Reduction Of Silica Research Articles

Electrochemical Reduction of Silicon Oxide and Codeposition of Al-Si Alloy from Cryolite Molten Salt

Electrochemical Reduction of Silicon Oxide and Codeposition of Al-Si Alloy from Cryolite Molten Salt

Microstructure Evaluation and Impurities in La Containing Silicon Oxynitrides.

Oxynitride glasses are not yet commercialised primarily due to the impurities present in the network of these glasses. In this work, we investigated the microstructure and instinctive defects in nitrogen rich La−Si−O−N glasses. Glasses were prepared by heating a powder mixture of pure La metal, Si3N4, and SiO2 in a nitrogen atmosphere at 1650–1800 °C. The microstructure and impurities in the glasses were examined by optical microscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy in conjunction with electron energy-loss spectroscopy. Analyses showed that the glasses contain a small amount of spherical metal silicide particles, mostly amorphous or poorly crystalline, and having sizes typically ranging from 1 µm and less. The amount of silicide was estimated to be less than 2 vol. %. There was no systematic relation between silicide formation and glass composition or preparation temperature. The microstructure examination revealed that the opacity of these nitrogen rich glasses is due to the elemental Si arise from the decomposition reaction of silicon nitride and silicon oxide, at a high temperature above ~1600 °C and from the metallic silicide particles formed by the reduction of silicon oxide and silicon nitride at an early stage of reaction to form a silicide intermetallic with the La metal.

New Methods of Obtaining Al–Si Alloys Using Amorphous Microsilica

The work presents the calculations of enthalpy of formation as well as Gibbs energy of reduction of silicon dioxide by aluminum. This way, the possibility of producing Al–Si alloys using amorphous silica fume has been established. The influence of alloying additives and impurities on the silicon reduction process has been determined. The possibility of using magnesium as a surface-active additive, which allows for the removal of oxygen from the surface of dispersed particles and the reduction of silicon, has been demonstrated. Effective methods for producing hypoeutectic and hypereutectic Al–Si alloys using amorphous silica fume have been developed. Alloys with a silicon content exceeding 6 wt% were obtained by blowing preheated (t = 300 °C) amorphous silica fume into the aluminum melt (t = 900 °C) along with the stream of argon followed by intense mixing. Alloys with a silicon content exceeding 16 wt% were manufactured by induction melting of a silicon-containing mixture (60% SiO2, 40% Al + 20% 3NaF·2AlF3) subjected to the presintering (t = 800 °C) when the amorphous silica fume was reduced to crystalline silicon. It has been established that crystalline silicon, which is formed during the roasting of the tableted burden (as a result of reactions in solid phases), is smoothly absorbed by the aluminum melt. Aluminum oxide, obtained during the redox reaction, dissolves in cryolite, after which aluminum and silicon are fused together and transferred to the melt. Industrial implementation of the proposed methods will result in the improved efficiency of the existing process of manufacturing Al–Si alloys, as the energy-intensive stage of the crystalline silicon production is partially excluded, as well as reduce adverse environmental impact.

Reduction of silicon dioxide from bamboo leaves and its analysis using energy dispersive x-ray and fourier transform-infrared

Silicon dioxide or silica from the organic materials such as bamboo leaf ash (BLA) was interesting because of its large content of 76-80% and it was the main ingredient in glass and solar cell industries. The objective was to study the effect of temperature rate and the acid leaching to silica content in bamboo leaves. This study consists of two main stages, namely 1) ashing the leaves which was conducted through burning the dry leaves and ashing the bamboo leaves charcoal with temperature rates of 0.3, 0.4, and 0.5 °C/min, and 2) reducting the silica which was conducted through leaching the ash with HCl 3% and then heating in a furnace. The results showed that BLA has a yield of 18.10 - 18.64% to dried bamboo leaves. Silica at rates of 0.3, 0.4, and 0.5 °C/min resulted in purity levels of 65.85, 74.49, and 72.69%, respectively. Silica still contained a low percentage impurities, namely rubidium oxide, aluminum oxide, and iron oxide. In addition, FTIR analysis showed that the silica rates of 0.3, 0.4, and 0.5 °C/min have absorption band at wave numbers of 1095 cm−1, 802 cm−1 and 455-463 cm−1 which indicated the asymmetric stretching vibration and bending vibration Si-O of siloxane groups (Si-O-Si) with force constant of 1030.531 N.m−1.

