SiOC modified carbon-bonded carbon fiber composite with SiC nanowires enhanced interfibrous junctions

Carbon-bonded carbon fiber (CBCF) composites are promising lightweight and high efficient thermal insulators to be applied in aerospace area, but their practical applications are usually restricted by the low mechanical performance and poor oxidation resistance. To overcome these drawbacks, many efforts have been made in the fabrication of ceramic coated CBCF composites. However, the densities of these modified composites are usually very high, which would result in the reduction in their thermal insulation performance. Herein, we prepared a CBCF composite with SiC nanowires enhanced interfibrous junctions and SiOC ceramic coated carbon fibers (SiCNWs-SiOC-CBCF). Similar to CBCF, the SiCNWs-SiOC-CBCF exhibits a low density of 0.35 g/cm³ and an anisotropic and highly porous architecture. The SiCNWs-SiOC-CBCF possesses a compressive strength of 3.8 MPa and a compression modulus of 195.7 MPa in the X (or Y) direction, ~26.7% and 150% higher than those of CBCF respectively. It can also suffer from an isothermal treatment in air at 900°C for 120 minutes. The combination of these properties makes the SiCNWs-SiOC-CBCF a good candidate for thermal insulator to be applied in extreme conditions.     

Preparation and mechanical behaviors of SiOC-modified carbon-bonded carbon fiber composite with in-situ growth of three-dimensional SiC nanowires

Carbon-bonded carbon fiber (CBCF) composites are novel and important high-temperature insulation materials owing to their light weight, low thermal conductivity and high fracture tolerance. To further improve the mechanical property of CBCF composite, we propose a three-dimensional (3D) SiC nanowires structure, which is in situ grown on a CBCF matrix via directly annealing silicon oxycarbide (SiOC) ceramic precursor. The synthesized multiscale reinforcements including microscale SiOC ceramics and nanoscale SiC nanowires are mainly attributed to the initial phase separation of SiOC phase and subsequent solid-phase reaction of SiO and C phases. Compared to SiOC/CBCF composite, the resulting 3D SiC nanowires/SiOC/CBCF hybrid structure exhibited high flexural/tensile strength and fractured strain due to the pull-out and bridging behavior of SiC nanowires. This one-step process supplied a feasible way to synthesize 3D SiC nanowires to reinforce and toughen SiOC-modified CBCF composite.     

Microstructural and compositional characterisation of the pyrocarbon interlayer in SiC coated low density carbon/carbon composites

SiC coated carbon bonded carbon fibre (CBCF) composites, a special class of carbon/carbon composites for thermal insulation, were investigated. Successful deposition of SiC requires the CBCF material to be first given a pyrocarbon coating. SiC coating on pyrocarbon coated CBCF was assessed using several analytical techniques. X-ray diffraction identified the coating as β SiC. The fibre orientation in two perpendicular planes was determined using X-ray microtomography, and it was found to be random in one plane whereas there was a preferred orientation in the other plane. A comparison was made between the uncoated and pyrocarbon coated substrates in terms of surface roughness, purity and crystallinity, using white light interferometry, neutron activation analysis/secondary ion mass spectrometry and transmission electron microscopy, respectively. The higher roughness, greater purity and increased levels of crystallinity of pyrocarbon coated CBCF are considered to be responsible for the successful deposition of a SiC coating on this material.     

An overview of C-SiC microwave absorption composites serving in harsh environments

Adapting to extremely harsh service environments is an unavoidable challenge for microwave absorption (MA) materials. Among MA materials, C-SiC composites stand out due to their excellent overall performance. This article provides a comprehensive review of the latest and most critical achievements regarding C-SiC MA materials. First, an introduction to the most basic preparation methods for obtaining C-SiC composites is presented. Next, the MA mechanisms of these composites are thoroughly analyzed to clarify the origin and contribution of the dielectric loss mechanism, providing theoretical support and guidance for the design of MA materials. Most importantly, the MA performance of C-SiC composites in harsh environments, including their high-temperature resistance, thermal conduction, thermal insulation, and anti-corrosion behavior, are highlighted. Finally, the achievements and challenges faced by C-SiC composites are summarized and some useful suggestions are proposed to guide the multi-functional application of C-SiC composites in harsh environments.     

