High-purity SiC Research Articles

Achieving Rapid Synthesis of High-Purity SiC at 1923 K via a Liquid-State Reaction

Achieving Rapid Synthesis of High-Purity SiC at 1923 K via a Liquid-State Reaction

Digital light processing of high-purity SiC ceramic membrane support modified by SiC whisker

High-purity SiC ceramic membrane has gained tremendous attention in the treatment of various corrosive wastewaters. Additive manufacturing technique makes it possible to fabricate high-purity SiC ceramic membrane with complex configurations. Here, we proposed a route for the preparation of high-purity SiC ceramic membrane support using digital light processing and SiC whisker reinforcement. With the increase of whisker content, the viscosity of SiCw/SiC photosensitive slurry increased due to the formation of whiskers agglomerations; the average pore size shifted from 3.15 μm to 1.35 μm with the occupation of large pores by SiC whiskers. In addition, the compressive strength of the ceramic support increased from 10.7 MPa to 16.7 MPa because of the decline in pore size and the toughening effects by SiC whiskers. So, the introduced SiC whiskers enhanced the pore connectivity and mechanical strength of the porous ceramics. This work provides a feasible path to manufacture high-purity SiC ceramic membrane support with complex configuration, high pore-connectivity and excellent mechanical properties.

Fabrication and evaluation of high-performance 3D interpenetrated network structures SiC/Al composites with high-purity plate-like α-SiC framework

To reinforce compatibility with the thermophysical and mechanical properties of SiC/Al composites for electronic packaging to improve the stability and reduce fatigue failure of electronic integrated devices, a novel 3D SiC reinforced framework with interpenetrated plate-like α-SiC grains was synthesized. A small amount of doped α-SiC was seeded to induce the transformation of β-SiC to plate-like α-SiC at 2,300 °C, forming a high-purity α-SiC strongly bonded framework. Vacuum/gas pressure infiltration of Al alloy was subsequently used to manufacture the 3D interpenetrated network structure SiC/Al (SiC3D/Al) composite. Characterization results showed that 15% (in mass) seeds provided the composite with the optimal comprehensive performance, including a low coefficient of thermal expansion (CTE) of 5.54 × 10−6 K−1, a high thermal conductivity (λ) of 239.08 W·m−1·K−1, the highest flexural strength of 326.84 MPa, and a low thermal deformation parameter (TDP) of 0.023. High-purity plate-like grains enhanced the purity of the framework promoting a significant improvement in λ. As the seed content increased to 20% (in mass), both λ and CTE reached optimal values of 5.22 × 10−6 K−1 and 243.14 W·m−1·didiK−1, but the mechanical properties declined by 10.30%. The synergistic effect of the well-bonded interface and the high-purity 3D SiC framework balanced excellent mechanical properties and multiple thermal functions.

Structure and optical band gap of porous nano-Cu-SiC composite films prepared via magnetron sputtering

Porous nano-Cu-SiC composite films were prepared using double-target co-sputtering technology combined with annealing process by using high-purity copper and SiC as target materials, methane and nitrogen as the reaction gas, and argon as the working gas. The surface morphology, crystal structure, and optical transmission properties of the composite films were characterized and analyzed using modern testing and analytical techniques. The results show that the prepared composite film has a uniform and porous microstructure. Further analysis shows that SiC was dispersed in the copper matrix and well combined with the copper matrix. Annealing was conducive to carrier transmission. After annealing, the composite films recrystallized and grew again, thus increasing the stability of the structure. Raman spectra show that annealing can lead to the separation and crystallization of silicon and carbon phases in composite films. With the increase of energy density, the crystallization degree of porous SiC increases continuously, and the crystallization quality of the composite film and the light transmittance are improved. The prepared porous nano-Cu-SiC composite films have semiconductor properties, and the optical band gap is 0.17 eV. The porous nano-Cu-SiC composite films prepared using this method have good application prospects in high-performance composite film materials, such as heat conduction and wave absorption.

Application of silicon carbide temperature monitors in 49-2 swimming-pool test reactor

High purity SiC crystal was used as a passive monitor to measure neutron irradiation temperature in the 49-2 research reactor. The SiC monitors were irradiated with fast neutrons at elevated temperatures to 3.2 × 1020 n/cm2. The isochronal and isothermal annealing behaviors of the irradiated SiC were investigated by x-ray diffraction and four-point probe techniques. Invisible point defects and defect clusters are found to be the dominating defect types in the neutron-irradiated SiC. The amount of defect recovery in SiC reaches a maximum value after isothermal annealing for 30 min. Based on the annealing temperature dependences of both lattice swelling and material resistivity, the irradiation temperature of the SiC monitors is determined to be ∼410 °C, which is much higher than the thermocouple temperature of 275 °C recorded during neutron irradiation. The possible reasons for the difference are carefully discussed.

