Synthesis and potential applications of silicon carbide nanomaterials / nanocomposites

The rapid development of nanotechnologies has accelerated the research in silicon carbide (SiC) nanomaterial synthesis and application. SiC nanomaterials have unique chemical and physical properties, such as distinctive electronic and optical properties, good chemical resistance, high thermal stability, and low dimensionality. These properties lead to a wide range of applications. The progress in SiC nanomaterials in recent years is significant, but a review of the progress is lacking. This article is designed to fill the gap. The review first summarizes various methods for preparing different SiC nanomaterials/nanocomposites, including the carbothermal method, chemical vapor deposition method, and other synthesis techniques using unconventional energy sources such as microwave, plasma, solar energy, and neutron irradiation. Discussion is then made on the significant applications of the SiC nanomaterials/nanocomposites, especially in sensors, catalyst supports, energy storage materials, structural reinforcement, and semiconductor materials. Finally, the conclusion of this review is made with the possible future development trends.     

形貌可控的银纳米颗粒合成及应用

银纳米材料具有独特的物理性质,在光学、生物和催化等领域应用潜力巨大,是近年来材料领域的研究热点。银纳米材料的很多性能与其形貌密切相关,如枝状银纳米颗粒局部表面等离子体共振较强,不同形貌的银纳米颗粒裸露不同的晶面,导致其催化选择性不同。因此,控制合成特定形貌和结构的银纳米颗粒一直是该领域的重要研究方向。本工作综述了近年来银纳米颗粒形貌可控的合成方法,包括溶液还原法、晶种法、生物合成法、光诱导法、反应-扩散调控的动力学法和模板法等,比较了不同方法的优缺点,分析了不同合成方法的机理。重点介绍了基于反应和扩散调控的动力学方法,总结了其优点和普适性。调研了不同形貌银纳米颗粒在抑菌、局部等离子体共振和催化等领域的应用研究,分析了不同形貌银纳米颗粒的工业化应用前景,并对银纳米形貌的可控合成和应用进行了展望。     

Ti3SiC2陶瓷的制备及性能研究

层状陶瓷材料Ti，SiC2结合了金属和陶瓷的许多优异性质，既具有与金属相似的良好的导热、导电性，良好的可加工性，相对柔软，抗热震性好，可塑性变形等性能，同时又具有与陶瓷相似的抗氧化、耐腐蚀、耐高温等特性；并且还有很好的自润滑性和超低磨擦系数，被认为在许多领域有着广泛的应用前景。     

Recent progress in synthesis,growth mechanisms,properties, and applications of silicon nitride nanowires

With advances in nanotechnology, nanowires have gained worldwide attention because of their novel properties and promising applications. Among them, silicon nitride (Si₃N₄) nanowires have attracted increasing attention due to their excellent performance and huge application potential. In this review, various synthesis methods of Si₃N₄ nanowires are introduced in detail, and then the growth mechanisms are also stated. Subsequently, the novel properties of Si₃N₄ nanowires including mechanical, optical, electrical, thermal, and wetting performance are highlighted. Applications corresponding to performance are also summarized later, such as composites, field emitters, field-effect transistors (FETs), photodetectors, photocatalysts, and microwave absorbers. Finally, the contents of this article are concluded and outlooks of future research directions are stated. This article reviews the recent advances and provides the prospects and challenges of Si₃N₄ nanowires.     

Synthesis and characterization of calcium aluminate nanoceramics for new applications

Two types of nanocalcium aluminate powders containing 70 and 60 wt.% Al₂O₃ were prepared by thermal decomposition and investigated in terms of mineralogical composition, hydration, mechanical properties and microstructure. The results revealed that S1 is composed mainly of the CA and CA₂ phases, while S2 composed of CA and C₁₂A₇ phases after heat-treatment at 1000 °C. The maximum crystallite sizes for S2 and S1 were 44 and 52 nm and the minimum ones 12 and 19, respectively. Both samples still have small crystallite size after heat-treatment at 1000 °C. The present phases, i.e. CA, CA₂ and C₁₂A₇ affect the properties of hydrated and sintered ceramic bodies. S2 hydrated sample achieved higher strength (58.5 MPa) than S1 (52.4 MPa). The higher strength of S2 is ascribed to the presence of CA and C₁₂A₇ as a major component, since it reacts rapidly with water. In S1, the poor hydration of CA₂ at the early stage of hydration lowers strength after 7 days hydration as compared with S2. Cold crushing strength (CCS) data of the sintered ceramics bodies exhibit high strength of both samples after firing at 1550 and 1450 °C for S1 and S2, respectively. This is due to the formation of a ceramic bond.     

