crystallization behavior in the process were studied. The results reveal that SiOC matrix was generated at annealed temperature 800°C and SiC nanoparticles were formed at 1300°C. In comparison to phase separation of SiOC, carbothermal reduction of SiO2 was domain in SiC formation. This research advances the understanding of SiOC/SiC nanocomposites, highlighting the value of repurposing industrial byproducts for sustainable and innovative materials development.

Sustainable synthesis of silicon carbide from sludge waste generated in organosilane industry

This study uses organosilane waste, a byproduct of the organosilane industry, to produce SiC particles through an accessible and effective method. Thermodynamic analysis was adopted to provide evidence of this route followed by exploring the effects of carbon content, time and temperature on SiC purity, crystallinity of, and the Si recovery ratio. The maximum purity of SiC of 88.4% and Si recovery of 95% was achieved at a temperature of 1750 °C, time of 45 min, and sludge waste: petroleum coke ratio of 2.8:1. The mechanism of the associated reaction is explained in three parts: phase separation of SiOC, nucleation in Si melt and carbothermal reduction of SiO2. This sustainable approach repurposes sludge waste, which contributes to environmental preservation and resource efficiency.

Synthesis of β-SiC powders by the carbothermal reduction of porous SiO2–C hybrid precursors with controlled surface area

SiO2–C precursors with various surface areas were derived from tetraethyl orthosilicate and phenolic resin as Si and C sources, respectively, by a modified sol–gel process using the in situ precipitation of phenol resin in a prepared wet gel. The surface area of the SiO2–C precursors was varied from 20 to 175 m2/g by changing the C/Si molar ratio in the preform. β-SiC powders were synthesized using carbothermal reduction in vacuum at the temperature range of 1200–1600 °C. The effects of the temperature and heat treatment time as well as that of the surface area of the preform on the formation of β-SiC powders were studied. It was determined that the formation of β-SiC started at 1200 °C and was considerably promoted as the heat treatment temperature and time further increased during the carbothermal reduction of SiO2–C preforms with high surface area. When high surface area SiO2–C preforms were used, highly crystalline SiC powders were synthesized at 1600 °C in vacuum with a high yield of 85%.

WxC-β-SiC Nanocomposite Catalysts Used in Aqueous Phase Hydrogenation of Furfural.

This study investigates the effects of the addition of tungsten on the structure, phase composition, textural properties and activities of β-SiC-based catalysts in the aqueous phase hydrogenation of furfural. Carbothermal reduction of SiO2 in the presence of WO3 at 1550 °C in argon resulted in the formation of WxC-β-SiC nanocomposite powders with significant variations in particle morphology and content of WxC-tipped β-SiC nano-whiskers, as revealed by TEM and SEM-EDS. The specific surface area (SSA) of the nanocomposite strongly depended on the amount of tungsten and had a notable impact on its catalytic properties for the production of furfuryl alcohol (FA) and tetrahydrofurfuryl alcohol (THFA). Nanocomposite WxC-β-SiC catalysts with 10 wt % W in the starting mixture had the highest SSA and the smallest WxC crystallites. Some 10 wt % W nanocomposite catalysts demonstrated up to 90% yield of THFA, in particular in the reduction of furfural derived from biomass, although the reproducible performance of such catalysts has yet to be achieved.

Low‐Temperature Molten‐Salt Production of Silicon Nanowires by the Electrochemical Reduction of CaSiO3

AbstractSilicon is an extremely important technological material, but its current industrial production by the carbothermic reduction of SiO2 is energy intensive and generates CO2 emissions. Herein, we developed a more sustainable method to produce silicon nanowires (Si NWs) in bulk quantities through the direct electrochemical reduction of CaSiO3, an abundant and inexpensive Si source soluble in molten salts, at a low temperature of 650 °C by using low‐melting‐point ternary molten salts CaCl2–MgCl2–NaCl, which still retains high CaSiO3 solubility, and a supporting electrolyte of CaO, which facilitates the transport of O2− anions, drastically improves the reaction kinetics, and enables the electrolysis at low temperatures. The Si nanowire product can be used as high‐capacity Li‐ion battery anode materials with excellent cycling performance. This environmentally friendly strategy for the practical production of Si at lower temperatures can be applied to other molten salt systems and is also promising for waste glass and coal ash recycling.

