Applied Surface Science 256 (2010) 3107–3115

Effect of ZnO on phase emergence, microstructure and surface modificationsof calcium phosphosilicate glass/glass–ceramics having iron oxide

K. Sharma a, A. Dixit a, S. Bhattacharya a, Jagannath a, M.N. Deo b, G.P. Kothiyal a,*a Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 085, Indiab High Pressure Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India

A R T I C L E I N F O

Article history:

Received 27 April 2009

Received in revised form 26 November 2009

Accepted 26 November 2009

Available online 2 December 2009

Keywords:

Glass ceramic

XPS

Magnetite

SEM

Simulated body fluid (SBF)

A B S T R A C T

The effect of ZnO on phase emergence and microstructure properties of glass and glass–ceramics with

composition 25SiO2–50CaO–15P2O5–(10 � x)Fe2O3–xZnO (where x = 0, 2, 5, 7 mol%) has been studied.

They have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS),

and scanning electron microscopy (SEM). Surface modifications of these glass–ceramics in simulated

body fluid have been studied using Fourier transform infrared reflection spectroscopy (FTIR), XPS and

SEM. Results have shown a decrease in the fraction of non-bridging oxygen with increase in zinc oxide

content. Emergence of crystalline phases in glass–ceramics at different heat treatment temperatures was

studied using XRD. When glass is heat treated at 800 8C calcium phosphate, hematite and magnetite are

developed as major phases in the glass–ceramics samples with ZnO up to 5 mol%. In addition to these,

calcium silicate (Ca3Si2O7) phase is also observed when glass is heat treated at 1000 8C. The

microstructure of the glass–ceramics heat treated at 800 8C exhibits the formation of nano-size (40–

50 nm) grains. On heat treatment at 1000 8C crystallites grow to above 50 nm size and more than one

phase are observed in the microstructure. The formation of thin flake-like structure with coarse particles

is observed at high zinc oxide concentration (x = 7 mol%). In vitro studies have shown the surface

modifications and formation of Ca–P-rich layer on the glass–ceramics when immersed in simulated body

fluids (SBF) for different durations. The bioactive response was found to depend on ZnO content.

� 2009 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Applied Surface Science

journa l homepage: www.e lsev ier .com/ locate /apsusc

1. Introduction

Bioactive glass–ceramics containing magnetic particles aredesirable for bone tumor treatment and drug delivery applications[1,2]. Glass–ceramics are prepared by controlled crystallization ofthe glasses. These have shown an improvement in physicalproperties like mechanical strength, corrosive resistance, etc. ofglasses [3,4]. Since the physical, optical and bioactive properties ofthese glass–ceramics depend on the emergence of different phasesas a result of controlled crystallization of glass, thus the knowledgeand study of structure of glasses and microstructure of glass–ceramics are helpful in designing new materials.

Biomedical applications of nano-size crystallites of hematite(Fe2O3) and magnetite (Fe3O4) as a drug delivery carrier havebeen reported [5,6]. It is known that the magnetic properties inthe ferrimagnetic glass–ceramics arise from the conversion ofiron oxide into magnetite [7–10]. However, the bioactivityproperties depend on the bioactive phases present in the glassmatrix. It is well accepted that calcium phosphosilicate glasses

* Corresponding author. Tel.: +91 022 25595652; fax: +91 022 25505296.

E-mail address: gpkoth@barc.gov.in (G.P. Kothiyal).

0169-4332/$ – see front matter � 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.apsusc.2009.11.082

and glass–ceramics are of great importance in the area ofbiomaterials. The addition of zinc oxide improves the magneticproperties of the ferrites system and properties of the zinc ferriteare highly affected by their particle size [11]. Zinc oxide is also anessential trace element that has stimulatory effects on boneformation and can be used to control the interfacial reactions invivo [12,13].

Bioactive glass/glass–ceramics have the tendency to form ahydroxyapatite layer on their surfaces when immersed insimulated body fluid. Since bioglass/glass–ceramics materialswhen implanted in body come in contact with living tissues, theyshould not have any harmful effects on the host tissues. Bioactiveresponse (formation of hydroxyapatite layer when immersed inbody fluid) of these materials depends on the surface compositionand surface interactions in body fluid [14–16]. Therefore, a study ofthe surface interactions with body fluid is needed to evaluate thebioactive response of the samples.

