The aim of this study was to prepare and to characterize the structure of Al2O3–3YSZ composites with 5% TiO2 addition as well as the surface modification upon treatments with SnF2 and NaBF4, respectively. SEM micrographs showed the controlled densification of the composites as an effect of 3YSZ and TiO2 addition to alumina matrix. By FTIR and XRD, the characteristics of Al-O and Zr-O vibrations, respectively, the diffractions lines related to a-corundum and zirconia in tetragonal phase were discussed. Qualitative and quantitative results obtained by XPS and ATR FTIR demonstrated that the proposed materials are more sensitive to SnF2 than to NaBF4 treatment.

1. Surface Modification of Alumina/ Zirconia Ceramics
Upon Different Fluoride-Based Treatments
Simona Cavalu* and Florin Banica
Faculty of Medicine and Pharmacy, University of Oradea, Oradea, Romania
Viorica Simon
Faculty of Physics & Institute of Interdisciplinary Research in Bio-Nano-Sciences,
Babes-Bolyai University, Cluj-Napoca, Romania
Ipek Akin and Gultekin Goller
Metallurgical & Materials Engineering Department, Istanbul Technical University, Istanbul, Turkey
The aim of this study was to prepare and to characterize the structure of Al2O3–3YSZ composites with 5% TiO2 addi-
tion as well as the surface modification upon treatments with SnF2 and NaBF4, respectively. SEM micrographs showed the
controlled densification of the composites as an effect of 3YSZ and TiO2 addition to alumina matrix. By FTIR and XRD,
the characteristics of Al-O and Zr-O vibrations, respectively, the diffractions lines related to a-corundum and zirconia in
tetragonal phase were discussed. Qualitative and quantitative results obtained by XPS and ATR FTIR demonstrated that the
proposed materials are more sensitive to SnF2 than to NaBF4 treatment.
*scavalu@rdslink.ro
© 2013 The American Ceramic Society
Int. J. Appl. Ceram. Technol., 1–10 (2013)
DOI:10.1111/ijac.12075

2. Introduction
Ceramics have a great potential in the biomedical
field, thanks to their biocompatibility, strength, and
wear resistance. The two dominant ceramic materials in
clinical use today as bearing surfaces are still alumina
(Al2O3) and zirconia (ZrO2).1–3
Alumina exhibits
excellent hardness and wear properties; fracture tough-
ness values are lower than those of the metals used in
orthopedic surgery. However, it is a brittle material,
with low resistance to the propagation of cracks. Zirco-
nia was introduced to overcome the limitations of alu-
mina. It is well known that transformation toughening
improves the mechanical properties of zirconia ceram-
ics, as their major drawback is the strength reduction,
due to an unfavorable tetragonal to monoclinic mar-
tensitic phase transformation during the contact with
physiological fluids.4–7
Zirconia, in contrast to alumina,
is an unstable material, existing in three crystalline
phases: monoclinic, tetragonal, and cubic. The tetrago-
nal phase that is the most resistant tends to transform
into the monoclinic phase under certain conditions
(aging, thermal treatment). The addition of stabilizing
materials such as Y2O3 or CeO2 during manufacture
can control the phase transformation of zirconia.5–7
Therefore, the ideal ceramic for orthopedic and dental
applications is a high-performance biocomposite mate-
rial that combines the excellent material properties of
alumina in terms of chemical stability, hydrothermal
stability, biocompatibility, and extremely low wear and
of zirconia with its superior mechanical strength and
fracture toughness.8–11
On the other hand, the surfaces
modification and postsynthesis treatment also influence
the performances of the bioceramics designed to dental
applications.12,13
It was demonstrated that the adminis-
tration of complex fluorides as compared with NaF
suggests the possibility of using them as effective agents
in dental caries prevention in human populations.14,15
For example, stannous fluoride converts the calcium
mineral apatite into fluorapatite, which makes tooth
enamel more resistant to bacteria generated acid attacks.
