2013. Vol.1, No.2, 32-36
Published Online October 2013 in SciRes (http://www.scirp.org/journal/ad) http://dx.doi.org/10.4236/ad.2013.12002
Copyright © 2013 SciRes.
Deposition of Transparent, Hydrophobic TiO2 Film for the
Protection of Outdoor and Marine Cultural Heritage Assets
Fabio Stranges1,2, Marianna Barberio1,2*, Pasquale Barone1,2, Andrea Abenante1,
Andrea Leuzzi1, Peppino Sapia1,2, Fang Xu1, Assunta Bonanno1
1Physics Department, University of Calabria, Cosenza, Italy
2Biology, Ecolgy and Earth Science Department, University of Calabria, Cosenza, Italy
Received June 28th, 2013; revised August 1st, 2013; accepted August 10th, 2013
Copyright © 2013 Fabio Stranges et al. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the
original work is properly cited.
In this work we present two new methods to obtain TiO2 transparent coverage and to impart superhydro-
phobicity to stones and ceramics surface of monuments. The first method, adapted for small artifacts eas-
ily transportable in restoration laboratory, consists of a simple evaporation of Ti directly on ceramic sur-
face in a controlled oxygen atmosphere. The second method consents the coverage of large surface di-
rectly in situ. The TiO2 is evaporated on a salt surface with desired dimensions and then deposited on ce-
ramic surfaces. In both cases the dioxide layers are transparent, don’t damage the ceramic surfaces and are
easily removable. In fact, the dioxide layer can be removed simply by 30 minutes of laser ablation process.
Keywords: Marine Artifacts; Photocatalic Activity; Protection of Cultural Heritage
In recent decades several scientific efforts have been made to
fabricate superhydrophobic surfaces by using numerous tech-
niques and methods, for example, plasma treatment (Manoudis,
2009; Chen, 1999; Coulson, 2000; Tserepi, 2006), photolitho-
graphy (Oner, 2000; Gao, 2006) and sol-gel (Shirtcliffe, 2003;
Mahltig, 2003; Hikita, 2005). Water repellent coatings can be
important in many applications including, for example, the
prevention of icing in cold weather, the promotion of self-
cleaning process induced by rainwater on outdoor surfaces, the
prevention of clotting in artificial blood vessels, the decrease of
corona activity developed in conductors of transmission lines
under rainy conditions, the production of waterproof and stain
resistent textiles, and the reduction of friction in water (Ma-
noudis, 2009; Gao, 2006; Zorba, 2008). One of the applications
of the superhydrophobic coatings is their use as surface protec-
tive barriers for the preservations and conservation of ceramic
and stone monuments. The most important degradation factor
of outdoor, immovable cultural heritage is the rainwater which
can causes stone deterioration through cycles of freezing and
thawing inside the pores of the stones or by intraporous cry-
stallization of the salts transferred by the water (Manoudis,
2009; Manoudis, 2008). For this reason, the application of hy-
drophobic coatings has been suggested for the surface pro-
tection of outdoor cultural heritage assets (Manoudis, 2009;
Manoudis, 2008). Moreover several monuments are collocated
in marine sites and cannot be removed from seabed, in these
conditions the corrosion caused by marine water and microor-
ganism can causes serious problems to conservation. Recently
Manoudis et al. described (Manoudis, 2009; Manoudis, 2008) a
simple method that can be used to impart superhydrophobicity
to different stones surfaces (used in restoration of the castle of
Prague). This method is based on the dispersion of nanoparticle
in a polymeric solution that can be sprayed on the substrate.
The resulting composite polymer-nanoparticle film exhibits
However, this method cannot be applied in marine archeo-
logical sites (in underwater conditions the spray process is im-
possible and the dispersed particles can create environmental
pollution). Moreover, in marine archeological sites the cover-
age of ceramic and stone must have an antibacterial action to
inhibit the deterioration caused by the attack of marine micro-
organisms. In this optics, a surface coverage by TiO2 substrate,
with its phocatalytic oxidation properties (Liu, 2005; Naeem,
2010), can solve both the problems: idrophobicity and antibac-
Here we describe two simple methods to obtain TiO2 cover-
age applicable in air and in marine water conditions. The ob-
tained coverages are transparent (so it don’t modify the artistic
properties of monument) and hydrophobic, don’t damage the
ceramic surface and are easily removable by a simple cleaning
process of laser ablation (Stranges, 2013).
