PHYSICAL PROPERTY OF MULTI WALLED CARBON NANOTUBE REINFORCED
ALUMINIUM NANO COMPOSITE
Umma A*, Maleque M.A, Iskandar I.Y. and Mohamed A.R.
Department of Manufacturing and Materials Engineering
Kulliyyah of Engineering, International Islamic University, Malaysia
P.O.Box 10, 50728 Kuala Lumpur, Malaysia
Email: yabi78@yahoo.com
Key words: Density, Aluminium, Carbon nano tube, nano-composite, Hot isostatic press machine.
ABSTRACT
The unique properties of carbon nanotube such as high strength, elastic modulus, flexibility and high aspect ratios
changed the direction of the research in the field of fibrous materials and are attracting much interest as
reinforcement to aluminium matrix for carbon nano tubes aluminium matrix (MWCNT-Al) nano-composite.
However, the quality of the dispersion is the major concerning factor which determines the homogeneity of the
enhanced physical, mechanical and tribological properties of the composite. This work study the physical property
of the MWCNT-Al nano-composite prepared with different weight percentage of MWCNT in aluminium matrix
using powder metallurgy route under high energy planetary ball milling operations at different time intervals. The
bulk nano-composite powder was sintered using hot isostatic process at the temperature of 500 oC for 60 minutes
under argon gas. The experimental results showed significant amount of mass reduction up to 55% which ensure
light weight material as a result of the effect of milling time and controlled atmospheres in the HIP machine.
Addition of small percentage of MWCNT in aluminium matrix is the main contributing factor in achieving mass
reduction, hence reduced the density of MWCNT-Al nano-composite material compared to pure aluminium.
INTRODUCTION
Composite materials can be tailored for various properties by appropriately choosing proportions, distributions, and
morphologies, as well as the structure and composition of the interface between components [1-3]. Due to this
strong tailor ability, composite materials can be designed to satisfy the needs of technologies relating to the
aerospace, automobile, electronics, construction, energy, biomedical and other applications. However, composites
became one of the most widely used materials because of their adaptability to different circumstances and the
relative ease of combination with other materials to serve specific purposes and exhibit desirable properties [1]. The
structural properties of composite material are derived primarily from the fiber reinforcement. High-performance
composites derive their structural properties from continuous, oriented, high-strength fiber reinforcement most
commonly carbon, aramid or glass in a binding matrix that promotes process ability and enhances mechanical
properties and physical properties such as stiffness and density of the material [3]. Many researchers reported that a
relatively small amount of nanoscale reinforcement can have a notable effect on the macroscale properties of the
composite due to the large amount of reinforcement surface area [4-6]. For example, reinforcement of carbon
nanotubes (CNT) in to the metal matrix enhanced the thermal conductivity and electrical properties, heat resistance
or mechanical properties such as stiffness, strength and can notably reduce the density of the material. These
enhance properties can only achieved when there is uniform dispersion of the CNT in to the Al matrix and the major
problems in the manufacture of MWCNT-Al nano-composite is the clustering of CNTs in the Al matrix. This is due
to the complex entanglements of long and smooth CNTs and resulting agglomeration due to strong van der Waals
forces of attraction between them. Furthermore, the weak interfacial bonding due to the poor wettability of carbon
nanotube with Al has been an obstacle to impart effective load transfer between the MWCNT and the Al matrix. In
addition, the formation of aluminium carbide (Al4C3) phase in the fabrication process complicates the strengthening
mechanism of the composite [4]. Recently, Kwon et al. [7] claim in their MWCNT-Al composites study that Al4C3
was formed and stabilized on the surface of the tip of CNT and also helped in the transfer of stress from Al matrix to
the CNTs. But, their experimental study was restricted to 0.5 vol % of MWCNT. More recently, Liao et al. [8] claim
in their CNT-Al nano-composite study that, a significant enhancement in the composite properties at initial loadings
0.5 wt % of MWCNTs when compared to Al samples without much increase in cost. There work is restricted to the
MWCNT weight fraction of 2.0% and they did not study the physical property of the composite. In view of the
limited experimental properties data on CNT-Al composites, the main objective of the present study is to synthesis
MWCNT reinforced Al nano-composite and study physical property for the light weight engineering application.
MATERIALS AND METHOD
Pure Al (99.7%), with particle size of 78 µm which has nearly spherical shape with some satellite sub-particles
obtained from Innovative Pultrusion Sdn Bhd, a local supplier for the aluminium powder was used as a matrix
material. The image of the aluminium powder obtained using scanning electron microscopy (SEM) is showed in
Fig.1a. The multi walled carbon nano tubes (MWCNTs) with a nominal diameter of 10 nm, length of 5-15 µm, and
surface area of 230-280 m2g-1 was also obtained from the same supplier in Malaysia and used as a reinforcement.
