Low density,three-dimensionally interconnected carbon nanotube/silicon carbide nanocomposites for thermal protection applications

Synthesis of silicon carbide (SiC) nanostructures and their composites has been a topic of interest for the scientific community due to the unique properties that can be obtained with nanoscale features. Herein, we report the scalable fabrication of anisotropic and low density, carbon nanotube/SiC (CNT/SiC) core-shell structures synthesized via chemical vapor infiltration (CVI) of silicon on aligned CNT foams followed by heat treatment at 1350 °C. Structures made of CNT/SiC nanotube networks with a thickness of 1 cm and length of 9 cm were prepared in the present work. Upon the removal of the CNT foam via calcination of the hybrid nanocomposite in air, a free-standing mechanically robust three-dimensional network of pure SiC nanotubes was left behind. The density of the synthesized CNT/SiC is the lowest reported for any C/SiC structure. Furthermore, the CNT/SiC hybrid nano-architecture demonstrated superb heat resistance and stability in ultrahigh temperature environment.     

A review on the processing technologies of carbon nanotube/silicon carbide composites

Due to the extraordinary electronic, mechanical, chemical, thermal, magnetic, and optical properties, carbon nanotube (CNT), an excellent one-dimensional nano-material, has been considered as a new filler for polymer, metal, and ceramic matrix composites with the main purpose of improving their mechanical performance, fracture behavior, and functional features. In the silicon carbide (SiC) ceramic field, there are many CNT reinforced SiC ceramic matrix composites and CNT/SiC hybrid structures, which have been investigated successfully using various of methods. This paper reviews the current status of researches and describes all different routes for effectively dispersing CNTs throughout SiC ceramic matrix, densifying composites, and synthesizing hybrid structures.     

Anisotropic compressive properties of porous CNT/SiC composites produced by direct matrix infiltration of CNT aerogel

Carbon nanotube‐reinforced silicon carbide composites (CNT/SiC) produced by direct infiltration of matrix into a porous CNT arrays have been demonstrated to possess a unique microstructure and excellent micro‐mechanical properties. However, the thickness of the array preforms is usually very small, typically less than 2 mm. Therefore, fabrication of macroscopic CNT/SiC composites by chemical vapor infiltration (CVI) process requires that the nanoscale fillers could form macroscopic architectures with an open pore network. Here, this study reports an experimental strategy for the fabrication of SiC matrix composites reinforced by CNT based on an ice‐segregation‐induced self‐assembly (ISISA) technique. Macroscopic CNT aerogel with well‐defined macroporous network was produced by ISISA technique and was subsequently infiltrated by SiC in a CVI reactor. After five CVI cycles, the porosity of as‐fabricated composites was 11.6±0.3% and the machined specimens exhibited lamellar structure with parallel lamellaes intersected at discrete angles. By observed, there are in fact five different representative anisotropic macrostructures, the compressive strengths of these five different loading modes with respect to lamella orientation were 933±55, 619±34, 200±45, 199±21, and 297±41 MPa, respectively, and the failure mechanisms were attributed to the anisotropic nature of the macrostructures. Energy dissipation toughening mechanism at the nanoscale such as CNT pull‐out was observed and the phase composition of the fabricated materials included β‐SiC, CNT, and SiO₂.     

泡沫碳化硅陶瓷材料的研究进展

泡沫碳化硅陶瓷材料除了孔隙率高、比表面积大,还具有相对密度小、优良的热学、力学、电学、声学性能等特性,已经广泛应用于化工、机械、生物、环保等领域。本文总结了泡沫碳化硅陶瓷材料的主要制备技术,包括粉末烧结法、固相反应烧结法、含硅树脂热解法以及气相沉积法等。阐述了泡沫碳化硅陶瓷材料的几种优良特性,包括结构特征、流体阻力、抗氧化性、吸波性等。最后举例介绍了该陶瓷在催化、过滤、生物学等领域的应用现状,重点介绍了其作为塔内件在化工领域中的应用,指出为满足对泡沫碳化硅陶瓷更高性能的需求,不仅要对现有技术进行集成创新,更要挖掘和开发泡沫碳化硅的潜在优势。     

Combustion synthesis of high porosity SiC foam with nanosized grains

High porosity silicon carbide (SiC) foam with nanosized grains was synthesized by a newly developed process involving two steps: (i) preparation of Si/C foam by gel-casting technique and (ii) fabrication of SiC foam by combustion Si/C foam in nitrogen atmosphere. The as-synthesized SiC foam with a high porosity in the range 70–90% exhibited an attractive strength up to 1.6 MPa. SEM analysis showed that the foam struts consisted of tightly bonded SiC particles with a grain size of 80–300 nm.     

