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mesocarbon microbead composites from coal tar pitch
Materials Letters 62 (2008) 3585–3587
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
In situ fabrication of carbon nanotube/mesocarbon microbead composites from coal tar pitch Zhi Wang a,b,⁎, Bin Wu a, Qianming Gong a, Huaihe Song c, Ji Liang a a b c
Department of Mechanical Engineering, Tsinghua University, Beijing 100084, PR China Shenyang Institute of Aeronautical Engineering, Shenyang 110034, PR China State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China
A R T I C L E
I N F O
Article history: Received 18 November 2007 Accepted 1 April 2008 Available online 8 April 2008 Keywords: Carbon nanotubes Mesocarbon microbeads Composite materials
A B S T R A C T Carbon nanotube/mesocarbon microbead composites have been synthesized from coal tar pitch with carbon nanotubes. How the carbon nanotubes affect the growth and the structure of mesocarbon microbeads are studied. The result shows that the size of beads decreases when more carbon nanotubes are added, and when the ratio of carbon nanotubes is set at 5%, we get the smallest sample with quite uniform shape. Carbon nanotubes exist both on the surface and inside of the samples and they will inhibit the growth and coalescence of these spheres. The addition of carbon nanotubes decreases the graphitization degree of the samples and makes their microtexture tend to be disordered. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Mesocarbon microbeads (MCMBs) are exceptional precursors of high density and strength carbon based materials because of their unique shape and structure. Much work has been focused on using MCMB to synthesis high-density isotropic carbon [1–6]. Recently, carbon fiber reinforced MCMB-based composites were developed by using carbon fibers as reinforcement and MCMB as matrix by press molding and carbonization, which provides a standard and inexpensive way to prepare high performance carbon based composites for successful commercial application [7]. Due to their unique structural and mechanical properties, carbon nanotubes (CNTs) have been viewed as ideal material for a composite enhancer. Many efforts have been made to realize their full potential [8–14]. However, no reports on the synthesis of CNTs reinforced MCMB-based composites have been published to date. In the paper, we present the first synthesis of CNT/MCMB composites by in situ condensation from a coal tar pitch with CNTs. The influence of CNTs on the MCMBs was studied. The size, shape, surface and cross sections of the CNT/MCMB composites were studied by using of scanning electron microscope (SEM). The microstructures of those composites were analyzed through X-ray diffraction (XRD).
The multiwalled CNTs used in this work were prepared by the catalytic decomposition of acetylene with Ni particles as the catalyst, purified and treated with blended acid [12]. Transmission electron microscopy (TEM) image shows that those CNTs have 30–50 nm in diameter and 0.5–2 μm in length. Coal tar pitch which contains 7.3 wt.% of quinoline-insoluble fraction was used as the raw material. First the CNTs were dispersed in ethanol by ultrasonication, then mixed and grinded with coal tar pitch by ball milling for 30 min. The coal tar pitch with CNTs was sealed off in a stainless-steel reactor and the CNTs content in raw pitch is 0%, 2%, 5%, 10% and 20% in weight as listed in Table 1. Liquid carbonization was carried out by heating the system up to 420 °C at a rate of 1 °C/min with continuous stirring of about 200 rpm and maintaining at the final temperature for 120 ~ 150 min, then the reactor was annealed naturally to room temperature. CNT/MCMB composites generated in the heat-treated pitch were separated out with pyridine and acetone using a Soxhlet apparatus and the isolated spheres were dried under 80 °C for 10h. The samples were carbonized at 900 °C for 2h under the protection of purified argon to obtain the carbonized samples. The obtained carbonized samples were heat-treated to 2550 °C under the protection of argon to obtain the graphitized samples. We used a field-emission type SEM (LEO-1530) to observe the morphologies of the samples by setting the acceleration voltage as
