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Vol. 8. Issue 5.
Pages 3795-3799 (September - October 2019)
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Vol. 8. Issue 5.
Pages 3795-3799 (September - October 2019)
Original Article
DOI: 10.1016/j.jmrt.2019.06.040
Open Access
An efficient way to produce a nano composites of pure copper reinforced by carbon nano tubes carboxylic
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Fathi A. Alshamma, Omar Ali Jassim
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omariiyy@yahoo.com

Corresponding author.
Baghdad University, Mechanical Department, Iraq
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Table 1. Comparison of mechanical properties of CNTs/Cu composites with various researches.
Abstract

The paper explains the easiest way to produce a nano-composite, the material of copper reinforced by carbon nano tubes (CNTs), with perfect dispersions of CNTs, to improve and enhance the mechanical properties and reduce the time of fabrication. High energy planetary ball milling device was used to get a homogeneous mixture of copper and CNTs.

A pure copper 99.99% was reinforced by Single Wall carbon nano tubes carboxyl (SWCNTs-COOH) and Multi-Wall carbon nano tubes carboxyl (MWCNTs-COOH), with a 6% volume percentage.

Acetone was added to CNTs as a solvent and to prevent oxidization and conglomerations in the mixture also it will spread out in the air after finishing ball milling.

The microhardness was found (Hv) = (112, 99, 54) kg/mm2 for (SWCNTs-COOH + copper, MWCNTs-COOH + copper, and copper) respectively. Results of the compression tests are showing the enhancement of strength for pure copper to 233.7% with SWCNTs carboxyl and 150% for MWCNTs carboxyl, for tensile test the strength was improved to 268% for SWCNTs-COOH and 166% MWCNTs-COOH.The density was found (7.98, 7.8 and 7.7 g/cm3) for pure copper, SW + Cu and MW + Cu, respectively.

Keywords:
CNTs-COOH
Powder metallurgy
Ball milling
Mechanical properties
Full Text
1Introduction

Copper is a generally utilized metal and it has an extensive variety of applications due to its good properties (high thermal and electrical conductivity). In the current age, the necessities of such materials have increased substantially. This has led to the development of many new composite materials. However, for many applications, pure Cu cannot be used because of its lower strength.

Carbon nanotubes (CNTs) are widely used as a reinforcing material due to their superior properties. When CNTs is discovered in 1991, a huge area of innovation has been opened with continued demand for high-performance mechanical, electrical and electronic devices with low cost, small size and more efficient systems, In most of these, composites carbon nanotubes (CNTs) are used as the reinforcement material because of its outstanding properties such as large aspect ratio (1000–10,000), low density, high rigidity (Young’s modulus of the order of (1 T Pa) and high tensile strength (up to 60 GPa) [1]. Also, the thermal conductivity of CNTs was found to be >3000 W/mK [2], making them a suitable candidate for the fabrication of composites with improved properties. In the area of metal–matrix composites, all composites have been paid great attention due to their use in automobile, aerospace and power plant industries because of their lightweight, high strength, good corrosion resistance, and good thermal, electrical conductivities. Therefore, the mechanical properties of Cu are improved by reinforcing it with CNTs using several methods like (ball milling, electro deposition [3], powder injection molding, molecular-level mixing) [4]. This paper was used Planetary ball milling for the powders of pure copper mesh 325 and CNTs-COOH and adding acetone to prevent oxidization, the attachment of functional groups (COOH) on the surface of CNTs will form a strong covalent bond at the interface between Cu ions and functionalized CNTs. So it was getting good dispersion of CNTs in copper by using a common powder metallurgy process.

There are three general solvents for CNTs, water, ethanol, and acetone, used to shrink the CNTs filaments, and acetone shows the best shrinking effect. The mechanism of the ethanol and acetone shrinking differs from that of the water shrinking, but they both result from the surface tension of the solvents [5].

The main objective of this work is to produce a nano-composite material Cu/CNT with high quality, quantity and time-consuming.

2Experimental work

For industrial work with the best dispersion of CNTs in Cu powder, a high energy planetary ball milling device was used. The copper powder used with particle size ≤45 µm (325 mesh) with 99.99% purity with bulk density = 1.62 g/cm3. SWCNTs carboxyl groups (COOH) purity ≥85%, with bulk density = 0.05 g/cm3, outer diameter 1.8 ± 0.4 nm length ˜5 µm) and MWCNTs carboxyl groups (COOH) purity >97%, with bulk density = 0.18 g/cm3 outer diameter 20–40 nm length <10 µm). The high energy planetary ball milling device (Fig. 1b) used with speed 300 r.p.m and with steel balls coated by tungsten (50 balls with 5 mm diameter and 7 g for each ball) and the jar also made of steel and coated by tungsten (65 mm outer diameter, 50 mm inner diameter 1000 mm length) as shown in Fig. 1(c). It is used to give perfect mixing and milling without notches. CNTs have been put in the jar then added acetone 80 mL and mixed then added the copper powder with the balls (the ratio of balls to composite powder is 3.5:1 (Cu 94 vol% and CNTs 6 vol%) then close the jar tightly and run the device for 2.5 h after that we add more acetone 80 mL and run the ball milling for the other 2.5 h. Every 5 h 100 g of the composite the material will be mixed. After that, the sample was dried on the air to remove the acetone for 2 h at room temperature then put it in a closed package. After that, the composite powder was pressed 600 MPa in close steel die as shown in Fig. 1(d), with a hydraulic pressing machine, then directly the sample was sintered in a tubular vacuum furnace (Fig. 1a) till 900 ºC [4,6] for 120 min (from 0 to 900 ºC takes 20 min) and the vacuum was 76 cm Hg (for vacuum used Quartz class tube with diameter 55 mm length 100 mm), then turn off the furnace till the room temperature with a vacuum.