An optimized process for in situ formation of multi-walled carbon nanotubes in templated pores of polymer-derived silicon oxycarbide

A reliable and optimized process to grow carbon nanotubes (CNTs) in templated pores of polymer derived ceramic (PDC) matrix was developed. It is realized through the pyrolysis of a preceramic polymer, i.e., poly (methyl-phenyl-silsesquioxane) (denoted as PMPS), in argon atmosphere at 1000 °C together with nickel-catalyst-coated poly-methyl-methacrylate (PMMA) microbeads (denoted as PMMA-Ni). PMPS served as both a precursor for the ceramic matrix and a carbon source for the CNT growth. PMMA microbeads were used as sacrificial pore formers and coated with nickel via an electroless plating method, which provides an improved control of particle size of the catalyst and its distribution in the material. The influence of PMMA-Ni loading on the in situ growth of CNTs and the properties of CNTs/SiOC nanocomposites were studied through thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and density/porosity measurements. Under optimized conditions, uniform distribution of in situ grown CNTs was observed within the templated pores of the SiOC matrix. The optimized process leads to reproducible high yield of CNTs in the pores. The development of such novel CNT/cellular ceramic nanocomposite materials is of significant interest for a variety of sensor applications.     

Processing of polymer-derived,aerogel-filled,SiC foams for high-temperature insulation

Porous polymer-derived ceramics (PDCs) are outperforming materials when low-density and thermal inertia are required. In this frame, thermal insulating foams such as silicon carbide (SiC) ones possess intriguing requisites for aerospace applications, but their thermal conductivity is affected by gas phase heat transfer and, in the high temperature region, by radiative mechanisms. Owing to the versatility of the PDC route, we present a synthesis pathway to embed PDC SiC aerogels within the open cells of a SiC foam, thus sensibly decreasing the thermal conductivity at 1000°C from 0.371 W·m⁻¹K⁻¹ to 0.243 W·m⁻¹K⁻¹. In this way, it was possible to couple the mechanical properties of the foam with the insulating ability of the aerogels. The presented synthesis was optimized by selecting, among acetone, n-hexane, and cyclohexane, the proper solvent for the gelation step of the aerogel formation to obtain a proper mesoporous colloidal structure that, after ceramization at 1000°C, presents a specific surface area of 193 m²·g⁻¹. The so-obtained ceramic composites present a lowest density of 0.18 g·cm⁻³, a porosity of 90% and a compressive strength of 0.76 MPa.     

Stereolithography 3D printing of SiC ceramic with potential for lightweight optical mirror

Silicon carbide (SiC) ceramic is the most prospective candidate material for space-based lightweight optical mirror. Stereolithography 3D printing has been reported to fabricate many kinds of ceramics, showing great potential for fabricating lightweight SiC ceramic optical mirror. In this paper, SiC ceramic was fabricated using stereolithography 3D printing combined with polymer burn-out, pre-sintering, and precursor infiltration and pyrolysis (PIP). The relative density, flexural strength, and microstructure during each step were investigated. The as-prepared lightweight SiC ceramic optical mirror exhibited high accuracy and high quality. Finally, it was proved that stereolithography 3D printing has a great potential for lightweight SiC ceramic optical mirror fabrication.     

