VIII

ABSTRAK

Elektrosaduran adalah salah satu proses biasa bagi objek logam salutan dan

urutan prarawatan yang perlu untuk membolehkan logam tertentu untuk electroplated

dengan salutan pengikut, keperluan ini adalah disebabkan oleh kehadiran dengan

hadir lapisan oksida yang sangat tipis yang membentuk kerana kereaktifan

kimia logam berkenaan.Tujuan projek ini adalah untuk menentukan kesan Karbon

Nano Tube (CNT) Ni yang electrodeposited tembaga logam asas dengan teknik

electrodeposition langsung.Sebaliknya kesan parameter electrodeposition seperti

ketumpatan arus dan masa penimbunan pada perekatan dan sifat-sifat mekanik

pemendapan telah dikaji. Logam yang didepositkan akan dicirikan oleh SEM,

Mikrograf Optical FESEM, EDAX dan ujian mekanikal Mikro.

IX

ABSTRACT

Electroplating is one of the common processes for coating metallic objects

and pretreatment sequences are necessary in order to enable certain metals to be

electroplated with adherent coating, this need is due to the presence with present of a

very thin oxide layer which forms due to chemical reactivity of the metal concerned.

The aim of this project is to study the suspension of carbon nano tubes and

synthesize a Ni-CNT composite coating by electro deposition using direct plating.

On the other hand the effect of electrodeposition parameters such as current density

and deposition time on the adhesions and mechanical properties of deposition have

been studied. The deposited Ni-CNT composite coating would be characterized by

SEM, Optical Micrograph, FESEM, EDAX and Micro mechanical testing.