⁎ Corresponding author. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, PR China. Tel.: +86 24 86141279; fax: +86 24 86141517. E-mail address: [email protected] (Z. Wang). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.04.001
3586
Z. Wang et al. / Materials Letters 62 (2008) 3585–3587
Table 1 Size ranges and yields of the different samples Sample designation A B C D E
CNTs ratio in the sample (wt.%)
Yield of sample (%)
Size range (μm)
Average size (μm)
0 2 5 10 20
45.5 42.1 41.4 50.4 51.3
10 – 25 8 – 20 5 – 16 5 – 30 6 – 30
19.8 12.3 11.1 15.9 16.8
10kV during the measurements. The variation of crystal parameters during pyrolysis was characterized by using XRD (D/max-IIIA). 3. Results and discussion The size ranges and the yields of the different samples are listed in Table 1. Fig. 1 shows the typical SEM images of as-received samples. As shown in Fig. 1 all the samples have very good spheroid structures. The size of carbon beads tends to be smaller when the ratio of the CNTs increased. At the ratio of 2%, the average size of the samples decreases from 19.8 to 12.3 μm, and the yield of samples also decrease. At the ratio of 5%, we have the sample with the smallest size (sample c) with more homogenous distribution. But when the ratio is beyond 5%, the spheroid shapes of the samples get worse. When the ratio of the CNTs is increased to 10%, the average size of the samples begins to increase because of the existence of the big shapeless particles. Fig. 2 shows SEM images of CNTs in the samples. As demonstrated by the surface morphology shown in Fig. 2(a), we can find some CNTs right on the surface of the sample (indicated by arrow). The CNTs are either attached to the surface or inserted into the sample, and the increase of the CNTs ratio leads to have more CNTs attached onto the surface, which will inhibit the growth and coalescence of these spheres [2]. The sample e was mounted with resin and then broken into pieces for cross section analysis under SEM. Fig. 2(b) is the cross-section of sample e, which shows some CNTs exist inside the sample (indicated by arrow). The result means CNTs have existed both inside and outside of the samples by our method.
Fig. 2. SEM images of CNTs in the sample d and e (a) surface of d (b) inside of e.
Fig. 1. SEM images of the samples with different CNTs ratio described in Table 1. (a) sample a, (b) sample b, (c) sample c and (d) sample d.
Z. Wang et al. / Materials Letters 62 (2008) 3585–3587
3587
The microtexture was also analyzed by observing the cross-section of the samples under SEM. Fig. 3 gives typical morphology of the cross-sections of samples. As shown in Fig. 3 the microtexture of sample b (2% CNTs) mainly has nice parallel layers, whereas the microtexture of sample d (10% CNTs) was more complicated due to the existing of CNTs. This means that the existence of CNTs makes the formation of the mesophase layers difficult. Fig. 4(a) shows the XRD spectrums of the carbonized samples. It shows that all the samples have a strong peak at about 25° and a weak peak at about 43°, which correspond to 002 and 100 planes of graphite. It shows that the aromatic molecules in the sample orientate to some degree but the other orientation is poor. In Fig. 4(b) the XRD spectrums show the excellent graphite property of graphitized samples. We can find that the interlayer distance of samples is slightly increased when the ratio of the CNTs gets increased, and the CNTs make the graphitization degree of samples decrease. The result implies that the existence of CNTs prohibits the natural orientation of large aromatic molecules, and tends to make the microtexture irregular.
4. Conclusions We have synthesized CNT/MCMB composites by in situ condensation from a coal tar pitch. The result shows that the size of samples is diminished and the microtexture of samples tends to be disorder when more CNTs are added. It can be deduced that the added CNTs restrict the growth and coalescence of spheres, which leads to the formation of the larger number of spheres with smaller diameter and decreases the yield of them. The addition of CNTs decreases the graphitization degree of the samples. The textural layers of the formed samples are disturbed by the CNTs. Acknowledgments This work was supported by National Natural Science Foundation of China (Grant Nos. 10332020), China Postdoctoral Science Founda-
Fig. 4. XRD spectrums of the samples. (a) carbonized at 900 ˚C (b) graphitized at 2550 ˚C.
