W. WALKE et al.: PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO AND STEAM STERILIZATION
323–329
PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO
AND STEAM STERILIZATION
FIZIKALNO KEMIJSKE LASTNOSTI ZLITINE Ti67 PO EO IN
PARNI STERILIZACIJI
Witold Walke1, Marcin Basiaga1, Zbigniew Paszenda1, Jan Marciniak,
Pawe³ Karasinski2
1Silesian University of Technology, Faculty of Biomedical Engineering, Roosevelta 40, 41-800 Zabrze, Poland
2Silesian University of Technology, Faculty of Electrical Engineering, Boles³awa Krzywoustego 2, 44-100 Gliwice, Poland
witold.walke@polsl.pl
Prejem rokopisa – received: 2014-09-23; sprejem za objavo – accepted for publication: 2015-05-15
doi:10.17222/mit.2014.242
The techniques of surface modification play a significant role in forming the physical and chemical properties of titanium and
its alloys. Among many techniques for the layers’ application, chemical and electrochemical methods are particularly intere-
sting, as they make it possible to control the process of depositing thin layers of the material and modifying their properties
through a change of reagents and the parameters of the deposition process. A special advantage the methods bring is the possibi-
lity to obtain layers that offer a perfect coating for geometrically complex surfaces. Apart from improved haemocompatibility, a
significant issue related to the creation of the layers is also a proper set of physicochemical properties. Therefore, the study
comprised tests of the physicochemical properties of oxide layers deposited on the surface of samples taken from a Ti-6Al-7Nb
alloy. The samples were subject to various surface modifications, i.e., grinding, electrolytic polishing, a SiO2 layer was applied
using the sol-gel method and TiO2 by means of an anodic oxide and medical sterilisation methods (EO and steam). The
corrosion-resistance tests were performed on the basis of registered anodic polarisation curves and the Stern method.
Electrochemical Impedance Spectroscopy (EIS) was also used in order to evaluate the phenomena taking place on the surface of
the tested alloys. As a part of the evaluation of the mechanical properties of surface layers created in such a way, hardness tests
and tests of the adhesion of those layers to a metallic substrate were made. Measurements of the instrumental hardness were
made with the Oliver & Pharr method, whereas the adhesion of the layers to the substrate was measured by means of a scratch
test. The suggestion of proper surface treatment variants has perspective significance and will help to develop the technological
conditions with specified parameters of the oxide coating’s creation on the surface of metallic implants.
Keywords: Ti-6Al-7Nb (Ti67) alloy, sol-gel, anodic oxide, scratch-test, nanohardness, EIS, potentiodynamic method
Tehnike modifikacije povr{ine igrajo pomembno vlogo pri doseganju fizikalnih in kemijskih lastnosti titana in njegovih zlitin.
Med mnogimi tehnikami uporabe tankih plasti so {e posebej zanimive kemijske in elektrokemijske metode, ker omogo~ajo
kontrolo postopka depozicije tanke plasti materiala in spreminjanje njihovih lastnosti, z zamenjavo reagentov in parametrov
procesa depozicije. Posebna prednost, ki jo omogo~ajo metode, je mo`nost izdelave plasti, ki omogo~ajo popolno prevleko pri
geometrijsko kompleksnih povr{inah. Poleg izbolj{ane hemokompatibilnosti je pomembno vpra{anje povezano z nastankom
plasti in tudi z doseganjem ustreznih fizikalno kemijskih lastnosti. Zato je {tudija obsegala preizkuse fizikalno kemijskih last-
nosti oksidnih plasti, po depoziciji na povr{ini vzorcev iz Ti-6Al-7Nb zlitine. Na vzorcih so bile opravljene razli~ne modifika-
cije povr{ine: bru{enje, elektrolitsko poliranje, SiO2 plast, izdelana po sol-gel postopku in TiO2 plast, izdelana z anodno
oksidacijo in metodo medicinske sterilizacije (EO in para). Preizkusi korozijske odpornosti so bili izvr{eni na osnovi zabele-
`enih polarizacijskih krivulj in metode Oliver & Pharr. Za oceno pojavov na povr{ini preizku{enih zlitin je bila uporabljena tudi
elektrokemijska impedan~na spektroskopija. Kot del ocene mehanskih lastnosti nastalih plasti na povr{ini, so bile izvr{ene tudi
meritve trdote in preizkusi oprijemljivosti plasti na kovinski podlagi. Meritve trdote so bile izvr{ene z metodo Oliver & Phar,
medtem ko je bila oprijemljivost izmerjena s preizkusom razenja. Predlog primernih na~inov obdelave povr{ine je pomemben,
ker bo v prihodnje pomagal pri razvoju tehnolo{kih pogojev za dolo~ene parametere oksidne plasti, nastale na povr{ini
kovinskih vsadkov.
