Silicon Carbide Whiskers Research Articles

Preliminary investigation on silicon carbide whisker-modified cement-based composites

Stable silicon carbide whisker (SiCw) dispersion was obtained and used for the preparation of SiCw-modified cement-based composites. Strength tests including compression test, flexural test, split tensile and “8” shape tensile tests were carried out on the composites. Fracture properties of the material were measured by the pre-notched three-point bending test based on digital image correlation (DIC) method. The microstructure of the SiCw-modified cement mortar was observed by SEM. The results showed that SiCw could obviously improve tensile strength of the cement-based material. The addition of SiCw significantly improved fracture toughness of the cement-based material, as there was a crack deflection of the materials occurring during crack growth.

Improving self-healing ability and flexural strength of ytterbium silicate-based nanocomposites with silicon carbide nanoparticulates and whiskers

In the emerging era of aircraft industry, silicon carbide (SiC) is regarded as an appropriate material for gas turbine engine blades. In order to protect this ceramic component against the oxidation and volatilization in hot steam environments, environmental barrier coating should be utilized. The composite of SiC/Yb2Si2O7–Yb2SiO5 with self-healing ability is a candidate for the top layer of this coating. In this study, the crack-healing behavior of SiC/Yb2Si2O7–Yb2SiO5 nanocomposites is investigated by pre-cracking followed by annealing in oxidizing environments. Comparing to previous studies, the healing time and healing temperature can be reduced to 15 min and 800 °C by increasing the volume fraction of SiC to 20 %. In addition, nanocomposites with both self-healing ability and superior strength were created in this research by combining two types of SiC filler (whiskers and nanoparticulates). The self-healing mechanism in these composites is the SiC oxidation and silicate transformation associated with their volume expansion, which is evidenced by X-ray diffraction and scanning electron microscope. According to the results, the best volume ratio between whisker and nanoparticulate is determined as 1/3.

Silicon carbide whiskers reinforced SiOC ceramics through digital light processing 3D printing technology

Polymer derived silicon oxycarbide ceramic materials and silicon carbide whiskers reinforced ceramic composite are prepared through digital light processing (DLP) 3D printing technology in the present work. A new type of UV-curable preceramic polymer is firstly synthesized and then two types of photopolymer resins with and without SiC whiskers as reinforcement are prepared. Due to the high curing rate and good fluidity of the resins, they are applied in DLP 3D printing and various 3D objects with complicated structures and high printing resolution have been printed. The derived ceramic materials show amorphous microstructure and there is no apparent porosity and cracking throughout the whole sample surface of the ceramic materials and the SiC whiskers are uniformly embedded in the ceramic matrix and remain intact and unaffected during the pyrolysis process. The SiC whiskers reduced the shrinkage and mass loss. More importantly, it significantly improves the mechanical performance of the derived ceramic materials in which the compressive strength increases from 77.5 ± 10.2 MPa to 98.4 ± 12.3 MPa. Benefiting from the easiness of the fabrication, high printing resolution and excellent mechanical performance, the derived ceramic materials have great potential applications in various areas.

Improvement of toughness of reaction bonded silicon carbide composites reinforced by surface-modified SiC whiskers

To improve the reliability, especially the toughness, of the reaction bonded silicon carbide (RBSC) ceramics, silicon carbide whiskers coated with pyrolytic carbon layer (PyC-SiCw) by chemical vapor deposition (CVD) were introduced into the RBSC ceramics to fabricate the SiCw/RBSC composites in this study. The microstructures and properties of the PyC-SiCw/RBSC composites under different mass fraction of nano carbon black and PyC-SiCw were investigated methodically. As a result, a bending strength of 550 MPa was achieved for the composites with 25 wt% nano carbon black, and the residual silicon decreased to 11.01 vol% from 26.58 vol% compared with the composite of 15 vol% nano carbon black. The fracture toughness of the composites reinforced with 10 wt% PyC-SiCw, reached a high value of 5.28 MPa m1/2, which increased by 39% compared to the RBSC composites with 10 wt% SiCw. The residual Si in the composites deceased below to 7 vol%, resulting from the combined actively reaction of nano carbon black and PyC with more Si. SEM and TEM results illustrated that the SiCw were protected by PyC coating. A thin SiC layer formed of outer surface of whiskers can provide a suitable whisker-matrix interface, which is in favor of crack deflection, SiCw bridging and pullout to improve the bending strength and toughness of the SiCw/RBSC composites.