X

Table of Contents

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION vi

ACKNOWLEDGEMENTS vii

ABSTRACT viii

ABSTRAK ix

TABLE OF CONTENTS x

LIST OF TABLES xiii

LIST OF FIGURES xiv

CHAPTER 1 INTRODUCTION 1

1.1 Background 1

1.2 Nickel 5

1.3 Nano-Nickel Crystals 9

1.4 Carbon Nano Tubes (CNT’s) 10

1.5 Problem statements 14

1.6 Scope 17

CHAPTER 2 LITERATURE REVIEW 18

XI

2.1 Plating sequences 18

2.2 Application of Electroplating 20

2.3 Application of composite coatings 22

2.4 Mechanism of general electrodeposition 25

2.5 Deposition of composite coatings 29

2.6 Methods of plating on copper as substrate 31

2.6.1 Mechanical roughening 31

2.6.2 Direct electroplating 32

2.6.3 Effect of Current Density on Grain Size 33

2.7 Agitation rate 38

2.8 Type of nickel plating solution 41

2.8.1 Watts nickel plating solution 43

2.9 Electrochemical solution’s temperature 44

2.10 Effect of Current on Hardness 45

2.11 Effect of Surfactant on dispersion 46

CHAPTER 3 METHODOLOGY 48

3.1 Overview 48

3.2 Design of equipment 49

3.3 Using different nickel plating solution 50

3.4 Schedule of experimental work 51

3.5 Microstructure testing 52

3.5.1 Optical Micrograph 52

3.5.2 FESEM & SEM 53

3.5.3 Atomic Force Microscopy (AFM) 54

3.6 Micro Hardness 54

3.7 Nano mechanical testing 55

3.8 X-Ray Diffraction (XRD) 56

3.9 Processes of experiments 57

CHAPTER 4 RESULTS and DISCUSION 58

4.1 Overview 58

4.2 Results for Pure Nickel plating 58

XII

4.2.1 Effect of time of plating 59

4.2.2 Effect of Current on the pure nickel coating 64

4.3 Ni-CNT Composite Coating 69

4.3.1 Effect of time of plating on Ni-CNT composite coating 71

4.3.2 Effect of Current on Ni-CNT composite coating 75

4.4 Discussion 83

4.4.1 Optical Micrograph for Pure Nickel Coatings 83

4.4.2 FESEM images of Pure Nickel Coatings 84

4.4.3 EDAX of Pure Nickel Coatings 84

4.4.4 Micro Hardness of Pure Nickel Coatings 85

4.4.5 FESEM images of Ni-CNT composite Coating 85

4.4.6 EDAX of Ni-CNT composite Coating 86

4.4.7 Micro hardness of Ni-CNT composite Coating 87

4.4.8 Effect of time of plating on pure nickel and Ni-CNT composite coating 88

4.4.9 Effect applied current on pure nickel and Ni-CNT composite coating 90

CHAPTER 5 CONCLUSION

REFERENCES 93

91

1 CHAPTER 1

INTRODUCTION

1.1 Background

“Surface finishing" is a generic term applied to a variety of processes for the

purpose of enhancing one or more properties of the surface of a metal. It is also applied

to a number of processes that involve the application of a metallic coating to a non-

metallic surface such as plastic, ceramic, epoxy, and even baby shoes. The art of

creating an altered surface on a metallic substrate dates back several centuries (1). There

are various processes to enhance the metal surface properties which are known as

surface finish. The concept of surface finish and altering the surface of materials has

been around for centuries, which includes grinding, painting, polishing and other non-

surface finishing processes such as heat treatment and tempering of metals.

Electroplating is considered as one of the most effective surface finishing processes,

which provides a thin surface coating over the substrate surface. The properties of

coating are superior to the substrate which results in protecting the substrate surface

Dennis and Such, 1993(1) . According to Zhong (2010), in 1950 decorative coatings

were introduced to toys and textile industry, since then its usage in engineering and

science areas provides an opportunity to improve the surface properties and

consequently increase sale of equipment and products. Alongside the industrial growth

2

and technological advancements, new processes such as electroplating and numerous

methods of altering non-conductors have been introduced. Deposition of metallic

coating is considered as one of the most important applications of electroplating. This

process is carried out in the solution which contains the related metal salt to provide

sufficient metal ions in the plating solution. ‘Chemical’, ‘electrochemical’, and ‘laser’

deposition are three main sources to provide the metallic coating which are shown in

Figure 1.1.

Figure 1.1 Schematic main source of plating techniques (Kennai 2006)

Poyner (1997) described, electroplating which is also known as electrodeposition is one

of the most common processes for providing a coating. In this process, metal ions or

3

complex metal ions in a chemical solution are transformed into solid metallic atoms onto

the surface of substrate, when an electrical pulse or current is applied (2)

This is more supported by Parthasaradhy (1989) who asserted, during the

electroplating process a metallic or composite coating has been produced on the surface

of material by applying electric current. The deposition is achieved by making the

material to be coated (cathode) negatively charged and immersed it into a solution which

contains the salt of the metal that is going to be deposited with the positive charge. The

metallic

.

ions of the salt carry a positive charge and are thus attracted to the cathode

surface. When they reach the negatively charged surface, it provides electrons to reduce

the positively charged ions to metallic form. Electroplating has many advantages over

other techniques. It is relatively inexpensive regarding to the process and its equipment,

and also it is a safe and simple process (2). This technique was used for decorative

purposes in the past, but nowadays it has become an important industrial technique

which can fulfill the requirements of a wide range of fields. Some of the functional

properties of this technique can be considered as corrosion and wear resistance, heat

resistance, tarnish resistance, electrical conductivity and solder ability (2).

Hadian (1990) said that one of the most popular electroplating methods in metal

finishing industry is ‘direct plating’. Direct electroplating has been achieved high

attention in recent years especially for providing the composite coating as it improves

the coating properties. The properties improvement is reported by many investigators

who asserted direct plating can provide a coating with fine grains, small grain size, high

purity and low porosity. Li et al (2007) also explained, direct plating is an effective

method for perturbing of adsorption and desorption process at cathode and plating

solution interface, which make it an economical process to provide a nanostructure

coating(3).

4

The modern surface finishing era, however, began with the invention of the

galvanic cell in the early 1800s (1)

It utilizes a combination of a chemical solution formulated to contain metal ions

or complex metal ions to convert the metal ions in solution to solid metal atoms on the

surface of the substrate that when a current is applied. Plated metal coatings can be used

for a variety of purposes, including corrosion resistance, appearance, solder ability,

electrical resistance, electrical conductivity, vibratory bonding, abrasion resistance,

electroforming of a product, and as a matrix to hold abrasives such as diamonds and

carbides in cutting tools

. By the middle of the 19th century, silver, gold,

copper, and brass plating were commercially performed. In addition to electroplating,

numerous competitive methods of altering the surface of metals and non-conductors

have been added to the common definition of surface finishing since the 19th century.

