Biomedical Engineering Reference
In-Depth Information
to a rather constant value of 70 GPa between 110 and 150 nm from the surface. The lower hardness
value in the fi rst 30 nm of this sample is probably due to surface moisture or oxide. In the oxygen-
implanted sample, the modulus is found to be 150 GPa near the surface and progressively decreases
to 55 GPa between 130 and 160 nm. The hardness is 9 GPa at 20 nm dropping to 3.5 GPa at 160 nm.
It should be noted that these values are higher than that of the control sample of 57 GPa. The results
suggest that the Young's modulus of the nitrogen-implanted sample is 163% or 14% higher than
that of the substrate, whereas the hardness is 144% and 11% higher throughout the measurement.
Hence, the nitrogen-implanted sample is mechanically stronger than the substrate. With regard
to the acetylene-implanted sample, the hardness of the treated layer between 20 and 150 nm is
110% and 11% greater than that of the substrate, whilst the Young's modulus is 92% and 23%
higher throughout the depth of the measurement. In the oxygen-implanted sample, the hardness at
20-70 nm is 100% and 11% higher and the modulus at 0-120 nm is 163% and 5% higher than that of
the untreated substrate. Thus, the mechanical properties of all the treated layers are more superior
to those of the untreated substrate [135,136].
Table 19.3 lists some of the essential readings from our electrochemical tests in lieu of the
more complicated potentiodynamic curves.
E
corr
and
E
b
represent the corrosion and the breakdown
potentials respectively. Higher
E
corr
and
E
b
values represent better corrosion resistance. The
E
corr
and
E
b
values of the control sample are
231 and 272 mV, respectively. The
E
corr
values measured
from the nitrogen-, acetylene-, and oxygen-implanted samples are
-
27 mV, respec-
tively. The
E
b
values of the nitrogen-, acetylene-, and oxygen-implanted samples are 1120, 1170,
and 867 mV, respectively. All the surface-treated samples exhibit higher
E
corr
and
E
b
values than
the untreated sample. These results suggest that the corrosion resistance of the implanted samples
is enhanced.
Table 19.4 displays the amounts of Ni leached from the surface-treated and untreated samples
after the electrochemical tests, as determined by inductively coupled plasma mass spectrometry
-
163,
-
114, a nd
-
TABLE 19.3
Essential Results from the Electrochemical Tests
Sample
Control
N-Treated
C-Treated
O-Treated
-
231
-
163
-
114
-
27
E
corr
(mV)
E
b
(mV)
272
1120
1170
867
Surface area (cm
2
)
0.181
0.181
0.181
0.181
Source
:
Yeung, K.W.K. et al.,
J. Biomed. Mater. Res.
, 75A, 256, 2005. With permission.
TABLE 19.4
Amounts of Ni and Ti Ions Detected in SBF by ICPMS after
Electrochemical Tests
Sample
Ni Content (ppm)
Ti Content (ppm)
Control
30.2324
0.1575
N-treated
0.0117
0.0527
C-treated
0.0082
0.057
O-treated
0.0123
Not detectable
Source
:
Yeung, K.W.K. et al.,
J. Biomed. Mater. Res.
, 75A, 256, 2005. With permission.
