SiC Si Research Articles

Enhanced mechanical properties of nanocrystalline B4C–SiC composites by in-situ high pressure reactive sintering

A unique optimized of core–shell structural B4C nanopowder, sintering aid additive of Si, and high-pressure sintering technique has been used to process nanocrystalline B4C–SiC ceramics with enhanced mechanical properties. C-coated B4C nanopowder was initially uniformly mixed with micron Si of different content by ball-milling. B4C–SiC composites with a homogenous distribution of SiC in B4C matrix were subsequently obtained by sintering the mixed powders at 6 GPa and 1600 °C. The added Si reacted with submicron amorphous carbon layer and amorphous carbon nanoshell to form dispersed SiC nanocrystals and Si–C phase filled at B4C grain boundaries and pores, respectively. The prepared composite had the most outstanding mechanical properties when the Si content in the precursor was 15 wt%, with a hardness reaching 37.8 GPa and a fracture toughness reaching 7.3 MPa·m1/2. Microstructural characterizations indicated that the multi deflection of nanoscale crack caused by intergranular fracture, the covalent bonding of Si–C phase at the grain boundary, and the abundant nanotwin substructure were jointly responsible for the superior performance in hardness and fracture toughness.

Short-circuit protection scheme with efficient soft turn-off for power modules

With the increased current density of power semiconductor devices, their short-circuit reliability becomes a critical concern, especially prominent in SiC MOSFETs, exhibiting a much narrower short-circuit withstanding time. This paper proposes an effective protection scheme utilizing a compact PCB Rogowski coil to detect the short-circuit fault fast, and an active gate clamping circuit with a soft turn-off for protection. This scheme is first experimentally verified in discrete Si IGBT and SiC MOSFET, and subsequently in power modules for both. The results confirm its benefits in decreasing overshoot drain or collector voltage, peak current, and limiting short-circuit energy to avoid thermal runaway failure. Furthermore, the influence of key circuitry parameters in the soft turn-off circuit is investigated, and the general design methodology aiming for different devices is proposed.

Ablation behavior of ZrB2–SiC–Si composites with WC and MoSi2 additives coated through SPS on graphite

The intention of this paper is to investigate the resistance to ablation of shielding composite coatings built with ultra-high temperature ceramic materials on graphite substrate. To apply the coating on the graphite, the spark plasma sintering route was employed. The applied monolayer coatings had the base compositions of ZrB2–SiC–Si with the additives of WC and MoSi2, both in the same contents of 1.25 and 3.75 vol%. The outcomes achieved from the ablation tests by oxyacetylene flame showed that applying the protective composite coatings notably enhances the resistance to ablation of the substrate made of graphite. The coating containing more of WC and MoSi2 additives had better performance in terms of ablation resistance in 30-210 seconds. The formation of an oxide layer of (Zr,Si)O2 at the beginning of the ablation process and creating a layer with a porous microstructure on the composite coating surface functioned as a barrier against the destruction and erosion of the inner parts during longer ablation times.

Antioxidant performance and oxidation mechanism of a liquid silicon infiltration (LSI) SiC–Si coating at an ultra-high temperature of 1873 K

A novel SiC–Si coating with a high amount of net-like distributed Si was fabricated on the graphite substrate by liquid silicon infiltration (LSI) method to improve the oxidation-resistant performance. The mass gain of this LSI coating after 300 h oxidation at 1873 K was only 3.018%, suggesting an excellent static antioxidant property at 1873 K. The detailed oxidation mechanism of this LSI coating was explored in this work. It was found that the high amount of Si with the net-like distribution in this LSI coating promoted the passivation growth of SiO2 glass layer and prevented the SiO2 glass from crystallizing into cristobalite. In addition, the Si in this coating retarded the active oxidation and enhanced the coating stability. In contrast, the infiltration (VSI) SiC–Si coating presented an apparent mass loss, and the pack cementation (PC) SiC coating showed the catastrophic failure. The oxidation mechanisms of these two coatings were also discussed against the backdrop of the LSI coating with high antioxidant performance.