tion (Grant Nos. 20060390041) and Foundation of Liaoning Provincial Education Committee of China (Grant Nos. 05 L327). References [1] Y.G. Wang, Y. Korai, I. Mochida, Carbon 37 (7) (1999) 1049–1057. [2] Y. Korai, Y.G. Wang, S. YOON, S. Ishida, I. Mochida, Y. Nakagawa, et al., Carbon 35 (7) (1997) 875–884. [3] C. Norfolk, A. Mukasyan, D. Hayes, P. McGinn, A. Varma, Carbon 42 (1) (2004) 11–19. [4] Y.Z. Song, G.T. Zhai, G.S. Li, J.L. Shi, Q.G. Guo, L. Liu, Carbon 42 (8–9) (2004) 1427–1433. [5] Y. Gao, H.H. Song, X.H. Chen, J. Mater. Sci. 38 (10) (2003) 2209–2213. [6] C.J. Zhou, P.J. McGinn, Carbon 44 (9) (2006) 1673–1681. [7] H.L. Hu, T.H. Ko, W.S. Kuo, Mater. Lett. 59 (22) (2005) 2746–2750. [8] X.Y. Gong, J. Liu, S. Baskaran, R.D. Voise, J.S. Young, Chem. Mater. 12 (4) (2000) 1049–1052. [9] E. Flahaut, A. Peigney, C.h. Laurent, C.h. Marlie, F. Chastel, A. Rousset, Acta. Mater. 48 (14) (2000) 3803–3812. [10] A. Peigney, C. Laurent, E. Flahaut, A. Rousset, Ceram. Int. 26 (6) (2000) 667–683. [11] C.L. Xu, B.Q. Wei, R.Z. Ma, J. Liang, X.K. Ma, D.H. Wu, Carbon 37 (5) (1999) 855–858. [12] X.W. Zhou, Y.F. Zhu, Q.M. Gong, J. Liang, Mater. Lett. 60 (2006) 3769–3775. [13] Q.M. Gong, Z. Li, D. Li, J. Liang, Solid State Commun. 131 (6) (2004) 399–404. [14] M. Cadek, J.N. Colemen, K.P. Ryan, V. Nicolosi, G. Bister, A. Fonseca, et al., Nano. Lett. 4 (2004) 353–356.
Fig. 3. SEM images of the cross-sections of the samples (a) sample b (b) sample d.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
In situ fabrication of carbon nanotube/mesocarbon microbead composites from coal tar pitch Zhi Wang a,b,⁎, Bin Wu a, Qianming Gong a, Huaihe Song c, Ji Liang a a b c
Department of Mechanical Engineering, Tsinghua University, Beijing 100084, PR China Shenyang Institute of Aeronautical Engineering, Shenyang 110034, PR China State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China
A R T I C L E
I N F O
Article history: Received 18 November 2007 Accepted 1 April 2008 Available online 8 April 2008 Keywords: Carbon nanotubes Mesocarbon microbeads Composite materials
A B S T R A C T Carbon nanotube/mesocarbon microbead composites have been synthesized from coal tar pitch with carbon nanotubes. How the carbon nanotubes affect the growth and the structure of mesocarbon microbeads are studied. The result shows that the size of beads decreases when more carbon nanotubes are added, and when the ratio of carbon nanotubes is set at 5%, we get the smallest sample with quite uniform shape. Carbon nanotubes exist both on the surface and inside of the samples and they will inhibit the growth and coalescence of these spheres. The addition of carbon nanotubes decreases the graphitization degree of the samples and makes their microtexture tend to be disordered. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Mesocarbon microbeads (MCMBs) are exceptional precursors of high density and strength carbon based materials because of their unique shape and structure. Much work has been focused on using MCMB to synthesis high-density isotropic carbon [1–6]. Recently, carbon fiber reinforced MCMB-based composites were developed by using carbon fibers as reinforcement and MCMB as matrix by press molding and carbonization, which provides a standard and inexpensive way to prepare high performance carbon based composites for successful commercial application [7]. Due to their unique structural and mechanical properties, carbon nanotubes (CNTs) have been viewed as ideal material for a composite enhancer. Many efforts have been made to realize their full potential [8–14]. However, no reports on the synthesis of CNTs reinforced MCMB-based composites have been published to date. In the paper, we present the first synthesis of CNT/MCMB composites by in situ condensation from a coal tar pitch with CNTs. The influence of CNTs on the MCMBs was studied. The size, shape, surface and cross sections of the CNT/MCMB composites were studied by using of scanning electron microscope (SEM). The microstructures of those composites were analyzed through X-ray diffraction (XRD).
