Stoichiometry of the C + SiO2 Reaction | Request PDF

Or you want a quick look:

The reaction of one-to-one molar carbon/silica powder mixtures was studied using simultaneous thermogravimetric analysis and mass spectroscopy with crystalline and amorphous silica. Reaction proceeded via a two-stage path in which there are at least three identifiable competing global reactions. During the first stage, silicon carbide is formed along with small amounts of silicon monoxide. The most likely reaction path during this stage is the following: SiO2(s) + C(s) → SiO(g) + CO(g); SiO(g) + 2C(s) → SiC(s) + CO(g). The second stage consists of reactions between silica with silicon carbide which form silicon monoxide and, where conditions permit, may also form silicon metal. The major reaction during this stage is 2SiO2(g) + SiC(s) → 3SiO(g) + CO(g).

Stoichiometry of the C + SiO2 Reaction | Request PDF

To read the full-text of this research,

you can request a copy directly from the authors.

[external_link_head]

... Chemical vapor deposition (CVD) method has been widely utilized in fabricating coating. However, the SiC coating layers for complex shape components can be easily formed by chemical vapor reaction method [6,7]. The SiC conversion layer obtained by such solid-vapor reaction has good adherence with graphite matrix. ...

... The conversion coating process is based on carbothermal reduction, in which silica reduction is carried out with carbon source. This process is independent of the molar ratio of silica to carbon; in the end, silica reduction with SiC source is excluded in overall process (SiO 2 + 3C → SiC + 2CO) [6]. Of particular importance to SiC phase nucleation is SiO generation from silica-carbon reaction [8]. ...

... bar. The SiO vapor partial pressure is calculated from the some data regarding carbothermal reduction process [6,16,17], while reaction zone (2) (1) silica melt in graphite crucible would have rather high vapor pressure as compared to that of reaction zone (1). Therefore, it seemed that the specimen in reaction zone (2) is exposed to higher SiO vapor pressure than that of reaction zone (1). ...

The β -SiC conversion coatings were successfully synthesized by the SiO(v)-graphite(s) reaction between silica powder and graphite specimen. This paper is to describe the effects on the characteristics of the SiC conversion coatings, fabricated according to two different reaction conditions. FE-SEM, FE-TEM microstructural morphologies, XRD patterns, pore size distribution, and oxidation behavior of the SiC-coated graphite were investigated. In the XRD pattern and SAD pattern, the coating layers showed cubic SiC peak as well as hexagonal SiC peak. The SiC coatings showed somewhat different characteristics with the reaction conditions according to the position arrangement of the graphite samples. The SiC coating on graphite, prepared in reaction zone (2), shows higher intensity of beta-SiC main peak (111) in XRD pattern as well as rather lower porosity and smaller main pore size peak under 1 μ m.

... Moreover, N content increased from 35.369 wt% to 36.609 wt% probably due to the formation of Si 3 N 4 from SiO 2 via a carbothermal reduction and nitridation process [32]. It was reported that SiO 2 could also be carbothermally reduced to SiO(g) or SiC at 1500°C [36]. Besides, C and Si 3 N 4 could coexist under the used reaction condition (1500°C, 1 MPa N 2 ), according to the thermodynamic stability range of Si 3 N 4 /SiC system relative to temperature and nitrogen pressure in a previous report [37]. ...

... Thus, the residual carbon inside the Si 3 N 4 samples was probably derived from unreacted carbon and generated SiC. Based on the discussions above, the following reactions probably occurred during the 1st-step sintering of Si 3 N 4 samples [28,32,36]: ...

In order to fabricate Si3N4 ceramic with enhanced thermal conductivity, 93 mol%α-Si3N4-2 mol%Yb2O3-5 mol%MgO powder mixture was doped with 5 mol% carbon, and sintered firstly at 1500 °C for 8 h and subsequently at 1900 °C for 12 h under 1 MPa nitrogen pressure. During the first-step sintering, the carbothermal reduction process significantly reduced the oxygen content and increased the N/O ratio of intergranular secondary phase, resulting in the precipitation of Yb2Si4O7N2 crystalline phase, higher β-Si3N4 content and larger rod-like β-Si3N4 grains in the semi-finished Si3N4 sample. After the second-step sintering, the final dense Si3N4 product acquired coarser elongated grains, lower lattice oxygen content, tighter Si3N4-Si3N4 interfaces and more devitrified intergranular phase due to the further carbothermal reduction of oxynitride secondary phase. Consequently, the addition of carbon enabled Si3N4 ceramic to gain a significant increase of ∼25.5% in thermal conductivity from 102 to 128 W∙m⁻¹ K⁻¹.

... In general, the chemical vapor deposition (CVD) process has been widely utilized to form such coatings. It seems that layers of SiC coating for components with complex shapes, such as spherical pebbles, can be more easily formed by the CVR method than by the CVD method [7,8]. ...

... The SiC-coated graphite pebbles, fabricated by silica powder with average particle size of 50 m, showed a substantial improvement on the conversion behavior of the surface region of the graphite into the cubic ␤-SiC phase (Fig. 9). The noticeable difference in the XRD patterns of the SiC coatings is directly related to the amount of SiO vapor, originating from silica powders of two different average particle sizes, that was used in the process [7][8][9][10]. ...

... Actually, the reactions between silica and carbon have been studied for many years because of their industrial importance, such as the production of iron, silicon, and silicon carbide. Experiments have shown that SiO 2 reacts with C to generate SiC and CO under such "metallurgic" conditions, C/SiO 2 1 (e.g., Klinger et al., 1966;Biernacki and Wotzak, 1989a). This is consistent with thermodynamic equilibrium calculations, which indicate that SiC and CO are stable at high temperatures. ...

Impact-induced vapor plumes produce a variety of chemical species, which may play an important role in the evolution of planetary surface environments. In most previous theoretical studies on chemical reactions within impact-induced vapor plumes, only volatile components are considered. Chemical reactions between silicates and volatile components have been neglected. In particular, silica (SiO2) is important because it is the dominant component of silicates. Reactions between silica and carbon under static and carbon-rich “metallurgic” conditions (C/SiO2 ≫ 1) are known to occur to produce CO and SiC. Actual impact vapor plumes, however, cool dynamically and have carbon-poor “meteoritic” composition (C/SiO2 ≪ 1). Reactions under such conditions have not been investigated, and final products in such reaction systems are not known well. Although CO and SiO are thermodynamically stable at high temperatures under carbon-poor conditions, C and SiO2 are stable at low temperatures. Thus, CO may not be able to survive the rapidly cooling process of vapor plumes. In this study, we conduct laser pulse vaporization (LPV) experiments and thermodynamic calculations to examine whether interactions between carbon and silica occur in rapidly cooling vapor plumes with meteoritic chemical compositions. The experimental results indicate that even in rapidly cooling vapor plumes with meteoritic compounds are rather efficiently oxidized by silica-derived oxygen and that substantial amounts of both CO2 and CO are produced. The calculation results also suggest that those oxidation reactions seen in LPV experiments might occur in planetary-scale vapor plumes regardless of impact velocity as long as silicates vaporize.