Synthesis of Ti3SiC2 coatings onto SiC monoliths from molten salts

Coatings with composition close to Ti₃SiC₂ were obtained on SiC substrates from Ti and Si powders with the molten NaCl method. In this work, the growth of coatings by reaction in the salt between monolithic SiC substrates and titanium powder is obtained between 1000 and 1200 °C. At 1000 °C, a coating of 8 µm thickness is formed in 10 h whereas a thin coating of 0.5 µm has been grown in 2 h. A lack in silicon was first found in the coatings prepared at 1100 and 1200 °C. For these temperatures, the addition of silicon powder in the melt had a favorable effect on the final composition, which is found very close to the composition of Ti₃SiC₂. The reaction mechanism implies the formation of TiC_x layers in direct contact with the SiC substrate and the presence of more or less important quantities of Ti₃SiC₂ and Ti₅Si₃C_x in the upper layers.     

Micromechanical properties and microstructural evolution of Amosic-3 SiC/SiC composites irradiated by silicon ions

In this work, Amosic-3 SiC/SiC composites were irradiated to 10 dpa and 115 dpa with 300 keV Si ions at 300 °C. To evaluate its irradiation behaviour and investigate the underlying mechanism, nanoindentation, AFM, Raman and electron microscopy were utilized. Nanoindentation showed that although micromechanical properties declined after irradiation, hardness and Young’s modulus were maintained better under 115 dpa. AFM manifested differential swelling among PyC interface, fiber and matrix and SEM showed irradiation-induced partial interface debonding, which are both more obvious under 115 dpa. TEM revealed the generation and proliferation of amorphous regions, which is according with the decline and broadening of peaks in Raman spectra. The material was almost completely amorphous after irradiated to 10 dpa while recrystallization occurred under 115 dpa. All results mentioned above contribute to the decline of hardness and Young’s modulus and may explain why the micromechanical degradation was more significant under 10 dpa.     

Enhancement of the microwave absorption properties of PyC-SiCf/SiC composites by electrophoretic deposition of SiC nanowires on SiC fibers

The employment of coating technique on the silicon carbide fibers plays a pivotal role in preparing SiC fiber-reinforced SiC composites (SiC_f/SiC) toward electromagnetic wave absorption applications. In this work, SiC nanowires (SiCNWs) are successfully deposited onto the pyrolytic carbon (PyC) coated SiC fibers by an electrophoretic deposition method, and subsequently densified by chemical vapor infiltration to obtain SiCNWs/PyC-SiC_f/SiC composites. The results reveal that the introduction of SiCNWs could markedly enhance the microwave absorption properties of PyC-SiC_f/SiC composites. Owing to the increasing of SiCNWs loading, the minimum reflection loss of composites raises up to −58.5 dB in the SiCNWs/PyC-SiC_f/SiC composites with an effective absorption bandwidth (reflection loss ≤ −10 dB) of 6.13 GHz. The remarkable enhancement of electromagnetic wave absorption performances is mainly attributed to the improved dielectric loss ability, impedance matching and multiple reflections. This work provides a novel strategy in preparing SiC_f/SiC composites with excellent electromagnetic wave absorption properties.     

Effects of SiC whiskers on the mechanical properties and microstructure of SiC ceramics by reactive sintering

As-received and pre-coated SiC whiskers (SiC_w)/SiC ceramics were prepared by phenolic resin molding and reaction sintering at 1650 °C. The influence of SiC_w on the mechanical behaviors and morphology of the toughened reaction-bonded silicon carbide (RBSC) ceramics was evaluated. The fracture toughness of the composites reinforced with pre-coated SiC_w reached a peak value of 5.6 MPa m^1/2 at 15 wt% whiskers, which is higher than that of the RBSC with as-received SiC_w (fracture toughness of 3.4 MPa m^1/2). The surface of the whiskers was pre-coated with phenolic resin, which could form a SiC coating in situ after carbonization and reactive infiltration sintering. The coating not only protected the SiC whiskers from degradation but also provided moderate interfacial bonding, which is beneficial for whisker pull-out, whisker bridging and crack deflection.     