Materials and Methods
All the experiments were conducted on several ceramic frag-
ments obtained from a “Carosello” (Gattuso, 2012), a structural
hollow element made of clay, placed in arches, in domes or
even and in the walls of buildings such as churches and houses,
with the function lighten the structures (the specific “carosello”
used in these experiments come from a site in Calabria: the
Sanctuary of “Madonna del Buonconsiglio” in san Giacomo di
Cerzeto, Cosenza, Italy dated back to 1844 ± 11). The frag-
F. STRANGES ET AL.
Copyright © 2013 SciRes. 33
ments have dimensions of about 1 cm × 2 cm and a thickness of
about 2 cm.
We implement two different TiO2 coverage process. One,
applicable to little fragments of ceramic artifacts, contemplates
a titanium evaporation in ultra high vacuum chamber, while the
second, applicable either in laboratory or in marine water, is a
process of deposition of TiO2 layer, previously evaporated on a
salt, on ceramic surface.
The direct evaporation process was conducted in an ultra
high vacuum chamber with a base pressure of 1 × 10−9 mbarr.
Ti was evaporated, in a controlled oxygen atmosphere (the
partial pressure of oxygen in UHV chamber is fixed at 5 × 10−6
mbar), by heating an outgassed Mo boat ﬁlled with Ti crystal
through a current of 60 A. The evaporation time ranged from 1
h to 7 h. The Titanium and oxygen atoms react on ceramic
surfaces forming a TiO2 layer (the formation of dioxide was
confirmed by XPS data) with a thickness which increases with
exposure time. Figure 1 shows samples obtained with exposure
times of 1, 2, 3 and 4 hours, the sample coloration is unchanged
after 1 h of exposure while becomes darker with time evapora-
tion, clearly indicating the formation of TiO2 layers with a
thickness greater than 30 mm (the dioxide coloration is strictly
related to layer thickness and only for dimensions greater than
30 microns the layer is colored and visible to the naked eye).
The deposition process includes two phases: a direct evapo-
ration on a water soluble salt surface (NaCl as example) using
the process in UHV previous described and then the deposition
of TiO2 layer on ceramic surface on archeological site (air or
marine water). The salt was deposed on Aluminum foil and
then inserted in UHV chamber where an evaporation process of
1 h deposes a TiO2 transparent layer. Following the TiO2 layer
is covered by a silicon adhesive layer (to favorite the ceramic
adhesion) and then sealed by aluminum foil to the application
on ceramic. The salt surface and the aluminum foil were eli-
minated after deposition simply dissolving the salt with
water. In this work we use as soluble salt the NaCl and the
Na2B4O7·10H2O obtaining the same results.
This process consent to prepare TiO2 layer with desired di-
mensions in a laboratory and the application on ceramic surface
directly in situ. Figure 1 shows the ceramic covered by TiO2
deposed via NaCl salt, the dioxide layer is transparent and not
modifies the sample coloration.
All the TiO2 covered sample are analyzed by X-ray photo-
electron spectroscopy (XPS), X-ray fluorescence spectroscopy
(XRF) and by contact angle measurements to testing the hy-
XPS measurements were conducted in an ultra-high vacuum
(UHV) chamber equipped for standard surface analysis with a
pressure in the range of 10−9 torr. Non monochromatic Mg-K
X-ray (hν= 1253.64 eV) was used as excitation source. The
Exposure 1 hExposure 4 h
Exposure 2 h
Exposure 3 h
Deposition via NaCl
After Laser Ablation
Images of “Carosello” fragments after Ti evaporation, after TiO2 evaporation via NaCl and after laser ab-
F. STRANGES ET AL.
Copyright © 2013 SciRes.
XPS spectra were calibrated with the C1s peak of a pure carbon
sample (energy position 284.6 eV). All XPS spectra have been
corrected by the analyzer transmission factor and background
subtracted using the straight line subtraction mode. Moreover
the XPS data were fitted assuming a Gaussian distribution.
XRF measurements were conducted by the X-123 SDD ap-
paratus by Amptek (USA), equipped by a gold cathode and a
beryllium revelator, operating at fixed angle.
The contact angle images was obtained placing a small drop
of distilled water (5 l) on the ceramic surface with and with-
out dioxide coverage. The equilibrium contact angle was de-
termined by drop shape analysis using an optical contact meter.
The contact angle was measured several times for each sample
to ensure data robustness.