... A similar phenomenon occurred for the Fe Fig. 2 Comparison of laser scanning confocal microscopy imaging from the center region on the high-carbon steel substrate samples: a HCS-BM, b HCS-1, c HCS-2, d HCS-3, and e HCS-4, with the edge region of the protective layer in a1, b1, c1, d1, and e1, respectively and Si elements, which possess greater bonding properties than Fe and C elements [17], enabling their synthesis into the steel substrate. The stoichiometry of the SiC formation can be explained by two-stage equations [18,19], where H 2 reacts with C to form CH 4 to accelerate reduction: ...

Due to their exceptional properties, low-cost high-carbon steels have long been extensively utilized in many industrial applications. However, their corrosion resistance is poor for many applications and requires further enhancement. Various methods have been developed to achieve this, but they suffer from some limitations. In the work presented herein, a single-stage heat treatment process was applied at low temperature and utilizing waste materials for comparison as new resources, being shown to be a cost-effective approach. In the framework of this study, a multi-hybrid coating structure was developed on the surface of high-carbon steel by applying a single-step heat treatment process and utilizing various waste materials, namely metallurgical slag, glass, and automotive shredder residue (ASR). The results reveal that not only was the process completed in a short time but significant enhancements in the corrosion resistance and hardness performance were achieved. Analyses were performed by high-resolution laser scanning confocal microscopy, electron probe microanalysis (EPMA), focused ion beam-scanning electron microscopy (FIB-SEM), and atomic force microscopy (AFM) in peak force quantitative nanomechanical (PF-QNM) mode. The electrochemical corrosion performance was tested using Tafel method. Both the Young’s modulus and corrosion resistance of the steels treated using the waste materials were improved compared with the base material. This approach opens a new perspective for utilizing waste materials to obtain environmentally sustainable products in a cost-effective fashion, thereby reducing reliance on new resources as well as disposal of waste materials in landfill.

... Recently, we reported the use of waste CD as carbon source to produce SiC nanoparticles. Using silica and conventional carbon sources, many studies [13][14][15][16][17] were carried out to investigate carbothermic reduction kinetics, effect of contact areas, and their mechanisms. However, with regard to replacing conventional carbonaceous material with waste to produce SiC, only a few studies [18,19] were reported in the literature. ...

A significant amount of end-of-life plastics and glass are currently landfilled, incinerated, or just illegally dumped even though conventional plastic and glass recycling practices are well established. This paper describes a novel approach to synthesize silicon carbide (SiC)-bearing product by utilizing waste automotive glass and plastic. The reduction of silica in glass by blend of graphite and plastic (Bakelite) to produce SiC was established experimentally under inert condition at a temperature 1,550 °C. The results from X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy EDS confirm the formation of SiC, and the reaction kinetics and the mechanism of reduction were investigated by means of infrared gas analyzer. Rate constant, k = 12.8 × 10−4 s−1, for the initial stage was measured for overall silica reduction, and the mechanism was established to be predominantly controlled by chemical reactions. This process innovation has two significant advantages: it is a major step toward transforming nonmetallic automotive waste into valuable resources like SiC-containing refractory materials, and it reduces the industry’s reliance on conventional raw materials including quartz and coke which are typically used as silicon and carbon bearing resources.

... Mechanical Properties of the SiC/SiC Composites fibers,18 which accelerated the damage of the composites. The following reactions occur when the temperature exceeded 1500°C26 :SiC 1þx ! SiC þ xC (1) SiC 1þx þ O ! ...

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been studied and developed for high temperature and fusion applications. In this study, SiC/SiC composite was fabricated by polymer impregnation and pyrolysis process with LPVCS, a liquid precursor with active Si–H and -CH=CH2 groups. The cross-link and ceramization processes of LPVCS were studied and SiC/SiC composite was fabricated with LPVCS. The porosity and mechanical properties of the SiC/SiC composite was investigated, and the results indicated that the SiC/SiC composite exhibited low porosity and superior mechanical properties owing to the compact matrix derived from LPVCS.

... Thermodynamically, the reaction in Eq. (1) occurs at 1,650℃, which is significantly lower than the temperatures prevailing in an electric arc furnace operating at temperatures above 2,000℃ [2] [1] [6]. ...

A new technology for the production of high-quality metallurgical-grade silicon (MG-Si) is presented using microwave heating. Advantages are a lower energy consumption combined with a purer MG-Si output. Microwave heating allows to produce silicon in a lab-scale furnace using high purity quartz crucibles. The technology is considered to be a first step in the production cycle towards upgraded metallurgical-grade silicon (UMG-Si). The reaction mechanism in the carbothermic reduction is discussed and how it is affected by a rapid microwave heating of the reaction mixture of silica and carbon. In bench-scale experiments, elemental silicon was produced. An outlook is provided onto a new project that is aimed at studying in detail the reaction mechanism, silicon purity and energy consumption.

... Niu and wang [61] recently reported an application of SiC nanowires covered with platinum as an efficient electrocatalyst for hydrogen adsorption/desorption and methanol oxidation. Various SiC nanostructures such as nanospheres, nanowires, nanorods, nanopowders, and even nanoflowers have been developed [51,56,[62][63][64][65][66]. Special efforts of the researchers were oriented to grow SiC nanoparticles on Si substrates [67,68]. ...

Silicon carbide (SiC) is a promising material due to its unique property to adopt different crystalline polytypes which monitor the band gap and the electronic and optical properties. Despite being an indirect band gap semiconductor, SiC is used in several high-performance electronic and optical devices. SiC has been long recognized as one of the best biocompatible materials, especially in cardiovascular and blood-contacting implants and biomedical devices. In this paper, diverse role of SiC in its nanostructured form has been discussed. It is felt that further experimental and theoretical work would help to better understanding of the various properties of these nanostructures in order to realize their full potentials.

... We observed a loss in carbon, oxygen and silicon content. It is very likely that gaseous products of SiO and CO were formed as it is claimed by Biernacki and Wotzak [35]. Admixtures of iron, phosphorus and potassium were also significant. ...

The biomass of one type cultivated diatoms (Pseudostaurosira trainorii), being a source of 3D-stuctured biosilica and organic matter—the source of carbon, was thermally processed to become an electroactive material in a potential range adequate to become an anode in lithium ion batteries. Carbonized material was characterized by means of selected solid-state physics techniques (XRD, Raman, TGA). It was shown that the pyrolysis temperature (600 °C, 800 °C, 1000 °C) affected structural and electrochemical properties of the electrode material. Biomass carbonized at 600 °C exhibited the best electrochemical properties reaching a specific discharge capacity of 460 mAh g−1 for the 70th cycle. Such a value indicates the possibility of usage of biosilica as an electrode material in energy storage applications.

[external_link offset=1]

... Although, chemical vapor deposition (CVD) has been widely utilized to form coatings, SiC coating layers for components with complex shapes such as spherical pebbles can be more easily formed by the CVR method than by the CVD method [6,7]. In addition, the SiC conversion layer formed via the CVR method adheres well to graphite matrices. ...