The multiwalled CNTs used in this work were prepared by the catalytic decomposition of acetylene with Ni particles as the catalyst, purified and treated with blended acid [12]. Transmission electron microscopy (TEM) image shows that those CNTs have 30–50 nm in diameter and 0.5–2 μm in length. Coal tar pitch which contains 7.3 wt.% of quinoline-insoluble fraction was used as the raw material. First the CNTs were dispersed in ethanol by ultrasonication, then mixed and grinded with coal tar pitch by ball milling for 30 min. The coal tar pitch with CNTs was sealed off in a stainless-steel reactor and the CNTs content in raw pitch is 0%, 2%, 5%, 10% and 20% in weight as listed in Table 1. Liquid carbonization was carried out by heating the system up to 420 °C at a rate of 1 °C/min with continuous stirring of about 200 rpm and maintaining at the final temperature for 120 ~ 150 min, then the reactor was annealed naturally to room temperature. CNT/MCMB composites generated in the heat-treated pitch were separated out with pyridine and acetone using a Soxhlet apparatus and the isolated spheres were dried under 80 °C for 10h. The samples were carbonized at 900 °C for 2h under the protection of purified argon to obtain the carbonized samples. The obtained carbonized samples were heat-treated to 2550 °C under the protection of argon to obtain the graphitized samples. We used a field-emission type SEM (LEO-1530) to observe the morphologies of the samples by setting the acceleration voltage as
⁎ Corresponding author. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, PR China. Tel.: +86 24 86141279; fax: +86 24 86141517. E-mail address: [email protected] (Z. Wang). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.04.001
3586
Z. Wang et al. / Materials Letters 62 (2008) 3585–3587
Table 1 Size ranges and yields of the different samples Sample designation A B C D E
CNTs ratio in the sample (wt.%)
Yield of sample (%)
Size range (μm)
Average size (μm)
0 2 5 10 20
45.5 42.1 41.4 50.4 51.3
10 – 25 8 – 20 5 – 16 5 – 30 6 – 30
19.8 12.3 11.1 15.9 16.8
10kV during the measurements. The variation of crystal parameters during pyrolysis was characterized by using XRD (D/max-IIIA). 3. Results and discussion The size ranges and the yields of the different samples are listed in Table 1. Fig. 1 shows the typical SEM images of as-received samples. As shown in Fig. 1 all the samples have very good spheroid structures. The size of carbon beads tends to be smaller when the ratio of the CNTs increased. At the ratio of 2%, the average size of the samples decreases from 19.8 to 12.3 μm, and the yield of samples also decrease. At the ratio of 5%, we have the sample with the smallest size (sample c) with more homogenous distribution. But when the ratio is beyond 5%, the spheroid shapes of the samples get worse. When the ratio of the CNTs is increased to 10%, the average size of the samples begins to increase because of the existence of the big shapeless particles. Fig. 2 shows SEM images of CNTs in the samples. As demonstrated by the surface morphology shown in Fig. 2(a), we can find some CNTs right on the surface of the sample (indicated by arrow). The CNTs are either attached to the surface or inserted into the sample, and the increase of the CNTs ratio leads to have more CNTs attached onto the surface, which will inhibit the growth and coalescence of these spheres [2]. The sample e was mounted with resin and then broken into pieces for cross section analysis under SEM. Fig. 2(b) is the cross-section of sample e, which shows some CNTs exist inside the sample (indicated by arrow). The result means CNTs have existed both inside and outside of the samples by our method.
Fig. 2. SEM images of CNTs in the sample d and e (a) surface of d (b) inside of e.
Fig. 1. SEM images of the samples with different CNTs ratio described in Table 1. (a) sample a, (b) sample b, (c) sample c and (d) sample d.