A novel strategy to prepare BN interface and its effects on microstructure and properties of SiCw/BN/SiC composites

Based on the microstructure and composition design idea of continuous fiber toughened ceramic matrix composites (CFCCs), a BN interface layer was prepared on the surface of silicon carbide whiskers (SiCw) for the first time. And SiCw toughened SiC ceramic matrix composites with BN interface (SiCw/BN/SiC composites) were prepared by precursor infiltration and pyrolysis (PIP) combined with reactive melt infiltration (RMI). The as-prepared SiCw/BN/SiC composites possess high strength and high density, as well as the isotropic characteristics. By adjusting the thickness of the BN interface, the residual stress inside the composites is reduced and the bonding strength between the whisker and the matrix is optimized, thereby improving the toughness of the SiCw/BN/SiC composites. When the thickness of BN interface is about 3 nm, the flexural strength and the fracture toughness of the composites attain 425 MPa and 6.6 MPa m1/2, respectively. The bulk density of the SiCw/BN/SiC composites is about 2.87 g cm−3 and the open porosity is less than 4%, indicating the high densification and excellent gas tightness. The toughening mechanisms of SiCw/BN/SiC composites contain SiCw toughening and micron-sized SiC particles (produced by RMI process) toughening, which ensure a good toughness for the dense composites together with the positive effect of BN interface.

Enhanced fracture toughness of ZrB2–SiCw ceramics with graphene nano-platelets

In this study, the spark plasma sintering technology was implemented to produce hybrid zirconium diboride ceramics comprising of silicon carbide whiskers (SiCw: 25 vol%) and various amounts of graphene nano-platelets (Gnp: 0–7.5 wt%). The effects of nano-graphene addition on the structural evolution, hardness, fracture toughness, and densification behavior of ZrB2–SiCw nanocomposites were investigated. Though all produced hybrid ceramics reached the full densification level, with relative densities of ≥99.9%, a negligible drop was observed in the relative density of the specimen reinforced with 7.5 wt% graphene nano-platelets. After the sintering step and due to the lack of any chemical interaction in the ZrB2–Gnp–SiCw system, no in-situ formed phases were detected by X-ray diffraction or electron microscopy investigations. The incorporation of nano-scale graphene additives resulted in grain coarsening inhibition significantly. The hardness slightly increased from 21.9 GPa for the specimen with no graphene to 22.2 GPa for the sample doped with 2.5 wt% graphene. However, with rising the nano-graphene amount, the hardness remarkably dropped to 16.6 GPa and 19.1 GPa for the samples doped with 7.5 wt% and 5 wt% nano-graphene, respectively. The fracture toughness remarkably enhanced, with a linear trend, by the addition of graphene nano-platelets from lower 5 MPa m½ in the carbon-free ceramic to above 6 MPa m½ in the specimen doped with 7.5 wt% nano-graphene. The identified dominant toughening mechanisms were crack bridging, crack arresting, and crack deflection.

Simultaneous effects of rice husk silica and silicon carbide whiskers on the mechanical properties and morphology of sodium geopolymer

The current research is focused on developing a geopolymer binder using rice husk ash–derived silica nanoparticles. Four types of rice husks were collected directly from various rice fields of Bangladesh in order to evaluate the pozzolanic activity and compatibility of the derived rice husk ashes with precursors of sodium-based geopolymers. Silicon carbide whiskers were introduced into sodium-based geopolymers in order to evaluate the response of silicon carbide whiskers to the interfacial bonding and strength of sodium-based geopolymers along with rice husk ashes. Compression, flexural and short beam shear tests were performed to investigate the synergistic effect of rice husk ashes–derived silica and commercially available silicon carbide whiskers. Results show that rice husk ashes–derived spherical silica nanoparticles reduced nano-porosity of the geopolymers by ∼20% and doubled the compressive strength. The simultaneous additions of rice husk ashes and silicon carbide whiskers resulted in flexural strength improvement by ∼27% and ∼97%, respectively. The increase in compressive strength due to the inclusion of silica nanoparticles is related to the reduction in porosity. The increase in flexural strength due to simultaneous inclusion of silica and silicon carbide whiskers suggest that silica particles are compatible with the metakaolin-based geopolymers, which is effective in consolidation. Finally, microscopy suggest that silicon carbide whiskers are effective in increasing bridged network and crack resistance.

