Biomedical Engineering Reference
In-Depth Information
7.2
MWCNTs treated with a mixture of sulphuric and nitric acid to
obtain stable aqueous dispersion.
heterocoagulation, which is produced using cationic surfactants, and finally
suitable composite powder suspensions are obtained by colloidal mixing.
The composite powder suspensions are dried, ground and sieved to obtain
powders for subsequent sintering into solid compacts. A calcination process
is usually performed on dried composite powders before sintering to remove
organic surfactants and CNT oxidation debris at temperatures less than
400
C. Figure 7.2 shows an image of MWCNTs after treating with sulphuric
and nitric acid to develop surface charges for stable aqueous dispersion.
In the earliest of these studies, 1wt% CNTs were dispersed in silica glass
(Arvanitelis et al., 2008) but high CNT contents were loaded successfully
(19vol%) in subsequent investigations (Cho et al., 2011). Both pressureless
sintering (PLS) (Subhani et al., 2011) and spark plasma sintering (SPS) (Cho
et al., 2011) have been used to prepare CNT-SiO
2
composites at near
theoretical densities. A uniform distribution of CNTs was obtained in the
silica glass powder, which was retained after sintering. SEM images of 5wt%
MWCNTs composite powder before and after sintering are shown in Fig.
7.3 and Fig. 7.4, respectively. The sintered sample exhibits homogeneously
dispersed CNTs. Individual CNTs are well separated from the others
without showing agglomerates.
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