SiC-coated Carbon Fibers Research Articles

Integrating high-efficiency thermal channel construction and structural wave absorption design within vertically oriented SiC-coated carbon fibers/silicone resin composites

To match the increasing miniaturization and integration of electronic devices, higher requirements are put forward for the electromagnetic wave absorption (EWA) and thermal conductivity (Tc) of heat conduction-microwave absorption integrated materials (HCMWAIMs) to overcome the problems of electromagnetic wave (EMW) pollution and heat accumulation. Herein, a simple and efficient shear force induction technique is used to construct a carbon/magnetic isolation network within the silicone resin matrix, where ferrite particles are well dispersed in vertically oriented SiC-coated carbon fibers array. Benefiting from the orderly interconnection of CFs@SiC in the array, the prepared composites have a high Tc of 7.86 W m−1 K−1. The introduction of magnetic ferrite particles within the CFs@SiC array can induce electrical-magnetic coupling, optimize impedance matching, and enhance EMW attenuation. This synergy of V-CFs@SiC/ferrite isolation network structure gives the composites an excellent effective absorption bandwidth (EAB) of 5.88 GHz and a minimal reflection loss (RLmin) of −47.5 dB at a thickness of 1.5 mm. Moreover, the as-prepared composites exhibit outstanding elastic compressibility of 43.2 % and rebound rate of 45.1 % under a pressure of 35psi. This strategy offers a distinguishing understanding of preparing high-performance HCMWAIMs in modern electronic devices.

Microstructure and oxidation behavior of a novel bilayer (c-AlPO4–SiCw–mullite)/SiC coating for carbon fiber reinforced CMCs

A novel cristobalite aluminum phosphate particle (c-AlPO4) modified SiC whisker toughened mullite coating (c-AlPO4-SiCw-mullite) was prepared on SiC coated carbon fiber reinforced SiC composites (C/SiC) by a new sol-gel method combined with air spraying to improve the oxidation resistance of SiCw-mullite coating. Results show that c-AlPO4-SiCw-mullite coatings with 10 and 20 wt.% of c-AlPO4 exhibited obviously improved oxidation resistance at 1773 K in ambient air for 100 h than SiCw-mullite coating. Moreover, the oxidation resistance of c-AlPO4-SiCw-mullite coatings were rapidly declined when the c-AlPO4 in c-AlPO4-SiCw-mullite coating were set to 30 and 40 wt.%. The c-AlPO4-SiCw-mullite coating with 20 wt.% of c-AlPO4 showed most pronounced oxidation resistance, the weight loss rate after the oxidation in ambient air for 210 h was merely 3.00 × 10−5 g·cm−2 h−1. The failure of c-AlPO4-SiCw-mullite coating with 20 wt.% of c-AlPO4 was due to the generation of penetrative micro-cracks and micro-holes in the coating, which cannot be self-healed by the silicate glass layer after long time oxidation at 1773 K.

Improvement of oxidation resistance of carbon fibers by coating SiC

SiC-coated carbon fibers (CFs) were prepared by spark plasma sintering, and their phase compositions and microstructures were identified by x-ray diffraction and characterized by field-emission scanning electron microscope, respectively. The oxidation behaviors of the SiC-coated CFs was examined through thermo gravimetric analysis and compared with that of pristine CFs. The effects of Si content in the SiC coatings on the surfaces of the CFs were also investigated. SiC coating with 25 wt% Si contributing to the reaction was thicker than that with 10 wt% Si but had weaker oxidation-resistant properties. When coated with SiC, the CFs exhibited considerable improvement in their oxidation resistance, and the temperature for its oxidation increased nearly by 140 °C.

Comparison in dielectric and microwave absorption properties of SiC coated carbon fibers with PyC and BN interphases

SiC coated carbon fibers with two different types of interphases, pyrolytic carbon and boron nitride (Cf-PyCi-SiC and Cf-BNi-SiC), were respectively prepared and their dielectric and microwave absorption properties were investigated. Results showed that both real (ε′) and imaginary part (ε″) of permittivity of these two SiC coated carbon fibers decrease significantly, in comparison to carbon fibers. The decreased permittivity is mainly due to the large decrease in electrical conductivity. Furthermore, electromagnetic impedance match is improved with the decreasing permittivity, leading to much better microwave absorption properties. Compared to PyC, BN with higher electrical resistivity and lower permittivity endues better impedance match and stronger microwave attenuation for Cf-BNi-SiC. Both Cf-PyCi-SiC and Cf-BNi-SiC with superior microwave attenuation performance exhibit promising prospects as microwave absorbing materials.

