Chengguo Wang

Controllable growth of uniform carbon nanotubes/carbon nanofibers on the surface of carbon fibers

An efficient method to obtain a good and uniform catalyst coating on the surface of carbon fibers was developed by modifying carbon fibers with electrochemical anodic oxidation (EAO), the homogeneous growth of carbon nanotubes (CNTs)/carbon nanofibers (CNFs) was then achieved on the surface of carbon fibers via chemical vapor deposition (CVD). According to the study on the effect of both the catalyst type and concentration on CNT/CNF growth, it was found that when the concentration of catalyst precursor is higher than a critical value, catalytic efficiency decreases apparently with the increase of catalyst concentration regardless of the catalyst type employed. The influence of CVD temperature on tensile strength of CNT/CNF-grafted carbon fibers was also investigated. At low temperatures, such as 500 °C and 550 °C, growing CNTs/CNFs without any degradation of mechanical properties of carbon fibers was successfully achieved, which demonstrated the feasibility of growing CNTs/CNFs directly on carbon fibers. A mathematical model for CNT growth was established to explain the experimental results successfully, which can be used to accurately control the morphology and yield of CNTs/CNFs grown on the surface of carbon fibers. Hence it provides theoretical guidance for the large-scale synthesis processes.

Study on the relationships of mechanical performance with the short-range and long-range structure of 500–900℃ carbonized fiber

The relationships of mechanical performance with the short-range and long-range structure of 500–900℃ carbonized fibers were studied by the combination of radial distribution function (RDF), Fourier transform infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HRTEM), etc. In the range of 500–900℃, there were different laws of change for tensile strength and elastic modulus during different temperature stages. The tensile strength was more nearly directly proportional to temperature, especially at higher than 600℃. The elastic modulus increased slowly from 500 to 700℃, and then elastic modulus increased rapidly after 700℃. The short-range structures had no effects on the mechanical performance. The uniform increasing rate of tensile strength was closely related to the crystallinity degree and crystal size. The outstanding increase of orientation degree was closely related to the change of elastic modulus.

Synthesis and properties of acrylonitrile-methyl itaconate copolymers as spun carbon fiber precursors

Acrylonitrile-methyl itaconate (AN-MIA) copolymers were successfully prepared by free-radical solution copolymerization, and then were spun into precursors of carbon fibers by one-step wet-spun method in this study. Effect of methyl itaconate(MIA), itaconic acid (IA) and methyl acrylate (MA) on the characteristics of the copolymers and precursors were studied in contrast. The monomer reactivity ratios for AN/MIA system were determined by Kelen-Tudos (K-T) method with r1=0.65, r2=1.80. The viscosity test shows that using MIA as a co-monomer is an effective way to decrease the viscosity of PAN solution. During the spinning and stretching processes, polyacrylonitrile (PAN) copolymer with MIA as co-monomer can reach the higher total draw-ratio of 12.0 folds, while PAN copolymer with IA as co-monomer can reach only 8.5 folds. The fineness and elongation at-break of the PAN precursors with MIA as co-monomer improve, but the tenacity decreases. DSC test shows MIA is less effective in improving the thermal property than IA.

Research on PAN Nascent Fiber Interior Microstructure through Ultrasonic Etching and Ultrathin Sectioning

The interior microstructures of polyacrylonitrile nascent fibers is studied by the scanning electronic microscopy and the high-resolution transmission electron microscopy through ultrasonic etching and ultrathin sectioning. Due to the orientation and fold of molecular chains, the lamellae of 50–80 nm in thickness are formed. A high number of pores, ranging from dozens to two hundred nanometers in diameters exist between the lamellae, which result from residual solvent. The fibril structure is formed in the nascent fiber during the coagulation process, which are oriented along the fiber axis. An uneven tensile stress distribution leads to the formation of skin-core structures in the nascent fiber during the dry-jet wet spinning process.

Synthesis and growth mechanism of carbon nanotubes growing on carbon fiber surfaces with improved tensile strength

An effective approach has been developed for the catalytic decomposition of acetylene (C2H2) by chemical vapor deposition (CVD), to achieve homogeneous growth of carbon nanotubes (CNTs) on the surfaces of carbon fibers. The morphology of CNTs grown on carbon fiber surfaces was observed by a scanning electron microscope and high-resolution transmission electron microscope, which revealed the uniform coverage of CNTs on the carbon fiber surfaces. The single fiber tensile test demonstrated that the tensile strength of carbon fibers could be increased by more than 12% with the catalytic growth of CNTs on their surface. The reparation of the damage caused during the formation of catalyst nanoparticles, and the cross-link of neighboring graphite crystallites induced by CNTs all occurred during the CVD process, which were considered to be the main reasons for improvement. The growth mechanism model of CNTs formation was established based on the thermodynamics principle and the interface microstructure of CNT-grown carbon fiber, illuminating the detailed mechanism for the growth of CNTs and the change of the shape of catalyst particles.

Research on the multi-scale microstructure of polyacrylonitrile precursors prepared by a dry-jet wet spinning process:

An understanding of the properties of polyacrylonitrile (PAN) precursors is an essential precondition for manufacturing high-performance carbon fibres, and the structure of the precursors has a direct and profound effect on the performance of carbon fibres. In this study, PAN precursors, formed in a multistage coagulation bath, were spun by a dry-jet wet spinning process, and the multi-scale microstructure and morphology of the precursors were investigated by separating the fibrils from the precursors. Scanning electron microscopy and high-resolution transmission electron microscopy were employed to examine the surface morphology, cross-sectional morphology and microstructure of the precursors. X-ray diffraction was used to characterize the crystal structure. The micropore sizes of the precursors were determined with nitrogen adsorption experiments; the adsorption increased after ultrasonic etching and decreased with an increase in the treated concentration. All the results demonstrated that the PAN precursors had a multi-scale microstructure, the precursors consisted of fibrils with diameters of 80–200 nm and the fibrils consisted of some microfibrils with diameters of 20–40 nm, including the periodic tissues with thicknesses of 16–30 nm perpendicular to the fibre axis.

Densification treatment and properties of carbon fiber reinforced contact strip

Abstract The high temperature caused by current-carrying wear could affect the thermal reliability of resin-based contact strip greatly. This study adopted liquid-phase impregnation-carbonization (IC) technique to improve the thermal stability and densification of carbon fiber reinforced contact strip (CFRCS). The influence of this method was investigated by scanning electron microscopy, Fourier transform infrared spectrometry, thermal gravimetric analysis and energy-dispersive spectrometry; meanwhile, specimen composition and friction and mechanism properties were also analyzed. The results show that heat treatment is helpful in improving the material’s temperature tolerance. When specimens undergo IC treatment four times, resistivity and wear rate would reduce gradually under impregnating conditions of carbonization temperature (800°C), dipping liquid concentration (60%), and dipping temperature (60°C). IC treatment is effective in reducing material porosity and improving the impact resistance performance compared with only carbonized sample. Densification treatment can also improve the samples’ compressive strength and bending strength. The main wear mechanisms of CFRCS-25 and CFRCS-800 against copper with electrical current are similar; these are arc erosion wear and oxidation wear accompanied by adhesive wear. Adhesive wear and oxidative wear is more severe for CFRCS-25 than CFRCS-800.