Preparing a stable suspension is a main step towards the electrophoretically depositing of
homogeneous and dense composite coatings on NiTi for its biomedical application. In the
present study, different composite suspensions of hydroxyapatite, silicon and multi-walled
carbon nano-tubes were prepared using n-butanol and triethanolamine as media and
dispersing agent, respectively. Multi-walled carbon nanotubes were first functionalized in
the nitric acid vapor for 15 h at 175°C, and then mixed into suspensions. Thermal
desorption spectroscopy profiles indicate the formation of functional groups on multiwalled carbon nano-tubes. An excellent suspension stability can be achieved for different
amounts of triethanolamine. The amount of triethanolamine can be increased by adding a
second component to a stable hydroxyapatite suspension due to an electrostatic interaction
between components in suspension. The stability of composite suspension is less than that
of the hydroxyapatite suspension, due to density differences, which under the gravitational
force promote the demixing. The scanning electron microscopy images of the coatings
surface show that more dense coatings are developed on NiTi substrate using
electrophoretic deposition and sintering at 850°C in the simultaneous presence of silicon
and multi-walled carbon nanotubes in the hydroxyapatite coatings. The atomic force
microscopy results of the coatings surface represent that composite coatings of
hydroxyapatite-20 wt.% silicon and hydroxyapatite-20 wt.% silicon-1 wt.% multi-walled
carbon nano-tubes with low zeta potential have rougher surfaces.