W-TiO2 Controls MIC on Galvanized Steel

Appl Microbiol Biotechnol
DOI 10.1007/s00253-012-4389-1

ENVIRONMENTAL BIOTECHNOLOGY

Effect of W–TiO2 composite to control microbiologically
influenced corrosion on galvanized steel
Rubina Basheer & G. Ganga & R. Krishna Chandran &
G. M. Nair & Meena B. Nair & S. M. A. Shibli

Received: 19 June 2012 / Revised: 14 August 2012 / Accepted: 24 August 2012
# Springer-Verlag 2012

Abstract Microorganisms tend to colonize on solid metal/
alloy surface in natural environment leading to loss of
utility. Microbiologically influenced corrosion or biocorrosion usually increases the corrosion rate of steel articles due
to the presence of bacteria that accelerates the anodic and/or
cathodic corrosion reaction rate without any significant
change in the corrosion mechanism. An attempt was made
in the present study to protect hot-dip galvanized steel from
such attack of biocorrosion by means of chemically modifying the zinc coating. W–TiO2 composite was synthesized
and incorporated into the zinc bath during the hot-dipping
process. The surface morphology and elemental composition of the hot-dip galvanized coupons were analyzed by
scanning electron microscopy and energy dispersive X-ray
spectroscopy. The antifouling characteristics of the coatings
were analyzed in three different solutions including distilled
water, seawater, and seawater containing biofilm scrapings
under immersed conditions. Apart from electrochemical
studies, the biocidal effect of the composite was evaluated
by analyzing the extent of bacterial growth due to the
presence and absence of the composite based on the analysis
of total extracellular polymeric substance and total biomass
using microtiter plate assay. The biofilm-forming bacteria
formed on the surface of the coatings was cultured on Zobell
Marine Agar plates and studied. The composite was found

R. Basheer : G. Ganga : R. K. Chandran : G. M. Nair
Inter University Centre for Genomics and Gene Technology,
University of Kerala,
Kariavattom Campus,
Thiruvananthapuram, Kerala 695 581, India
M. B. Nair : S. M. A. Shibli (*)
Department of Chemistry, University of Kerala,
Kariavattom Campus,
Thiruvananthapuram, Kerala 695 581, India
e-mail: smashibli@yahoo.com

to be effective in controlling the growth of bacteria and
formation of biofilm thereafter.
Keywords Corrosion . Hot-dip galvanization . Steel . Zinc .
W–TiO2 composite . Biofilm . Biocorrosion

Introduction
The physicochemical interactions between a metallic material and its environments can lead to corrosion. The interaction of bacteria with metal surface results in the formation of
biofilms in a process known as biofouling. A biofilm can be
defined as a surface attached (sessile) community of microorganisms growing embedded in a self-produced matrix of
extracellular polymeric substances (EPS). Bacteria colonizing on a surface produce EPS that will glue the cells to the
surface and eventually form the biofilm matrix. Generally,
EPS are composed of polysaccharides but may also contain
proteins, nucleic acids, and polymeric lipophilic compounds. In terms of weight and volume, EPS represents
the major structural component of biofilms, being responsible for the interaction of microbes with each other as well as
with interfaces (Flemming 2002; Neu et al. 2001).
The primary colonizers of inanimate underwater surfaces
are bacteria, which creates a favorable environment in the
form of biofilm for the attachment of algae and the invertebrates like barnacles and other invertebrate larvae. Such an
association creates a complex local environment on the
surface of the metal, thereby enhancing the rate of corrosion
of the metal surface exposed, leading to biofouling. Traditionally, it has been assumed that the interaction of bacteria
with metal surfaces always causes increased corrosion rates
(Ameer et al. 2011; Mansfeld 2007). Microbial activity
within the biofilms formed on the surface of metals can
affect the kinetics of cathodic and/or anodic reactions (Jones
and Amy 2002) and can also considerably modify the