In toothpastes containing calcium minerals, sodium
fluoride becomes ineffective over time, while stannous
fluoride remains effective in strengthening tooth
enamel. Stannous fluoride has been shown to be more
effective than sodium fluoride in reducing the incidence
of dental caries and controlling gingivitis.16
Further
aspects related to the action of these new bioceramics
upon different surface treatments on dentinal tissue are
to be analyzed, to be properly used by professionals, so
that they can make the best of properties during clini-
cal applications.17
Even if increasing attention has been
paid to elucidating the influence of fluoride chemistry
in tooth mineralization, there are also some debates
about the use of fluoride in osteoporosis treatment, par-
ticularly concerning the beneficial effects on bone mass
and quality.18
NaF has been known to be one of the
most effective agents for the treatment of vertebral oste-
oporosis by its stimulating effect on new bone forma-
tion.19
In this study, we are focused on the possible
beneficial effect of fluorination with respect to dental
bioceramics. The surface modifications of alumina and
alumina/zirconia bioceramics are investigated upon dif-
ferent treatments with sodium tetrafluoroborate and
stannous fluoride, respectively. The proposed bioceram-
ics are designed for orthopedic or dental implants,
being prepared by Spark Plasma Sintering.20
Using
complementary spectroscopic tools such as Attenuated
Total Reflection Fourier Transform Infrared Spectros-
copy (ATR FTIR) and X-rays Photoelectron Spectros-
copy (XPS), the chemical changes on the surface
induced by fluoride treatment are discussed in terms of
their effectiveness.
Materials and Methods
Preparation and Structural Characterization of
Alumina and Alumina/Zirconia Specimens
Al2O3 (Baikowski grade SM8, an average particle
size of 0.6 lm), 3 mol% yttria stabilized ZrO2 (3YSZ,
Tosoh grade, an average particle size of 0.1 lm), and
TiO2 (Merck, an average particle size of 1 lm) pow-
ders were used as starting materials. The raw materials
were weighed in appropriate quantities, ball milled in
ethanol for 24 h and then dried. A graphite die 5 mm
inner diameter was used in the sintering process. Al2O3
and Al2O3–3YSZ composites with 5% (wt) TiO2 addi-
tion were prepared using a spark plasma sintering
method (SPS apparatus SPS-7.40 MK-VII Syntex, Fuji
Electronic Industrial, Saitama, Japan) at 1350°C for
5 min with a heating rate of 100°C/min in vacuum,
under a pressure of 40 MPa, resulting three different
specimens with the chemical composition as follows:
specimen 1- monolithic Al2O3; specimen
2- 80%Al2O3 À 20%3YSZ; specimen 3- 80%Al2O3
À 20%3YSZ + 5%TiO2. The specific Al2O3/3YSZ
ratio was chosen because it was previously demon-
2 International Journal of Applied Ceramic Technology—Cavalu, et al. 2013

3. strated that zirconia has a reinforcing effect up to
30%.20
In the same time, as a result of our optimiza-
tion studies (not presented here), it was found that
5 wt% TiO2 addition had a remarkable effect with
respect to their mechanical properties. Structural char-
acterization of the specimens was made by FTIR spec-
troscopy (BXII spectrometer using K Br pellet
technique, resolution of 2/cm, at room temperature;
Perkin-Elmer, Waltham, MA), and X-ray diffraction
analysis carried out with a Shimadzu XRD- 600 diffrac-
tometer, using Cu-Ka radiation (k = 1.5418
A) with
Ni-filter. The morphology of the specimen surface (on
fracture) was investigated by scanning electron micros-
copy (JSM 7000F, JEOL, Tokyo, Japan).
Fluoride Surface Treatment and Surface
Investigation of the Specimens
High purity stannous fluoride (Tin II fluoride) and
sodium tetrafluoroborate (Sigma Aldrich, St. Louis,
MO) were used to prepare saturated solutions (0.4 g/
mL and 1 g/mL, respectively) for surface treatment of
the specimens by conventional anodization during 2 h
at 12V. Upon the anodization treatment, the specimens
were ultrasonically treated for 90 min to remove the
deposits, then air-dried. The modifications of samples
surface upon both fluoride treatment were investigated
by ATR FTIR spectroscopy using ATR Miracle device
(single reflection with ZnSe crystal) and XPS measure-
ments performed with SPECS PHOIBOS 150 MCD
system equipped with monochromatic Al-Ka source
(250W, hm = 1486.64 eV) and Epass = 50 eV, with a
resolution of 1 eV/step. The vacuum in the analysis
chamber during the measurements was kept in the
range 10À9
–10À10
mbar.
