SiO Vapor Research Articles

Synthesis of nano-silicon carbide by SiO–C reaction

Carbon black has been successfully converted into silicon carbide by reacting it with SiO vapor at 1500 °C under Ar gas environment. The influence of reaction temperature, duration and Ar gas flow rate on the final product was examined. The structural and microstructural property of synthesized SiC was characterized using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Micrographs of synthesized SiC showed that the final product was an agglomeration of SiC nano-powder of 50–500 nm size and nano-whiskers/fibres having a diameter of 50–500 nm and lengths in 0.1–10 μm depending on Ar gas flow rate. The higher conversion of C into SiC was observed at 1500 °C with Ar gas flow rate ∼250 ml/min.

Synthesis mechanism of different morphological SiC and its electromagnetic absorption performance

This article presents a facile synthesis of different morphological silicon carbides (SiC) absorbers by adjusting the weight ratio of carbon spheres to waste glass powder. With the decreased proportion of waste glass powder, the diffusion rate of SiO vapour decreases, which is lower than the deposition rate, leading to the morphology change from fluffy spheres to nanofibers. The electromagnetic wave (EMW) absorbing results show that the fluffy spherical SiC possesses the optimal EMW absorption performance with an effective absorption bandwidth 4.81 GHz at 1.6 mm, mainly due to stacking faults-induced polarisation loss and conductive loss. By comparison, the EMW absorbing ability of SiC obtained through wasted glass powder is better than the normal SiC prepared through commercial SiO2. Thus, the waste glass has shown great promise as silicon resources to prepare high-performance SiC absorbers.

Degradation Kinetics of Automotive Shredder Residue and Waste Automotive Glass for SiC Synthesis: An Energy-Efficient Approach

Generally, fossil carbon materials (coal, coke/char, and petroleum coke), biological carbon materials (charcoal, woodchips), and quartz from the earth’s crust are sources of carbon and silica to synthesise silicon carbide (SiC) at temperatures between 2000 and 2200 °C. The study investigated the isothermal and non-isothermal kinetics of synthesising SiC from automotive shredder residues (ASR) and windshield glass of end-of-life-vehicle (ELVs) at 1300 °C, 1400 °C, and 1500 °C for 30 min. The kinetics of ASR and waste glass degradation were studied by relating the thermogravimetric data via the Coats–Redfern model. The reaction mechanism includes the rapid formation of a gaseous SiO intermediate, and carbon reduction of the SiO to SiC is reaction-rate-controlling. The understanding of kinetics inferred that the optimisation of SiC formation is entirely associated with the conversion of SiO2 to SiO vapour and their reaction with CO and carbon particles. The kinetic parameters of the degradation of mixed ASR and waste glass were determined, and the activation energy of mixed ASR and glass for non-isothermal conditions are 22.48 kJ mol−1, 2.97 kJ mol−1, and 6.5 kJ mol−1, and for the isothermal study to produce SiC is 225.9 kJ mol−1, respectively. The results confirmed that this facile way of synthesising SiC would conserve about 50% of chemical energy compared to the traditional way of producing SiC. A beneficial route of transforming the heterogenous ASR and glass wastes into SiC with economic and environmental benefits is recognised.

Structure control and growth mechanism of beaded SiC nanowires with microwave absorption properties

Large-scale SiC nanowires (SiCnws) were successfully synthesized on graphite substrates by a catalyst-free carbon thermal reduction process using low-cost silicone oil, silica powder, and activated carbon. The control of different nanowire structures was achieved by parameter regulation. An in-depth discussion of their growth mechanisms is provided. Beaded SiCnws consisting of amorphous SiO2 beads and SiC strings were synthesized at 1400 °C. The formation of beads is mainly due to the supersaturation of SiO vapor, which leads to the reaction of excess SiO to form SiO2 at the defects of the SiCnws. The dielectric parameters of beaded SiCnws were analyzed, and it was found that the beaded SiCnws have a maximum effective absorption width of 1.84 GHz and a maximum reflection loss of −16.03 dB. The exploration of the growth mechanism of beaded SiCnws in this study provides a useful reference for the preparation of one-dimensional nanomaterials.

