Synthesis and characterization of nanoporous Pt–Ni alloys

Synthesis and characterization of nanoporous sodium-substitutedhydrophilic titania ceramics coated on 316L SS for biomedicalapplications

K. Bavya Devi, Kulwant Singh, N. Rajendran

� ACA and OCCA 2011

Abstract Bioactive sodium-substituted titania coatingon 316L SS substrate was prepared. XRD patternsexhibited the formation of a mixture of two phases(Na2Ti3O7, Na2Ti6O13) with monoclinic structure.FTIR spectra showed that the set of overlapping peaksin the range of 800–400 cm�1 are related to Ti–O andTi–O–Ti groups. SEM-EDAX, AFM, and TEMshowed the surface morphology of the coated surfaceto be nanoporous and uniform. The influence of thebioactivity of the coating in a simulated body fluid(SBF) medium was examined. Excellent adhesion ofthe ceramic composites to the substrate was achieved.The hydrophilic nature of the sodium titanate coatinginduced the formation of hydroxyapatite layer on themetal surface. The corrosion protection performanceof the coatings has been evaluated using potentiody-namic polarization and electrochemical impedancespectroscopy measurements, which proved increasedcorrosion resistance of nanosodium titanate-coated316L SS. These results imply that the sodium tita-nate-coated 316L SS acts as a barrier layer to themetallic substrate.

Keywords Adhesion, Bioactivity, Contact angle,Stainless steel, Hydroxyapatite

Introduction

An essential condition for an artificial material to bondto living bone is the formation of bonelike apatite on

its surface in the living body.1,2 The bonelike apatitecan be reproduced on the bone-bonding material evenin an acellular simulated body fluid (SBF)3 with ionconcentration almost equal to that of human bloodplasma.4 Artificial materials implanted into bonedefects are generally encapsulated by a fibrous tissueso that they are isolated from the surrounding bone.Bioactive ceramics such as bioglass,5 sintered hydroxy-apatite,6 and glass–ceramic A-W,7 spontaneously bondto living bone without forming a surrounding fibroustissue. However, due to their poor mechanical proper-ties, these materials cannot be used in load-bearingapplications, such as those encountered in femoral andtibial bones. Urgent requirements have exerted strongpressure on bioengineers to formulate adequate solu-tions. In this connection, sol–gel thin film processingrepresents one such alternative to obtain the desiredcoatings, offering a number of advantages, such asprecise microstructural and chemical control, ease offabrication and low-temperature processing.8 Amongthe metallic materials which are used for orthopedicdevices, 316L SS is one of the most commonlyused,9 due to its relatively low cost and acceptablebiocompatibility.10

In this present investigation we report the synthesisof sol–gel derived sodium-substituted titanate films on316L SS with the main objective to reduce thecorrosion of the substrate in the body, allowing thegrowth of hydroxyapatite on the coated surface.

Experimental procedure

Substrate pretreatments

Commercially available AISI stainless steel (316L SS)specimens (composition given in Table 1) of size5 9 3 9 0.2 cm were used as the substrate in thepresent study. The specimens were mechanically

K. B. Devi, N. Rajendran (&)Department of Chemistry, Anna University,Chennai 600 025, Indiae-mail: [email protected]

K. SinghFRMS, MG, BARC Trombay, Mumbai 400 085, India

J. Coat. Technol. Res.

DOI 10.1007/s11998-011-9344-z

abraded using 400 grit silicon carbide paper, degreasedusing 5% NaOH solution at 50 ± 1�C and then etchedin a mixed acid solution of HNO3 (150 g/L) and HF(50 g/L) for 5 min, at a temperature of 28 ± 1�C toensure that the surface was free from oxides, impuri-ties, etc. The substrate was then dipped in 30% NH4Clsolution for 30 min at 50 ± 1�C to avoid further

surface oxidation and to enhance adhesion of themolten metal onto the substrate during the dippingprocess.