All binding energies were referenced to the C 1 s
peak arising from adventitious carbon at 284.6 eV. The
peak areas combined with the appropriate sensitivity
factors allowed to quantify the elemental composition
at the surface. The depth of analysis was about 5 nm.
Results
Structural Investigation of the Specimens by SEM,
FTIR, XRD Spectroscopy
The morphological characteristics and the details
of the fractured surfaces of the proposed specimens
were evidenced by SEM analysis and presented in
Fig. 1. The details including the size and shape of the
alumina (micron size, gray) and zirconia (submicron,
bright white) grains clearly demonstrate that Spark
Plasma Sintering makes possible the densification of
Al2O3 based composites at a lower temperature and in
a shorter time compared with some other conventional
techniques.9,11,21
Furthermore, the microstructure and
grain size can be controlled by a fast heating rate and
shorter processing time. The structural details were
observed from the analysis of the FTIR spectra
recorded between 400 and 1400/cm and presented in
Fig. 2. The FTIR spectra are dominated by absorption
lines arising from Al2O3 phase (1088/cm, 780 and
797/cm). The addition of zirconia phase clearly modi-
fies the relative intensity of these bands. The vibration
of Zr-O bond in tetragonal phase is visible at 518 and
580/cm. A superposition of the characteristic absorp-
tion bands occurs in the spectral region 500–650/cm
upon TiO2 addition to alumina/zirconia matrix and, as
a consequence, Ti-O vibration band cannot be distin-
guished. The XRD patterns of the proposed specimens
are presented in Fig. 3 showing the characteristic peaks
of a-corundum (JCPDS: 30-0415) and tetragonal
zirconia (JCPDS: 42-1164). The reflection lines occur-
ring from crystallographic planes related to a-corundum
are clearly marked at 2h = 25.6; 35.2; 37.9; 43.4;
57.5; 61.3; 66.4; 68.2; 76.9, and 80.7°,
while the iden-
tification of tetragonal zirconia is assigned to
2h = 29.9; 49.9; 59.7, and 62.5° in specimen 2 and 3.
The pattern show highest tetragonal intensities of (111)
planes at 2h = 29.9° and (220) planes at 2h = 59.7°
and lower intensities of (113) and (311) at 2h = 62.5°.
The presence of rutile TiO2 is assigned to small peaks
at 2h = 26.4 and 36° in specimen 3. No monoclinic
phase of ZrO2 was detected from the XRD results.
Surface Modification Upon Fluoride Treatments
Investigated by ATR FTIR and XPS Spectroscopy
In Fig. 4a are presented the vibrational ATR FTIR
details of both fluoride as received from the supplier
(crystalline powder). The fingerprints of SnF2 are
observed at 492, respectively, 548/cm and assigned to
symmetric and asymmetric stretch mode, whereas for
NaBF4, the marker bands in the selected region are
443, 472, 498, and 575/cm, as the [BF4] species
belongs to a symmetry group with four normal modes
of vibration. For the wide range of tetrafluoroborates
and other [XF4] compounds (X = C, Si, Al, Ge, N, P,
www.ceramics.org/ACT Alumina Zirconia Bioceramics 3

4. etc.), the position of the normal modes follows the
trend: m3 m1 m4 m2.
Upon the fluoride treatment, the surface of the
specimens was strongly affected as revealed by the ATR
FTIR spectra presented in Fig. 4(b-d). The marker
bands of both SnF2 and NaBF4 can be observed along
with the characteristic features of Al-O stretching vibra-
tions at 435/cm and, respectively, Zr-O at 526/cm.
The survey XPS spectra recorded on the surface of the
specimens before and after fluoride treatment are pre-
sented comparatively in Fig. 5. The main photoelectron
peaks in the spectra of the specimens before treatments
are assigned to Al 2s (117.9 eV), Al 2p (74.3 eV), O
1s (531.8 eV) (specimen 1), Zr 3d (180 eV), and Ti
2p (456 eV) (specimen 2 and 3 respectively). After
SnF2 treatment, a strong peak at 487.1 eV indicates
the contribution of Sn 3d electrons, while the presence
of fluorine is proved by F 1s photoelectrons peak at
685 eV. These marker peaks are strongly visible for all
the specimens, but as presented in Table 1, the atomic
concentration of the elements shows a higher percent
of Sn on the surface of composites (specimen 2 and 3)
(a) (b)
(c) (d)
(e) (f)
Fig. 1. SEM micrographs recorded on the fractured surface of the specimens, with different details and magnifications along with the
EDAX spectrum: specimen 1 (a, b); specimen 2 (c, d); and specimen 3(e, f).