Green Silicon Carbide (SiC) and SiC/Graphite Composite Anodes for Lithium-Ion Batteries

Arising from concerns of continuously deteriorating environmental issues, worldwide efforts are dedicated to developing more sophisticated energy storage techniques to replace traditional nonrenewable sources. Given the significant greenhouse gas emissions that occur coincident with current battery production and operation, the introduction of agricultural waste rice hull ash (RHA), a byproduct of biomass combustion, as a source for battery components could facilitate the actual realization of green and sustainable energy storage. Herein, we focus on using RHA to produce SiC with hard carbon (HC) nanocomposites and their mixtures with graphite as Li+ battery anodes.Using a simple method developed in our laboratories to control SiO2:HC ratios, the intrinsic nanoscale mixing of SiO2 and HC in RHA provides a natural starting material for carbothermal reduction producing high purity SiC without the need to add an external carbon source. The optimized SiC/HC nanocomposites contain ≈13 wt. % HC, showing BET surface areas >200 m2/g.We previously reported the SiC/HC nanocomposites derived from RHA exhibit charge/discharge capacities 3× of current graphite anodes at > 950 mAh g-1, accompanied by distinct capacity increases. In particular, SiC can be lithiated to Li1.1-1.4SiC without forming LixSi or LixC. Investigations of the lithiation/delithiation mechanisms using multiple techniques coupled with modeling suggest a cubic (3C-SiC) to hexagonal phase transition (6H-SiC) after long-term cycling, which may explain the origins of extraordinary capacity increments. Moreover, lithiation/delithiation occur without significant volume changes according to XRD and SEM, suggesting that SiC can compete with metallic Si as an anode material as free volumes equivalent to 3× the charged Si are required.Most recently, inspired by the developed concept of adding graphite to improve the performance of silicon-based anodes, we find adding graphite to SiC/HC nanocomposites results in a 3× improvement in capacity increases on cycling, reaching >950 mAh g-1 after 150 cycles. The proposed interactions within the composites will also be addressed in this presentation. It should be noted most silicon/graphite composite anodes use low Si contents of < 30 wt. % to limit the total electrode volume expansion and ensure contacts and conductivities between components, which restrains the practical energy density improvements from using Si in the anodes. In comparison, mixing only 30 wt. % graphite with SiC/HC in the current work results in specific capacities competitive with Si. Furthermore, Si metal can be synthesized via the carbothermal reduction at ≈1900 °C, while battery-grade graphite used today is produced in an environmentally harmful and expensive multistep method that involves heating to ≈3000 °C. The SiC/HC need only be heated to 1450 °C, with hard carbon forming coincidentally providing positive effects on anode performance. In this aspect, directly using SiC/HC or adding a low amount of graphite to further boosts its performance in an apparently more environmentally friendly route to alternative anodes.

Preparation of high-purity SiC ceramics with good plasma corrosion resistance by hot-pressing sintering

High-purity SiC ceramic devices are applied in semiconductor industry owing to their outstanding properties. Nevertheless, it is difficult to densify SiC ceramics without any sintering additive even by HP sintering. In this work, high-purity and dense SiC ceramics were fabricated by HP sintering with very low amounts of sintering aids. Residual B content was only 556 ppm and relative density was more than 99.5%. Furthermore, thermal conductivity of as-prepared SiC ceramics was improved from 155 W m−1 K−1 to 167 W m−1 K−1 by increasing holding time and their plasma corrosion resistance was promoted in the meantime. The as-prepared high-purity SiC ceramics have broad application prospects in the field of semiconductor industry.

Study on the sintering mechanism and properties of porous ceramics prepared by silicon carbide abrasive particles with multi-mineral sintering additives and silica sols

Reducing the sintering temperature of SiC ceramics while maintaining performance has been a significant challenge. This study proposes the preparation of SiC porous ceramics at lower sintering temperatures using industrial-grade SiC abrasives, instead of expensive high purity SiC ceramic particles, as ceramic aggregates by combining two process routes, namely liquid-phase sintering and additive doping, with industrial silica sol as the liquid-phase binder and three common minerals, namely kaolin, talc, and bentonite, as sintering additives. SiC ceramic precast blanks were first prepared by a semi-solid injection moulding process. The reasonable SiC sintering temperature was determined to be 1400 °C by studying the effect of sintering temperature on the component composition and microscopic morphology of the blanks. Then, SiC porous ceramics with macroscopic and microscopic pore structures were successfully prepared using an organic foam impregnation-high temperature sintering process, in which the maximum compressive load was 210.2 N at a porosity of 72.66%. Finally, the rationality of this process route was determined, which shows that this technology can reduce the complexity and production cost with cheaper raw materials and lower sintering temperature without atmosphere protection.

