Effects of graphite on the mechanical and microwave absorption properties of geopolymer based composites

In this paper graphite/metakaolin was first ball-milled to get homogeneous powder, which was then mixed with potassium silicate solution through mechanically stirring. Post curing, we got graphite/geopolymer composites with graphite to geopolymer ratio from 0 to 18 and part the samples were further dealt with heat treatment at 600 °C. Effects of the graphite content on the mechanical properties and microwave absorption properties of the composites were systematically investigated. The results proved that when graphite to geopolymer ratio is not higher than 12, graphite dispersed homogeneously in the composites. However, graphite agglomeration was noted when graphite to geopolymer ratios are 15 and 18. With the increase in graphite to geopolymer ratio, flexural strength and fracture toughness of the composites first increased, reaching the peak value and then decreased. When the graphite to geopolymer ratio is 12, the composite showed the highest flexural strength and fracture toughness, which should be explained by the mixing rule of composites since the mechanical properties of graphite are much higher than geopolymer matrix. With the increase in graphite content, the dielectric constants of the composite increased gradually, but the magnetic constants nearly kept unchanged. It implied that the main microwave absorbing mechanism would be dielectric loss of the composites. The maximum wave reflection loss showed similar trend to the mechanical properties of composites. It reached the peak value when graphite to geopolymer ratio is 12 and then started to decline, which might also be related to the graphite agglomeration. After 600 °C heat treatment, slight decline of the reflect loss peak and obvious decrease on the thickness corresponding to the maximum reflection loss were observed.     

Tensile properties and fracture toughness of carbon-fiber felt reinforced carbon composites at high temperature

Two kinds of carbon felt reinforced carbon composites, C/C-A and C/C-B, containing respectively pitch carbon fibers and PAN carbon fibers, have been developed to enhance the fracture mechanics properties. The fracture toughness values of these new composites were measured as a function of temperature up to 2400°C. These results are compared with those of a carbon fiber cloth reinforced carbon composite containing rayon fibers (C/C-C) and a fine grain isostatic graphite (IG-11). Major differences among these materials and their distinctive features are discussed.     

Preparation and properties of SiOC ceramic modified carbon fiber needled felt preform composites

SiOC ceramic modified carbon fiber needled felt preform composites (C_f/SiOC) with densities of 0.4 and 0.7 g/cm³ were prepared by precursor infiltration and pyrolysis (PIP) method using methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) as precursors. The densification behavior was investigated through scanning electron microscopy (SEM) analysis of microstructure of C_f/SiOC composites undergoing different PIP times. The results indicate that with increase of PIP times, a great amount of SiOC ceramic was introduced into the preform, completely covering on the carbon fibers and occupying the open pores. The thermal performance, mechanical properties, and oxidation resistance of the composites were studied via various tests. The results illustrate that after two-time PIP procedure, thermal conductivities of the composites are 0.41–2.54 and 1.28–4.04 W/(m·K) in z direction and x/y plane, respectively, at RT-1500 °C. The compressive strengths of the composite arrive at 2.1 MPa in z direction and 7.8 MPa in x/y plane, which are almost 3.5 times and 6.5 times, respectively, counterparts of the raw preform. The incorporation of SiOC ceramic can remarkably improve anti-oxidation ability of the composites at 600 °C. The oxidation weight loss is merely 2.1 wt% after 60-min oxidation at 600 °C.     