chemistry of any protective layers, leading to either acceleration or inhibition of corrosion (Little and Ray 2002;
Ornek et al. 2002a,b). The main types of bacteria associated
with metals in terrestrial and aquatic habitats are sulfate
reducing bacteria (SRB), sulfate-oxidizing bacteria, ironoxidizing bacteria, manganese-oxidizing bacteria, and bacteria secreting organic acids and slime (Beech and Sunner
2004). von Wolzogen Kuehr in 1923 proposed the so-called
cathodic depolarization mechanism, which assumes that the
SRB remove atomic hydrogen from the iron surface, which
causes accelerated corrosion of iron (Mansfeld 2007). When
exposed to seawater media containing toxic metals and
chemicals, such as Cd(II), Cu(II), Pb(II), Zn(II), Al(III), Cr
(III), glutaraldehyde, and phenol, the SRB in the biofilm
aggregated into clusters and increased the production of
EPS (Fang et al. 2002).
In the present work, hot-dip galvanizing technique,
where by zinc is applied on the surface of steel, was adopted
to prevent the corrosion of mild steel in seawater. Certain
metals/metal oxides are used to enhance the antifouling
characteristics of hot-dip galvanized coatings. Generally,
metal oxides play an important role in the corrosion protection of mild steel. Various metal oxides such as ZnO, ZrO2,
and TiO2 have been used as oxide barrier coatings on
galvanized steel substrate (Hamid et al. 2010; Shibli and
Francis 2008; Shibli and Francis 2011a). The use of TiO2 as
a photo catalyst for the decomposition of organic compounds and microbial organisms including viruses, bacteria,
and cancer cells has been reported (Blake et al. 1999;
Kangwansupamonkon et al. 2009). Shieh et al. (2006) have
reported an antibacterial performance of TiO2 against
Escherichia coli that could reach 99.99 % bacterial reduction
under activation by visible light. It has been reported that the
incorporation of TiO2 increases the antifouling characteristics
of hot-dip zinc coatings (Shibli and Francis 2011b).
There are several literature reports for the modification of
TiO2 surface with metals, such as Pt, Fe, Ag, Au, and Pd.
This technique is considered as a promising tool to enhance
the photo catalytic activity of TiO2 and to increase the
quantum yield (Li and Li 2002; Sakthivel et al. 2004;
Wodka et al. 2010). In the present work, TiO2 surface was
modified using tungsten because of its high density, hardness, very high melting temperature, relatively high radiation opacity, and good thermal conductivity combined with
very low thermal expansion (German et al. 2006). The effect
of W–TiO2 composite on bacteriologically enhanced corrosion of hot-dip galvanized coupons was discussed in this
paper. This was studied through X-ray diffraction (XRD),
scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDS), open circuit potential (OCP), optical microscopy, and biological parameters like bacterial
growth characteristics, biomass estimation and difference
in the EPS formation.

Materials and methods
Preparation of tungsten wetted TiO2 composite by chemical
reduction method
The precursor materials used were sodium tungstate,
Na2WO4⋅2H2O (Nice, India; assay, 96.0 %), titanium dioxide,
TiO2 (CDH, India; assay, 99.5 %), and hydrazine hydrate
(Ottokemi, India; assay, 80.0 %). A 1 M solution of sodium
tungstate was prepared. To one part by weight of this
standard solution, three parts by weight of TiO2 was added.
The mixture was then stirred well using a magnetic stirrer
and heated in a temperature range of 70–80 °C for 6 h. The
resultant paste was dried in an oven and transferred to
alkaline hydrazine hydrate (100 mL) taken in a breaker,
and the whole mass was kept in a water bath (80 °C) with
constant stirring for about 3–4 h. The resultant product was
filtered and then dried in an oven. The dried product was
powdered, and one portion of it was heated at 800 °C in
order to ensure that no changes occur at this high temperature because it had to be used at molten zinc bath. The
nature of the phases and the crystallite size of the powder
before and after heating at 800 °C were determined
using an X-ray powder diffractometer using Cu Kα radiation
(λ01.5405 Å).
Antifouling characteristics of W–TiO2 composite
The ability of W–TiO2 to act as an antifouling agent was
assessed microbiologically. For this, seawater along with
samples of biofilm formed under boat hulls was collected
aseptically from the Vizhinham harbor, Thiruvananthapuram, Kerala, India. The microbial samples collected were
then isolated through plating methods in Zobell Marine
Agar. EPS production by consortium of marine bacteria in
the presence of the composite was checked against various
concentrations (1–4 %) of the composite. After incubation
of 24 h at 25 °C, the amount of total carbohydrates in the
EPS produced was assessed by phenol-sulfuric acid method
(Dubois et al. 1956) as a means of assessing extent of
biofilm formation.
Selection of substrate and pretreatment methods
Mild steel is the material mostly used for construction as
well as for other commercial processes because it is commercially affordable and possesses good mechanical
strength. It is generally subjected to hot-dip galvanizing
process because it is the substrate most suitable for the zinc
alloying process, i.e., the hot dipping process. Other substrate will not undergo the hot-dip galvanizing process efficiently. In the present work, mild steel coupons of a
dimension of 3.5 × 2.5 × 0.1 cm 2 having the elemental