In the present work, we report a systematic study on phaseformation, microstructure and surface modification of 25SiO2–50CaO–15P2O5–(10 � x)Fe2O3–xZnO (where x = 0, 2, 5, 7 mol%)glass–ceramics using XRD, XPS, FTIR and SEM. These glass–ceramics are prepared by controlled heat treatment of glass. Thephase evolution was studied after heat treatment at 8008 C and

Table 1Base glass compositions (nominal) in mol%.

Sample SiO2 P2O5 CaO Fe2O3 ZnO

ZF0 25 15 50 10 0

ZF2 25 15 50 8 2

ZF5 25 15 50 5 5

ZF7 25 15 50 3 7

Fig. 1. XRD patterns of (a) ZFC0, ZFC2, ZFC5 and ZFC7 glass–ceramics prepared at

800 8C; (b) ZFC0 glass–ceramics prepared at different temperatures; and (c) ZFC0,

ZFC2, ZFC5 and ZFC7 glass–ceramics prepared at 1000 8C.

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–31153108

10008 C for 6 h. Effects of ZnO on the structure and microstructurehave been studied and the surface modifications of these samplesin simulated body fluid (SBF) as a function of exposure time wereinvestigated. We found that glass–ceramics surfaces are modifieddifferently upon immersion in SBF and their bioactive responsesdepend on the ZnO content.

2. Experimental

Base glasses with compositions 25SiO2–50CaO–15P2O5–(10 � x)Fe2O3–xZnO (where x = 0, 2, 5, 7 mol%) (Table 1) wereprepared. About 100 g batches were prepared by mixing reagentgrade SiO2, CaCO3, NH4H2PO4, Fe2O3, and ZnO.

Since NH4H2PO4 and CaCO3 decompose at around 210 8C and830 8C respectively, we have heated the charge first at 210 8C andthen to 830 8C, holding at each temperature for 6 h. The charge wasfinally heated to 9008 C (12 h) to ensure complete decompositionof precursors. Melting was carried out in a covered Pt–10% Rhcrucible at 1450–15008 C in a lowering and raising hearth furnace.The melt was held for 30 min at this temperature for homogeni-zation and then was poured into water. The base glass waspowdered in a ball mill and pelletized. They were converted intoglass–ceramics (hereafter called ZFC) through controlled heattreatment. Glass–ceramics ZFC0, ZFC2, ZFC5 and ZFC7 with ZnOconcentration 0, 2, 5 and 7 mol%, respectively, were heat treated at800 8C and 1000 8C for 6 h.

Phase emergence in these glass–ceramics was investigatedusing XRD (Philips PW 1710 X-ray diffractometer) of the powdersamples. The phases were identified using MATCH1 software. Themicrostructure of glass-ceramic is characterized by scanningelectron microscopy (Model: Tescan Vega MV 2300T/40). Priorto mounting sample in analysis chamber of microscope, a thin Auconducting coating was deposited on the sample surface.

For XPS measurements samples was mounted on a specimenholder using silver paste. The conducting path was provided frombottom to the top surface of the sample by silver paste, to avoid thesurface charging effect. The sample chamber was then evacuatedto a vacuum better than 1 � 10�9 Torr. The sample was excited byMg-Ka radiations (hn = 1254.6 eV), photoelectron spectra wereanalyzed using a VG make CLAIM 2 analyzer system in the energyrange of 0–1000 eV.

For studying surface modifications, the pellets of around 10 mmin diameter are made using approx. 500 mg of glass powder. Thesewere heat treated at 1000 8C for 6 h. The simulated body fluid (SBF)was prepared according to the procedure proposed by Kokubo andTakadama [17]. These samples pellets of around 500 mg areimmersed in 50 ml for 1–4 weeks, incubated at 37.4 8C. These wereremoved periodically and surfaces were analyzed using XPStechnique. Changes in concentrations of Ca, Zn and Fe in SBFsolutions as a result of surface modifications (dissolution, etc.)were measured using atomic absorption spectrophotometer(Model Chemito AA 203) after the removal of samples at differentintervals. Structural changes on the surface of the samples treatedin SBF were analyzed using diffuse reflection Fourier transforminfrared reflection spectroscopy (Model Bruker Vertex 80 V Fouriertransform infrared (FTIR) spectrometer) and scanning electronmicroscopy (SEM) techniques.

