Effect of Accelerated Aging Temperature under Artificial Seawater on the Properties of Carbon Fiber/Epoxy Composites and the Erosion Mechanism

In order to explore the effect of artificial accelerated aging temperature on the performance of carbon fiber/epoxy resin composites,we used artificial seawater as the aging medium,designed the aging environment of seawater at different temperatures under normal pressure,and studied the aging behavior of carbon fiber/epoxy composites.The infrared spectroscopy results show that,with the increase of aging temperature,the degree of hydrolysis of the composite is greater.At the same time,after 250 days of aging of artificial seawater at regular temperature,40 and 60 ℃,the moisture absorption rates of composite materials were 0.45%,0.63%,and 1.05%,and the retention rates of interlaminar shear strength were 91%,78%,and 62%,respectively.It is shown that the temperature of the aging environment has a significant impact on the hygroscopic behavior and mechanical properties of the composite,that is,the higher the temperature,the faster the moisture absorption of the composite,and the faster the decay of the mechanical properties of the composite.

Effects of Conductive Carbon Black on Thermal and Electrical Properties of Barium Titanate/Polyvinylidene Fluoride Composites for Road Application

In the field of roads,due to the effect of vehicle loads,piezoelectric materials under the road surface can convert mechanical vibration into electrical energy,which can be further used in road facilities such as traffic signals and street lamps.The barium titanate/polyvinylidene fluoride(BaTiO_(3)/PVDF)composite,the most common hybrid ceramic-polymer system,was widely used in various fields because the composite combines the good dielectric property of ceramic materials with the good flexibility of PVDF material.Previous studies have found that conductive particles can further improve the dielectric and piezoelectric properties of other composites.However,few studies have investigated the effect of conductive carbon black on the dielectric and piezoelectric properties of BaTiO_(3)/PVDF composites.In this study,BaTiO_(3)/PVDF/conductive carbon black composites were prepared with various conductive carbon black contents based on the optimum ratio of BaTiO_(3)to PVDF.The effects of conductive carbon black content on the morphologies,thermal performance,conductivities,dielectric properties,and piezoelectric properties of the BaTiO_(3)/PVDF/conductive carbon black composites were then investigated.The addition of conductive carbon black greatly enhances the conductivities,dielectric properties,and piezoelectric properties of the BaTiO_(3)/PVDF/conductive carbon black composites,especially when the carbon black content is 0.8%by weight of PVDF.Additionally,the conductive carbon black does not have an obvious effect on the morphologies and thermal stabilities of BaTiO_(3)/PVDF/conductive carbon black composites.

Preparation and Properties of Rare Earth Modified Carbon Black/Natural Rubber Composites

The oxides Eu, Ho, Er and Dy were used to prepare the hydroxides of rare earth modified carbon black. Then natural rubber latex （NRL） was added into the reactor. The system reacted at 85 ℃ with stirring for 1 h to prepare powdered HAF-Ln（OH）3/NR composites. The effects of the kind and content of Ln on the particle size distribution of P [ NR/HAF-Ln （OH）3 ] and mechanical properties of its vulcanizate were studied respectively. It is found that rare earth can help to get the powder of the composite, the product particle with a diameter less than 0.9mm will be get when the composites containing the compound of Ho, Er and Dy with dosage of 1.0, 1.0, O. 5 percent, respectively. The adding of Ln can improve the tensile strength and tear strength of the vulcanizate effectively, what＇s more, Er and Dy can decrease the permanent set of vulcanizate significantly. The SEM studies shows that P[ NR/HAF-Dy （OH）3 ] vulcanizate shows superior mechanical properties that depend primarily on the absence of free carbon black, the fine dispersion of carbon black in the rubber matrix and better polymer-filler interaction.