Critical evaluation and thermodynamic optimization of the Si-N, Si-C, C-N and Si-C-N systems and its applications to high purity SiC production

Thermodynamic optimization of the Si-N, Si-C, C-N and Si-C-N systems were performed using the CALculation of PHAse Diagrams (CALPHAD) method based on critical evaluation of all available experimental data. The liquid and solid solutions within the Si-C-N system were described using the Modified Quasichemical Model and Compound Energy Formalism, respectively. The Gibbs energies of β-Si3N4 and β-SiC were carefully optimized to resolve inconsistencies among existing thermodynamic properties and phase equilibria data. The solubilities of C and N in both solid and liquid Si solutions were critically optimized. Besides, the solubility of N in β-SiC to form a narrow homogeneity range of β-Si(C,N) solid solution is considered for the first time in the present thermodynamic modeling. Based on the present thermodynamic database, experimentally unexplored phase diagrams and thermodynamic properties within the Si-C-N alloys were predicted. As an application of the database, the influences of various operation conditions on high purity SiC production using sublimation process were calculated.

Characterization of radiation damage in 3D printed SiC

• High-purity SiC composites fabricated by additive manufacturing were irradiated. • Radiation-induced defects are easily observed in α-SiC particles but not CVI matrix. • Defect swelling measured by STEM-EELS is similar in α-SiC particles and CVI matrix. • Defect types and swelling are consistent with other forms of nuclear-grade SiC. • Interface denuded zone reveals sink strength bias and relative defect-type mobility. The SiC fuel matrix for advanced gas-cooled high temperature reactors as part of the Transformational Challenge Reactor program serves as the fuel particle container structure, a barrier to fission gas release, and a heat transfer medium. Its performance is particularly important because the fuel matrix must demonstrate good structural stability and thermal behaviors. An additive manufacturing methodology combining a binder jet 3D printing process with chemical vapor infiltration (CVI) for the production of SiC was recently developed. In this study, post irradiation examination by transmission electron microscopy shows that defect accumulation within the printed particles is very similar to other forms of high-purity SiC. However, damage accumulation was not directly observed in the CVI matrix because black spot damage and dislocation loops are difficult to image within the nanoscale highly faulted CVI matrix and because interstitial defects may rapidly annihilate at the stacking faults. Therefore, electron energy loss spectroscopy (EELS) analysis was used to analyze defect swelling in both the printed particles and the CVI matrix. The EELS analysis helped reveal that the radiation-induced swelling in the CVI matrix is similar to that of the printed SiC particles. This work shows that 3D printed SiC has behavior that is comparable to SiC processed by other means and that 3D printing could serve as a suitable processing technique for high-purity SiC for nuclear applications.

High Purity and High Yield Sic Nanowires Synthesis Without Catalyst by Graphite Sheet Layer Assembly and Thermal Evaporation

High Purity and High Yield Sic Nanowires Synthesis Without Catalyst by Graphite Sheet Layer Assembly and Thermal Evaporation

Critical Evaluation and Thermodynamic Optimization of the Si-N, Si-C, C-N and Si-C-N Systems and its Applications to High Purity Sic Production

Critical Evaluation and Thermodynamic Optimization of the Si-N, Si-C, C-N and Si-C-N Systems and its Applications to High Purity Sic Production

Radiation damage analysis in SiC microstructure by transmission electron microscopy

Microstructures of monolithic high purity SiC and SiC with sintering additives after neutron irradiation to a fluence of 2.0–2.5 × 1024 n/m2 (E > 0.1 MeV) at 333–363 K and after post-irradiation annealing up to 1673 K were observed using a transmission electron microscopy. Results showed that no black spot defects or dislocation loops in SiC grains were found after the neutron irradiation for all of the specimens owing to the moderate fluence at low irradiation temperature. Thus, it is confirmed that these specimens were swelled mostly by the formation of point defects. Black spots and small dislocation loops were discovered only after the annealing process in PureBeta-SiC and CVD-SiC, where the swelling almost diminished. Anomalous-shaped YAG grains were found in SiC ceramics containing sintering additives. These grains contained dense black spots defects and might lose crystallinity after the neutron irradiation, while these defects may annihilate by recrystallization during annealing up to 1673 K. Amorphous grain boundary phase was also presented in this ceramic, and a large part of it was crystallized through post-irradiation annealing and could affect their recovery behavior.

High accurate multi-angular polarized spectrum thermometry for smooth surface

A new multi-angular polarized spectrum thermometry based on the optimal inversion wavelength selection method was proposed to accurately measure the surface temperature of optically smooth opaque surface. The surface temperature was inverted from the multi-angular polarized spectral radiance of sample by the least square method. The optimal inversion wavelength was iteratively determined by using the relation of λTS=2410 μm·K. The optimal inversion model was proved to be inverting the refractive index and the extinction coefficient by the ratio model P/S firstly and then calculating the surface temperature by the non-ratio model P+S. A proof-of-principle experiment with a high-purity SiC sample was carried out to validate the reliability of the inversion method. The result shows that the relative deviation of temperature is less than 1% at the optimal wavelength for the calculation performed by the optimal inversion model.

