1) The document examines the effect of a W-TiO2 composite coating on microbiologically influenced corrosion of hot-dip galvanized steel.
2) A W-TiO2 composite was synthesized and incorporated into molten zinc during hot-dipping of steel coupons. Scanning electron microscopy showed the composite was distributed on the zinc coating surface.
3) Electrochemical and biological assays showed the W-TiO2 composite coating reduced bacterial growth, biofilm formation, and extracellular polymeric substance production on the steel surface compared to a pure zinc coating. This indicates the composite helped control microbiologically influenced corrosion.
MIC (Microbial Influenced Corrosion) in Environmental SustaiabilityBita Rahmani
An introduction on MIC, Microbial corrosion or aka Biocorrosion; corrosion cased by microorganisms, Advantages and Disadvantages, how it takes place and which types are microbes are involved in this process. Lastly a brief look on how to manage and minimize corrosion.
MIC (Microbial Influenced Corrosion) in Environmental SustaiabilityBita Rahmani
An introduction on MIC, Microbial corrosion or aka Biocorrosion; corrosion cased by microorganisms, Advantages and Disadvantages, how it takes place and which types are microbes are involved in this process. Lastly a brief look on how to manage and minimize corrosion.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
ENRICHMENT OF ORES BY MICROORGANISMS- Bioaccumulation and biomineralizationSijo A
Microbial ore leaching (bioleaching) is the process of extracting metals from ores with the use of microorganisms. This method is used to recover many different precious metals like copper, lead, zinc, gold, silver, and nickel. Microorganisms are used because they can:
lower the production costs.
cause less environmental pollution in comparison to the traditional leaching methods.
very efficiently extract metals when their concentration in the ore is low.
A presentation covering the various methods of prevention of corrosion. Material selection, design of structures, alteration of materials, alteration of environment, cathodic & anodic protection, and coatings are the different methods used. These are briefly described.
Acid Corrosion Inhibitor is designed specifically to inhibit the acidic attack on various metals such as Brass, Copper, Tin, Nickel, Zinc, Lead, Galvanized surface and all other type of steel.
Biosorption Tool for enviromental cleaning by microorganismsIke Nwiyi
Biosorption is one of the main components of environmental and bioresource technology. Microbes have been widely used in the process of environmental clean-up and are known as bioremediators
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
ENRICHMENT OF ORES BY MICROORGANISMS- Bioaccumulation and biomineralizationSijo A
Microbial ore leaching (bioleaching) is the process of extracting metals from ores with the use of microorganisms. This method is used to recover many different precious metals like copper, lead, zinc, gold, silver, and nickel. Microorganisms are used because they can:
lower the production costs.
cause less environmental pollution in comparison to the traditional leaching methods.
very efficiently extract metals when their concentration in the ore is low.
A presentation covering the various methods of prevention of corrosion. Material selection, design of structures, alteration of materials, alteration of environment, cathodic & anodic protection, and coatings are the different methods used. These are briefly described.
Acid Corrosion Inhibitor is designed specifically to inhibit the acidic attack on various metals such as Brass, Copper, Tin, Nickel, Zinc, Lead, Galvanized surface and all other type of steel.
Biosorption Tool for enviromental cleaning by microorganismsIke Nwiyi
Biosorption is one of the main components of environmental and bioresource technology. Microbes have been widely used in the process of environmental clean-up and are known as bioremediators
Isolation and Characterization of Nickel Tolerant Bacterial Strains from Elec...Agriculture Journal IJOEAR
Abstract— In the present study, an attempt was made to isolate and characterize nickel tolerant bacterial strains from the electroplating effluent contaminated soil. The effluent sample was collected at the direct outlet of electroplating industry and analyzed for physico-chemical characteristics such as pH (6.5), temperature (33), electrical conductivity (15.1 ms/cm), total solids (2309mg/l), total dissolved solids (5573 mg/l), chloride (0.20mg/l), sodium (0.13ppm), calcium (2.23ppm), potassium (0.20ppm), Biological Oxygen Demand (4200mg/l), Chemical Oxygen Demand (5243 mg/l) and nickel (4.063ppm). Enumeration of total bacterial population from the electroplating effluent contaminated soil sample was made in nutrient agar medium. Sixteen bacterial colonies were selected based on their abundance growth all of them were identified through morphological and biochemical characteristics. All the sixteen bacterial isolates were screened for its metal tolerance using nutrient agar medium incorporated with nickel metal. Based on the better growth performance, six bacterial strains were selected as potential metal tolerant organism. The selected metal tolerant bacterial strains were further characterized in the various environmental conditions such as pH (5, 7 & 9) temperature (5°C, 28°C, 37°C & 45°C) and concentration of metal ions (100ppm, 200ppm, 300ppm & 400ppm) for 5 days. The result reveals that one bacterial strain, Pseudomonas sp 1 was showed better growth in nickel metal based medium with pH 7 at 37°C temperature.
