 Open Access
 Total Downloads : 378
 Authors : O.S. Fatoba, O. Popoola, O.L Akanji, O. Imoru, A.P.I Popoola
 Paper ID : IJERTV2IS100665
 Volume & Issue : Volume 02, Issue 10 (October 2013)
 Published (First Online): 23102013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
The Influence of Sic Particle Size on the Thermal and Electrical Conductivities of Cu/Sic Composites
O.S. Fatoba 1*, O. Popoola 2, O.L Akanji 1, O. Imoru 2, A.P.I Popoola 1
1Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, South Africa.
2Department of Electrical Engineering, Tshwane University of Technology, Pretoria, South Africa.
ABSTRACT.
The Potential demands for reliable materials in electronic industries are ever increasing. The main pronounced failure that occurs during microelectronic circuits application involves thermal fatigue. Heat generated in electronic packages can be dissipated by developing suitable materials as heat sinks. Copper metal matrix composites reinforced with silicon carbide (SiC) proffer possibility of meeting these demands. Thus, the interest for appropriate coefficient of thermal expansion (CTE) of packaging materials in combination with a high thermal and electrical conductivity is inevitable in the design and selections of heat sink material. This research work entails producing copper matrix using silicon carbides (SiC) as reinforcement. This is aimed at getting a material with high thermal and electrical conductivities by non convectional liquid metallurgy. Copper silicon carbide composites were produced in 80%Cu 20%SiC, 70%Cu30%SiC, 60% Cu40% SiC, 50% Cu50%SiC,
40%Cu60%SiC ratios with an average grain size of 212Âµm, 425Âµm and 710Âµm respectively via liquid metallurgy method. The result revealed that increasing volume fraction and p a r t i c l e s i z e s of t h e particulate h a d significant effect o n the thermal and electrical conductivity of the composites.
Keywords: Composite, particle size, volume fraction, thermal conductivity, electrical conductivity.

INTRODUCTION
Copper has been extensively used in electronic and thermal applications because of its high thermal and electrical conductivity, plasticity, high melting point and good corrosion resistance. Copper is second to Silver in electrical conductivity ranking of copper [14]. High
temperature mechanical property can be improved with the inclusion of ceramic particulate reinforcement without severe deterioration of electrical and thermal conductivity of the matrix. Therefore, these types of materials are considered to be potential candidates for required mechanical property and high conductivity applications [4].
Composite materials are emerging mainly in response to exceptional demands from technology because of rapid advancing activities in automotive, aircrafts, aerospace industries and electronic devices. These materials have low density that makes their properties particularly superior in modulus and strength in comparison with many metals. The intensive studies into the essential nature of the composite [59] and enhanced understanding of their property relationship [10, 12, 14], has made it imperative to develop new composite materials with improved mechanical and physical properties.
Metal matrix composites (MMCs) are materials with great potential due to combinations of unique properties that can be achieved. These include: low thermal expansion (CTE), better electrical conductivity and superior thermal conductivity. MMCs proffer the opportunity to modify the properties of a metal (Cu) by adding a suitable reinforcement phase (SiC) to meet the demands for high thermal conductivities in thermal management applications [11, 17]. An important consideration in MMC manufacture is the nature of the interface between the reinforcement and matrix. The incompatibility between the reinforcement and the matrix coefficient of thermal expansion (CTE) will give rise to high residual stress, which leads to low tensile ductility of the composite [7, 9, 13, 15, 16]. This often depends on the processing methodological process, and since this occurs at high temperature, it is more chemical in nature than mechanical.
This study investigates the mechanism controlling thermal conductivity of CuSiC particulate composite produced by liquid metallurgy method. Furthermore, the relationship and impact between particle sizes, volume fraction and processing parameters are evaluated for high thermal and electrical conductivity.