composition of 0.090 % carbon, 0.340 % manganese,
0.036 % phosphorus, 0.048 % silicon and 0.029 % aluminium and remaining iron was used. The substrate was abraded with 100 grit emery paper, degreased using 5 % NaOH
solution and then etched in 8 % HCl solution for 20 min at
room temperature to ensure that the substrate was free from
any superficial oxide layer. The coupons were then fluxed
with 30 % NH4Cl solution for 30 min at 50±1 °C to avoid
any further oxidation of the surface and to enhance the
adhesion of molten metal onto the substrate.
The galvanizing process
Commercially available pure zinc (99.95 wt%) was used for
the present work. The required quantity of zinc was melted
in a graphite crucible kept at 450±10 °C in a muffle furnace.
A required quantity of the prepared W–TiO2 composite was
added into the molten zinc bath and stirred well using
silicon carbide rod. The coupons were preheated to a temperature of 200±10 °C and then dipped into the molten bath
for 10–15 s. The process parameters were fixed based on the
performance of the coating prepared under varying experimental conditions. The excess zinc on the coupons was
removed by blowing hot air while withdrawing the strips
from the bath. Different compositions of W–TiO2 composite
incorporated hot-dip zinc coatings were developed. At the
preliminary stage, different stages of coupons, as a function
of different W–TiO2 content, were prepared and subjected to
different analysis and evaluation. Based on the electrochemical performance of the galvanized coupons, the optimum
amount of composite added into the bath was fixed as 0.2 %.
Pure zinc coating and 0.2 % W–TiO2 composite incorporated
coating were used for the entire study.
Morphological characterization of the coatings

aeration and sunlight. Temperature was maintained at 25 °C.
Previously weighed metal strips were then immersed in
triplicates in each trough such that equal surface area
(10 cm2) of each coupon remains dipped in water. The
experimental setup is kept for 20 days.
Open circuit potential and pH measurement
OCP of a metal signifies its tendency to corrode, and
changes in its potential with time without the application
of an external current can be related to the nature of the
metal surface. It is a sensitive measurement to detect various
stages of dissolution of a coating during long-term immersion tests. In this method, metal coupons were the working
electrode, saturated calomel electrode was the reference
electrode, and the three solutions were the medium for the
measurements. OCP of the coupons (using Aplab digital
multimeter model 1089) and pH of the solutions (using
Eutech pH Tutor) were recorded periodically for a period
of 20 days and plotted as a function of time to understand
the changes that take place on metal coupons and solutions
respectively.
Screening of biofilm formation and biofouling activity
by bacteria
After 20 days of incubation, the metal coupons were recovered and washed thoroughly with sterile distilled water to
remove any corroded debris and loosely attached bacterial
cells. One of the two sides of the coupons was then swabbed
and inoculated onto Zobell Marine Agar (Hi Media) and
incubated for 24 h at 25 °C. Other side of the metal coupons
was microscopically evaluated using an optical microscope
(Olympuz SZ61, Taiwan) at a magnification of ×4.5. Individual bacteria were isolated from the consortia that formed
the biofilm on the coupons. Five microliters of overnight-

Microstructure of the coatings was evaluated using a scanning electron microscope JEOL 6390 LV equipped with an
energy dispersive X-ray spectroscope, JEOL 2200. The
surface morphology and particle distribution in coatings
were compared using SEM images. The grain size of the
coatings was also compared using SEM images. The elemental composition of the coatings was analyzed using EDS
patterns.
Biological and electrochemical assay of antifouling
characteristics of the coatings
Immersion of metal coupons in water for biofilm formation
Three sets of experimental set up, viz., distilled water as
control, seawater, and seawater with biofilm scrapings were
maintained in wide-mouthed glass troughs to ensure proper

Fig. 1 X-ray diffraction patterns of W–TiO2 composite a without
heating and b after heating at 800 °C

Table 1 Antifouling
activity of W–TiO2
composite at various
concentrations

Percentage composition
of composite (%)