Transient and in situ Growth of Nanostructured SiC on Carbon Fibers toward Highly Durable Catalysis

AbstractCarbon is ubiquitously used as catalyst supports in various clean energy technologies, particularly emerging electrocatalysis, yet it often suffers slow oxidation and corrosion along with performance degradation. The harmonious combination of refractory silicon carbide (SiC, chemically inert) with carbon is alluring but often a great challenge, particularly to achieve desirable nanostructures and strong interfaces. Herein, a shockwave‐type transient heating is designed (> 1750 °C for 1 s per pulse) for controllable growth of conformal SiC coating and massive SiC nanowires on carbon fibers (denoted as CF/SiC‐NW), which serves as a high surface area and durable support for catalysis under harsh environments. The transient heating in SiO vapor triggers in situ transformation of the carbon surface into a seamless SiC protective layer, while the following fast cooling is essential for the growth of numerous self‐assembled SiC nanowires. The CF/SiC‐NW exhibits excellent structural stability in the air at high temperatures, in concentrated acidic/alkaline solutions after electrochemical stressing for 2000 cycles, and in oxygen evolution reaction after 10 h of continuous operation. This strategy enables delicate structure control in refractory carbides and is also general for various carbon/carbide functional materials (e.g., C/TiC, C/WC) for electro‐ or electrified catalysis under harsh conditions.

Synthesis mechanism of α-Si3N4 whiskers via SiO vapor in reaction bonded Si3N4-SiC composite

An indirect nitridation mechanism was designed to realize a high conversion rate to α-Si3N4 whiskers in reaction bonded Si3N4-SiC composite via VS mechanism, in which the dominant vapor-phase source of reactants is SiO vapor produced by the active oxidation of Si. The role played by the temperature-time program and addition of ultra-fine Si powder on the formation of SiO vapor and the resulting Si3N4 whiskers was clarified based on the experimental results and the thermodynamic calculations. The result shows that during sintering, in the presence of trace O2, ultra-fine Si particles preferentially undergo active oxidation and volatilized completely in the form of SiO(g). While an equilibrium of SiO(g) and Si(s) is formed on the surface of the coarse Si particle meanwhile. By stepped holding temperature further, this equilibrium is constantly upgraded, so the coarse Si particles is evaporated as SiO(g) shell layer by layer. Massive α-Si3N4 whiskers is formed by SiO(g) nitridation while the stepped holding temperature sintering. A reasonable model of the controllable indirect nitridation mechanism was established.

COMPARATIVE CHARACTERISTICS OF COATINGS WITH SiO AND GeO ON LEUCOSAPPHIRE

The reasons for the sharp difference in the adhesion of multilayer coatings containing SiO or GeO together with Ge on a leucosapphire (Al2O3) plate have been established. It should be mentioned that Silicon(II) and Germanium(II) oxides are quite stable in the gaseous state and, contrary, are metastable in condensed state; at high temperature they disproportionate into ultra-dispersed composites of amorphous nature. A comparison is made of the surface properties of ultramicroscopic droplets formed on solid surfaces – a substrate or the previous layer – upon condensation of SiO, GeO, or Ge vapors on leucosapphire. A qualitative assessment of the ratio of the corresponding contact angles of wetting by the indicated melts, formed at the first moment of contact, has been carried out. In assessing the surface tension of SiO and GeO melts (or Si – SiO2 and Ge – GeO2 composites), we proceeded from the corresponding values for SiO2 and GeO2, which are 296 and 248 mJ/m2 near the crystallization temperatures. On this basis, it was established that the smallest value of the contact angle, and hence the best wetting, is observed for the GeO melt (somewhat less for the SiO melt) on the solid surface of Al2O3 or Ge; the solid surface of SiO or GeO (especially, the first of them) with molten germanium should be much weaker wetted. Hence, it follows that thin-film multilayer coatings obtained from Ge and GeO on a leucosapphire substrate should have a significantly higher climatic resistance due to higher adhesion compared to multilayer coatings from SiO and Ge. Indeed, a multilayer coating containing SiO on a leucosapphire substrate with a large surface can withstand storage in air for no more than 2–3 months and begins to peel off; at the same time, the GeO coating remains intact after 4 years of storage. Thus, the GeO film-forming material is a promising one for use in multilayer coatings such as cut-off filters in interference optics of the near and mid-IR spectral ranges.