Controllable preparation of SiC coating protecting carbon fiber from oxidation damage during sintering process and SiC coated carbon fiber reinforced hydroxyapatite composites

As a kind of ideal artificial bone materials, poor mechanical properties especially brittleness of pure hydroxyapatite (HA) have limited its clinical application. In order to achieve pressureless sintering of carbon fiber (CF) reinforced HA bioceramics, SiC coating was successfully prepared on CF surface by low pressure chemical vapor deposition (LPCVD). The structure, morphology, and thickness of the SiC coating are controllable. The SiC coated CF (SiC-CF) reinforced HA composites (SiC-CF/HA) were prepared via pressureless sintering at 1373 K for 20 min. The bending strength of the SiC-CF/HA composite reaches its maximum achievable value of 28.4 MPa, when 0.5 wt% of SiC-CF was added. It is almost three times that of pure HA sintered under an identical condition. The corresponding fracture toughness is as high as 1.28 MPa·m1/2, which are 26.6% and 19.5% increase over those of HA and CF/HA composites, respectively. The enhancements of the bending strength and fracture toughness are mainly due to enhancing and toughening mechanism (crack-bridging and pull-out of SiC-CF). In practice, SiC coating acts as an oxygen diffusion barrier to prevent the oxidative damage of CF caused by dehydroxylation of HA during pressureless sintering. Furthermore, the SiC coating has the ability to form a transitional SiO2 layer in an oxidizing atmosphere which fills the cracks of the coating, enhances the interfacial compatibility, and lessens the interfacial stress. The study provides additional insights into the feasibility of SiC-CF/HA composites as load-bearing implant materials in clinical applications.

Microstructure and properties of SiC-coated carbon fibers prepared by radio frequency magnetron sputtering

SiC-coated carbon fibers are prepared at room temperature with different radio-frequency magnetron sputtering powers. Results show that the coated carbon fibers have uniform, continuous, and flawless surfaces. The mean strengths of the coated carbon fibers with different sputtering powers are not influenced by other factors. Filament strength of SiC-coated carbon fibers increases by approximately 2% compared with that of uncoated carbon fibers at a sputtering power of <200W. The filament strengths of the coated fibers increase by 9.3% and 12% at sputtering powers of 250 and 300W, respectively. However, the mean strength of the SiC-coated carbon fibers decreased by 8% at a sputtering power of 400W.

Oxidation protective silicon carbide coating for C/SiC composite modified by a chromium silicide–chromium carbide outer layer

A chromium silicide–chromium carbide (Cr3Si–Cr7C3) outer layer mainly composed of Cr3Si, Cr7C3, and a small amount of Cr3C2 was prepared on a SiC coated carbon fiber reinforced silicon carbide (C/SiC) composite using a Powder Immersion Reaction Assisted Coating (PIRAC) method. The Cr3Si–Cr7C3 outer layer showed folded ridge morphology. The width of the largest microcracks on the outer layer of the Cr3Si–Cr7C3/SiC/SiC coating was only one forth of that on the outer layer of the SiC/SiC/SiC coating. The Cr3Si–Cr7C3/SiC/SiC coating showed significantly enhanced oxidation protection compared to the SiC/SiC/SiC coating. After oxidation for 10h, the Cr3Si–Cr7C3/SiC/SiC coated composite showed nearly the same failure behavior and residual flexural strength as that of the as-received composite.

