1
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.
2
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
3
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
4
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
5
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.
References [1] Q. Yu, X. Ma, M. Wang, C. Yu, T. Bai, Influence of embedded particles on microstructure, corrosion resistance and thermal conductivity of CuO/SiO2 and NiO/SiO2 nanocomposite coatings, Applied Surface Science 254 (16) (2008) 5089e5094. [2] M. Morshed, Titan C. Paul, Jamil Khan; “Effect of CueAl2O3 nanocomposite coating on flow boiling performance of a microchannel”; Applied Thermal Engineering (2013); 51; pp 1135-1143 [3] A. Akarapu, Surface Property Modification of Copper by Nanocomposite Coating, National Institute of Technology, Rourkela, 2011. [3] Y. Gan, D. Lee, X. Chen, J.W. Kysar, Structure and properties of electrocodeposited Cu2Al2O3 nanocomposite thin films, Journal of Engineering Materials and Technology 127 (4) (2005) 451-456. [4] J.M. McHale, A. Auroux, J. Perrotta, A. Navrotsky, Science 277, 788 (1997) [5] D.J. Suh, T.-J. Park, J.-H. Kim, K.-L. Kim, Chem. Mater. 9, 1997 (1903)
6
[6] J.R. Jensen, T. Johannessen, S. Wedel, H. Livbjerg, J. Nanopart. Res. 2, 363 (2000) [7] T. Johannessen, S.E. Pratsinis, H. Livbjerg, Chem. Eng. Sci. 55, 177 (2000) [8] P.V. Ananthapadmanabhan, T.K. Thiyagarajan, K.P. Sreekumar, N. Venkatramani, Scr. Mater. 50, 143 (2004) [9] J.M. Wu, Mater. Lett. 48, 324 (2001) [10] Y.-q.Wu, Y.-f. Zhang, X.-x. Huang, J.-k. Guo, Ceram. Int. 27, 265 (2001) [11] R. Sivarajan, S. Elena, C. Baruch, C. Rachman, G. Aharon, J. Am. Ceram. Soc. 83, 89 (2000)
Top Related