Klju~ne besede: Ti-6Al-7Nb (Ti67) zlitina, sol-gel, anodni oksid, preizkus razenja, nanotrdota, EIS, potenciodinami~na metoda
1 INTRODUCTION
The haemocompatibility of titanium alloys, including
the Ti-6Al-7Nb alloy, is increased by, e.g., modification
of the surface layer of cardiovascular implants with sur-
face-engineering methods. The methods used to modify
the surface layers must ensure the repeatability and
uniformity of their physical and chemical properties.1
The structure and chemical composition of the titanium
and titanium-alloy implant layer may be modified with
the use of various methods, among which the main ones
are mechanical, chemical, electrochemical and thermal
methods. Mechanical treatment techniques are used to
modify the surface topography. The properties of the
oxide layer after the application of these techniques are
difficult to control.2 Chemical methods include primarily
etching and passivation, which result in the formation of
a thin (<10 nm) oxide layer composed mostly of TiO2
and oxides of the alloying elements, as well as impurities
from chemical reagents.3–6 Repeatable layers with a fully
controlled thickness, microstructure and chemical com-
position are obtained with high-temperature treatments,
immersion in H2O2, alkaline etching, electropolishing,
anodic oxidation and vacuum treatments. However, the
Materiali in tehnologije / Materials and technology 50 (2016) 3, 323–329 323
UDK 67.017:669.295:669.148 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(3)323(2016)
method for increasing the haemocompatibility of tita-
nium and titanium-alloy surfaces, which is increasingly
often applied, involves using the sol-gel technique to
produce thin oxide coatings based on Si. The advantage
of this method is the low temperature at which the
coating is produced, which guarantees unchanged me-
chanical properties of the metal base. Moreover, this
method ensures the sol’s homogeneity, the possibility to
regulate polycondensate molecules, a large number of
metalorganic and inorganic metal salt compounds, used
as precursors, as well as the possibility to obtain multi-
ingredient coatings of high purity on different bases.7,8
Another important factor affecting the final quality of the
products that come into contact with blood is the proper
resistance of the modified surface to medical sterilisa-
tion. Presently, cardiovascular implants are usually steri-
lised with ethylene oxide (EO) and with pressurised-
water steam in an autoclave. The positive results of
already-published papers by the authors regarding the
assessment of the usefulness of the surface-layer modi-
fication processes involving anodic oxidation, as well as
the creation of a SiO2 layer with the sol-gel method,
enabled the selection of the most beneficial parameters
for the process.1,9–11 An analysis of the literature data
indicates that reducing the number of failed blood-
system disease treatments depends to a large extent on
the electrochemical stability of the surface layer under
the medical sterilisation conditions. Therefore, this
article evaluates the effects of steam and ethylene oxide
sterilisation processes on the physical and chemical
properties of the surface layer of the Ti-6Al-7Nb (Ti67)
alloy.