Mechanical anisotropy in polymer composites produced by material extrusion additive manufacturing

Extrusion-based additive manufacturing technologies, such as direct ink writing of filled polymer resins, have shown a great potential for the development of printed components with superior structural and functional properties. However, the associated extrusion process induces preferred orientation on high-aspect-ratio filler materials as they extrude through the deposition nozzle, causing strong mechanical anisotropy in printed components. Printing-induced anisotropy is a critical issue that complicates the straightforward design of additively manufactured components. The goal of this work is to gain a better understanding of the anisotropy in printed polymer composites by investigating the effects of filler morphology and print parameters on the mechanical properties of printed composites. Inks are formulated using fumed silica particles or nanoclay platelets as the primary viscosifying agent, and silicon carbide (SiC) whiskers as the primary mechanical reinforcement. Mechanical anisotropy is characterized via 3pt-flexural tests for epoxy ink formulations utilizing fumed silica or nanoclay, with or without SiC whiskers, and printed at three different print speeds, using three different nozzle sizes. Orientation of nanoclay is also characterized using small- and wide-angle x-ray scattering. Results show that smaller nozzle diameters and higher deposition rates lead to greater anisotropy when nanoclay or SiC fillers are utilized, while the use of fumed silica alone results in mechanical behavior that is independent of print parameters and print path. Superior flexure strength values up to 215 MPa are obtained with SiC whisker-reinforced composites when tested parallel to the print direction.

Fabrication and characterization of SiC whiskers toughened Al2O3 paste for stereolithography 3D printing applications

To prevent the agglomeration of silicon carbide whiskers (SiCw) in photosensitive ceramic paste, a butanone-ethanol azeotropic solvent is employed to facilitate the dispersion of alumina particles, SiC whiskers and UV resins. Moreover, SiCw/Al2O3 ceramic pastes, with 5–15 vol % SiCw, are prepared by using ball milling, stirring and distillation processes. The mixture of butanone-ethanol solvent and resins can be effectively separated at 70 °C without weakening the polymerization of UV resin. Moreover, an empirical equation is established to evaluate the relationship between SiCw content, aspect ratio and viscosity of resulting ceramic paste. The 15 vol % SiCw/Al2O3 composite ceramic, with SiCw aspect ratio of 50, renders higher resistance to liquid flow and results in a high viscosity of 30,000 mPa s at the shear rate of 30 s−1. Furthermore, a modified equation is established to predicate the curing depth of ceramic pastes with different amounts of SiCw, where 15 vol % SiCw/Al2O3 composite results in higher light scattering properties, leading to lowest Cd of ∼0.061 mm. Finally, the complex-shaped SiCw/Al2O3 ceramic component, prepared by SL 3D printing technology, debinding and sintering processes, exhibited a superior fracture toughness of 7.1 ± 1.20 MPa m1/2 and a higher hardness of 17.6 ± 0.78 GPa.

Influence of SPS temperature on the properties of TiC–SiCw composites

Titanium carbide (TiC) composites containing 10 vol% silicon carbide whisker (SiCw) were spark plasma sintered at different temperatures of 1800, 1900, and 2000 °C under a pressure of 40 MPa and a holding time of 7 min. At the sintering temperature of 1900 °C, the relative density, Vickers hardness, and flexural strength of the sintered samples hit their maximum values of 98.7%, 24.4 GPa, and 511 MPa, respectively. The microstructural characteristics of the sintered samples were assessed by optical and field emission scanning electron microscopy (FESEM) and XRD. The results revealed that at 1900 °C, the dispersion of SiCw in the TiC matrix was homogenous, no chemical reaction took place between the reinforcement and the matrix, and produced a fine-grained microstructure. It was found that the thermal conductivity of SPSed samples did not have the same trend with relative density and mechanical properties. A maximum value of 32.3 W/mK was measured for the thermal conductivity of the composite sintered at 2000 °C.

Improved toughness and delamination resistance in continuous fiber reinforced geopolymer composites via incorporation of nano-fillers

Geopolymer matrix composites (GMC) have the potential to bridge the processing performance gap between polymer matrix and ceramic matrix composites. Yet one drawback of GMCs is their extreme brittleness and weak inter-laminar shear strength. The aim of this study was to evaluate the effectiveness of Silicon Carbide Whisker (SCW) nano-filler on the mechanical performance of neat unreinforced geopolymer and unidirectional fiber reinforced GMCs containing variations in fiber surface chemistry. In order to evaluate, neat and SCW populated geopolymer matrices were fabricated for comparison. Nextel 610 fiber reinforced GMCs were also fabricated with SCW for comparison to GMCs without the SCW nano-filler. The effect of the nano-filler was evaluated using three-point flexural methods to obtain strength and fracture toughness (KIC). Results indicate that the addition of SCWs up to 4 vol% improved Mode-I fracture toughness of the baseline geopolymer matrix by 113%. The improvements to the neat matrix also resulted in improved flexural strength, inter-laminar shear strength, and delamination resistance of the continuous fiber reinforced composites.

