graphene coatings

A study of Graphene coatings as corrosion protective barrier for mild

steel in different chemical environments

Dissertation

Submitted in partial fulfillment of the requirements of

BITS G629T Dissertation

By

Allampalli Satya Sai Pavan

(2013H101012G)

Under the supervision of

Prof. Sutapa Roy Ramanan

Professor Department of Chemical Engineering

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE, PILANI,

K.K BIRLA GOA CAMPUS

ii

Acknowledgements

I have taken efforts in this project. However it would have not been possible without the kind of

support and help of many individuals. I would like to express my sincere thanks to all of them.

I am highly indebted to my Dissertation guide Prof. Sutapa Roy Ramanan for her guidance,

constant support and motivation.

I would like to express my gratitude towards other members of chemical engineering department

for their kind co-operation and encouragement which helped in completion of my project.

I would like to express my special thanks to my friends and last but not least my parents for their

continuous support and motivation during all times.

Place: BITS-Pilani, Goa Campus Allampalli Satya Sai Pavan

Date: 29/4/2015

iii

Certificate

This is to certify that the Dissertation entitled “A study of Graphene coatings as corrosion

protective barrier for mild steel in different chemical environments” and submitted by

Allampalli Satya Sai Pavan ID No. 2013H101012G in partial fulfillment of the requirement of

BITS G629T Dissertation embodies the work done by him/her under my supervision.

Date: Signature

Sutapa Roy Ramanan

Professor Chemical Engg Dept.

iv

Abstract

Mild Steel is one of cheapest and widely used engineering material. It is used in making chemical storage

vessels, tanks, machine parts of various equipments etc. However it has very low corrosion resistance.

Research has been going on to develop an anticorrosion coating for mild steel which doesn’t largely the

change properties of mild steel once coating has been applied. Graphene a single atomic monolayer of

graphite, possess a unique combination of properties that are ideal for anticorrosion coatings. Graphene is

chemically inert and stable in ambient atmosphere up to 400⁰C and can be grown on meter scale and can

be transferred on to metal substrates. Both single-layer and multilayer graphene films are exceptionally

transparent (>90% for layered graphene), so graphene coatings do not bring changes in the optical

properties of underlying metal. Graphene was synthesized using both Hummers and Modified Hummers

method. Graphene was then dispersed in 1- propanol using ultra sonic bath. The potential of graphene

coatings to serve as protective coating for mild steel against corrosion in various environments were

investigated. The graphene coatings were deposited on mild steel surface by dip coating technique. Multi

layers of graphene were coated on metal surface. The corrosion effect of these graphene coatings was

determined by open circuit potential test. Corrosion rates were determined using tafel analysis. Obtained

results indicated that graphene coating was showing anticorrosion coating properties in various

environments like acidic, basic and neutral media. Furthermore graphene was prepared using modified

method and corrosion test was carried in a similar fashion. These results were much better than those

obtained from previous. Multilayered coating (>4 layer coating) was not effective on mild steel surface as

van der Waal’s forces between two graphene layers come into play and coating was not adhering to mild

steel.

v

List of Figures and Tables

Table 1: Different forms of corrosion 1

Table 2: Chemicals and amount of chemicals used in Modified Hummers Method 7

Table 3: Chemicals and amount of chemicals used in Hummers Method 8

Figure 4.1: Uncoated metal tested in Distilled Water 12

Figure 4.2: Uncoated metal tested in Tap Water 12

Figure 4.3: Uncoated metal tested in NaCl (Salt Water) 13

Figure 4.4: Uncoated metal tested in NaOH 13

Figure 4.5: Uncoated metal tested in HCl 14

Figure 4.6: Metal coated (1 layer) with graphene (Hummers Method) tested in Distilled 15

Water

Figure 4.7: Metal coated (1 layer) with graphene (Modified Hummers Method) in Distilled 15

Water

Figure 4.8: Metal coated (1layer) with graphene (Hummers Method) tested in Tap 16

Water

Figure 4.9: Metal coated (1layer) with graphene (Modified Hummers Method) in Tap 16

Water

Figure 4.10: Metal coated with (1layer) graphene (Hummers Method) tested in NaCl 17

Figure 4.11: Metal coated with (1layer) graphene (Modified Hummers Method) in NaCl 17

Figure 4.12: Metal coated (1layer) with graphene (Hummers Method) tested in HCl 18

Figure 4.13: Metal coated (1layer) with graphene (Modified Hummers Method) tested in HCl 18

Figure 4.14: Metal coated (1layer) with graphene (Hummers Method) tested in NaOH 19

Figure 4.15: Metal coated (1layer) with graphene (Modified Hummers Method) tested in NaOH 19

Figure 4.16: Metal coated (2 Layer) with graphene (Hummers Method) tested in Distilled 20

Water

Figure 4.17: Metal coated (2 Layer) with graphene (Modified Hummers Method) tested in 20

