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Super resilience of a compacted mixture of natural graphite and agglomerated carbon nanotubes under cyclic compression
CARBON
309
4 8 (2 0 1 0) 3 0 5–31 2
Super resilience of a compacted mixture of natural graphite and agglomerated carbon nanotubes under cyclic compression Tong Wei a, Kai Wang a, Zhuangjun Fan
a,* ,
Jun Yan a, Weizhong Qian b, Fei Wei
b,*
a
Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, School of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin, Heilongjiang 150001, China b Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
A R T I C L E I N F O
A B S T R A C T
Article history:
We have prepared and evaluated the performance of natural graphite (NG)/agglomerated
Received 27 May 2009
carbon nanotubes (ACNTs) composite materials for future mechanical dampening devices.
Accepted 14 September 2009
The mechanical performance of a compressed mixture of NG and ACNTs was examined
Available 18 September 2009
over the pressure range of 30–300 MPa. NG–ACNT composite materials showed improved performance over the ACNT materials alone. Nanocomposites containing 5% NG mixed with ACNTs had an expansion ratio of 2.7 and illustrated a lower loss of resilience as compared to the ACNTs alone, 7% loss versus 34% loss, respectively. Ó 2009 Elsevier Ltd. All rights reserved.
Carbon nanotubes (CNTs) are potential materials for energy-absorbing, mechanical dampening devices due to their unique mechanical properties including their strength, resilience and their ability to undergo large deformations without structural failure [1–3]. Mechanical strength (compressive stress) and compressibility (strain) are two important factors that determine the performance and applications of devices [4]. Previously, advances in the fabrication of CNTs at multimillimeter length scales provided an opportunity to investigate the compression behaviour of aligned CNTs [5–7]. Aligned CNTs were shown to fold tightly to enable high compressibility (85%) and exhibited superb durability with negligible mechanical and electrical degradation after being repetitively bent (millions of compression cycles) [4]. Recently, we have reported the cushioning behaviour of highly agglomerated carbon nanotubes (ACNTs) [8]. The nanotube agglomerates were shown to be capable of repetitive compressions at large volume reductions (>50%) yielding high expansion ratios (2–3) and significant energy absorption over a range of pressures (1–100 MPa). However, under high pressure cyclic loading nanotube seizure and entanglement with each other would eventually happen leading to the inhibition of CNT recovery. In this letter, we combined ACNTs and NG to form a spring–shim structure in which ACNTs act as the ‘‘spring’’ that facilitates configurational recovery, and NG acts as the ‘‘shim’’ that transfers the force and prevents ACNT entanglement and subsequent mechanical seizure. The relationships
between microstructure and compression resilience properties of samples were investigated. ACNTs (agglomerated ball with the size of 1 mm) were prepared by the catalytic decomposition of propylene on Fe/Al2O3 catalyst in a nano-agglomerated fluidized-bed reactor [9]. NG with an average size of 1 mm was supplied by Qingdao Graphite Company (Qingdao, China). Powders with different mass ratio of NG and ACNTs were mechanically stirred for 1 h in a flask. The experimental setup used for measuring compression resilience and expansion ratio is shown in Fig. 1. About 3 g of each powder was loaded to the cavity of a cylindrical die (diameter of 10 mm), and hydrostatic pressure was applied through an oil jack to push the top of the padding. The powder was preloaded at pressure of 30 MPa, and the displacement and pressure were measured by micrometer caliper and pressure gauge. Compression resilience ratio is defined as ðt2 t1 Þ=ðt0 t1 Þ, and expansion ratio is defined as t2 =t1 , where t0 , t1 and t2 are the height of preloading, loading and unloading, respectively. In this work, the particle sizes of NG and ACNTs are almost the same order of magnitude (Fig. 2a, inset). The primary aggregates of CNTs by catalytic pyrolysis of propylene in a fluidized-bed reactor are about 1 lm [9], and the primary aggregates further combine with each other to form secondary aggregates (10 lm, Fig. 2a), even to multilevel aggregates (1 mm, Fig. 2a, inset). After the 10th cycle, the breakdown of CNT agglomerates into a compacted structure can be
* Corresponding authors: Fax: +86 451 82569890 (Z. Fan). E-mail addresses: [email protected] (Z. Fan), [email protected] (F. Wei). 0008-6223/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2009.09.045
310
CARBON
4 8 ( 2 0 1 0 ) 3 0 5 –3 1 2
Fig. 1 – The experimental setup used for measuring the compression resilience and expansion ratio.
