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Development and Characterisation of Nanocomposite Coating

Gohar Ali Siddiqui, Shabbir Tahir, Ahsan Ahmed Nomani

Department of Materials Engineering,

NED University of Engineering & Technology,

Karachi, Pakistan.

Abstract

Introduction Today nanotechnology is at the forefront of

materials science. It utilizes engineering of

materials at the very fine level having

dimensions in nano meter range. On the other

hand, composite materials are also used

widely today to make new set of properties by

combining two or more materials. The current

study involves both nanotechnology and

composite technology to develop a

nanocomposite. Incorporation of nano-sized

particles in the surface metal matrix which is

called as nanocomposite coating offers

opportunities for generating multifunctional

coating [1].

Metals and ceramic are two different classes of

materials generally having opposite

properties. While metals are generally tough,

conductive and relatively soft, ceramics are

generally brittle, insulator and hard.

Combination of ceramic and metals can impart

interesting set of properties like wear

resistance to metals but also affect favourable

properties like thermal conductivity. This

problem can be overcome by decreasing the

size of dispersion phase to nano meter range

[2]. Alumina nanoparticles in copper matrix

have been reported to have favourable

properties. The coating is reported to be

robust in nature and have applications like

microchannel heat exchanger [2], dispersion

hardening, self-lubricity, wear resistivity,

chemical compatibility, corrosion resistivity,

etc. [2,3].

The main requirement of such coating is the

nanoparticles. Nanoparticles of Alumina are

readily available commercially but is quite

expensive. They can also be synthesized easily

The objective of the study was to develop Alumina-Copper metal matrix nanocomposite coating

on copper metal surface. The project is divided into two phases; First being synthesis of Alumina

nanoparticles and Second, the development and characterisation of nanocomposite of synthesized

alumina and copper on copper surface. Alumina nanoparticles were synthesized using sol-gel

method using aluminium chloride and ammonia water as reactants to precipitate alumina particles

in a solution of ethanol. The obtained gel was dried at 100oC and calcined at 1000oC to obtained

fine particles of aluminium oxide. The characterisation of the obtained powder was done by XRD

and the particle size was estimated using debye-scherrer formula. In the second phase,

nanocomposite coating was developed by electrocodeposition in copper sulphate solution in water

in which hydrochloric acid was added to make the solution acidic to archive electrostatic repulsion

and avoid agglomeration. The resulted coating was characterised by Scanning electron microscopy

(SEM), Micro Hardness Test, Optical Microscopy, Surface Wettability, Heat transfer and Scratch

Test.

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by a number of techniques including can be

generated by a number of techniques,

including chemical methods [4, 5], flames

synthesis [6, 7] or thermal plasma synthesis [8],

ball milling [9, 10], electric spark discharge, and

sono-hydrolysis of alkoxide precursor [11]. In

the current study, chemical precipitation by

Ammonia water and Aluminium chloride in

ethanol was used to synthesize Alumina

nanoparticles.

Development of nanocomposite coating can

also be done using a number of ways including

PVD, CVD, thermal spraying and pyrolysis.

Previous research has demonstrated that,

using electrocodeposition technique a thin

composite coatings (1-100 um) can be

developed on a solid surface from nano-sized

particles.

Experimental Setup Synthesis of Alumina nanoparticles: Aluminum chloride and ammonia water was used to precipitate nanoparticles of alumina in ethanol. 0.2 mol/lit solution of aluminium chloride in ethanol was added drop-wise to 4.5 mol/lit ammonia water solution precipitating alumina nanoparticles according to below given chemical equation. The alumina sols were filtered, dried at 100oC for 2 hours and then calcined at 1000oC for 2 hours to obtain finely dispersed particles of alumina. 2AlCl3.6H2O + 6NH3 -----> 2Al(OH)3 + 6NH4Cl

Development of Nanocomposite Coating:

Nanocomposite coating was developed by

electrocodeposition of copper and alumina in

copper sulphate (CuSO4.5H2O) bath

containing sulphuric acid to adjust pH of

solution to 4. The acidic pH assist

electrophoretic deposition of alumina as well

as keep the alumina nanoparticles dispersed in

the solution by electrostatic repulsion. The

cathode and anode were both of copper metal

and the coating was developed on the cathode

electrode. 30 gm/l alumina nanoparticles was

added to the solution. Coating was performed

at current density of 12 A/dm3 for 10 min to

obtain the coating. Constant stirring was done

during the deposition process to keep the

concentration of nanoparticles same

throughout the solution and keep up the

supply of alumina particles to the metal

surface. The metal specimen were finely

grinded and polished before the coating

process to archive better adherence. The

coating process is schematically shown in

Figure 1.

Figure 1 Electrocodeposition Setup

Characterisation The nanoparticles were characterized using a

Phillips PANalytic powder diffractometer using

30 mA 40 KV copper X-ray source with

wavelength of 1.541 Ǻ. Nanocomposite

coating was confirmed by stereo microscope,

characterized by FEI Quanta 200 SEM

microscope, micro hardness tester, Olympus

high magnification optical microscope and

surface wettability by static contact angle

comparison.

Results and Discussion The XRD pattern obtained for the synthesized

nanoparticles is shown in Figure 2

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Figure 2 XRD Pattern on Alumina

The five peaks detected were all found to be

characteristic of alumina. The peak data is

given in Table 1.

