Carbon nanotubes (CNT) discovered by Iijima [1] in 1991 are one of the most studied nanostructural materials for a broad range of applications because they have attracted mechanical as well as physical properties. Theoretical and experimental studies [2][3][4][5][6] have shown that CNT have high Young's modulus of โผ 1500 GPa, great tensile strength of above 100 GPa, and very high length to diameter ratio of 1000 or more, as well as high electric conductivity and good thermal conductivity. These unique mechanical and physical properties have never been achieved by other fiber or whisker reinforcements. This has made applications of the CNT to reinforce metal, polymer and ceramic matrix composites an important topic of interest.
Recently, many attempts have been made to develop advanced engineering composites with improved mechanical and physical properties by incorporating CNT in metal, [7] polymer, [8,9] and ceramic matrices. [10,11] These studies showed that incorporation of CNT result in remarkable increase in mechanical properties, e.g. strength and fracture toughness, as well as noticeable improvement in physical properties, e.g. electrical and thermal conductivities, compared with those of matrix. Most of early studies in composites have focused on CNT-polymer-based composites because incorporation of CNT to polymer significantly improved its stiffness, strength and electrical conductivity as well as good interfacial compatibility of CNT with polymer matrix. However, the use of CNT to reinforce ceramic-matrix composites has not been very successful in improving mechanical properties due to damage of CNT during sintering. In particular, the damage of CNT could not be prevented during hot-press sintering, subsequently weakening reinforcing effect of CNT. These disadvantages limited developing CNT-ceramic-based com-