Optical
density

0

0.364

1
2
3
4

0.259
0.182
0.146
0.141

grown cultures of the bacterial isolates as well as the consortia was inoculated onto 45 μL of Zobell Marine Broth
(ZMB) in microtitre plates and incubated at 25 °C for 48 h.
After incubation, the wells were washed with sterile physiological saline and fixed with 99.99 % ethanol for 10 min.
Ethanol was then removed, and the attached bacterial cells
were stained in 2 % crystal violet for 20 min. The plates
were washed with distilled water, and the amount of attached cells was measured using an ELISA reader at
570 nm (Abdi-Ali et al. 2006; Peeters et al. 2008).
Biological assay for extracellular polymeric substance
produced by bacteria
ZMB was also inoculated with the bacteria that formed the
biofilm on metal coupons by dipping the coupons in ZMB
for 1 h. Glycerol [3 % (v/v)] was added as extra carbon
source, and incubation was done in a shaker incubator at
Fig. 2 The SEM micrographs
of a pure zinc coating and b
0.2 % W–TiO2 composite
incorporated coating with
magnifications ×1,000
and ×1,500

25 °C with 120 rpm for three consecutive days. The supernatant was then collected by centrifugation at 10,000 rpm
for 10 min to collect cell-free extract containing EPS. An
estimate of total carbohydrate in the supernatant was estimated using phenol-sulfuric acid test.
Determination of self-corrosion rate
After 20 days of exposure in three different solutions, the
corroded coupons were washed with 10 % ammonium persulfate solution, dried, and weighed. Self-corrosion rate of
these coupons were calculated from the difference in their
weights and was plotted against composition of W–TiO2
composite.
Self À corrosion rate ¼ weight loss=ðsurface area Â timeÞg cmÀ2 hÀ1

Results
Chemical composition and antifouling characteristics
of W–TiO2 composite
The phase structure and chemical composition of the prepared composite before and after heating at 800 °C were
analyzed using the XRD patterns shown in Fig. 1. The sharp
peaks revealed the crystalline nature of the composite. The
peaks at 2 theta values of 27.54 and 36.19 corresponding to


the presence of titanium tungsten oxide (Ti 54 W 46 O 2 )
(JCPDS 85-0270) and the peaks at 2 theta value 54.42 and
56.73 corresponding to the rutile phase of TiO2 (JCPDS 860147) and tungsten (JCPDS 04-0806), respectively, were
also noted. The antifouling efficacy of the composite was
also analyzed, and the enhanced efficacy with increase in
concentration is evident from Table 1.
Fig. 3 The energy dispersive
spectrum of a pure zinc coating
and b 0.2 % W–TiO2 composite
incorporated coating

Microstructure of the coatings
The surface morphology and elemental composition of the
hot-dip galvanized coupons were examined by SEM-EDS
analysis. The incorporation of the composite generally suppressed a massive surface finish of the coating leading to
microstructural uniformity. The SEM images of the pure


zinc coating and the one incorporated with W–TiO2 composite are shown in Fig. 2, at magnifications of ×1,000
and ×1,500. The micrograph of W–TiO2 incorporated galvanized coupon revealed a significant improvement on the
morphology with the particles distributed uniformly throughout the surface (Fig. 2b).
The elemental composition of the pure zinc coating and
that of W–TiO2 incorporated coating was examined based
on the EDS patterns. The EDS spectrum of the composite
incorporated coating (Fig. 3b) revealed the presence of W,
Ti, and O along with zinc on the top layers when compared
with that of the pure zinc coating (Fig. 3a).
Biological and electrochemical assay of antifouling
characteristics of the composite
The trend of shift in OCP and pH measurements
The OCP decay curves of hot-dip galvanized coupons (pure
zinc coating and W–TiO2 composite incorporated coating)
immersed in different solutions (distilled water, seawater,
and scrapings containing seawater) for a period of 20 days
are shown in Fig. 4. Both the coupons exhibited a zigzag
variation of OCP in distilled water. But in the case of
seawater, there was a steady OCP variation during the initial
stages of exposure. After 10 days of exposure, the W–TiO2
incorporated coating showed least anodic shift compared
with pure zinc coating. But in the case of seawater containing scrapings, both the coatings exhibited a remarkable
anodic shift after 10 days, but the extent of potential shift
was comparatively less in the case of W–TiO2 composite
incorporated coating.