Effects of high-temperature heat treatment on the mechanical properties of unidirectional carbon fiber reinforced geopolymer composites

Unidirectional carbon fiber reinforced geopolymer composite (C_uf/geopolymer) is prepared by a simple ultrasonic-assisted slurry infiltration method, and then heat treated at elevated temperatures. Effects of high-temperature heat treatment on the microstructure and mechanical properties of the composites are studied. Mechanical properties and fracture behavior are correlated with their microstructure evolution including fiber/matrix interface change. When the composites are heat treated in a temperature range from 1100 to 1300 °C, it is found that mechanical properties can be greatly improved. For the composite heat treated at 1100 °C, flexural strength, work of fracture and Young's modulus reach their highest values increasing by 76%, 15% and 75%, respectively, relative to their original state before heat treatment. The property improvement can be attributed to the densified and crystallized matrix, and the enhanced fiber/matrix interface bonding based on the fine-integrity of carbon fibers. In contrast, for composite heat treated at 1400 °C, the mechanical properties lower substantially and it tends to fracture in a very brittle manner owing to the seriously degraded carbon fibers together with matrix melting and crystal phases dissolve.     

Dynamic mechanical properties of carbon fiber reinforced geopolymer concrete at different ages

In order to improve the strength and toughness of geopolymer concrete (GC) at different ages under impact load, using slag and fly ash as cementitious materials, NaOH and sodium silicate as alkaline activators, carbon fiber as reinforcement, carbon fiber reinforced geopolymer concrete (CFRGC) was prepared. The dynamic compression test of CFRGC was carried out by Φ 100 mm SHPB test system. The effects of age (3 d, 7 d, 28 d) and fiber content on the dynamic mechanical properties of CFRGC were studied, and the strengthening and toughening effects of carbon fiber on GC were analyzed. In addition, the strengthening and toughening effects of carbon fiber on GC and ordinary Portland cement based concrete (PC) were compared and analyzed. The results show that the performance indicators of CFRGC at different ages have strain rate effect under impact load, and the dynamic compressive strength and specific energy absorption of CFRGC increase approximately linearly with the strain rate. With the increase of age, the dynamic compressive strength and specific energy absorption of CFRGC increase, and the strain rate sensitivity of dynamic compressive strength and specific energy absorption also increases. With the increase of carbon fiber content, the dynamic compressive strength and specific energy absorption of CFRGC increase first and then decrease, and the strain rate sensitivity of dynamic compressive strength and specific energy absorption also increase first and then decrease. When the carbon fiber content is 0.2%, the dynamic mechanical properties of CFRGC are the best, and the strain rate sensitivity of performance indicators is the strongest. Carbon fiber has strengthening and toughening effects on GC and PC. When the fiber content is 0.2%, carbon fiber has the best strengthening and toughening effects on GC and PC. The strengthening and toughening effects of carbon fiber on GC is better than that of PC. Compared with 28 d, carbon fiber has better strengthening and toughening effects on GC at the ages of 3 d and 7 d.     

Effect of fiber type on mechanical properties of short carbon fiber reinforced B4C composites

In order to enhance the mechanical properties of B₄C without density increase, the short carbon fibers M40, M55J and T700 reinforced B₄C ceramic composites were fabricated by hot-pressing process. The addition of the carbon fibers accelerates the densification of the B₄C, decreases their densities, and improves their strength and toughness. The enhancement effects of the three kinds of carbon fibers were studied by investigating the density, Vickers hardness and the mechanical properties such as flexural strength, flexural modulus and fracture toughness of the composites. The fiber type has a great influence on the mechanical properties and enhancement of the short carbon fiber reinforced B₄C composites. The flexible carbon fiber with high strength and low modulus such as T700 is appropriate to reinforce the B₄C matrix ceramic composites.     

短切碳纤维及碳纤维布增强硅橡胶复合材料的制备及力学性能

将短切碳纤维(CF)、白炭黑和甲基乙烯基硅橡胶(VMQ)共混后,与碳纤维布(CFC)复合制备VMQ复合材料.考察了CFC层数对复合材料的拉伸性能、邵尔A硬度、耐磨性能及动态力学性能的影响.结果表明,随着CFC层数的增加,复合材料的扯断伸长率基本不变,拉伸强度逐渐升高.与仅添加10份(质量,下同)CF的复合材料相比,加入...     