Dielectric properties of Cf–Si3N4 sandwich composites prepared by gelcasting

Cf–Si3N4 sandwich composites were prepared by gelcasting using α-Si3N4 powder, SiC-coated carbon fibers and sintering additives as starting materials. The microstructure and composition, dielectric properties of Cf–Si3N4 sandwich composites were investigated. SEM and EDS analysis results reveal that the SiC interphase could effectively overcome incompatibility between carbon fiber and silicon nitride matrix under the condition of pressure-less sintering at 1700°C. The investigation of microwave absorbing property reveals that, compared with the Si3N4 ceramics, both the real (ε׳) and imaginary (ε׳׳) permittivity of Cf–Si3N4 sandwich composites show strong frequency dispersion characteristics at X-band. Microwave absorption ability of the Cf–Si3N4 sandwich composites are significantly enhanced compared with pure Si3N4 ceramic, and the reflection loss gradually decreases from −3.5dB to −14.4dB with the increase of frequency, while the pure Si3N4 ceramic keeps at −0.1dB. Particularly, the relationship between permittivity of Cf–Si3N4 sandwich composites and frequency at X-band has been established through an equivalent RC circuit model. Results showed that both ε׳ and ωε׳׳ are inversely proportional to the frequency square ω2, and the predicted results agree quite well with the measured data.

Preparation of anti-oxidative carbon fiber at high temperature

In this paper, carbon fibers with improved thermal stability and oxidation resistive properties were prepared and evaluated their physical performances under oxidation condition. Carbon fibers were coated with SiC particles dispersed in a polyacrylonitrile solution and then followed by pyrolyzed at 1400°C to obtain the SiC nanoparticle deposition on the surface of the carbon fiber. The SiC coated carbon fiber showed extended oxidation resistive property as remaining 80–88% of the original weight even at high temperature 1000°C under air, as compared with the control of zero weight at 600°C. The effects of the coating conditions on the oxidation resistive properties of the coated fibers were studied in detail.

Synthesis of a silicon carbide coating on carbon fibers by deposition of a layer of pyrolytic carbon and reacting it with silicon monoxide

A method for preparing a SiC coating on carbon fibers is presented. The SiC coating was generated from the reaction of silicon monoxide (SiO) with a pyrolytic carbon (PyC) layer deposited on the fibers. The influence of holding time on the microstructure of the SiC layer was discussed. The oxidation behaviors of the uncoated and SiC coated carbon fibers were compared. The formation mechanism of the SiC coating was evaluated. With increased reaction time, the SiC coating becomes thicker and its surface becomes rough. The oxidation resistance of the carbon fiber was improved by the SiC coating. The initial oxidation temperature of the SiC coated carbon fiber is about 200 °C higher than that of the uncoated carbon fiber. The growth of the SiC coating is mainly attributed to the indirect reactions of SiO with PyC in the SiO/SiC/C system, in which silicon is considered a critical intermediate product.

Coating of continuous carbon fibers with double layers by chemical vapor deposition

A theoretical approach for the description of the chemical vapor infiltration (CVI) of continuous carbon fiber bundle is used to predict the homogeneity of the infiltration into a fiber bundle as a function of the temperature. Required input for the model is the rate constant of the chemical reaction and the effective diffusion coefficient, including the geometric parameter of the fiber bundle. The mechanical properties of SiC coated carbon fibers are measured in a single filament test and evaluated using the Weibull statistics. SiC nanolayer of about 45 nm thickness decreases the fiber tensile strength to 88% of the value of an uncoated fiber. On the other hand, pyrolytical carbon (pyC) films improve their mechanical properties. Combining these two effects in applying a double layer coating consisting of pyC/SiC or pyC/TiN in a single step process, it is possible to slightly increase the tensile strength of the carbon fibers. SEM and TEM analysis also show a uniform distribution of the layer thickness within the fiber bundle and confirm the layer thickness measured experimentally.

Tensile strength and morphological investigation of SiC-coated carbon fibers

SiC-coated film onto carbon fibers as a barrier of oxidation resistance and reaction between carbon fibers and metals was investigated. The chemical vapor deposition of silicon carbide onto carbon fibers was performed at various temperatures ranging from 700 to 1000°C using triisopropylsilane vapor carried by hydrogen gas. The strength of the SiC-coated carbon fibers was decreased due to deterioration of fibers and chemical attack of hydrogen on the surface of carbon fibers during the coating process. The oxidation and the thermal resistance of the SiC-coated carbon fibers compared to the uncoated carbon fibers were improved at temperature range of 600–800°C and 1000–1200°C, respectively. Morphological change by air oxidation at temperature range of 500–800‡C was also investigated for the SiC-coated and the uncoated carbon fibers, respectively. The SiC-coated film between carbon fiber and aluminum was sufficient as a barrier of reaction on carbon fiber reinforced aluminum at temperature of above 1000°C.

