Physical and electromagnetic shielding properties of green carbon foam prepared from biomaterials

100%green carbon foam from the fibrous fruits of Platanus Orientalis-L(Plane)along with the tar oil as binder has been prepared using a powder molding technique.The objective was to develop a porous monolithic carbon from biomaterials with a considerable strength necessary for various physical,thermal and electromagnetic shielding applications.Fast carbonization was carried out at1000°C under the cover of Plane tree pyrolyzed seeds without using any external protective gas.For comparative analysis,some samples were mixed with5%(mass fraction)iron chloride during the molding process.Iron chloride being a graphitization catalyst and activating agent helped in increasing the specific surface area from88to294m2/g with a25%decrease in flexural strength.Thermal stability was improved due to the incorporation of more graphitic phases in the sample resulting in a little higher thermal conductivity from0.22to0.67W/(m·K).The catalytic carbon foam exhibited shielding effectiveness of more than20dB over the X-band frequency.Absorption was dominant with only8.26%?10.33%reflectance,indicating an absorption dominant shielding mechanism.The new material is quite suitable for high temperature thermal insulation being lightweight,highly porous with interconnected porous morphology most of which is preserved from the original biomaterial.

Monitoring Three-point Bending Behavior of Carbon/Carbon Composites Using Electrical Resistance Change Methods

Damage behavior of unidirectional carbon fiberreinforced carbon(C/C)composites underthree-point bending load by electrical resistancechange(ERC)methods was presented.Staticbending tests and ERC tests were exam-ined simultaneously to obtain the relationship be-tween damage types and electrical resistance chang-es.In order to identify the occurring time and

Influence of cryogenic thermal cycling treatment on the thermophysical properties of carbon/carbon composites between room temperature and 1900℃

Influence of cryogenic thermal cycling treatment （from -120 ℃ to 120 ℃ at 1.3 × 10^-3 Pa） on the thermo- physical properties including thermal conductivity （TC）, thermal diffusivity （TD）, specific heat （SH） and coefficient of thermal expansion （CTE） ranging from room temperature to 1900 ℃ of carbon/carbon （C/C） composites in x-y and z directions were studied. Test results showed that fiber/matrix interracial debonding, fiber pull-out and microcracks occurred after the cryogenic thermal treatment and they increased significantly with the cycle number increasing, while cycled more than 30 times, the space ofmicrodefects reduced obviously due to the accumulation of cyclic thermal stress. TC, TD, SH and CTE of the cryogenic thermal cycling treated C/C composites were first decreased and then increased in both directions （x-y and z directions） with the increase of thermal cycles. A model regarding the heat conduction in cryogenic thermal cycling treated C/C composites was proposed.

In Vitro Biocompatibility of MC3T3-E1 Osteoblast-like Cells on Arg-Gly-Asp Acid Peptides Immobilized Graphite-like Carbon Coating on Carbon/Carbon Composites

Carbon/carbon （C/C） composites were deposited with graphite-like carbon （GLC） coating, and then, Arg-Gly- Asp acid （RGD） peptides were successfully immobilized onto the functionalized GLC coating. GLC coating was utilized to prevent carbon particles releasing and create a uniform surface condition for C/C composites. RGD peptides were utilized to improve biocompatibility of GLC coating. Surface chemical characterizations of functionalized GLC coating were detected by contact angle measurement, X-ray photoelectron spectroscopy and Raman spectra. Optical morphology of GLC coatings was observed by confocal laser scanning microscopy. In vitro biological performance was determined using samples seeded with MC3T3-E1 osteoblast-like cells and cultured for 1 week. Surface characterizations and morphological analysis indicated that C/C composites were covered by a dense and uniform GLC coating. Contact angle of GLC coating was reduced to 27.2° when it was functionalized by H202 oxidation at 40 ℃ for 1 h. In vitro cytological test showed that the RGD peptides immobilized GLC coating had a significant improvement in biocompatibility. It was suggested that RGD peptides provided GLC coating with a bioactive surface to improve cell adhesion and proliferation on C/C composites.

Effect of Growth Temperature on Carbon Nanotube Grafting Morphology and Mechanical Behavior of Carbon Fibers and Carbon] Carbon Composites

High-purity carbon nanotubes （CNTs） with different orientation and lengths were grafted on carbon fibers （CFs） in woven fabrics by using double injection chemical vapor deposition and adjusting the growth temperature. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and Raman investigations reveal that the grafted CNTs change from being predominantly aligned and uniform in di- ameter to absolutely disordered and variable in diameter, whilst they show significantly increased crystallinity, as the growth temperature is increased from 730 ~C to 870 ~C. In tensile tests of fiber bundles, much more strength degradation of CFs was observed after the growth process at higher temperature than that at lower temperature. These hybrid preforms produced at different growth temperatures were used to reinforce carbon/carbon （C/C） composites. An increment of 34.4% in out-of-plane compressive strength （OCS） was obtained for the composites containing CNTs grown at 730℃, while the OCS increment exhibits an obvious decrease with increasing the growth temperature. Compared with the higher growth temperature, the lower temperature contributes to the decrease in the strength loss of reinforcing fibers and meanwhile the growth of large extending length of CNTs, which can provide long reinforcement to the pyrocarbon matrix, and thus increase the compressive strength better.

Ablation Mechanism of Carbon/Carbon Composites Modified by HfC–SiC in Two Conditions Under Oxyacetylene Torch

C/C-HfC-SiC composites prepared by precursor infiltration and pyrolysis process were ablated by oxyacetylene torch under two different flame conditions. The ablation performance of the composites was investigated in the heat flux of 2.38 MW/m2 （HF-L） and 4.18 MW/m2 （HF-H） for 60 s. The mechanical denudation in 4.18 MW/m2 （HF-H） was higher than that in 2.38 MW/m2 （HF-L）, while the results indicated that the composites had a similar and good ablation property under two different flame conditions. C/C- HfC-SiC composites can adapt the heat flux from 2.38 MW/m2 to 4.18 MW/m2. The Hf02 was not melted completely in the heat flux of 2.38 MW/m2 （HF-L）. So, both Hf02 and Si02 layers acted as an effective barrier to the transfer of heat and oxidative gases into the underlying carbon substrate. SiO2 was severely consumed in 4.18 MW/m2 （HF-H）, where the HfO2 molten layer played a more important role in protecting the inner composite.