Synthesis of the coatings

The hydrophilic nanoporous sodium titanate wasprepared by the sol–gel method. The starting com-pounds were titanium (IV) n-butoxide (99.9% AlfaAesar), sodium hydroxide (99% Merck), ethanol(Fisher Scientific), and double distilled water. Thealkoxides were mixed in an ethanol medium (1:2 ratio)and the sodium hydroxide was dissolved in doubledistilled water (1:20 ratio). The aqueous sodiumhydroxide was added simultaneously with the alkoxidesolution in order to obtain a fast hydrolysis-condensation

Table 1: Chemical composition of 316L stainless steel(wt%)

Alloy Main alloying elements (wt%)

Cr Ni Mo N C Mn Fe

316L SS 17.20 12.60 2.40 0.02 0.03 1.95 Balance

0 200 400 600 800 1000

30

110

90

70

50

Wt

%

Temperature (°C)

10

Fig. 1: TGA curves of sol–gel sodium titanate-coated316L SS

Channel: Lock-in amplitude; traceFilename: Bavya-S-Nati-2-2010.90.13-16.39.26.jpk

0

0 2 4

0 mV

198.8 mV42S

low

(μm

)

Fast (μm)

Fig. 2: AFM image of sodium titanate-coated 316L SS

10 20 30 40 50

2θ (°)

Inte

nsi

ty (

arb

. un

its)

(101

)

(201

)

(210

)(3

02) (1

03)

(313

) (313

)

(200

)

(111

) 316L SS

Na2Ti3O7

Na2Ti6O13

(220

)

(402

)

(205

)

60 70 80

Fig. 3: X-ray diffraction pattern of sodium titanate-coated316L SS

Fig. 4: Transmission electron microscopy of sodiumtitanate-coated 316L SS


reaction. The prepared suspensions were stirred vigor-ously at 80�C until a gelatinous solution was obtained.The prepared solution was kept in the dark for thenucleation process for 48 h. Then the 316L SS sub-strates were immersed in the sol solution and with-drawn at a speed of 5 cm/min at room temperature toensure the elimination of organic residues, as well as todevelop a thin film. The sol–gel sodium titanate thusobtained on the 316L SS substrate was later dried in anoven at 70�C for a period of 10 h for the gelationprocess. The samples were sintered with a heating rateof 700�C for 1 h according to thermal analysis.

Characterization techniques

Surface characterization

Thermogravimetric analysis was carried out in a nitro-gen atmosphere, using a Netzsch STA 409 instrumenton green powders. The heating rate was fixed at 10�C/min. The contact angle subtended by SBF was mea-sured using an FTA 200 contact angle goniometer.X-ray diffraction patterns were recorded with a Pan-analytical X-pert Pro diffractometer using Cu Ka

radiation, with 40 kV and 30 mA, at a scan rate of

Fig. 5: Optical micrograph of sodium titanate-coated 316L SS (a) without any load, (b) 1, (c) 5, (d) 14.5, (e) 17, (f) 22, (g) 27,and (h) 30 N


Normal load and friction

Acoustic emission

Penetration depth

Penetration depth

Acoustic emission

30.0

27.0

24.0

21.0

18.0

15.0

12.0

9.0

6.0

3.0

0.0 N

30.0

27.0

24.0

21.0

18.0

15.0

12.0

9.0

6.0

3.0

0.0 N

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

0.000.90 N

0.00 mm

Friction Coefficient Friction Force Normal Force

0.30 0.60 0.90 1.20 1.50 1.80 2.10 2.40 2.70 3.00

3.81 6.72 9.63 12.54 15.45 18.36 21.27 24.18 27.09 30.00

0.90 N

0.00 mm 0.30 0.60 0.90 1.20 1.50 1.80 2.10 2.40 2.70 3.00

3.81 6.72 9.63 12.54 15.45 18.36 21.27 24.18 27.09 30.000%

10

20

30

40

50

60

70

80

90

100

0.90 N

0.00 mm 0.30 0.60 0.90 1.20 1.50 1.80 2.10 2.40 2.70 3.00

3.81 6.72 9.63 12.54 15.45 18.36 21.27 24.18 27.09 30.0030.0 μm

26.9

23.8

20.7

17.6

14.5

11.4

8.3

5.2

2.1

–1.0

Fig. 6: Scratch test results (a) normal load and friction, (b) acoustic emission, and (c) penetration depth


(2h) 0.02�. FTIR spectra were recorded in the 400–4000 cm�1 range on an FTIR (Thermo ElectronCorporation, USA). The surface morphology of porousnanosodium titanate film was recorded using transmis-sion electron microscopy (TE, JEOL 2000FX), scan-ning electron microscopy on a Hitachi Model-S 3400.The Nanosurf easyScan 2 (Nanosurf AG, Grammest-rasse 14, CH-4410 Liestal, Switzerland) instrument wasused to record AFM. The images were recorded underair atmosphere at room temperature. Adhesion per-formance was done by a scratch adhesion testersupplied by CSM Instruments with a Rockwell-typediamond indenter having a 200 lm tip radius. Thescratch length was 3 mm and the load was varied from1 to 30 N. The thickness of the coating was measuredusing an Elcometer instrument.