READ  Cl2 + H2O → HCl + HClO – Balanced equation

The Helium Cooled Ceramic Reflector (HCCR) Test Blanket Module (TBM), recently planned for installation and testing in the nuclear fusion energy project of International Thermonuclear Experimental Reactor (ITER), uses graphite in the form of pebbles as a neutron reflector, opening the possibility of avoiding the use of a beryllium neutron multiplier. A silicon carbide (SiC) coating should be formed on the graphite pebbles to prohibit the reaction of graphite with steam and/or air and to reinforce the surface strength. In this work, a dense β-SiC coating was formed over the surface of the graphite pebbles by a chemical vapor reaction (CVR) process of the solid–solid (SS) and vapor–solid (VS) reaction of the SiO 2 (s)–C(s)–SiO(v)–CO(v) system. The microstructural features, XRD patterns, pore size distribution, porosity and oxidation behavior of the SiC-coated graphite pebbles were investigated. A SiC coating with a thickness of approximately 30 μm remarkably improved the oxidation resistance and the density of the graphite pebbles. In an isothermal oxidation test conducted at 700 1C, the SiC-coated graphite pebbles showed strong oxidation resistance and a weight loss of approximately 2 wt% over the course of 2 h. This paper describes the major results obtained from our experiments on the CVR-SiC coating of nuclear graphite pebbles, recently conducted in the Korean HCCR TBM team of the ITER project.

The method for carbothermal reduction of spherical particles of amorphous silicon dioxide is developed, and hexagonal alpha-SiC polytype nanocrystals are synthesized. The prepared samples are characterized by X-ray diffraction, Raman spectroscopy, photoluminescence spectroscopy, and electron microscopy. The silicon carbide nanocrystals prepared have sizes in the range 5-50 nm depending on the diameter of initial silicon dioxide particles. A detailed analysis of the positions of the lines in the Raman spectra, their broadening, and shift makes it possible to reliably establish that the samples under investigation predominantly contain the 6 H and 4 H silicon carbide polytypes and insignificant amounts of the 2 H and 3 C phases. The 15 R and 21 R polytypes in the samples are absent. It is noted that the samples are characterized by a substantial size effect: the luminescence intensity of small silicon carbide nanocrystals is more than three times higher than that of large SiC nanocrystals.

A non-conventional preparation way to synthesize a tubular silicon carbide material from carbon fibres by a reactive templating process is presented in this paper. By this way, SiC materials keeping the morphology of the carbon source can be obtained. Particular attention has been paid in this paper to the mechanism of formation of SiC which occurs via a two stages process. In particular, the kinetics of formation of SiC, the structural and textural morphology of the final SiC material have been explained in relationship with the chemical surface properties of the carbon source characterized by the active surface area. The formation of SiC has been also followed by several muti-scale characterization techniques.

Nanocrystalline β-SiC powder was synthesized by thermal plasma in-flight technique. From the transmission electron microscopy, the nanocrystalline product was found to be consisting of nano particles, and nano rods of average diameter 20 nm and length 500 nm. The structural evidence of formation of nanocrystalline β-SiC is observed from the X-ray diffraction studies. The β-phase of the SiC product was also detected through micro-Raman spectrum from two distinct phonon vibration modes at 783 and 982 cm–1. The transmittance peak observed at 817 cm –1in Fourier transform infrared spectroscopy confirms the product as β-SiC.

Kinetic analysis of silicon carbide prepared by carbon-thermal reduction is introduced in this paper. Through the dynamic analysis, kinetic parameters of Si-C are calculated, and it is estimated that the time required reaction materials of different diameter completely converted to SiC at different temperatures. Reaction time is nearly 1 hour long when the reaction particle diameter is 1μm around 1900K.

Nanometer-sized β-SiC were synthesized by carbothermal reduction of silica sol with acetylene carbon black at 1600 °C for 2h. Three kinds (straight, bamboo-like, branch-like) of SiC nanowires were deposited on the graphite plate, while SiC particle agglomerates and nanowires were formed in the graphite crucible. All the nanowires were formed via VS mechanism through the reaction between gaseous SiO and CO produced from the process of carbothermal reduction.

The reactions taking place between coarse grained mixtures of silica (cristobalite) and carbon (graphite) at 1558°C in pure CO as well as mixtures of CO and Ar, have been subjected to a thermogravimetric investigation. A model is developed in the regime where the formation of SiC does not take place. The primary steps are assumed to be: Reaction betweefn SiO 2 and CO to give SiO(g) and CO 2 followed by the reaction between CO 2 and C to give CO. The model predicts the prevailing partial pressure of SiO throughout the charge, and the correlation between observations and model strongly supports the above given reaction mechanism. Enhanced and accelerating reaction rates were observed when the formation of β-SiC took place. It is suggested that this is due to the continuous formation of stable SiC-nucleus on the Csurface and the subsequent shortening of the diffusion path for SiO.

A polyacrylonitrile (PAN)-based carbon fiber-silicon carbide core-shell hybrid (SiC/PAN-CF) was prepared by carbothermal reduction of SiO2/PAN-CF, which was obtained by dip coating a SiO2 sol on the surface of PAN-CF. The surface of the PAN-CF was uniformly covered with the SiC, and the decomposition temperature of SiC/PAN-CF was higher than that of the uncoated PAN-CF. In addition, the thermal conductivity of epoxy composites consisting of PAN-CF or SiC/PAN-CF was measured using a laser flash method. At a 80 wt% filler loading, the thermal conductivity of SiC/PAN-CF-epoxy composite was found to be 0.750 W/mK, which is 2 times higher than that of the PAN-CF-epoxy composite and approximately 3.5 times greater than that of unmodified epoxy resin. Furthermore, the thermal conductivity of SiC/PAN-CF-epoxy composite increased with increasing carbothermal reduction time. This increased thermal conductivity is due to improving the specific surface area and wettability with epoxy matrix, thus resulting in an improved the interfacial adhesion with epoxy matrix.

The SiC/SiO2 deposition was performed to improve the oxidation resistive properties of carbon nanofiber (CNF) from electrospinning at elevated temperatures through sol–gel process. The stabilized polyacrylonitrile (PAN) fibers were coated with SiO2 followed by heat treatment up to 1000 and 1400°C in an inert argon atmosphere. The chemical compositions of the CNFs surface heat-treated were characterized as C, Si and O existing as SiC and SiO2 compounds on the surface. The uniform and continuous coating improved the oxidation resistance of the carbon nanofibers. The residual weight of the composite was 70–80% and mixture of SiC, SiO2 and some residual carbon after exposure to air at 1000°C.

Cubic shells and spherical nanoparticles of-SiC were produced at 1273 K by processing the ceramic precursors formed from the reactions between vapors of organochlorosilanes, Me2SiCl2 ,M eSiCl3 ,M eSiHCl2, and PhSiCl3, and liquid Na at 523-723 K. From Me2SiCl2, a flexible linear polycarbosilane precursor was synthesized and covered the NaCl byproduct surface to form a cubic shape. Hollow cubic -SiC shells were produced after the NaCl templates were removed. From MeSiCl3, a rigid cross-linked polycarbo- silane was produced and phase segregated from the NaCl byproduct. The precursor was transformed into nanoparticleswithoutspecialmorphology.MeSiHCl2producedacross-linkedpolysilaneprecursoratlow temperatures, which can be converted into a mixture of-SiC and Si nanoparticles. At high temperatures, the polysilane converted to polycarbosilane and produced hollow cubic -SiC shells. The carbon-rich PhSiCl3 generated cube-like particles as the final product, which contained -SiC and carbon.