Micro Model of Carbon Fiber/Cyanate Ester Composites and Analysis of Machining Damage Mechanism

Machining damage occurs on the surface of carbon fiber reinforced polymer (CFRP) composites during processing. In the current simulation model of CFRP, the initial defects on the carbon fiber and the periodic random distribution of the reinforcement phase in the matrix are not considered in detail, which makes the characteristics of the cutting model significantly different from the actual processing conditions. In this paper, a novel three-phase model of carbon fiber/cyanate ester composites is proposed to simulate the machining damage of the composites. The periodic random distribution of the carbon fiber reinforced phase in the matrix was realized using a double perturbation algorithm. To achieve the stochastic distribution of the strength of a single carbon fiber, a novel method that combines the Weibull intensity distribution theory with the Monte Carlo method is presented. The mechanical properties of the cyanate matrix were characterized by fitting the stress-strain curves, and the cohesive zone model was employed to simulate the interface. Based on the model, the machining damage mechanism of the composites was revealed using finite element simulations and by conducting a theoretical analysis. Furthermore, the milling surfaces of the composites were observed using a scanning electron microscope, to verify the accuracy of the simulation results. In this study, the simulations and theoretical analysis of the carbon fiber/cyanate ester composite processing were carried out based on a novel three-phase model, which revealed the material failure and machining damage mechanism more accurately.

Structural characteristics and formation mechanisms of crack-free multilayer TaC/SiC coatings on carbon-carbon composites

In order to improve high temperature(over 2 273 K)ablation resistance,TaC and TaC/SiC composite coatings were deposited on carbon-carbon composites by CVD method utilizing reactive TaCl5-C3H6-H2-Ar and TaCl5-C3H6-CH3SiCl3-H2-Ar systems respectively.The structure and morphology of these coatings were analyzed by XRD and SEM.The results show that the double carbide coatings have good chemical compatibility during preparation.Two distinctive composition gradients are developed and used to produce multilayer TaC/SiC coatings with low internal stress,free crack and good resistant to thermal shock.A transition layer consisting of either C-TaC or C-SiC formed between the coating and the C/C matrix can reduce the residual stress effectively. The processing parameters were optimized and the possible growth mechanisms for these coatings were proposed.A designing methodology to prepare high performance multilayer TaC/SiC composite coatings was developed.

Ablation mechanism of TaC coating fabricated by chemical vapor deposition on carbon-carbon composites

Ablation characteristics and mechanism at high temperature for TaC coatings on carbon-carbon composites were investigated by ablation experiments with low power laser and oxyacetylene flame. The results show that the TaC coating is decomposed at the initial stage of laser ablation in atmosphere, and free carbon diffused to the surface, then oxidized to the melt including carbon, oxygen and tantalum. With the increase of ablation time, the melt is oxidized to low valent tantalum-oxide and Ta2O5 is formed finally. During the melt cooling, needle-like crystals of Ta2O5 are precipitated. Between the melt and TaC coating, there exists a diffusion transition layer with thickness of 1-2 μm. The transition layer consists of fine crystals and pores including carbon, oxygen and tantalum. The oxyacetylene flame ablation at 2 300 ℃ results in the rapid oxidation of TaC and formation of protective liquid films of tantalum oxide on the coating surface, where the liquid film can fill up the cracks and cover the coating. In such case, the oxidation mechanism of TaC is converted to the oxygen solution and diffusion control mechanism.

Simultaneously enhanced thermal conductivity and mechanical performance of carbon nanotube reinforced ZK61 matrix composite

Alloying seriously deteriorates the thermal conductivity of magnesium(Mg)alloys,thus,restricts their applications in the fields of computer,communication,and consumer products.In order to improve the thermal conductivity of Mg alloys,adding carbon nanotube(CNT)combined with aging treatment is proposed in this work,i.e.fabricating the D-CNT(a kind of dispersed CNT)reinforced ZK61 matrix composite via powder metallurgy,and conducting aging treatment to the composite.Results indicate the as-aged ZK61/0.6 wt.%D-CNT composite achieved an excellent thermal conductivity of 166 W/(mK),exhibiting 52.3%enhancement in comparison with matrix,as well as tensile yield strength of 321 MPa,ultimate tensile strength of 354 of MPa,and elongation of 14%.The simultaneously enhanced thermal conductivity and mechanical performance are mainly attributed to:(1)the embedded interface of the D-CNT with matrix and(2)the coherent interface of precipitates with matrix.It is expected the current work can provide a clue for devising Mg matrix composites with integrated structural and functional performances,and enlarge the current restricted applications of Mg alloys.