The influence of firing parameters on the formation of nitride phases in nitride bonded silicon carbides

In this study the influence of parameters like heating rate and dwell time on the kinetics of the nitridation process and microstructural development of nitride bonded silicon carbides was investigated. A combination of in situ and ex situ methods was used with special focus on the spatial formation of nitride phases.The nitridation of SiC–Si green bodies was carried out at heating rates of 1, 3 and 5 K/min and different multi-stage firing profiles were used. All samples were analysed by Raman spectroscopy and SEM. It was observed that with higher heating rates the number of α-Si3N4 whiskers in the matrix was reduced. An effect that was achieved with the direct firing to a temperature above the silicon melting point at 1409 °C as well. However, high heating rates have the disadvantage of a higher amount of residual silicon in the matrix after cooling.

Solid-State Transformer Based on Naturally Cell Balanced Series Resonant Converter With Cascaded H-Bridge Cells Switched at Grid Frequency

This paper proposes a closed-loop control architecture for a three-stage (MV, isolated DC/DC, LV) Solid State Transformer (SST) system and a modulation technique for the MV stage that shows better performance over existing solutions in terms of control simplicity, semiconductor loss, and cost. A simple and effective closed-loop control architecture is proposed for the entire SST system using the natural cell balancing ability of the Series Resonant Dual Active Bridge (SRDAB) converters in the DC/DC stage. In order to reduce semiconductor losses and cost, Si IGBT and SiC MOSFET devices are introduced properly in the MV stage of the SST power architecture, and the proposed modulation technique switches these devices appropriately according to their merits. The proposed modulation scheme ensures more than 50% semiconductor loss reduction in the MV stage. A circulating logic is proposed to achieve equal power sharing among cells in the MV stage and associated components. Detailed dynamic modeling, closed-loop control architecture, and modulation scheme are discussed in this paper. The proposed control technique and modulation scheme are verified experimentally in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{600}~V/100~V, \text{5}~kW$</tex-math></inline-formula> SST system.

Microstructural characterization of ZrB2–SiC–Si–MoSi2–WC coatings applied by SPS on graphite substrate

The aim of this research was to apply a protective composite coating made of ultra-high temperature ceramics (UHTCs) on the graphite substrates. The spark plasma sintering (SPS) method was used to apply this coating on the graphite substrate. First, efforts were made to choose the right chemical composition for the composite material of the coating and the sintering conditions (temperature, pressure, and holding time) for applying the coating. Then, single-layer coatings with the basic composition of ZrB2–SiC–Si with WC and MoSi2 additives in equal amounts of 1.25 and 3.75 vol% of each were successfully applied on the graphite substrates under sintering conditions of 1875±25 °C final temperature, 10 MPa initial pressure, 25 MPa final pressure and 5 min holding time. The presence of the Si element in the basic composition of these coatings, in addition to helping to form an intermediate diffusion layer at the interface between the composite coating and the graphite substrate, caused the strengthening of the joining despite the difference in the coefficient of thermal expansion between the graphite and the composite coating.

Radiation study on the parallel topology of SiC MOSFET and Si IGBT inverter

The electromagnetic radiation interference mechanism from multiple noise sources on the parallel topology of SiC MOSFET and Si IGBT Inverter is blurred, which will seriously affect the high reliability application of the structure. In order to solve this problem, a topological radiation EMI prediction method is proposed, the method includes the establishment of radiation equivalent models and radiation guidelines, the proposed inverter parallel topology radiation. The modeling method of electromagnetic interference can effectively analyze the influence of radiation interference of SiC and Si devices coupled with each other, and the established PCB radiation near and far field simulation can effectively realize the accurate prediction of radiation interference of inverter parallel topology, and finally the experimental platform of the parallel SiC MOSFET and Si IGBT inverter is built and tested, the test results demonstrate the accuracy of the proposed method.