Distilled Water

Figure 4.18: Metal coated (2 Layer) with graphene (Hummers Method) tested in Tap Water 21


Tap Water

Figure 4.20: Metal coated (2 Layer) with graphene (Hummers Method) tested in NaCl 22

Figure 4.21: Metal coated (2 Layer) with graphene (Modified Hummers Method) tested in NaCl 22

vi

Figure 4.22: Metal coated (2 Layer) with graphene (Hummers Method) tested in HCl 23

Figure 4.23: Metal coated (2 Layer) with graphene (Modified Hummers Method) tested in HCl 23

Figure 4.24: Metal coated (2 Layer) with graphene (Hummers Method) tested in NaOH 24


NaOH

Figure 4.26: Metal coated (3 Layer) with graphene (Hummers Method) tested in Distilled Water 25

Figure 4.27: Metal coated (3 Layer) with graphene (Modified Hummers Method) tested in Distilled 25

Water

Figure 4.28: Metal coated (3 Layer) with graphene (Hummers Method) tested in Tap Water 26

Figure 4.29: Metal coated (3 Layer) with graphene (Modified Hummers Method) tested in Tap 26

Water

Figure 4.30: Metal coated (3 Layer) with graphene (Hummers Method) tested in NaCl 27

Figure 4.31: Metal coated (3 Layer) with graphene (Modified Hummers Method) tested in NaCl 27

Figure 4.32: Metal coated (3 Layer) with graphene (Hummers Method) tested in HCl 28

Figure 4.33: Metal coated (3 Layer) with graphene (Modified Hummers Method) tested in HCl 28

Figure 4.34: Metal coated (3 Layer) with graphene (Hummers Method) tested in NaOH 29

Figure 4.35: Metal coated (3 Layer) with graphene (Modified Hummers Method) tested in NaOH 29

Table 4: % decrease in corrosion when tested in Distilled Water 30

Table 5: % decrease in corrosion when tested in Tap Water 30

Table 6: % decrease in corrosion when tested in NaCl 30

Table 7: % decrease in corrosion when tested in HCl 30

Table 8: % decrease in corrosion when tested in NaOH 31

Figure 4.36: Plot between corrosion rate and number of coatings 31

Figure 4.7.1: Bare metal when exposed to NaCl environment 32

Figure 4.7.2: 3 layer graphene coated metal exposed to NaCl environment 32

Figure 4.8.1: XRD plot 33

vii

Contents

Title Page i

Acknowledgements ii

Certificate iii

Abstract iv

List of Figures and Tables v

Table of Contents vi

1. Introduction 1

2. Literature Survey

2.1 Corrosion of Material 2

2.2 Types of Coatings

2.2.1 Metallic Coatings 3

2.2.2 Inorganic Coatings 3

2.2.3 Organic Coatings 3

2.3 Graphene

2.3.1 Introduction 4

2.3.2 Applications 4

2.4 Graphene – Potential Candidate for Anticorrosion Coating 5

2.5 Types of Corrosion Tests 6

3. Experimental

3.1 Raw Materials 7

3.2 Synthesis of GO (Modified Hummers Method) 7

3.3 Reduction of GO using Sodium Borohydride 7

3.4 Synthesis of GO (Hummers Method) 8

3.5 Reduction of GO using Sodium Borohydride 8

3.6 Protocol for Dip Coating 9

3.7 Protocol for Corrosion Test 10

3.8 Characterization 11

4. Results and Discussion

4.1 Uncoated Metal 12

4.2 Graphene 1 Layer Coating 15


viii


4.5 Comparison of Results 30

4.6 Metal Coupons with more than 3 Layer Coatings 31

4.7 Characterization of Metal Coupon 32

4.8 Characterization of Graphene using XRD 33

5. Conclusions 34

6. References 35

1

1. Introduction

Mild steel is cheapest and commonly used construction material. It has been extensively used for many

centuries in many areas for water pipes, vessels, tanks, docks and in process industries etc. Because of its

low nobility and structural defects mild steel corrodes quickly when it is exposed to different

environments (Pierre R et al – 2007).

Depending on corrosion environment mild steel can be protected in many ways: by applying different

organic coatings, by using cathodic or anodic inhibitors, cathodic and anodic protection, by using

conductive polymeric coatings, by introducing a stable protective layer of inert metals etc. However,

organic coatings are expensive, inhibitors cannot be applied under certain conditions and polymeric

coatings are relatively thick and may change the physical properties of underlying materials.

Graphene, a single atomic monolayer of graphite, possess a unique combination of properties that can

potentially be ideal for anticorrosion coatings. Graphene is chemically inert and stable in ambient

atmosphere up to 400⁰C (Dhiraj et al – 2012) and can be grown on meter scale and can be transferred on

to metal substrates. Both single-layer and multilayer graphene films are exceptionally transparent (>90%

for layered graphene), so graphene coatings do not bring changes in the optical properties of underlying

metal (Blake P et al – 2008). However, one thing that is lacking in literature is detailed investigations of

the effect that graphene on the electrochemical response of underlying metals. Little research has been

done on graphene as protection coating for steel. However, pure graphene was not used. Graphene was

mixed with different polymers and its anticorrosion ability was seen.