Fig. 1.

(a) Tubular vacuum furnace, (b) planetary ball milling, (c) jar + balls, (d) steel die, (e) XRD result for SWCNTs + copper after ball milling, (f) XRD for MWCNTs + copper after ball milling, (g) tensile test, (h) compression test, (i) E8 specimen for tensile test, (j) E8 specimen for comp. test.

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For pressing the powder, it was fabricated a new die to produce a flat plate with the dimensions (25, 150, 3.5 mm). That die was made off tool steel metal to hold out the 600 MPa stress (around 210 ton pressing) (Fig. 1d). Also, was used a circular die to produce a sample for compression test with a diameter 10 mm and height 50 mm, to obtain the mechanical properties.

3Results and discussion3.1XRD results

Fig. 1(e and f) shows the final composition of Cu/CNT composite obtained after ball milling. For CNTs, generally, the peak associated with the (002) diffraction is located at 26.2, copper fine particles show characteristic peaks at 43.29, 50.378 and 73.4071 corresponding to the FCC phase of copper. At 36.47, copper oxide was located. XRD data help establish the successful synthesis of Cu/CNT composite material [6,9].

3.2Mechanical properties

A tensile test was done with a samples standard ASTM E8-04 sub size specimens fabricated by using wire-cut machine as shown in Fig. 1(g and i). And it shows clearly the effects of CNTs for improving the tensile strength of pure copper[10]. This work did not reach to the actual density of copper (9.84 g/cm3) because of the porosity, so it is seen there are differences between these values and standard values of copper tensile strength, but this work has shown clearly the increase in tensile strength for SWCNTs + Cu 2.68 time from the pure copper and 1.66 times for MWCNTs + Cu. Because of the bounds that created between COOH groups and Cu, also between CNTS fibers and Cu. The density was found by dividing the weight (gram) on the volume (cm3) for pure copper, it was 7.98 g/cm3, and for SWCNTs + Cu is 7.8 g/cm3 and 7.7 g/cm3 for MWCNTs + Cu. For compression test, the sample was prepared with close cylindrical die with diameter 10 mm and length 50 mm and it produces the samples with diameter 10 mm and height 10 mm as shown in Fig. 1(j and h), the compression strength was (305, 763 and 1018 MPa) for pure Cu, MWCNT and SWCNTs, respectively. The micro hardness (Vickers) was tested 10 times for each sample and the average was taken, (Hv) = (54, 99 and 112) kg/mm2 For (Cu, MWCNTs and SWCNTs), respectively

3.3SEM image

Micro structure analysis and the dispersion of acid functionalized CNTs in Cu matrix were studied using SEM. Figs. 2a, 3a and 4a show the SEM image of Cu/CNTs composite powder produced by ball milling. And Figs. 2b, 3b and 4b are for the solid state cracked face after sintering. CNTs-COOH can be seen clearly on the surface of Cu and the mixing of CNTs can be seen dispersed in a highly homogeneous method with the copper matrix, CNTs are not agglomerated at one site, this establishes that the CNTs- Carboxyl with the ball milling only producing homogeneously dispersed Cu/CNTs powders. Also, there is no damage to the CNTs. So CNTs-COOH can be seen coating the copper particles. The bulk production of Cu/CNT powders is possible with this method. SEM micro graphs establish the dispersion and hence overall quality of the Cu/CNT powder [7].

Fig. 2.

(a) Cu powder, (b) Cu solid (for cracked face).

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Fig. 3.

(a) MW + Cu powder, (b) MW + Cu solid (for cracked face).

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Fig. 4.

(a) SW + Cu powder, (b) SW + Cu solid (for cracked face).

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The efficiency of this paper can be found by comparing the results with other papers and also the time-consuming for using the furnace once because it was used acetone that can be separate out easily from the composites after ball milling, see Table 1.

Table 1.

Comparison of mechanical properties of CNTs/Cu composites with various researches.

Composite materials  Micro hardness Hv improvement %  Compressive strength improvement %  Tensile strength improvement % 
Cu + SWCNTs (6 vol%) for this project  100.07%  233.7%  268% 
Cu + MWCNTs (6 vol%) for this project  83.4%  150%  166% 
Cu + MWCNTs (6 vol%) for Reference [1]  100.05%  89.45%  13% 
Cu + MWCNTs (5%vol) for Reference [8]  –  50%  – 
Cu + MWCNTs (1%wt) (6%vol) for Reference [7]  94.4%  180.44%  28.57% 
4Conclusions

This method is fast and efficient and it can be used in industrial sectors, also leads to the enhancement of various mechanical properties of CNTs/Cu. The high level of dispersion leading to better interfacial bonding between the Cu matrix and CNTs can be achieved as seen through the SEM and XRD tests. Also, because of the large application of this nano-composite metal, it can be tested in various applications to give a good understanding of the behavior of this material. If it is needed to reach to the actual density of copper it can increase the time of sintering temperature or the temperature its self can be increased to 950 ºC or 1000 ºC.

Conflicts of interest

The authors declare no conflicts of interest.

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Copyright © 2019. The Authors
Journal of Materials Research and Technology

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