Fig. 2 – (a) SEM images of CNT agglomerates (the inset shows the photo of NG and ACNT powders). (b and c) SEM images of cross-section (perpendicular to the pressure) of ACNTs and 5% NG–ACNTs after the 10th cycle under 300 MPa, respectively. (d) SEM image of cross-section (parallel to the pressure) of 5% NG–ACNTs after the 10th cycle under 300 MPa.
311
4 8 (2 0 1 0) 3 0 5–31 2
Expansion ratio
3.5
ACNTs 5% NG-ACNTs ACNTs 5% NG-ACNTs 20% NG-ACNTs
3.0
(0~120MPa) (0~120MPa) (0~300MPa) (0~300MPa) (0~300MPa)
2.5
2.0
Resilience ratio / %
observed (Fig. 2b), and 5% NG–ACNTs remains a loose structure (Fig. 2c) with hybrid multilayer arrays of NG and ACNTs (Fig. 2d). However, the breakdown of graphite particles, about the size of 3–6 lm, are also observed due to mechanical extrusion after the 10th cycle. The recovery of ACNTs can be directly observed from the height change of powders filled in the die. Cyclic compression (Fig. 3) was performed with a preloading of 30 MPa, between a maximum and minimum pressure of 120/300 MPa and zero, respectively. A good resilience is maintained in CNTs over a wide pressure range (30–300 MPa), while polystyrene foam (PS, conventional packaging material) has high expansion ratio of 4.5 under pressure less than 1 MPa and expansion ratio is only less than 1.5 over a pressure range from 1 to10 MPa [8]. With an increase of pressure, all CNT samples show that compression resilience ratio decreases and expansion ratio increases. Under relatively lower pressure (120 MPa), the addition of NG has no obvious effect on improving CNT recovery, and CNT superagglomerates are capable of protecting the original structure from being completely collapsed and maintaining a higher level porosity after repeated compression [8]. However, under relatively higher pressure (300 MPa), the loss of resilience ratio of ACNTs after the 4th cycle is about two times higher than that of 120 MPa due to CNT seizure and entanglement each other. Afterwards, the loss of resilience ratio is 7% for 5% NG–ACNTs, while the losses are 20% and 34% for 20% NG–ACNTs and ACNTs, respectively. The expansion ratio of 5% NG–ACNTs has gradually decreased in the first four cycles and then stabilized 2.7 in the subsequent cycles (even after 100 cycles) under a loading pressure of 300 MPa. The resilience and expansion properties of ACNTs are remarkably improved by combination of NG due to the formation of layer by layer structure, resulting in effective inhibition of the interactions between CNT agglomerates, such as nanotube seizure and entanglement under compression. In order to investigate the stress–strain behaviour of the CNT block, samples after 10 cycles under a load of 300 MPa were measured using universal testing machine (compression head was set at a speed of 0.5 mm/min). It can be observed that compression stress of 5% NG–ACNT block at 40% strain is higher than CNT array block [5] and polyvinyl alcohol–polyacrylic acid copolymer (PVA–PAA) [10] as shown in Fig. 4. Compared with CNT block, 5% NG–ACNT block exhibits a nonlinear stress–strain behaviour composed of two distinct modulus regions (Fig. 4, marked by circle), having modulus of around 1 MPa between 0% and 3% strain and a sharp increase of modulus up to 5 MPa above 3% strain. This behaviour can be explained that NG can effectively inhibit the interactions between CNT agglomerates and has a cushion effect on deformation of CNT agglomerates in low elastic region. With the increase of strain, the collapse and densification of CNT agglomerates result in rapid increase of the modulus. In addition, NG also can improve the integrity of ACNT block through interaction between NG and nanotubes. For example, ACNT block without NG has happed serious breakdown or collapse above 20% strain. In conclusion, a compacted mixture of NG and ACNTs exhibited excellence compressibility and resilience performances at a relatively high pressure range (30–300 MPa). After
80
60
2
4
6
8
10
Number of cycles Fig. 3 – Compression resilience and expansion ratio of NG– ACNTs and ACNTs during loading and unloading cycles (three specimens of each cycle were tested, and the standard error was ±5%).