Bioelectrochemical measurement

A conventional three-electrode cell was used for all theelectrochemical measurements. A saturated calomelelectrode (SCE) was used as a reference electrode,platinum foil as a counter electrode and the testmaterial as the working electrode. The preparation ofSBF, the procedure for the electrochemical experimentand the in vitro studies were carried out according toan earlier report.11 Potentiodynamic polarization stud-ies were carried out for the test specimens in SBFsolution. The potentiostat (model PGSTAT 12,AUTOLAB, The Netherlands B.V.) controlled witha personal computer was used for conducting theexperiments. In order to test the reproducibility of theresults, the experiments were performed in triplicate.

Results and discussion

Surface characterizations

The thickness of the coating was porous, registering aregular thickness of 1 lm depending upon the numberof applied layers.12 The TGA analysis (Fig. 1) showstwo peaks (about 37.33%) with the first one around116.35�C. This was taken to be the result of evapora-tion of debonding of bonded water and its diffusionreaction from the gel surfaces. The second peak at704.15�C (about 4.2%) corresponded to the desorptionof the deposited organic residues and the formation ofthe sodium titanate phase observed by XRD analysis.13

Figure 2 shows the AFM images of the sodiumtitanate-coated 316L SS. The surface of the coatingappears to be made up of well-packed agglomerates.The topography of the image revealed that the coatingswere uniform and porous in nature. The TF-XRD ofsodium titanate-coated 316L SS (Fig. 3) substrate leadsto the formation of a mixture of two phases in eachsubstrate as Na2Ti3O7 (JCPDS No. 31-1329) andNa2Ti3O13 (JCPDS No. 73-1398). It can be seen that

the peaks at 2h values of 14.18, 24.17, 33.15, 35.55, and49.31 are due to the formation of Na2Ti3O7 (JCPDSNo. 31-1329). In addition, the other phases of sodiumtitanate Na2Ti3O13 (JCPDS No. 73-1398) are alsoseen.14 The average grain size of the sodium titanatewas calculated using Scherrer’s equation dhkl = kk/(Bcos (2h).15 The calculated crystallite size of the twophases of sodium titanates, namely, (Na2Ti3O7) and(Na2Ti6O13), are in the range of 48 and 38 nm,respectively. Because of the porous nature of thecoatings, the X-ray diffraction pattern was also dom-inated by the peaks originating from the 316L SSsubstrate. The strong signal observed at 2h values of74.56, 50.78, and 43.60 corresponds to the planes (220),(200), and (111) of cubic centric Cr0.19 Fe0.7 Ni0.11,respectively.16 Figure 4 shows the HR-TEM image ofcoated nanosodium titanate. The nanoparticles arecomposed of aggregates of discrete particles with anaverage particle size of 30 nm, and are highly porous innature.17

Mechanical properties

In order to evaluate the adhesion and cohesionstrengths, different loads were applied on the coatedspecimen. As a result, two critical loads for failure werenoticed from the optical image, and the results areshown in Fig. 5. It is observed that the first crack andchipping appear at load 5 and 14.5 N, respectively,because of the cohesive and adhesion strength of thecoating. However, on increasing the load, the coatingfailed partially. The failure of the coating was accom-panied by an increase in the friction coefficient and inthe acoustic emission background. The online mea-surements of friction force, acoustic emission, andpenetration depth are shown in Fig. 6. The friction wasfound to increase linearly from 0.05 to 0.34 with theincrease in applied load from 1 to 30 N. The depth ofpenetration was found to be 27 lm. Thus, sodiumtitanate coatings on 316L SS possess good adherencewith less peel off tendency.18

In vitro characterizations

In contact angle processes, higher hydrophilicity isusually favorable in order to achieve high surface