3. Results and discussions

3.1. Structural studies

The XRD patterns of different glass–ceramics prepared bycontrolled heat treatment at 800 8C are depicted in Fig. 1a. It shows

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–3115 3109

the formation of calcium phosphate (Ca3(PO4)2), magnetite andhematite phases. With addition of 5 mol% ZnO, peak correspondingto calcium phosphate (around 328) have become finer. But at7 mol% of ZnO, peak corresponding to hematite around 318 hasreduced in the intensity while peaks corresponding to calciumphosphate have become sharper. The CaO has the more affinitytowards phosphate thus forming calcium phosphate phase.Magnetite phase has been formed in the glass matrix. Calciumand zinc oxides have the high affinity for oxygen and thusreduction of Fe2O3 takes place by the reaction:

Fe3þðmeltÞ $ Fe2þðmeltÞ (1)

The extent of conversion of hematite (Fe2O3) into Fe3O4 depends onthe reducing environment produced by the presence of ZnO andCaO in the melt.

The XRD patterns of sample of ZFC0 at different heat treatedtemperatures are shown in Fig. 1b. We find that crystallinityimproves with heat treatment temperatures as peaks becomesharper. XRD patterns of sample heat treated at 1000 8C, exhibitsharp peaks corresponding same as in the case of sample heattreated at 800 8C (where peaks are broad and less in numbers). Inaddition to calcium phosphate, magnetite and hematite, someadditional peaks corresponding to rankinite (Ca3Si2O7) have also

Fig. 2. (a) XPS spectra of ZF0, ZF2, ZF5 and ZF7 glass samples; (b) deconvolution of oxyge

experimental points are shown by solid squares.)

been observed for samples heat treated at 900 8C and 1000 8C. Thisphase seems to have been produced by the following reaction inthe glass matrix:

3CaOðglassÞ þ 2SiO2ðglassÞ ! Ca3Si2O7ðcrystalÞ (2)

XRD plots for different glass–ceramics samples (ZFC0–ZFC7)heat treated at 1000 8C are shown in Fig. 1c.The glass–ceramicswithout ZnO (ZFC0) shows mostly calcium phosphate (Ca3(PO4)2),rankinite (Ca3Si2O7), magnetite and hematite phases. With theaddition of 2 mol% ZnO content the intensity of peak correspond-ing to rankinite has decreased while the intensity of peakscorresponding to calcium phosphate Ca3(PO4)2 phase has in-creased. With further increase in ZnO to 5 mol%, there is increase inthe formation of calcium phosphate phase. However, when ZnOcontent is increased to 7 mol% (ZFC7) the peak corresponding tomagnetite phase could not be detected and only few lines of lowintensity for hematite were observed.

3.2. XPS study

X-ray photoelectron scans for as prepared glass samples in thebinding energy (BE) region 0–1000 eV are shown in Fig. 2a. Thecore level peaks for the constituent elements are identified and

n core level spectra of glass samples (a). (Fitted peaks are shown by solid lines and

Table 2Ratio of non-bridging and bridging structure units for different glass samples

obtained from XPS data (Fig. 2b).

Sample Ratio of non-bridging to bridging oxygen groups

ZF0 0.30

ZF2 0.193

ZF5 0.057

ZF7 0.045

Fig. 3. (a) XPS spectra of ZFC0, ZFC2, ZFC5 and ZFC7 glass–ceramics prepared at

1000 8C samples. (b) Magnified view for core level P2p spectra of glass–ceramics (a)

samples. (c) Magnified view for core level O1s spectra of glass–ceramics (a) samples.

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–31153110

marked on the spectra. The peak at the binding energy around284.6 eV for C1s core level used as a reference. The peaks at around346 eV assigned to Ca2p, around 531 eV to O1s and around 710 eVto Fe2p photoelectrons.

In order to bring clarity about the O1s photoelectron spectra wehave re-plotted the data in the vicinity of the peak (core level) andshown in Fig. 2b. The peak shape changes with increasing ZnOcontent and the maximum peak width (FWHM) is 1.7 eV observedfor sample ZF0 (without ZnO). The O1s peak is fitted with twoGaussian peaks and shown in Fig. 2b. (Fitted curves are shown bysolid line and experimental data are shown by solid squares.) SinceFe2O3 is replaced by ZnO in the silica network, the electronicdensity of the bonding states of the silicon and oxygen atoms aremodified. As a result, the fractions of bridging and non-bridgingoxygen are also changed.