In this thesis work, graphene was synthesized from graphite oxide by using Hummers and Modified

Hummers method instead of direct growth of graphene layers on metal surfaces by Chemical Vapor

Deposition (CVD) technique. Graphene was then dispersed in 1- propanol using ultra sonication bath.

Graphene coating is amenable to dipping on a clean metal. The heat treatment of coated metal is needed

to obtain a proper protective film.

The proposal of this thesis provides an important insight of how effectively graphene can behave as

anticorrosion coating for mild steel. Quality of graphene produced by Hummers and Modified Hummers

method was evaluated, by comparing corrosion rates of metal coupons.

2

2. Literature Survey

2.1 Corrosion of Material

Corrosion is defined as the destruction or deterioration of a material because of reaction with its

environment. Corrosion can be fast or slow. For example 18-8 stainless steel is badly attacked in

hours by polythionic acid. Deterioration of metal by physical causes is not called as corrosion it is

referred as erosion. Rusting applies to the corrosion of iron or iron base alloys with the formation of

corrosion products largely containing hydrous ferric oxides. Nonferrous metals therefore corrode does

not rust.

Practically all environments are corrosive to some degree. In general inorganic materials are more

corrosive than organic materials. Higher temperatures and pressures usually involve more severe

corrosion conditions. Materials are susceptible for different types of corrosion such as uniform

corrosion, pitting corrosion and filiform corrosion etc. The type of corrosion depends on metal alloy

composition and the surrounding medium.

Types of Corrosion Definition

Uniform Attack It is normally characterized by chemical or

electrochemical reaction that proceeds uniformly

over the entire exposed area.

Galvanic Corrosion A potential difference usually exists between two dissimilar metals when they are immersed in

corrosive or conductive solution. Electrons start to

flow due to potential difference and less corrosion resistant metal starts to get corroded.

Crevice Corrosion Intensive localized corrosion frequently occurs

within crevices and other shielded areas on metal

surfaces exposed to corrosives. This type of attack is usually associated with small volumes of

stagnant solution caused by holes, gasket

surfaces, crevices under bolts and rivet heads.

Filiform Corrosion This is a special type of crevice corrosion. It

occurs under protective films and for this reason it

often referred as underfilm corrosion. This type of corrosion doesn’t affect metal’s strength. It affects

only surface appearance.

Pitting Pitting is form of extremely localized attack that

results in holes in the metal. It causes equipment to fail because of perforation.

Table 1: Different forms of corrosion

3

2.2 Types of Coatings

2.2.1 Metallic coatings

Metal coatings are applied by dip coating, electro plating, spraying. The selection of a coating

process depends on several factors, including corrosion resistance that is required, the anticipated

lifetime of the coated material and environmental considerations. Hot dipping is carried out by

immersing the metal on which the coating is to be applied, usually steel, in a bath of molten metal

that is to constitute the coating, most commonly zinc, but also aluminum and aluminum-zinc

alloys. In electroplating the substrate or the base metal is made cathode in an aqueous electrolyte

from which the coating is deposited. A wide variety of coatings can be applied by electro plating

for example zinc, cadmium, copper, nickel etc.

2.2.2 Inorganic coatings

Vitreous enamels, glass linings and porcelain enamels are all essentially glass coatings of suitable

coefficient of expansion fused on metals. Glass in powdered form (as glass frits) is applied to a

pickled or otherwise prepared metal surface, then heated in a furnace at a temperature that softens

the glass and allows it to bond to the metal. Several coats may be applied Vitreous enamel

coatings are mostly used on steel, but some coatings are possible on copper, brass and aluminum.

Portland cement coatings have advantage of low cost, ease of application or repair. These

coatings can be applied by centrifugal casing, by toweling or by spraying. Usual thickness ranges

from 5 to 25mm, thick coatings are usually reinforced with wire mesh. These coatings are used to

protect cast iron and steel water pipelines on water or soil side or both. These are also used as

interior of oil tanks and chemical storage tanks.

Chemical conversion coatings are protective coatings formed in situ by chemical reaction with

the metal surface. They include special coatings such as PbSO4 which forms when lead is

exposed to sulfuric acid and iron fluoride which is formed when steel containers are filled with

hydrofluoric acid ( >65% HF)

2.2.3 Organic coatings

Synthetic resins like phenol-formaldehyde formulations which can withstand boiling water or

slightly higher temperatures are used in chemical industry by applying multiple coats, baked on,

for resisting a variety of corrosive media. Silicone and polyamide resins are useful at still higher

temperatures. Alkyd resins, because of favorable cost, fast-drying properties and durability have

found wide applications for protecting the metal surfaces of machinery and home appliances.