Polymethylmethacrylate grafting onto polyvinyl alcohol/modified feldspar composites: preparation,properties and structure characterization

The orthogonal experiment design methods were used to select the optimal conditions of preparation for modified feldspar via conventional wet method with silane coupling agent KH570. The optimum scheme was followed by: reaction time 1.5 h, modifier content 8 wt%, pulp density 12 wt%, reaction temperature 70 °C, respectively. Furthermore, polyvinyl alcohol (PVA)/modified feldspar composites were prepared with feldspar coated with silane coupling agent KH570 via solution method. To improve the water resistance of PVA-based composites, polymethylmethacrylate grafted onto PVA/modified feldspar composites (PMMA-g-PVA) was obtained by surface-initiated atom transfer radical polymerization (SI-ATRP). PVA/modified feldspar composites before and after SI-ATRP were characterized by X-ray photoelectron spectroscopy, thermal gravimetric analyzer, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, successively. The tensile performance and water resistance of PVA/modified feldspar composites were tested by mechanical test and contact angle, respectively. It was shown that 5 wt% of modified feldspar could significantly improve the tensile strength of PVA-based composites. Moreover, both thermal stability and hydrophobicity for PVA/modified feldspar composites were distinctly enhanced after SI-ATRP. In all, this study provided an effective and feasible method for optimizing interface performance and enhancing the water resistance of PVA-based composites.     

Protective coatings for carbon bonded carbon fibre composites

Carbon bonded carbon fibre composites (CBCF) were modified by direct reaction with molten silicon in order to obtain a silicon carbide layer on the composite surface. Subsequently, the Si-infiltrated CBCF material was coated with a silica-based glass containing yttria and alumina by means of a slurry-dipping technique. On heat treatment the glass yielded a glass-ceramic layer thus giving a multi-layered oxidation and erosion protection system. The microstructural characterisation of the coating was conducted by standard microscopy techniques and by X-ray diffraction. The controlled crystallization of the glass-produced cristobalite, yttrium silicate (Y₂Si₂O₇, keiviite, β-form) and mullite as main crystalline phases. These are excellent ceramic materials for oxidation and erosion protection of SiC-coated carbon-based composites since their coefficients of thermal expansion (CTE) closely match that of SiC. The possibility of healing (closure) of micro cracks by a thermal treatment at 1375 °C, thus exploiting the viscous flow of the residual glass in the glass-ceramic, was explored in order to extend the service life of the protection system.     

Super-elastic carbon-bonded carbon fibre composites impregnated with carbon aerogel for high-temperature thermal insulation

A novel super-elastic carbon fibre composite was prepared by impregnating carbon aerogel into carbon-bonded carbon fibre (CBCF) through vacuum impregnation. The compressive strength of CBCF-CA was increased to 1.24?MPa in the z-direction, which was 6-fold more than that of neat CBCF. The CBCF-CA spontaneously recovered its size and shape without significant deformation when the pressure was released. The thermal conductivity of CBCF-CA was 0.246?W?(m·K)^?1 at 1400°C in the z-direction, which is lower than that of CBCF (0.341?W?(m·K)^?1). The average electromagnetic interference shielding e?ectiveness of CBCF-CA composites in the range of 12.4–18?GHz was higher than 40?dB, suggesting an absorption-dominant shielding feature. The CBCF-CA composite will be a new multifunctional material due to its low density, low thermal conductivity, high specific strength, excellent processability, super-elastic property and high electromagnetic shielding, which can be used for thermal insulation and protection of aerospace.     

纤维增强Al2O3-SiO2气凝胶隔热复合材料研究进展

Al₂O₃-SiO₂气凝胶是一种低密度、高比表面积、高孔隙率、低热导率的三维结构纳米多孔材料,在航空航天、建筑保温、石油化工等领域具有广泛的应用前景,是理想的高温隔热基体之一。但纯Al₂O₃-SiO₂气凝胶力学性能和抑制高温辐射传热能力较弱,限制了自身在隔热领域的应用。采用纤维作为增强体,制备的Al₂O₃-SiO₂气凝胶复合材料同时具有较好的力学和隔热性能,是目前国内外高温隔热材料方向的研究热点之一。本文介绍了纤维增强Al₂O₃-SiO₂气凝胶隔热复合材料的制备方法,综述了目前国内外该材料的研究进展,并对其未来发展趋势做了展望。     

A review on machining of carbon fiber reinforced ceramic matrix composites

Carbon fiber reinforced ceramic matrix ceramic/polymers composites have excellent physical-mechanical properties for their specific strength, high hardness, and strong fracture toughness relative to their matrix, and they also possess a good performance of wear resistance, heat resistance, dimensional stability, and ablation resistance. It is a choice for thermal protection and high temperature structural materials. However, this kind of composites owning characteristics of high hardness and abrasion is difficult to machine which impedes the large-scale industrial application of manufacturing. This paper mainly reviews the research on machining status of carbon fiber reinforced ceramic matrix composites including carbon fiber reinforced polymer matrix composites from the aspects of conventional machining and unconventional machining method. The machining trends, problems existing in various machining methods and corresponding solutions are generalized and analyzed.     