XPS technique can be used to resolve the contributions ofbridging and non-bridging oxygen atoms [18–20]. The fraction ofnon-bridging oxygen units is calculated from the core level XPSspectra of O1s peak. The difference between bridging and non-bridging oxygen atoms is reflected in the XPS chemical shift ofabout 1.2 eV to the O1s peak (Fig. 2b). The low binding energy peakat �529 eV corresponds to the contribution from the non-bridgingoxygen atoms, while the peak at �531 eV is attributed to thebridging oxygen. The areas of the two peaks (non-bridging andbridging) are calculated to find out the fraction of non-bridgingoxygen. The fraction of non-bridging oxygens decreased as the zincoxide content was increased to 7 mol% (Table 2). This is correlatedto the fact that the zinc oxide behaves as poor modifier than ironoxide resulting in a strong network with increase in ZnO content.

XPS spectra of different glass-ceramic samples are shown inFig. 3a. Peaks have become sharper as compared to the peaks ofglasses. Fig. 3b shows the P2p core level spectra as a function ofcomposition. The P2p peak observed at binding energy 133 eV. Asthese peaks are broad in nature it implies that phosphate is presentas mixture of phosphate and pyrophosphate (Q1).

Fig. 3c shows the O1s core level peak of heat treated samples asa function of composition. The peak shifts to the higher energy sidewith an increase in ZnO content (x > 5 mol%). The binding energyfor the oxygen in phosphate is in the range of 530–532.8 eV. Theshift of O1s core level peak with increase in ZnO content(x > 5 mol%) to the higher energy side is possibly due to increasein the formation of phosphate.

3.3. Microstructure studies

Fig. 4(a–d) shows the scanning electron micrographs of glasssamples heat treated at 800 8C. The microstructure exhibits thegranular morphology; grains having size of about 50 nm. Themicrostructure becomes more homogeneous and granular withthe addition of ZnO content. The microstructure without ZnO doesnot appear to be densely packed. With the addition of ZnO (2 mol%)sample exhibits the microstructure with smaller size particles(<50 nm). The crystallite size further decreases with increase inZnO content (x = 5, 7 mol%).

The microstructures of glass samples after heat treatment at1000 8C are shown in Fig. 5(a–d). Glass–ceramics sample (prepared

Fig. 4. SEM micrographs of different glass–ceramics samples prepared at 800 8C. (a) ZFC0; (b) ZFC2; (c) ZFC5 and (d) ZFC7.

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–3115 3111

at 1000 8C) without ZnO content shows the evolution of small sizeparticles. The microstructure is seen to have densely packedcrystallites when compared to that of glass samples heat treated at800 8C. The densification has occurred at higher temperature(1000 8C) because there is an increase in the atomic and molecularmobility at higher temperature sintering and consequentlyenhanced diffusion, resulting in densely packed structure. Overallmicrostructure is seen to be composed of elongated grains andincrease in particle size. In specimen with 5 mol% zinc oxide thisfeature dissolved into a microstructure with smaller particles(Fig. 5c). The formation of thin flake-like structure with coarseparticles is observed at high zinc oxide concentration (x = 7 mol%).The average size of spherical particles is 50 nm and that of thinflake-like grains is of the order of 30–60 nm in width and 1000 nmlength.

The crystallite size has also been determined from XRD data(using Debye–Scherer formula), and the measured values areroughly in agreements with measured values from SEM micro-graphs. Fig. 6 shows the variation in crystallite size with ZnOcontent of glass–ceramics samples heat treated at differenttemperatures. The crystallites sizes are sub 50 nm in glass–ceramics samples heat treated at 800 8C and are above 50 nm in theglass–ceramics samples heat treated at 1000 8C.

3.4. In vitro studies

Fig. 7 shows the infrared spectra of the ZFC0 sample after theimmersion in the simulated body fluid for 0, 1 and 4 weeks. The

spectrum before the immersion reveals bands at around 1200, 985,784, and 648 cm�1 which correspond to P–O stretching, Si–Ostretching, Si–O–Si stretching and Fe–O stretching frequencies,respectively [21]. After 1 week of immersion in SBF, new bandaround 3360 cm�1appears. This band is associated with non-hydrogen bonded hydroxyl group of apatite [22]. This implies theformation of hydroxyapatite upon immersion in SBF. The intensityof this band has increased with increase in immersion time ofsample in SBF. This is related with the increase in surface coveragewith apatite. In addition, the band around 980 cm�1, related tocalcium phosphate (hydroxyapatite) surface layer is observed. Theband at 1300–1600 cm�1 is assigned to C–O vibration mode ofCO3

2�. These bands signify the incorporation of carbonate anionsfrom the SBF in the apatite crystal lattice.

