100% Positive Material Identification

Poster Session Scholars at TITANIUM EUROPE 2016 (continued)
The tensile and high cycle fatigue
properties of the resulting bonded
parts were only slightly reduced when
compared to that the bulk material and
are equivalent to or better than those
obtained by the traditional canned
route. Adopting a can-less route offers
significant time and cost savings with
what appears to be no detriment to the
bond strength and integrity.
Beatriz Eugenia Sanabria
Arenas, Politecnico di Milano -
Dipartimento di Chimica, Materiali e
Ingegneria Chimica “Giulio Natta,”
Italy
Sanabria Arenas obtained her M.Sc.
degree in Chemical Engineering from
university of Sao Paulo, Brazil, in 2014
and currently is a Ph.D. student in
Materials Engineering from Politecnico
di Milano, Italy. Her current research
interests include functional nanomaterial
synthesis by electrochemical processes
for environmental applications. Her
advisors include Davide Prando, Alberto
Strini, Luca Schiavi, Andrea Brenna,
Maria Vittoria Diamanti, and MariaPia
Pedeferri.
Abstract:
In the environmental field, the
efficiency of nanostructured titanium
dioxide for degrading inorganic and
organic substances is demonstrated.
However, one of the major concerns
about the use of nanostructured
materials for water remediation and
air purification by photocatalysis is
their potential dispersion in the gas or
liquid phase, where they are used, and
the hazard related to their dispersion
in the environment. In this context,
the use of anodic oxidation represents
a powerful technique for generating
photoactive oxides strongly adherent
to a metallic substrate—i.e. titanium,
and modify their chemical composition
by doping. In this work, we present a
robust method to obtain immobilized
TiO2 by anodic oxidation, in the form
of either nanotubes or nanoporous
anodic spark deposition (ASD) coatings.
36 TITANIUMTODAY
The photocatalytic efficiency of these
nanostructures was tested and compared
in gaseous and liquid phases.
Commercial purity titanium sheets
were anodized in three different
electrolytes: aqueous solution, fluoride
containing aqueous solution and fluoride
containing organic solution. The voltage
applied and the duration of the essays
were changed in order to obtain the
best nanostructures in each electrolyte.
After anodizing in solutions containing
fluorides, samples were annealed at
400°C for two hours to promote the
formation of anatase phase TiO2.
Photocatalytic activity was evaluated
in the degradation of dyes (rhodamine
B, RhB) or VOCs (toluene). Degradation
was performed by immersing a sample
in 25 ml of 105 m/L RhB solution,
irradiating for six hours with a solar
spectrum lamp (UV-A intensity 3 mW/
cm2) and monitoring color variations.
Toluene degradation was assessed
in air (25°C and 50-percent RH)
in a continuous-flow stirred photo
reactor operating at constant toluene
concentration (0.75 µmol/m3), under
UV-A irradiation of 0.6 mW/cm2.
In aqueous and organic solutions
containing fluorides, self-aligned vertical
nanotubes stem from the substrate;
in organic solution the detachment of
single nanotubes is less pronounced,
creating a sort of porous template
rather than a nanotubular array, but
with higher thickness. Conversely, in
absence of fluorides a large voltage
is applied, generating an oxide with
glassy appearance and larger pores. The
photocatalytic degradation of dyes with
these oxides increases with increasing
voltage up to 150V; for higher voltages,
too much rutile formation and lower
anatase content reduce photo activity.
When a nanotubular oxide is obtained, a
larger reactivity is ensured.
Although nanotubes obtained in
organic solution show the highest
efficiency, preliminary results in toluene
degradation show a larger dispersion
of results compared to other the
nanostructures. Conversely, nanotubes
produced in aqueous solution exhibit
excellent repeatability and good
efficiency. Oxides without nanotubular
morphology exhibit a very low reactivity
in gas phase, while showing good
degradation of RhB. This is interesting,
because it points out the increased
differentiation among the oxides
photocatalytic activities in gas phase, in
spite of the lower differences observed in
liquid phase reactions.
In conclusion, the processes
here described open the way to the
production of photocatalytically efficient
nanostructured TiO2 films immobilized
onto a metallic substrate at low cost,
avoiding environmental issues related
to the use and recycle of conventional
photocatalysis.
Davide Prando, Politecnico di
Milano, Milano, Italy.
Prando, a Ph. D. student at the
faculty of Materials Engineering of
the University Politecnico di Milano,
graduated in 2015 with a thesis about
photocatalysis on titanium dioxide. He
is currently working on the corrosion
phenomena of commercially pure
titanium. His advisors include Maria
Vittoria Diamanti, Andrea Brenna, Silvia
Beretta, MariaPia Pedeferri, and Marco
Ormellese.
Abstract:
Titanium is well known to have an
excellent corrosion resistance in
natural environment. However much
more severe conditions are found
in industrial applications and alloys
with better behavior were developed;
these alloys are often prepared
with elements more expensive than
titanium (such as palladium in ASTM
Grade 7 titanium). This work aims
to find a surface treatment capable of
improving the performances of the
cheaper titanium ASTM Grade 2 on the
electrochemical point of view, enable it
to be used in critical conditions (such as