Optical spectroscopy study of damage in ion-irradiated 3C-SiC epilayers on a silicon substrate

Epitaxial cubic (100) 3C-SiC films on a (100) silicon wafer were irradiated at room temperature with 2.3-MeV Si+ or 3.0-MeV Kr+ ions up to a fluence of 1 × 1016 cm−2. The evolutions of the epilayer and the substrate were followed as a function of ion fluence by using micro-Raman spectroscopy, optical absorption, and diffuse reflectance spectroscopy in the UV-visible and near infrared range. Raman spectra evidence the amorphization of SiC films at an estimated dose of about 0.1 displacement per atom (dpa) for both ion irradiations. The narrow peaks of the Raman-allowed TO and LO modes of SiC and Si are recorded in the virgin sample, together with few peaks assigned to zone-edge modes of SiC arising from the intrinsic disorder in the strained films. Those crystal phonon peaks broaden or disappear with increasing fluence. The spectra finally exhibit broad extra peaks assigned to the formation of Si–Si and C–C wrong homonuclear bonds in the local order of the amorphous phase. The optical transmission and diffuse reflectance spectra feature interference fringe patterns in the SiC film that are smoothened out with irradiation due to the matching of refractive indices of the amorphous SiC film and Si substrate. The evolution of the refractive index of SiC and optical gap of Si are deduced from those spectra. The respective roles of ballistic effects and electronic excitations in the radiation damage of both SiC and Si are discussed for those two ions with about the same electronic stopping power and about one order-of-magnitude difference in nuclear stopping power. The damage is dominated by the nuclear collision processes and rather well correlated with the estimated irradiation dose in dpa. Optical spectra show that electronic excitations induce damage recovery of the amorphized substrate below the SiC/Si interface. Raman spectra and optical absorption/reflection spectra yield complementary pictures of the radiation damage.

Mathematical Design and Analysis of Three-Phase Inverters: Different Wide Bandgap Semiconductor Technologies and DC-Link Capacitor Selection

This paper introduces a mathematical design and analysis of three-phase inverters used in electric drive applications such as aerospace, electric vehicles, and pumping applications. Different wide bandgap (WBG) semiconductor technologies are considered in this analysis. Using SiC MOSFETs and Si IGBTs, two drive systems are developed in order to show the improvement in the efficiency of the inverter. The efficiency, total losses of the drive systems and the power losses of two inverters are computed and compared for both drive systems at the same operating condition. The drive system with SiC MOSFET shows much better performance compared to the drive system with Si IGBT. The SiC MOSFET system provides a 59.39%, 86.13%, and 29.76% lower conduction losses, switching losses and drive’s total losses, respectively, compared to the Si IGBT system. The efficiency of the SiC MOSFET system is 2.46%pu higher than the efficiency of the Si IGBT drive system. Moreover, this paper introduces a detailed analysis for the dc-link voltage and current ripples in three-phase inverters. Furthermore, the minimal dc-link capacitor needed to deal with the ripple current and voltage is investigated. Finally, the performance of the drive with Si IGBT is experimentally tested under different operating speeds and loads.

Role of nano-Al2O3 particles in improving the properties of MgO–C slide plate materials

The unfired Al–Si incorporated MgO–C slide plate materials were manufactured using magnesia aggregates and fines, SiC aggregates, Al, Si and B4C powders as the raw materials, trace nano-Al2O3 particles as additive, and phenolic resin as binder. The contributions of nano-Al2O3 in the properties, phase composition and microstructure of MgO–C materials were studied. The reseult indicates that nano-Al2O3 is beneficial to improve mechanical properties of the materials, which is attributed to the good filling and pinning effects of nanoparticles. Highly reactive nano-Al2O3 can promote the densification of MgO–C materials and in-situ formation of ceramic phases at high temperatures, and a large number of non-oxide whiskers contributes to the formation of a continuous interlocking networks, which improves the high-temperature strength and TSR of MgO–C materials. Moreover, nano-Al2O3 promotes the formation of fine-grained pinel and forsterite protective layer in the high-temperature oxidizing atmosphere and prevents the diffusion of oxygen into the interior of the material, thus improving the oxidation resistance of MgO–C refractories.

