J. Jac Faripour Maybody, A. Nemati, E. Salahi,
Volume 10, Issue 2 (6-2013)
Abstract
In the present study, bioceramic composites based hydroxyapatite (HAp) reinforced with carbon nanotubes (CNTs) was synthesized via sol-gel technique. The dried gels were individually heated at a rate of 5°C/min up to 600°C for 2 h in a muffle furnace in order to obtain HAp-MWCNTs mixed powder. Composites were characterized by XRD, FT-IR, SEM, TEM/SAED/EDX and Raman spectroscopy techniques. Results showed the synthesis of HAp particles in the MWCNTs sol which was prepared in advance, leads to an excellent dispersion of MWCNTs in HAp matrix. Apparent average size of crystallites increased by increasing the percentage of MWCNTs. The average crystallite size of samples (at 600°C), estimated by Scherrer’s equation was found to be ~50-60 nm and was confirmed by TEM. MWCNTs kept their cylindrical graphitic structure in composites and pinned and fastened HAp by the formation of hooks and bridges.
Amin Rezaei Chekani, Malek Naderi, Reza Aliasgarian, Yousef Safaei-Naeini,
Volume 21, Issue 0 (3-2024)
Abstract
This paper presents the novel fabrication method of a three-dimensional orthogonally woven (3DW) C/C-SiC-ZrB2 composite and the effects of ZrB2 and SiC particles on microstructure and the ablation behavior of the C/C–SiC–ZrB2 composite are studied. C/C–SiC–ZrB2 composite was prepared by isothermal-chemical vapor infiltration (I-CVI), slurry infiltration (SI), and liquid silicon infiltration (LSI) combined process. Pyrolytic carbon (PyC) was first infused into the 3DW preform by I-CVI at 1050°C using CH4 as a precursor in order to form a C/C preform with porous media. The next step was graphitization at 2400°C for 1hr. Then ZrB2 was introduced into 3DW C/C preform with a void percentage of 48 by impregnating the mixture of ZrB2 and phenolic resin, followed by a pyrolysis step at 1050°C. A liquid Si alloy was infiltrated, at 1650 °C, into the 3DW C/C composites porous media containing the ZrB2 particles to form a SiC–ZrB2 matrix. An oxyacetylene torch flame was utilized to investigate The ablation behavior. ZrB2 particles, along with the SiC matrix situated between carbon fiber bundles, form a compact ZrO2-SiO2 layer. This layer acts as a barrier, restricting oxygen infiltration into the composite and reducing the erosion of carbon fibers. The findings were supported by FESEM imaging and further confirmed through x-ray diffraction and EDS analysis. The addition of ZrB2 to the C/C-SiC composite resulted in a lower mass and linear ablation rate; 2.20 mg/s and 1.4 µm/s respectively while those for C/C-SiC composite were 4.8 mg/s and 6.75 µm/s after ablation under an oxyacetylene flame (2500°C) for 120 s.