Inverse Problem for Composites with Imperfect Interface: Determination of Interfacial Thermal Resistance, Thermal Conductivity of Constituents, and Microstructural Parameters

An explicit method is introduced to solve inverse problems for composites with imperfect interfaces. We apply the method to determine the thermal conductivity of constituents and the interfacial thermal resistance in SiC-particulate-reinforced aluminum-matrix composites and to estimate the whisker thermal conductivity, the interfacial thermal resistance, and the whisker alignment distribution in two types of SiC-whisker-reinforced lithium aluminosilicate glass-ceramic composites from their measured effective thermal conductivity reported in the literature. Certain bounds for these three properties of both SiC-whisker-reinforced glass-ceramic composites are obtained, and reasonable estimates for their exact values from room temperature to 500°C are made. The inverse problem is quite sensitive to noise in the measurements. We also comment on existing estimates.     

二维片层材料在轮胎橡胶复合材料中的应用

综述了二维片层材料的结构、性能特点、功能化改性方法以及与橡胶复合的制备方法。着重介绍了不同二维片层材料在轮胎橡胶复合材料中的应用及其对复合材料力学性能、动态性能、气体阻隔性能、导电性能和导热性能的影响。总结了二维片层材料大规模应用面临的关键性技术问题。     

Comparative Review on Structure,Properties, Fabrication Techniques,and Relevance of Polymer Nanocomposites Reinforced with Carbon Nanotube and Graphite Fillers

Owing to their remarkable electrical, mechanical, thermal, catalytic, and optical properties as well as their unique structure, carbon nanotubes and graphite have been exploited to produce high performance and multifunctional composites. The resultant composites are differentiated on the basis of their properties to meet various applications. In the framework of this review article, we have mainly focused on the preparation, structure, and properties of two families of composite materials with an emphasis on the differences between them. Moreover, the current challenges, future prospectives, and applications of carbon nanotubes- and graphite-based materials in sensors and in photovoltaic and energy storage devices (Li-ion battery) have been discussed.     

预测聚合物基复合材料导热系数方法综述

由聚合物与高导热填料共混制得的导热聚合物基复合材料,被应用于防腐和节能要求较高的换热场合,符合换热设备新材料的要求;而聚合物基复合材料的等效导热系数预测比较复杂。总结了预测聚合物基复合材料等效导热系数的多种方法,包括最小热阻力法、热阻网络法、傅里叶定律法、均匀化方法和逾渗理论方法,归纳了这些模型和方法的特点,对应用这些模型和方法提出了建议。     

Wear and thermal behavior of basalt fiber reinforced rice husk/polyvinyl chloride composites

Plant fiber reinforced polymer composites (PFRPs) in practical application are often subjected to both complex friction and variable temperature environments. The present work explores the possibility of reinforcing rice husk/polyvinyl chloride (RH/PVC) composites with basalt fibers (BF) for developing a new wear resistant material with improved thermal stability. The results showed that the structural strength and wear resistance of the composites increased at first and then decreased with an increasing ratio of BF/RH, the highest value occurred at a BF/RH ratio of 8/42. The thermal stability of composites had a positive relationship with BF/RH ratio. The composites added with BF all possessed improved performance in comparison with unadded composites. Hence, the findings of this article proposed some new perspectives on improving the wear resistance and thermal stability of PFRPs that would broaden their practical application.     

Influence of CLVD thermal gradient on the deposition behavior,microstructure and properties of C/C-ZrC composites

Chemical liquid vapor deposition (CLVD) is a rapid preparation method, but it is rarely involved in fabrication of C/C-UHTCs composites and its technology parameters are hardly discussed. In the present study, C/C-ZrC samples were prepared by CLVD process, and the effects of thermal gradient on the deposition behavior, microstructure and properties were investigated. Results exhibited the density, ZrC content and uniformity of the composites increased as the thermal gradient decreased from 30.4 to 9.8?°C/mm, indicating the deposition behavior was improved gradually. When the thermal gradient was 30.4?°C/mm, the deposition behavior of the specimen was poor, which resulted in the high porosity, small numbers of ZrC blocks and uneven distribution. Therefore, the specimen had a low flexural strength with brittle fracture and poor ablation resistance. As the thermal gradient decrease to 9.8?°C/mm, there was an excellent deposition in the composites, and the composites possessed large amounts of ZrC particles and their dispersion were improved remarkably. In this case, the composites displayed a non-brittle fracture with high strength, and the linear and mass ablation rates were reduced, which indicated an improvement of anti-ablation property. Nevertheless, the deposition was deteriorated evidently when the thermal gradient reached to 0?°C/mm. The density, ZrC content and uniformity of the sample became poor, leading to the decline of mechanical property and ablation resistance.     