Direct electroplating is the most common metal finishing process.

(2)

Electroplating is often also called "electrodeposition", and the two terms are used

interchangeably. As a matter of fact, "electroplating" can be considered to occur by the

process

. The widest variety of metal surface properties can be

obtained through electroplating processes.

electrodeposition. Electrodeposition is the process of producing a coating,

usually metallic, on a surface by the action of electric current. The deposition of a

metallic coating onto an object is achieved by putting a negative charge on the object to

be coated and immersing it into a solution which contains a salt of the metal to be

deposited (in other words, the object to be plated is made the cathode of an electrolytic

cell). The metallic ions of the salt carry a positive charge and are thus attracted to the

object. When they reach the negatively charged object (that is to be electroplated), it

provides electrons to reduce the positively charged ions to metallic form. Figure 1.2 is a

schematic presentation of an electrolytic cell for electroplating a metal "M" from

an aqueous (water) solution of metal salt "MA".

5

Figure 1.2 Schematic of an electrolytic cell for plating metal "M" from a solution of the

metal salt MA”

1.2 Nickel

The use of nickel has been traced as far back as 3500 BC, but it was first isolated

and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who initially

mistook its ore for a copper mineral. Its most important ore minerals are laterites,

including limonite and garnierite, and pentlandite. Major production sites

include Sudbury region in Canada, New Caledonia and Norilsk in Russia (2). The metal

is corrosion-resistant, finding many uses in alloys, as a plating, in the manufacture of

coins, magnets and common household utensils, as a catalyst for hydrogenation

Electrodeposited nickel is widely used in decorative and protective applications

where it can be applied to cheap mild steel, aluminum alloys and die-cast zinc to protect

them in corrosive environments. Dennis and Such stated, during 2000 about 90% of

nickel consumed in electroplating industry, was in the form of thin, corrosion resistant

and decorative coatings which applied to strong or cheaply produced substrates

, and in a

variety of other applications (2).

(4).

6

Most of the nickel which is used for decorative purposes is in the form of nickel-

chromium composite system as the bright appearance is required (5). According to the

ASM Handbook, nickel is used as an undercoating of nickel-chromium coating in

decorative applications in order to enhance the corrosion resistance of system as

deposition of nickel itself provides a yellow cast which tarnishes easily.

Chandrasekar and Pushpavanam pointed out, nickel plating is applied in industry

to improve the surface properties such as ductility, wear and corrosion resistance and

also enhance surface hardness in the range of 150-700 Hv (6).

It is also used for engineering applications and in areas that fully bright finish is

not essential. One of the applications of nickel coating is in automotive industry,

especially in pistons, cylinder walls and transmission thrust washers and other parts

which are subject to friction, for the purpose of increasing the wear resistance. The

amount of nickel incorporated in different applications varies with 60% in nickel steels,

14% in nickel-copper alloys and nickel silver, and 9% used to make other super alloys

such as malleable nickel, nickel clad and Inconel(7). These, alongside the rest of the

applications are illustrated in Figure 1.3.

7

Figure 1.3 Nickel incorporation in different applications (Source: Hadian, 1990)

Nickel is used in many industrial and consumer products, including stainless

steel, magnets, coinage, rechargeable batteries, electric guitar strings and special alloys.

It is also used for plating and as a green tint in glass. Nickel is pre-eminently an alloy

metal, and its chief use is in the nickel steels and nickel cast irons, of which there are

many varieties (8). It is also widely used in many other alloys, such as nickel brasses and

bronzes, and alloys with copper, chromium, aluminum, lead, cobalt, silver, and gold.