Two sets of tuyere drillings were carried out in a medium-size blast furnace operating with oil injection rates of 70 and 110 kg/thm. This study reports the effect of the oil injection rate on the modification of coke properties as it descends into tuyere-level regions. The changes in the mineralogy, the degree of graphitization, and the reaction rate of tuyere-level cokes with CO2 were characterized using SIROQUANT, X-ray diffraction, and a fixed-bed reactor, respectively. The effect of the injection rate was found to be most distinct in the bosh and raceway regions. High injection rate cokes were distinguished by a greater degree of graphitization, less amount of SiC, and complete absence of the mullite phase. Irrespective of the tested injection rates, the magnitude of ferro silicide phases in the tuyere-level cokes was found to be of similar range. During a higher injection rate, the apparent reaction rates of cokes were marginally lower because of a higher degree of graphitization as well as less amount of adsorbed potassium. The study suggests that the effect of injection rates on the coke properties is mainly influenced by their consequences on the changes in the associated temperature profile of various tuyere-level regions. In both operations, the proportion of −3.0 mm fines at various locations was found to be of similar range. However, a high injection rate campaign indicated a marginally higher proportion of −0.45 mm coke fines, which was attributed to a higher degree of the graphitization of cokes at various tuyere-level locations. The study has implications for improving coal selection criterion and coke performance in a working blast furnace.

SiC powder was synthesized by carbothermal reduction method using silica sol and amylum as reactants in closed and open graphite crucibles, respectively. The phase composition and morphology of the powders were characterized. Formation of phase-pure silicon carbide can be achieved at 1700°C for 1h. Increasing reaction temperature and extending holding time can greatly promote the production of SiC The products synthesized in open graphite crucibles are mainly composed of equiaxial β-SiC particles while those synthesized in closed graphite crucibles are β-SiC particles and nanorods.

C/C–SiC composites were prepared by molten infiltration of silicon powders, using porous C/C composites as frameworks. The porosities of the C/C–SiC composites were about 0.89–2.8 vol%, which is denser than traditional C/C composites. The ablation properties were tested using an oxyacetylene torch. Three annular regions were present on the ablation surface. With increasing pyrocarbon fraction, a white ceramic oxide layer formed from the boundary to the center of the surface. The ablation experimental results also showed that the linear and mass ablation rates of the composites decreased with increasing carbon fraction. Linear SiO2 whiskers of diameter 800 nm and length approximately 3 μm were formed near the boundaries of the ablation surfaces of the C/C–SiC composites produced with low-porosity C/C frameworks. The ablation mechanism of the C/C–SiC composites is discussed, based on a heterogeneous ablation reaction model and a supersaturation assumption.

NbC-SiC micro/nanowires (MNWs) with NbC content varying from 5 to 20 mol.-% were synthesised at updating degrees C via carbothermal reduction utilising silica sol, niobium pentoxide powder and carbon black as starting materials. The synthesis process and growth mechanism of NbC-SiC system were investigated. Results show that the morphology of the synthesised products mainly appears as curve shaped microwires or nanowires. The crystalline consists of both SiC and NbC phases which doped with each other by substitution and interstitial reactions in solid solution. NbC-SiC MNWs were developed by vapour-liquid-solid mechanism according to the existence of liquid droplet phase in the tip at reaction temperature. beta-SiC twin crystal growing along [112] direction was formed in the stem, and NbC polycrystal was dissociated from Nb-Si liquid phase. The varied concentration of Nb and Si in the Nb-Si liquid phase could be a significant reason for the curved growth of NbC-SiC MNWs.

Promising high-temperature glass-ceramic and ceramic composite materials developed at VIAM, are examined. These materials are distinguished by their capability to retain their properties at high temperatures in an oxidative environment, good durability, excellent corrosion properties, low density, and low thermal expansion. In regards to their performance properties these materials are as good as, and in some respects even surpass, the best foreign analogs, making them the only available materials for use in heat-loaded units and the components of prospective articles.

Mesoporous, highly structured silicon carbide (β-SiC) was synthesised from renewable plant materials (two Equisetaceae species) in a one-step carbothermal process at remarkably low temperatures down to 1200 °C. The SiC precursor is a silicon–carbon mixture with finely dispersed carbon prepared by pyrolysis of the organic plant matrix. Yields are 3 to 100% (ωSi/Si related to the silicon deposited in the plant material), depending on reaction temperature and time. IR spectroscopy, X-ray diffraction, and nitrogen sorption prove the formation of high-purity β-SiC with minor inorganic impurities after purification and a high specific surface area of up to 660 m2 g−1. Scanning electron microscopy shows that the plant morphology is maintained in the final SiC. Sedimentation analysis finds a mean particle size (diameters d50) of 20 μm.

In this contribution, we report on the influence of nitrogen-hydrogen plasma treatment on the chemical composition of fused silica surfaces with and without additional argon fluoride laser irradiation. Therefore, the compositions of pristine and plasma treated fused silica samples were investigated by secondary ion mass spectrometry before and after laser irradiation. Transmission data were moreover obtained via UV-VIS spectroscopy. The plasma treatment most likely generates optically active defects such as non-bridging oxygen hole centers (NBOHCs), oxygen-deficiency-related defects (ODCs), and E' centers, which serve as precursor sites for hydrogen saturated defects. The resulting enhanced laser coupling leads to a loss of oxygen from the fused silica network and a further generation of defect centers. Possible explanatory approaches for the observed plasma- and laser-induced changes in carbon, hydrogen, and oxygen content are discussed. This includes the formation of silicon monoxide, hydrogen saturated defects, and nanocrystalline domains in the matrix containing silicon-carbon bonds.

Silicon carbide (SiC) coating on pitch-based carbon fiber (SiC/pitch-CF) was prepared by the carbonization of a SiO2 coating layer onto pitch-CF. SiO2 sol and pitch-CF were mixed together and carbonized in a furnace under argon. The effect of the SiC coating on the thermal properties of pitch-CF was investigated. The thermal conductivity of the SiC/pitch-CF-epoxy composite was measured using the laser flash method. Because of the increase in the contact point of pitch-CF owing to the formation of particulate SiC, the thermal conductivity of SiC/pitch-CF was 38% higher than that of uncoated pitch-based CF when compared with epoxy composites comprising 60 wt% filler loading. However, the thermal conductivity of an epoxy composite comprising SiC/microwave-treated pitch-CF (SiC/M.pitch-CF) was lower than that of the pitch-CF-epoxy composite because of the defects resulting from acid treatment, even though the coating layer was fully covered and uniform compared microwave untreated pitch-CF.

To improve the oxidation resistance of C/C composites, a double SiC protective coating was prepared by a two-step technique. Firstly, the inner SiC layer was prepared by a pack cementation technique, and then an outer uniform and compact SiC coating was obtained by low pressure chemical vapor deposition. The microstructures and phase compositions of the coatings were characterized by SEM, EDS and XRD analyses. Oxidation behaviour of the SiC coated C/C composites was also investigated. It was found that the double SiC coating could protect C/C composites against oxidation at 1773 K in air for 178 h with a mass loss of 1.25%. The coated samples also underwent thermal shocks between 1773 K and room temperature 16 times. The mass loss of the coated C/C composites was only 2.74%. Double SiC layer structures were uniform and dense, and can suppress the generation of thermal stresses, facilitating an excellent anti-oxidation coating.