Investigations on the Sensing Mechanism of Humidity Sensors Based on Poly(4-vinylpyridine)/carbon Black Composite by AC Impedance Spectra

1 Results Investigations on the sensing mechanism is important for understanding the electrical responses of humidity sensors to humidity change,and could provide guidelines for the design and synthesis of humidity sensitive materials with desirable properties.In this work,the sensing mechanism of humidity sensors based on quaternized poly(4-vinylpyridine) (PVP)/carbon black (CB) composite[1] was studied by measuring their AC impedance spectra at various humidities at room temperature.Under low humidity...

Optimization of mixing speed and time to disperse the composite conductive agent composed of carbon black and graphene in lithium-ion battery slurry

This paper proposed an optimal approach to disperse the composite conductive agent which is composed of carbon black(CB)and graphene(Gr)within lithium-ion battery(LIB)slurry with different mixing speeds and mixing times.The internal structures of LIB slurry are characterized by Electrochemical Impedance Spectroscopy,Scanning Electron Microscopy,and Raman experiment.Initially,a composite conductive solution is prepared by mixing the composite conductive agent with NMP solvent under the conditions of five different mixing speeds n_(1)(n_(1)=1000,1100,1200,1300,1400 rpm)in the case of mixing time t_(1)=10 min.Subsequently,LIB slurry is prepared by blending the composite conductive solution,LiCoO_(2)and PVDF-NMP solution under the conditions of five different mixing speeds n_(2)(n_(2)=1000±280,1100±280,1200±280,1300±280,1400±280 rpm)in the case of mixing time t_(2)=6 min.By analyzing the internal structure of different LIB slurries,it shows that in the case of n_(1)=n_(2)=1200 rpm,a conductive network structure is well formed within LIB slurry.Additionally,in order to determine the optimal time to prepare the composite conductive solution for LIB slurry,nine different t_(1)(t_(1)=0,10,20,30,40,50,60,70,80 min)are selected.By analyzing the internal structure of different LIB slurries,a well-formed conductive network structure and a uniformly distributed composite conductive agent are deduced in LIB slurry when t_(1)=50 min.Therefore,it can be concluded that the composite conductive agent composed of CB and Gr is able to be uniformly dispersed in LIB slurry by establishing a well-formed conductive network structure under the optimal mixing speed n_(1)=n_(2)=1200 rpm and the optimal mixing time t_(1)=50 min,t_(2)=6 min.This kind of the internal structure has the potential to be used to further analyze the dispersion characterizations of LIB slurry under different composite conductive agent and CB/Gr ratios with the aim of improving the final performance of LIB.

Durability Testing of Composite Aerospace Materials Based on a New Polymer Carbon Fiber-Reinforced Epoxy Resin

In this study,the durability of a new polymer carbonfiber-reinforced epoxy resin used to produce composite material in the aerospacefield is investigated through analysis of the corrosion phenomena occurring at the microscopic scale,and the related infrared spectra and thermal properties.It is found that light and heat can con-tribute to the aging process.In particular,the longitudinal tensile strength displays a non-monotonic trend,i.e.,itfirst increases and then decreases over time.By contrast,the longitudinal compressive and inter-laminar shear strengths do not show significant changes.It is also shown that the inter-laminar shear strength of carbonfiber/epoxy resin composites with inter-laminar hybrid structure is better than that of pure carbonfiber materials.The related resistance to corrosion can be improved by more than 41%.

