Volume 21 Preprint 69
Influence of surface treatment on corrosion and other electrochemical properties of titanium
J. Hlinka, S. Lasek, R. Chlebus
Keywords: titanium, colouring, corrosion properties, polarization biocompatibility
Titanium is widely used across many medicinal fields like implantology or surgery. Electrochemical colouring of titanium tools or implants is one of the common ways how to differentiate different sizes or types of each application. Titanium grade 4 plates 50 x 20 x 0.1mm were tested to obtain their electrochemical and other technological properties. Colouring process was done using potential of 15, 30, 45, 60 and 75 Volts for 5s in 1 wt. % citric acid in demineralized water solution. Contact angle of coloured surface was measured by sessile drop method. Electrochemical impedance spectroscopy was used for determination of some surface layers parameters like capacitance or resistance. Potentiodynamic polarization was used for corrosion testing of this samples and corrosion potential, polarization resistance or corrosion rate of each sample was found using Taffel or Stern method. There was found that anodization process before colouring decreases significantly corrosion potential. There was also found that higher potential used for colouring results in higher polarization resistance but also decreases corrosion potential. Titanium colouring at 75V results into lowest corrosion rate under 1nm/year and the most noble corrosion potential.
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Influence of surface treatment on corrosion and other
electrochemical properties of titanium
Josef Hlinka1*, Stanislav Lasek1, Radek Chlebus2
of Materials Engineering, VSB-Technical University of Ostrava, 17. listopadu
2172/15708 00 Ostrava-Poruba, Czech Republic
2Department of Physics, VSB-Technical University of Ostrava, 17. listopadu 2172/15708 00
Ostrava-Poruba, Czech Republic
Titanium is widely used across many medicinal fields like implantology or surgery.
Electrochemical colouring of titanium tools or implants is one of the common ways how to
differentiate different sizes or types of each application. Titanium grade 4 plates 50 x 20 x
0.1mm were tested to obtain their electrochemical and other technological properties.
Colouring process was done using potential of 15, 30, 45, 60 and 75 Volts for 5s in 1 wt. %
citric acid in demineralized water solution. Contact angle of coloured surface was measured
by sessile drop method. Electrochemical impedance spectroscopy was used for
determination of some surface layers parameters like capacitance or resistance.
Potentiodynamic polarization was used for corrosion testing of this samples and corrosion
potential, polarization resistance or corrosion rate of each sample was found using Taffel or
Stern method. There was found that anodization process before colouring decreases
significantly corrosion potential. There was also found that higher potential used for
colouring results in higher polarization resistance but also decreases corrosion potential.
Titanium colouring at 75V results into lowest corrosion rate under 1nm/year and the most
noble corrosion potential.
Keywords: titanium, colouring, corrosion properties, polarization biocompatibility
During last couple decades CP titanium or titanium alloys became very popular in medicinal
and other fields where combination of good mechanical properties, low weight and high
corrosion resistance is needed. As there are large variety of titanium implants and tools
used in medicine, especially in implantology, there is a need of quick differentiation
between them as they can be similar sized or shaped. Each tool or application can be simply
marked by different colour, which allow one to distinguish proper tool quickly. As the
electrochemical colouring process of titanium is very simple and no hi-tech instrument are
needed, it can be easily used in implant postproduction processes or as one of steps in
implants manufacturing , .
On the other hand, there are strict requirements on medical implant or other application
regard to their corrosion properties as they are closely connected to ion release into
surrounding tissue during their lifetime. Localized corrosion damage of coloured surface
can also act as a stress concentrator, where crack can nucleate. From this point of view,
colouring process should also increase corrosion properties .
During electrochemical colouring process, character of protective passive layer on surface is
significantly change, especially in case of titanium. Microstructure of the layer actively react
with photon light, when photon of each wave length can be absorbed or reflected. Final
colour of titanium surface is determinated by the particular interaction between oxide layer
and light and can be judged easily by comparative method using standards or by
reflectometry methods . Electrochemical process of titanium colouring is called
anodization and even slight change of anodization voltage can highly affect shade or colour
of anodized surface . Change of surface layer characteristics affects surface energy,
which can result into change of surface contact angle. Electrical parameters of the layer can
be also changed, which can be studied by electroimpedance spectroscopy.:
Material and Chemicals
CP titanium grade 4 was used for these particular experiment, as this grade is commonly
used in implantology for its valuable mechanical and corrosion properties , . Large
sheet of 0,1mm thickness supplied by Bibus Metal was cut into smaller 50 ˣ 20 mm pieces,
which were rinsed by demineralized water and cleaned by acetone in ultrasonic bath.