Fig. 4 The OCP decay curves
of galvanized coupons during
long term immersion in a
distilled water, b seawater,
and c seawater scraping for
biogrowth. Temperature: 25 °C
(empty circle pure zinc coating,
filled circle 0.2 wt% W–TiO2
composite incorporated
coating)

The pH of distilled water, seawater, and seawater containing scrapings were monitored for a period of 20 days
and are shown in Fig. 5. Variation in pH from alkalinity to
acidity was noticed in both seawater and seawater containing scrapings (from pH9 to 6); this may be attributed to the
acidic byproducts of bacterial metabolism.
Screening of biofilm formation and biofouling
activity by bacteria
Bacterial swabs from the surface of metal coupons were
plated and counted. In distilled water control, little or no
growth occurred in both coupons (Fig. 6, - top). In the case
of the coupons dipped in seawater and seawater with scrapings, profuse growth occurred on pure zinc coating, while
only five colonies were observed on the W–TiO2 incorporated coupon (Fig. 6, middle and bottom). It revealed that
the microbial attack was less in the case of W–TiO2 incorporated coating in both the cases.
Microstructural evaluation of corroded coupons
The optical micrographs showing the surface of pure zinc
and W–TiO2 composite incorporated coatings after exposure to experimental solutions are shown in Fig. 7. From
these figures, it was evident that the surface of both the
coatings was not seriously affected by distilled water. But
in the case of seawater and seawater containing scrapings,
the microbial attack was least in W–TiO2 composite incorporated coating compared with pure zinc coating. From
these three solutions, coupons in seawater containing scrapings undergo relatively high biocorrosion.

11

the biofilm even though the biocidal effect was not that
much significant on individual organisms (Figs. 8 and 9).
The significance of variation among the individual batch on
the extent of antifouling was not critical for all organisms.

pH

9

Determination of self-corrosion rate

7

5

0

5

10

15

The self-corrosion rate of galvanized coupons (pure zinc coating and W–TiO2 composite incorporated coating) immersed in
different solutions (distilled water, seawater and scrapingcontaining seawater) is shown in Fig. 10. The self-corrosion
rate of all the coupons was very low in distilled water. But in
the case of seawater and seawater with biofilm scrapings, low
corrosion rate was observed in the case of composite incorporated coating than pure zinc coating. No significance of variation on the corrosion rate among the individual batch was
noted revealing high reproducibility on the results.

20

Time (days)
Fig. 5 pH variation of solutions in which metal strips were immersed
for biogrowth (circle distilled water, square seawater, triangle seawater
scraping)

Characterization of EPS produced by bacteria
The supernatant collected after centrifugation was filtered in
0.22-μm filters and analyzed for total carbohydrate content.
After the analysis, it was understood that the culture containing
W–TiO2 composite showed lower optical density (0.364) when
compared to the culture in the absence of the composite (0.913).

Discussion
Biofouling generally refers to the adherence of micro- and
macroorganisms on to the metal surfaces in marine and fresh
water systems leading to the formation of fouled layers.
Bacteria form biofilm with the aid of extracellular polymeric
substances to gain attachment to the surfaces. The present

Screening of biofouling activity by microtiter plate assay
Microtiter plate assay showed significant antifouling activity by the composite on the bacterial consortium that formed
Fig. 6 Bacterial growth
observed in Zobell Marine Agar
plates. Biofilms were collected
from the surface of galvanic
coatings with composition a
pure zinc and b 0.2 % W–TiO2
incorporated coatings immersed
in distilled water, seawater, and
seawater scraping

Distilled
water

Sea
water

Sea waterScraping

a

b

Fig. 7 The optical micrographs
of a pure zinc coating and b W–
TiO2 composite incorporated
coating immersed in distilled
water, seawater, and seawater
scraping for 20 days at a
magnification of ×4.5

study indicates that W–TiO2 incorporated zinc coating was
effective in controlling the biofilm-forming capacity of bacteria, the initial stage of biofouling process. For this study,
W–TiO2 composite was synthesized by chemical reduction
0.35

control

W-TiO2

method, and its chemical composition and thermal stability
were analyzed using XRD technique. It is evident from the
XRD patterns that Ti54W46O2, rutile TiO2, and tungsten can
be obtained by the chemical reduction of sodium tungstate
and TiO2 using hydrazine hydrate. The presence of identical

without composite

0.3

Absorbance

0.35

0.25

Absorbance

0.3

0.2
0.15
0.1
0.05
0

0.25
0.2
0.15
0.1
0.05

1

2

3

4

5

6

7

8

9

10

Organisms

Fig. 8 Growth of individual bacterium under various conditions—
control (uninoculated broth), in the presence of composite (W–TiO2),
and without composite