Electrical Percolation of Carbon Black Filled Poly (ethylene oxide)Composites in Relation to the Matrix Morphology

The present work studies the electrical conduction performance of carbon black (CB)filled poly(ethylene oxide) (PEO) composites. The addition of CB leads to reduced matrixcrystallinity as the fillers which are partly situated inside the lamellae and hinder the growth of PEOcrystallites. As a result, the electrical percolation behavior is related with the matrix morphology.

Novel C_(sf)/SiBCN composites prepared by densifying C_(sf)/MA-SiBCN with the PIP process:Oxidation behavior and damage mechanism

To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon （C/C） composites was 1.89 g/cm3 after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.

Improved wettability and mechanical properties of metal coated carbon fiber-reinforced aluminum matrix composites by squeeze melt infiltration technique

In order to improve the wettability and bonding performance of the interface between carbon fiber and aluminum matrix,nickel-and copper-coated carbon fiber-reinforced aluminum matrix composites were fabricated by the squeeze melt infiltration technique.The interface wettability,microstructure and mechanical properties of the composites were compared and investigated.Compared with the uncoated fiber-reinforced aluminum matrix composite,the microstructure analysis indicated that the coatings significantly improved the wettability and effectively inhibited the interface reaction between carbon fiber and aluminum matrix during the process.Under the same processing condition,aluminum melt was easy to infiltrate into the copper-coated fiber bundles.Furthermore,the inhibited interface reaction was more conducive to maintain the original strength of fiber and improve the fiber−matrix interface bonding performance.The mechanical properties were evaluated by uniaxial tensile test.The yield strength,ultimate tensile strength and elastic modulus of the copper-coated carbon fiber-reinforced aluminum matrix composite were about 124 MPa,140 MPa and 82 GPa,respectively.In the case of nickel-coated carbon fiber-reinforced aluminum matrix composite,the yield strength,ultimate tensile strength and elastic modulus were about 60 MPa,70 MPa and 79 GPa,respectively.The excellent mechanical properties for copper-coated fiber-reinforced composites are attributed to better compactness of the matrix and better fiber−matrix interface bonding,which favor the load transfer ability from aluminam matrix to carbon fiber under the loading state,giving full play to the bearing role of carbon fiber.

Silver Supported on White Carbon Black Containing Rare Earths as Antibacterial Material

The antimicrobial effect of the Ag-White Carbon Black containing rare earth was investigated. Inorganic antibiotic materials consist of the antibacterial ion, the additive and the carrier. The sol-gel method was used to prepare the white carbon black carrier. Ag+ was selected to be the antibacterial ion, and cerous nitrate was selected to be the additive. They were synthesized on the white carbon black carrier. The structures and properties of antibacterial material were characterized by inductively coupled plasma, particle size measurement instrument, fourier transform infrared and enumeration tests (Escherichia coli as experimental bacterium). Results showed that the amount of antibacterial ions and bacteriostasis rate of this new material are higher than those for the general Ag-antibacterial white carbon black (without containing rare earth). Ag+ was bound to white carbon black by ion exchange process and adsorption process. Bacteriostasis rate is over 99%, and the particle size can be extended down to 7 μm with a narrow size distribution. Other advantages of this material are good thermal and light stability. Furthermore, from the antibacterial experiment in rubber and the coating surface of metal, this new material showed promising results. The possible antibacterial mechanism was also proposed through all the experimental data in this study.