READ  2 Ag + O2 → 2 AgO – Balanced equation

Silicon carbide is a superior material for the manufacturing of semiconductors. This is where the project on the gaseous phase synthesis of SiC components made of carbon precursors comes in. On the basis of graphite substrates and a reaction with thermally evaporated silicon monoxide in the CVI process (chemical vapor infiltration), silicon carbide with strongly process dependent structural composition is formed. The process can be used for the coating of C substrates as well as for the manufacturing of complex components. With the help of new approaches in process development and via detailed materialographic microstructural analysis, the understanding of gaseous phase synthesis was promoted. The transi-tion of different carbon structures in equivalent silicon carbide structures was verified.

Transpiration cooling in the thermal protection system of hypersonic vehicles still remains a challenge due to the lack of lightweight porous ceramic with excellent permeability. C/SiC/SiO2 porous ceramics with low density and good permeability are fabricated by optimized grinding-mould pressing-sintering process. The influences of different mass ratios between SiC particles and chopped carbon fibers on the microscopic structure, mechanical performance, pore-size distribution and permeability of the porous ceramics are studied systematically. C/SiC/SiO2 porous ceramics with density of 1.092~1.327 g/cm3, compressive strength of 1.55~15.7 MPa, permeability of 5.903×10-8~13.434×10-8 mm2, as well as uniform microstructure and pore-size distribution have been obtained with the increasing of the mass ratios. Notably, the densities and compressive strengths of C/SiC/SiO2 porous ceramics improve gradually but their permeabilities decrease with the increasing of mass ratio between SiC particles and chopped carbon fibers from 0.3:1 to 1:1. The porous ceramics fabricated by optimized processing method can have a potential application in the transpiration cooling.

The present work is the second part of a study conducted with the aim to determine the amount of active sites present on the surface of a biomass char participating in the gasification reaction with CO2 using the temperature programmed desorption (TPD) technique. In part 1, the methodology and experimental results during TPD of partially gasified samples of beech wood char (WC1600) using CO2 as gasification agent are presented. This work focusses on the influence of the main inorganic ash components of WC1600 on the CO2 and CO signals obtained during TPD of partially gasified char samples. Furthermore, an activated carbon with ash content lower than 1 wt-% is impregnated with Ca and K and partially gasified followed by a TPD analysis. CO2 and CO signals obtained during TPD result from decomposition of oxygenated surface complexes and decomposition reactions of ash components. During gasification, three different kinds of sites are present on the surface of the char: stable, reactive and catalytically active sites. The latter are a measure of the catalytic influence of inorganic matter during char gasification. From the analysis of the TPD spectra, it can be concluded that gasification of WC1600 is dominated by the catalytic influence exerted by Ca and K. Formation of oxygenated surface complexes on WC1600 is limited, possibly due to the high temperature at which the sample was pyrolyzed (1600 °C). However, a direct correlation between specific conversion rate and the amount of reactive and catalytically active sites is developed from the experimental results, corrected by the contribution of ash decomposition.

Reactive melt infiltration of Si-based alloys into C preforms and SiC/C composites may be an affordable alternative route to fabricate highly performant light-weighting metal matrix (MMCs) and ceramic matrix (CMCs) composites, as well as to obtain reliable and long-term stable joints. In order to optimize reactive infiltration process and to tailor the joint microstructures, the knowledge of intefacial phenomena including thermodynamics, kinetics and surface properties of involved phases (i.e. metals and ceramics) as well as wettability and reactivity occurring between dissimilar materials is of crucial importance. In the present work, the feasibility study of a novel brazing method using Si-Ti alloys as filler for SiCf/SiC, is reported and supported by the analysis of microstructural evolution and interfacial phenomena observed during the joining process. Namely, the CMC joining was successfully obtained via the reactive infiltration approach. The results obtained were critically discussed and compared with the know-how coming from the previously carried out investigations on the wetting and reactivity of Si-Ti melts in contact with Glassy-C and HP-SiC substrates. In particular, the microstructural evolution of the Si-Ti/C and Si-Ti/SiC interfaces during wetting tests and at the joint of CMC-parts was analyzed and related to the operating conditions.

The contact heating sessile drop and capillary purification methods were applied for a fundamental study concerning the wettability and reactivity of liquid Si-16.2at%Ti alloy (eutectic composition) in contact with Glassy Carbon and SiC at T = 1450°C under an Ar atmosphere. Different spreading stages with different slopes, depending on the starting conditions of the materials used, where observed. On the contrary, the final contact angle value seemed not affected and the values of θ ≈ 44°± 2 and θ ≈ 42°± 2 where displayed on Glassy Carbon and SiC, respectively. The solidified Si-Ti eutectics/GC and Si-Ti eutectics/SiC samples were examined both at the top of the drop and at the cross-section by SEM/EDS. The presence of a SiC layer as unique reaction product at the Si-Ti eutectics/GC interface, confirmed that wettability is mainly driven by reactivity. Contrarily, as non-reactive system, at the Si-Ti eutectics/SiC interface a weak dissolution of SiC substrate was detected.

A kind of glucose derived carbon‐rich silicon oxycarbide (glucose‐SiOC) nanocomposite with excellent electromagnetic wave absorbing performance is obtained via solvothermal method, and then pyrolyzed at high temperature (1300°C and 1400°C) under argon atmosphere. The structural evolutions and the electromagnetic wave absorbing capabilities of the nanocomposites have been systematically investigated. The resultant 3 mol/L glucose‐SiOC ceramic exhibits a heterostructure, in which nanosized glucose‐derived‐carbon and SiC particles decorate on amorphous SiOC network. Benefitting from the nanosized carbon, SiC particles and the heterostructure attributes, the 3 mol/L glucose‐SiOC ceramic displays a strong electromagnetic wave‐absorbing property. The minimum reflection coefficient of the 3 mol/L glucose‐SiOC ceramic pyrolyzed at 1400°C reaches ‐27.6 dB at 13.8 GHz. The widest effective absorption bandwidth attains 3.5 GHz in Kμ‐band. This work opens up a novel and simple route to fabricate polymer‐derived‐ceramics with excellent electromagnetic wave‐absorbing performance. This article is protected by copyright. All rights reserved.

Synthesis of Silicon Carbide (SiC) has been performed using a solid-state reaction method. We used silica and activated carbon as raw materials. The silica was synthesized from silica rice husk using an alkali extraction and a sol-gel method. The purified silica was then mixed with the activated carbon at the same ratio, homogenized, and then cold pressed into pellets by adding polyvinyl alcohol to glue them perfectly. The pellets were then sintered in a vacuum of a high-temperature furnace in an inert arc-furnace at 1200, 1300, and 1400 °C for 6 hours. The samples were characterized for their particle size, surface area, phase composition, microstructure, and resistivity. The XRD data analysis showed that the samples are dominated by the SiC phase in the form of 3C-SiC and 6H-SiC, CO (Carbon (II) oxide), and SiO2 phases. The weight fractions of SiC samples were respectively fallen to 68, 98, and 69% for 1200, 1300 and 1400 °C sintering temperatures.