2 MATERIALS AND METHODS
The tested material was a titanium alloy Ti-6Al-7Nb
(Ti67) in the form of discs of diameter d = 14 mm and
thickness g = 2 mm. A number of surface-treatment
methods were applied to the samples, including the
following processes: grinding with the use of 1000- and
1200-grit sand paper, electrolytic polishing, the appli-
cation of layers with the sol-gel technique, and anodic
oxidation. The electrolytic polishing was conducted in a
solution based on chromic acid z (E-395 by POLIGRAT
Gmbh), with a current density i = 10–30 A/cm2. The
final stage of the surface treatment consisted of applying
layers with two different techniques: sol-gel and anodic
oxidation. In the case of the sol-gel method, a layer of
SiO2 was applied with the following process parameters:
v = 2.5 cm/min, T = 430°C, t = 60 min. The silica pre-
cursor used in the test was tetraethoxysilane Si(OC2H5)4,
TEOS, and tetramethoxysilane Si(OCH3)4, TMOS. The
remaining starting ingredients contained ethyl alcohol
(EtOH) and water.1,9 In the case of anodic oxidation a
layer of TiO2 was applied in an electrolyte based on
phosphoric acid and sulphuric acid (TitanColor by
POLIGRAT GmbH) at a potential of 90 V. Previous
studies conducted by the authors made it possible to
select the most favourable parameters, both for the
sol-gel technique and for the anodic oxidation.10,11
Next, the prepared samples were sterilised with ethy-
lene oxide and steam. The sterilisation with ethylene
oxide was conducted in a 12-h cycle of exposure to ethy-
lene oxide at 30 °C. After the process was completed, the
samples were ventilated for 2 h with the use of an
EOGas series steriliser from the Andersen Products com-
pany. The sterility assurance level (SAL) obtained during
the cycle was 10–6. The process was controlled with a
chemical and biological indicator, as well as an indicator
of exposure to the ethylene oxide control. The steam
sterilisation was conducted in a Basic Plus autoclave at
T = 134 °C, under a pressure of p = 2.1 bar for t = 12
min.
To evaluate the effect of ethylene oxide sterilisation
and steam sterilisation on the mechanical and electroche-
mical properties of the proposed Ti67 surface modifi-
cation, the authors suggested the following tests of the
mechanical properties: measurements of the adhesion of
the analysed layers to the base and their hardness.
Electrochemical tests included potentiodynamic and
impedance measurements.
First, as part of the mechanical properties’ tests, the
measurement of a layer’s adhesion to the base was
performed using the scratching method, with the use of
an open platform equipped with a Micro-Combi-Tester
from the CSM company, in accordance with the stan-
dard.12 The test consisted of making a scratch using a
penetrator – a Rockwell diamond cone – with a gra-
dually increasing normal force weighting the penetrator.
To assess the value of the critical force Lc, records of
variations in the acoustic emission signals, the friction
force and the friction coefficient were used, as well as a
microscopic observation with the use of an optical
microscope, and an integral component of the platform.
The tests were performed with an increasing weighting
force of 0.03–20 N, and with the following parameters:
weighting speed 10N/min, table movement speed 1.5
mm/min, and length of the scratch ~3 mm.
Later, measurements of the nanohardness of the
layers applied with the sol-gel method, and with the
anodic oxidation method, were conducted. The instru-
mental hardness measurement was performed with the
Oliver and Pharr method, using a Berkovich penetrator.
The speed of the increasing weighting and relieving
force was 0.40 mN/min. The measurement of the layer’s
nanohardness was made with the Micro-Combi-Tester
open platform from the CSM Instruments company,
where the weighting force of the penetrator was 0.20
mN.13
Subsequently, as part of the electrochemical proper-
ties testing, the resistance to pitting erosion was tested
with the potentiodynamic method, recording the polari-
sation curves. They were used as a base to determine the
values of specific parameters: the corrosion potential
324 Materiali in tehnologije / Materials and technology 50 (2016) 3, 323–329
W. WALKE et al.: PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO AND STEAM STERILIZATION
Ecorr (V) and the polarisation potential Rp (	cm2). At the
beginning of the testing, the value of the opening po-
tential EOCP was determined without any electric current.
