Along with the effect of precursor concentration, the influence of temperature and H2O2content on the morphology, structure and composition of the coating was thoroughly discussed with th
Trang 1Controlling the electrodeposition, morphology and structure of hydroxyapatite coating on 316L stainless steel
Thai Hoanga, Tran Dai Lamb,
⁎⁎
a
Institute for Tropical Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Hanoi, Viet Nam
b
Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Hanoi, Viet Nam
c
School of Chemical Engineering, Hanoi University of Science & Technology, 1 Dai Co Viet Road, Hanoi, Viet Nam
a b s t r a c t
a r t i c l e i n f o
Article history:
Received 18 June 2012
Received in revised form 30 December 2012
Accepted 11 January 2013
Available online 17 January 2013
Keywords:
316L stainless steel
Hydroxyapatite (HAp)
Electrodeposition
Simulated body fluid (SBF)
Electrochemical measurements.
Hydroxyapatite (HAp) coatings were prepared on 316L stainless steel (316LSS) substrates by electrochemical deposition in the solutions containing Ca(NO3)2·4H2O and NH4H2PO4at different electrolyte concentrations Along with the effect of precursor concentration, the influence of temperature and H2O2content on the morphology, structure and composition of the coating was thoroughly discussed with the help of X-ray dif-fraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra The in vitro tests in simulated body fluids (SBF) were carried out and then the morphological and structural changes were estimated by SEM and electrochemical techniques (open circuit potential, polarization curves, Nyquist and Bode spectra measurements) Being simple and cost-effective, this method is advantageous for producing HAp implant materials with good properties/characteristics, aiming towards in vivo biomedical applications
© 2013 Elsevier B.V All rights reserved
1 Introduction
Stainless steel (316LSS) as well as titanium and titanium alloys are
widely used as the most popular load-bearing implants due to their
low cost, high corrosion resistance, excellent biocompatibility and
make them to be the first choices in orthopedic and dental applications
[3,4]
However, these materials expose to an obvious shortage that they
re-searches on coatings on bio-inert metallic prostheses are being
processed, having improved biocompatibility and bioactivity that
have received enormous considerations owing to its chemical,
crystallo-graphically structural and mineralogical compositions close to human
bone and tooth minerals In addition, their strong chemical bonding
makes its metal-implant coating to promote the new bone growth
over-come the disadvantages of metallic materials as well as the HAp coating
shortages such as its brittleness and poor mechanical properties, enable
these materials to succeed in long term load-bearing applications
[12–14] Many methods have been developed to deposit HAp onto
Alter-natively, the electrochemical method has a variety of advantages for homogeneity and availability of HAp deposition on complex shaped
con-trolling the process allows varying the layer thickness on demand This process depends on numerous parameters such as concentration of cal-cium and phosphorus and their ratio in the electrolyte, pH of the solu-tion, ionic strength, processing temperature, and additives The impact
of these parameters on crystallization behavior needs careful investiga-tion in order to find out optimal condiinvestiga-tions for HAp layer deposiinvestiga-tion with desirable properties and thickness
In this study, the influence of key experimental conditions (such
electrodeposition process of the HAp coatings on 316LSS substrates was investigated Then, the morphology, structure and the composi-tion of the coating were thoroughly characterized by X-ray diffrac-tion (XRD), Scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectra To give an insight view of control-ling this electrodeposition process, the in vitro tests in simulated body fluids (SBF) were carried out The morphological and structural changes of the coating were monitored and correlated with SEM,
⁎ Corresponding author Tel.: +84 4 37564333x1095; fax: +84 437564696.
⁎⁎ Corresponding author Tel.: +84 4 37564129; fax: +84 438360705.
E-mail addresses:dmthanh@itt.vast.vn (D.T.M Thanh), lamtd@ims.vast.ac.vn
(T.D Lam).
0928-4931/$ – see front matter © 2013 Elsevier B.V All rights reserved.