Vinyl resins have good resistance to penetration by water. Their resistance to alkali makes them

useful for painting structures that are to be protected cathodically. Epoxy resins are also resistant

to alkali and to many other chemical media and have distinguishing property of adhering well to

metal surface. These epoxy coatings are mainly useful in coatings of ferrous pipelines. Plastic

coatings of vinyl or polyethylene can be applied as adhesive tape, particularly to buried metal

structures. Such tape finds practical use for coating pipe and auxiliary equipment including pipe

connections and valves exposed to soil. One of the most stable plastics in terms of resisting a

wide variety of chemical media is Teflon. It successfully resists aqua medium and boiling

concentrated acids such as HF, H2SO4, and HNO3. It resists boiling concentrated alkalis, gaseous

chlorine and all organic solvents up to 250⁰C.

4

2.3 Graphene

2.3.1 Introduction

Graphene is a thin layer of pure carbon; it is single, tightly packed layer of carbon atoms that are

bonded together in a hexagonal honeycomb lattice. In more complex terms it is an allotrope of

carbon in the structure of planar sp2 bonded atoms with a C-C bond length of 0.142 nanometers

and with an inter planar spacing of 0.335 nanometers.

It is the thinnest known compound to man at one atom thick. It is the lightest known material

(with 1 square meter coming in around 0.77 milligrams), the strongest compound (between 100-

300 stronger than steel and with a tensile stiffness of 150,000,000), best conductor of heat at

room temperature and best conductor of electricity.

With such kind of exceptional properties it is obvious that Graphene is being currently used in

many fields like biological engineering, optical electronics, ultra filtration, composite materials,

photovoltaic cells, energy storage device.

2.3.2 Applications

2.3.2.1 Biological engineering

With graphene offering a large surface area, high electrical conductivity, thinness and strength, it

would make a good candidate for the development of fast and efficient bioelectric sensory

devices, with the ability to monitor such things as glucose levels, hemoglobin levels, cholesterol

and even DNA sequencing.

2.3.2.2 Optical electronics

Graphene is an almost completely transparent material and is able to optically transmit up to

97.7% of light. It is also highly conductive, as we have previously mentioned and so it would

work very well in optoelectronic applications such as LCD touch screens for smart phones, tablet

and desktop computers and televisions.

2.3.2.3 Ultrafiltration

Another standout property of graphene is that while it allows water to pass through it, it is almost

completely impervious to other liquids and gases (even relatively small helium molecules). This

means that graphene could be used as an ultrafiltration medium to act as a barrier between two

substances.

2.3.2.4 Composite materials

Graphene is strong, stiff and very light. Currently, aerospace engineers are incorporating carbon

fiber into the production of aircraft as it is also very strong and light. However, graphene is much

stronger whilst being also much lighter. Ultimately it is expected that graphene is utilized

(probably integrated into plastics such as epoxy) to create a material that can replace steel in the

structure of aircraft, improving fuel efficiency, range and reducing weight. Due to its electrical

conductivity, it could even be used to coat aircraft surface material to prevent electrical damage

resulting from lightning strikes.

2.3.2.5 Energy storage

One area of research that is being very highly studied is energy storage. While all areas of

electronics have been advancing over a very fast rate over the last few decades, the problem has

always been storing the energy in batteries and capacitors when it is not being used. Graphene

based micro-supercapacitors will likely be developed for use in low energy applications such as

5

smart phones and portable computing devices and could potentially be commercially available

within the next 5-10 years.

2.4 Graphene – potential candidate for anticorrosion coating

As graphene possesses some exceptional properties mentioned above, it can be used in many

fields. However there are some special properties which make graphene a potential candidate for

anticorrosion coatings. To date the ability of graphene to serve as effective protection barrier has

not been widely pursued. In such a context, if graphene can be used as a coating on metals, it can

not only provide the opportunity to have an extremely light weight coating that does not

significantly alter optical properties or decrease bulk thermal/electrical conductivity but can

potentially halt the formation of oxide layer on metal surfaces.

Graphene is considered inert under conditions where other protective coatings will undergo rapid

chemical reactions. This property is due to graphene film is impermeable to gas molecules

(Raman Singh et al – 2012). Along with high inherent capacity graphene also provides large

surface which means only small quantities of this material is required to coat metal surfaces.

Graphene also provides oxidation resistance while its hydrophobocity prevents hydrogen bonding

with water. Furthermore graphene being thermally stable even at high temperatures (around

400⁰C), where other protective coatings will be thermally degraded makes graphene a possible

candidate for anticorrosion coating at higher temperatures too.