Table 1 XRD Peak Data of Alumina Peak Position

(Degree) Height (Counts)

FWHM (Degree)

d-Spacing Angstrom

Relative Intensity (%)

1 37.642950 28.53714 2.20416 2.38961 59.16

2 44.557080 38.569810 0.354240 2.03355 79.95

3 45.986210 36.665840 1.102080 1.97362 76.01

4 61.546110 10.121790 1.889280 1.50680 20.98

5 66.500210 48.239570 1.259520 1.40606 100.00

The peak data was used to estimate the

particle size by using debye-scherrer equation

(Eq. 1)

D = 𝐾 𝜆

𝛽 cos 𝜃 ( Eq. 1 )

Where, K = Geometrical factor, typically 0.9 λ = Wavelength of X-ray used, typically for copper λ = 1.541 Ǻ ß = Line broadening at half height of the peak (FWHM) 𝜃 = Peak Position

The particle size obtained from each peak and

the average particle size is given in Table 2. This

result is significant enough to conclude that

the synthesised particles are in nano meter

range because they were synthesised by a

route that do not induce any inhomogeneous

strains in the material.

Table 2 Particle Size of Alumina

Peak Particle Size (nm) Mean size (nm)

1 7.6 2 48.4

3 15.6 ~ 20

4 9.8

5 15

The nanocomposite coating was developed by

electrocodeposition. Stereo microscope image

of the coating is shown in Fig 3

Figure 3 Stereo Microscope Image of coated sample

The coating thickness measured by using

optical microscope (Fig. 4)and was found to be

about 28 μm which is in close proximity to the

theoretical thickness of 27.4 μm calculated as

follows by Faraday’s law of electrolysis (Eq. 2)

d = (I x t x Z) / (n x F x ρ x A) (Eq. 2)

Where;

d = Thickness (m), I = Current (Ampere)

t = Time (Sec), A = Area (m2) Z = Atomic Mass (0.0635 kg/mol for Cu) n = Oxidation state (2 for Cu in electrolyte) F = Faraday’s Constant (=96500 C/mol) ρ = Density of coating material (8960 kg/m3 for Cu) I/A = 1200 A/m2 t = 600 sec Thus d = (1200 x 600 x 0.0635) / (2 x 96500 x 8960) d = 26.43 x 10-6 d = 26.43 μm

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Figure 4 Optical Microscope Image of Coated Sample

Micro hardness results are summarized in

Table 3. The specimen show increased

hardness from the bare copper value (about 70

HV) which can be attributed to the

incorporated hard alumina nanoparticles.

Table 3 Micro Hardness Test Results

Test No.

Local Micro Hardness (HV)

Mean Hardness (HV)

1 134.2 119 2 106.4

3 115.9

4 119.1

The surface wettability was characterised by

determining the difference between the static

contact angle of water on bare copper and

coated sample. There was a decrease in angle

recorded as shown in Fig 5 indicating that the

coated surface have rough texture attributed

to the incorporated nanoparticles on the

surface.

Figure 5 Static contact angle of bare copper (Left) and coated sample (Right)

To detect any influence on the thermal

conductivity due to coating, a simple

comparing test was done in which a specific

amount of water in a beaker was heated

through both bare copper and coated sample.

The temperature of water was recorded after

10 min to detect any large decrease in thermal

conductivity. The results shown in Table 4

show that the coating at worst do not have any

adverse effect on the thermal conductivity of

copper.

Table 4 Thermal Conductivity Comparison

Samples Initial Temp. oC

Final Temp. oC

Difference

oC

Bare Copper Metal

32oC 55oC 23oC

Coated Sample 1

32oC 62oC 30oC

Coated Sample 2

32oC 57oC 25oC

The SEM image of coating is shown in Fig 6. The

images show a thick coating on the base metal.

Small particles of alumina are can also be seen

attached to the coating.

Figure 6 SEM image of coated sample

Conclusion

In the current work, alumina nanoparticles

were synthesised by chemical precipitation

using aluminium chloride and ammonia water

in ethanol. The synthesised particles were

characterised to be of alumina with particle

size in nano meter range

Nanocomposite coating was developed on

copper surface by electrocodeposition of

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copper and alumina. The coating thickness was

27 μm. Hardness is found to be increased by

80%. The comparison of surface wettability

shows that the coated surface is relatively

more wetting than that bare copper surface.

The coating seems to have no adverse effect

on the thermal conductivity of copper. SEM

images show that the coating is adhered to the

substrate and alumina particles are

incorporated inside it. All these results are

attributed to the alumina particles embedded

inside the metal matrix composite of copper.

Future Work

Although the current work is done, the field of

study is so vast that this work can be continued

in a number of directions. Some suggestions

for the future work continued from this study

is as follows;

1. The coating can be characterized on its wear

properties. Although the increased hardness

indicate an increase in the wear properties,

wear resistance is not a material property thus

should be studied for specific conditions

encountered in areas of potential applications

like microchannel heat exchanger and liquid

coolant system.

2. Corrosion is yet another property which can

be characterised. Corrosion properties of the

coating should be studied and modifications to

the experiment can be used to alter and

enhance the corrosion resistance of the

coating.

3. Nanocomposite films can be developed by

altering the experiment parameters such that

the coating can be easily detached from the

substrate. The obtained nanocomposite film

can be characterised by its mechanical

properties and can also be used is a composite

material as a dispersed phase after making

long flakes of the film.

4. Nanocomposite coatings employing

different particles than alumina and using

different matrix than copper can be developed

and characterised using suitable techniques.

5. Different deposition routed can be explored

and their influence on the properties of the

coating can be recorded

6. The study can be taken one step further by

using two different types of nanoparticles in

the same nanocomposite each imparting

different enhancement to the matrix and

obtain new sets of properties.

7. Bulk nanocomposite can also be made and

characterised, they have the advantage that

the dispersed phase have a very high surface

area and is very finely distribution in the matrix

thus they can impart interesting set of

properties to the nanocomposite.

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