Low‐Temperature Molten‐Salt Production of Silicon Nanowires by the Electrochemical Reduction of CaSiO3

Silicon is an extremely important technological material, but its current industrial production by the carbothermic reduction of SiO2 is energy intensive and generates CO2 emissions. Herein, we developed a more sustainable method to produce silicon nanowires (Si NWs) in bulk quantities through the direct electrochemical reduction of CaSiO3 , an abundant and inexpensive Si source soluble in molten salts, at a low temperature of 650 °C by using low-melting-point ternary molten salts CaCl2 -MgCl2 -NaCl, which still retains high CaSiO3 solubility, and a supporting electrolyte of CaO, which facilitates the transport of O2- anions, drastically improves the reaction kinetics, and enables the electrolysis at low temperatures. The Si nanowire product can be used as high-capacity Li-ion battery anode materials with excellent cycling performance. This environmentally friendly strategy for the practical production of Si at lower temperatures can be applied to other molten salt systems and is also promising for waste glass and coal ash recycling.

Ultralight, Strong, Three-Dimensional SiC Structures.

Ultralight and strong three-dimensional (3D) silicon carbide (SiC) structures have been generated by the carbothermal reduction of SiO with a graphene foam (GF). The resulting SiC foams have an average height of 2 mm and density ranging between 9 and 17 mg cm(-3). They are the lightest reported SiC structures. They consist of hollow struts made from ultrathin SiC flakes and long 1D SiC nanowires growing from the trusses, edges, and defect sites between layers. AFM results revealed an average flake thickness of 2-3 nm and lateral size of 2 μm. In-situ compression tests in the scanning electron microscope (SEM) show that, compared with most of the existing lightweight foams, the present 3D SiC exhibited superior compression strengths and significant recovery after compression strains of about 70%.

Synthesis of ceramics by sol–gel method in molybdenum, silicon and carbon containing systems. Thermogravimetric studies

The results of investigations on synthesis of ceramics in nanometric systems containing molybdenum compounds, silicon compounds and active carbon have been presented. As precursors ammonium molybdatetetrahydrate ((NH4)6Mo7O24 4H2O) and tetraethyl orthosilicate (Si(OC2H5)4) were used. The samples for analysis were obtained by sol–gel method. The course of the process was investigated by thermogravimetric method. The gaseous products were analysed by mass spectrometry. X’ray diffraction (XRD) method was used for identification of solid phases, and morphology of the samples was studied by scanning electron microscopy (SEM). The process proceeded in the following way. At temperature t⩽673K (NH4)6Mo7O24 4H2O decomposes into MoO3. Then at temperature range of 1046⩽t⩽1065K MoO3 is reduced into MoO2 (or also into Mo). Synthesis of Mo2C proceeds at temperature in the order of 1273K. Before the carbothermal reduction of SiO2 and synthesis of compounds containing molybdenum and silicon we have the Mo2C–SiO2-active carbon mixtures. In one stage, at temperature of 1523K in argon, the synthesis of SiC and the synthesis of compounds containing molybdenum and silicon takes place. In the wide range of initial compositions of the mixtures Mo4.8Si3C0.6 was obtained as the main phase.

The Synthesis and Photoluminescence of 3C-SiC Nanorods

The 3C-SiC nanorods were grown by using carbothermal reduction of SiO\(_{2}\) without any catalyst. The intensive broad photoluminescence peak around 480-500 nm was observed at room temperature. The 3C-SiC nanorods with green -- blue emitting light may have great application in display devices and light emitting diodes.

Fabrication of High-Porosity Silicon Nitride Ceramics with Excellent Mechanical Properties

High-porosity silicon nitride ceramics with excellent mechanical properties were fabricated by the carbothermal reduction of SiO2. The influences of sintering conditions on microstructure and mechanical properties were studied. The results showed that microstructure and mechanical properties of porous silicon nitride ceramics were dependent mostly on the sintering conditions. The sintered porous silicon nitride ceramics exhibited the formation of fibrous microstructure with submicrometer-sized, high-aspect ratio b-Si3N4 grains, and uniform pore structure. Porous Si3N4 ceramics with a porosity of about 70%, and a flexural strength of about 70 MPa were obtained by sintering at 1750°C, with lower rate of temperature rise and no retaining time. The high strength was attributed to fine, high-aspect ratio b-Si3N4 grains and uniform pores between grains.