2.0
Our work
1.5
Compressive stress / MPa
CARBON
1.0
Multiwalled CNT array block [5]
ACNTs
0.5 MPa
0.5
0.3 MPa PVA-PAA [10]
5%NG-ACNTs
0.0 0
10
20
30
40
50
Compressive strain / % Fig. 4 – Compressive stress–strain curves of 5% NG–ACNTs and ACNT blocks after the 10th loading and unloading cycle under 300 MPa (the inset shows initial compression state).
10 cycles under 300 MPa, expansion ratio of 5% NG–ACNTs reached a constant 2.7, and the loss of resilience ratio of 5% NG–ACNTs (7%) was much less than that of ACNTs (34%). This indicates that the addition of NG into ACNTs can effectively inhibit the interactions between CNT agglomerates under compression. Therefore, the lightweight, highly resilient NG–ACNT mixture may be useful as mechanical damping, energy-absorbing and cushioning devices in future applications.
312
CARBON
4 8 ( 2 0 1 0 ) 3 0 5 –3 1 2
Acknowledgements Supports from the Foundation of Harbin Innovation Fellow (2007RFQXG028) and Fundamental Research Foundation of Harbin Engineering University (Project HEUFT07094) are appreciated.
R E F E R E N C E S
[1] Falvo MR, Clary GJ, Taylor RM, Chi V, Brooks FP, Washburn S, et al. Bending and buckling of carbon nanotubes under large strain. Nature 1997;389(6651):582–4. [2] Qian D, Wagner GJ, Liu WK, Yu MF, Ruoff RS. Mechanics of carbon nanotubes. Appl Mech Rev 2002;55(6):495–533. [3] Tang J, Qin LC, Sasaki T, Yudasaka M, Matsushita A, Iijima S. Compressibility and polygonization of single-walled carbon nanotubes under hydrostatic pressure. Phys Rev Lett 2000;85:1887–9.
[4] Cao AY, Dickrell PL, Sawyer WG, Ghasemi-Nejhad MN, Ajayan PM. Super-compressible foamlike carbon nanotube films. Science 2005;310(265):1307–10. [5] Suhr J, Victor P, Ci L, Sreekala S, Zhang X, Nalamasu O, et al. Fatigue resistance of aligned carbon nanotube arrays under cyclic compression. Nat Nanotechnol 2007;2:417–21. [6] Suhr J, Koratkar N, Keblinski P, Ajayan PM. Viscoelasticity in carbon nanotube composites. Nat Mater 2005;4:134–7. [7] Daraio C, Nesterenko VF, Jin SH. Highly nonlinear contact interaction and dynamic energy dissipation by forest of carbon nanotubes. Appl Phys Lett 2004;85(23): 5724–6. [8] Liu Y, Qian WZ, Zhang Q, Cao AY, Li ZF, Zhou WP, et al. Hierarchical agglomerates of carbon nanotubes as highpressure cushions. Nano Lett 2008;8(5):1323–7. [9] Hao Y, Zhang Q, Wei F, Qian WZ, Luo GH. Agglomerated CNTs synthesized in a fluidized bed reactor: agglomerate structure and formation mechanism. Carbon 2003;41(14):2855–63. [10] Caldwell DG. Pseudomuscular actuator for use in dextrous manipulation. Med Biol Eng Comput 1990;28:595–600.