Thermodynamics of the Lu2O3 – SiO2 system and comparison to other rare earth silicates

Environmental barrier coatings are necessary to protect SiC based ceramics and composites from water vapor degradation in harsh engine environments. Currently, rare earth (RE) silicates are the most promising systems to protect SiC based ceramics and composites. This protection is largely based on reduced silica activity in these rare earth silicates which results in a lowered reactivity with water vapor. To that end, previous Knudsen effusion mass spectrometry (KEMS) studies have explored RE = Yb, Y silicates to measure the reduced silica activity and subsequent water vapor reactivity. Similarly, this work employs the KEMS technique to measure the SiO(g) vapor pressure in Lu containing RE silicates to calculate the activity of silica within the monosilicate [log(a(SiO2)) = -2351.1*1/T-1.6731] and the disilicate (log(a(SiO2)) = -4884.0*1/T + 2.2208) as a function of temperature. The enthalpies of formation for Lu monosilicate from the oxides and the elements were calculated to be −45 ± 3 kJ/mol at 1550 K and −2831.1 ± 12 kJ/mol at 298 K, respectively. The measured enthalpy of formation and those found in literature are compared to modeled values from density functional theory and those estimated using electronegativity.

Simultaneous improvement in porosity and strength of porous β-Si3N4 ceramics by formation of ultrafine fibrous grains

Si3N4 ceramic with ultrafine fibrous grains are expected to exhibit remarkable mechanical properties. In this work, highly porous Si3N4 ceramic monoliths composed of ultrafine fibrous grains were developed via a novel vapor-solid carbothermal reduction nitridation (V-S CRN) reaction between SiO vapor and green bodies comprised of carbon nanotubes (CNTs), α-Si3N4 diluents and Y2O3 in a N2 atmosphere. The unique fibrous grains-interconnected structure was developed through in-situ formation of Si3N4 and following liquid phase sintering. The porous Si3N4 monoliths with porosity of 61–78% was developed by controlling the contents of α-Si3N4 diluents and densities of the CNT green bodies. With increasing of the α-Si3N4 contents, Si3N4 fibrous grains with an aspect ratio of approximate or higher than 20 could be achieved, and the grains were gradually refined. For the samples with 40 wt% α-Si3N4, the minimum mean grain diameter and pore size of 164 nm and 0.79 μm were achieved, respectively, and the resultant porous Si3N4 monolith exhibited a flexural strength of as high as 73–102 MPa with the porosity of 61–73%, which is much higher than that of the reported in literature. The improvement of mechanical strength could be attributed to the densely interconnected bird's nests structure formed by the ultrafine fibrous grains. The effects of the α-Si3N4 diluents on the resulting porous Si3N4 monolith via this method were analyzed.

Optimized mechanical properties and oxidation resistance of low carbon Al2O3-C refractories through Ti3AlC2 addition

The mechanical properties and oxidation resistance of the Al2O3-C refractories are of critical importance for iron and steel making processes. However, the evaporation of antioxidants related phases such as Al(g), Si(g), and SiO(g) would deteriorate these properties, especially during high-temperature treatment/application. Therefore, in the present work, a small amount of Ti3AlC2 compared with Al was introduced to overcome these problems. The phase compositions, microstructures, mechanical properties, and oxidation resistance of Ti3AlC2 containing refractories were investigated. The partial oxidation of Ti3AlC2 led to inherited lamellar structures such as Ti3Al1-xC2, TiC, and granular Al2TiO5 phases. The controlled oxidation of Ti3AlC2 and its volume expansion contributed to the compact-structure, thereby limiting the escape of Si and SiO vapors at high temperatures. Consequently, the mechanical properties and oxidation resistance of Ti3AlC2 containing Al2O3-C refractories treated at 1600 ℃ were improved.