Carbon nanofibers–SiO2 composites: Preparation and characterization

A method has been developed for preparing carbon fibers–SiO2 composites using oligomethylhydridesiloxane (OMHS) as the precursor for SiO2. The presence of active hydrogen in OMHS made it possible to attain chemical interaction between the surface of carbon nanofibers (CNFs) and the applied silicon oxide layer. The oxidation rate of CNF–SiO2 composite is found to be lower by about one order of magnitude compared to that of the as-synthesized CNF. The thermal stability of CNF–SiO2 composites has been studied. Under an inert atmosphere, CNF–SiO2 composite has thermal stability up to 1300°C. At temperatures above 1350°C, silicon carbide (SiC) fibers are formed as a result of the carbothermal reduction of silicon oxide.

New technologies for production of polycrystalline silicon for solar power engineering

Problems of production of polycrystalline silicon for solar cells at present and in the near future are considered. New promising technologies (implemented already for small-scale production) and some unique recent developments are presented. In particular, the process of reduction of silicon oxides in the gaseous phase is very promising for production of high-purity silicon.

Preparation of High-Purity Silicon for Solar Cells

This article addresses the problems in the preparation of high-purity silicon for solar cells. The growing application field of silicon solar cells requires a substantial reduction in the cost of semiconductor-grade silicon, which is currently produced by the classical trichlorosilane process. Here, we analyze alternative processes for the preparation of solar-grade silicon: the reduction of volatile silicon compounds, refining of metallurgical-grade silicon, reduction of silicon fluorides, and reduction of silicon dioxide. We believe that carbothermal reduction followed by the refining of melted silicon is the most attractive process from the viewpoint of manufacturing cost.

Silicon carbide polycrystalline fibers and single-crystal whiskers

The origin of the high inhomogeneity of powders of nonoxide refractory compounds, related to the chemical nature of the compounds and the preparation procedure (usually, solid-state reactions) is considered. Conclusive evidence is presented that vapor transport reactions have considerable potential for the reproducible synthesis of such compounds. It is shown that carbothermic reduction of silicon dioxide can be run as a vapor transport reaction using activated carbon fibers as a reductant. The forming polycrystalline SiC fibers are similar in particle morphology to the parent carbon fibers, suggesting that the reaction proceeds through the incorporation of silicon into the lattice of amorphous carbon. Experimental data are presented for the first time which demonstrate that, under similar process conditions, silicon carbide can be obtained in the form of polycrystalline fibers, single-crystal whiskers, or fine powder. The reaction products differ not only in morphology but also in the crystal structure of SiC (α or β form). The mechanisms of α- and β-SiC nucleation and growth are discussed.

Production of metallurgical silicon of enhanced quality for land-based solar cells

1. Based on a thermodynamic analysis we determined the conditions of the process of reduction of silicon dioxide by silicon carbide that yields metallurgical silicon of enhanced quality, namely,T=2450–2600 K,X=1.4–1.6, andp=0.1 MPa. 2. We have obtained low-temperature silicon carbide from a lumped charge containing disperse silicon dioxide and gas black. The bonding agent was silica gel. 3. The obtained metallurgical silicon of enhanced quality with a content of boron and phosphorus at a level of 1 apm (each) can be used for the production of solar cells after plasmochemical refining.

Kinetics of synthesis of silicon carbide by carbothermal reduction of silicon dioxide

Kinetics of synthesis of silicon carbide by carbothermal reduction of silicon dioxide

X-ray Photoelectron Spectroscopic Studies of Cu-AI alloy/SiO2 Interfaces

AbstractCu-Al alloys have been recommended for application as the diffusion barriers/adhesion promoters for advanced copper based metallization schemes. In this study interfacial reaction between Cu-Al alloy/SiO2 is investigated by x-ray photoelectron spectroscopy (XPS). A set of thin Cu-Al alloy films, about 30Å in thickness, are deposited on SiO2 substrates. These were directly examined by XPS. This is followed by a study of the interface formation during bias temperature stressing (BTS) of metal/dielectric interfaces in Cu/Cu-5at.%AI/SiO2 subjected to the electrical testing. Core-level spectra of silicon and aluminum obtained indicate that the reduction of silicon dioxide initiates at room temperature when the aluminum concentration in the copper alloys reaches about 5 atomic percent. The silicon diffusion into metal or vice versa is found to be suppressed during the low temperature anneal (300°C) by the Al2O3 interfacial layer. Also, a difference is present in the observed chemical states and interfacial reaction progressing between sputter and electron-beam deposited films. The films of Cu doped with Al appear to act as a suitable diffusion barrier and adhesion promoter between SiO2 and Cu.