A hybrid ceramic-polymer composite fabricated by co-curing lay-up process for a strong bonding and enhanced transient thermal protection

A hybrid ceramic-polymer composite is fabricated by a co-curing lay-up process by combining a carbon nanotube (CNT) reinforced ceramic composite thin film with a carbon fiber reinforced polymer (CFRP) composite substrate. The ceramic nanocomposite thin film has good flexibility, thermal conductivity and high temperature tolerance. The polymer composite substrate is a carbon fiber reinforced bismaleimide composite that is widely used in aerospace and automotive industries. Finite element analysis (FEA) is used to investigate the maximum survival temperature with different thicknesses of the ceramic nanocomposite. The resultant hybrid composite shows good structural integrity and displays a pull-off bonding strength up to 8.3?MPa. In addition, thermal study illustrates that such a flexible CNT reinforced ceramic composite can effectively protect CFRP in an elevated temperature environment by delaying transient thermal conduction.     

Structure and performance of Si3N4/SiC/CNT composite fibres

Herein, a homogeneously distributed and well-orientated ceramic-CNT composite fibre (Si₃N₄/SiC/CNTs) has been prepared using carbon nanotube fibres (CNTFs) premixed with silicon powder, followed by the reaction-bonded sintering process. The SiC layers around the CNT bundles interspersed in the composite are formed during the silicon reaction stage through the contact of silicon and CNTs, and the densification of the ceramic through the further reaction-bonded silicon carbide and nitride. Due to strong interface bonding, the composite fibres exhibit the potential for CNT-based damage sensing with a tensile strength upto 225 Mpa. Furthermore, the high-volume distribution of CNT sresults in a significant enhancement of the electrical and thermal conductivities as well as photoluminescence properties. Our work provides a useful approach for thefabrication of multifunctional fibres for imaging, engineering, and other complex applications.     

Microstructure and mechanical properties of SiC platelet reinforced BaOAl2O32SiO2 (BAS) composites

BaOAl₂O₃2SiO₂ (BAS) glass–ceramic powders were prepared by sol–gel technique. SiC platelet reinforced BAS glass–ceramic matrix composites with high density and uniform microstructure were fabricated by hot-pressing. The effect of additional crystalline seeds on hexagonal to monoclinic phase transformation of Barium aluminosilicate was studied. The effects of SiC platelet content on the microstructure and mechanical properties of the composites were also investigated. The results showed that the flexural strength and fracture toughness of the BAS glass–ceramic matrix composites can be effectively improved by the addition of silicon carbide platelets. The main toughening mechanism was crack deflection, platelets' pull-out and bridging. The increased value of flexural strength is contributed to the load transition from the matrix to SiC platelets.     

Developing high performance in titanium carbide nanocomposites containing hybrid SiC nanowire and CNT

Lightweight titanium carbide (TiC) has garnered considerable engineering applications in various advanced manufacturing industries. However, the intrinsic brittleness of TiC significantly limited its further applications. High-toughness and damage-tolerance TiC is always highly desirable for industry. Herein, we developed high-performance TiC nanocomposites reinforced by hybrid carbon nanotube (CNT) and SiC nanowire (SiC_nw) through two-step spark plasma sintering, highlighting the synergic role of CNT and SiC_nw on the microstructure and properties of the TiC matrix. Specifically, CNT was helpful in maintaining the high aspect ratio of SiC_nw during the sintering process, while SiC_nw contributed to the homogeneous distribution of CNT throughout the TiC matrix. The flexural strength and fracture toughness were simultaneously enhanced by 48.1% and 56.9% in case of CNT/SiC_nw ratio of 1:2 comparing with pure TiC, respectively. This study provided the new insight on developing high-performance TiC materials.     

In situ growth of SiC wires on CVI densification of SiC foam

Silicon carbide (SiC) foam prepared by polymer infiltration and pyrolysis (PIP) process was further densified with β-SiC by chemical vapor infiltration (CVI) technique. Scanning electron microscopy and high-resolution transmission electron microscopy images confirmed the presence of highly entangled and branched in situ grown SiC wires of uniform diameter (∼500 nm) over the struts of open-cell SiC foam. A uniform rate increase in diameter from nanometer to micron range (∼11 μm) was observed with an increase in the CVI reaction period. X-ray diffraction results showed the formation of highly crystalline β-SiC structure along the <111> direction with stacking faults. The formation of SiC wires was explained by the vapor–liquid–solid mechanism and evenness of the surface and uniform growth rate of SiC confirmed the homogeneous concentration of gaseous species during CVI reaction. The compressive strength increased with relative density, with maximum values of 5.5 ± 1.26 MPa for ultimate SiC foam (ρ = 400 kg/m³) prepared by hybrid PIP/CVI technique. The thermo-oxidative stability of the resultant foam was evaluated up to 1650°C under air and shows excellent thermal stability compared to SiC foam prepared by PIP route. The densified SiC foam can find potential applications in the field of hot gas filters, catalyst supports, microwave absorption properties, and heat insulation for high-temperature applications.     

