Biomedical Engineering Reference
In-Depth Information
electrolyte so that the HA and Ti particles could be codeposited
on a titanium substrate [106]. The electrolyte used for deposition
of coatings contained 0.0105M Ca(NO 3 ) 2 , 0.0063M NH 4 H 2 PO 4 ,
0.1M NaNO 3 , and 0-100 g/L Ti particles. The pH of the electrolyte
was adjusted to 4.60. The HTEC deposition was carried out at
-0.4 mA/cm 2 and 200°C for 120 min. The pressure was about
1.60 MPa. The SEM images of the HA/Ti coatings (Fig. 9.69)
reveals the Ti particles and a needle-like HA. HA and Ti particles
are uniformly distributed in the coating with a rough surface.
Some small HA particles are deposited on Ti particles surface. The
pure HA coating (Fig. 9.69d) has much larger particle size than
that in the HA/Ti composite coating (Fig. 9.69a-c), indicating the
function of Ti particles as the HA crystal growth inhibitor during
HTEC deposition [106].
Because the hydrogen evolution on the surface occurs during
the process, the HA coatings prepared by electrodeposition are
porous, and the addition of Ti leads to a decrease in porosity and
an increase in density of the composite coatings. Smaller porosity
and higher density of coating lead to higher cohesive strength of the
coatings [106].
In the process, the Ti particles are deposited on the cathode
surface, and around them are build HA crystals incorporated of
Ti particles as reinforcement within the coating, which improves
the bonding strength between coating and metal substrate.
The addition of Ti reduces the HA crystallite size. The bonding
strength of HA/Ti composite coatings increases with addition of Ti
[106]. The results of bonding strength of HA/Ti composite coatings
after heating at 500°C for 2 h are shown in Fig. 9.70. The pure HA
coating shows the lowest bonding strength and the bond strength
of the composite coating increases with the addition of Ti content.
The strengthening mechanism of HTEC codeposited HA/Ti coatings
is related to the dispersion strengthening by homogeneous
distribution of Ti particles in the HA [106].
The surface morphology of the HA/Ti composite coatings
heated at 500°C for 2 h after additional soaking in SBF for 7 days is
shown in Fig. 9.71. The surface of the coating is covered by a newly
formed granular layer with many cracks (often observed in many
works). The addition of Ti reduces the HA content in the coating, but
it does not distinctly affect the formation of bone-like apatite layer
in SBF [106].
 
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