The material removal processes generate interesting surface topographies, unfortunately, that was usually considered to be surface defects. To date, little attention has been devoted to the positive applications of these interesting surface defects resulted from laser ablation to improve C/SiC surface wettability. In this study, the formation mechanism behind surface defects (residual particles) is discussed first. The results showed that the residual particles with various diameters experienced regeneration and migration, causing them to accumulate repeatedly. The effective accumulation of these residual particles with various diameters provides a new method about fabricating bionic microstructures for surface wetting control. The negligible influence of ablation processes on the chemical component of the subsurface was studied by comparing the C-O-Si weight percentage at the C/SiC subsurface. A group of microstructures were fabricated under different laser trace and different laser parameters. Surface wettability experimental results for different types of microstructures were compared. The results showed that the surface wettability increased as the laser scanning speed decreased. The surface wettability increased with the density of the laser scanning trace. We also demonstrated the application of optimized combination of laser parameters and laser trace to simulate a lotus leaf’s microstructure on C/SiC surfaces. Of course the parameter selection depends on the specific material properties.

Reaction mechanism study of ferrosilicon synthesis was carried out by using reagent grade material, graphite and waste plastic, Bakelite as reducing agent over a temperature range of 1623 K to 1823 K (1350°C to 1550°C) under inert atmosphere. Reaction rate was determined by using off-gases evolving from reduction reactions. Results showed that reduction mechanism was predominantly controlled by chemical reactions with both the reducing agent. Initially Bakelite bearing pellet showed faster reaction rate compared to graphite due to volatiles generation and less crystalline nature of Bakelite derived carbon. Extent of reduction can be improved by increasing temperature; however Bakelite bearing pellet showed lower dependency on temperature compared to graphite. Activation energy for graphite and Bakelite pellet is 238.07 kJ/mol and 140.29 kJ/mol respectively. This comparative study will create new opportunities to use waste Bakelite as a reductant even at moderately lower temperature to synthesise ferrosilicon alloy.

Many of the advantages that make C/SiC functional materials desirable are also largely responsible for the machining difficulties encountered. The time-lag of water droplet adsorption (WDA) arised from the complex fabricated carbon fiber precast body may cause cooling condition deterioration in near dry machining of C/SiC, which then gives rise to a lower machinability with respect to the surface integrity. However, little attention has been devoted to the fiber induced time-lag of WDA on C/SiC surfaces. In this study, theoretical models of WDA of two typical C/SiC surfaces, namely, pillar fiber ending and circle fiber ending C/SiC surfaces, were first established. Uni-directional C/SiC was fabricated to experimentally simulate the WDA process on these two typical surfaces. The complete WDA process on a single sample was analyzed first. Considering the stochastic shape of the flow channel, WDA experiments conducted on two typical C/SiC surfaces were repeated 2000 times. The frequency occurrence of the water droplet adsorption time (WDAT) of these 2000 experiments was fitted using the normal distribution function. The statistical evaluation methods indicated that the WDAT of a pillar fiber ending C/SiC surface lagged behind the WDAT of a circle fiber ending C/SiC surface. Furthermore, the time-lags were dependent on both the volume of the water droplet volume and increase in temperature. A critical discussion was conducted regarding the prevention of the WDA time-lag on C/SiC surfaces, and it is suggested that reducing the tiny droplet diameter of cooling mists and spray mists in advance and properly improving the cutting heat can limit, to some extent, the fiber induced time-lag of the WDA of C/SiC surfaces, which is an important factor for optimizing the cooling supply of near dry machining of C/SiC composites.

The Helium Cooled Ceramic Reflector (HCCR) Test Blanket Module (TBM), recently planned for installation and testing in the nuclear fusion energy project of International Thermonuclear Experimental Reactor (ITER), uses graphite in the form of pebbles as a neutron reflector, opening the possibility of avoiding the use of a beryllium neutron multiplier. A silicon carbide (SiC) coating should be formed on the graphite pebbles to prohibit the reaction of graphite with steam and/or air and to reinforce the surface strength. In this work, a dense β-SiC coating was formed over the surface of the graphite pebbles by a chemical vapor reaction (CVR) process of the solid–solid (SS) and vapor–solid (VS) reaction of the SiO2(s)–C(s)–SiO(v)–CO(v) system. The microstructural features, XRD patterns, pore size distribution, porosity and oxidation behavior of the SiC-coated graphite pebbles were investigated. A SiC coating with a thickness of approximately 30 μm remarkably improved the oxidation resistance and the density of the graphite pebbles. In an isothermal oxidation test conducted at 700 °C, the SiC-coated graphite pebbles showed strong oxidation resistance and a weight loss of approximately 2 wt% over the course of 2 h. This paper describes the major results obtained from our experiments on the CVR-SiC coating of nuclear graphite pebbles, recently conducted in the Korean HCCR TBM team of the ITER project.

The micro-scale heat dissipation fins significantly contribute to cool off a brake system. However, micro-scale heat dissipation fins will change the surface wetting and then change the humidity of components in the brake system. A higher humidity is helpful for improving the thermal conductivity coefficient of the C/SiC component, which aids in further improving the cooling performance. To the best knowledge of the authors, little attention has been devoted to improving the humidity of the C/SiC brake lining by micro-scale fins. The aim of this study is mainly to discuss the surface wetting of the porous C/SiC brake lining with micro-scale heat dissipation fins to facilitate heat dissipation in the brake system by increasing the humidity. In this study, micro-scale heat dissipation fins with various intervals were fabricated by a laser on three typical C/SiC surfaces. Surface wetting was characterized by the spreading time of the water droplets. The theoretical model of the water droplet spreading time was established by a Washburn-type equation. Both the experimental and theoretical results indicated that: (1) a hydrophilic C/SiC surface could be achieved by fabricating micro-scale heat dissipation fins on a circular fibre-ending surface compared with a pillar fibre-ending surface; (2) wetting control of the C/SiC surface is not obvious by changing of the micro-fin interval on the order of micrometers; and (3) the surface wetting of the pillar fibre-ending C/SiC surface was more sensitive to increased repetitions of laser scanning. In the current stage, the experimental results presented a stochastic surface wetting. In this regard, more details on the irregularity of micro-scale heat dissipation fins resulting from a laser process are discussed. The conclusions can be extended to optimize the heat dissipation fin arrangement of the C/SiC brake lining and optimize the overall cooling performance of the brake system.

READ  Solubility of Carbon Dioxide in Aqueous HCl and NaHCO3 Solutions from 278 to 298 K

An innovative approach, based on recycling waste glass and plastic, was investigated with an aim to maximize use of waste resources for production of silicon carbide (SiC). SiC is a value added material in ferrous industries to make ferroalloys. Pellets were prepared by cold-bonding method using thermoplastic, high-density polyethylene (HDPE) along with graphite blend as carbonaceous materials and glass as silica rich material. The effect of iron oxide was also observed to understand its influence on the carbothermic reduction of silica which is the dominant oxide in glass (Approximately 70%). High temperature (1450 °C) studies were carried out in a lab scale horizontal tube furnace under inert condition.