Then, the anode polarisation curves were recorded. The
measurements started for the potential of Estart = EOCP –
100 mV, and the change of potential in the anodic
direction was at a speed of 0.16 mV/s, until the anodic
current density reached a value of i = 1 mA/cm2, or the
measurement range of 4V was reached.14
As part of the EIS testing, the impedance spectra of
the analysed corrosive systems were determined, and
then the obtained measurement data were adjusted to the
corresponding substitute systems. The impedance spectra
of the systems tested are presented on Nyquist diagrams
for the different frequencies as well as on Bode
diagrams. Also, the numerical values of the resistance R
were established, as well as the capacities C of the
analysed corrosive systems. The resulting spectra were
interpreted after being adjusted with the least-squares
method to the substitute electric systems. Based on the
results obtained, it was possible to characterise the impe-
dance of the phase boundaries, i.e., Ti-6Al-7Nb (Ti67) –
surface layer – blood plasma, with an approximation of
the impedance data using an electric model of a sub-
stitute circuit. The testing environment was an artificial
blood-plasma solution of T = 37±1 °C. The measure-
ments were performed using the AutoLab PGSTAT
302N measurement system, equipped with a FRA2 (Fre-
quency Response Analyser) module. The reference elec-
trode was a saturated calomel electrode SCE, type
KP-113, whereas the supporting electrode was a plati-
num electrode type PtP-201. The system used made it
possible to conduct tests within the frequency range 104
to 10–3 Hz. The voltage amplitude of the sinusoid stimu-
lating signal was 10 mV.15, 16
Materiali in tehnologije / Materials and technology 50 (2016) 3, 323–329 325
W. WALKE et al.: PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO AND STEAM STERILIZATION
Figure 1: Results of the adhesion tests of the sample Ti67+TiO2 (steam)
Slika 1: Rezultati preizkusov oprijemljivosti vzorca Ti67+TiO2 (para)
Table 1: The results of the adhesion of the layer on the Ti67 substrate
Tabela 1: Oprijemljivost plasti na podlagi iz Ti67
Failure of the layer
The value of registered indenter load Fn, N
Ti67+SiO2 Ti67+TiO2
inital state steam EO inital state steam EO
Measure-
ment 1
Delamination Lc1 2.01 1.57 1.54 6.64 2.98 3.14
Complete break Lc2 3.57 2.24 3.21 8.01 6.54 5.03
Measure-
ment 2
Delamination Lc1 2.48 1.33 1.89 3.06 3.14 2.36
Complete break Lc2 3.89 2.45 3.22 6.88 6.18 4.27
Measure-
ment 3
Delamination Lc1 3.55 1.41 2.41 4.33 3.52 2.86
Complete break Lc2 5.02 2.12 4.31 7.37 6.88 4.81
Average
Delamination Lc1 2.68 1.43 1.94 4.67 3.21 2.78
Complete break Lc2 4.16 2.27 3.58 7.42 6.53 4.70
Standard
deviation
Delamination Lc1 ±0.78 ±0.12 ±0.43 ±1.81 ±0.59 ±0.39
Complete break Lc2 ±0.76 ±0.16 ±0.63 ±0.56 ±0.35 ±0.39
3 RESULTS AND DISSCUSION
The test results for the adhesion of the analysed
layers to the base made of Ti-6Al-7Nb (Ti67) alloy are
presented in Table 1, Figures 1 and 2. It was found that
in the case of samples in the initial state the critical value
that caused the layer delamination, the external and the
internal delamination, was Lc2 = 4.16 N – Ti67+SiO2 and
Lc2 = 7.42 N – Ti67+TiO2. While using both steam and
ethylene oxide sterilisation, the critical force value was
reduced and for Ti67+SiO2 it was Lc2 = 2.27 N (steam),
Lc2 = 3.58 N (EO), whereas for Ti67+TiO2 it was Lc2 =
6.53 N (steam), Lc2 = 4.70 N (EO). Regardless of the
analysed sample type, an acoustic emission signal did
not occur during the test, which indicates that the
binding energy between the coating and the base was too
low. Moreover, no significant differences between using
steam sterilisation or ethylene oxide sterilisation were
found.
Furthermore, the hardness of the analysed layers was
tested. The test results are presented in Figures 3 and 4.
On the basis of the results obtained, an increase in the
hardness value following the steam sterilisation, as well
as the ethylene oxide sterilisation, compared to the initial
state was observed. The polarisation curves determined
for the samples with a Ti67(TiO2) layer are presented in
Figure 5, and for the samples with a Ti67(SiO2) layer in
Figure 6.