The interactions of SBF solutions with bioglass/glass–ceramicsas suggested by Hench [14,15] start with ion exchange processresulting in the increase in pH of solution. This causes the surfacedissolution. The sample surface of ZFC0 (Fig. 8a) has got depleted ofSi and Ca during its interaction with SBF (after 1 week). This isevident from the decrease in the intensity of peaks correspondingto Ca and the absence of peak corresponding to Si2p in the XPSspectra (after 1 week). As immersion time in SBF is increased, wehave also observed that the Si concentration in the SBF solution isincreased (Fig. 9). This increase of Si in SBF solution has resultedfrom the surface dissolution. Fig. 9 has clearly shown an increase inSi concentration in SBF solution after immersion of samples.Chemical analyses of SBF solutions after immersion period for 1–2weeks are given in Table 3. After 1-week immersion, the

Fig. 5. SEM micrographs of different glass–ceramics samples prepared at 1000 8C. (a) ZFC0; (b) ZFC2; (c) ZFC5 and (d) ZFC7.

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–31153112

concentration of Ca is slightly increased from the as prepared SBFconcentration while the Fe and Zn were not detected in the SBFsolution. This implies the dissolution of Ca from the surface.

On exposure of these samples to SBF solution for after 2 weeks,intensity of XPS peaks corresponding to Ca and P was increasedwhen compared with that of spectra of sample after 1 weekimmersion (Fig. 8a–d). This indicates the formation of the some

Fig. 6. Variation of crystallites size with ZnO content as calculated from the XRD

data using Debye–Scherer formula.

Ca–P-rich layer at the surface. This kind of behaviour is shown forall the samples. However, as far as the samples ZFC7 concerned andvery thin calcium phosphate layer was formed. The presence of theSi2p signal (with some attenuation in intensity), observed in thewide scan spectra for ZFC7, provides the evidence of partiallycoverage of surface after 2 weeks of exposure (Fig. 8d).

Fig. 10(a–f) illustrates the evolution of microstructure of thesamples heat treated at 1000 8C, upon immersion in SBF fordifferent durations. Fig. 10(a and b) shows the surface morphology

Fig. 7. FTIR spectra of glass–ceramics (ZFC0) samples after immersion in SBF for

different time-periods.

Fig. 8. XPS spectra of different glass–ceramic (1000 8C) before and after immersion in SBF. (a) ZFC0, (b) ZFC2, (c) ZFC5, and (d) ZFC7.

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–3115 3113

and cross-section of the surface of the ZFC0 sample immersed inSBF for 1 week. Fig. 10(c–f) shows the surface morphology of ZFC0,ZFC2, ZFC5, and ZFC7 after immersion in SBF for 4 weeks. It is seenthat the growth of apatite-like layer starts growing on the samplesurface after 1-week immersion in SBF (Fig. 10a and b). Surfacemorphology and cross-section of the surface of ZFC0 sampleexhibits the growth of the apatite layer. The surface morphology

Fig. 9. Si concentration in the SBF solution after different time of immersion of ZFC0

samples.

also shows the presence of some fine voids on the surface. InFig. 10(c–f) surface morphologies of the samples exhibit thegrowth of the particles of different sizes with some localizedcoagulation of the particles. With increase in immersion time to 4weeks there is increase in growth of the particles, along with thepresence of some voids. These voids could be the gaps between theagglomerates as the particles have grown with increase inimmersion time.

Table 3Concentration (ppm) of different constituents (Ca, Zn and Fe) of SBF solutions after

immersing glass–ceramic samples for different durations.

Sample Concentration (ppm)

Ca Fe Zn

ZFC0

One week 25�2 Nd Nd

Two weeks 23�3 Nd Nd

ZFC2

One week 21�2 Nd Nd

Two weeks 24�2 Nd Nd

ZFC5

One week 19�3 Nd Nd

Two weeks 18�2 Nd Nd

ZFC7

One week 21�3 Nd Nd

Two weeks 22.�3 Nd Nd

SBF 21�2 Nil Nil

Fig. 10. SEM micrographs of ZFC0 sample after immersion in SBF for 1 week (a) surface morphology; (b) the cross-section of the surface; and, surface morphology of different

glass–ceramics (1000 8C) sample after 4 weeks immersion in SBF (c) ZFC0; (d) ZFC2; (e) ZFC5 and (f) ZFC7.