0

control

without
composite

W-TiO2

Fig. 9 Growth of consortium under various conditions—control (uninoculated broth), in the presence of composite (W–TiO2), and without
composite

Self corrosion rate X 10 -5(g/cm2/h)

5
Pure Zn

4

Zn+W-TiO2

3

2

1

0

Distilled water

Sea water

Sea waterscraping

Fig. 10 Comparison of the rate of corrosion of galvanized coupons
after 20 days of immersion in three different solutions for biogrowth. (a
pure zinc coating, b 0.2 wt% W–TiO2 composite incorporated coating)

peaks at 2 theta values in both the XRD patterns indicated
that the composite was thermally stable up to 800 °C. The
crystalline and chemical nature of the composite was thus
identified, and also it was ensured that the composite would
not undergo any change if it would be added into molten
zinc bath. In this study, a bacterial consortium, comprising
of 13 prominent organisms isolated from biofilm scrapings
collected from the boat hulls, was initially used. But during
subsequent subculturing, three of them failed to show considerable growth. The efficacy of this composite in antifouling was confirmed by inoculating the consortium in media
containing various concentrations of the composite. As the
percentage composition of composite increases, the optical
density decreases revealed the better antifouling activity of
W–TiO2 composite. The W–TiO2 composite, which is thermally stable and having high antifouling activity, was then
added into molten zinc bath during hot-dip galvanization.
The surface morphology and chemical composition of the
zinc coatings were analyzed using SEM-EDS technique.
From the SEM images, it was clear that the W–TiO2 particles were distributed uniformly throughout the surface and
have uniform grain size. Tiny ridged spangles were also
observed in the case of the composite incorporated coating.
It has been reported that the TiO2 incorporated zinc coatings
could have ridged spangles, and the size of the spangles
would be larger than what observed in the case of pure zinccoated surface (Shibli et al. 2006). The coating incorporated
with W–TiO2 exhibited more compact structure due to the
formation of Fe–W–TiO2–Zn inner layers. Based on these
observations, the structural improvement due to the incorporation of the W–TiO2 composite was attributed to the
individual property of the composite along with suppression
of the alloying reaction.
The advantage of the present study using bacterial consortium obtained from boat hulls is that it represents the
effect of the composite on the indigenous niche of biofilm

formers. Previously, similar works were carried out by
Shibli and Francis (2011b) with Vibrio alginolyticusa as
the test organism. Rickard et al. (2003) reported coexistence
of diverse species of bacteria in natural settings of biofilm
formation like oral cavities and drinking water supplies that
exhibit fascinating universe of specific interspecies interactions. Furthermore, bacterial consortia showed a distinct
pattern in the reduction of growth as well as biofilm formation in the presence of W–TiO2 as compared to individual
organisms in microtiter plate assay. This could be due to the
resistance of certain organisms to the composite when
grown individually. However, it is difficult to explain the
ecophysiology of a consortium of biofilm formers due to the
complexity in biodiversity among the communities (Jiao et
al. 2010).
The pure and composite incorporated hot-dip galvanized
coatings were immersed in three experimental solutions for
a period of 20 days by measuring the OCP and pH consecutively. The bacterial consortia present in the seawater
resulted in high microbial attack on the surface of galvanized coatings leading to high corrosion. During the initial
stages of exposure, both the coatings exhibited high negative OCP values in the range of −1.10 to −1.05 V in both
seawater and seawater with biofilm scrapings. This is due to
the sacrificial action of η phase (pure zinc) by protecting the
inner layers from biocorrosion during the exposure. As the
time of exposure increases, the dissolution rate increases
due to the attack of bacteria and the OCP values of the
coupons shifted to more anodic region. During the course
of exposure, the protective barrier layer formed on the
composite incorporated coating minimizes the dissolution
of zinc. The pure zinc coating exhibited remarkable anodic
shift in the range of −0.85 to −0.80 V in seawater and −0.90
to −0.88 V in seawater with biofilm scraping. This is due to
the high bacterial attack on the surface of pure zinc coating.
The composite incorporated coating in both seawater and
seawater with biofilm scraping showed least shift in OCP in
the range of −1.05 to −1.00 V and −1.00 to −0.98 V
due to its better antifouling characteristics. This was due
to the less bacterial attack on the surface of W–TiO2
composite incorporated coatings. The pH measurement
ensured that the solution became more acidic as the time of
exposure increases due to the presence of acid-producing
bacteria.
Very high corrosion was observed in the case of pure zinc
coating immersed in experimental solutions, during selfcorrosion rate analysis, due to high bacterial attack in the
absence of W–TiO2. The self-corrosion rate measurements
are in good agreement with OCP measurements. The surface
morphology of the corroded samples was analyzed by optical micrography. The optical micrographs of pure zinc and
W–TiO2 composite incorporated coating after 20 days of
immersion in experimental solutions also revealed the