The amounts of nickel used for various applications are 60% used for making nickel

steels, 14% used in nickel-copper alloys and nickel silver, 9% used to make malleable

nickel, nickel clad, Inconel and other super alloys, 6% used in plating, 3% use for nickel

cast irons, 3% in heat and electric resistance alloys, such as Nichrome, 2% used for

nickel brasses and bronzes with the remaining 3% of the nickel consumption in all other

applications combined(9).

In the laboratory, nickel is frequently used as a catalyst for hydrogenation,

sometimes raney nickel, a finely divided form of the metal alloyed

with aluminum which adsorbs hydrogen gas. Nickel is often used in coins, or

occasionally as a substitute for decorative silver. The American 'nickel' five-cent coin is

60%

14%

9%

6%

3%3% 2%

3%nickel steel

nickel-copper & nickel silver

other supperalloys

plating

nickel cast irons

heat and electric resistance alloys

8

75% copper and 25% nickel. The Canadian nickel minted at various periods

between1922-81 was 99.9% nickel, and was magnetic (10). Various other nations have

historically used and still use nickel in their coinage.

The corrosion – resistant properties of nickel electrodeposits are often thought

of as being of use only for protecting consumers, items, large or small, where decorative

embellishment is the most important factor, However nickel plate has many applications

in the engineering field where its functional behavior, rather than its appearance, is the

main criterion. When nickel is electroplated for this purpose, the coating deposited are

usually thicker than for decorative corrosion- protective uses, and so these are termed

heavy nickel coatings, which may be arbitrarily define as those greater than 50 microns

thick. These were first used to reclaim components which had worn or corroded in

service, or which had in correctly machined during manufacture(10).

Nickel was used to build up either the whole or just the effected portion of the

unserviceable article to a size greater than that actually required. Heavy nickel coating

are now often applied to new iron or steel components to prevent their corroding or

otherwise suffering damage caused by the normal wear or tear experienced in certain

uses, the thickness uses varying from 50 to 500 micro meter according to service

condition(10).

Matching of such coating is frequently not necessary. These nickel coating

prevent the basis metals from being corroded and by preventing this attack they those

reduce the danger of corrosion products of these substrates being produced which could

be contaminate nickel electrodeposits ideal for food-handling plant. This ability to

prevent metallic contamination together with their non-toxity, renders whose products

must not be contaminated by metallic impurities particularly iron, also make use of thick

electrodeposits nickel. Certain cylinders which are subject to wear have their service life

greatly extended in this manner (11).

9

Figure 1.4 Applications of Ni plating

1.3 Nano-Nickel Crystals

Most of the material properties have been changed when their structure turns into the

nano-sized. This is due to the different properties of nano-sized materials such as high

thermal and electrical conductivity, as well as high wear and corrosion resistance

(Chandrasekar and Pushpavanam). Using direct electroplating technique provides an

opportunity to produce a nano structure matrix. Because of the nature of nano-sized

materials, a higher thermal and wear resistance can be predicted for nano-nickel crystals

(12). Nano-nickel coatings can be potentially used as lubricants due to their low-friction

resistance. Therefore they have found applications in various industries ranging from

aerospace and marine to medical and chemical (12).

10

Figure 1.5 Nano- Nickel Particles

1.4 Carbon Nano Tubes (CNT’s)

Carbon Nanotubes (CNTs; also known as Bucky tubes) are allotropes of

carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-

to-diameter ratio of up to 132,000,000:1 which is significantly larger than any other

material. These cylindrical carbon molecules have novel properties that make them

potentially useful in many applications in nanotechnology, electronics, optics and other

fields of materials science, as well as potential uses in architectural fields. They exhibit

extraordinary strength and unique electrical properties, and are

efficient thermal conductors(3) .Carbon Nanotubes are nanofillers with a very high

potential in different industrial applications, e.g. for static dissipative or conductive parts

in automotive or electronic industries. In figure below SEM image of multi wall carbon

nano tube has been shown (3).