Phase Transformations in Silicon-containing Solid Sample During Synthesis of Silicon Carbide Through Carbothermal Reduction of Silicon Dioxide

Phase Transformations in Silicon-containing Solid Sample During Synthesis of Silicon Carbide Through Carbothermal Reduction of Silicon Dioxide

Effect of contact area on synthesis of silicon carbide through carbothermal reduction of silicon dioxide

Effect of contact area on synthesis of silicon carbide through carbothermal reduction of silicon dioxide

Reduction of silicon dioxide by aluminum in metal–oxide–semiconductor structures

The reduction of SiO2 by Al was studied in Al/SiO2/Si structures above 350 °C. It was found that Al displaces Si in the oxide, forming an Al–O compound with an Al:O concentration ratio between 1:1 and 1.3:1. In the reacted areas, less than 1 at. % Si is left in what was originally a pure SiO2 matrix. The activation energy for the reaction in a pyrogenic oxide is approximately 2 eV. The reaction was found to be responsible for electrical failure of diodes manufactured using Al/SiO2/Si technology.

Silica Porous Glasses With Silicon Impregnations

ABSTRACTQuantum-size silicon enriched regions were formed in silica porous glasses obtained by three different technologies. Processing in the spark discharge and carbon reduction of silicon dioxide in the solid phase were performed for this purpose. All fabricated specimens have been investigated in relation to their electrical and photoluminescence (PL) properties. A pronounced increase of visible luminescence and single-type changes in the a.c. conductivity were registered in all cases.

Optical sensing technique for in situ determination of gas components at elevated temperature by infrared spectroscopy

A technique for the in situ determination of gas components such as CO, CO 2 and H 2O, at pyrometallugical temperatures of more than 1000°C, has been developed in the present investigation. Gases in the experimental furnace are monitored by an infrared optical sensor with a Fourier transform infrared (FT-IR) spectrometer. The infrared optical sensor consists of a water-cooled probe, an infrared optical fiber and a zinc selenide lens. The contents of CO, CO 2 and H 2O are measured at 800–1600°C by this technique, demonstrating that the minimum content of CO detected is less than 100 ppm with an optical depth of 200 mm at 1550°C. Furthermore, changes in partial pressure of gases evolved during the reduction of silicon dioxide (SiO 2) by graphite can be quantitatively analyzed as a practical application.

Free energy minimization calculation of complex chemical equilibria: Reduction of silicon dioxide with carbon at high temperature

For large systems, minimization of the Gibbs free energy becomes a more attractive method of solving for equilibrium compositions since knowledge of the reactions occurring in the system, and thus equilibrium constants, is not required.

ニッケル基超合金へのアルミニウム-珪素複合拡散被覆

The aluminum-silicon multi-component diffusion coating, using the powder pack process, was applied to nickel and Inconel X-750 to investigate the oxidation resistance and the high-temperature corrosion resistance of the specimens.The results obtained are as follows:(1) Effects of the blending ratio of silicon in the pack material on the high-temperature oxidation resistance were examined. It was found that when 24 mass% aluminum, 6 mass% silicon, 67 mass% alumina and 3 mass% ammonium chloride were used, a coating with excellent high-temperature oxidation resistance was obtained.(2) The aluminum-silicon multi-component diffusion coating using pack material containing more than 6 mass% silicon, and another coating by reduction of silicon dioxide with aluminum, were tried, but neither was effective in improving the high-temperature oxidation resistance.(3) In an Al-Si treated layer containing 6 mass% silicon, the presence of a small amount of Si was observed at the interface between the treated layer and the basis metal before oxidation. It was also confirmed that the oxide layer consisted of silicon oxide on the surface and aluminum oxide beneath.(4) The specimen treated by the aluminum-silicon multi-component diffusion coating showed excellent resistance to high-temperature corrosion, which may be caused by synthetic ashes, V2O5-Na2SO4 and Na2SO4-NaCl. Particularly the specimen treated by the aluminum-silicon multi-component diffusion coating using silicon dioxide has better corrosion resistance than that treated by aluminum-silicon multi-component diffusion coating using silicon.

Decomposition and Reduction of Silicon Dioxide in a Low-Temperature Plasma Jet

Decomposition and Reduction of Silicon Dioxide in a Low-Temperature Plasma Jet

Decomposition and Reduction of Silicon Dioxide in a Low-Temperature Plasma Jet

Decomposition and Reduction of Silicon Dioxide in a Low-Temperature Plasma Jet