Effect of co-deposited SiC nanowires and carbon nanotubes on oxidation resistance for SiC-coated C/C composites

To protect carbon/carbon composites (C/Cs) against oxidation, SiC coating toughened by SiC nanowires (SiCNWs) and carbon nanotubes (CNTs) hybrid nano-reinforcements was prepared on C/Cs by a two-step technique involving electrophoretic co-deposition and reactive melt infiltration. Co-deposited SiCNWs and CNTs with different shapes including straight-line, fusiform, curved and bamboo dispersed uniformly on the surface of C/Cs forming three-dimensional networks, which efficiently refined the SiC grains and meanwhile suppressed the cracking deflection of the coating during the fabrication process. The presence of SiCNWs and CNTs contributed to the formation of continuous glass layer during oxidation, while toughed the coating by introducing toughing methods such as bridging effect, crack deflection and nanowire pull out. Results showed that after oxidation for 45 h at 1773 K, the weight loss percentage of SiC coated specimen was 1.35%, while the weight gain percentage of the SiCNWs/CNTs reinforced SiC coating was 0.03052% due to the formation of continuous glass layer. After being exposed for 100 h, the weight loss percentage of the SiCNWs/CNTs reinforced SiC coating was 1.08%, which is relatively low.     

Noncatalytic synthesis of carbon nanotubes, graphene and graphite on SiC

Graphene and carbon nanotubes (CNT) can be produced by vacuum decomposition of SiC, but discrepancies and conflicting data in the literature limit the use of this method for CNT synthesis. A systematic study of the effects of SiC surface morphology and carbon transport through the gas phase leads to reproducible and controlled growth of arrays of small-diameter (1–4 walls) nanotubes, which show pronounced radial breathing modes in Raman spectra, on either carbon or silicon (0 0 0 1) face of 6H SiC wafers at 1400–1900 °C. These nanotube arrays have a very high density and are catalyst-free with no internal closures. They show a higher oxidation resistance compared to CNTs produced by catalytic chemical vapor deposition (CVD). Their integration with graphite/graphene or silica layers on SiC wafers is possible in a simple 2-step process and opens new horizons in nanoscale device fabrication.     

Fabrication of dense SiSiC ceramics by a hybrid additive manufacturing process

In this work, we report the fabrication of Silicon infiltrated Silicon Carbide (SiSiC) components by a hybrid additive manufacturing process. Selective laser sintering of polyamide powders was used to 3D print a polymeric preform with controlled relative density, which allows manufacturing geometrically complex parts with small features. Preceramic polymer infiltration with a silicon carbide precursor followed by pyrolysis (PIP) was used to convert the preform into an amorphous SiC ceramic, and five PIP cycles were performed to increase the relative density of the part. The final densification was achieved via liquid silicon infiltration (LSI) at 1500°C, obtaining a SiSiC ceramic component without change of size and shape distortion. The crystallization of the previously generated SiC phase, with associated volume change, allowed to fully infiltrate the part leading to an almost fully dense material consisting of β-SiC and Si in the volume fraction of 45% and 55% respectively. The advantage of this approach is the possibility of manufacturing SiSiC ceramics directly from the preceramic precursor, without the need of adding ceramic powder to the infiltrating solution. This can be seen as an alternative AM approach to Binder jetting and direct ink writing for the production of templates to be further processed by silicon infiltration.     