After characterization all the samples was subjected to a La-
ser Ablation (LA) cleaning process to verify the reversibility of
dioxide coverage and the possibility of future restoration on
covered artifacts. The laser ablation procedure was performed
irradiating for several minutes (15' or 30') each sample, im-
mersed in an acetone solution, by the output of the first har-
monic (1064 nm) of a Quanta-Giant series 710 Nd:YAG laser
operating at 10 Hz. The spot size of the laser beam on the sur-
face of carosello is about of (7 - 8) mm and the power of laser
is fixed at 500 mJ/pulse. The immersion in acetone is necessary
to prevent the oxidation and carbonization of surface induced
by LA in air (Naeem, 2010). Figure 1 shows the images of
ablated artifacts, it is clear that the TiO2 layer is completely
removed as also confirmed by the results of XPS, XRF and
contact angle measurements.
The static water contact angle was analyzed to qualitatively
assess the effectiveness of the surface coverage process and
their influence on surface wetting. The sessile drop technique
was employed. Indeed, the simple observation of a small liquid
drop on a solid substrate provides useful information concern-
ing the liquid-solid interaction and the hydrophobicity. The
obtained results for both processes are summarized in Figure 2.
The ceramic surface is completely hydrophilic and the water
TiO2 directly evaporated on ceramic
(evaporation times (h)) Contact angle Θ (˚)TiO
2 deposited with NaCl salt on ceramic Contact angle Θ (˚)
After TiO2 deposition
After 15' LA
After 30' LA
Contact angle after all treatments described in paper.
F. STRANGES ET AL.
Copyright © 2013 SciRes. 35
drop is completely adsorbed. These properties of ceramic is the
origin of surface degradation in marine water or after exposure
to atmospheric wet. So, the coverage with hydrophobic layer
ensure the conservation of artifacts. However, the coverage
must be transparent to not change the artistic and historic value
of artifacts. For this we realize TiO2 coverage with different
thickness (and different coloration) verifying the hydrophobic-
ity for each obtained layer. Figure 2 shows that the contact
angle, and then the hydrophobicity, increases with evaporation
time indicating for all samples an angle greater than 90˚ (hy-
drophobicity limit). In particular we obtain a contact angle of
about 110˚ for transparent layer obtained by 1 h evaporation
and an angle of 96˚ for transparent layer deposed via NaCl.
These clearly indicate that in both process it is possible to ob-
tain hydrophobic and transparent coverages.
LA process remove the TiO2 layer and the surface goes back
to being hydrophilic. The contact angle, in fact, decreases to
40˚ after 15' of LA and until get to 0 after 30' of ablation. All
these results was also confirmed by XRF and XPS analysis.
XPS data in Figure 3 indicated that both process (direct
evaporation and deposition) induce the only presence of Tita-
nium and oxygen on ceramic sample without alter the sample
composition or introducing impurities (Mo from evaporator
boat, aluminum, sodium or chlorine from salt and deposition
support foil). In particular in both process the Ti 2p lines are
centered at 458.5 eV clearly indicated the only presence of
TiO2 structures on surface (without presence of isolated Ti
atoms) (NIST database).
XRF data in Figure 4(A) indicated that the amount of TiO2
increases with evoparation times indicating the formation of
layer with thickness gradually larger. Data in Figure 4(B) indi-
cates, moreover, the composition of deposed layer of TiO2 on
salt (curve a for NaCl and b for Na2B4O7), it is clear that only
TiO2 is present on salt surface without any presence of impuri-
ties. Curve c and d in Figure 4(B) indicates the surface compo-
sition after LA cleaning process (15' curve c and 30' curve d) it
is clear that the Ti present on surface is completely removed
and the sample spectrum is identical at this of pure ceramic
Both process are, so, able to cover the ceramic surface giving
to ceramic an hydrophobic characteristic which can protect the
artifact from corrosion caused by marine water or atmospheric
XPS survey spectra for samples treated with different deposition proc-
XRF spectra for sample s treated with different deposition process.
wet. The obtained substrate are moreover completely transpar-
ent and can be removed simply by laser ablation process with-
out change the ceramic properties.
In this work, we present two methods to cover ceramic arti-
fact surfaces by a TiO2 transparent layer which gives surface to
the properties of hydrophobicity which ensure a protection by
water corrosion in marine water or in moist. The first process is
a simple evaporation of Ti in a controlled oxygen atmosphere
directly on ceramic surfaces. This process is applicable on
small artifacts, and easily transportable in a restoration labora-
tory. The second method contemplates the evaporation of TiO2
on a salt surface (deposed on an aluminum foil) which can be
successively deposed on artifacts. These methods prefer to the
coverage of artifacts of different dimensions directly in situ,
without damages of ceramics.
Both the process leads to the formation of transparent layer
which don’t damage the surfaces and don’t introduce defects.
Moreover the coverage is completely reversible. The dioxide
layer can, in fact, be removed simply by a cleaning process of
F. STRANGES ET AL.
Copyright © 2013 SciRes.
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