Microstructure of studied material is illustrated in Fig. 1. For preparation of anodization
solution citric acid (C6H8O7, Sigma-Aldrich) was used. There was NaCl from Sigma-Aldrich
used for preparation of solution for corrosion and electrochemical tests. For contact angle
measurement high purity demineralized water was used.
Fig. 1. Microstructure of CP Ti Grade 4 used as a
Devices and Experimental Methods
There was a 1% solution of citric acid in water prepared for anodization solution. After each
sample was marked, it was connected as working electrode (anode) to direct current supply
(“Matrix MPS-7162”) and immersed into solution electromagnetically stirred at 300 RPM.
There was a platinated mesh used as counter electrode (cathode). Distance between sample
and counter electrode was ~ 3 cm to create homogenous electric field around tested
surface. Anodization process took only 5s, during which shade of titanium substrates was
significantly changed from its shiny metallic colour. Systematic arrangement of anodization
cell is illustrated in Fig. 2.
After anodic colouring samples were rinsed by demineralized water and dried by warm air.
After that colour was assessed using comparative method according to RAL standard
samples and by ASTM D2805 reflectometry (“S2000, Ocean Optics”) method ,  . There
are coloured RAL standards compared with coloured samples and final colours code and
name is given to the each sample. Reflectometry method is based on evaluation of intensity
of reflected light when intensity of each single wave length is evaluated separately.
Fig. 2. Arrangement of anodization cell
After that contact angle and surface energy was tested by sessile drop method using “See
system device” with integrated software according to ASTM D7334 standard. 2 µl drops of
high purity water were used during this experiment.
After that samples were mounted into corrosion cell, which were filled with physiological
solution (0,9% NaCl). 1 Hour time gap was used for stabilization of corrosion reaction and
corrosion potential. Potenciostat “Voltalab PGZ 100” equipped by “Voltamaster 10” software
were used for both electrochemical testing methods. The corrosion tests were
performed using a three electrode set-up, with extra pure carbon rod and saturated
calomel electrode (SCE) as counter and reference electrodes, respectively. All EIS
measurements were performed in potentiostatic mode at the open-circuit potential (OCP).
The amplitude of the perturbation signal was 10 mV and the investigated frequency range
was from 100 kHz to 1 Hz with an acquisition rate of 10 points per decade. All polarization
measurements were started after the non-destructive EIS tests. Start potential was 100mV
below OCP, polarization rate was 1mV/s and polarization was ended when potential of
working electrode reached value +500 mV vs. SCE.
Samples after anodization colouring process are shown in Fig. 3.After the surface was
cleaned and dried there were graphic dependences of intensity of reflected light on its wave
length obtained by reflectometry method. Each sample is characterized by one curve. All
the curves were placed into one graph for better orientation and are illustrated in Fig. 4.
Curve’s colours match with real colours of samples. Another step was to compare coloured
sheets with RAL standards. This was made by eye observation. RAL codes for colours
obtained by using different voltage are listed in Table 1.
Fig. 3. Anodic coloured samples
Fig. 4. Reflectometric curves of coloured samples
Tab.1Anodized samples colours classification according RAL standard
Images of drop on studied surface were captured and analyses respectively. Mean values
and standard deviations are listed for each anodization voltage separately in Table 2. There
were 10-12 droplets analyses on each sample as only limited parts of surfaces were eligible
for this test-best results are obtained when droplets are analysed near to the edge of the
sample. Surface energy of each coloured specimen was calculated by Li-Neumann method
Tab. 2 Anodized samples contact angles of water droplets
Electroimpedance spectroscopy (EIS) curves were measured before polarization tests as this
method is considered as very friendly to the surface and does not affect it characteristics
. After electroimpedance curves were obtained, equivalent electrical circuit were found.