309
4 8 (2 0 1 0) 3 0 5–31 2
Super resilience of a compacted mixture of natural graphite and agglomerated carbon nanotubes under cyclic compression Tong Wei a, Kai Wang a, Zhuangjun Fan
a,* ,
Jun Yan a, Weizhong Qian b, Fei Wei
b,*
a
Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, School of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin, Heilongjiang 150001, China b Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
A R T I C L E I N F O
A B S T R A C T
Article history:
We have prepared and evaluated the performance of natural graphite (NG)/agglomerated
Received 27 May 2009
carbon nanotubes (ACNTs) composite materials for future mechanical dampening devices.
Accepted 14 September 2009
The mechanical performance of a compressed mixture of NG and ACNTs was examined
Available 18 September 2009
over the pressure range of 30–300 MPa. NG–ACNT composite materials showed improved performance over the ACNT materials alone. Nanocomposites containing 5% NG mixed with ACNTs had an expansion ratio of 2.7 and illustrated a lower loss of resilience as compared to the ACNTs alone, 7% loss versus 34% loss, respectively. Ó 2009 Elsevier Ltd. All rights reserved.
Carbon nanotubes (CNTs) are potential materials for energy-absorbing, mechanical dampening devices due to their unique mechanical properties including their strength, resilience and their ability to undergo large deformations without structural failure [1–3]. Mechanical strength (compressive stress) and compressibility (strain) are two important factors that determine the performance and applications of devices [4]. Previously, advances in the fabrication of CNTs at multimillimeter length scales provided an opportunity to investigate the compression behaviour of aligned CNTs [5–7]. Aligned CNTs were shown to fold tightly to enable high compressibility (85%) and exhibited superb durability with negligible mechanical and electrical degradation after being repetitively bent (millions of compression cycles) [4]. Recently, we have reported the cushioning behaviour of highly agglomerated carbon nanotubes (ACNTs) [8]. The nanotube agglomerates were shown to be capable of repetitive compressions at large volume reductions (>50%) yielding high expansion ratios (2–3) and significant energy absorption over a range of pressures (1–100 MPa). However, under high pressure cyclic loading nanotube seizure and entanglement with each other would eventually happen leading to the inhibition of CNT recovery. In this letter, we combined ACNTs and NG to form a spring–shim structure in which ACNTs act as the ‘‘spring’’ that facilitates configurational recovery, and NG acts as the ‘‘shim’’ that transfers the force and prevents ACNT entanglement and subsequent mechanical seizure. The relationships
between microstructure and compression resilience properties of samples were investigated. ACNTs (agglomerated ball with the size of 1 mm) were prepared by the catalytic decomposition of propylene on Fe/Al2O3 catalyst in a nano-agglomerated fluidized-bed reactor [9]. NG with an average size of 1 mm was supplied by Qingdao Graphite Company (Qingdao, China). Powders with different mass ratio of NG and ACNTs were mechanically stirred for 1 h in a flask. The experimental setup used for measuring compression resilience and expansion ratio is shown in Fig. 1. About 3 g of each powder was loaded to the cavity of a cylindrical die (diameter of 10 mm), and hydrostatic pressure was applied through an oil jack to push the top of the padding. The powder was preloaded at pressure of 30 MPa, and the displacement and pressure were measured by micrometer caliper and pressure gauge. Compression resilience ratio is defined as ðt2 t1 Þ=ðt0 t1 Þ, and expansion ratio is defined as t2 =t1 , where t0 , t1 and t2 are the height of preloading, loading and unloading, respectively. In this work, the particle sizes of NG and ACNTs are almost the same order of magnitude (Fig. 2a, inset). The primary aggregates of CNTs by catalytic pyrolysis of propylene in a fluidized-bed reactor are about 1 lm [9], and the primary aggregates further combine with each other to form secondary aggregates (10 lm, Fig. 2a), even to multilevel aggregates (1 mm, Fig. 2a, inset). After the 10th cycle, the breakdown of CNT agglomerates into a compacted structure can be
* Corresponding authors: Fax: +86 451 82569890 (Z. Fan). E-mail addresses: [email protected] (Z. Fan), [email protected] (F. Wei). 0008-6223/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2009.09.045
310
CARBON
4 8 ( 2 0 1 0 ) 3 0 5 –3 1 2
Fig. 1 – The experimental setup used for measuring the compression resilience and expansion ratio.