Thermodynamic and Electrochemical Aspects of Green Corrosion Inhibitors in Ac...ijtsrd
Mild steel a low carbon steel is an affordable engineering material used for many purposes in various environments including mild acidic environment with some precautions. The corrosion behaviour of mild steel MS in 0.5 M H2SO4 and 0.5 M HCl, in the temperature range 303–323 K without and with the inhibitor N 3,4 dimethoxyphenyl methyleneamino 4 hydroxy benzamide DMHB , was investigated using Potentiodynamic polarization and Electrochemical impedance spectroscopy EIS techniques supplementing with surface characterization study using scanning electron microscope SEM and atomic force spectroscopy AFM . Experimental observations were found to be in agreement with Density functional theory DFT calculations. The inhibition efficiency increases with increase in DMHB concentration and showed maximum inhibition efficiency of 86 in 0.5 M H2SO4 and 81 in 0.5 M HCl, respectively, at concentration of 3 × 10 3 M at 303 K. The inhibition efficiency of DMHB obtained relatively at its lower concentration 3 × 10 3 M compared to other reported related compounds confirms its potential towards corrosion inhibition. Dr. Rakesh Kumar Dubey "Thermodynamic and Electrochemical Aspects of Green Corrosion Inhibitors in Acidic Media at Mild Steel Surfaces" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-6 | Issue-4 , June 2022, URL: https://www.ijtsrd.com/papers/ijtsrd50128.pdf Paper URL: https://www.ijtsrd.com/chemistry/other/50128/thermodynamic-and-electrochemical-aspects-of-green-corrosion-inhibitors-in-acidic-media-at-mild-steel-surfaces/dr-rakesh-kumar-dubey
Effect of plant extracts on corrosion rate of mild steel in acidic mediumPremier Publishers
2.5ml Ethanol is used on plant extracts of locus bean (parkiabiglobosa) and banana sap (musaparadisiaca) as corrosion inhibitors for mild steel in 1M dilute HCl was investigated using weight loss techniques. Corrosion tests were first carried out for 1 and 3 hrs of immersion time respectively at various concentrations of extracts (0.5ml, 1.0ml, 1.5ml, 2.0ml and 2.5ml) and 2.5ml were used as corrosion inhibitors and at different temperatures (38oC, 45oC and 55oC). Results showed that the minimum corrosion rate obtained for 1 hr at 38oC with extract of Pakiabiglobosa is 0.85×10-4g/cm3/min and efficiency of 18.75% for 1hr, while at 55oC the corrosion rate was 4.37×10-4 g/cm3/min and efficiency of 33%. With ethanol extract of banana sap, minimum corrosion rate and efficiency recorded at 38°C were (4.16×10-4 g/cm3/min and efficiency of (22.1%), while at 55oC they were (0.83×10-4 g/cm3/min) and (7.6%) respectively. From these results, it is concluded that extracts of locust bean and banana sap can be successfully used as corrosion inhibitors in specified acidic medium.
