Preparation And Properties Of Modified Carbon Fibers/HA Composites

Carbon fibers/Hydroxyapatite (HA) composite is one kind of the excellent hard tissueimplants. However, the significant difference in heat expansion coefficient and surfacechemical properties between carbon fibers and hydroxyapatite leads to the poor bondingstrength of the carbon fiber/HA interface, and to the appearance of cracks, which results in thelow reliability of the mechanical properties of the composite. These reasons limited theapplication of the composite in the bearing position in human body. The technologies ofoxidation at the low temperature, or disposal with HCl acid have been used to pretreat carbonfibers. The pretreated carbon fibers were pulled through in HA sol and further modified toform coating HA layer on carbon fibers. The modified carbon fibers are used to reinforce HAcomposites by dry pressing and centrifugal slip casting methods. The modified technologiesof carbon fibers are studied, micro-morphology of the modified carbon fibers is observed.During centrifugal slip casting process, the dispersion and stability of the carbon fiber-HAslurries were studied. The effects of centrifugal process parameters on uniformity of greendensities of modified carbon fiber/HA composites are analyzed. The sintering technologies fortwo kinds of HA composites are studied. The bending strength and fracture toughness ofcomposites prepared by two methods are measured. The mechanism of strengthening strengthand toughness is analyzed and micro-morphology of the fracture of the composites isobserved.The results show that there are a lot of portrait flutes and holes on the surface of thecarbon fibers after modified by oxidation at the low temperature, and disposal with HCl acid.The surface of the modified carbon fibers has high roughness. After dip in the HA solprepared by sol-gel technology for5times, the surface of carbon fibers has a compact andfastness HA layer. The HA layers have special porous structure after sintering at hightemperature, which is beneficial to solve the heat expansion coefficient difference andimprove the mechanical properties of HA matrix.During dry pressing process, with the increase of sintering temperature, the sinteringdensity of the modified carbon fiber/HA composites increase. With the increase of the contentof carbon fibers, the bending strength and fracture toughness of the composites first increaseand then decrease. When the content of carbon fiber is2wt%and2.5wt%, the carbonfiber/HA composites have the highest bending strength of82.4MPa and flexural toughness of1.84MPa·m1/2, which improve79.1%and46.1%compared with the un-modified carbonfiber/HA composites.During centrifugal slip casting process, the50wt%carbon fiber-HA slurries have lowestviscosity of481.7mP·s, good dispersion and stability at pH=9and the dispersant of5wt%.After centrifuged at4000r/min with50wt%carbon fiber-HA slurries, the green compacts haveuniform density. SEM observation shows the sintered composites have compact microstructure and no obvious mass segregation phenomenon. The treated carbon fiber/HAcomposites prepared by centrifugal slip casting have the highest bending strength of93.5MPaand flexural toughness of1.96MPa.m1/2, respectively, when the contents of carbon fibers is2wt%and2.5wt%, which is13.5%and6.5%higher than those of carbon fiber/HAcomposites prepared by dry pressing method.