http://dx.doi.org/10.1016/j.msec.2013.01.018
Materials Science and Engineering C
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / m s e c
Trang 2open circuit potential, polarization and impedance (Nyquist and
Bode plots) measurements
2 Materials and methods
2.1 Materials
Commercial 316LSS sheets (100×10×2 mm, composed of carbon
0.03%, manganese 2%, silicon 0.75%, chromium 17.98%, nickel 9.34%,
molybdenum 2.15%, phosphorus 0.045%, sulfur 0.03%, nitrogen 0.1%
and iron 67.575% (%wt)) were used as substrates (working electrodes)
for electrodeposition Substrate surfaces were polished with SiC emery
papers (sandy ranging from P320 to P1200 grit), followed by ultrasonic
rinsing in distilled water and acetone for several times Epoxy resin was
used to cover the substrate surface and leave a precise exposed area of
2.2 Deposition procedure
All chemicals were purchased from Merck with an analytical reagent
grade and used without any further purification A series of electrolytes
constant at ca 1.67, equal to that in the stoichiometric composition of
calomel (SCE), respectively
The electrodeposition was carried out on an AUTOLAB with scanning
26.667 min (5 cycles) The reaction temperature was kept by a
thermo-stat (model NNT-2400, Eyel) A linear polarization method with
poten-tial ranging from equilibrium potenpoten-tial to −2.5 V/SCE was used to
determine the reduction potential of reactions occurring on the 316LSS
electrode Thickness of the HAp coatings could be approximately
esti-mated from the mass difference before and after the deposition
(according to the following equations: d=m/V; V=S×h; where d is
V is the HAp volume; S is the working area; and h is the thickness of the
film)
2.3 Morphological characterizations of the coatings
The phase purity and crystallinity of the HAp coating on the 316LSS
were analyzed by X-ray diffraction (Siemens D5000 Diffractometer,
CuKα radiation (λ=1.54056 Å)), step angle of 0.030°, scanning rate
size along c-direction of HAp coatings was calculated from (002)
L002¼ Kλ
where λ is the wavelength of the X-ray radiation (CuKα), θ (rad) is the
diffraction angle, and K is the Scherrer's constant, related to the
at half-maximum FWHM (rad) of the peak along (002) direction
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
β2obs−β2inst q
ð2Þ
the instrumental profile width, respectively
Another important parameter, extracted from XRD analysis is the
HAp coatings can also be estimated from the (002) reflection according
βm: ffiffiffiffiffiffi
Xc
3
p
The microstructure was characterized by FE-SEM combined with EDX (S4800 of Hitachi, Japan) Fourier transform infrared (FTIR) spectra were recorded with a Nicolet 6700 spectrometer,
temperature
2.4 Preparation of simulated body fluid (SBF) and vitro test
In order to evaluate in vitro bioactivity of HAp/316LSS, simulated body fluid (SBF) soaking was used SBF was prepared according to
samples were immersed singly into SBF for in vitro test (37±1 °C in water bath for 0, 1, 3, 5, 8, 10, 14 and 17 days)
The open circuit potential (OCP), electrochemical impedance spectra (EIS Nyquist and Bode plots) and Tafel curves were measured
vs immersion time EIS studies were carried out at OCP in the
the samples were rinsed with absolute alcohol and distilled water, then incubated at 80 °C for 24 h for further analyses
Table 1
The composition of electrolytes (used in HAp electrodeposition) and HAp mass
variation.
Electrolytes Ca(NO 3 ) 2 ·4H 2 O
(M)
NH 4 H 2 PO 4
(M)
NaNO 3
(M)
H 2 O 2 (mass fraction)
HAp mass (mg) S1 1.68×10 −2 1.0×10 −2 0.15 6 2.7
S2 2.5×10 −2 1.5×10 −2 0.15 6 8.5
S3 3.0×10 −2 1.8×10 −2 0.15 6 13.6
S4 4.2×10 −2 2.5×10 −2 0.15 6 7.0
-60 -50 -40 -30 -20 -10 0
-0.5 -0.6 -0.7 -0.8 -0.9 -1.0 -1.1 -1.2 -1.5
-1.0 -0.5 0.0
S4
S3 S2 S1
S4
S3
S2 S1
2 )
E (V/SCE)
Fig 1 Cathodic polarization curves of HAp/316LSS formation in different electrolyte concentrations (S1, S2, S3 and S4) The inset shows a zoomed-in view of the potential ranging from −0.5 to −1.2 V.