Performance Comparison of Si IGBT and SiC MOSFET Power Module Driving IPMSM or IM under WLTC

The cumulative inverter losses and power consumption of a silicon insulated gate bipolar transistor (Si IGBT) and three types of silicon carbide metal-oxide-semiconductor field-effect transistors (SiC MOSFETs) were evaluated on an electric motor test bench under a worldwide harmonized light vehicles test cycle (WLTC). SiC MOSFETs showed higher performance than Si IGBT regardless of the motor type and test vehicles. In the case of driving an interior permanent magnet synchronous motor (IPMSM), the latest 4th generation SiC MOSFET (SiC-4G) in ROHM has the lowest inverter loss and energy consumption compared with the other generations. In the case of driving an induction motor (IM), on the other hand, the 2nd generation SiC MOSFET (SiC-2G) in ROHM has the best energy consumption despite the fact that the inverter losses of SiC-2G are slightly larger than the loss of SiC-4G. The latest or later generation power device does not necessarily contribute to better performance in a total system by simply replacing early power devices.

Characterization of MoAlB ceramics synthesized via spark plasma sintering with Si addition and SiC reinforcement

The MoAlB phase with high purity and density from elemental precursors was successfully synthesized with SPS (Spark Plasma Sintering) at 1200 °C. Then, MoAlB-Si solid solution and MoAlB-SiC (5% SiC by volume) composite were fabricated to improve the mechanical properties and oxidation behavior of the MoAlB further. XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and EDS (Energy Dispersive X-Ray Spectroscopy) investigated the composition and microstructure of the MoAlB ceramics. The hardness was measured by the Vickers indentation test, and fracture toughness was calculated by radial cracks formed during the indentation test. The hardness and fracture toughness of pure MoAlB was 10.30 GPa and 6.73 MPa.m1/2. With the Si solid solution, the hardness increased to 11.93 GPa, while the fracture toughness decreased to 5.49 MPa.m1/2. The highest hardness and fracture toughness were obtained in the MoAlB-SiC composite, 12.39 GPa, and 7.38 MPa.m1/2, respectively. The oxidation tests of the samples were characterized in the air at 1200 ℃ for 12 h. A dense and continuous oxide layer was formed in all samples after 12 h at 1200 °C. While both Si solid solution and SiC reinforcement increase the oxidation resistance, the best results were obtained in the MoAlB-Si-SiC composite. The effect of Si addition and SiC reinforcement on electrical and thermal conductivity was measured from room temperature to 1000 ⁰C. The electrical conductivity of all samples decreased exponentially with the increase in temperature. The electrical conductivity of pure MoAlB was 2.82 S⋅m−1 at room temperature and decreased with the Si addition (2.49 S⋅m−1) or SiC reinforcement (2.67 S⋅m−1). On the other hand, thermal conductivity tends to decrease between room temperature to 400 °C but showed an increasing trend above 400 °C. In conclusion, the mechanical properties and oxidation resistance of MoAlB ceramics were improved with Si addition and SiC reinforcement.

A Single Phase GaN GITs-Based Bidirectional Multilevel Inverter for High Voltage Grid Tied Photovoltaic Power System