Corrosion can be inhibited or controlled by introducing a stable protective layer made of inert

materials, conductive polymers or even thiol based monolayer. However these protective layers

have many limitations like thiol monolayer cannot be used for temperatures greater than 100⁰C

(Chang et al – 2014). Polymeric coatings are relatively thick and will significantly change the

physical properties of the underlying material. Graphene being monolayer of graphite possess a

unique combination of properties as mentioned above which make this material ideal for

anticorrosion coating. Both single and multi layered (up to 4 layers) are exceptionally transparent

(>90% transmittance for 4 layered graphene) thus graphene coatings does not disturb the optical

properties of underlying material.

Combination of all these exceptional properties of graphene gives us a chance to explore

graphene as anticorrosion coating.

6

2.5 Types of Corrosion Tests

Corrosion tests are mainly divided into electrochemical tests and non electrochemical tests.

Electrochemical tests are non destructive tests and can be completed quickly. Whereas non

electrochemical tests are destructive tests and takes lot of time to determine corrosion rate.

2.5.1 Non Electrochemical Test

These tests include salt spray test, immersion test etc.

2.5.1.1 Salt Spray Test

Salt spray test is a popular test used to check the corrosion resistance of materials and surface

coatings. It is an accelerated test that produces corrosive attack to coated samples. Results are

reported in hours (number of hours without corrosion appearance)

2.5.1.2 Immersion Test

Polished coupons are immersed in corrosive environment for particular time period of 14, 28 and

42 hours. After that these coupons are taken out and dried. Then coupons are weighed to

determine weight loss and corrosion rate.

2.5.2 Electrochemical Test

These tests include Open Circuit Potential,Impedance

2.5.2.1 Open Circuit Potential

The open circuit potential (also referred to as the equilibrium potential, the rest potential, or the

corrosion potential) is the potential at which there is no current; that is, experiments based on the

measurement of the open circuit potential are potentiometric experiments.

2.5.2.2 Impedance

Measurement of impedance of corroding electrode has become important in corrosion prediction

for such diverse applications as coatings and corrosion rate estimation in low conductivity media.

As most commonly practiced an electrode is subjected to small amplitude (5-10 mV) in

sinusoidal variation in the voltage of varying frequency, usually about corrosion potential.

7

3. Experimental

3.1 Raw Materials

Graphite powder with 99% purity from Sigma – Aldrich was used to prepare Graphite Oxide

(GO). KMnO4 99% was obtained from Fisher Scientific. NaNO3 (99% purity) and H2O2 (30%

Analytical Reagent) were obtained from S D Fine Chem Limited. NaBH4 with 99% purity from

Sigma - Aldrich was used as reducing agent to prepare Graphene.

3.2 Synthesis of GO (Modified Hummers Method)

Graphite powder was dried at 60⁰C in a oven for 2 hours. This was done to remove moisture

present in graphite powder. 0.40 grams of graphite powder which was free of moisture and 0.30

grams of Sodium Nitrate were added in a 250ml glass beaker which was placed in an ice bath.

Then 14ml of Sulfuric Acid (98% conc.) was added slowly into 250ml beaker. This mixture was

under continuous magnetic stirring for 2 hours. Sulfuric Acid was added slowly (for 10 minutes)

in order to avoid excess heat. Next 1.8 grams of Potassium Permanganate was added slowly to

above solution while stirring in ice bath. Potassium Permanganate too was added slowly. This

solution was kept on stirring for 2 hours. Then solution was kept ageing for 5 days. At the end of

5th day 5 weight% H2SO4 was added. After 2 hours of magnetic stirring 16ml of H2O2 was added

to above solution and it turned to little yellow (during hydrogen peroxide addition). This light

yellow colored solution was magnetically stirred overnight. The solution then turned into brown

color and it was washed with 3 weight% H2SO4 (100 ml) by centrifugation. Centrifugation was

performed for 10 minutes at 10000 rpm. The solution obtained was Graphite Oxide.

3.3 Reduction of GO using Sodium Borohydride

13ml of graphite oxide was added with 35ml of distilled water into 250ml glass beaker. Then

10ml of 0.15 M Sodium Borohydride aqueous solution was added to above mixture. Temperature

of above solution was maintained at 80⁰C for 2 hours while magnetically stirring. Final solution

was washed with 100ml distilled water by centrifugation. Then graphene is obtained in the form

of solution.

Chemical Quantity used

Graphite Powder 0.40 grams

Sodium Nitrate 0.30 grams

Potassium Permanganate 1.80 grams

Sulfuric Acid 14ml – before ageing 1ml – after ageing

3ml – during centrifugation

Hydrogen Peroxide 16ml

Distilled Water 19ml – after ageing 97ml – during centrifugation

35ml – during reduction of GO

Sodium Borohydride 57 milligrams

Table 2: Chemicals and amount of chemicals used in Modified Hummers method

8

3.4 Synthesis of GO (Hummers Method)

2 grams of graphite powder was added to 46ml of H2SO4 under continuous magnetic stirring in an

ice bath. 1 gram of Sodium Nitrate and 6 grams of Potassium Permanganate were added gradually

and successively. Ice bath was removed and suspension was allowed to come to room

temperature. 92ml of distilled water was added to this mixture. Following this, 20ml of Hydrogen

Peroxide was added and the solution turned bright yellow. The suspension was filtered and filter

cake was washed with distilled water and this solution was subjected to centrifugation.