Trang 33 Results and discussion
3.1 Effect of precursor concentrations
In this section, the variation of electrolyte concentration is discussed
Obviously, electrolyte composition and its concentration significantly
affect the deposition kinetics as well as the HAP coating thickness
The cathodic polarization curves of 316LSS electrode in a series of
electrolyte solutions (S1 to S4) were recorded with predetermined
potential scanning from the equilibrium potential to −2.5 V/SCE
The obtained plots indicate that as the applied potential becomes
more negative than −0.5 V/SCE, the cathodic current could be
observed, corresponding to different reactions occurred on the
than −0.7 V, the current was mainly contributed by the reduction of
More negative potentials induce other species being reduced The following reactions can be proposed:
H2PO−
4 þ e−→HPO2−4 þ1
The water reduction occurs when the voltage is more negative than −1.5 V/SCE, resulting in the rapid change of cathodic current:
ions to form HAp coating on the cathode substrate Based on the anal-ysis of the cathodic polarization curves, we performed HAp deposi-tion on 316LSS electrodes in different electrolyte soludeposi-tions with potential scanning from 0 to −1.6 V, in 26.667 min (5 cycles), then estimated the HAp film thickness by determining their mass The variation of HAp deposition mass with respect to precursor
concentration (from S1 to S4), the HAp film weight first increases from 2.7 mg to 13.6 mg (from S1 to S3, respectively), and then de-creases to 7.0 mg (S4) This result is well consistent with the above polarization curves From the reaction equilibrium point of view this weight variation might be explained as follows Increasing reactant
ions on the electrode surface, leading to the increase of the current
-15
-10
-5
0
5
10
15
8% H 2 O 2 6% H 2 O 2 4% H 2 O 2
2% H 2 O 2
0% H 2 O 2
2 )
E (V/SCE)
-0.5 -0.6 -0.7 -0.8 -0.9 -1.0 -1.1 -1.2 -1.3 -3.5
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
8% H2O2
6% H 2 O 2
4% H 2 O 2 2% H 2 O 2
0% H2O2
Fig 2 Cathodic polarization curves of HAp/316LSS formation in S3 electrolyte, H 2 O 2
concentration is varied from 0 to 8% (mass fraction) The inset shows a zoomed-in
view of the potential ranging from −0.5 to −1.2 V.
O concentration was 0% (A), 2% (B), 4% (C), and 6% (D).
Trang 4form HAp on the electrode surface will be more favorable At a certain
point, when the concentrations continue increasing (S4) the diffusion
of those ions from the electrode surface into solution will be
predom-inant, resulting in HAp solubility and its observed weight loss on the
electrode surface
For the above reasons, S3 solution was treated as the optimal one
and was chosen in further investigations
3.2 Effect of H 2 O 2
at the 316LSS surface generate hydrogen gaseous bubbles, which, in
their turn may attack the surface sites afterwards, preventing HAp
de-position and/or reducing adhesion of HAp coatings to the substrate
[30]:
mecha-nism of the deposition process because it provides an alternative
expected to be minimized, and the adhesion of HAp deposition will
cathodic polarization curves were recorded under the following
experimental conditions: S3 electrolyte solution, the temperature of
morphological changes were then studied by FE-SEM images, presented
inFig 3 It was found that the presence of H2O2could induce more
0% to 6%, it can be observed that HAp morphological changes from rod
3.3 Effect of deposition temperature
The influence of temperature on the mass of HAp deposition formed on the electrode surface (in electrolyte S3) was studied in
with increasing temperature and reaches a maximum at 70 °C At this temperature, the HAp coating becomes more porous (image
is not shown) Deposition temperature can affect HAp coatings in several ways First, it may change the reaction rate as well as the diffusion rate of ions High temperature can either promote the for-mation of HAp films on the surface or the bulk precipitation due to high diffusion rate Second, the decrease of HAp solubility with
and thus favor film deposition on the substrate Finally, the rise of temperature can lower hydrogen bubble attachment on the sub-strate surface, making the growing HAp films and the coatings less damaged and more adherent, accordingly In summary, by adjusting the temperature, whole deposition process, the mass and thickness of HAp can be rigorously controlled It should be em-phasized that beyond a certain value of temperature (70 °C in our case), the mass of HAp films on the electrode surface could be re-duced, being solubilized (effectively, increasing temperature leads
to a simultaneous increase in the concentration of phosphate and hydroxide ions that diffuse from the surface of the electrode into the solution to form HAp there)
4
6
8
10
12
14
Temperature ( o C)
Fig 4 The variation of the HAp mass vs electrodeposition temperature (HAp coatings
were deposited from S3 electrolyte).
Table 2 The assignments of IR spectra of the HAp coatings.