DFT Thermodynamic Research of the Pyrolysis Mechanism of the Carbon Matrix PrecursorTol uene for Carbon Material

Based on the experiments, the standard enthalpy△H■of the possible pyrolysis reactions of the carbon matrix precursor toluene was investigated by means of DFT method UB3LYP/ 3-21G *(based on semi-empirical method UAM1 and ab initio method UHF/3-21G*). The com- putation results with UB3LYP/3-21G* coincide with the experimental values well. Then, the mechanism for all types of the pyrolysis reactions of toluene was studied by UB3LYP/3-21G * The geometries of the reactant and the product radicals were optimized, meanwhile, the standard thermodynamic parameters of the pyrolysis reaction at different temperatures (298, 773, 843, 963 and 1 073 K) were calculated. The thermodynamic computation result shows that when the pyrolysis temperature of toluene is lower than 963 K, the reaction path supported by thermody- namics is that the C-H bond of the methyl on the benzene ring breaks and bitoluene form, while the temperature increases (about 1 073 K), the thermodynamic calculation result turns to support the reaction path producing phenyl radicals and methyl radicals. This mechanism is in accord with the experiments.

Effect of Water Absorption on the Impact Properties of Carbon Fiber/Epoxy Composites

In this paper, the effects of test temperatures and time on the impact damage behavior of unidirectional carbon fiber reinforced epoxy resin composites, immersed in pure water, on a pendulum impact tester, was studied. The results show that immersion in liquids has a significant effect on the impact resistance of the unidirectional composite material. It is obvious that after immersion, the mass of the material increases. The fracture initiation forces as well as the fracture initiation energy decrease as the immersion time lengthens. Moreover, the higher the temperature and the longer the time are, the more the crack propagation energy and the ductility index will be. Immersion makes the fracture mode change from the dominant fiber fracture into dominant delamination. All in all, immersion decreases the impact resistance of the composites and causes the fracture mode to change.

Effects of Carbon Nanotubes by Electrophoretic Deposition on Interlaminar Properties of Two Dimensional Carbon/carbon Composites

Carbon nanotubes（CNTs） were deposited uniformly on carbon cloth by electrophoretic deposition（EPD）. Thereafter, CNT-doped clothes were stacked and densified by pyrocarbon via chemical vapor infiltration to fabricate two-dimensional（2 D） carbon/carbon（C/C） composites. Effects of EPD CNTs on interlaminar shear performance and mode Ⅱ interlaminar fracture toughness（GⅡc） of 2 D C/C composites were investigated. Results showed that EPD CNTs were uniformly covered on carbon fibers, acting as a porous coating. Such a CNT coating can obviously enhance the interlaminar shear strength and GⅡc of 2 D C/C composites. With increaing EPD CNTs, the interlaminar shear strength and GⅡc of 2 D C/C composites increase greatly and then decrease, both of which run up to their maximum values, i e, 13.6 MPa and 436.0 J·m-2, when the content of EPD CNTs is 0.54 wt%, 2.27 and 1.45 times of the baseline. Such improvements in interlaminar performance of 2 D C/C composites are mainly beneficial from their increased cohesion of interlaminar matrix, which is caused not only by the direct reinforcing effect of EPD CNT network but also by the capacity of EPD CNTs to refine pyrocarbon matrix and induce multilayered microstructures that greatly increase the crack propagation resistance through ＂crack-blocking and-deflecting mechanisms＂.

Effects of Nanometer Carbon Black on Performance of Low-Carbon MgO-C Composites

The low-carbon magnesia-carbon （MgO-C） composites containing 3% （mass fraction, the same below） carbon were prepared by adding various types of carbon black （CB）. The mechanical properties, oxidation resistance at 1 100 ℃ in oxidizing atmosphere, and thermal shock resistance after 5 times dipping in 1 600 ℃molten steel of the low-carbon composite samples were investigated, compared with a commercial high-carbon MgO-C composite contai- ning carbon of 16 %. The results show that the mechanical properties, oxidation resistance and thermal shock resist- ance of the low-carbon samples are improved with the decrease of CB particle size. Thermal shock resistance of the low-carbon sample containing nanometer CB N220 is obviously better than that of other low-carbon samples, and rea- ches the level of the high-carbon samples.