Polymer Precursor‐Based Preparation of Carbon Nanotube–Silicon Carbide Nanocomposites

Abstract

Multiwalled carbon nanotubes were dispersed in a silicon carbide matrix to examine nanotube influence on mechanical properties of the resulting composite. The ceramic matrix was generated through high temperature conversion of poly(methylsilyne), a preceramic polymeric precursor. Nanotube alkylation was explored using two functionalization schemes: organic peroxide workup and alkyllithium displacement of fluorinated nanotubes, which promoted extensive mixing within precursor solutions, thereby ensuring nanotube dispersion within the polymer matrix while facilitating interfacial bonding. The former scheme was less effective at displacing inner nanotube shell bound fluorine and resulted in lower alkyl chain grafting density on the outer shell. Polymer nanocomposites were pyrolyzed and consolidated using an optimized spark plasma sintering scheme to generate fully densified ceramics. The pure polymer‐derived ceramic displayed exceptional Young's modulus and Vickers microhardness of 126 ± 12 and 9.6 ± 0.5 GPa, respectively, while maintaining a fracture toughness of 2.8 ± 0.3 MPa·m1/2. Increased sintering time further augmented the fracture toughness to 3.6 ± 0.4 MPa·m1/2, approaching the 4 MPa·m1/2 that characterizes pure silicon carbide, while maintaining both Young's modulus and microhardness. Nanotube addition resulted in some loss of the intrinsic mechanical properties, but enhanced monolith damage tolerance behavior, raising the Vickers indent force needed to induce cracks to an excess of 98.1 N in contrast to the pure polymer‐derived sample, which began crack propagation below 49.0 N.

Microstructure and Mechanical Properties of Unidirectional, Laminated Cf/SiC Composites with α-Al2O3 Nanoparticles as Filler

“…The measured average Young's modulus and hardness of the nano α-Al 2 O 3 modified SiC matrix were 138.2 ± 8.66 and 10.3 ± 1.03 GPa, respectively. These are clearly higher than those of the pyrolytic β-SiC matrix in previous works, which range from 74 to 126 GPa and 6 to 9.58, respectively [52][53][54]. The higher Young's modulus and hardness of the matrix facilitate higher breaking strength for composites [55].…”

“…As shown in Figures 7 and 10, the C f /SiC-Al 2 O 3 composite shows excellent mechanical properties (flexural strength and fracture toughness) and considerable mechanical properties of the matrix (Young's modulus and hardness) compared with previous works [6][7][8][9][10][11][12][13][52][53][54]. The good mechanical properties of the SiC-Al 2 O 3 matrix could be related to the relatively dense matrix using nano α-Al 2 O 3 as a filler, which generally acts as a sintering aid for SiC to improve the densification of the matrix [56].…”

The mechanical properties of microscale area in CNT-C<sub>f</sub>/SiC hierarchical composite

“…无定形相主要为Si-C-O结构 [24] . 图 瓷(E=451 GPa, H v =25 GPa) [25] 和化学气相沉积制备的 SiC涂层(E=400~460 GPa) [26] 的模量和硬度, 但是与 聚合物转化的SiC(E=70~100 GPa, H v =~10 GPa)性能 相近 [27,28] . 较低的模量和硬度是由于PCS热解制备的 SiC中含有一定量的无定形玻璃相和游离碳 [23] .…”

Anisotropic compressive properties of porous CNT/SiC composites produced by direct matrix infiltration of CNT aerogel

“…CNT agglomerates, forming spontaneously unless otherwise controlled, are undesirable since they can act as internal defects causing stress concentration and crack initiation, hence hampering the beneficial reinforcement effect offered by the tubes. Current CNT/SiC composite fabrication methods include (i) disperse-mixsintering, 11,12,16,17,[22][23][24][25][26][27][28][29][30] (ii) chemical vapor infiltration (CVI) of arrays, 13,14,31,32 (iii) precursor infiltration pyrolysis of polymer precursor/CNT mixtures, 15,19,33,34 (iv) in situ grown of CNTs on SiC powders or porous SiC ceramics, 18,20,35 (v) deposition or synthesis of SiC on CNTs, 28,36,37 and others. 38 Compared with other ceramic processing methods, the CVI method possesses several significant advantages including near-net final shapes, minimization of the mechanical damage of the tubes due to much lower pressures and temperatures in the range of 900°C-1100°C, low mechanical stress, higher purity of the matrix.…”