Silicon carbide (SiC) is an important ceramics for engineering and industrial applications due to its advantage to withstand in high temperatures. In this article, a demonstration of SiC nanowhiskers synthesis by using microwave heating has been shown. The mixtures of raw materials in the form of pellets were heated, using a laboratory microwave furnace, to 1400 °C for 40 minutes at a heating rate of 20 °C/min. The characterization process proved that the mixture of graphite and silica in the ratio of 1:3 is an ideal composition for synthesizing single phase β-SiC nanowhiskers. Vapor-solid mechanism was suggested to explain the formation of SiC nanowhiskers by the proposed microwave heating.

In this study, the spreading and infiltration behavior of liquid slag in contact with different grades of graphite was investigated. The wetting and infiltration of slag into graphite were found to be highly material dependent. The reduction of silica by carbon is a characteristic of the system, and it generates gaseous products as evidenced by the observation of bubble formation. The higher the temperature and silica activity of the slag is, the greater the slag infiltration and the faster the rate of spreading. Silicon infiltrated into the graphite substrates much deeper than the oxide phases, indicating gas-phase transport of SiO(g) into the graphite pores. Fundamentally, in this system where the liquid and substrate are reacting, the driving force for spreading is the movement of the system toward a lower total Gibbs energy. Reduction of silica in the slag near the interface may eventually lead to the formation of a solid, CaO-rich layer, slowing down or stopping the reduction reaction.

Silicon carbide (SiC) and ferrosilicon are the main solid by-products in the production of calcium carbide (CaC2) from coke and lime. Both of these silicon compounds are formed from silicon-bearing minerals in the raw materials but the routes of their formation are unclear. This paper presents a detailed study about transformation of the silicon-bearing minerals in a CaC2 furnace and its influence on CaC2 formation. The research was carried out in a thermogravimetric analyzer coupled with a mass spectrometer. It is found that the silicon-bearing minerals transform to SiC via reduction by C when the raw materials are large in size or to calcium silicates via reaction with CaO when the raw materials are pulverized and well mixed. The main calcium silicate, Ca3SiO5, reacts further with coke to form SiC and CaC2 via an intermediate Ca2SiO4. At exhaustion of coke, the calcium silicates react with CaC2 to form SiC. SiC may react with Fe to form ferrosilicon which is the main route for ferrosilicon formation in industrial furnaces. Low-temperature eutectics are formed from calcium silicates and CaC2. Calcium silicates inhibit the reaction of C and CaO to CaC2.

The reactions and transformations of mineral and nonmineral inorganic species in Victorian (MOR) and Rhenish (HKT) coals were investigated in a two-stage process under high temperature, entrained flow pyrolysis, and gasification conditions. The parent coals were pyrolyzed at a temperature between 1100 and 1400 °C in 100 vol % nitrogen. The resulting char samples were collected and gasified at their corresponding pyrolysis temperatures in 10–80 vol % CO2 in N2. Low temperature (500 °C) ash subsamples from the parent coals, chars, and gasification residues were analyzed for elemental and mineral phase composition. The phase composition analysis was in agreement with the proportions of various inorganic constituents in the elemental analysis. In general, the extent of reaction and phase transformation increased with increasing temperature and carbon conversion, which is related to increasing temperature and CO2 concentration. The char elemental and phase compositions were similar to those of the corresponding parent coal and consisted predominantly of SiO2, CaSO4, and CaCO3 with minor amounts of MgO and Fe2O3 in the MOR samples. Char gasification resulted in consistently increasing reaction and transformation trends, which indicates that thermodynamic equilibrium was not reached. Low temperature gasification of MOR and HKT char samples resulted predominantly in thermal decomposition of CaSO4, retention of CaCO3 due to recarbonation, and formation of MgO. The ash composition at high temperature differed based on the amounts of and reactions between various parent coal inorganic constituents. In particular, the fate of Ca and Mg differed markedly between the two coals. For MOR, decomposition of MgO resulted in depletion of Mg at high temperatures, whereas Mg was retained in HKT gasification residues as MgAl2O4 and Ca2MgSi2O7 due to higher Si and Al content. CaO from CaSO4 and CaCO3 decomposition was retained in MOR samples as Ca2Fe2O5 and Ca2SiO4, and in HKT as Ca2MgSi2O7.

Functional micro-structures on laser-ablated carbon fibre reinforced composites surfaces exhibit distinct advantages A variety of fibre endings with different orientations may coexist on the C/SiC sectional plane the anisotropic nature of C/SiC (carbon fibre reinforced silicon carbide) composites present a new challenge to the laser ablation process. However, few reports describing the influence of the fibre ending orientations on the laser-ablated C/SiC surface topography could be found. In this investigation, micro-ridges were established on three typical C/SiC surfaces by laser ablation, and a comparative study was performed to identify the topography variations on these laser-ablated C/SiC surfaces. The results show that C/SiC surfaces with different fibre ending orientations present distinct surface characters (Sz, Sq) after laser ablation. Although all of the laser ablation processes are similar in nature, the fibre ending variation made the laser and material interaction different greatly. Attention should be devoted to the influence of the fibre ending orientation on surface topography formation before performing the laser ablation of carbon fibre reinforced composite materials. Finally, some typical surface defects on these laser-ablated surfaces were also discussed.

Introduction Previous Studies Experimental Details Results and Discussion Conclusions Acknowledgements

A SiO2@ PPy core/shell structure was synthesized by performing the polymerization of pyrrole monomers around SiO2 spheres. For the first time, the SiC hollow spheres with a high surface area were prepared from the SiO2@ PPy with a core/shell structure by using a carbothermal reduction reaction technique. The preparation process and the structures of the products were characterized with XRD, TEM, SEM, N2 adsorption-desorption isotherms and XPS. The results indicate that β-SiC hollow spheres with a specific surface area of 101.3 m2/g could be prepared from the SiO2@ PPy with a core/shell structure.

[external_link offset=2]

Nanosized silicon carbide powders were synthesised from a mixture of silica gel and carbon through both the conventional and microwave heating methods. Reaction kinetics of SiC formation were found to exhibit notable differences for the samples heated in microwave field and furnace. In the conventional method SiC nanopowders can be synthesised after 105 min heating at 1500 °C in a coke-bed using an electrical tube furnace. Electron microscopy studies of these powders showed the existence of equiaxed SiC nanopowders with an average particle size of 8.2 nm. In the microwave heating process, SiC powders formed after 60 min; the powder consisted of a mixture of SiC nanopowders (with two average particle sizes of 13.6 and 58.2 nm) and particles in the shape of long strands (with an average diameter of 330 nm).

A testing procedure is described which makes it possible - by combining heat and mass balances, differential thermoanalysis, and gas analysis - to measure the reduction of iron oxides and the oxides of the companion elements present in iron blast furnaces up to 1400 C. Methods of evaluating the measurements are described, and the applicability of the procedure is illustrated by examples.