Fig. 2 – (a) SEM images of CNT agglomerates (the inset shows the photo of NG and ACNT powders). (b and c) SEM images of cross-section (perpendicular to the pressure) of ACNTs and 5% NG–ACNTs after the 10th cycle under 300 MPa, respectively. (d) SEM image of cross-section (parallel to the pressure) of 5% NG–ACNTs after the 10th cycle under 300 MPa.
311
4 8 (2 0 1 0) 3 0 5–31 2
Expansion ratio
3.5
ACNTs 5% NG-ACNTs ACNTs 5% NG-ACNTs 20% NG-ACNTs
3.0
(0~120MPa) (0~120MPa) (0~300MPa) (0~300MPa) (0~300MPa)
2.5
2.0
Resilience ratio / %
observed (Fig. 2b), and 5% NG–ACNTs remains a loose structure (Fig. 2c) with hybrid multilayer arrays of NG and ACNTs (Fig. 2d). However, the breakdown of graphite particles, about the size of 3–6 lm, are also observed due to mechanical extrusion after the 10th cycle. The recovery of ACNTs can be directly observed from the height change of powders filled in the die. Cyclic compression (Fig. 3) was performed with a preloading of 30 MPa, between a maximum and minimum pressure of 120/300 MPa and zero, respectively. A good resilience is maintained in CNTs over a wide pressure range (30–300 MPa), while polystyrene foam (PS, conventional packaging material) has high expansion ratio of 4.5 under pressure less than 1 MPa and expansion ratio is only less than 1.5 over a pressure range from 1 to10 MPa [8]. With an increase of pressure, all CNT samples show that compression resilience ratio decreases and expansion ratio increases. Under relatively lower pressure (120 MPa), the addition of NG has no obvious effect on improving CNT recovery, and CNT superagglomerates are capable of protecting the original structure from being completely collapsed and maintaining a higher level porosity after repeated compression [8]. However, under relatively higher pressure (300 MPa), the loss of resilience ratio of ACNTs after the 4th cycle is about two times higher than that of 120 MPa due to CNT seizure and entanglement each other. Afterwards, the loss of resilience ratio is 7% for 5% NG–ACNTs, while the losses are 20% and 34% for 20% NG–ACNTs and ACNTs, respectively. The expansion ratio of 5% NG–ACNTs has gradually decreased in the first four cycles and then stabilized 2.7 in the subsequent cycles (even after 100 cycles) under a loading pressure of 300 MPa. The resilience and expansion properties of ACNTs are remarkably improved by combination of NG due to the formation of layer by layer structure, resulting in effective inhibition of the interactions between CNT agglomerates, such as nanotube seizure and entanglement under compression. In order to investigate the stress–strain behaviour of the CNT block, samples after 10 cycles under a load of 300 MPa were measured using universal testing machine (compression head was set at a speed of 0.5 mm/min). It can be observed that compression stress of 5% NG–ACNT block at 40% strain is higher than CNT array block [5] and polyvinyl alcohol–polyacrylic acid copolymer (PVA–PAA) [10] as shown in Fig. 4. Compared with CNT block, 5% NG–ACNT block exhibits a nonlinear stress–strain behaviour composed of two distinct modulus regions (Fig. 4, marked by circle), having modulus of around 1 MPa between 0% and 3% strain and a sharp increase of modulus up to 5 MPa above 3% strain. This behaviour can be explained that NG can effectively inhibit the interactions between CNT agglomerates and has a cushion effect on deformation of CNT agglomerates in low elastic region. With the increase of strain, the collapse and densification of CNT agglomerates result in rapid increase of the modulus. In addition, NG also can improve the integrity of ACNT block through interaction between NG and nanotubes. For example, ACNT block without NG has happed serious breakdown or collapse above 20% strain. In conclusion, a compacted mixture of NG and ACNTs exhibited excellence compressibility and resilience performances at a relatively high pressure range (30–300 MPa). After
80
60
2
4
6
8
10
Number of cycles Fig. 3 – Compression resilience and expansion ratio of NG– ACNTs and ACNTs during loading and unloading cycles (three specimens of each cycle were tested, and the standard error was ±5%).