炭纤维增强水泥基复合材料(CFRC)的电磁性能

炭纤维增强水泥基复合材料(Carbon Fiber Reinforced Cement Composites,CFRC)是新发展起来的一种电磁屏蔽材料,它是防止电磁污染的防护性功能材料之一。本文阐述了炭纤维增强水泥基复合材料的制备成型工艺;分析了炭纤维掺入量和长度、水灰比和密实成型制备工艺、炭纤维分散性、养护龄期、外加剂、炭纤维表面化学气相沉积(CVD)处理等因素对CFRC力学性能、导电性能、压敏性能及电磁性能的影响。合适的炭纤维掺入量和长度、炭纤维的均匀分散、合理的水灰比和炭纤维表面处理是影响CFRC导电性能和电磁性能的主要因素。CFRC对电磁波的屏蔽效果除利用屏蔽效能从反射电磁波角度衡量外,亦可从吸收电磁波角度利用反射率进行评价。     

Effects of needle-punched felt structure on the mechanical properties of carbon/carbon composites

The effects of needle-punched felt structure, including mass ratio of non-woven cloth to short-cut fiber web, PAN-based carbon fiber types of non-woven cloth and thickness of unit (one layer of non-woven cloth and short-cut web was named as a unit), on the flexural properties of C/C composites from pressure gradient CVI are discussed. Results show that flexural strength and modulus increase when mass ratio of non-woven cloth to short-cut fiber web changes from 7:3 to 6:4 and that PAN-based carbon fiber types of non-woven cloth strongly influence the flexural properties. The strength of C/C composites is not linear with the strength of non-woven cloth carbon fiber because of the important interface between carbon fiber and matrix carbon. It is suitable to choose T300 or T700 as reinforcing carbon fiber for C/C composites in the present study. An optimum unit number per cm of the needle-punched felts for higher flexural properties exists.     

Synthesis and mechanical properties of lightweight hybrid geopolymer foams reinforced with carbon nanotubes

A lightweight hybrid geopolymer foams reinforced with carbon nanotubes (CNTs) was exploited by adding the CNTs into geopolymeric matrix through hydrogen peroxide method. The synergistic effects of nanotubes and foaming agent on the phase evolution, microstructure, and mechanical properties were investigated. After introduction of nanotubes, the geopolymer foams reinforced with CNTs (CNTs/KGP) still showed amorphous structure. Porosity of the foams increased with the H₂O₂ content and decreased with the increase in CNTs content. The addition of CNTs (1-9 wt%) in foams refined the distribution of pore size from 523 to 352 μm. Compression strength of the CNTs/KGP samples elevated with the increasing content of CNTs, which was contributed to the crack propagation and bridging of CNTs in foams. The CNTs/KGP foams with considerable porosity show potential applications in adsorption, filtration, membrane supports, other industries, etc     

Effect of graphite felt and activated carbon fiber felt on performance of freshwater sediment microbial fuel cell

BACKGROUND: Sediment microbial fuel cells (SMFCs) could be used as power sources and one type of new technology for the removal of organic matters in sediments. Various types of materials have been used as electrodes. Nevertheless, there is still room to improve electrode materials and enhance their effect on the performance of SMFCs. In this work, performances of SMFCs with activated carbon fiber felt (ACFF) and with nitric acid‐treated ACFF were compared with graphite felt (GF) materials. RESULTS: The maximum power density of the SMFC with ACFF electrode was the highest (33.5 ± 1.5 mW m^?2). Nitric acid‐treated GF electrode slightly increased the maximum power density of SMFC, while the nitric acid treated‐ACFF resulted in significant decline in the maximum power density of SMFC. The maximum power density further increased to 74.5 ± 7.5 mW m^?2 in SMFC using GF cathode and ACFF anode. CONCLUSIONS: ACFF as anode can enhance the transport of electrons from the oxidation of organic matter in the sediment, while the output power was found to reduce in SMFC with ACFF cathode. Further efforts are needed to study the formation conditions of the biocathode and new electrode modification technology. Copyright © 2012 Society of Chemical Industry     