MATERIALS AND METHOD
Commercial pure copper wire C10200 (98.8% Cu) used for the experimentation was obtained from Cable Metal Nigeria Limited. The chemical composition, as well as the density, thermal expansion, thermal conductivity and electrical conductivity of the copper wire C10200 are
presented in Table 1 and 2.
Table 1: Chemical composition of Copper wire C10200.
Element
% Composition
Element
% Composition
Element
% Composition
Cu
98.80
Si
0.032
Cr
0.043
Pb
0.490
Mn
0.013
Sb
0.012
Zn
0.073
Fe
0.450
Mg
0.0005
Table 2: Density, thermal expansion, thermal conductivity and electrical conductivity of copper wire C10200.
Variable
Units
Values
Density
Kg/m3
8940
Thermal Conductivity
W/mK
380
Electrical Conductivity
S / m
5.18 x 107
Thermal expansion
/K
17.6 x 106
Table 3: Density and thermal conductivity of silicon carbide (SiC).
Variable
Units
Values
Density
Kg.m3
3180
Thermal conductivity
W/mK
120
The alloys were produced in 80% Cu20% SiC, 70% Cu30%SiC, 60%Cu40%SiC, 50% Cu 50%SiC, 60% Cu40%SiC from pure copper wire (C10200) with variation in SiC particle grain sizes of 212Âµm, 425Âµm and 710Âµm. The materials were synthesized by liquid metallurgy
process in an oil fired pit furnace. The copper wires were properly cleaned prior to melting so as to eliminate any surface impurities and superheated to 1090oC. The addition of SiC particulates to the molten copper was done at the tail end of the melting. The mixture was continuously stirred before casting. The casting of the melt was done in a metal mould of diameter of 1.45cm
x 14.5cm. 15 samples of the resulting CuSiC metal matrix composite were later heat treated in a muffle furnace to 490oC for 8 hours for homogeneous distribution.
Resistivity test was conducted on DV power microohmmeter RM 0600 at 10 amperes and 20 amperes respectively. For each of the sample, tests were carried out 3 times, and the observed values were the average of all the samples taken. Thermal conductivity was conducted using
thermal transport sample station (TTO) P670. The value of resistivity of a wire can be evaluated from the expression below:
Resistivity, =
(1)
– Resistivity in Ohmmeter (m); R – Resistance of materials in Ohms; A – Cross sectional area in m2; L – Length in meter.
While the value of electrical conductivity () in per ohm per meter was derived from the relationship
= 1 Siemens per metre (Sm1) (2)
= Resistivity in Ohmmeter ( m).