2.0
Our work
1.5
Compressive stress / MPa
CARBON
1.0
Multiwalled CNT array block [5]
ACNTs
0.5 MPa
0.5
0.3 MPa PVA-PAA [10]
5%NG-ACNTs
0.0 0
10
20
30
40
50
Compressive strain / % Fig. 4 – Compressive stress–strain curves of 5% NG–ACNTs and ACNT blocks after the 10th loading and unloading cycle under 300 MPa (the inset shows initial compression state).
10 cycles under 300 MPa, expansion ratio of 5% NG–ACNTs reached a constant 2.7, and the loss of resilience ratio of 5% NG–ACNTs (7%) was much less than that of ACNTs (34%). This indicates that the addition of NG into ACNTs can effectively inhibit the interactions between CNT agglomerates under compression. Therefore, the lightweight, highly resilient NG–ACNT mixture may be useful as mechanical damping, energy-absorbing and cushioning devices in future applications.
312
CARBON
4 8 ( 2 0 1 0 ) 3 0 5 –3 1 2
Acknowledgements Supports from the Foundation of Harbin Innovation Fellow (2007RFQXG028) and Fundamental Research Foundation of Harbin Engineering University (Project HEUFT07094) are appreciated.
R E F E R E N C E S
[1] Falvo MR, Clary GJ, Taylor RM, Chi V, Brooks FP, Washburn S, et al. Bending and buckling of carbon nanotubes under large strain. Nature 1997;389(6651):582–4. [2] Qian D, Wagner GJ, Liu WK, Yu MF, Ruoff RS. Mechanics of carbon nanotubes. Appl Mech Rev 2002;55(6):495–533. [3] Tang J, Qin LC, Sasaki T, Yudasaka M, Matsushita A, Iijima S. Compressibility and polygonization of single-walled carbon nanotubes under hydrostatic pressure. Phys Rev Lett 2000;85:1887–9.
[4] Cao AY, Dickrell PL, Sawyer WG, Ghasemi-Nejhad MN, Ajayan PM. Super-compressible foamlike carbon nanotube films. Science 2005;310(265):1307–10. [5] Suhr J, Victor P, Ci L, Sreekala S, Zhang X, Nalamasu O, et al. Fatigue resistance of aligned carbon nanotube arrays under cyclic compression. Nat Nanotechnol 2007;2:417–21. [6] Suhr J, Koratkar N, Keblinski P, Ajayan PM. Viscoelasticity in carbon nanotube composites. Nat Mater 2005;4:134–7. [7] Daraio C, Nesterenko VF, Jin SH. Highly nonlinear contact interaction and dynamic energy dissipation by forest of carbon nanotubes. Appl Phys Lett 2004;85(23): 5724–6. [8] Liu Y, Qian WZ, Zhang Q, Cao AY, Li ZF, Zhou WP, et al. Hierarchical agglomerates of carbon nanotubes as highpressure cushions. Nano Lett 2008;8(5):1323–7. [9] Hao Y, Zhang Q, Wei F, Qian WZ, Luo GH. Agglomerated CNTs synthesized in a fluidized bed reactor: agglomerate structure and formation mechanism. Carbon 2003;41(14):2855–63. [10] Caldwell DG. Pseudomuscular actuator for use in dextrous manipulation. Med Biol Eng Comput 1990;28:595–600.