— In this article, a performance comparison has been conducted between Si MOSFETs, SiC MOSFETs, and Gallium nitride (GaN) GITs in single phase BSNPC inverter. The PSpice study shows that the All GaN GITs BSNPC inverter has the highest efficiency of 98.97% compared to all other power devices used in the simulations. Due to a low dead time of 50 ns, the THD in output voltage for the All GaN GITs BSNPC inverter has decreased by 10% compared to the All Si MOSFETs BSNPC inverter and by 0.5% compared to the All SiC MOSFETs BSNPC inverter. The operation of GaN GITs at 200 kHz resulted in a 63% reduction in output filter size compared to the operation at 10 kHz. The Gate Drive circuit for GaN GITs and its complete design is presented. The All GaN GITs BSNPC inverter laboratory prototype study shows that at 16 kHz, 700 W the maximum efficiency of 99.4% is achieved whereas at 64 kHz, 350 W the lowest efficiency of 98.7% is achieved. The performance of the two GaN GITs connected in series to make a single series bidirectional switch is very reliable and robust. When the switching frequency is increased from 16 kHz to 64 kHz at 700 W output power, the reduction in the output filter size is 35%. The reduction in THD in the output voltage is 8.3% for the GaN GITs when operated at 150 ns dead time compared to 1 μs dead time.

Preparation of high thermal conductivity diamond/SiC composites with 3D connected diamond at low volume fraction

Diamond/SiC composite with 3D connected diamond as the reinforcements are prepared for the first time using the foam SiC as a template. The fabricated composite consisted of diamond, SiC and residual Si; nearly fully dense composite obtained by liquid Si infiltration as densification process. The results show that construction of efficient diamond heat transport channels in composite can greatly improve its thermal conductivity. Finally, the thermal conductivity of 3D connected diamond particles reinforced diamond/SiC composite reached up to 298 W/mk, at diamond volume fraction of only 26 vol%, which is almost the same as that of composite with 38 vol% diamond in the literature. Construction of heat transfer channels greatly reduces the diamond content in the diamond/SiC composite, effectively decreasing its preparation cost and providing a new development direction for diamond/SiC composite.

Bifunctional SiC/Si 3N 4 aerogel for highly efficient electromagnetic wave absorption and thermal insulation

SiC ceramics are attractive electromagnetic (EM) absorption materials for the application in harsh environment because of their low density, good dielectric tunable performance, and chemical stability. However, the performance of current SiC-based materials to absorb EM wave is generally unsatisfactory due to poor impedance matching. Herein, we report ultralight SiC/Si₃N₄ composite aerogels (~15 mg·cm⁻³) consisting of numerous interweaving SiC nanowires and Si₃N₄ nanoribbons. Aerogels were prepared via siloxane pyrolysis and chemical vapor reaction through the template method. The optimal aerogel exhibits excellent EM wave absorption properties with a strong reflection loss (RL, −48.6 dB) and a wide effective absorption band (EAB, 7.4 GHz) at a thickness of 2 mm, attributed to good impedance matching and multi attenuation mechanisms of waves within the unique network structure. In addition, the aerogel exhibits high thermal stability in air until 1000 ℃ and excellent thermal insulation performance (0.030 W·m⁻¹·K⁻¹). These superior performances make the SiC/Si₃N₄ composite aerogel promising to become a new generation of absorption material served under extreme conditions.

A Si/SiC Hybrid Full-Bridge Submodule for Modular Multilevel Converter With its Control Scheme

Due to the high dc voltage utilization and capability of dc fault blocking, the full-bridge submodule-based modular multilevel converter (FBSM-MMC) becomes a prevalent topology for medium voltage high power applications. However, using the Si IGBT for each FBSM can induce high switching loss while the SiC MOSFET suffers from high cost because of limitations of fabrication technologies. To address this issue, a hybrid FBSM consisting of both SiC MOSFET and Si IGBT is studied in this article. In addition, an optimal control scheme is proposed, which adjusts the current conducting path of the FBSM and concentrates the high-frequency switching actions into the SiC module. The proposed control scheme only modifies the submodule (SM) level switching and has good compatibility with the existing MMC modulation schemes. Compared with the MMC solely formed by SiC MOSFET, the hybrid SM has similar switching loss and better performance in terms of conduction loss and cost. The experimental results prove the validity of the proposed topology and control scheme, and the further loss and cost analysis verifies that the Si/SiC hybrid FBSM can reduce the loss by 16.3% and save the device cost by 41.0% compared with the SiC FBSM.

