Fabrication process and characterization of carbon nanotube reinforced cobalt nanocomposite

Abstract

Because carbon-carbon bond observed in graphite is one of the strongest in nature, carbon nanotubes(CNTs) are excellent materials to be the stiffest and most robust structure ever synthesized. The combination of high-aspect ratio, small size, strength, stiffness and low density makes the CNTs perfect candidates as reinforcements in composites. As a consequence, there has been lots of interest in the development of CNT reinforced composites. Although most research has focused on the development of CNT reinforced polymer composites, several attempts have also been made to develop CNT reinforced metal composites with nanotubes as reinforcement. However, because of the difficulties in distributing CNTs homogeneously in a metal matrix by the powder metallurgy processes, it has been doubted whether CNTs can really reinforce metals. In this study, by introducing novel fabrication processes which are different from conventional powder metallurgy processes, CNT reinforced cobalt nanocomposite was successfully fabricated. First of all, CNTs were functionalized with acid-treatment to be homogeneously dispersed in oleylamine as a solvent. Multi-walled carbon nanotubes(MWCNTs), with diameters of 3~15nm and fabricated by thermal chemical vapor deposition, were purified and functionalized by acid treatment using HF, $H_2SO_4$ and $HNO_3$. The CNTs were stirred for 24h in HF and then cleansed with a mixed solution of $H_2SO_4/HNO_3$ in a 3:1 ratio. In addition, by decomposing cobalt (Ⅱ) acetylacetonate at 250℃ in a mixture of oleylamine and functionalized CNTs, CNT/cobalt oxide nanocomposite powders with 100nm of mean diameter can be fabricated. CNT/cobalt oxide nanocomposite powders were reduced into CNT/cobalt nanocomposite powders at 410℃, 2hours of holding time. Spark plasma sintering was utilized to fabricate CNT/cobalt nanocomposite with high relative density. As a result, CNT/cobalt nanocomposite with relative density over 99% was successfully fabricated. Mechanical ...