This circuit simulates electrochemical behaviour of coloured surface layers. EIS curves and
equivalent electric circuit are illustrated in Fig. 5. These curves can be used for so called
circuit fitting, when parameters of each circuit element can be assessed.
During potenciodynamic polarization test dependence of current density on applied
potential was recorded for each sample, for easier orientation were these curves combined
into one graph, which is illustrated in Fig. 6. There were parameters like corrosion
potential, corrosion rate, polarization resistance, etc., calculated from Taffel region on
polarization curve. Values of these parameters are listed in Table 3. Taffel region can be
found around area where current is very close to zero value (V-like shape region on
polarization curve) .
Fig. 5. Electroimpedance spectroscopy curves
Fig. 6. Polarization curves
Tab. 2 Values of corrosion parameters for samples coloured at different voltages
Corrosion potential vs. SCE
Polarization resistance Rp
The colouring of titanium by anodization is produced by means of the intervening action of
the reflecting light from the titanium samples surface covered with mixture of titanium rich
oxides and hydroxides film and the reflecting light of interface between this film and matrix
of titanium substrate . When titanium substrate is immersed in solution and electric
current passes through, oxygen is produced on anodized substrate surface. Molecules of
oxygen intermediately bond with titanium atoms forming oxides, which structure is
primarily determined by applied voltage and activity/chemical composition of solution.
Different microstructure and thickness of oxide film causes variation of refractive &
reflective indexes or luminous flux, which results into changes of shades or colours of
anodized surfaces . There were various compositions of anodizing solutions pre-tested
before this particular research. It was found that solutions containing organic acids
produces more pronounced and brighter colours. Coloured layers are also more compact
with better adhesive connection to the substrates. When oxidative inorganic acids were
used in solution composition, there were blisters, layers delamination and other smaller or
lager imperfections observed in emerging coloured layers. This is why solution of citric acid
was used for this particular experiment. Key to homogenously colourisation is also clean
surface without dust particles or grease residues.
Reflectometry method was used for recording of reflected spectres of light, which differed
for each wave length. As shown in Fig. 4, there is obvious shift of maximal values of
reflected light to higher wave lengths for higher applied voltage. According to that there is
and assumption that surfaces anodized at higher voltage preferably absorb light radiation
of longer wave lengths, on the other hand more light of shorter wave lengths is reflected
. Unfortunately curve of sample anodized at 75V doesn’t correspond to this
affirmation-its minimum value of reflectance is occur at ~460 nm, which is similar also for
15V anodization. According to previous research there is another assumption that says
increasing of anodization voltage produce periodically repetition of colours, but their shade
become more bright and saturated at higher voltages . There was also found that colours
is not determinated by time of anodization, but only by applied voltage, it means that
colours are not produced by light intervention, but by absorption of particular wavelengths
from light spectrum. It was confirmed that very long anodization times results into surface
blistering and deadhesion of anodized layer .
Titanium surface colouring became very popular especially for marking of implants for their
easier and reliable differentiation. For better orientation each implant set is accompanied by
list of sizes, and each size is marked with different colours. This is why it is so important
to find which anodization voltage produces chosen colours. These colours are can be found
at RAL list of standards under its specific name and code. This standard is used
internationally and is going to become part of ASTM soon . As illustrated in Fig. 3, 15V
and 75V anodization produced yellow/brown colours shades and 30-60V anodization
resulted mostly into blueish shades.
There was only non-significant (statistically irrelevant) differences of wettability found for
between all coloured samples. Mean value of contact angles for all surfaces was ~ 81°. As
all the surfaces were shiny and mirror like, effect of roughness was not considered into
calculation. The value of standard deviation was also insignificant as surface colouring was
very homogenous without any macro or microdefects and contact angle was very similar for
all evaluated droplets. As published earlier , fibroblast bonds to implants and grown on
implants surface the best if contact angle of exposed surface is 60-80°. The wettability of
tested samples predetermines titanium with coloured surface for construction of short and
medium term implants, as there is need to not bond with the bone strictly. There is a
prediction of fibroblast layer growing of surface of coloured titanium implants which allow
them to be easily removed after proper time of service. This is an example internal bones
screws or fixators which are commonly removed when damage bone is restored completely
. If the contact angle will be significantly lower (close to zero value), grow of osteoblast
will be preferred on the surface which would make the titanium implants difficult for
removing and there is high probability to damage surrounding tissue during the process of
its removal . The surface energy of the implant surface obtained by Li-Neumann
method  has a significant impact on tissue integration process. Mean value of free
surface energy obtained by testing using water of high purity was ~ 34,5mJ/m2.