4 International Journal of Applied Ceramic Technology—Cavalu, et al. 2013

5. compared with the monolithic Al2O3. With respect to
the NaBF4 treatment, the marker peaks in this case are
F1s at 685.7 eV and Na 1s at 1072 eV, but this treat-
ment shows a less effectiveness compared with SnF2.
Anyway, the maximum effect in this case is observed
toward the specimen 3. The results obtained by both
XPS and ATR FTIR spectroscopy show a good correla-
tion from the standpoint of qualitative and quantitative
aspects.
Discussion
To overcome the low toughness of alumina and
the aging sensitivity of zirconia, alumina-zirconia, com-
posites have been proposed for biomedical applications.
The toughening mechanism in ZTA ceramics (zirconia
toughened alumina) is related to structural properties
of these materials, conferred especially by zirconia due
to its versatile structural properties. The details pre-
sented in Fig. 1 demonstrate that the presence of zirco-
nia as a second phase is beneficial with respect to the
inhibition of grain growth. Fine zirconia particles
located on the boundaries inhibit the movement and
prevent the grain growth of alumina (about 50%
reduction in alumina grain size was observed). It has
been previously demonstrated that the zirconia addition
to alumina matrix promotes composites with higher
densities, higher flexural strength, and fracture tough-
ness.11,21
Moreover, as shown in Fig. 1 (e, f), adding
TiO2 particles is more effective, as the size of alumina
grains is reduced by comparison with Fig.1 (c, d). A
special behavior with respect to the evolution of the
structural units present in these samples was observed
from the analysis of the FTIR spectra recorded between
400 and 1400 cm (Fig. 2). The correlation between IR
(a)
(b)
(c)
Fig. 2. Fourier transform infrared spectroscopy (FTIR) spectra
of alumina and alumina-zirconia specimens: (a) specimen 1, (b)
specimen 2, and (c) specimen 3.
0 10 20 30 40 50 60 70 80 90 100
0
500
1000
1500
2000
T
T
A
A
AZ
AA
A
Z
A
A
Z
Z
Z
A
A
A
A
AA
AA
A
(b)
(a)
Intensity(a.u.)
2 theta (degrees)
(c)
Fig. 3. XRD patterns of specimen 1 (a), specimen 2 (b), and specimen 3 (c).
www.ceramics.org/ACT Alumina Zirconia Bioceramics 5

6. absorption bands and different types of aluminate poly-
hedral is based on previous results obtained for alumi-
nate crystals.22–25
The Al-O stretching vibrations of tetrahedral AlO4
groups are related to the broad, strong band at 1088/
cm with the shoulder at 1168/cm and to the doublet at
780 and 797/cm. The aluminum atoms are differently
coordinated, usually by four or six oxygen atoms, and
less likely by five oxygens. The absorption bands and
shoulders recorded in the spectral region between 465
and 648/cm are assigned to six coordinated aluminum
which are associated with stretching modes of AlO6
octahedra. The addition of zirconia phase clearly modi-
fies the relative intensity of these bands. In some previ-
ous studies on zirconia structural characteristics, the
authors mentioned absorption bands at 410, 445, 500,
572, 740, 1104, and 1187/cm.26
Other studies27,28
reported FTIR bands at 740/cm corresponding to Zr-O
vibrations in monoclinic ZrO2 and bands at 510/cm
and 590/cm corresponding to Zr-O vibrations in
tetragonal ZrO2. In our spectra, the vibrations of Zr-O
in tetragonal phase are visible at 518 and 580/cm.