Fig. 7: The contact angle measurements for sodiumtitanate-coated 316L SS in the presence of SBF drops


coverage. The typical shape of an SBF droplet onsodium titanate-coated 316L SS is shown in Fig. 7. TheSBF droplet on uncoated 316L SS was hydrophobicwith contact angle value of 83.2�19; and on the sodiumtitanate-coated 316L SS was hydrophilic with the valueof 15�.20 The SBF solution spreads evenly over thecoated surface, making it hydrophilic. The hydrophilicnature of the nanosized coating facilitates the ionexchange behavior from the SBF solution, which favorseffective apatite growth. The Ti–OH groups on thesurface enhance the hydrophilic property of the coat-ing, which is suitable for orthopedic implants.21

The HRSEM–EDAX analyses of uncoated, sodiumtitanate-coated samples are shown in Figs. 8a–8d. The

uncoated specimen shows the presence of a smoothuniform surface. However, sodium titanate-coated316L SS substrate revealed distinctive agglomeratedmorphology. The sodium titanate-coated 316L SSsubstrate was immersed in SBF for 7 days, andwhite precipitates were observed all over the surface(Figs. 8e–8f), which revealed the presence of apatite.The EDAX pattern shows the appreciable decrease insodium intensity after immersion in the SBF. Thisimplies that the sodium containing titania gels releasessodium into the SBF during the immersion. As a result,the pH of the solution and thus the degree of the super-saturation with result to apatite increases. The higherthe sodium content in the sample, the more sodium

3000

Fe

Fe

Fe

Mn

Mn

Cr

Cr

Cr

Cr

Cr

ONa

Na

Ti

Cr

CrCr

O

TiTi

TiNi

TiFe

Fe

Fe

Fe

FeFeP

P

MgCl Ca

Ca

K

Al

Si

Si

Ni

Ni

Ti

Cr

Mo

NiNi

Ni

SSi

Cr

2500

2000

1500

1000

500

00 1 2 3 4 5 6 7 8 9 10

keV

2000

1500

1000

500

00 1 2 3 4 5 6 7 8 9 10

keV

2000

1500

1000

500

00 1 2 3 4 5 6 7 8 9 10

keV

(a) (b)

(d)

(f)

(c)

(e)

Fig. 8: SEM/EDAX micrographs of uncoated 316L SS (a, b), sodium titanate-coated 316L SS (c, d), sodium titanate coatingimmersed in SBF for 7 days (e, f)


ions can be exchanged by H3O+ ions in the solution,and the more Ti–OH groups can be formed which reactwith Ca2+ ions from SBF to form calcium titanate, anintermediate for apatite.22 The FTIR spectrum ofsodium titanate-coated 316L SS before and afterimmersion in SBF solution for 7 days is shown inFig. 9. Before immersion, a broad band between 3300and 3500 cm�1 was assigned to fundamental stretchingvibration of O–H hydroxyl groups. Another peakrelated to O–H hydroxyl group was found at1650 cm�1. Another peak at 1455 and 1410 cm�1

related to C–H deformations. The set of overlappingpeaks in the range of 900–400 cm�1 is related to Ti–Oand Ti–O–Ti groups.23 These results indicate theformation of a sodium titanate coating on the 316LSS substrate. However, after immersion in SBF, thepeak at 3500 cm�1 clearly indicates the presence of theO–H group of hydroxyapatite. The band with a smallshoulder over the region 1600 cm�1 together with theabsorption band at 1359 cm�1 is related to the CO3

2�

group from the carbonate apatite. The peak at1050 cm�1 corresponds to the stretching of the P=Obond on the hydroxyapatite.23 The peaks between 500and 710 cm�1 are related to Ti–O and Ti–O–Tivibrations which might overlay the bands of CO3

2�

or P–O and O–P–O vibrations.

Bioelectrochemical corrosion studies

The sodium titanate coatings on 316L SS haveprofound effects on the electrochemical behavior. Inorder to understand the electrochemical changes, thespecimens were subjected to potentiodynamic cyclicpolarization and electrochemical impedance spectro-scopic (EIS) studies.

