Biomedical Engineering Reference
In-Depth Information
In order to develop more advanced bioceramic coatings on metallic biomaterials, many
calcium phosphate coating processes including vapor deposition, biomimetics, and elec-
trochemical deposition have been investigated.
(9)
These coating processes are shown in
Figure 7.2, where they are categorized by processing temperature and thickness of coating,
and also as to adherence and coating area.
(5)
Vapor deposition can be advantageous for the
preparation of uniform and dense coatings of calcium phosphate with a well-controlled
phase, composition, film thickness, and high bonding strength to metallic biomaterials.
Vapor deposition is generally classified into physical vapor deposition (PVD) and chemi-
cal vapor deposition (CVD). Both PVD and CVD are used to prepare solid films or pow-
ders from a gas phase. Although hybrid processes such as activated reactive evaporation
(10)
have been reported, chemical reactions in the gas phase are basically involved in the CVD
methods but not in the PVD methods. Ceramics are generally fabricated by powder sin-
tering with various additives due to their high melting points, covalent nature, low self-
diffusivities, and so forth. Vapor deposition techniques are suitable for the fabrication of
highly pure and dense ceramics at relatively lower temperature without additives. Typical
methods of PVD and CVD are summarized in Figure 7.3. The details of each method are
described in the next section. All the vapor deposition methods require energy for the
activation of source gases. The interaction between the particles (atoms/ions/clusters) and
solid surface changes depending on their kinetic energy as shown in Figure 7.4: deposi-
tion, sputtering, and ion implantation.
(11)
Sputtering as a PVD method utilizes the above-
mentioned phenomena of the kinetic energy of particles less than 10
3
eV for vaporization
of target materials and of the kinetic energy of particles less than 10 eV for deposition from
the gas phase.
PVD and CVD Methods
In PVD, a solid source material is physically vaporized by energy such as heat, plasma, or
laser, and then thin films are deposited on a substrate. Consequently, the composition of
1200
Good
IBD
Dip coating
900
Sputtering
CVD
CVD
Sol-gel
ermal
spraying
PLD
600
ermal spraying
Sputtering
PLD
IBD
Sol-gel
Biomimetics
300
Dip coating
Biomimetics
Electrochemical
deposition
Electrochemical
deposition
Poor
R.T.
0.1
1
10
100
1000
0.1
1
10
100
1000
ickness of coating,
t
(µm)
Coating area,
S
(cm
2
)
FIGURE 7.2
Processes for coating calcium-phosphate film on Ti substrate.
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