SiC-Fiber Reinforced Silicon Carbide-Based Ceramic Composite

Dense silicon carbide-based ceramic composites reinforced with SiCf fiber have been produced by hot pressing at a temperature of 1850°C. The reinforcing agent used was silicon carbide fiber produced by siliciding carbon cloth with SiO vapor. It has been shown that raising fiber content from 1 to 7 wt % increases the density, bending strength, and fracture toughness of the material, which reach ρ = 3.20 ± 0.01 g/cm3, δb = 450 ± 26 MPa, KIс = 5.6 ± 0.1 MPa m1/2 at 7 wt % SiC fiber.

Interaction of Fluorocarbon with Silicon Monoxide and Processes of SiC Nanowire Formation

A study of the processes of the thermal carbonization of silicon monoxide in the presence of nonstoichiometric carbon monofluoride demonstrated that raising the annealing temperature of mixtures of SiO and CFx powders in a quasi-closed volume to 1000°C and higher leads to the formation of whisker-like SiC nanocrystals. It is found that, in parallel with the known crystallization of SiC nanowires as a result of the interaction of SiO vapor with carbon monoxide, the previously undescribed interaction of CO with gas-phase silicon difluoride SiF2 takes part in their formation. At temperatures below 1200°C, this reaction is dominant and makes the most pronounced contribution to the yield of SiC nanowires.

Properties of composites SiC/SiCf obtained by hot pressing of SHS of silicon carbide powder

Dense ceramic samples based on SiC were obtained by hot pressing. We used the Use of silicon carbide powder as the initial components of SHS, due to the spherical shape of the particles, allows obtaining a denser workpiece. The reinforcing component in the form of silicon carbide fibers is obtained by siliconizing carbon fabric with SiO vapours. The phase composition of SiC fibers obtained by silicification by SiO vapour was determined. The properties of the obtained SiC/SiCf composites were studied: density 3.20 g/cm3, strength 520 MPa (for monolithic ceramics 390 MPa), the value of the crack resistance coefficient 5.9 MPa-m1/2.

Properties of silicon carbide fibers obtained by silicification of carbon fabric with SiO vapours

The method of siliconizing carbon fabric with SiO vapours yields a textile SiC material that preserves the structure and integrity of the fibers of the original fabric, as well as the average diameter of the monofilament. According to X-ray phase analysis, it was found that SiC fibres obtained by siliconizing silicon fabric with SiO vapor consist of a mixture of two modifications of 3C–SiC and 6H–SiC. According to infrared absorption, the oxygen content in the composition of silicon carbide fibers does not exceed 2.1 wt%. The mechanical properties of the obtained fibers were investigations: the mechanical tensile strength of silicon carbide fibers is σp = 1350 ± 120 MPa, the nanoscale hardness is 10 ± 0.5 GPa, and the elastic modulus is 100 ± 10 GPa.

Synthesis and carbothermal nitridation mechanism of ultra-long single crystal α-Si3N4 nanobelts

One-dimensional Si3N4 nanostructures are desirable for constructing nanoscale electric and optoelectronic devices due to their peculiar morphologies. Herein, a facile and environmentally friendly catalyst-free method is proposed to synthesize ultra-long single crystal α-Si3N4 nanobelts via carbothermal nitridation of carbon nanotubes at 1750 °C. The obtained α-Si3N4 nanobelts with a flat surface (thickness of ∼150 nm, length of several millimeters) exhibited an extremely high aspect ratio, perfect crystal structure, and high specific surface area of 7.34–10.09 m2 g−1. In addition, the width was increased from approximately 80 nm to 8 μm by increasing the holding time from 1 to 3 h. The nanobelt formation was governed by the vapor–solid (VS) reaction between SiO vapor, N2 and carbon nanotubes, and the vapor–vapor reaction between SiO, CO and N2. The former was responsible for the initial nucleation and successive base-growth of α-Si3N4 nanotubes. The latter additionally contributed to the nanorod and subsequent proto-nanobelt formation and to the growth of the nanobelts. During high-temperature annealing at 1750 °C, the original Si3N4 nanotubes gradually transformed into nanorods, and, finally, nanobelts with stable shapes as a result of surface energy minimization.