Moreover, upon TiO2 addition to alumina-zirconia
matrix, the relative intensity of 648/617/cm is consider-
ably modified, as a superposition of the characteristics
absorption bands occurs in this region.29
The analysis
of XRD patterns (Fig. 3) led to results that are in
agreement with previously reported studies with respect
(a) (b)
(c) (d)
Fig. 4. (A) Attenuated total reflection fourier transform infrared spectroscopy (ATR FTIR) spectra of SnF2 and NaBF4 powders as
received from the supplier (a), and ATR FTIR spectra recorded on specimen surface before and after treatment using SnF2 and NaBF4:
specimen 1 (b), specimen 2 (c), and specimen 3 (d).
6 International Journal of Applied Ceramic Technology—Cavalu, et al. 2013

7. to the effect of zirconia content on properties of Al2O3
–ZrO2 (Y2O3) composites.30–32
As expected, the con-
straint exerted by the alumina matrix on the zirconia
particles maintains them in tetragonal state. In the same
time, the intensity ratio of the main peaks for alumina
and zirconia is in agreement with the ZrO2 content in
samples. The results demonstrate that the high density
of the matrix correlated with the optimization of the
zirconia particles microstructure can assure the parame-
ters of better material performances.33
According to their interaction with surrounding
tissue, bioceramics can be categorized as “bioinert” or
“bioactive.” Tough and strong ceramics like zirconia,
alumina, or alumina-zirconia composites are not capa-
ble of creating a biologically adherent interface layer
with bone due to the chemically inert nature of these
two stable oxides.34
It has been demonstrated that sur-
face morphology and bone–implant interactions deter-
mine the predictability of endosseous implant bone
integration.13,35
Different surface treatments such as
Table 1. Atomic concentration of Sn, F, and Na on
the surface of the specimens after fluoride treatment
determined from X-rays photoelectron spectroscopy
(XPS) survey spectra
Specimen
Elemental composition (at %)
Sn
F
NaSnF4 NaBF4
1 3.4 4.9 3.2 2.1
2 12.8 3.9 2.4 1.9
3 12.4 3.3 6.8 4.2
1200 1000 800 600 400 200 0
O1s
F1s
O2s
Al2s
Al2p
F1s
Al2p
OAuger
Na1s
O1s
C1s
Intensity(a.u)
Binding Energy (eV)
Sn3d
Al2s
O2s
Sn4dF2sNa2p
Specimen 1
SnF2
NaBF4
1200 1000 800 600 400 200 0
F1s
Al2s
Zr3d
Al2p
C1s
N1s
O1s
Sn4dZr4pF2s
Sn3p
1
Sn3d
Zr3d
N1s
F1s
Al2p
Na1s
O1s
C1s
Intensity(a.u)
Binding Energy (eV)
Sn3p
3
Al2s
OAuger
Zr4p
Specimen 2
SnF2
NaBF4
1200 1000 800 600 400 200 0
Sn4d,Zr4p,F2s,Na2p,Ti3p
B1s
FAuger
Al2s
Al2p
OAuger
F1s
Al2p
C1s
Ti2p
O1sO1s
Sn3p
1
Sn3d
F1s
Na1s
O1s
C1s
Intensity(a.u.)
Binding energy (eV)
Al2s
Zr3d
Ti2p
OAuger
Sn3p
3
SnAuger
Specimen 3
SnF2
NaBF4
(a) (b)
(c)
Fig. 5. X-rays photoelectron spectroscopy (XPS) survey spectra of specimen 1 (a), specimen 2 (b), and specimen 3 (c) before and after
treatment with SnF2 and NaBF4.