Construction of multiple heterogeneous interface and its effect on microwave absorption of SiBCN ceramics

Iron-containing siliconboron carbonitride (SiBCN) ceramics with multiple heterogeneous interfaces were fabricated using the microstructural design and polymer-derived ceramics (PDC) approach. The characterization results revealed the in-situ generation of nanocrystals, including graphite, belt-like silicon nitride (Si3N4), and silicon carbide (SiC) whiskers, in amorphous SiBCN matrix after annealing. At the same time, these dielectric lossy phases successfully constructed multiple heterogeneous interfaces and three-dimensional network structures. Consequently, the conductivity of the ceramics increased from 4.49 × 10−9 (annealed at 800 °C) to 0.67 × 10−4 S cm−1 (annealed at 1600 °C). The real part of permittivity improved from 4.57–3.36 (annealed at 800 °C) to 10.90–8.38 (annealed at 1600 °C) in the frequency range of 2–18 GHz. The formation of multiple heterogeneous interfaces caused interfacial polarization and increased the multiple relaxations, which ultimately led to a superior microwave absorption property with a minimum reflection loss (RLmin) of −34.28 dB and an effective absorption bandwidth (EAB) of 3.76 GHz (8.64–12.4 GHz).

Effect of Crack Length on Strength Recovery of Silicon-Carbide-Whisker-Reinforced Silicon Nitride Upon Healing Treatment

A silicon carbide whisker (SiCw) reinforced silicon nitride (Si3N4) composite ceramic was selected to study the crack-healing performance. Pre-cracks of various length were introduced on the tensile side of specimens by Vickers hardness tester. The crack-healing performance as a function of heating temperature and crack dimension, as well as the crack-healing mechanism were investigated. The optimal heat treatment temperature for crack-healing of Si3N4/SiCw is 1200–1300 °C. The treatment allows complete healing of a crack of 200 μm after heat treated at 1300 °C, and achievement of a substantial strength recovery for pre-cracked specimens even with much longer cracks (1200 μm). Crack closure and strength recovery of the pre-cracked specimen were considered to be triggered by the creation of SiO2, liquid aluminosilicate glass and silicon yttrium oxide by the oxidation reaction as filling mechanism during heat treatment.

Synthesis of Organic Modified SiCw/PVDF Composite Membrane and Its Dielectric Properties under Low Temperature

Cetyltrimethylammonium bromide (CTAB) was incorporated into silicon carbide whiskers (SiCw) to improve their hydrophobicity. The solution casting method was employed to develop composite membranes of polyvinylidene fluoride (CTAB-SiCw/PVDF) with different feed ratios. FT-IR spectroscopic studies proved that CTAB was successfully incorporated into the SiCw. SiCw phase structure was maintained after modification by CTAB according to XRD results. SEM studies indicated that the surface became smoother with CTAB dispersal in the PVDF membrane. The dielectric properties of the composite membranes containing various amounts of CTAB-SiCw were measured at low temperature. It was found that the dielectric constant of the composite membranes with 13.0wt% whiskers reached a maximum value of 25 at low frequency, and decreased to nine at high frequency (from 500 Hz to 1 MHz ) at 0 ℃. The dielectric loss of each composite membrane increased with increasing temperature and reached a maximum value. The value shifted with corresponding frequency increases. In addition, the dielectric loss reached a maximum value of 0.2 when 16.7wt% of CTAB-SiCw was fed at each frequency (from -30 ℃ to 10 ℃). At room temperature, the dielectric constant could be maintained at 42 and the loss factor decreased to 0.8 at 100 Hz when 13.0wt% of CTABSiCw was incorporated. Additionally, TGA experiments indicated that the decomposition temperature of a PVDF membrane was increased by 10 ℃ and its heat resistance was improved by adding 13.0wt% of CTAB-SiCw. This PVDF composite membrane has potential for use as an insulator and capacitor.

Combined role of SiC particles and SiC whiskers on the characteristics of spark plasma sintered ZrB2 ceramics

In this research work, the effects of silicon carbide (SiC) as the most important reinforcement phase on the densification percentage and mechanical characteristics of zirconium diboride (ZrB2)-matrix composites were studied. In this way, a monolithic ZrB2 ceramic (as the baseline) and three ZrB2 matrix specimens each of which contains 25 vol% SiC as reinforcement in various morphologies (SiC particulates, SiC whiskers, and a mixture of SiC particulates/SiC whiskers), have been processed through spark plasma sintering (SPS) technology. The sintering parameters were 1900 °C as sintering temperature, 7 min as the dwell time, and 40 MPa as external pressure in vacuum conditions. After spark plasma sintering, a relative density of ~96% was obtained (using the Archimedes principles and mixture rule for evaluation of relative density) for the unreinforced ZrB2 specimen, but the porosity of composites containing SiC approached zero. Also, the assessment of sintered materials mechanical properties has shown that the existence of silicon carbide in ZrB2 matrix ceramics results in fracture toughness and microhardness improvement, compared to those measured for the monolithic one. The simultaneous addition of silicon carbide particulates (SiCp) and whiskers (SiCw) showed a synergistic effect on the enhancement of mechanical performance of ZrB2-based composites.