Regardless of the surface-preparation method or the
sterilisation technique, a hysteresis loop was not present
in the anodic range up to 4 V, which is a positive pheno-
menon, indicating the absence of pitting erosion. The deter-
mined values of the corrosive potential Ecorr and the polari-
sation resistance Rp for the individual variant of the samples
tested were as follows: Ti67+TiO2 – Ecorr = –112 mV,
326 Materiali in tehnologije / Materials and technology 50 (2016) 3, 323–329
W. WALKE et al.: PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO AND STEAM STERILIZATION
Figure 2: Results of the adhesion tests of the sample Ti67+SiO2 (steam)
Slika 2: Rezultati preizkusov oprijemljivosti vzorca Ti67+SiO2 (para)
Figure 4: Results of the nanohardness tests of the sample Ti67+TiO2
Slika 4: Nanotrdota vzorca Ti67+TiO2
Figure 3: Results of the nanohardness tests of the sample Ti67+SiO2
Slika 3: Nanotrdota vzorca Ti67+SiO2
Rp = 7480 k	 cm2; Ti67+TiO2 (steam) – Ecorr = –67 mV,
Rp = 3340 k	 cm2; Ti67+TiO2 (EO) – Ecorr = –217 mV,
Rp = 8340 k	 cm2; Ti67+SiO2 – Ecorr = –108 mV, Rp =
1460 k	 cm2; Ti67+SiO2 (steam) – Ecorr = –118 mV, Rp =
1850 k	 cm2; Ti67+SiO2 (EO) – Ecorr = –219 mV, Rp =
4290 k	 cm2, respectively. Figures 7 and 8 present the
impedance spectra recorded for the samples before and
after the sterilisation process for different variants of the
surface preparation. To analyse the experimentally deter-
mined impedance spectra for the corrosive system of
Ti67+SiO2, Ti67+SiO2 (steam), Ti67+SiO2 (EO), a sub-
stitute electric system was used, which indicates the
presence of a double layer (two time invariables visible
in the diagram), where Rs signifies the electrolyte resis-
tance, Rp is the electrolyte resistance in pores, and CPEp
is the capacity of the double layer (porous layer, surface
layer), while Rct and CPEdl are the resistance and capa-
city of the oxide layer. Using two constant phase
elements in the electric substitute circuit had an advan-
tageous effect on the quality of the adjustment of the
experimentally determined curves (Figure 9a and Table
2).
The impedance spectra obtained for the Ti67+TiO2
and Ti67+TiO2 (steam) samples were interpreted by
comparing them to the substitute electric system, which
indicates the presence of an anodic layer composed of
two sublayers:9–11 a compact internal layer and a porous
external one, composed primarily of titanium oxide TiO2
(Figure 9b). It is indicated by the presence of the War-
burg impedance, which in this case represents probable
oxygen transport to the alloy surface. In addition, the
CPEp element models the capacity of the surface mate-
rial sphere with a significant surface extension, while Rp
Materiali in tehnologije / Materials and technology 50 (2016) 3, 323–329 327
W. WALKE et al.: PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO AND STEAM STERILIZATION
Figure 7: Impedance spectra for the sample Ti67+SiO2: a) Nyquist
plot, b) Bode diagram
Slika 7: Impedan~ni spekter vzorca Ti67+SiO2: a) diagram Nyquist,
b) diagram Bode
Figure 6: Anodic polarisation curves of Ti67+SiO2
Slika 6: Krivulje anodne polatizacije Ti67+SiO2
Table 2: EIS analysis results
Tabela 2: Rezultati EIS-analize
Surface
Rs,
	 cm2
Rpore,
	 cm2
CPEpore Rp
k	 cm2
CPEp Rct
M	 cm2
CPEdl W
μ	 cm2Y0,	–1 cm–2 s–n n
Y0,
	–1 cm–2 s–n n
Y0,
	–1 cm–2 s–n n
Ti67(TiO2)
inital state 17 – – – 68 0,3580E-4 0,92 25,00 0,2306E-4 0,90 3
EO 18 54 0,5407E-6 0,93 1830 0,6381E-6 0,83 20,88 0,1455E-5 0,81 –
steam 17 – – – 42 0,2534E-6 0,96 0,96 0,2504E-6 0,90 35
Ti67(SiO2)
inital state 17 53 0,9823E-5 0,98 9,44 0,5294E-5 0,93 –
EO 18 – – – 52 0,7975E-5 0,92 11,87 0,1068E-4 0,87 –
steam 18 – – – 87 0,1213E-4 0,89 4,84 0,1524E-6 0,96 –
Figure 5: Anodic polarisation curves of Ti67+TiO2
Slika 5: Krivulje anodne polarizacije Ti67+TiO2
reflects the electrolyte resistance in this sphere of the
material (Table 2).