Biosorption of Copper (II) Ions by Eclipta Alba Leaf Powder from Aqueous Solu...ijtsrd
The removal of heavy metals from industrial wastewater is of great concern as heavy metals are non-biodegradable, toxic elements that cause serious health problems if disposed of in the surrounding environment. The present study, Karisalangkani (Eclipta Alba) leaves were used for the adsorption of heavy metals like copper (Cu (II)) ions. The bio sorbent was characterized using SEM and BET analysis. The bio sorption experiments are conducted through batch system. The operating parameters studied were initial metal ion concentration, adsorbent dosage, initial solution pH, contact time and effect of temperature Adsorption equilibrium is achieved in 30 min and the adsorption kinetics of Cu (II) is found to follow a pseudo-second-order kinetic model. Equilibrium data for Cu (II) adsorption are fitted well by Langmuir isotherm model. The maximum adsorption capacity for Cu (II) ions is estimated to be 9.2 mgg at 25 °C. The experimental result shows that the materials have good potential to remove heavy metals from effluent and good potential as an alternate low cost adsorbent. Due to their outstanding adsorption capacities, Eclipta Alba is excellent sorbents for the removal of copper (II) ions. B. Kavitha | R. Arunadevi"Biosorption of Copper (II) Ions by Eclipta Alba Leaf Powder from Aqueous Solutions" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-5 , August 2018, URL: http://www.ijtsrd.com/papers/ijtsrd17156.pdf http://www.ijtsrd.com/chemistry/environmental-chemistry/17156/biosorption-of-copper-ii-ions-by-eclipta-alba-leaf-powder-from-aqueous-solutions/b-kavitha
Removal of Lead Ion Using Maize Cob as a BioadsorbentIJERA Editor
The intensification of industrial activity and environmental stress greatly contributes to the significant rise of
heavy metal pollution in water resources making threats on terrestrial and aquatic life. The toxicity of metal
pollution is slow and interminable, as these metal ions are non bio-degradable. The most appropriate solution for
controlling the biogeochemistry of metal contaminants is sorption technique, to produce high quality treated
effluents from polluted wastewater. Maize cob readily available was used as sorbent for the removal of lead ions
from aqueous media. Adsorption studies were performed by batch experiments as a function of process
parameters such as sorption 500ppm,2.5g, 400minutes, 400 rpm and 5 PH. Concentration, Dosage, time, rpm,
and pH. I have found that the optimized parameters are Freundlich model fits best with the experimental
equilibrium data among the three tested adsorption isotherm models. The kinetic data correlated well with the
Lagergren first order kinetic model for the adsorption studies of lead using maize cob. It was concluded that
adsorbent prepared from maize cob as to be a favorable adsorbent and easily available to remove the heavy
metal lead (II) is 95 % and can be used for the treatment of heavy metals in wastewater.
Effect of Inhibitor Concentration and Immersion Time on the Corrosion Rate an...AJSERJournal
The effect of inhibitor concentration and immersion time on the corrosion rate and inhibition efficiency of
AISI 1019 steel in seawater environment were investigated by means of weight loss measurement (WLM) at an interval
of 6days for a period of 60 days. AISI 1019 steel were immersed in seawater solution in the absence and presence of
varying inhibitor concentrations of potassium chromate (PC), Sodium Nitrite(SN), Methyl Orange (MO), Methyl Red
(MR), Terminalia Catappa Leaves (TCL) Extract, Carica papaya Leaves (CPL) Extract. The results showed that there is an
increase in inhibition efficiency with increase in inhibitor concentration and decrease in inhibition efficiency with
increase in immersion time. The inorganic inhibitor (potassium chromate), inorganic inhibitor (Sodium Nitrite), the
organic Inhibitor (Methyl Orange), the organic inhibitor (Methyl Red), the green inhibitor (Terminalia Catappa Leaves)
and green inhibitor (Carica Papaya Leaves) produced their best inhibition efficiency of 71.94%, 634%, 68.94%, 68.32%,
627% ,59.79% respectively at a concentration of 10g/L. From the result obtained, the potassium chromate inhibitor has
better inhibitory property than other inhibitors, which revealed that it is best suited for inhibition of corrosion of mild
steel in seawater environment.
