Guo-Bin Zheng

A TEM study of microstructure of carbon fiber/polycarbosilane-derived SiC composites

The structures of two types of mesophase pitch-based cal bon fibers (M30 and M70) reinforced SIC composites, prepared by the polycarbosilane impregnation-pyrolysis process, were investigated using transmission electron microscopy (TEM). It was found that M70 possessed a highly-ordered graphite structure despite occasional misorientation of some crystallites. However, the skin of M70 was less ordered than the interior of M70. The structure of M30 was uniform throughout, and was less ordered than that of M70. The fiber and matrix in M70/SiC bonded weakly, whereas the fiber and matrix in M30/SiC bonded tightly and locked together. This difference in. the interface feature originates from the difference of the surface crystalline structures of M30 and M70, and is formed during the first impregnation-pyrolysis cycle of polycarbosilane

The properties of carbon fibre/SiC composites fabricated through impregnation and pyrolysis of polycarbosilane

Unidirectional carbon fibre reinforced SiC composites were prepared from four types of carbon fibres, PAN-based HSCF, pitch-based HMCF, CF50 and CF70, through nine cycles or twelve cycles of impregnation of polycarbosilane and subsequent pyrolysis at 1200°C. The polycarbosilane-derived matrix was found to be β-SiC with a crystallite size of 1.95 nm. The mechanical properties of the composites were evaluated by four-point bending tests. The fracture behavior of each composite was investigated based on load-displacement curves and scanning electron microscope (SEM) observation of fracture surfaces of the specimens after tests. It was found that CF50/SiC and CF70/SiC exhibited high strength and non-brittle fracture mode with multiple matrix cracking and extensive fibre pullout, whereas HSCF/SiC and HMCF/SiC exhibited low strength and brittle fracture mode with almost no fibre pullout. The differences in the fracture modes of these carbon fibre/SiC composites were thought to be due to differences in interfacial bonding between carbon fibres and matrix. Values of flexural strengths of CF70/SiC and CF50/SiC were 967 MPa and 624 MPa, respectively, which were approximately 75% and 38% of the predicted values. The relatively lower strength of CF50/SiC, compared with CF70/SiC, was mainly attributed to the shear failure of CF50/SiC during bending tests.

Effect of Boron Addition on Oxidation Resistance of Carbon Fiber Polycarbosilane–derived SiC Composites

Nagasaki Univ, Dept Mat Sci & Engn, Nagasaki 8528521, Japan. Acad Sinica, Inst Met Res, Shenyang 110015, Peoples R China.;Zheng, GB (reprint author), Nagasaki Univ, Dept Mat Sci & Engn, Bunkyo Machi 1-14, Nagasaki 8528521, Japan

CeO2 nanoparticles deposited on carbon nanotubes

Carbon nanotubes (CNTs) with average diameter of 14 nm were modified by oxidation in nitric acid and followed by treatment in sodium dodecyl sulfate (SDS). XPS analysis verified the introduction of carboxyl group and SDS molecules onto the CNT surface. The CeO2 coatings on CNTs were synthesized using two different processes; chemical precipitation method and solvothermal method. TEM observation showed that the coatings consisted of CeO2 nanoparticles with size of several nanometers. It is believed that in chemical precipitation method, the surface modification with carboxyl group and SDS provided nucleation sites of CeO2, thus facilitating further growth and attachment of CeO2 nanoparticles. In solvothermal method, due to the interaction between graphene surface of CNTs and solvent pyridine, CeO2 particles could form on the pristine CNTs, and the surface modification decreased the nucleation sites of CeO2 and thus led to thinner or incomplete coating.