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–31153114

The formation of a CaO–P2O5-rich layer on the surface ofbioactive glasses upon interaction with simulated body fluids hasbeen reported by many authors [23–26]. The formation of suchlayer on the ZFC samples surfaces was observed, however, the areaof surface covered with Ca–P layer increase with the addition ofZnO content up to 5 mol% as seen from SEM (Fig. 10). Furtherincrease of ZnO content resulted in the decrease in growth of thelayer.

The formation of Ca–P bioactive layer involves several steps andgoverned by the nucleation and growth of particles at the surface[14,27]. The formation of hydroxyapatite is commenced whensurface dissolution takes place. Chemical analysis of the SBFsolution has shown the surface dissolution has taken place. Itinvolves the dissolution of residual glass and crystallites in glassmatrix. Hence, the interactions of SBF solution with surface willdepend on both the structure of residual glass and the emergenceof different crystallite phases.

We have seen by XRD that the composition of phases evolvedin the microstructure has changed with addition of ZnO. As it isevident from XRD, three major phases calcium phosphate,calcium silicate and hematite phases are formed in glasseswhen heat treatment at 1000 8C. The peaks intensities corre-sponding to calcium phosphate, calcium silicate increased as theZnO content in the glass is increased. Ca3(PO4)2 and calciumsilicate (rankinite) phases are reported to be bioactive [28]. Thusthe area of the Ca–P layer formed at the surface increased withincrease in ZnO content up to 5 mol% as the content of bioactivephases has increased. Though the contents of bioactive phaseshave been increased with increase in ZnO content to 7 mol%, butthe growth of additional layer formed on the surface has reduced.

With the increase in ZnO content, the fraction of non-bridgingoxygen decreases (Table 2). This will decrease the selectivesurface dissolution during the interactions of the body fluids withthe sample. Hence the subsequent surface reactions, whichinvolve nucleation and growth of the apatite particles, areaffected. Thus reduction in growth of Ca–P-rich layer has beenobserved. Hematite and magnetite have also been developed asothers crystalline phases. We have observed that the content ofmagnetic phase has reduced with increase of ZnO becauseincrease in ZnO content resulted in decrease of Fe2O3 content. Acomparison of the results suggests that, for the glass–ceramicsamples containing ZnO up to 5 mol%, the formation of the Ca–P-rich layer occurred rapidly as compared to sample without anyZnO. Further increase in the ZnO content to 7 mol% the surfacedissolution decreases as the fraction of non-bridging oxygen hasdecreased with consequent decrease in the ability of formingbioactive layer.

4. Conclusion

Structural and microstructural studies of glass/glass–ceramicswith chemical composition 25SiO2–50CaO–15P2O5–(10� x)Fe2O3–xZnO (x = 0, 2, 5, 7 mol%) have been studied. The addition of ZnOcontent modified the glass network and the fraction of non-bridgingoxygen has decreased with increase in ZnO content. On heattreatment at 1000 8C calcium phosphate and calcium silicate aredeveloped as major crystalline phases with nano-size crystallites.Hematite and magnetite have also been developed as otherscrystalline phases. These were observed to develop Ca–P-rich layerat the surface when immersed in SBF, thereby indicating the

K. Sharma et al. / Applied Surface Science 256 (2010) 3107–3115 3115

bioactive nature of the material. According to the surface analysis,glass–ceramics containing up to 5 mol% ZnO have shown betterbioactive response than the sample having no ZnO. Higher ZnOcontent (7 mol%) decreases the surface activity due to reduction innon-bridging oxygens. Thus a small amount of ZnO up to 5 mol% willbe conducive for the formation of hydroxyapatite-like layer at thesurface.

Acknowledgements

The authors wish to thank Dr. J.V. Yakhmi for encouragementand support to this work. The authors thank Drs. S.K. Gupta andA.K. Tyagi for SEM and XRD facilities, respectively. They would alsolike to thank Dr. P.K. Sharma for absorption spectrophotometryanalysis.