antifouling activity of W–TiO2. The biofilm formed on the
surface of coatings were swabbed and inoculated into Zobell
Marine Agar plate, and the colony count was noted. The
colony count was less in the case of composite incorporated
coating compared with pure zinc coating. From these
results, it was confirmed that the W–TiO2 composite caused
remarkable improvement in the antifouling characteristics of
galvanized coatings in different experimental solutions.
It should be noted that at this concentration, the composite would pose negligible threat of toxicity to aquatic life/
ecosystem. Lower content of the composite led to lower
performance against biocorrosion, while little higher content
revealed a slight variation against biocorrosion. Higher content of TiO2 also led to poor mechanical stability of the
coating. Moreover, it should be noted that higher concentration of TiO2 normally leads to toxicity. In particular, Ferin
and Oberdörster have demonstrated that both anastase and
rutile forms of TiO2 were toxic and that the retention time
was long (half times of 51–53 days in the rat lung at low
milligram doses) (Ferin and Oberdörster 1985; Gillian et al.
2007).
The excellent antifouling characteristics of TiO2 incorporated zinc coating had been reported from our lab itself
(Shibli et al. 2006; Shibli and Francis 2011b) and again
reproduced the same during the preliminary studies of the
present work. The present work had the objective of further
improving the antifouling effect along with the advantage of
utilizing the wetting effect that would be exerted by tungsten. Hence, the present study highlights the additional
effect than the effect of TiO2 alone. In order to improve
the wetting nature of TiO2, tungsten, which increases the
wettability of the composite during the hot-dip process, was
incorporated along with TiO2. The comparison of wetting
nature of TiO2 and W–TiO2 composite to zinc bath was
done through contact angle measurements.
Acknowledgments The authors thank the Head of the Department of
Chemistry and the Director of IUCGGT, University of Kerala for
extending support to carry out the research work.

References
Abdi-Ali A, Mohammadi-Mehr M, Alaei A (2006) Bactericidal activity of various antibiotics against biofilm producing Pseudomonas
aeruginosa. Int J Antimicrob Agents 27(3):196–200
Ameer MA, Fekry AM, Shanab SM (2011) Electrochemical behavior
of titanium alloy in 3.5% NaCl containing natural product substances. J Elecrochem Sci 6:1572–1585
Beech IB, Sunner J (2004) Biocorrosion: towards understanding interactions between biofilms and metals. Curr Opin Biotechnol
15:181–186
Blake DM, Maness PC, Huang Z, Wolfrum EJ, Huang J (1999)
Application of the photocatalytic chemistry of titanium dioxide