The potentiodynamic cyclic polarization curves ofuncoated and sodium titanate-coated 316L SS sub-strate are shown in Fig. 10. The sodium titanate-coated316L SS substrate shows a shift in the cathodic currentdensities toward much lower values. The corrosionparameters obtained from the electrochemical mea-surements are given in Table 2. The coated substrateshowed a lower current density, which reveals arelatively high corrosion resistance of the coatingcompared to that of the uncoated substrate. Thisshows that there was no detachment or decohesion ofthe coatings from the substrate. For instance, thecorrosion rate of the uncoated substrate was around3.75 9 10�2 mmpy, whereas the corrosion rate ofsodium titanate coatings was only 0.87 9 10�2 mmpy.This behavior is due to the high stability of thecoatings.24

The electrochemical impedance spectra of uncoatedand sodium titanate-coated 316L SS substrates duringimmediate immersion in SBF solution are shown inFig. 11a. The Bode phase angle shows a considerableshift when compared to that of the uncoated substrate.The presence of two time constants confirms thesodium titanate coatings on the 316L SS substrate.The uncoated and sodium titanate-coated 316L SSsubstrates immersed in SBF solution for 7 days areshown in Fig. 11b. The sodium titanate-coated 316L SSsubstrate shows an additional time constant withdistinct phase angle behavior, which confirms theformation of a new layer over the porous surface; thiscan be attributed to a growth of apatite as inferredfrom the SEM analysis.25 The Bode resistance plot ofsodium titanate-coated 316L SS substrate immersed inSBF for 7 days shows the higher resistance behaviorcompared to uncoated substrate. The coated substrateindicates that the barrier effect on the film remainsunaltered, which shows the ingress of anions in theelectrolyte from attacking the metal surface.26 The EISspectra were analyzed with an equivalent circuit andthe curve fitting was performed for all the substrates,

4000 3500 3000 2500 2000 1500 1000 500

% T

ran

smit

tan

ce

Wavenumbers (cm–1)

(a)

(b)

Fig. 9: FTIR spectra of sodium titanate-coated 316L SS(a) before immersion (b) after immersion in SBF solution for7 days

0

1500

1000

500

Uncoated 316L SS Sodium titanate

Coated 316L SS

10–8 10–410–5

10–610–710–9

Current density (i/A cm–2)

Pot

entia

l (m

V/S

CE

)

–500

Fig. 10: Potentiodynamic polarization curves for uncoatedand sodium titanate-coated 316L SS in SBF solution


which shows an excellent agreement between theexperiments and the fitting. The fitted values are givenin Table 3. They show that the sodium titanate-coated316L SS substrate exhibited the higher charge transferresistance compared to uncoated substrate; this revealsthat the sodium titanate coating acts as a barrier layerto the metallic substrate. The spectra of uncoated andsodium titanate-coated 316L SS substrates immersed inSBF solution for 7 days fit the equivalent circuit modelshown in Figs. 12a and 12b, and the correspondingvalues are given in Table 4. The equivalent circuitobtained for uncoated 316L SS is Rs (RbQb), where Rs,Rb, and Qb represent the solution resistance, chargetransfer resistance, and double layer capacitance of thebarrier layer of titanium. The equivalent circuitobtained for sodium titanate coated 316L SS substrate

is Rs (RcQc) (RbQb). However, the circuit for thesodium titanate coated 316L SS substrate immersed inSBF is Rs (RaQa) (RcQc) (RbQb), where Rc and Ra

represent the charge transfer resistances of the sodiumtitanate-coated and apatite layers, and Qc and Qa arethe double layer capacitances of the coated and apatitelayers, respectively.

Conclusions

The nanosodium titanate coatings were deposited on316L SS by the dip-coating method. The thermaldecomposition and the XRD patterns showed that thecrystallization of the monoclinic sodium titanate phaseoccurred at 700�C. The surface morphological studiesrevealed that the coating obtained was continuous andnanoporous. The in vitro response of coated samplesshowed the growth of hydroxyapatite over the coatedsample. The scratch test revealed that the coatingspossessed good adhesion to the substrate. The contactangle measurements depicted the hydrophilic nature ofthe coatings with increased bioactivity. The bioelec-trochemical studies confirmed the lower passive cur-rent density and nobler corrosion potential for sodiumtitanate coating compared to uncoated 316L SS in SBFsolution. Thus, the nanosodium titanate coating couldbe reasonably proposed as an alternative coating inorder to prepare low metal release prostheses withenhanced osteointegrability.