Oxidation behavior of C/SiC-SiBCN composites at high temperature

In order to improve the anti-oxidation performance of C/SiC composites at high temperature, C/SiC composites should be modified by self-healing components. SiBCN ceramic is an ideal self-healing component because of excellent oxidation resistance and thermal stability. C/SiC composites were modified by PDC SiBCN ceramic (C/SiC-SiBCN) by using CVI combined with polymer infiltration and on-line pyrolysis (PI-OP). The oxidation behaviors of C/SiC composites fabricated by CVI method and C/SiC-SiBCN composites fabricated by CVI + PI-OP method and CVI + PIP method at different temperatures in air were compared. The results showed that the strength retention ratios of the composites fabricated by the three methods decreased with the increase of temperature. Compared with the samples fabricated by the other two methods, the weight loss of the samples fabricated by CVI + PI-OP method was greater, but the strength retention ratio was higher.     

Powder bed fusion of polyamide powders combined with different preceramic polymers infiltration and pyrolysis to produce complex-shaped ceramics

The fabrication of a wide range of polymer-derived ceramic parts with high geometric complexity through a novel hybrid additive manufacturing technique is presented in this article. The process that we introduced in a previous work uses the powder bed fusion technology to manufacture high porous polymeric preforms to be then converted into ceramics through preceramic polymer infiltration and pyrolysis. The cellular architectures of a rotated cube (strut-based) and a gyroid (sheet-based) with 25 mm diameter, 44 mm height and 67 % of geometric macroporosity were generated and used for the fabrication. The complex structures were 3D printed and polycarbosilane, polycarbosiloxane, polysilazane and furan liquid polymers were used to produce SiC, SiOC, SiCN and glassy carbon, respectively. Despite a linear shrinkage of about 24 %, the parts maintained their designed complex shape without deformations. The significant advantages of the proposed method are the maturity of powder bed fusion for polymers with respect to ceramic additive manufacturing techniques and the possibility to fabricate net-shape complex ceramic parts directly from preceramic precursors.     

Spark plasma sintering of TiN ceramics codoped with SiC and CNT

In this research, we investigated the effects of SiC and multi-walled carbon nanotube (MWCNTs) addition on the densification and microstructure of titanium nitride (TiN) ceramics. Four samples including monolithic TiN, TiN-5?wt% MWCNTs, TiN-20?vol% SiC and TiN-20?vol% SiC-5?wt% MWCNTs were prepared by spark plasma sintering at 1900?°C for 7?min under 40?MPa pressure. X-ray powder diffraction patterns and scanning electron microscope (SEM) micrographs of the prepared ceramics showed that no new phase was formed during the sintering process. The highest calculated relative density was related to the TiN ceramic doped with 20?vol% SiC, while the sample doped with 5?wt% MWCNTs presented the lowest density. In addition, the SEM investigations revealed that the addition of sintering aids e.g. SiC and MWCNTs leads to a finer microstructure ceramic. These additives generally remain within the spaces among the TiN particles and prohibit extensive grain growth in the fabricated ceramics.     

Bio-inspired modification of silicon carbide foams for oil/water separation and rapid power-free absorption towards highly viscous oils

A bio-inspired strategy for the fabrication of superhyrophobic silicon carbide (SiC) ceramic foams (SCFs) using commercially available melamine foam (MF) as the template and vinyl-containing hyperbranched liquid polycarbosilane (VHPCS) as the binder was developed. The pre-oxidation process and crystallization degree during the sintering were monitored by Fourier transform infrared spectroscopy and X-ray diffraction. A plausible reaction was proposed and the thermogravimetry analysis results indicated that VHPCS was more suitable for the adhesive agent of SiC powders. By optimizing the mass ratio of VHPCS and SiC, a maximum compression strength of 1.25?MPa for SCFs was achieved with a low density of 0.514?g/cm³ and only 6.72% of volume shrinkage. The obtained SCFs exhibited rapid power-free absorption towards highly viscous oils after a biomimetic surface modification with n-octadecylamine (ODA). It took only 22?s for the complete absorption of 200?μL ultra-high viscosity oil (5000?mPa?s). A probable mechanism for the rapid absorption of viscous oil had been revealed and the decoration of low-surface-energy molecules together with the distinct porous structure were regarded as the critical factors.