Biomedical Engineering Reference
In-Depth Information
7.11
Percentage variation of the hardness of glass and glass-ceramic
matrix composites containing CNTs from the literature.
dispersing CNTs in silica glass by a colloidal mixing technique and
consolidating the composite mixtures by PLS and SPS to near theoretical
densities (Cho et al., 2011, Subhani et al., 2011). The results of Subhani
(2012b) showed a continuous decrease of hardness with CNTs addition. The
effect of inhomogeneous CNT dispersion and insufficient densities was
avoided in the model silica matrix system investigated. Figure 7.11 shows
published hardness data of CNT-glass/glass-ceramic matrix composites,
obtained by Vickers macro/microhardness and Berkovich nanohardness
techniques. None of the CNT-glass/glass-ceramic matrix composites
showed a continuous increase in hardness to high CNT loadings, although
improvements up to 5wt% are reported in several systems. In those
experiments that probe higher loadings, a systematic decrease in hardness
was observed at up to 15wt% CNTs. Sharp increases at very low filler
contents are most likely related to changes in matrix morphology or
crystallinity.
Elastic modulus
Like hardness, published data for the elastic modulus of CNT-glass/glass-
ceramic matrix composites show different trends, as a direct result of
different composite microstructures. Considering the high stiffness of CNTs,
which should be greater than that of glasses/glass-ceramics, an increase in