Centrifugation was performed for 10 minutes at 10000 rpm.

3.5 Reduction of GO using Sodium Borohydride

13ml of graphite oxide was added with 35ml of distilled water into 250ml glass beaker. Then

10ml of 0.15 M Sodium Borohydride aqueous solution was added to above mixture. Temperature

of above solution was maintained at 80⁰C for 2 hours while magnetically stirring. Final solution

was washed with 100ml distilled water by centrifugation. Then graphene is obtained in the form

of solution.

Chemical Quantity used

Graphite Powder 2 grams

Sodium Nitrate 1 gram

Potassium Permanganate 6 grams

Sulfuric Acid 46 ml

Hydrogen Peroxide 20 ml

Distilled Water 92 ml – for dilution of solution 100 ml – during centrifugation

Sodium Borohydride 57 milligrams

Table 3: Chemicals and amount of chemical used in Hummers method

Difference between Modified Hummers and Hummers method was in ageing of solution. In

Modified Hummers method solution was kept for ageing (5 days) before addition of Hydrogen

Peroxide. This ageing was done to give more time for oxidation of solution. But in Hummers

method there is no ageing involved.

Graphene obtained from above solution was then dispersed in 1-propanol using ultra sonication

bath. This dispersed solution was used as anticorrosion coating for mild steel.

9

3.6 Protocol for Dip Coating

Take metal coupon and hang it in dip coating set up with the help of strings

Transfer the above prepared graphene solution to cultured bottle which is placed just

below the metal coupon which is hanging

Dip the coupon in the solution and start the motor, now metal coupon is lifted from the

solution at a speed of 0.0125 m/s

Take out the metal coupon which is hanging and put it in air oven at 75⁰C for 10 minutes

After heat treatment of metal coupon take the metal coupon from the oven and allow it to

cool up to room temperature.

Repeat same steps (according to number of coats required) for multi layered coatings

10

3.7 Protocol for Corrosion Test

This test is done on CH Instruments, model no. 680

After completion of coating, put metal coupon in glass beaker containing electrolyte (test

solution)

Put Ag/AgCl electrode as reference and Platinum wire as counter electrode

Connect metal coupon (working electrode) with green wire, counter electrode to be connected

with red wire and reference electrode will be connected with white wire.

Start CH Instrument, then amp booster and connect the system with computer

Start CH Instrument software and click on techniques to select Open Circuit Potential – Time

Run it for 400 seconds, and click on Controls Open Circuit Potential Equilibrium

Potential is displayed

Click on techniques to select Tafel Plot and give initial and final potential values by adding and

subtracting 0.2 to equilibrium potential

Select autosense and click on OK button

Click on play button to run Tafel Plot test for the system

When the run is completed, click on curve fitting to get exact plot

Click on analysis Special Analysis

New dialogue box will open

Enter the values for molecular weight, valency and density of the metal used

Click on calculate to get the corrosion rate of material

By just changing the chemical in glass beaker (testing cell) we can calculate corrosion of same

metal coupon in different chemical conditions

11

3.8 Characterization

The microstructural characterization of metal coupons which were coated with graphene and

exposed to corrosive environment were carried out using Optical Microscope.

Morphological characterization of Graphene was carried out using X-Ray Diffraction (XRD)

12

4 Results and Discussion

After coating process was done corrosion rate was determined by following above mentioned protocol.

Corrosion test was carried in five different chemical media such as Distilled Water (pH 7.07), Tap Water

(pH 7.77), NaCl (3.5 wt %), HCl (0.1 N) and NaOH (1 M)

4.1 Uncoated Metal

This set of graphs show how uncoated metal behaves in five different media

Fig 4.1: Uncoated metal tested in Distilled Water

Fig 4.2: Uncoated metal tested in Tap Water

13

Fig 4.3: Uncoated Metal tested in NaCl (Salt Water)

Fig 4.4: Uncoated metal tested in NaOH (Basic Environment)

14

Fig 4.5: Uncoated metal tested in HCl (Acidic Environment)

15

4.2 Graphene 1 Layer Coating

Graphene prepared by both methods were coated on metal coupons and tests were carried out in five

different media

Fig 4.6: Metal coated with Graphene (Hummers method) tested in Distilled Water

As compared to uncoated metal corrosion rate is reduced by 90.4%

Fig 4.7: Metal coated with Graphene (Modified Hummers method) tested in Distilled

Water


16

Fig 4.8: Metal coated with Graphene (Hummers method) tested in Tap Water

As compared to uncoated metal corrosion rate is decreased by 68.9%

Fig 4.9: Metal coated with Graphene (Modified Hummers Method) tested in Tap Water