Accuracy improvement for directional polarized spectral emissivity measurement in the wavelength range of 4–20 μm

A new directional polarized spectral emissivity measurement apparatus with the wavelength range of 4–20 μm was established to promote the development of thermal radiation transfer and polarization engineering. The measurement accuracy was improved by eliminating the background radiation with a high emissive thermostatic shutter and precisely determining the sample surface temperature. An accurate expression for directional polarized spectral emissivity was obtained taking into account the multiple reflection between the sample and the chamber. The linearity of spectral response was calibrated respectively in parallel and perpendicular polarized directions. The directional polarized spectral emissivity of a high-purity SiC sample was measured in a controlled environment to validate the capability of the apparatus. The excellent agreement between the measurement result and the literature data proved the reliability of the experiment apparatus and the measurement method. The measurement uncertainty was evaluated for each experiment, and the relative uncertainty was estimated to be less than 4.1%.

Synthesis of High-Purity SiC Nanowires via Catalyst-Free Pyrolysis of SiO2/Si and Sponge-Like Graphene Oxide.

The large-scale synthesis of high-purity SiC nanowires is a challenge. In this context, sponge-like graphene oxide (GO) was used as a carbon source as well as a reaction template for directly synthesizing SiC nanowires. GO was completely reacted with SiO to prepare high-purity 3C-SiC nanowires by thermal evaporation and carbothermal reduction without the use of any catalyst, rather than by epitaxy. Characterization was conducted using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction. The SiC nanowires had lengths of several tens of micrometers and a perfect single-crystalline structure with a bamboo-like morphology.

Thermodynamic Study on the Synthesis of SiC with Silicon Cutting Waste

In this paper, a simple, efficient and commercial available approach for recycle and reutilization of silicon cutting waste(SCW) to prepare high purity SiC is proposed, and the thermodynamic characterization of the SiC preparation and its growth mechanism are investigated. The effects of thermodynamic temperature, Si/C ratio and system pressure on the influence of recovering SCW are studied in detail with HSC 6.0 software. SiC balanced amount was about 1.7 mol/100 g and its content reached 66%, when the temperature reached 1880 °C. A decrease of Si/C ratio in the range of 1/1–1/4 will contribute to a decrease of smelting temperature, and the ordinary pressure of 1 bar is considered as the optimum pressure for the synthesis of SiC.

Synthesis of Silicon Carbide Powders from Methyl-Modified Silica Aerogels

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

Current-Mode Deep Level Spectroscopy of Vanadium-Doped HPSI 4H-SiC

SiC has currently attracted the interest of the scientific community for qubit applications. Despite the importance given to the properties of color centers in high-purity semi-insulating SiC, little is known on the electronic properties of defects in this material. In our study, we investigated the presence of electrically active levels in vanadium-doped substrates. Current mode deep level transient spectroscopy, carried out in the dark and under illumination, together with 1-D simulations showed the presence of two electrically active levels, one associated to a majority carrier trap and the other one to a minority carrier trap. The nature of the detected defects has been discussed in the light of the characterization performed on low-energy electron irradiated substrates and previous results found in the literature.

Recycle of silicon slurry cutting waste to prepare high purity SiC by salt-assisted carbothermic reduction

A technological route for recycling silicon slurry cutting waste (SSCW) as silicon source to prepare high purity silicon carbide as well as reducing the industry cost and avoiding the environmental pollution aroused by the waste was explored. The effect of Fe2O3, NaCl addition and smelting temperature on production of high quality SiC were studied. The existence of Fe element acts like a catalyst and contributes to the synthesis of SiC at relatively low temperatures (1550 °C). The excess of Fe element in the SSCW, however, would inhibit further improvement of the purity of the SiC product since Fe element would remain in the final product as Si–Fe alloy. Slight addition of salt was also verified to be positive for the improvement of SiC yield and purity. SiC product with a purity of more than 93 wt% was obtained after acid leaching for the removal of Fe impurity and under the optimized conditions as NaCl addition of 7 wt% and smelting temperature of 1850 °C. The thermodynamic analysis shows that a series of intermediate gas products (CO, SiO, SiO2) have been generated and taken an important role in the synthesis of SiC and excess carbon source is necessary for promoting the utilization of the SSCW since it can efficiently contribute to the formation of SiC and the intermediate products namely SiO and CO. The nucleation mechanism analysis indicates that both the original size and morphology of the carbon source and SiC particles have great influence on the forming particle size and morphology of the generated SiC since both can act as a nucleation center for a certain amount of SiC which is verified by the SEM analysis.