短碳纤维增强碳化硅基复合材料的制备

短纤维的分散均匀性一直是短纤维复合材料应用受限的主要原因．采用固相球磨分散和熔融渗硅工艺,可得到均匀分散的短碳纤维增强碳化硅基复合材料．并利用金相显微镜见察复合材料微观形貌,测试复合材料的抗弯强度和断后韧性．     

碳纤维增强硅橡胶复合材料制备

由于硅橡胶具有较好的耐热性但力学性能比较差,本文用高性能的碳纤维作增强剂,硅橡胶（MVQ）作基相及偶联剂作为相容剂制备了碳纤维/硅橡胶复合材料。通过力学性能和热老化测试,确定碳纤维的用量。用偶联剂作相容剂研究了偶联剂对硅橡胶和碳纤维相容性影响;通过傅里叶变换红外光谱（FTIR)和扫描电镜(SEM)分析了碳纤维和硅橡胶交联结构和相容性。结果显示,制备了碳纤维/硅橡胶复合材料的最佳配方为硅橡胶 100份,碳纤维 12份,KH-550 2.5份。碳纤维增强硅橡胶的最佳硫化条件为：温度 175℃,压力为10MPa,时间为30min。由扫描电镜和红外光谱分析,进一步论证了用KH-550处理的比没有处理及用Si69处理的碳纤维与硅橡胶的混合相容性好。     

Erosion resistant composite coating on rigid carbon fiber felt

Rigid carbon fiber felt (RCFF) was surface modified with a composite coating via a two-step technique of pasting and chemical vapor deposition. Scanning electron microscopy and X-ray diffraction were performed to analyze the microstructure of the substrate and the composite coating. The effect of the deposition time on solid particle erosion properties of RCFF modified by a composite coating was investigated. The pyrolytic carbon can decrease the surface porosity of a carbon fiber cloth, resulting in a dense composite. Compared with the substrate, the composite coating exhibited good erosion resistance and reduced the mass loss of the substrate by a factor of 19. The strengthening mechanism was discussed in this paper, and crack propagation along the interface between a carbon fiber and pyrolytic carbon sheath was found to occur; the crack propagation is an important factor for improving erosion resistance.     

V2O5 nanosheets assembled on 3D carbon fiber felt as a free-standing electrode for flexible asymmetric supercapacitor with remarkable energy density

As an emerging energy storage device, supercapacitor is widely investigated owing to its excellent capability, quick charge-discharge and tremendous cycle life. The operation potential window, energy density and mass loading of supercapacitor must be taken into deep consideration for its practical application. In this work, an outstanding electrode based on CFF@V₂O₅ nanosheets was prepared. Then a free-standing asymmetric supercapacitor with CFF@V₂O₅ composite as positive electrode and CFF@AC as negative electrode was assembled. Owing to the functional groups produced on CFF after the activation, V₂O₅ nanosheets was immobilized. The composite exhibits remarkable specific capabilities of 1465 mF cm^?2 (492 F g^?1). The energy density of the assembled free-standing asymmetric supercapacitor achieves 0.928 mWh cm^?3 when the power density is 17.5 mW cm^?3. After 6000 charging-discharging cycles as under normal, bended and anti-bended conditions for respective 2000 cycles, the device retains 89.7% of the initial capacitance, exhibiting fascinating cycle stabilization. Finally, two devices linked series can lighten a LED of 1.8 V for 2 min after charging for 2.5 min, which is inspiring for the practical application and production of self-supporting asymmetric supercapacitors.     