Table 2: Corrosion characteristics of uncoated and sodium titanate-coated 316L SS in SBF solution

Sample OCP (mV) Eb (mV) Ep (mV) DE Corrosion rate (mmpy 9 10�2)

Uncoated 316L SS �205 400 �450 850 3.75Sodium titanate-coated 316L SS �355 90 50 40 0.87

–2 –1 0 1 2 3 41

2

3

4

5

6Sodium titanate coated 316L SS Uncoated 316L SS

Simulated

-Ph

ase

ang

le (

Deg

(+)

)-P

has

e an

gle

(D

eg (

+))

0

10

20

30

40

50

60

70

80

90(a)

–2 –1 0 1 2 3 4

8Sodium titanate coated 316L SS Uncoated 316L SS Simulated

log

|Z| (

Ω c

m )

2

log

|Z| (

Ω c

m )

2

log (f ) (Hz)

log (f ) (Hz)

1

0

2

3

4

5

6

7

5

10

15

20

25

30

35(b)

Fig. 11: Impedance spectra of uncoated and sodium tita-nate-coated 316L SS (a) immediate immersion, and(b) immersion for 7 days in SBF solution

RE/CE

(c)

(b)

(a)

RE/CE

RE/CE

WE

WE

WE

Rs

Rs

Rs

Qb

Qc

Qa Qc Qb

Rc

Ra Rc Rb

Rb

Qb

Rb

Fig. 12: Equivalent circuit diagram for (a) uncoated,(b) sodium titanate-coated, and (c) sodium titanate-coated316L SS surface immersed for 7 days in SBF


Acknowledgment One of the authors, Ms. K. BavyaDevi, is thankful to the All India Council of TechnicalEducation (AICTE-NDF), New Delhi for its financialassistance.

References

1. Kokubo, T, ‘‘Bio-active Glass-Ceramics: Properties andApplications.’’ Biomaterials, 12 155–163 (1991)

2. Hench, LL, ‘‘Bioceramics.’’ J. Am. Ceram. Soc., 81 (7) 1705–1728 (1998)

3. Kokubo, T, Ito, S, Huang, ZT, Hayashi, T, Sakka, S, Kitsugi,T, Yamamuro, T, ‘‘Ca, P-Rich Layer Formed on HighStrength Bioactive Glass-Ceramics A-W.’’ J. Biomed. Mater.Res., 24 331–343 (1990)

4. Kokubo, T, ‘‘Surface Chemistry of Bioactive Glass-Ceram-ics.’’ J. Non-Cryst. Solids, 120 138–151 (1990)

5. Hench, LL, Anderson, O, ‘‘Bioactive Glasses.’’ In: Hench,LL, Wilson, J (eds.) An Introduction to Bioceramics, pp. 41–62. World Scientific, Singapore (1993)

6. LeGeros, RZ, LeGeros, JP, ‘‘Dense Hydroxyapatite.’’ In:Hench, LL, Wilson, J (eds.) An Introduction to Bioceramics,pp. 139–180. World Scientific, Singapore (1993)

7. Hench, LL, ‘‘Bioceramics: From Concept to Clinic.’’ J. Am.Ceram. Soc., 74 (7) 1487–1510 (1991)

8. Zarzycki, J, ‘‘Past and Present of Sol–Gel Science andTechnology.’’ J. Sol-Gel Sci. Technol., 8 17–22 (1997)

9. Mudali, KU, Sridhar, TM, Raj, B, ‘‘Corrosion of Bio-implants.’’ Sadhana, 28 601–637 (2003)

10. Kluba, A, Bociaga, D, Dudek, M, ‘‘Hydrogenated Amor-phous Carbon Films Deposited on 316L Stainless Steel.’’Diamond Relat. Mater., 19 (5–6) 533–536 (2010)

11. Kokubo, T, Takadam, H, ‘‘How Useful is SBF in PredictingIn Vivo Bone Bioactivity?’’ Biomaterials, 27 (15) 2907–2915(2006)

12. Balamurugan, A, Kannan, S, Rajeswari, S, ‘‘Structural andElectrochemical Behaviour of Sol-Gel Zirconia Films on316L Stainless Steel in Simulated Body Fluid Environment.’’Mater. Lett., 57 (26–27) 4202–4205 (2003)

13. Baliteau, S, Sauvet, AL, Lopez, C, Fabry, P, ‘‘ControlledSynthesis and Characterisation of Sodium Titanate Compos-ites Na2Ti3O7/Na2Ti6O13.’’ Solid State Ion., 178 (27–28)1517–1522 (2007)

14. Becker, I, Hofmann, I, Muller, FA, ‘‘Preparation of Bioac-tive Sodium Titanate Ceramics.’’ J. Eur. Ceram. Soc., 27 (16)4547–4553 (2007)

