Biomedical Engineering Reference
In-Depth Information
7.21 2.5wt% MWCNT-SiO
2
composites thermally aged at 5008C and
10008C for 12 h and 96 h. MWCNTs did not oxidize at 5008C ((a) and (b))
but at 10008C, MWCNTs started oxidizing ((c) and (d)), producing a
decarburized surface layer.
temperature at which such composites can be used for long periods of time
without oxidizing the embedded CNTs. The effect of ageing temperature
and time was studied in the same unpublished investigation on CNT-SiO
2
composites (Subhani, 2012c), which showed that CNTs did not oxidize at a
temperature of 500
8
C but started oxidizing at 750
8
C and the rate of CNTs
8
oxidation increased at 1000
C. Figure 7.21 shows cross-sectional views of
2.5wt% CNT-SiO
2
composites thermally aged at 500
C for 12 h
and 96 h; an increased decarburized depth in CNT-SiO
2
composite
specimens is evident with the increase in time and temperature. Finally,
the effect of CNT concentration in composites was also assessed by
thermally ageing CNT-SiO
2
composites with CNT loadings from 2.5wt% to
10wt%. A completely CNT-free, porous silica glass was obtained by heating
the 10wt% CNT-SiO
2
composite, as shown in Fig. 7.22.
8
C and 1000
8