ChemInform Abstract: Synthesis of Pentacoordinate Silicon Complexes from SiO2

THE potential role of inorganic and organometallic silicon compounds in the development of new chemical reagents, polymers, glasses and ceramics1 is limited at present by the paucity of simple silicon-containing starting materials. Whereas industrial carbon-based chemistry can draw on the diversity of compounds produced from crude oil, coal or other natural sources, silicon chemistry2 relies almost exclusively on the carbothermal reduction of SiO2 to silicon. This is then transformed into feedstock chemicals by reaction with HCl, or by routes such as the 'direct process' for making methylchlorosilanes2, in which silicon is reacted with methyl chloride at 200–350°C over a copper/tin catalyst. Organosilicon compounds are in demand in fields ranging from organic synthesis to ceramics to the electronics industry. New synthetic routes to these materials are therefore highly desirable, especially if they rely on low-cost SiO2 and on rocessing methods that avoid the energy-intensive and equipment-intensive carbothermal reduction step which currently precedes almost all silicon chemistry. Here we describe a direct process in which SiO2 is reacted with ethylene glycol and an alkali base to produce highly reactive, pentacoordinate silicates which provide access to a wide variety of new silicon compounds.

Synthesis of Hierarchical Tree-Like and Jellyfish-Like Silicon Oxide Nanostructures

Hierarchical tree-like and jellyfish-like SiOx nanostructures have been synthesized by annealing a mixture of carbon coated Ni nanoparticles (Ni@C) and SiO2 powers under argon atmosphere at 1400 degrees C. The synthesized products were characterized by electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The tree-like SiOx nanostructures consisting of the trunks and many branches and subbranches with diminishing diameters have been observed for the first time. The diameters of the trunks are about 150-1000 nm, and the branches become more slender for each branching, ultimately to 20-40 nm in diameter for the ends. The jellyfish-like SiOx nanostructures are constructed by the catalyst heads with sizes of about 1-10 microm and many connected quasi-aligned SiOx nanowires with diameters about 20-40 nm. The Ni species of the Ni@C nanoparticles acts as the catalyst and the surface carbon as the reducing agent for carbothermal reduction of SiO2. The experimental results suggest that the formation of different SiOx nanostructures mainly depend on the dimensions of the congregated Ni catalyst droplets during the reaction process and the growth mechanism is reasonably discussed.

Synthesis of Single-Phase, Hexagonal Plate-Like Al<sub>4</sub>SiC<sub>4</sub> Powder

Single-phase and hexagonal plate-like Al4SiC4 powder was successfully synthesized using a mixture of Al(OH)3, SiO2 and carbon via a carbothermal reduction process. Two-step reaction was compartmentally observed during the calcination; the carbothermal reduction of SiO2 between 1300 and 1600oC and that of Al2O3 above 1500oC. The mechanisms which were responsible for the synthesis of the ternary carbide (Al4SiC4) powder were discussed.

Direct Formation of SiO2 Nanohole Arrays via Iron Nanoparticle-Induced Carbothermal Reduction

Hexagonally patterned SiO2 nanohole arrays having sub-10 nm of width were directly formed via carbothermal reduction of SiO2 with carbon-dissolved iron nanoparticles (NPs) (C(on iron NPs, s) + SiO2(s) ↔ SiO(g) + CO(g)). Iron NPs prepared by hydroxylamine-mediated synthesis method resulted in not only nanoholes but also nanotrenches because the diameter of these iron NPs is suitable for the growth of single-walled carbon nanotubes (SWNTs) that further react with underneath SiO2 to produce nanotrenches. Higher yields of nanoholes were obtained by using larger-sized iron NPs (diameter: 3−8 nm) prepared from ferritins and by reducing the amount of active carbon precursor sources during the reaction, by which the growth of SWNTs were substantially suppressed. SiO2 nanohole arrays were then obtained from hexagonally self-arrayed iron NPs, which were fabricated using polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) micelles. In addition to the reactivity of carbothermal reduction, interparticular distance of ...

