Biomedical Engineering Reference
In-Depth Information
dies at 1200
C for 20min at a pressure of 75MPa in an argon atmosphere
(Cho et al., 2011). 13vol% (10wt%) MWCNT-SiO
2
composites were
consolidated by PLS at a temperature of 1200
8
C for 3 h in an argon
atmosphere; the composite powders were compacted by uniaxial and
isostatic pressing before PLS (Subhani et al., 2011). The densities of the
composites are discussed in Section 7.6.1.
8
7.5 Microstructural characterization
The microstructure of CNT-glass/glass-ceramic matrix composites is
usually characterized using SEM, TEM and XRD. High-resolution TEM
(HRTEM) is used to observe CNT/matrix interfacial features. A variety of
CNT composites containing glasses and glass-ceramics have been micro-
structurally characterized including silica (Ning et al., 2004, Xu et al., 2009,
Zhan et al., 2005, Zheng et al., 2008), borosilicate (Thomas et al., 2009),
barium aluminosilicate (Ye et al., 2006), aluminoborosilicate
(Mukhopadhyay et al., 2010, Otieno et al., 2010) and vanadium-doped
silicates (Giovanardi et al., 2010).
7.5.1 X-ray diffraction (XRD)
XRD is used to confirm the amorphous structure of glass matrices after
sintering and to determine the extent of glass devitrification (Arvanitelis
et al., 2008, Babooram and Narain, 2009, Boccaccini et al., 2005, 2007, Cho
et al., 2011, de Andrade et al., 2009, Ning et al., 2003a, 2003b, Zhang et al.,
2006). In the case of glass-ceramic matrices, it identifies the presence of
crystalline phases in the glassy phase (Chu et al., 2008, Giovanardi et al.,
2010, Mukhopadhyay et al., 2010, Wang et al., 2007). Cristobalite usually
forms in silica and borosilicate glass matrices when SPS (de Andrade et al.,
2009, Guo et al., 2007a), HPS (Boccaccini et al., 2005, Ning et al., 2003a) or
PLS (Subhani et al., 2011) are used to sinter the composites. However,
careful control of sintering conditions can avoid crystallization that can
considerably affect the composite microstructure and properties, confound-
ing attempts to understand the underlying science (Cho et al., 2011, Ning
et al., 2003a, Subhani et al., 2011). Cristobalite can also be suppressed by the
addition of Al
2
O
3
but causes the crystallization of mullite and transforms an
amorphous glass into a glass-ceramic matrix, as observed in CNT-
aluminoborosilicate composites (Chu et al., 2008, Mukhopadhyay et al.,
2010). It can be argued that a large interfacial surface area in CNT-glass/
glass-ceramic matrix composites should accelerate matrix crystallization
through heteronucleation, but studies on CNT-SiO
2
composites have
instead identified a suppression of matrix devitrification, possibly due to the
dissolution of carbon (Subhani et al., 2011).
