Narrow Results

Low-cost carbon fibers (CFs) are fabricated from jute fibers after pre-oxidation, carbonization and surface repair. This paper investigates the effects of pre-oxidation heating rate on jute fibers, and explores a repair method for surface defects of CFs in C/C composite. The results show the reaction mechanism of jute fibers in air is not changed at higher pre-oxidation heating rates while a low heating rate is still required as the oxidation of jute fibers cannot be fully achieved under rapid heating. The tensile strength of CFs increases after repair with a 5% phenolic resin solution. Jute-based CFs play a positive role in C/C composite performance through crack bridging and deflection.

The dynamics of cathode spot movements on a three-dimensional carbon fiber reinforced carbon/carbon composite were investigated by a scanning electron microscope and a digital high-speed video camera. The results show that the motion direction of the cathode spots is parallel to the carbon fibers. The directed motion of the cathode spots is accompanied by the cycle of alternative splitting and extinguishment of cathode spots. The group of the cathode spots can split into two small groups when it moves far away from the ignition site. Within 40 μs, the two small groups completely depart each other. The splitting of the cathode spots group is caused by the current degradation. The former group continues to go forward, and the latter extinguishes within 40 μs. The transient and the average velocity of the "lead" spot are estimated to be 0.9–3.4 m/s and ~ 2.11 m/s, respectively. The diffusion constant of the cathode spot is (9.11±0.59) ×10^-5 m²/s.

In this research, aluminum matrix composites reinforced with continuous carbon fibers (CFs) were fabricated using A356 aluminum alloy and PAN-based CFs by squeeze casting. For this purpose, CFs were first coated with a nickel layer using the electroless method and then the microstructure of the nickel–phosphorus (Ni–P) electroless coating was investigated. In the next step, composite samples reinforced with volume fractions of 5, 10, and 15 vol.% CFs coated with Ni–P coating were fabricated by squeeze casting at 60 MPa, and then microstructure and mechanical properties were examined. The results of the bending test on the composite samples indicated that the nickel coating had a significant effect on the flexural strength of the composite and increased the flexural strength by up to 30%. In addition, with the increase in the volume percentage of the fibers, the hardness of the samples increased while both the wear rate and the coefficient of friction decreased. Moreover, the best wear resistance was observed in the sample containing 15 vol.% as-coated carbon fibers. The Ni coating led to the formation of a mechanically mixed layer (MML) containing a fine mixture of metallic oxides and carbon thus enhancing the wear resistance.

The large surface area of inert carbon nanotubes (CNTs) and carbon fibers (CFs) renders insufficient interaction between the CNTs and CFs with the organic matrix. The filler–matrix interactions consequently become important to ensure sufficient wetting and filler dispersion in the matrix. The optimized functionalization method for both the CNTs and CFs will improve the viability of the entities for applications. In this report, we present a comparison between single-walled, multi-walled CNTs and pitch-based CFs in terms of their susceptibility to oxidation. The effects of functionalization reactions and extent of reaction are analyzed in terms of morphology, destruction of graphitization and hydrophobicity of the CNTs and CFs.