11

Figure 1.6 SEM Micrograph of MWCNT’s

For the effective use of carbon Nanotubes (CNTs) an excellent distribution and

dispersion is an essential precondition. The CNTs properties like Nanotubes type

(single-, double, multi-walled), length, diameter, bulk density, and waviness are

dependent on the CNT synthesis conditions, e.g. Catalyst, temperature of synthesis,

and synthesis method used. The purity and functional groups on the surface of the CNTs

as well as mainly their entanglements and strength of agglomerates affect the

dispensability of CNTs in different media. In addition, due to strong Vander Waals

forces CNTs tend to agglomerate. Ultrasonication of CNT dispersions is a common tool

used to break up CNT agglomerates in solution based processing techniques (13).

Ultrasonication can be done by different ways: using either an ultrasonic bath or

in setting an ultrasonic sonotrode into the solvent. The tip of ultrasonic sonotrode

oscillates at a fixed frequency and produces a conical field of high energy in the fluid.

The solvent within this conical field undergoes nucleated boiling and bubble collapse

that is the primary mechanism by which ultrasonic energy disperses particles (14). This

may help to debundle Nanotubes by providing high local shear, particularly to the

Nanotubes ends. For the preparation of CNT dispersions, surfactants are quite often used

as additives (14).

12

During the dispersion process the surfactant adsorbs on the Nanotubes surface.

Pores within the bundles or primary agglomerates help in the propagation of surfactant

adsorption. Finally, the bundles or agglomerates are ideally separated into individual

Nanotubes and are kept in homogeneous and stable suspension (14).The final

configuration of sodium dodecyl sulfate (SDS) covered Nanotubes was described as a

cylindrical micelle with a Nanotubes in the center(14). The destruction of agglomerates in

aqueous suspensions using ultrasonic energy was described by different authors. Lu et

al. (15) reported that multiwall carbon Nanotubes (MWNTs) get shorter with ultrasonic

time.

Nadler et al. (16) described for aqueous dispersions containing Bay tubes C150P

agglomerates that with increasing ultrasonic time (1 min up to 16 h) a bimodal

agglomerate size distribution pass into a finally mono modal distribution, whereas the

mean particle size decreased significantly as investigated using a disc centrifuge.

These very broad size distributions of the dispersions were explained with the presence

of mass fractions of exfoliated CNTs and residual agglomerates. It was not possible to

deduce results concerning the carbon Nanotubes length using the disc centrifuge. Yu et

al. (17) described the dispersion of multiwalled carbon Nanotubes in an aqueous sodium

dodecyl sulfate solution at different ultrasonic treatment times. With higher sonication

energy a better exfoliation and disentanglement of CNTs was found using UV–

visible spectroscopy and transmission electron microscopy. Figure below

shows the SEM Image of the agglomeration of MWCNT’s.

13

Figure 1.7 Scanning Electron Microscopy Images of MWCNT’s (A) NanocylTM

NC7000,(B) Baytubes_C150P, (C) Future Carbon CNT-MW, (D) Graph strength_ C100.

Carbon Nanotubes are the strongest and stiffest materials yet discovered in terms

of tensile strength and elastic modulus respectively. This strength results from the

covalent sp² bonds formed between the individual carbon atoms. In 2000, a multi-walled

carbon Nanotubes was tested to have a tensile strength of 63 GPa. Since carbon

Nanotubes have a low density for a solid of 1.3 to 1.4 g·cm−3, its specific strength of up

to 48,000 kN·m·kg−1 is the best of known materials, compared to high-carbon steel's

154 kN·m·kg−1. Under excessive tensile strain, the tubes will undergo plastic

deformation, which means the deformation is permanent (13)

This deformation begins at strains of approximately 5% and can increase the

maximum strain the tubes undergo before fracture by releasing strain energy. CNTs are

not nearly as strong under compression. Because of their hollow structure and high

.

14

aspect ratio, they tend to undergo buckling when placed under compressive, torsional or

bending𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠(13).