RESULTS AND DISCUSSION
The results of the different investigations carried out in respect of the study are shown in the Figures 1, 2, 3 and 4. In Figure 1, the thermal conductivity value of particle size 710Âµm was well above the other values of 212Âµm and 425Âµm respectively; 425Âµm performed slightly above 212Âµm. As a result of interfacial thermal resistance between copper and silicon carbide, the thermal conductivity decreases with a decrease in particles of SiC. Therefore, it can be inferred that thermal conductivity reduction varies in relation to decreasing particle size [16]. Furthermore validation of the result shows that there exist polynomial relationships between the thermal conductivity and the % volume fraction of the Cu/Sicp composites in relation to the
particle sizes; i.e. R2 shows 0.7, 0.81 and 0.93 respectively for 212Âµm, 710Âµm and 425Âµm. The
larger the cross sectional area of the conductor, the more electrons per unit length is available to carry or dissipate the current as a result the particle size was above the others.
450
400
350
300
250
200
150
212Âµm
425Âµm
710Âµm
450
400
350
300
250
200
150
212Âµm
425Âµm
710Âµm
30
40
50
60
70
80
90
100
110
30
40
50
60
70
80
90
100
110
Volume fraction of Cu/SiC (%).
Volume fraction of Cu/SiC (%).
100
50
0
100
50
0
y = 0.190×2 – 26.28x + 1162.
RÂ² = 0.815
y = 0.190×2 – 26.28x + 1162.
RÂ² = 0.815
350
300
y = 0.058×2 – 7.298x + 429.8
250 RÂ² = 0.936
200
350
300
y = 0.058×2 – 7.298x + 429.8
250 RÂ² = 0.936
200
212Âµm
425Âµm
710Âµm
Poly. (212Âµm)
Poly. (425Âµm) Poly. (710Âµm)
212Âµm
425Âµm
710Âµm
Poly. (212Âµm)
Poly. (425Âµm) Poly. (710Âµm)
Thermal conductivity (W/mK).
Thermal conductivity (W/mK).
Thermal conductivity (W/mK).
Thermal conductivity (W/mK).
Figure 1a: Thermal conductivity of Cu/SiCp composites
450
400
450
400
0
0
30
40
50
60
70
80
90
100
110
30
40
50
60
70
80
90
100
110
Volume fraction of Cu/SiC (%).
Volume fraction of Cu/SiC (%).
150
100
150
100
y = 0.083×2 – 10.41x + 490.3
RÂ² = 0.701
y = 0.083×2 – 10.41x + 490.3
RÂ² = 0.701
50
50
Figure 1b: Thermal conductivity of Cu/SiCp composites (Polynomial regression)
The heat treated Cu/SiCp composite in Figure 2 indicates that increase in volume fraction of SiC leads to decrease in thermal conductivity until 70/30 volume fraction when it rose sharply with an increase in thermal conductivity for particle size 710Âµm. Increase in volume fraction of Particle sizes 212Âµm and 425Âµm lead to decrease in thermal conductivity and further decrease from 70/30 to 50/50 volume fraction with a steady rise at 40/60 Cu/SiC volume fraction. These values are slightly lower than the untreated composites but also decreased with a decrease in particle sizes.
400
Thermal conductivity (W/mK).
Thermal conductivity (W/mK).
350
300
250
200
212Âµm
425Âµm
710Âµm
150
100
50
0
30 40 50 60 70 80 90 100 110
Volume fraction of Cu/SiC (%).
Figure 2a: Thermal conductivity of Heattreated Cu/SiCp composites.
0
0
30
40
50
60
70
80
90
100
110
30
40
50
60
70
80
90
100
110
Volume fraction of Cu/SiC (%).
Volume fraction of Cu/SiC (%).
400
350
300
400
350
300
y = 0.103×2 – 14.94x + 787.6
RÂ² = 0.666
y = 0.103×2 – 14.94x + 787.6
RÂ² = 0.666
250 y = 0.050×2 – 5.930x + 352.1 RÂ² = 0.541
200
250 y = 0.050×2 – 5.930x + 352.1 RÂ² = 0.541
200
150
100
150
100
y = 0.026×2 – 3.008x + 248.6
RÂ² = 0.220
y = 0.026×2 – 3.008x + 248.6
RÂ² = 0.220
50
50
212Âµm
425Âµm
710Âµm
Poly. (212Âµm)
Poly. (425Âµm) Poly. (710Âµm)
212Âµm
425Âµm
710Âµm
Poly. (212Âµm)
Poly. (425Âµm) Poly. (710Âµm)
Thermal conductivity (W/mK).
Thermal conductivity (W/mK).
Figure 2b: Thermal conductivity of Heattreated Cu/SiCp composites (Polynomial regression).
In Figure 3, the electrical conductivity of 212Âµm, 425Âµm and 710Âµm particle sizes of SiC decreased with increased volume fractions of SiC but increased with increasing particle sizes of SiC [15]. 710Âµm particle size showed a projectile decrease in value till 50/50 and rose slightly at 40/60 volume fraction. The electrical conductivity decreased slightly with particle size 425Âµm and rose slightly at 50/50 before decreasing again. 212Âµm particle size gave a sharp decrease in values of electrical conductivity till 40/60 volume fraction. The heat treated electrical conductivity values were lower than that of untreated values of Cu/SiC composites. Validation