As compared to uncoated metal corrosion rate is decreased by 80%

17

Fig 4.10: Metal coated with Graphene (Hummers Method) tested in NaCl


Fig 4.11: Metal coated with Graphene (Modified Hummers Method) tested in NaCl


18

Fig 4.12: Metal coated with Graphene (Hummers Method) tested in HCl


Fig 4.13: Metal coated with Graphene (Modified Hummers Method) tested in HCl


19

Fig 4.14: Metal Coated with Graphene (Hummers method) tested in NaOH


Fig 4.15: Metal coated with Graphene (Modified Hummers method) tested in NaOH


20

4.3 Graphene 2 Layer Coating

Metal coupons are coated double layer and tested in five different media

Fig 4.16: Metal coated with Graphene (Hummers method) tested in Distilled Water


Fig 4.17: Metal coated with Graphene (Modified Hummers Method) tested in Distilled

Water


21

Fig 4.18: Metal Coated with Graphene (Hummers Method) tested in Tap Water




22

Fig 4.20: Metal coated with Graphene (Hummers method) tested in NaCl




23





24

Fig 4.24: Metal coated with Graphene (Hummers method) tested in NaOH


Fig 4.25: Metal Coated with Graphene (Modified Hummers Method) tested in NaOH


25

4.4 Graphene 3 layer coating

Metal coupons are 3 layered coatings with Graphene and tests were conducted in 5 different media

Fig 4.26: Metal coated with Graphene (Hummers Method) tested in Distilled Water


Fig 4.27: Metal coated with Graphene (Modified Hummers Method) tested in Distilled Water


26

Fig 4.28: Metal coated with Graphene (Hummers Method) tested in Tap Water




27

Fig 4.30: Metal Coated with Graphene (Hummers Method) tested in NaCl




28





29

Fig 4.34: Metal Coated with Graphene (Hummers method) tested in NaOH


Fig 4.35: Metal Coated with Graphene (Modified Hummers method) tested in NaOH


30

4.5 Comparison of Results

Metal coupon tested in Distilled Water (pH – 7.07)

Metal Surface CR – mpy

(Graphene via

Modified Hummers Method)

CR – mpy

(Graphene via

Hummers Method)

% decrease in

corrosion (graphene

via Modified Hummers Method)

% decrease in

corrosion (graphene

via Hummers Method)

Uncoated 282 282 NA NA

1 Layer Coating 39 27 86 90.4

2 Layer Coating 6.5 25 97.6 91.1

3 Layer Coating 3.5 22.5 98.7 92

Table4: % decrease in corrosion when tested in Distilled Water (pH – 7.07)

Metal coupon tested in Tap Water (pH – 7.77)


(Graphene via

Modified

Hummers Method)

CR – mpy

(Graphene via

Hummers Method)

% decrease in

corrosion (graphene

via Modified

Hummers Method)

% decrease in

corrosion (graphene

via Hummers

Method)


1 Layer Coating 44 64 80 70.9

2 Layer Coating 36 42.5 83.6 80.6

3 Layer Coating 20.5 37 90.6 83.1

Table 5: % decrease in corrosion when tested in Tap Water (pH – 7.77)

Metal coupon tested in NaCl (3.5 wt %)


(Graphene via


CR – mpy

(Graphene via

Hummers Method)

% decrease in

corrosion (graphene


% decrease in

corrosion (graphene

via Hummers Method)


1 Layer Coating 17 208 97.4 68.6

2 Layer Coating 5 148 99.2 77.8

3 Layer Coating 3 60 99.5 91

Table 6: % decrease in corrosion when tested in NaCl (3.5 wt %)

Metal coupon tested in HCl (0.1 N)


(Graphene via

Modified

Hummers Method)

CR – mpy

(Graphene via

Hummers Method)

% decrease in

corrosion (graphene

via Modified

Hummers Method)

% decrease in

corrosion (graphene

via Hummers

Method)


1 Layer Coating 207 490 60.4 6.3

2 Layer Coating 135 184 76 64.8

3 Layer Coating 68.5 164 86.9 68.6 Table 7: % decrease in corrosion when tested in HCl (0.1 N)

31

Metal coupon tested in NaOH (1 M)


(Graphene via


CR – mpy

(Graphene via

Hummers Method)

% decrease in

corrosion (graphene


% decrease in

corrosion (graphene

via Hummers Method)


1 Layer Coating 189 86.5 78.6 90.2

2 Layer Coating 27 20 96.9 97.7

3 Layer Coating 10 7 98.8 99.2

Table 8: % decrease in corrosion when tested in NaOH (1 M)

4.6 Metal Coupons with more than 3 Layered Coatings

Graphene coatings of 4, 5 and 6 layers were made on metal coupons. At 5 and 6 coatings the corrosion

rate was almost similar. If we add further coatings on it Graphene will not adhere to metal coupon as there

will be more van der Waal’s forces between two successive coatings. Corrosion test was conducted for

these multilayered coatings in Distilled Water environment and results are plotted as shown below.