Peak position (cm −1 )
Assignments Peak position
(cm −1 )
Assignments
3425 O\H stretching
(OH − , H 2 O)
964 P\O symmetric
stretching mode ν 1
2360 CO 2 in air 863 B-type CO 3 2− vibration
mode ν 2 /HPO 4 2−
1635 H\O\H bending mode 602 O\P\O asymmetric
bending ν 4a
1390 B-type CO 3 2− vibration
mode ν 3
563 O\P\O asymmetric
bending ν 4b,ac
1099 P\O asymmetric
stretching mode ν 3a
471 O\P\O doublet
bending ν 2
1034 P\O asymmetric
stretching mode ν 3b, 3c
Trang 5The effect of temperature on deposited HAp coatings is also
consid-ered in terms of FTIR and XRD results in the following sections
3.4 IR analysis
Fig 5presents FTIR results of the HAp coatings deposited at
dif-ferent temperatures (60, 70, 75, 80 and 85 °C) The peak positions
The modification of phosphate ion configuration in HAp structure
band is also at the position of the stretching mode of adsorbed water,
[30,38]
It also appears that carbonate ions could exist in HAp films, taking
could be attributed to a degenerate asymmetric stretching mode of
C\O group whereas the latter could be assigned to the out-of-plane
Briefly, all data confirm that HAp films were successfully deposited
onto 316LSS substrate within the considered temperature range
HAp samples prepared at different temperatures do not show signifi-cant discrepancies in FTIR spectra, except for a minor difference in peak
Namely, at 60 °C, such ratio is about 2.4 whereas these values in the other samples (70, 75, 80 and 85 °C) vary from 0.2 to 0.4 Thus, for pro-ducing HAp coating with low level carbonate, a temperature higher than 60 °C is strongly required
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
001
0
400
800
1200
1600
2000
2400
2800
3200
3600
4000
SiKa SiKsum
ClLl ClKesc
CrKa CrKb
FeKesc FeKa FeKb
Fig 7 EDX spectra of HAp/316LSS coatings.
Table 3
EDX results of HAp/316LSS.
% w/w 4 46.11 0.73 17.20 0.69 31.27
% atom 7.24 62.63 0.69 12.07 0.42 16.96
-300 -250 -200 -150
Time (days)
E o
Fig 8 The variation of OCP vs different immersion times in SBF solution.
1E-9 1E-8 1E-7 1E-6 1E-5
E(V/SCE)
17days
8 days
5 days
3 days
5 10 15
i corr
2 )
R p
Time (days)
R p
2 )
0.05 0.10 0.15 0.20 0.25 0.30 0.35
0.40
i corr
A
B
Fig 9 A Tafel polarization curves vs different immersion times in SBF solution B The
variation of corrosion current density (I ) and polarization resistance (R).
Trang 65
days
8
days
14
days
17
days
Fig 10 FE-SEM images of HAp/316LSS coatings vs different immersion times in SBF solution.
Trang 73.5 XRD and EDX analyses
XRD analyses also demonstrate a weak effect of temperature (in
the above mentioned temperature range) on diffraction patterns of
sub-strate peaks in XRD pattern implies that the coatings are quite
po-rous All recorded peaks can be ascribed to single hydroxyapatite
phase Except for the peaks of Fe and CrO from SS L316 itself, no
other phases were detected, confirming that pure apatite phase
was achieved Namely, characteristic peaks at 2θ ≈26° and 2θ ≈32°
It is well stated that in electrochemical deposition, the growth of
HAp crystals commonly occurs in the direction perpendicular to
the electrode surface (c-direction) Therefore, the peak at 2θ ~ 26°
corresponding to the (002) plane is stronger than other peaks in
along c-direction of the HAp deposition were in range of 20–35 nm
(obtained from Scherrer's equation, using 2θ at (002) diffraction peak) (see the experimental part) These values are similar to those
the presence of 3 main elements Ca, P and O in HAp composition, cor-responding to 31.27%, 17.20% and 46.11% (w/w) respectively As mentioned above, the peak of carbon can be explained as follows:
0
2
4
6
8
10
10 mHz
1 Hz
0 day
0.0 0.2 0.4 0.6 0.8 1.0
0 5 10 15 20 25
1 Hz
0.0 0.2 0.4 0.6 0.8 1.0
0
5
10
15
20
1 Hz
0.0 0.2 0.4 0.6 0.8
'' (kΩ
2 )
0 1 2 3 4 5
10 mHz
1 Hz
5 days
0.0 0.1 0.2 0.3
Z ' (kΩ.cm 2 )
0
10
20
30
1 Hz
10 mHz
8 days
0.0 0.4 0.8 1.2 1.6 2.0 2.4 0.0
0.2 0.4 0.6 0.8 1.0 1.2
0 5 10 15 20
1 Hz
10 mHz
10 days
0.0 0.2 0.4 0.6 0.8 1.0
0
5
10
15
20
1 Hz
10 mHz
14 days
0.0 0.2 0.4 0.6 0.8 1.0
Z ' (kΩ.cm 2 )
0 2 4 6 8 10
1 Hz
10 mHz
'' (kΩ
2 )
17 days
0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0
0.2 0.4 0.6
A
Trang 8[24] This phenomenon certainly lowers the obtained Ca/P ratio from
stoichiometric 1.67 to 1.4 The presence of Na and Cl in HAp coatings
and KCl diffusion from Calomel reference electrode
3.6 In vitro tests
When metal and alloy materials are used as implants in the body,
they can be corroded This can result in the weakness of the implants
and/or release undesired and harmful corrosion products to the
sur-rounding tissue In order to investigate the behavior of HAp/316LSS
