Geoscience Reference
In-Depth Information
Figure 10.64 Mechanism of
HAp deposition on iron and
titanium plates
[321]
.
Dissolution
of iron
Fe + Ca(edta)
2
−
Ca
10
(PO
4
)
6
(OH)
2
Fe(edta)
2
−
, H
2
, OH
−
H
2
PO
−
, OH
−
H
2
edta
2
−
Ca(edta)
2
−
Ca
10
(PO
4
)
6
(OH)
2
Thermal
dissociation
Surface flaw formed by the
dissolution of iron
(a)
H
2
PO
4
, OH
−
H
2
edta
2
−
Ca(edta)
2
−
Ca
10
(PO
4
)
6
(OH)
2
Thermal
dissociation
Surface flaw formed by
polishing
(b)
c
shows SEM photographs of the surfaces of titanium plates
coated with HAp (experimental
Figure 10.66a
conditions 0.05 M Ca(EDTA)
2
2
2
0.05 M
NaH
2
PO
4
solution at 160
C for 2 h) at pH (a) 4, (b) 5, and (c) 6.
Figure 10.67
represents SEMs of the surfaces and cross sections of titanium
plates after the second coating in 0.05 M Ca(EDTA)
2
2
2
0.05 M NaH
2
PO
4
solution
at 160
C for 4 h at pH (a) 6 and (b) 9. The first coating was carried out with a solu-
tion of the same composition at initial pH 5 and 160
C for 2 h
[321]
.
Thick films of HAp are also attempted for the use of gas sensors. There are sev-
eral varieties of HAp-based composites like HAp/bioactive glass composites, HAp/
polymer composites, and HAp/HAp (whiskers). Among the commonly used organ-
ics for HAp/polymer composites are phosphorylated cotton fibers, polymeric sub-
strate, polymethyl methacrylate, and poly [bis (sodium carboxylatophenoxy)
phosphase]
[321]
.
A comprehensive study undertaken at the Tokyo Institute of Technology, Japan,
under the leadership of Prof. M. Yoshimura, has moved HAp whisker-reinforced
HAp (HAw/HA) composites closer to real-world use. Researchers have long eyed
HA implants as replacements for natural bone. The two materials share the same