to disinfection and the killing of cancer cells. Sep Purif Methods
28:1–50
Dubois M, Gilles KA, Hamilton JK, Rebers PA, Smith F (1956)
Colorimetric method for determination of sugars and related substances. Anal Chem 28:350–356
Fang HHP, Xu LC, Chan KY (2002) Effects of toxic metals and
chemicals on biofilm and biocorrosion. Water Res 36:4709–
4716
Ferin J, Oberdörster G (1985) Biological effects and toxicity assessment of titanium dioxides: anastase and rutile. Am Ind Hyg Assoc
J 46:69–72
Flemming HC (2002) Mini-review—biofouling in water systems—
cases, causes and countermeasures. Appl Microbiol Biotechnol
59:629–640
German RM, Ma J, Wang X, Olevsky E (2006) Processing model for
tungsten powders and extension to nanoscale size range. Powder
Metall 49:19–27
Gillian F, Benjamin JS, Richard DH (2007) Toxicity of titanium
dioxide nanoparticles to rainbowtrout (Oncorhynchus mykiss): gill
injury, oxidative stress, and other physiological effects. Aquat
Toxicol 84:415–430
Hamid ZA, Aal AA, Hassan HB, Shaaban A (2010) Process and
performance of hot-dip zinc coatings containing ZnO and Ni–P
under layers as barrier protection. Appl Surf Sci 256:4166–
4170
Jiao Y, Cody GD, Harding AK, Wilmes P, Schrenk M, Wheeler KE,
Banfield JF, Thelen MP (2010) Characterization of extracellular
polymeric substances from acidophilic microbial biofilms. Appl
Environ Microbiol 76:2916–2922
Jones DA, Amy PS (2002) A thermodynamic interpretation of microbiologically influenced corrosion. Corrosion 58:638–645
Kangwansupamonkon W, Lauruengtana V, Surassmo S, Ruktanonchai
U (2009) Antibacterial effect of apatite-coated titanium dioxide
for textiles applications. Nano Med: Nano Technol, Biol Med
5:240–249
Li XZ, Li FB (2002) The enhancement of photodegradation efficiency
using Pt–TiO2 catalyst. Chemosphere 48:1103–1111
Little B, Ray R (2002) A perspective on corrosion inhibition by
biofilms. Corrosion 58:424–428
Mansfeld F (2007) The interaction of bacteria and metal surfaces.
Electrochim Acta 52:7670–7680
Neu TR, Swerhone GDW, Lawrence JR (2001) Assessment of lectinbinding analysis for in situ detection of glycoconjugates in biofilm systems. Microbiology 147:299–313
Ornek D, Jayaraman A, Syrett BC, Hsu CH, Mansfeld F, Wood TK
(2002a) Pitting corrosion inhibition of aluminum 2024 by Bacillus
biofilmes secreting polyaspartate or polyglutamate. Appl Microbiol
Biotechnol 58:651–657
Ornek D, Wood TK, Hsu CH, Sun Z, Mansfeld F (2002b) Pitting
corrosion control of aluminium 2024 using protective films that
secrete corrosion inhibitors. Corrosion 58:761–767
Peeters E, Nelis HJ, Coeny T (2008) Comparison of multiple methods
for quantification of microbial biofilms grown in microtiter plates.
J Microbiol Method 72(2):157–165
Rickard AH, Gilbert P, High NJ, Kolenbrander PE, Handley PS (2003)
Review—bacterial co-aggregation: and integral process in the
development of multi-species biofilms. Trends Microbiol 11:94–
100
Sakthivel S, Shankar MV, Palanichamy M, Arabindoo B, Bahnemann
DW, Murugesan V (2004) Enhancement of photocatalytic activity
by metal deposition: characterisation and photonic efficiency of
Pt, Au and Pd deposited on TiO2 catalyst. Water Res 38:3001–
3008
Shibli SMA, Francis C (2008) Development of nano CeO2-incorporated high performance hot- dip zinc coating. Surf Coat Technol
202:4971–4975

Shibli SMA, Francis C (2011a) Development of nano TiO2-incorporated phosphate coatings on hot-dip zinc surface for good paintability and corrosion resistance. Appl Surf Sci 257:3111–3117
Shibli SMA, Francis C (2011b) CeO2–TiO2 mixed oxide incorporated high
performance hot-dip zinc coating. Surf Coat Technol 205:2931–2937
Shibli SMA, Dilimon VS, Antony SP, Manu R (2006) Incorporation of
TiO2 in hot-dip zinc coating for efficient resistance to biogrowth.
Surf Coat Technol 200:4791–4796

Shieh KJ, Li M, Lee YH, Sheu SD, Liu YT, Wang YC (2006)
Antibacterial performance of photocatalyst thin film fabricated by defection effect in visible light. Nano medicine 2:121–
126
Wodka D, Bielańska E, Socha RP, Elzbieciak-Wodka M, Gurgul J,
Nowak P, Warszyński P, Kumakiri I (2010) Photocatalytic activity
of titanium dioxide modified by silver nanoparticles. Appl Mater
Interfaces 2:1945–1953

W-TiO2 Controls MIC on Galvanized Steel

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à W-TiO2 Controls MIC on Galvanized Steel

Similaire à W-TiO2 Controls MIC on Galvanized Steel (20)

Dernier

Dernier (20)

W-TiO2 Controls MIC on Galvanized Steel