Effect of Cu/Si Additive on the Microstructure of Pyrolysis Carbon Derived from Phenolic Resin

Phenolic resin has been widely applied as a carbonaceous binder in the field of carbon composites and carbon materials. The microstructure of pyrolysis carbon that derived from carbonaceous binders played an important role in the properties of carbon-containing refractories. In this study, the effects of copper and silicon on the pyrolysis behavior of phenolic resin and the microstructure of the pyrolysis carbon were investigated by using thermosetting phenolic resin as raw material, and using silicon powder (99%, 200 mesh) as well as copper nitrate (AR, w(Cu(NO3)2)⩾99%) as additives. The results showed that the copper nano-particles in-situ formed from copper nitrate could be served as catalyst in the pyrolysis process of resin. Catalytic synthesis of carbon nanofibers could improve the degree of carbonization with pyrolysis carbon microstructure at low temperature (below 800 °C). The carbon nanofibers had lamellar structure and layered stacking characteristic. Silicon carbide whiskers were produced by Cu-doping phenolic resin with copper and silicon at 1400 °C.

High Yield Silicon Carbide Whiskers from Rice Husk Ash and Graphene: Growth Method and Thermodynamics

A new stacking bed method to prepare high-quality silicon carbide whiskers (SiCws) with high yield has been proposed. To provide a steady and high concentration SiO atmosphere during the carbotherm...

Synergy Effects in Electromagnetic Properties of Phosphate Ceramics with Silicon Carbide Whiskers and Carbon Nanotubes

Hybrid composite materials based on an aluminium phosphate matrix with silicon carbide whiskers and multi-walled carbon nanotubes were studied in a wide frequency range (20 Hz to 36 GHz). It was demonstrated, that the addition of the silicon carbide whiskers enhances the dielectric permittivity and conductivity. This was explained by the difference in tunnelling parameters. Hybrid ceramics with nanotubes and whiskers also exhibits substantially improved electromagnetic shielding properties. The hybrid ceramics with 10 wt. % silicon carbide whiskers and a 1 mm thick 1.5 wt. % carbon nanotube layer, show higher than 50% absorption of electromagnetic radiation.

Electromagnetic Wave Absorption Performance of Carbonized Rice Husk Obtained at Various Temperatures.

Agricultural wastes such as rice husks (RHs) are valuable due to their feasibility to be converted into carbon materials, low cost, and abundancy in contrast to the conventional carbon material sources. In this study, RHs are carbonized at various temperatures from low to high temperatures, and their electromagnetic (EM) wave absorption properties are evaluated. Carbon materials, silicon carbide (SiC) whiskers, and SiC particles are obtained from RHs carbonized at 1500 °C (CRH1500) for 0.5 h with presence of Ar gas at 1 atm. In order to evaluate their EM wave absorption performance, complex permittivity and permeability are measured by using vector network analyzer, and the values are utilized in the reflection loss (R.L.) calculation according to the transmission line theory. CRH1500, 40 wt% with thickness of 1.6 mm exhibits minimum R.L. of ≈−55.4 dB (>99.9997% absorption) at 11.37 GHz and response bandwidth (R.L. < 10 dB, > 90% absorption) of 4.21 GHz. Low‐cost and abundant RHs, carbonized at various temperatures, show significant absorption performance. Their absorption performance and response bandwidth are highly dependent on matching thickness, indicating that they can be easily modulated for promising electromagnetic wave absorber materials.

Influence of the crack area on the crack-healing performance of silicon carbide whisker reinforced silicon nitride composite

The crack healing properties of Si3N4 composite ceramic reinforced by SiC whiskers (Si3N4/SiCw) was studied. Six kinds of pre-cracks were introduced on the center of the tensile side of the specimens, and the relationship between the crack area and crack healing properties was studied. The results show that the healing effect of strength recovery is similar with that of smooth specimens for pre-cracked specimens with crack depth less than 60 μm. As for the propagated crack and the central through crack, the strength recovery rapidly decreases due to the increase of crack depth. It could be concluded that it is difficult to heal pre-cracked specimens with the crack depth over 90 μm. The main reason is considered to be that the melted glass phase blocked in the surface, and prevented the oxidation reaction in the inner of crack.