Advanced technology for fabrication of reaction-bonded SiC with controlled composition and properties

An advanced fabrication technology of reaction-bonded SiC is developed, which includes the preparation of a C/SiC preform by repeated cycles of phenolic resin impregnation and pyrolysis, followed by infiltration with silicon melt. The use of different number of impregnation stages provides control of carbon content in the preform and the corresponding SiC content in final ceramics. The effect of the impregnation number on the preform characteristics and ceramics composition, thermal and mechanical properties are investigated comprehensively. With an increase of impregnation number up to four, SiC fraction in the ceramics enlarges to 93 vol%, thermal conductivity and Young’s modulus increase to 186 W/(m?K) and 427 GPa respectively, which are superior to most reaction-bonded SiC. Flexural strength (225 MPa) and thermal expansion coefficient (2?10^?6 K^-1) are not dependent on the impregnation number. The obtained results provide an opportunity to design and fabricate reaction-bonded SiC ceramics with a given set of properties.     

Advanced polyimide materials: Syntheses, physical properties and applications

Polyimides rank among the most heat-resistant polymers and are widely used in high temperature plastics, adhesives, dielectrics, photoresists, nonlinear optical materials, membrane materials for separation, and Langmuir-Blodgett (LB) films, among others. Additionally, polyimides are used in a diverse range of applications, including the fields of aerospace, defense, and opto-electronics; they are also used in liquid crystal alignments, composites, electroluminescent devices, electrochromic materials, polymer electrolyte fuel cells, polymer memories, fiber optics, etc. Polyimides derived from monomers with noncoplanar (kink, spiro, and cardo structures), cyclic aliphatic, bulky, fluorinated, hetero, carbazole, perylene, chiral, non-linear optical and unsymmetrical structures have been described. The syntheses of various monomers, including diamines and dianhydrides that have been used to make novel polyimides with unique properties, are reported in this review. Polyimides, with tailored functional groups and dendritic structures have allowed researchers to tune the properties and applications of this important family of high-temperature polymers. The synthesis, physical properties and applications of advanced polyimide materials are described.     

Effect of in situ grown SiC nanowires on microstructure and mechanical properties of C/SiC composites

Hexagonal-shaped SiC nanowires were in situ formed in C/SiC composites with ferrocene as catalyst in the densification process of polymer impregnation and pyrolysis. The effect of SiC nanowires on microstructure and properties of the composites were studied. The results show that the in situ formed SiC nanowires were hexagonal, mostly with diamer of about 250 nm, and grew by the vapor–liquid–solid (VLS) mechanism. The C/SiC composite with nanowires shows higher bulk density and flexural strength than the one with no SiC nanowires, and the high temperature flexural strength behavior of C/SiC composites with SiC nanowires was evaluated.     

TiN modified SiC with enhanced strength and electrical properties

SiC based composites were manufactured with varying TiN content (0–50 V%) using Al₂O₃ and Y₂O₃ sintering aids. Basic dilatometry measurements were performed to determine when densification begins within the composite system. Samples were consolidated via uni-axial hot pressing at 1900 °C to produce ceramic composites with >98% theoretical density. Electrical measurements show increasing TiN additions reduce resistivity and begin to plateau at 40–50V%. Resistivity decreased from 2.0 × 10⁵ Ω − cm (0% TiN) to 2.0 × 10⁻⁴ Ω − cm (50V% TiN). Flexural strengths were characterized and compared against a baseline (0% TiN) SiC. Strengths increased gradually with TiN content. A maximum strength 921 MPa was observed at 40V% TiN content vs. 616 MPa for the baseline SiC. This was a gain of 50% over baseline. Additions beyond that range did not produce further gains in strength.     

Recent advances in bionanocomposites: Preparation,properties, and applications

The authors report recent advances in the research and development of bionanocomposites based on four types of nanofillers, namely organically modified layered silicate (OMLS), cellulose nanofibers (CNs), carbon nanotubes (CNTs), and halloysite nanotubes (HNTs). These composite materials have received significant attention from academia and industries due to their unique advantages such as excellent biodegradability, availability, cost effectiveness, and eco-friendliness. The preparation and properties of bionanocomposites have been reviewed in detail together with their current and potential applications in the fields of electronics and sensors, tissue engineering, drug delivery, gene therapy, and cosmetics, as well as packaging.     