Surface free energy of carbon fibers with circular and non-circular cross sections coated with silicon carbide

Mesophase pitch-based carbon fibers with circular and non-circular (ribbon, C-shaped) cross sections were coated with a thin, approximately 100–150 nm SiC-layer, using a CVD technique. The surface free energy of the uncoated and SiC-coated carbon fibers was determined by measuring the contact angle of a variety of liquids with known polar and dispersive components of their total surface free energy. It was shown that the polar and dispersive components of the total surface free energy of the carbon fibers depends strongly on both the SiC-layer as well as on the shape of the cross section.

Strength and toughness of carbon fiber reinforced aluminum matrix composites

Two sets of aluminum matrix composites reinforced with both uncoated and SiC-coated Pitch-55 aligned carbon fibers were prepared having a volume fraction f=0.2 of reinforcement to test certain toughening strategies proposed earlier (A.S. Argon and V. Gupta, in G.K. Haritos and O.O. Ochoa (eds.), Damage and Oxidation Protection in High Temperature Composites, Vol. 25-2, ASME, New York, 1991, p. 1). Preparatory studies showed that the Pitch-55 fibers are damaged to some degree as a result of composite sample preparation. The loss of strength in the SiC-coated fibers was much less than in the uncoated fibers. Tensile tests of both smooth and precraked composite sheets showed that while the composites reinforced with SiC-coated carbon fibers were stronger than the composites reinforced with uncoated fibers, the former had less than half the tensile toughness of the latter. The higher tensile toughness of the composites with uncoated fibers is a direct result of the more extensive debonding of fibers from the matrix during fiber fracture. This permits the formation of a thicker fracture process zone in the composites reinforced with uncoated fibers. The measured composite strength values and their trends were consistent with the predictions of theory (P.M. Scop and A.S. Argon, J. Composite Mater., 3 (1969) 30). The different tensile toughness of the composites with the coated and uncoated fibers could be accounted for by simple fracture models of fiber composites incorporating the beneficial effects of controlled debonding of fibers.

The tensile strength of SiC-coated carbon fibers and an application of the fibers to FRM.

Two types of high-modulus carbon fibers were coated with various thicknesses of silicon carbide by the chemical vapor deposition method, and the tensile-test of the mono-filament was carried out. Two failure modes of fibers, i.e., a fracture followed by a cracking of a coated layer (bonding-mode), and a fracture including a debonding of a coated layer (debonding-mode), were observed by SEM, depending on the type of fiber. The tensile strength of fiber in the debonding -mode decreased with increasing thickness of a coated layer, whereas the fiber in the bonding-mode did not reduce its strength up to a certain thickness of a coated layer. And, the strength in the bonding-mode was higher than that in the debonding-mode. Aluminum matrix composites using the SiC-coated carbon fibers were produced by the squeeze casting method. The tensile strength of the composites increased with increasing thickness of the coated layer. In this case, also, the composites using the fiber in the debonding-mode were not so strong compared with that of the fiber in bonding-mode.

SiCコーティングをした炭素繊維のアルミニウムマトリックスに対する適合性

The compatibility of SiC-coated carbon fiber with aluminum was investigated. The carbon fiber was coated with SiC by chemical vapour deposition. The elastic modulus and the tensile strength of the carbon fiber increased after the SiC coating treatment.The compatibility of carbon fiber with aluminum was assessed by strength testing after heating the aluminum-coated fiber specimens in an argon atmosphere. The heat treatments were carried out for 90 ks at temperatures of the solid state of aluminum, or for 1.8 ks at temperatures of the liquid state of aluminum. Though the uncoated carbon fibers showed a marked loss in strength after the heat treatments, the SiC coated coarbon fibers showed no loss in strength after the heat treatments at 673 to 873 K for 90 ks and at 973 to 1073 K for 1.8 ks. However, the noticeable degradation in strength of the SiC-coated carbon fibers was observed after the heat treatments at temperatures higher than 1173 K for 1.8 ks. The wettability between carbon fiber and liquid aluminum was improved by the SiC coating.