Current research art of rare earth compound modified SiC-CMCs for enhanced wet-oxygen corrosion resistance

Silicon carbide fiber reinforced silicon carbide ceramic matrix composites (SiC-CMCs) currently present wide application potential as thermal structure component in aero-engine. To solve the wet-oxygen corrosion induced degradation of SiC-CMCs attract growing global attention. In this work, the main preparation methods via introduction of rare earth compound like rare earth phosphates, rare earth oxides, rare earth silicates and rare earth silicide carbides into SiC-CMCs matrix and interphase and their microstructures, mechanical properties and wet-oxygen corrosion resistance are summarized in details. Finally, the challenges and prospects of rare earth compound modified SiC-CMCs are proposed.     

聚合物基导热电子封装材料的研究进展

概述了电子封装材料常用的基体材料、导热填料及制备方法。阐述了聚合物本征导热的影响因素及填料物理性能对聚合物基复合体系导热性能的影响。重点介绍了复合型导热聚合物的导热机理、导热模型以及提高复合体系热导率的途径。对今后的研究工作提出了建议。     

Synthesis and microstructural characterization of kaolin–polyethylene composites

In this article, the preparation and characterization of kaolin/polyethylene composites are presented. Microstructural characteristics of six different kaolin–polyethylene composites with varying percentage compositions of kaolin and polymer were produced using a modified melt compounding approach, was explored. The characterization methods employed are scanning electron microscopy (SEM), attenuated total reflectance mid Infrared (ATR‐MIR), X‐ray powder diffraction (XRD), thermogravimetric and differential thermal analysis (TGA‐DTA), compressive, flexural strengths and impact resistance analysis. The implications of the results are discussed for the design of kaolin/polymer composites for constructional purposes. POLYM. COMPOS., 35:1507–1515, 2014. © 2013 Society of Plastics Engineers     

硅藻土基磁性复合材料的研究进展

硅藻土基磁性复合材料因其具有大的比表面积、良好的抗腐蚀性能,能够在外加电场下定向移动且易于分离,同时兼具光电、电磁性,常作为吸附剂、催化剂和吸波基材广泛应用于环境、生物、光电及催化工程中。其磁性组分性能多样使得硅藻土基复合材料具有不同的效能评价,硅藻土表面因磁性组分的复合发生化学和物理变化,因此需要不同的制备方法。本文将磁性硅藻土复合材料基于磁性组分进行分类,综述了近年来的最新硅藻土基磁性复合材料的研究进展,主要探讨了此类复合材料表面及结构、活性机理、制备方法等对其性能的影响,最后根据不同应用领域对复合材料取得的新进展进行介绍。分析表明：硅藻土基磁性复合材料的天然多孔结构所具有的吸收、吸附性能和半导体的磁光性能结合,使得材料性能得到改善的同时具有更好的综合性能。特别是尖晶石型铁氧体-硅藻土在光电催化和吸波领域的性能表现更好,应用前景广泛。     

Diels-Alder Macromolecular Networks in Recyclable,Repairable and Reprocessable Polymer Composites for the Circular Economy – A Review

In the expanding field of high-performance materials, polymer-based thermoset composites play an important role due to their favorably-high strength/weight ratio and their mechanical performance, thermal stability, and chemical resistance. However, their chemically-crosslinked nature hampers their re-processability and efficient recyclability, thus making them not compliant with the principles of the circular economy and of end-of-life valorization. Dynamic covalent polymers able to modify their network topology upon thermal stimulus can be considered valid alternatives to commonly used thermosets as they offer advantages in terms of recyclability and reusability, normally not achievable with conventional cross-linked systems. Within the broad field of dynamic polymers, thermally-triggered Diels-Alder based materials represent reliable platforms with enormous technological and industrial potential as repairable, reusable and recyclable matrices in composites given their chemical versatility, suitable mechanical performance and ease of production and processing. In this review, a comprehensive discussion of the most recent demonstrations of the reversibility, reprocessability and recyclablability of such systems is provided, in the context of their use as polymer matrices in composites. It is hoped that this work will stimulate further discussion and research in the area of reversible polymer composites with increased functionality and extended lifetime, in view of their application in future circular economy scenarios.