Effect of anodization on electrochemical properties was studied by electroimpedance
spectroscopy to find curves of electrical impendence. Characteristic impedance curves as
shown in Fig. 5 shows the impedance shift for each anodization voltage. There is significant
difference between 15V and rest of curves. There is an assumption that anodization at low
voltage produces very compact surface layers with highly organized titanium oxide in its
microstructure. This layer contain less microdefects and behaves like highly effective
electric insulator . As there is large amount of oxygen molecules developed in
anodization process at higher voltage, there in not enough time and driving force to react
with titanium atoms and form into deffectless structure. Therefor the samples anodized at
higher voltage shows different shape of impedance curve as coloured layer on their surface
probably contains high amount of morphologic defects .
Potentiodynamic polarization in physiological isotonic solution proved differences between
corrosion properties of samples anodized at different voltage. There was significant relation
of anodization voltage and corrosion potential observed. It was found that higher colouring
voltage produce surface layers with more noble corrosion potential, -340 mV (15V) vs. 193 mV (75V). Values of polarization resistance of surface layers produced at higher
voltage is also higher (67 kΩ*cm2 for 15V vs. 95 kΩ*cm2 for 75V). More noble corrosion
potential of surface decreases risk of bimetallic corrosion if connected to another material.
Higher polarization resistance finally results into lower corrosion rate if corrosion damage
occurs in case of bad implant design. More noble corrosion potential also shows that higher
voltage creates more stable oxide layer on surface ,. As highly positive can be
colouring anodization evaluated regard to corrosion rate of the samples. Even maximal
corrosion rate for implants considered as “limit” is 0,13mm/year, coloured samples showed
significantly lower corrosion rate . Potentiodynamic test proved, that surface coloured
at 15V will corrode 2,1 nm/year and 75V sample will corrode as little as 0,7nm/year. This
if far below the corrosion rate limit for implants and prosthesis. According to these results,
titanium colouring may be highly recommended as a post-manufacturing surface treatment
to increase final application corrosion properties , .
These research proved, that electrochemical anodization colouring of titanium alloy in
solution of citric acid produces colours varying from yellow/brown to green/blue colour
shades. These colours may be compared with RAL standards. Contact angle of coloured
surface predetermines this technology in implants manufacturing as there is assumption of
fibroblast (cells of soft tissues) cells grown on surface and bond to it. Electroimpedance
spectroscopy test prove there are differences in electrical parameters of surfaces produced
at different voltage. This may be caused by different microstructure of titanium dioxide
formed on the top of studied samples. Corrosion properties of studied specimens were
excellent as corrosion rate was far (~4-5 numerical orders) below standardized maximum.
It was also found that higher voltage used for anodization produces surface with more
noble corrosion potential.
Aknowledgement This paper was prepared with a contribution of the projects “SP2018/70
Study of relationships between the technology and processing of advanced materials, their
structural characteristics and utility properties” and “SP2018/60 Specific research in the
metallurgical, materials and process engineering”.
Producing hip implants of titanium alloys by additive manufacturing, A. Popovich, V.
Sufiiarov, I. Polozov, E. Borisov, and D. Masaylo, Int. J. Bioprinting, 2, no. 2, 2016.
Colouring titanium alloys by anodic oxidation, G. Napoli, M. Paura, T. Vela, and A. Di
Schino, Metalurgija, 57, pp. 1–2, 2018.
Titanium corrosion mechanisms in the oral environment: A retrieval study, D. C.
Rodrigues et al., Materials (Basel)., 2013.
Effect of anodic oxidation parameters on the titanium oxides formation, M. V.
Diamanti and M. P. Pedeferri, Corros. Sci., 2007.
Influences of Electrolyzing Voltage on Chromatics of Anodized Titanium Dentures, Z.