Rice hulls contain silica (15 to 20 wt%) and cellulose which will yield carbon when thermally decomposed. These are the raw materials for the formation of silicon carbide. With the very high surface area and intimate contact available from the reactants in the rice hulls, it is possible to form silicon carbide readily and economically. In the present investigation, extensive experiments were carried out on the kinetics of the above reaction using a thermogravimetric technique at various temperatures (1290 degree to 1600 degree C) and partial pressures of carbon monoxide (0. 01 to 1. 00atm). Silicon carbide formation reaction followed a linear rate law and was largely affected by temperature and partial pressure of carbon monoxide. The reaction rate was enhanced with increasing surface area of catalyst, such as iron.

Knudsen effusion experiments with SiO2(β-cristobalite) on a thermomicrobalance have been carried out over the temperature range 1823–1983 K. Interpretation of the effusion data is based on the following reactions: (a) SiO2(s)→ SiO(g)+½ O2(g), and (b) O2(g)→ 2O(g). Third law calculations give the standard Gibbs free energy of the reaction (a) as ΔGT= 182 050–58.29 T± 2500 cal mol–1 in the measured temperature range, the heat of formation of SiO(g) as ΔH°298=–27.9 ± 3.5 kcal mol–1, and the dissociation energy of SiO(g) as D°0= 8.45 ± 0.20 eV. Determination of the vaporization coefficient of SiO2(s) gives αv=(2.2 ± 0.8)× 10–2 in the experimental temperature range.

DOI:https://doi.org/10.1103/PhysRev.40.465

The instabilities of FeO, NiO, MnO, and SiO2 upon vaporization, and upper limits to the heats of dissociation of these oxides and SiO have been determined by effusion experiments. The data available in the literature have been treated to obtain the heats of dissociation, or the upper limits thereof, of the gaseous oxides SnO, ZnO, CdO, CuO, PbO, GeO, and TiO.

A combination of Knudsen effusion and mass spectrometric techniques have been employed in studying the species existing in the vapor in thermodynamic equilibrium with a condensed mixture of boron and boric oxide in the temperature range 1300°K to 1500°K. Positive ions were produced by electron bombardment of vapor effusing from the Knudsen cell and were analyzed mass spectrometrically. Ion currents of B+, BO+, B2O2+, and B2O3+ were observed. The mixture, B+B2O3, was shown to vaporize mainly as the gaseous molecule, B2O2. The heat of vaporization of B2O2(g) from the condensed phase is ΔH14000=94±8 kcal/mole. The ΔH00 for the reaction ⅔B(s)+⅔B2O3(g)→B2O2(g) is found to be 35.7±3.5 kcal. The BO+ and B+ ions observed were found to be formed mainly in processes of dissociative ionization. The concentration of BO(g) in the vapor is at least an order of magnitude lower than that of B2O2(g) showing the dimerization energy is greater than 99.6 kcal. Results obtained with pure B2O3 liquid in the Knudsen cell agree with earlier published work.

Reactions between silica and graphite were studied in vacuum from 1445° to 1765°C by continuously measuring the amount of carbon monoxide formed. At low temperatures and/or short times, the reaction followed a linear rate law with an apparent activation energy of 117 kcal. At higher temperatures and/or longer times, the reaction showed a more complex behavior, indicative of a nucleation-growth process with an apparent activation energy of 122 kcal. It is shown that the reaction could proceed via the gas phase by dissociation of silica into oxygen and silicon monoxide and subsequent reaction with graphite. The onset of the nucleation-growth-controlled process could be correlated with the transformation of quartz to cristobalite.

The kinetics of high-temperature carbon-silica reactions for a widely used glass-filled phenolic resin have been studied. Weight-loss and rate-of-weight-loss data were obtained at four heating rates ranging from 5 to 50°C per minute using standard thermogravimetric techniques. Experimental data were obtained at temperatures between 30 and approximately 1700°C. The kinetic parameters were calculated from these data using a multiple heating rate technique. Close agreement was obtained between the fractional weight loss calculated using the kinetic parameters and the measured values.

Typescripts. Thesis (Eng. D.)--Cleveland State University, 1987. Includes bibliographical references.

Formation of Silicon Monoxide and Application to the Growth of Vapor-Liquid-Solid Silicon Carbide Whiskers " ; Doctoral Dissertation. Fenn College of Engineering

24J. I. Biemacki, " Formation of Silicon Monoxide and Application to the Growth of Vapor-Liquid-Solid Silicon Carbide Whiskers " ; Doctoral Dissertation. Fenn College of Engineering, Cleveland State University, Cleveland, OH, 1987.

Thermodynamics of Sili-con Monoxide

  • h F Ramstad
  • F D Richardson
  • P J Bowles

14H. F. Ramstad, F. D. Richardson, and P. J. Bowles, " Thermodynamics of Sili-con Monoxide, " Trans. Metall. Soc. AIME, 221 [Oct.] updating).

Vapor Pressure of Silicon Monoxide

'P. V. Gel'd and M. I. Kochnev, "Vapor Pressure of Silicon Monoxide," Dokl. Akad. Nauk SSSR, 61 [4] (1948).

Conversion of Certain Refractory Oxides to a Suboxide Form No. 182082, 1905. bon, Boron, and Aluminum

'C. A. Zappfe, " Conversion of Certain Refractory Oxides to a Suboxide Form No. 182082, 1905. bon, Boron, and Aluminum, " Proc. Soc. London, Ser. A, 106A, updating, updating).

Band Spectra of Silicon Oxide and Chloride, and Chlorides of Car-4K. F. Bonhoeffer Existence of Gaseous Silicon Monoxide

*H. N. Potter, Fi. Pat. No. 360875, 1905; Br. Pat. No. 26788, 1905; Ger. Pat. 'W. Jevons, " Band Spectra of Silicon Oxide and Chloride, and Chlorides of Car-4K. F. Bonhoeffer, " Existence of Gaseous Silicon Monoxide, " Z. Phys. Chem., 'P. G. Saper, " Ultraviolet Bands of S O, " Phys. Rev., [Series 21, 40, updating).

Reduction of Oxides by Magnesium

C. Winkler, "Reduction of Oxides by Magnesium," Ber. Dfsch. Chem. Ges., updating).

The Silicon Monoxides. I. Precipitated Forms of Sili-con Monoxide from the Vapor Phase

9G. Gmbe and H. Speidel, " The Silicon Monoxides. I. Precipitated Forms of Sili-con Monoxide from the Vapor Phase, " Z. Elektrochem., 53, updating).

Conversion of Certain Refractory Oxides to a Suboxide Form No. 182082

'C. A. Zappfe, "Conversion of Certain Refractory Oxides to a Suboxide Form No. 182082, 1905.

bon, Boron, and Aluminum," Proc. Soc. London, Ser. A, 106A, updating, updating).

at High Temperatures," J. Am. Ceram. Soc., 27 [lo] updating).

'H. Schafer and R. Z. Hornle, Z. Anorg. Allg. Chem., 245, 1 (1940).

Phase Equilibria and Reaction Kinetics in the Si-0-C System

Kamkina, "Phase Equilibria and Reaction Kinetics in the Si-0-C System,'' Izv. Akad. Nauk SSSR, Met., 6, updating).

[external_footer]
See more articles in the category: Hóa học

Leave a Reply