References

[1] K. Ohura, M. Ikenaga, T. Nakamura, T. Yamamuro, Y. Ebisawa, T. Kokubo, Y.Kotoura, M. Oka, Bioceramics 3 (1992) 225.

[2] D. Arcos, R.P. Real, M. Vallet-Regi, Biomaterials 23 (2002) 2151.[3] P.W. McMillan, Glass–ceramics, Academic Press, London, 1979, pp. 1–5.[4] N. Rezlescu, E. Rezlescu, I. Ciobotaru, M.L. Craus, P.D. Popa, Ceram. Int. 31 (1998)

24.[5] P. Tartaj, M.P. Morales, T. Gonzalez-Carreno, S. Veintemillas-Verdaguer, C.J. Serna,

J. Mag. Magn. Mater. 290 (2005) 28.[6] M. Gonzales, K.M. Krishnan, J. Mag. Magn. Mater. 293 (2005) 265.

[7] K. Takegami, T. Sano, H. Wakabayashi, J. Sodona, T. Yamazaki, S. Morita, T. Shibuya,A. Uchida, J. Biomed. Mater. Res. 43 (1998) 210.

[8] Y.K. Lee, S.Y. Choi, J. Am. Ceram. Soc. 79 (1996) 992.[9] S.H. Oh, S.Y. Choi, Y.K. Lee, K.N. Kim, J. Biomed. Mater. Res. 54 (2001) 360.

[10] R.K. Singh, G.P. Kothiyal, A. Srinivasan, J. Mag. Magn. Mater. 320 (2008) 1352.[11] D. Cullity, Introduction to Magnetic Materials, Addison-Wesley, Reading, 1972.[12] A. Ito, H. Kawamura, M. Otsuka, M. Ikeuchi, H. Ohgushi, K. Ishikawa, Mater. Sci.

Eng. C 22 (2002) 21.[13] M. Yamaguchi, A. Igarashi, S. Ychiyama, J. Health Sci. 50 (2004) 75.[14] L.L Hench, J. Am. Ceram. Soc. 81 (1998) 1705.[15] L.L. Hench, J. Am. Ceram. Soc. 74 (1991) 1487.[16] L.M. Bjursten, L. Emanuelsson, L.E. Ericson, P. Thomsen, J. Lausmaa, L. Mattson, U.

Rolander, B. Kaserno, Biomaterials 11 (1990) 596.[17] T. Kokubo, H. Takadama, Biomaterials 27 (2006) 2907.[18] B.P. McGrail, J.P. Icenhower, D.K. Shuh, P. Liu, J.G. Darab, D.R. Baer, S. Thevuthasen,

V. Shutthananandan, M.H. Engelhard, C.H. Booth, P. Nachimuthu, J. Non-Cryst.Solids 296 (2001) 10.

[19] Y. Miura, H. Kusano, T. Nanba, S. Matsumoto, J. Non-Cryst. Solids 290 (2001) 1.[20] J. Serra, P. Gonzalez, S. Liste, C. Serra, S. Chiussi, B. Leon, M. Perez-Amora, H.O.

Ylanenc, M. Hupa, J. Non-Cryst. Solids 332 (2003) 20.[21] C.Y. Kim, A.E. Clark, L.L. Hench, J. Non-Cryst. Solids 113 (1989) 195.[22] A. Slosarczyk, Z. Paszkiewicz, C. Paluszkiewicz, J. Mol. Struct. 744 (2005) 657.[23] M.R. Filgueiras, G. La Torre, L.L. Hench, J. Biomed. Mater. Res. 27 (1993) 445.[24] A. Balamurugan, G. Balossier, S. Kannan, J. Michel, A.H.S. Rebelo, J.M.F. Ferreira,

Acta Biomater. 3 (2007) 255.[25] G. Lusvardi, D. Zaffe, L. Menabue, C. Bertoldi, G. Malavasi, U. Consolo, Acta

Biomater. 5 (2009) 419.[26] S.B. Cho, K. Nakanishi, T. Kokubo, N. Soga, C. Ohtsuki, T. Nakamura, Biomed. Mater.

Res. 33 (1996) 145.[27] W.D. Kingery, H.K. Bowen, D.R. Bowen, Introduction to Ceramics, 2nd ed., Wiley,

New York, 1960.[28] T. Kitsugi, T. Yamamuro, T. Nakamura, M. Oka, Biomaterials 16 (1995) 1101.