Graphene-based SiC nanowires with nanosheets: synthesis, growth mechanism and photoluminescence properties

3C-SiC nanowires with nanosheets were synthesized via a direct reaction of Si vapor (from solid silicon) and SiO vapor (from silicon and silicon dioxide) with graphene nanosheets at 1500 °C without any additional metal catalyst.

Взаимодействие фторуглерода с моноокисью кремния и процессы образования нанонитей SiC

When studying the processes of thermal carbonization of silicon monoxide in the presence of non-stoichiometric carbon monofluoride, it was found that increasing the annealing temperature of mixtures of SiO and CFx powders in a quasiclosed volume to 1000°C and higher leads to the release of whisker-like SiC nanocrystals. The studies showed that in parallel with the known crystallization of SiC nanowires as a result of the interaction of SiO vapors with carbon monoxide, previously undescribed interaction of CO with gas-phase silicon difluoride SiF2 takes part in their formation. At temperatures below 1200°C, this reaction is dominant, making the largest contribution to the yield of SiC nanowires.

Active metal brazing of graphite foam-to-titanium joints made with SiC-Coated foam

Medium-density, high-conductivity carbon foams were joined to titanium using a two-step process that first exposed foam to SiO vapor at 1450 °C for 30 min. under vacuum followed by vacuum brazing Ti using Cusil-ABA to the sides of prismatic foam pieces along the ‘with-rise’ (WR) or foaming direction and the ‘against rise’ (AR) or transvers direction. Well-bonded joints with braze-infiltrated foam and Ti-rich interfaces formed along WR and AR. The un-bonded foam was stronger along WR (785 kPa) than along AR (277 kPa) as were the joints made using coated and uncoated foams. Foam thickness minimally affected joint strength along WR but along AR, joints with thick foam were 58 % stronger. The coating marginally (9 %) lowered joint strength along WR but led to a nearly 50 % strength drop along AR. The experimental foam is more robust and amenable to coating and joining along foaming direction than transverse to it.

Silicon nanowhisker formation during SiO2 evaporation by arc discharge

Nanoscale silicon is interesting in various areas, including electronics, photovoltaics, solar and Li-ion energetics. This work describes processes of electric arc sputtering of SiO2 in a graphite electrode in a helium medium, leading to formation of silicon nanowhiskers. A fan- shaped turbulent jet of vapors of the sprayed electrode flowing from the interelectrode space, resulting in formation of areas with different component compositions and temperatures, is considered. Interaction of SiO and Si vapors leads to the formation of the silicon nanowhisker structure.

Synthesis and mechanical properties of highly porous ultrafine-grain Si3N4 ceramics via carbothermal reduction-nitridation combined with liquid phase sintering

Highly porous Si3N4 ceramics have been prepared via a novel carbothermal reduction-nitridation (CRN) reaction between carbon nanotubes (CNTs) and SiO vapor in a N2 atmosphere. The green bodies consisted of 49.0 wt% CNT, 40.4 wt% α-Si3N4 as seed and 10.6 wt% Y2O3 as sintering additive, and SiO powders were located under the green bodies during sintering. By heating at temperatures ranging from 1550 to 1650 °C, fibrous β-Si3N4 nanograins were obtained. Complete reaction was achieved after soaking at 1650 °C, and a mean grain diameter of approximately 290 nm and aspect ratio of as high as 20 were obtained, and a porosity of 73% was reached due to the low density of the green bodies. The bending and compressive strengths were up to 62 MPa and 82 MPa, respectively, which were higher than the values in the literature, as a result of the fine elongated fibrous β-Si3N4 grains. It should be noted that the Si3N4 ceramics exhibited a large strain to failure and ‘pseudoplastic’ deformation behavior during the compressive test, which was attributed to the high porosity.