Synthesis of mono-phase, hexagonal plate-like Al<sub>4</sub>SiC<sub>4</sub> powder via a carbothermal reduction process

Mono-phase and hexagonal plate-like Al 4 SiC 4 powders were successfully synthesized using a mixture of Al(OH) 3 , SiO 2 and phenolic resin via the carbothermal reduction process. Two-step reaction was compartmentally observed during calcination; the carbothermal reduction of SiO 2 between 1300 and 1600°C and that of Al 2 O 3 above 1500°C. X-ray diffraction data indicated the orientation of the compacted powders along c-axis due to the stacking of plate-like Al 4 SiC 4 powders. Microscopic observation showed that the synthesized powders were mainly hexagonal platelets. The main synthetic mechanism of the ternary carbide powder during the carbothermal reduction process was gas-solid reaction. Possible reaction mechanisms which are responsible for the synthesis of Al 4 SiC 4 by the carbothermal reduction process are discussed.

Silicon carbide transport during carbothermic reduction of SiO2: Thermodynamic evaluation and experimental study

Mass-transfer processes during the high-temperature carbothermic reduction of silicon dioxide have been studied using thermodynamic modeling. The chemical vapor transport of silicon carbide has been investigated using SiO2 + xSiC mixtures—major reaction products in the SiO2-C system—as examples. Thermodynamic modeling results indicate that the vapor transport of silicon carbide is possible at temperatures from 1300 to 1500°C, and that the major gaseous species involved are Si and CO. Vapor transport processes have been studied experimentally. It is shown that the thermal reaction between carbon monoxide and silicon leads not only to direct conversion of silicon particles to silicon carbide but also to the growth of silicon oxycarbide fibers. The synthesized material has been characterized by x-ray diffraction and high-resolution optical microscopy.

Low-cost preparation of Si 3N 4–SiC micro/nano composites by in-situ carbothermal reduction of silica in silicon nitride matrix

SiC/Si 3N 4 nano/micro composites were prepared from a mixture of α-Si 3N 4, amorphous carbon (carbon black), and Y 2O 3 by carbothermal reduction of SiO 2 present at the surface of Si 3N 4 matrix grains, or added deliberately to the starting mixture. A special heating regime allowed the outgassing of CO(g) (a product of carbothermal reduction) and reduced the residual porosity to less than 2%. The inter- and intragranular SiC inclusions containing the amorphous oxygen-rich layer at the interface between SiC and the Si 3N 4 grains were present, originating from the reaction of free carbon with the silica melt. The reaction consumes silica in the grain boundary phase. The change of the grain boundary chemistry influences both room and high temperature properties of the nanocomposite.

Preparation of Si<sub>3</sub>N<sub>4</sub> from Carbothermal Reduction of SiO Employing the CRTA Method

The synthesis processes of Si 3 N 4 from the carbothermal reduction of SiO and SiO 2 , respectively, are studied. It has been concluded that the reaction temperature is lower if SiO instead of silica is used as raw material. The use of the Constant Rate Thermal Analysis (CRTA) method allows a silicon nitride to be obtained with an average crystallite size of 1 μm, a narrow size distribution, and a percentage of alpha-silicon nitride higher than 98%.

Carbon reduction reaction in the Y2O3–SiO2 glass system at high temperature

Abstract In order to assess the role of carbon with respect to the grain boundary chemistry of Si3N4-based ceramics model experiments were performed. Y2O3–SiO2 glass systems with various amount of carbon (from 1 to 30 wt.%) were prepared by high-temperature treatment in a graphite furnace. High carbon activity of the furnace atmosphere was observed. EDX analysis proved the formation of SiC by the carbothermal reduction of SiO2 either in the melt or in the solid state. The melting temperature of the Y2O3–SiO2 system is strongly dependent on the amount of reduced SiO2. XRD analysis of the products documented the presence of Y2Si2O7, Y2SiO5 and Y2O3 crystalline phases in that order with an increasing amount of free C in the starting mixture. The reduction of Y2O3 was not confirmed.