The impedance spectra obtained for the Ti67+TiO2
(EO) sample were adjusted to the substitute system,
which indicates the presence of three time invariables
(Figure 9c). The symbols in Figure 9c signify the
following: CPEpore – capacity of the surface sphere of the
material with a high level of surface extension (porous),
Rpore – electrolyte resistance in pores, CPEdl – capacity of
the double layer, Rct – charge-transfer resistance at the
phase boundary (it characterises the speed of the corro-
sive process), Cdl – capacity of the double layer, CPEP –
capacity of the passive layer (oxide), RP – passive (oxide)
layer resistance (Table 2).9–11
4 CONCLUSIONS
An important problem in the process of modelling
the performance properties of the implants used in car-
diology is the proper selection of the physical and
chemical characteristics of their surface. The physico-
chemical properties of the implant surface should be
adjusted to the characteristics of the human tissue
environment – in this case, to the blood environment.
The safety of the device’s use is also associated with the
need to follow the proper procedures preventing the
transfer of pathogenic microorganisms into the human
organism. The aim of these procedures is to remove and
effectively destroy the microorganisms, i.e., to obtain
sterile devices that meet the quality requirements defined
in the standards. For medical devices that come into
contact with blood, sterilisation with ethylene oxide or
pressurised-water steam are the most frequently used.
Therefore, accounting for the effect of these sterilisation
processes on the properties of the analysed surface layer
will enable their complete characterisation.17
The conducted impedance tests revealed that on the
surface of the Ti-6Al-7Nb alloy, modified through ano-
dic oxidation, a porous layer (TiO2) is found, in which
parallel channels with an ionic conduction are formed. It
is a layer that forms as a result of diffusion processes,
which is indicated by the presence of the Warburg impe-
dance. These processes intensify during the activity of
pressurised-water steam in the sterilisation process. As a
consequence, it leads to the partial dissolution of TiO2,
as indicated by the lower value of the ionic transfer
resistance Rct. Sterilisation with ethylene oxide positively
increases the Rct value. This phenomenon may be caused
by the increased oxygen concentration near the surface
during the process, and the formation of an additional
oxide layer. Diffusion processes associated with the
partial dissolution of oxide in the solution were not
observed in the samples with an applied SiO2 layer. This
layer appears to be more compact than the TiO2. Regard-
less of the sterilisation method used, no changes in the
properties of the layer were found. Only, as was the case
with the samples undergoing anodic oxidation, a reduc-
tion in the ion-transfer resistance Rct was observed. The
conducted tests for layer adhesion to the base revealed a
slight reduction in the adhesive force of the sterilised
layers versus the samples in the initial state. The tests de-
monstrated the better adhesion of TiO2 than SiO2 to the
Ti-6Al-7Nb alloy base. The hardness testing conducted
in the study revealed that pressurised steam does not
cause significant changes to the hardness of the TiO2 or
SiO2, whereas sterilisation with ethylene oxide results in
an increased hardness of the SiO2 and a significant
reduction in the hardness of the TiO2. This phenomenon
328 Materiali in tehnologije / Materials and technology 50 (2016) 3, 323–329
W. WALKE et al.: PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO AND STEAM STERILIZATION
Figure 9: Physical models of an electrical equivalent system of the
corrosion system metal – solution9–11
Slika 9: Fizikalni model elektri~nega ekvivalentnega sistema korozij-
skega sistema kovina-raztopina9–11
Figure 8: Impedance spectra for the sample Ti67+TiO2: a) Nyquist
plot, b) Bode diagram
Slika 8: Impedan~ni spekter vzorca Ti67+TiO2: a) diagram Nyquist,
b) diagram Bode
may cause increased porosity of the TiO2 layer, resulting
from the effect of ethylene oxide, as demonstrated in the
EIS tests. The SiO2 layer also reacts when in contact
with ethylene oxide. Its hardness significantly increases,
which may be the cause of the formation on its surface of
an additional oxide layer, based on Ti and Si, revealing
better mechanical properties. To sum up, the conducted
study of the modified surfaces of the Ti-6Al-7Nb alloy
samples with the TiO2 and SiO2 layers demonstrated that
the medical sterilisation process affects the physical and
chemical properties of these layers. The selection of the
proper surface layers should also depend on the manner
and the method of sterilisation.
Acknowledgements
The project was funded by the National Science
Centre, allocated on the basis of decision No. 2011/03/
B/ST8/06499.