Diamond is considered to be the hardest material, and it is well known that

graphite transforms into diamond under conditions of high temperature and high

pressure. One study succeeded in the synthesis of a super-hard material by compressing

SWNTs to above 24 GPa at room temperature. The hardness of this material was

measured with a nanoindenter as 62–152 GPa. The hardness of reference diamond

and boron nitride samples was 150 and 62 GPa, respectively. The bulk modulus

All Nanotubes are expected to be very good

of

compressed SWNTs was 462–546 GPa, surpassing the value of 420 GPa for

diamond(13).

thermal conductors along the tube,

exhibiting a property known as "ballistic conduction", but good insulators laterally to the

tube axis. Measurements show that a SWNT has a room-temperature thermal

conductivity along its axis of about 3500 W·m−1·K−1;] compare this to copper, a metal

well-known for its good thermal conductivity, which transmits 385 W·m−1·K−1. A

SWNT has a room-temperature thermal conductivity across its axis of about 1.52

W·m−1·K−1, which is about as thermally conductive as soil. The temperature stability of

carbon Nanotubes is estimated to be up to 2800 °C in vacuum

1.5 Problem statements

and about 750 °C

inair(14)

CNT’s are difficult material on which to produce adherent electroplated

deposition coating due to their hydrophobic behaviors. Carbon Nano Tubes instantly

agglomerates when they face aqueous solution because of their high surface energies. In

fact because of their high surface over volume ratio (𝑆𝑆𝑉𝑉%) they are thermodynamically

15

unstable in solution, hence at the moment they added to the solution, they will

accumulate to gather.

Figure 1.8 SEM image of CNT’s agglomeration.

Figure 1.8 shows the agglomeration of CNT’s. Experiments have been carried out to

make CNT’s suspend in the solution. There are two different techniques for suspension

of CNT’s in solution: 1. using ultra sonic bath to suspend and disperse CNT’s in

solution. 2. Using a certain surfactant which can surround CNT’s and forces them to

suspend, because these kinds of surfactants have hydrophilic behaviors such as SDS,

SDDBS and Benzyl alcohol.

Additionally the cathode surface must be as smooth and clear as possible to increase the

adsorption and nucleation of Ni particles on the surface; the suggested processes for

electroplating of Ni are listed as follows:

Recommendation pre-treatments:

• Ultra Sonic Cleaning by Ultra Sonic Bath for 20 minutes • Grinding the surface by grinding paper from 200-4000 • Polishing the cathode surface • Etching in sulfuric acid for 5 minutes

• Making nickel solution (Watt bath), and heat the solution by heater about

50𝐶𝐶0.

16

• Suspend CNT’s in the solution by applying benzyl alcohol as a surfactant.

• CNT’s were poured in to 1Lit nickel solution and then ultra sonic bath was

used for 8hours for dispersing the CNT’s.

• Surfaces of anode and cathode should be micro roughened (6)

.

Figure 1.9 Surface image of soft copper, used as a cathode

Figure1.9. shows a surface image of soft copper which used as a cathode in direct

electrodeposition techniques. In electroplating technique, solution is designed to

generate oxygen gas which forms the coating by reaction with the basis metal ions, as

the basis metal dissolves. Direct Electrodeposition is a unique technique for producing

fine coatings. The thickness of the coating is depended on some crucial parameters such

as agitation, current density, intensity, distance between cathode and anode and etc. DC

rectifier is used to generate current in range of milliamps; consequently the first embryos

will nuclei in nano size. On the other hand by applying this rectifier and by changing

some variables such as agitation rate, temperature, current density and etc. the growth of

these nano embryos could be controlled as well. All this operation must be in nickel

solution which the combination and producing procedure of this solution will be

discussed in chapter two. In this electrodeposition project, stainless steel would be anode

and soft copper would be cathode. To prevent the polarization effect, the size of anode

would be 3 or 4 times bigger than the cathode.

17

1.6 Scope

Recent work shows that it is hard to plate CNT’s on the surface because of

agglomeration problem; hence the main scope is to make a stable suspension of CNT in

Ni solution. Other characteristics of the direct electroplating of CNT’s on the nano-Ni

crystals are: Current density, and deposition time. The deposited metal is expected to be

Nano crystalline-hence the deposited metal would be characterized by using SEM,

FESEM, XRD, AFM and Micro hardness testing. By studying the interface between

Nano-Ni Crystals and CNT’s an effect will be made to put forward a hypotheses on

how, the hydrophobic carbon nano tubes(CNT’s) are deposited and grow on Ni in direct

electrodeposition technique