coatings in corrosion media, corrosion tests were carried out The
strong fluctuation of open circuit potential (OCP) vs immersion
time in SBF solution (for HAp/ 316LSS, deposited from S3 electrolyte,
phe-nomenon, the discussion about the occurrence of two major
process-es (HAp dissolution and HAp precipitation) during the immersion
period is necessary In the first 5 days, the dominant process is
dislution and/or detachment of few parts of HAp specimen into SBF
cav-ities makes local concentration of such ions relatively high Very
few crystal nuclei are formed because of low supersaturation
How-ever, for a longer immersion period, when crystal nuclei are formed
Such an observation is confirmed by the polarization tests of HAp/ 316LSS in SBF solution and SEM image of the sample immersed in
17 day-period The polarization potential in the range ±10 mV around the OCP was recorded against immersion times with potential scan rate
func-tion of immersion time were also observed, that is completely consis-tent with the variation in OCP, at the same time interval These data indicate that the HAp coating was not in stationary condition within the above mentioned time period
SEM images of leaf-like HAp coating after 5, 8 14 and 17
formation in SBF, associated with the preferential orientation of crystal growth, occurs only in the initial stage of immersion (4–7 days), when
Ca and P ion concentrations (dissolved from biocomposite surfaces into SBF) are still low (slow nucleation) But as the immersion time prolongs (beyond 7 days), due to increasing concentrations of Ca and P ions (rapid nucleation) as well as energy minimization principle, this prefer-ential orientation disappears, leaf-like crystals cannot be observed in the late stage of immersion Theoretically, the spherical apatite formed particles should have been obtained However, in our case, the prefer-ential orientation, leading to leaf-like HAp formation is still clearly ob-served after 17 days of SBF This interesting feature, stemming from dissolution to reprecipitation mechanism, can be related to the differ-ence in pristine crystal morphology and compactness of our HAp
noted that the above feature could be also used advantageously for pro-ducing HAp coating on predetermined and complex geometries
To confirm the results, obtained from polarization tests,
shows EIS spectra of HAp/316LSS vs different immersion time of HAp/316LSS in SBF solution It is clearly seen from Nyquist plots (Fig 11A) that only intermediate frequency (103to 10 Hz) and low frequency regions (f b10Hz), corresponding to capacitive behavior
of the HAp films and mass transfer process (diffusion or migration) were observed Next, the obtained impedance data are in good agreement with OCP and polarization results and further demon-strate the formation of dynamic but well resisted HAp layer on the 316LSS surface Effectively, after 3 day-immersion, imaginary Z″
5 day- and 8 day-periods respectively The same “up and down” fluctuation was recorded for the remaining periods (10, 14 and
that instead of a typical two-component shape for 316LSS (figure not shown), only one-component plot was observed and character-ized for HAP layer at the low frequency domain This degeneration confirms the successful formation of HAp on entire electrode surface
fluctu-ation tendency as the Nyquist and polarizfluctu-ation plots previously do
4 Conclusion HAp coatings have been successfully electrodeposited on 316LSS sur-face via a simple technique The characteristics of the HAp/316LSS films can be easily adjusted by optimizing some controlling factors The opti-mal conditions were determined as follows: potential range from 0 to
−1.6 V/SCE, temperature of 70 °C, with the electrolyte composition of
coatings, when intervening the reaction mechanism The in vitro tests
in SBF were carried out and then the morphological and structural changes were estimated by SEM, OCP, polarization curves, and Nyquist and Bode measurements It was also found that the occurrence of two
1
2
3
4
5
0 day
1 day
3 days
5 days
8 days
10 days
14 days
17 days
log (f,Hz)
-10
0
10
20
30
40
50
60
70
log (f,Hz)
B
C
Fig 11 (continued).
Trang 9processes (dissolution and formation of HAp on the surface) should be
taken seriously into account in order to produce good implant materials
with the desired properties and characteristics
Acknowledgments
This work was supported by the National Foundation for Science and
Technology Development of Vietnam (under grant no 104.03-2010.11,
NAFOSTED)
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