of the result also showed polynomial relationships between the thermal conductivity and the % volume fraction of the Cu/SiCp composites in relation to the particle sizes; i.e. R2 shows 0.905, 0.9365 and 0.958 respectively for 710Âµm, 425Âµm and 212 Âµm.
6
5
4
3
212Âµm
425Âµm
710Âµm
6
5
4
3
212Âµm
425Âµm
710Âµm
30
40
50
60
70
80
90
100
110
30
40
50
60
70
80
90
100
110
Volume fraction of Cu/SiC (%).
Volume fraction of Cu/SiC (%).
2
1
0
2
1
0
6
6
y = 0.000×2 + 0.108x – 1.371
RÂ² = 0.904
y = 0.000×2 + 0.108x – 1.371
RÂ² = 0.904
5
4
5
4
y = 0.000×2 – 0.027x + 4.335
RÂ² = 0.937
y = 0.000×2 – 0.027x + 4.335
RÂ² = 0.937
3
2
1
3
2
1
212Âµm
425Âµm
710Âµm
Poly. (212Âµm)
Poly. (425Âµm) Poly. (710Âµm)
212Âµm
425Âµm
710Âµm
Poly. (212Âµm)
Poly. (425Âµm) Poly. (710Âµm)
Electrical conductivity (Siemen/m) x107
Electrical conductivity (Siemen/m) x107
Electrical conductivity (Siemen/m) x107
Electrical conductivity (Siemen/m) x107
Figure 3a: Electrical conductivity of Cu/SiCp composites
Volume fraction of Cu/SiC (%).
Volume fraction of Cu/SiC (%).
y = 0.000×2 + 0.133x – 2.298
RÂ² = 0.958
y = 0.000×2 + 0.133x – 2.298
RÂ² = 0.958
0
0
30
30
40
40
50
50
60
60
70
70
80
80
90
90
100
100
110
110
Figure 3b: Electrical conductivity of Cu/SiCp composites (Polynomial regression).
Figure 4 shows that electrical conductivity of heattreated samples decreased with increasing volume fraction of SiC but increased with increasing particle sizes of SiC. 710Âµm particle size indicated a sharp decrease in values till 70/30volume fraction followed by a slight decrease till 40/60 volume fraction. 425Âµm particle size showed a slight decrease till 70/30 and became steady but later decreased sharply at 60/40 volume fraction while 212Âµm showed a sharp
decrease till 40/6 volume fraction. Validation of the result also showed polynomial relationships between the electrical conductivity and the % volume fraction of the Heattreated Cu/Sicp composites in relation to the particle sizes; i.e. R2 shows 0.89, 0.918 and 0.994 respectively for 425Âµm, 212Âµm and 710 Âµm.
Electrical conductivity (Siemen/m) x107
Electrical conductivity (Siemen/m) x107
6
5
4 212Âµm
3 425Âµm
710Âµm
2
1
0
30 40 50 60 70 80 90 100 110
Volume fraction of Cu/SiC (%).
Figure 4a: Electrical conductivity of Heat treated Cu/SiCp composites
Electrical conductivity (Siemen/m) x107
Electrical conductivity (Siemen/m) x107
6
5 y = 0.000×2 + 0.092x – 0.850 RÂ² = 0.918
4
3
2 y = 0.000×2 + 0.16x – 2.254 RÂ² = 0.889
1
y = 0.000×2 – 0.067x + 5.554 RÂ² = 0.993
212Âµm
425Âµm
710Âµm
Poly. (212Âµm) Poly. (425Âµm) Poly. (710Âµm)
0
30 40 50 60 70 80 90 100 110
Volume fraction of Cu/SiC (%).
Figure 4b: Electrical conductivity of Heat treated Cu/SiCp composites (Polynomial regression).

CONCLUSIONS.
The mechanism controlling thermal conductivity of CuSiC particulate composite produced by liquid metallurgy was investigated with further emphasis on the evaluation of the relationship and impact between particle sizes, volume fraction and processing parameters for high thermal and electrical conductivity. Deduction from this study has shown that:

The electrical conductivity increases with increase particle sizes but decreases with increasing volume fraction of SiC in the copper matrix. Also, with decrease grain sizes, thermal conductivity decreases but increases with increasing particle sizes i.e. the larger the cross sectional area of the particle size (conductor), the more electrons per unit length is available to carry or dissipate the current.

The strengthening of the C10200 alloy with the particulate SiC shows to an appreciable extent the influence of the volume fraction and particle sizes on the electrical conductivity and thermal conductivity which was also validated by the regression analysis carried out.

This will be found useful in sectors where high thermal conductivity, low resistivity and high electrical conductivity, as well as low thermal expansion (CTE) are required such as aerospace, defence technology and electronic industries.


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