Microstructure and mechanical properties of a metakaolinite-based geopolymer nanocomposite reinforced with carbon nanotubes

The preparation and mechanical behavior of metakaolin-based geopolymer nanocomposite reinforced with multi-walled carbon nanotubes are presented in this study. In this work, Multiwall carbon nanotubes (MWCNTs) were added to the metakaolin-based geopolymer paste at 0, 0.5, or 1 wt% concentration. For each specimen, the mechanical properties were tested at the age of 7, 14 and 28 days. TEM and FESEM were employed to evaluate the dispersion quality of MWCNTs within the metakaolin geopolymer matrix and determine their strengthening mechanism. The test results showed that the addition of about 0.5 wt% MWCNTs increased the compressive and flexural strength by as much as 32% and 28%, respectively. Based on these results, the MWCNTs can act as effective bridges to minimize and limit the propagation of micro cracks through the metakaolin-based geopolymer nanocomposite under the conditions of homogenous dispersion and good bonding between the MWCNTs and the surrounding metakaolin-based geopolymer paste.     

Synergistic modification of carbon fiber by electrochemical oxidation and sizing treatment and its effect on the mechanical properties of carbon fiber reinforced composites

In this article, The CF surface was modified by the synergistic modification of electrochemical oxidation and sizing treatment. Firstly, the electrochemical oxidation was carried out using fatty alcohol polyoxyethylene ether phosphate (AEOPK) as the electrolyte. The content of active groups on the modified CF surface increased by 235%. However, the strength of CF monofilament decreased due to the etching. Then, the electrochemically oxidized CFs were sized with the phosphate modified epoxy resin (PAEK). The etched defects on CF surface caused by the electrochemical oxidation were repaired by sizing agent molecules according to the AFM results. Furthermore, the spreadability of PAEK emulsion on the CF surface, the content of CF surface groups and the interaction of CFRC were characterized by using the monofilament contact angle, XPS and Raman spectroscopy. The results suggested that the synergistic modification could improve the CF surface activity, facilitate the spreading of PAEK on the CF surface, and increase the interaction between the CFs and the resin matrix. There were 20.3 and 22.6% enhancement in the breaking strength and elongation of CF monofilament. In addition, the interlaminar shear strength (ILSS) of CFRC prepared with synergistically modified CFs was increased from 12.81 to 33.04 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48028.     

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.     

Fiber length distribution and thermal,mechanical and morphological properties of thermally conductive polycarbonate/chopped carbon fiber composites

Chopped carbon fibers (CCFs) coated by poly(ethylene terephthalate) (PET) were treated using 3‐aminopropyltriethoxysilane (Si), and then used for fabricating thermally conductive polycarbonate/CCF (PC/(Si + PET)@CCFi) composites with various filler contents. Optical microscopy measurements indicated that CCF fillers in the composites had a wide length distribution and, with CCF content increasing, the mean fiber length and mean fiber aspect ratio steadily decreased. Compared to PC/(Si + PET)@CCF0, the molten flowability of composites declined. Thermogravimetric analysis and pyrolysis–gas chromatography–mass spectrometry characterizations showed that introducing CCFs could enhance the thermal stability of the composites and restrict the pyrolytic degradation of the polymer matrix. Moreover, both in‐plane and through‐thickness thermal conductivities increased with increasing CCF content. These conductivities at 50% CCF content reached 2.45 and 0.59 W m^?1 K^?1, and were improved by 11.25 and 1.95, respectively. Furthermore, the tensile and flexural properties of the composites continuously enhanced, accompanying decreased impact strength and elongation at break. Fractography revealed that fillers dispersed in matrix uniformly and a great many fiber cross‐sections and circular cavities coexisted in fracture surface, besides a clear interface and reduced long fibers. And the fracture behavior was mainly the breaking and peeling of fibers from matrix. © 2018 Society of Chemical Industry     

Coefficient variation of the mechanical properties of carbon fiber during carbonization

The approaches of the development for carbon fibers are how to improve their mechanical properties and to reduce the cost of the production as well as to maintain or to control the stability of their properties, i.e., the reproducibility. The coefficient variation of the mechanical properties immediately influenced the reproduction. In this paper, the effect of the operating conditions during carbonization on the coefficient variation of the properties for carbon fiber is discussed.