15. Lindgren, T, Muabora, JH, Avendeno, E, Jonsson, J, Hoel,A, Granquist, CG, Lindquist, SE, ‘‘Photoelectrochemicaland Optical Properties of Nitrogen Doped Titanium DioxideFilms Prepared by Reactive DC Magnetron Sputtering.’’J. Phys. Chem. B, 107 (24) 5709–5716 (2003)

16. Teufer, G, ‘‘The Crystal Structure of Tetragonal ZrO2.’’ ActaCrystallogr., 15 1187 (1962)

17. Ravi, V, Navale, SC, ‘‘A Co-precipitation Technique toPrepare CaNb2O6.’’ Ceram. Int., 32 (4) 475–477 (2006)

18. Shtansky, DV, Petrzhik, MI, Bashkova, IA, Kiryukhantsev-Korneev, FV, Sheveiko, AN, Levashov, EA, ‘‘Adhesion,Friction, and Deformation Characteristics of Ti–(Ca, Zr)–(C,N, O, P) Coatings for Orthopaedic and Dental Implants.’’Phys. Solid State, 48 (7) 1301–1308 (2006)

19. Ding, MH, Wang, BL, Li, L, Zheng, YF, ‘‘A Study of TaxC1-x Coatings Deposited on Biomedical 316L Stainless Steel byRadio-Frequency Magnetron Sputtering.’’ Appl. Surf. Sci.,257 (3) 696–703 (2010)

20. Chen, G, Bedi, RS, Yushan, S, Yan, S, Walker, L, ‘‘InitialColloid Deposition on Bare and Zeolite-Coated StainlessSteel and Aluminium: Influence of Surface Roughness.’’Langmuir, 6 (15) 12605–12613 (2010)

21. Yu, J, Zhao, X, Zhao, Q, Wang, G, ‘‘Preparation andCharacterisation of Super-Hydrophilic Porous TiO2 Coat-ing Films.’’ Mater. Chem. Phys., 68 (1–3) 253–259 (2001)

22. Kokubo, T, Kim, H-M, Kawashita, M, ‘‘Novel BioactiveMaterials with Different Mechanical Properties.’’ Biomate-rials, 24 (13) 2161–2175 (2003)

23. de Andrade, MC, Filgueiras, MRT, Ogasawara, T, ‘‘Hydro-thermal Nucleation of Hydroxyapatite on Titanium Sur-face.’’ J. Eur. Ceram. Soc., 22 505–510 (2002)

24. Nagarajan, S, Rajendran, N, ‘‘Surface Characterisation andElectrochemical Behaviour of Porous Titanium Dioxide-Coated 316L Stainless Steel for Orthopaedic Applications.’’Appl. Surf. Sci., 255 (7) 3927–3932 (2009)

Table 3: Impedance parameter for uncoated and sodium titanate-coated 316L SS after immediate immersion in SBFsolution

Rs (X cm2) Qc (lF/cm2) nc Rc (kX cm2) Qb (lF/cm2) nb Rb (kX cm2)

Uncoated 316L SS 208 ÆÆÆ ÆÆÆ ÆÆÆ 25.60 0.79 74.5Sodium titanate-coated 316L SS 227.4 0.6 0.79 984 17.48 0.82 202

Table 4: Impedance parameter for uncoated and sodium titanate-coated 316L SS after immersion in SBF solution for7 days

Rs

(X cm2)Qa

(lF/cm2)na Ra

(kX cm2)Qc

(lF/cm2)nc Rc

(kX cm2)Qb

(lF/cm2)nb Rb

(kX cm2)

Uncoated 316L SS 202 0.17 0.85 1.20 ÆÆÆ ÆÆÆ ÆÆÆ 36.79 0.61 170Sodium titanate-coated

316L SS116 0.39 0.62 182.79 0.42 0.72 692 13.32 0.79 289


25. Nagarajan, S, Rajendran, N, ‘‘Sol–Gel DerivedPorous Zirconium Dioxide-Coated on 316L SS for Ortho-pedic Applications.’’ J. Sol-Gel Sci. Technol., 52 188–196(2009)

26. Nagarajan, S, Raman, V, Rajendran, N, ‘‘Synthesis andElectrochemical Characterization of Porous Niobium Oxide-Coated 316L SS for Orthopaedic Applications.’’ Mater.Chem. Phys., 119 (3) 363–366 (2010)


Synthesis and characterization of nanoporous Pt–Ni alloys

Documents