www.ceramics.org/ACT Alumina Zirconia Bioceramics 7

8. surface blasting or acid etching can increase the rate
and amount of new bone formation on the implant
surface. Sandblasting procedure may be performed
using either medium or large grit Al2O3 particles,
whereas acid-etching process can employ hydrofluoric
acid/nitric acid. Some authors36
evaluated and reported
the apatite-forming ability of a zirconia/alumina nano-
composite (10Ce-TZP/Al2O3) in SBF as a result of the
formation of ZrAlOH groups on the surface after
chemical treatment of the material in H3PO4, H2SO4,
HCl, and NaOH at 95°C for 4 days. Hence, many dif-
ferent techniques are currently in use to condition the
surfaces of abutments and fixtures of implants.37
Sev-
eral in vitro and in vivo studies have demonstrated that
the surface structure of implant abutments influences
both the orientation and proliferation of connective tis-
sue cells and inhibits epithelial downgrowth.38
In this
study, the surface modifications of the proposed alu-
mina and alumina/zirconia ceramics upon different
fluoride treatments are emphasized by complementary
techniques ATR FTIR and XPS spectroscopy. The
ATR FTIR spectra recorded on the specimens’ surface
(Fig. 4) clearly demonstrate that the surface is being
treated, emphasized by the presence of the marker
bands of both SnF2 and NaBF4 according to their spe-
cific vibration modes.39,40
By comparing with the
FTIR spectra of the specimens before fluoride treat-
ments (Fig. 2), the changes are evident. On the other
hand, taking account of the relative intensities of the
fluoride marker bands with respect to each specimen,
one can observe that, even after the removal of the
surface deposits, different fluoride concentration can
be detected on the surface. To obtain more details,
XPS survey spectra were recorded on the specimens’
surface before and after fluoride treatment (Fig. 5). In
some previous studies, XPS has been successfully used
to investigate the surface chemistry of the commercial
zirconia implants, showing substantial differences from
bulk.41
After sandblasting procedure performed by the
manufacturer, large differences in the XPS elemental
composition were identified for the collar and threaded
root of the commercial implants. These values may
imply that the residual Al2O3 particles are aggregated
in a thinner superficial layer. Other studies related to
XPS analysis of tin oxide on glass surface demon-
strated the presence of several valences of tin that gave
rice to Sn 3d3/2 and Sn 3d5/2 typical peaks at
494.70 eV and 486.24 eV, along with two additional
peaks at 493.13 eV and 484.71 eV.42–45
The binding
energy of the doublet at 495.5 and 487.1 eV is in
good agreement with the data reported for In2O3–
SnO2 films prepared using as starting material for tin
oxide the hydrated stannic chloride (SnCl4 9
5H2O).43
By comparing the results presented in Fig. 5
(a-c), we can notice that all the specimens present a
high sensitivity to the SnF2 treatment. These results
are in a good agreement with those obtained by ATR
FTIR spectroscopy. To our knowledge, this is the first
study dealing with the aspects of different fluoride
treatment applied to alumina/zirconia-sintered compos-
ites. Although it is known that fluoride is responsible
for the regulation of biomineralization process, the
chemical process that combines zirconia dental ceram-
ics with fluorine is still unexplained, as mentioned in
a very recently published report on dental ZrO2-based
materials.46
The most well-documented effect of fluo-
ride is that this ion substitutes for an hydroxyl in the
apatite structure, giving rise to a reduction in crystal
volume and, consequently, a more stable structure.47
Free fluoride ions in solutions can react with apatite
crystal or biomaterial in several different ways, depend-
ing on their concentrations and solution composition.
Of course, further in vitro tests are required to be per-
formed to establish a correlation between the effective-
ness of surface treatment in improving the bioactivity
of alumina/zirconia composites.
Conclusions
The composites investigated in this study are
designed for orthopedic and dental implants, being pre-
pared by Spark Plasma Sintering. The structural prop-
erties of alumina and alumina/zirconia composites were
determined by SEM analysis, X-ray diffraction, and
FTIR spectroscopy. As showed by SEM micrographs,
the grain growth of alumina particles was suppressed by
the addition of zirconia. No monoclinic phase of ZrO2
was detected from the XRD results, as supported also
by the FTIR spectra. The samples were fluorinated to
improve the performances of these bioceramics as con-
sidered for dental applications. The surface modifica-
tion of the specimens upon different treatments with
sodium tetrafluoroborate and stannous fluoride, respec-
tively, was investigated by ATR FTIR and XPS. Quali-
tative and quantitative results obtained by XPS and
ATR FTIR demonstrated that the proposed materials
are more sensitive to SnF2 than to NaBF4 treatment
8 International Journal of Applied Ceramic Technology—Cavalu, et al. 2013

9. for samples fluorination. These results support other
previously reported studies justifying the long-term
effectiveness of topical fluoride treatment in dentistry
and maxillofacial applications.
Acknowledgments
This work was supported by the Romanian
National Authority for Scientific Research CNCS-UE-
FISCDI, project PNII-ID-PCE 2011-3-0441 contract
237/2011 and Bilateral Cooperation between Romania
and Turkey 2012-2013.
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