Fig 4.36: Plot between corrosion rate and number of coatings

32

4.7 Characterization of Coated Metal Coupons

Coupons which were coated with Graphene by using Dip Coating and exposed to corrosive environment

are characterized using Optical Microscope. The images produced by microscope gave clearer picture of

coupons.

Fig 4.7.1: Bare Metal Exposed to NaCl environment

Fig 4.7.2: 3 Layer Graphene coated metal coupon exposed to NaCl environment

33

4.8 Characterization of Graphene using XRD

Graphene which was synthesized previously was heated up to 100⁰C for 36 hours. Then Graphene

powder was obtained. This powder was subjected to characterization using XRD.

Fig 4.8.1: XRD Plot

From analysis it can be seen that there is sharp peak at 26.5 degrees. There are two small peaks at 42

degrees and 55 degrees.

Glaucio Carley et al (2013), Titash Mondal et al (2012) have reported same results. In their analysis too

Graphene was showing a sharp peak at 26.5 degrees. From this we can confirm that graphene synthesized

here was of good quality.

34

5 Conclusions

From the experimental setup and analysis we found that Graphene prepared by Modified Hummers

method was acting as affective anticorrosion coating compared to Graphene prepared by Hummers

method. When compared to other corrosion inhibitors like vapor phase organic inhibitors, paints etc

Graphene as anticorrosion coating for Mild Steel is giving almost same results. If Graphene is directly

grown on metals by using techniques like Chemical Vapor Deposition (CVD) then we will get much

better results for graphene as anticorrosion coating.

Graphene coatings don’t change optical and physical properties of metal. If there are more than 6 layered

coating of graphene on metal surface those coatings will not be affective as van der Waal’s forces come

into action and coatings will not adhere to previous coatings. Graphene prepare by Modified Hummers

method was of better quality because this method involved ageing. Due to this lot of time for oxidation

reaction was available. But it was not same in the case of Hummers method as there was no ageing of

solution.

35

6 References

[1] Mars G. Fontona, Corrosion Engineering 3rd

edition. Tata McGraw Hill

[2] Allen J. Bard and Larry A. Faulkner, Electrochemical Methods Fundamental and Application 2nd

edition. Wiley Student Edition

[3] Y. Zhu , S. Murali , W. Cai , X. Li , J.W Suk, J.R. Potts, R.S. Ruoff : Graphene and Graphene

Oxide: Synthesis, Properties, and Applications: Advanced Materials 22 [3906–3924] (2010)

[4] W. Hummers, R. Offeman: Preparation of graphitic oxide: Journal of the American

Chemical Society 80 [1339] (1958)

[5] D.C. Marcano et al: Improved synthesis of graphene oxide: Journal of the American

Chemical Society 4 [4806-4814] (2010)

[6] T. Chen, B. Zeng, J.L. Liu, J.H. Dong, X.Q. Liu, Z. Wu, X.Z. Yang, Z.M. Li: High throughput

exfoliation of graphene oxide from expanded graphite with assistance of strong oxidant in modified Hummers method : Journal of Physics: Conference Series 188 (2009)

[7] F. Ali, N. Agarwal, P.K. Nayak, R. Das, and N. Periasamy: Chemical route to the formation of graphene: Current Science 97 [683-685] (2009)

[8] W. Choi, I. Lahiri, R. Seelaboyina, Y.S. Kang: Synthesis of Graphene and Its Applications:

A Review: Solid State and Materials Sciences 35 [52-71] (2010)

[9] N.T. Kirkland, T. Schiller, N. Medhekar, N. Birbilis: Exploring Graphene as a corrosion protection

barrier: Corrosion Science, Volume 56 (2012) 1-4

[10] Vesna Misˇkovic´-Stankovic et al: Electrochemical Study of corrosion behavior of graphene coatings

on copper and aluminum in chloride solutions: Carbon 75 (2014) 335-344

[11] Dhiraj Prasai et al: Graphene: Corrosion Inhibiting coating, ACS NANO 6 (2012) 1102-1108

[12] Ellie Teo Yi Lih, Rubaiyi bt. Mat Zaid, Tan Ling Ling, and Kwok Feng Chong: Facile corrosion protection coating from Graphene: International Journal of Chemical Engineering and Applications,

Volume 3, (2012)

[13] R.K. Singh Raman and Abhishek Tiwari: Graphene: The thinnest known coating for corrosion

protection, Journal of Minerals, Metals and Materials Society, Volume 66 (2014)

[14] M. Topsakal et al: Graphene Coatings – An efficient protection from Oxidation: Physical Review, Volume 85 (2012)

graphene coatings

Documents

study of graphene coatings

potential of graphene

layered graphene

multilayer graphene

multi layers of graphene

mild steel surface

abstract mild steel

anticorrosion coatings