M. Yan, T. W. Guo, H. B. Pan, and J. J. Yu, Mater. Trans., 2002.
Titanium as a Biomaterial for Implants, C. Oldani and A. Dominguez, Recent
Advances in Arthroplasty, 2012.
Standard Specification for Titanium and Titanium Alloy, ASTM Standard B348, ASTM
B. Stand., 03, pp. 1–9, 2013.
Standard Test Method for Determining the Hiding Power of Paint by Visual Evaluation
of Spray Applied Coatings, ASTM, 2015.
Databases for spectral color science, O. Kohonen, J. Parkkinen, and T. Jääskeläinen,
Color Res. Appl., 2006.
 Methods for the calculation of surface free energy of solids, M. Żenkiewicz, J. Achiev.
Mater. Manuf. Eng., 2007.
, Electrochemical Impedance Spectroscopy Study of the Adsorption Behavior of
Bovine Serum Albumin at Biomimetic Calcium – Phosphate Coating, Q. Mohsen, S. A. FadlAllah, and N. S. El-Shenawy, Int. J. Electrochem. Sci, 2012.
Evaluation of corrosion rate from polarisation curves not exhibiting a Tafel region,H.
J. Flitt and D. P. Schweinsberg, Corros. Sci., 2005.
Anodic Film Growth of Titanium Oxide Using the 3-Electrode Electrochemical
Technique: Effects of Oxygen Evolution and Morphological Characterizations,Z. J. Liu, X.
Zhong, J. Walton, and G. E. Thompson, J., Electrochem. Soc., 163, 3, pp. E75–E82, 2016.
Anodic coloring of titanium and its alloy for jewels production,M. V. Diamanti, B. Del
Curto, V. Masconale, C. Passaro, and M. P. Pedeferri, Color Res. Appl., 37, 5, pp. 384–390,
Corrosion Behaviour of the Anodic Oxide Film on Commercially Pure Titanium in
NaCl Environment,Z. Liu, X. Liu, U. Donatus, G. E. Thompson, and P. Skeldon, Int. J.
Electrochem. Sci, 9, pp. 3558–3573, 2014.
ASTM Works on Standard to Specify Color | www.astm.org. [Online]. Available:
 Influence of surface wettability on competitive protein adsorption and initial
attachment of osteoblasts, J. Wei et al., Biomed. Mater., 4, 4, 2009.
., Biofunctional porous anodized titanium implants for enhanced bone regeneration,I.
K. Shim et al, J. Biomed. Mater. Res. - Part A, 102, 10, pp. 3639–3648, 2014.
Technical difficulties in hardware removal in titanium compression plates with
locking screws,M. Ehlinger, P. Adam, P. Simon, and F. Bonnomet, Orthop. Traumatol., Surg.
Recent progress in the determination of solid surface tensions from contact
angles,H. Tavana and A. W. Neumann, Advances in Colloid and Interface Science. 2007.
Titanium dioxide nanomaterials: Synthesis, properties, modifications and
applications,X. Chen and S. S. Mao, Chemical Reviews. 2007.
Corrosion characterization of titanium alloys by electrochemical techniques,S. L. De
Assis, S. Wolynec, and I. Costa, Electrochimica Acta, 2006.
Corrosion properties of anodized titanium, J. Hlinka, S. Lasek, and N. Faisal, Acta
Metall. Slovaca, 23, 3, pp. 270–275, 2017.
Corrosion resistances and passivation of powder metallurgical and conventionally
cast 316L and 2205 stainless steels,W. Fredriksson, D. Petrini, K. Edström, F. Björefors, and
L. Nyholm, Corros. Sci., 67, pp. 268–280, 2013.
Corrosion in titanium dental implants/prostheses - A review, R. Bhola, S. M. Bhola, B.
Mishra, and D. L. Olson, Trends Biomater. Artif. Organs, 2011.
Biomedical Implants: Corrosion and its Prevention - A Review, G. Manivasagam, D.
Dhinasekaran, and A. Rajamanickam, Recent Patents Corros. Sci., 2, 1, pp. 40–54, 2010.
Spinal fixation device: A 6-year postimplantation study,M. Mohanty, S. Baby, and K.
V. Menon, J. Biomater. Appl., 18, 2, pp. 109–121, 2003.