The hybrid halide perovskite: Synthesis strategies,fabrications, and modern applications

The organic–inorganic hybrid halide perovskite has several outstanding properties that are beneficial for optoelectronic and photovoltaic applications. Their interesting properties and the use in several modern application, attracted attention of the materials researchers. However, in this review, we describe how hybrid perovskite-based solar cells has become an important renewable source of energy along with historical background and the future of this potential material. We also describe the synthesis and fabrication methods for preparing ultrathin to bulk perovskites and their crystallographic nature of pure and mixed metallic hybrid perovskite system. This review not only focused on properties of hybrid perovskite but also represents the drawback as well as the development and performance in different fields of application.     

Synthesis of SiC Whiskers from Silicon Nitride in Argon Atmosphere

SiC whiskers were synthesized by carbothermal reduction of silicon nitride. α-Si3N4 and β-Si3N4 powders were used as silicon sources, and graphite, active carbon and black carbon as carbon sources, as well as boron oxide as catalyst. The synthesized SiC whiskers were characterized by XRD and SEM. The results showed that the synthesizing temperature should be above 1 716 K; the decomposition of Si3N4 was the limited step in the synthesis of SiC whiskers; and catalyst not only offered the liquid condition, bu...     

聚吡咯纳米粒子的制备与应用

综述了导电性聚吡咯纳米粒子的制备方法、特殊性能与应用。     

Synthesis of centimeter-scale monolithic SiC nanofoams and pore size effect on mechanical properties

By pressure infiltrating pre-ceramic polymer polycarbosilane (PCS) into thermally and mechanically stable silica nanofoam, followed by PCS pyrolysis and silica template removal, synthesis of large-scale monolithic SiC nanofoams has been accomplished. Tailoring of the porosity and cell size of the SiC nanofoam has been realized by dissociating the porosity and pore size of the silica nanofoam. Because of the surface hardening and increased surface volume ratio of deformable nanopores, with the same porosity, the decrease of nanopore size has led to an increase in the quasi-static and dynamic indentation resistance for SiC nanofoams.     

Microstructure evolutions of SiC whiskers at high temperature and its effects on silicon carbide ceramics

SiC whisker with a single-crystal structure is promising in enhancing the strength and toughness of advanced structural ceramics, owing to its excellent properties. However, studies on its microstructure evolution at high temperature (>2000 °C) are scarce. Herein, SiC whiskers were calcined at 2100 °C, and XRD, SEM, and TEM were employed to analyze microstructure evolutions. Compared with raw whiskers, XRD results indicated serious annihilation of stacking faults after calcination. The annihilation led to the fracture of whiskers and the formation of β-SiC grains, and then partial grains underwent the phase transformation to form hexagonal prism and triangular prism α-SiC grains with diameters of about 10 μm, according to SEM and TEM results. Furthermore, SiC ceramics containing different whisker contents were innovatively fabricated by pressureless solid-state sintering. The flexural strength and fracture toughness of SiC ceramic containing 10 vol% whiskers were 540 MPa and 5.1 MPa m^0.5, resulting in 38% and 11% higher values than those without whiskers, respectively.     

Advances in modifications and high-temperature applications of silicon carbide ceramic matrix composites in aerospace: A focused review

This article is a detailed review of the measures to modify the high-temperature mechanical properties of silicon carbide ceramic matrix composites (SiC CMCs), namely toughness, high-temperature stability and wear resistance. Additionally, it briefly describes the common processing methods of the SiC CMCs and their application in the high-temperature field of aerospace. The advantages and disadvantages of various existing processing and molding methods for the SiC CMCs are also discussed. The high-temperature mechanical properties of the SiC CMCs are mainly affected by the properties of the matrix, added phase and interface. It is crucial to reduce the crystal defects of the matrix and select a suitable enhancement phase for an elevated performance. Moreover, it is important to improve the bonding at the interface between the enhancement phase and the matrix. This review is expected to provide useful information for the subsequent development of complex SiC CMCs for high-temperature applications.