Z. Wang et al. / Materials Letters 62 (2008) 3585–3587
3587
The microtexture was also analyzed by observing the cross-section of the samples under SEM. Fig. 3 gives typical morphology of the cross-sections of samples. As shown in Fig. 3 the microtexture of sample b (2% CNTs) mainly has nice parallel layers, whereas the microtexture of sample d (10% CNTs) was more complicated due to the existing of CNTs. This means that the existence of CNTs makes the formation of the mesophase layers difficult. Fig. 4(a) shows the XRD spectrums of the carbonized samples. It shows that all the samples have a strong peak at about 25° and a weak peak at about 43°, which correspond to 002 and 100 planes of graphite. It shows that the aromatic molecules in the sample orientate to some degree but the other orientation is poor. In Fig. 4(b) the XRD spectrums show the excellent graphite property of graphitized samples. We can find that the interlayer distance of samples is slightly increased when the ratio of the CNTs gets increased, and the CNTs make the graphitization degree of samples decrease. The result implies that the existence of CNTs prohibits the natural orientation of large aromatic molecules, and tends to make the microtexture irregular.
4. Conclusions We have synthesized CNT/MCMB composites by in situ condensation from a coal tar pitch. The result shows that the size of samples is diminished and the microtexture of samples tends to be disorder when more CNTs are added. It can be deduced that the added CNTs restrict the growth and coalescence of spheres, which leads to the formation of the larger number of spheres with smaller diameter and decreases the yield of them. The addition of CNTs decreases the graphitization degree of the samples. The textural layers of the formed samples are disturbed by the CNTs. Acknowledgments This work was supported by National Natural Science Foundation of China (Grant Nos. 10332020), China Postdoctoral Science Founda-
Fig. 4. XRD spectrums of the samples. (a) carbonized at 900 ˚C (b) graphitized at 2550 ˚C.
tion (Grant Nos. 20060390041) and Foundation of Liaoning Provincial Education Committee of China (Grant Nos. 05 L327). References [1] Y.G. Wang, Y. Korai, I. Mochida, Carbon 37 (7) (1999) 1049–1057. [2] Y. Korai, Y.G. Wang, S. YOON, S. Ishida, I. Mochida, Y. Nakagawa, et al., Carbon 35 (7) (1997) 875–884. [3] C. Norfolk, A. Mukasyan, D. Hayes, P. McGinn, A. Varma, Carbon 42 (1) (2004) 11–19. [4] Y.Z. Song, G.T. Zhai, G.S. Li, J.L. Shi, Q.G. Guo, L. Liu, Carbon 42 (8–9) (2004) 1427–1433. [5] Y. Gao, H.H. Song, X.H. Chen, J. Mater. Sci. 38 (10) (2003) 2209–2213. [6] C.J. Zhou, P.J. McGinn, Carbon 44 (9) (2006) 1673–1681. [7] H.L. Hu, T.H. Ko, W.S. Kuo, Mater. Lett. 59 (22) (2005) 2746–2750. [8] X.Y. Gong, J. Liu, S. Baskaran, R.D. Voise, J.S. Young, Chem. Mater. 12 (4) (2000) 1049–1052. [9] E. Flahaut, A. Peigney, C.h. Laurent, C.h. Marlie, F. Chastel, A. Rousset, Acta. Mater. 48 (14) (2000) 3803–3812. [10] A. Peigney, C. Laurent, E. Flahaut, A. Rousset, Ceram. Int. 26 (6) (2000) 667–683. [11] C.L. Xu, B.Q. Wei, R.Z. Ma, J. Liang, X.K. Ma, D.H. Wu, Carbon 37 (5) (1999) 855–858. [12] X.W. Zhou, Y.F. Zhu, Q.M. Gong, J. Liang, Mater. Lett. 60 (2006) 3769–3775. [13] Q.M. Gong, Z. Li, D. Li, J. Liang, Solid State Commun. 131 (6) (2004) 399–404. [14] M. Cadek, J.N. Colemen, K.P. Ryan, V. Nicolosi, G. Bister, A. Fonseca, et al., Nano. Lett. 4 (2004) 353–356.
Fig. 3. SEM images of the cross-sections of the samples (a) sample b (b) sample d.