The Use Of Ecchornia crassipes To Remove Some Heavy Metals From Romi Stream: ...iosrjce
The study involved a laboratory experiment on the use of Ecchornia crassipes in the removal of
some heavy metals from a stream polluted by waste water from Kaduna Refinery and Petrochemical Company.
Water sample was collected from Kaduna Refinery effluent point, Romi up and Romi down. The
Bioconcentration (BCF) and Biotranslocation (BTF) Factors of each metal were determined. The experinmental
study showed that Ecchornia crassipes is a suitable candidate for effective removal of heavy metals (Hg, Cd,
Mn, Ag, Pb, Zn) from Romi stream.
Red Dragon Fruit (Selenicereus costaricensis) Waste Peels as Corrosion Inhibi...Innspub Net
Metal corrosion is brought about by the oxidation of atoms on the surface, resulting in irreversible damage to structures at staggering costs. Hence, the search for efficient and cost-effective corrosion inhibitors is relevant. Waste agricultural by-products which have no food or economic value serve as good potential sources for these environmentally benign corrosion inhibitors. Ethanolic extracts of Red Dragon Fruit (RDF) have been previously reported to contain high amounts of flavonoids and polyphenols, which can manifest inhibitory activity against corrosion brought about by aggressive electrolytes. In this study, the ethanolic extract of Selenicereus costaricensis waste peels was tested for its anti-corrosion property using weight loss method. We have also probed its performance as a potential corrosion inhibitor at a range of different temperatures from 303 to 343 K. The calculated inhibition efficiency of 2% RDF was 97%. Thermodynamic studies reveal that increasing inhibitor concentration raises the activation parameters of mild steel in an acidic medium such as activation energy (Ea) and changes in enthalpy (DHo) and entropy (DSo). It was found that the corrosion inhibition process using RDF waste peel extract mainly occurs under diffusion control. Moreover, increased immersion time, inhibitor concentration, and temperature led to increased inhibition efficiency. The spontaneous process (DGoads = -23.47 kJ/mol) of adsorption of RDF on mild steel surfaces obeys the Langmuir isotherm model.
Sorption and transformation of toxic metals by microorganismsKhadija tul kubra
in which i discuss about the metals which are remediate by some microorganisms, these mtals poduce toxicity in the enviorment. some technologies or techniiques used to remove the heavy metals by the help of enginnered microorganisms.
Nanoparticles Methods for Nanoparticles Synthesis Overviewijtsrd
Nanoparticles exist in several different morphologies such as spheres, cylinders, platelets, tubes etc. The word nanoparticles are used to describe a particle with size in the range of 1nm to 100nm, at least in one of the three possible dimensions. In this size range, the physical, chemical and biological properties of the nanoparticles changes in fundamental ways from the properties of both individual atoms molecules and of the corresponding bulk materials. The enormous diversity of the nanoparticles arising from their wide chemical nature, shape and morphologies, the medium in which the particles are present, the state of dispersion of the particles and most importantly, the numerous possible surface modifications the nanoparticles can be subjected to make this an important active field of science now a days. Dr. Ilamathi Jayaraman | Dr. Vijayakumari. S "Nanoparticles: Methods for Nanoparticles Synthesis: Overview" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-6 , October 2021, URL: https://www.ijtsrd.com/papers/ijtsrd46478.pdf Paper URL : https://www.ijtsrd.com/biological-science/biotechnology/46478/nanoparticles-methods-for-nanoparticles-synthesis-overview/dr-ilamathi-jayaraman
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
Francesca Gottschalk - How can education support child empowerment.pptxEduSkills OECD
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Francesca Gottschalk - How can education support child empowerment.pptx
Biocorrosion 1
1. 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
2. Appl Microbiol Biotechnol
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
3. Appl Microbiol Biotechnol
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
4. Appl Microbiol Biotechnol
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  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
5. Appl Microbiol Biotechnol
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
6. Appl Microbiol Biotechnol
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.
7. Appl Microbiol Biotechnol
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
8. Appl Microbiol Biotechnol
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
9. Self corrosion rate X 10 -5(g/cm2/h)
Appl Microbiol Biotechnol
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
10. Appl Microbiol Biotechnol
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.
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