Laser ablation of RB-SiC composite by femtosecond laser irradiation

Reaction-bonded silicon carbide composites (RB-SiC), consisting of SiC grains and Si matrix, have a complex ablation mechanism as two-phase composites under femtosecond laser irradiation. The ablation threshold of RB-SiC was calculated, which decreases (from 1.01 J/cm2 to 0.56 J/cm2) with increasing pulse number N and finally stabilized. At low fluence (F/Fth ≤ 5) and a low number of pulses, photochemical ablation dominates. For a higher number of pulses and high fluence (5 <F/Fth ≤ 50), photothermal ablation dominates with photochemical ablation. The results show that structures such as pits, convex, and holes exist on the surface of Crater I, while Laser-induced Periodic Surface Structures (LIPSS), and condensation structures exist on the surface of Crater II. In both types of ablation craters, the SiC grain surface produces the Low Spatial Frequency LIPSS (LSFL) with a period of about 900 nm and the High Spatial Frequency LIPSS (HSFL) with a period of about 300 nm. Based on the surface morphology, microstructure, and physical phase analysis of the ablation craters, a preliminary model of the removal mechanism of the ablation craters by femtosecond laser irradiation was established. These findings are expected to provide theoretical and experimental support for the precision processing of RB-SiC by femtosecond laser.

Calcium hydroxide and porous silicon-impregnated silicon carbide-based composites for thermochemical energy storage

Thermal energy storage has a prospect for large-scale storage of renewable energy. Thermochemical energy storage using reversible gas–solid reactions can store thermal energy for unlimited periods with high energy density. Calcium hydroxide (Ca(OH)2), which is abundant and environmentally friendly, is one of the most promising materials for thermochemical energy storage systems. However, pure Ca(OH)2 powder has poor power density and bulk stability owing to its low thermal conductivity, volume change, and agglomeration over dehydration–rehydration cycles. Practical composites that can simultaneously overcome these problems have not been reported yet. This study combines Ca(OH)2 with ceramic foam and honeycomb structures of silicon-impregnated silicon carbide (Si–SiC) and demonstrates the improved power density and bulk stability of the resulting composites. The Si–SiC foam composite, loaded in a laboratory-scale fixed-bed reactor, exhibits a thermal discharging power density of 0.71 MW mbed−3, which is 1.6 times that of the pure Ca(OH)2 powder. In addition, the foam composite reduces the volume change by 80% and does not form centimeter-scale agglomerates even after 15 cycles, unlike the pure powder. The results suggest that embedding solid storage materials into thermally conductive open-cell foams can simultaneously enhance power density and bulk stability.

Oxidation and ablation behaviours of a SiCnw@SiC–Si coating fabricated for carbon-fibre-reinforced carbon-matrix composites via thermal evaporation and gaseous silicon infiltration

A SiC-nanowire-modified SiC–Si (SiCnw@SiC–Si) coating was prepared for carbon-fibre-reinforced carbon-matrix (C/C) composites using a two-step method based on thermal evaporation and gaseous silicon infiltration, and the effects of SiC nanowires on the oxidation and ablation behaviours of the coated samples were studied. Oxidation tests conducted at 1500 °C revealed that the weight loss of the SiC–Si-coated C/C composite was 15.85% after 6 h, whereas the SiCnw@SiC–Si-coated C/C composite experienced a significantly lower weight loss of 1.27% after 50 h. Ablation tests suggested that the mass and linear ablation rates of the SiCnw@SiC–Si-coated C/C composite were 0.05 mg/s and 0.09 μm/s, respectively; they were reduced by 78.26 and 92.74%, respectively, compared with those of the SiC–Si-coated C/C composite. Careful characterisation suggested that the network structure of the SiC nanowires in the SiC–Si phase can suppress crack propagation and firmly attach to the coating surface to enhance the interfacial adhesion between the coating and substrate, leading to improved anti-oxidation and anti-ablation properties. The SiCnw@SiC–Si coating could offer a technological foundation for preventing the oxidation and ablation of C/C composites in aerospace engineering.