5 REFERENCES
1 W. Walke, Z. Paszenda, M. Basiaga, P. Karasiñski, M. Kaczmarek,
EIS study of SiO2 oxide film on 316L stainless steel for cardiac
implants. Information Technologies in Biomedicine, 4, Advances in
Intelligent Systems and Computing, 284 (2014), 403–410
doi:10.1007/978-3-319-06596-0_38
2 N. Ibris, J. C. M. Rosca, EIS study of Ti and its alloys in biological
media, Journal of Electroanalytical Chemistry, 526 (2002), 53–62,
doi:10.1016/S0022-0728(02)00814-8
3 J. Y. Park, J. E. Davies, Red blood cell and platelet interactions with
titanium implant surfaces, Clinical Oral Implants Research, 11
(2000) 6, 530–539, doi:10.1034/j.1600-0501.2000.011006530.x
4 J. E. Ellingsen, Pre-treatment of titanium implants with fluoride im-
proves their retention in bone, Biomaterials, 12 (1991) 6, 593–596,
doi:10.1016/ 0142-9612(91)90057-H
5 M. Basiaga, Z. Paszenda, A. Kajzer, The effect of EO and steam ste-
rilization on mechanical and electrochemical properties of titanium
Grade 4, Mater. Tehnol., 50 (2016) 1, 153–158 doi:10.17222/mit.
2014.241
6 C. Sitting, G. Hahner, A. Marti, M. Textor, N. D. Spencer, R. Hauert,
Mechanoelectrochemical synthesis of porous Ti-based nanocompo-
site biomaterials, Journal of Materials Science: Materials in Medi-
cine, 10 (1999), 191–198
7 S. Shibli, S. Mathai, The role of calcium gluconate in electroche-
mical activation of titanium for biomimetic coating of calcium
phosphate, J. Mat. Sci., 19 (2008), 2971–2981
8 P. Karasiñski, J. Jaglarz, M. Reben, E. Skoczek, J. Mazur, Porous
silica xerogel films as antireflective coatings. Fabrication and
characterization, Optical Materials, 33 (2011), 1989–1994
9 M. Basiaga, Z. Paszenda, W. Walke, P. Karasiñski, J. Marciniak,
Electrochemical impedance spectroscopy and corrosion resistance of
SiO2 coated cpTi and Ti-6Al-7Nb alloy, Information Technologies in
Biomedicine, 284 (2014), 411–420, doi:10.1007/978-3-319-06596-
0_39
10 W. Walke, M. Basiaga, Z. Paszenda, Tests of mechanical properties
of SiO2 layers for implants used in vascular system, Engineering of
Biomaterials, 124 (2014), 36–41
11 A. Kajzer, W. Kajzer, J. Dzielicki, D. Matejczyk, The study of physi-
cochemical properties of stabilizing plates removed from the body
after treatment of pectus excavatum. Acta of Bioengineering and
Biomechanics, 2 (2015), 35–44 doi:10.5277/ABB-00140-2014-02
12 J. von Stebut, Multi-mode scratch testing – a European standards,
measurements and testing study, Surface and Coatings Technology,
200 (2005), 346–350, doi:10.1016/j.surfcoat.2005.02.055
13 EN ISO 14577-1 Metallic materials-Instrumented indentation test for
hardness and materials parameters-Part1: Test method
14 ASTM F2129-08 Standard Test Method for Conducting Cyclic
Potentiodynamic Polarization Measurements to Determine the
Corrosion Susceptibility of Small Implant Devices
15 M. Kaczmarek, W. Walke, Z. Paszenda, Application of electroche-
mical impedance spectroscopy in evaluation of corrosion resistance
of Ni-Ti alloy, Electrical Review, 12b (2011), 74–78
16 M. Kiel-Jamrozik, J. Szewczenko, W. Walke, J. Marciniak, Zastoso-
wanie EIS do oceny w³asnoœci fizykochemicznych modyfikowanego
powierzchniowo stopu Ti-6Al-4V ELI, Electrical Review, 12b
(2012), 232–235
17 W. Walke, J. Przondziono, J. Szade, Electrochemical and XPS
studies of AISI 316L after Development of warm forging method for
magnesium alloyEuropean Cells and Materials, 26 (2013) 6, 117
Materiali in tehnologije / Materials and technology 50 (2016) 3, 323–329 329
W. WALKE et al.: PHYSICOCHEMICAL PROPERTIES OF A Ti67 ALLOY AFTER EO AND STEAM STERILIZATION