The image of the MWCNTs obtained through field emission scanning electron microscopy (FESEM) is shown in
Fig. 1b. Three compositions such as 1.5, 2 and 2.5 wt% MWCNT with the balance in each case being Al were used
for the preparation of CNT-Al nano-composite and studied in this investigation. Each composition was compacted
using cold unidirectional pressing machine at the pressure of 17 MPa for each sample. The samples were sintered
using hot isostatic press (HIP) machine (HP630) at 500 oC and the argon gas was supplied at the pressure of 17 MPa
for 60 min to control the atmosphere in the process. The densities were calculated using Archimedes principle with
digital densitometer and the weight of each sample was taken outside and inside the liquid. The densities were
calculated by the machine and final average reading was taken after repeating the test three times for accuracy in the
result.
(b)
(a)
100µm
100nm
Fig.1 Image of the as-received raw materials: (a) aluminium powder and (b) MWCNT
RESULT AND DISCUSSION
At the initial stage the weight of each sample was measured before and after the sintering using HIP machine. Fig. 2
shows the mass for all the composition of the nano-composite. For all the composition samples shows same
behavior with the mass in air double the mass in liquid. However, the mass decrease with almost 55% after HIP
sintering process the density increased for the entire sample with the highest density for the green compact nanocomposite powder milled for 2 hr for 1.5 and 2 wt% MWCNT. Whereas, for 2.5 wt% MWCNT the density is high
from the initial hour and decreased slightly at the 2 hr and remained the same at 3 hr. The relative density of each
sample was calculated and it followed the same trend with the density as shown in Fig. 3. From the experimental
results, for 1.5% wt % MWCNT light weight material (mass reduction) can be achieved even from the first hour of
milling, while for 2 wt % and more mass reduction was achieved after the second hour of milling. In contrast the
densities of the sintered samples without argon gas is higher than that sintered using HIP machine, this is because
MWCNT may react with aluminium to form carbide compounds such as Al 4C3 which may increase the density of
the material. Furthermore, properly controlled atmosphere can prevent the reaction at high temperature and this may
cause the material to maintain its actual enhanced density.
Before sintering
After sintering
Before sintering
After sintering
Before sintering
After sintering
Fig. 2 Measured mass (g) of MWCNT-Al nano-composite before and after sintering plotted against the milling time for (a) 1.5,
(b) 2 and (c) 2.5 wt% MWCNT . Sintering condition: Argon gas pressure 17 MPa, temperature 500 OC for 60 min.
0.86
Relative Density (g/cm 3)
Relative Density (g/cm 3)
0.88
0.84
0.82
0.8
0.78
0.76
0.74
0.72
1
2
3
0.805
0.8
0.795
0.79
0.785
0.78
0.775
0.77
0.765
0.76
0.755
1
2
Milling Time (hr)
Milling Time (hr)
(a)
(b)
3
Relative Density (g/cm 3)
0.762
0.76
0.758
0.756
0.754
0.752
0.75
0.748
0.746
0.744
1
2
3
Milling Time (hr)
(c)
Fig. 3 Relative Density (bulk density/theoretical density) of MWCNT-Al nano-composite plotted against the milling time for (a)
1.5, (b) 2 and (c) 2.5 wt% MWCNT. Sintering condition: Argon gas pressure 17 MPa, temperature 500 OC for 60 min
Several research works have been conducted on MWCNT nano-composite with composition range of 0.5, 2 and 5
wt % and general findings showed better results with 2 wt% MWCNT in terms of uniform distribution, homogeneity
and mechanical properties [9-11]. In this investigation, the 1.5 wt% showed better physical properties with mass
reduction from where better mechanical properties can be predicted for light weight applications. For 1.5% wt %
MWCNT light weight material can be achieved even from the first hour of milling, while for 2 wt % and more mass
reduction was achieved after the second hour of milling.
SUMMARY
The results presented in this paper illustrated that small MWCNTs contents can affect the physical property of the
material. Hot isostatic pressing is a promising technique for completing powder metallurgy processes. Controlled
atmosphere during sintering can prevents the formation of carbides at high temperature. A light weight and cost
effective MWCNT-Al nano-composite material were developed, hence powder metallurgy is the easier and
economical way of nano-composite synthesization. The 1.5 and 2 wt% MWCNT in MWCNT-Al nano-composite
contribute to the formation of better MWCNT-Al nano-composite with better enhanced physical property. There is a
significant amount of mass reduction up to 55% due to the effect of milling time and HIP machine with controlled
atmosphere as a sintering method. For 1.5% wt % MWCNT light weight material (mass reduction) can be achieved
even from the first hour of milling, while for 2 wt % and more mass reduction was achieved after the second hour of
milling.
ACKNOWLEDGEMENT
The authors acknowledge the laboratory support from Department of Manufacturing and Material Engineering,
International Islamic university Malaysia which made this study possible.
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