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The experimental determination of mechanical properties of zeolite ferrierite crystal
Materials Letters 59 (2005) 1595 – 1597 www.elsevier.com/locate/matlet
The experimental determination of mechanical properties of zeolite ferrierite crystal J. Lina, X.F. Shua,T, J.X. Dongb,T a
Research Institute of Applied Mechanics, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China
b
Received 29 April 2004; accepted 14 December 2004 Available online 2 February 2005
Abstract Large zeolite ferrierite (FER) single crystal was synthesized according to the method of A. Kuperman et al. in a near non-aqueous solvent. The mechanical properties of zeolite FER single crystal were measured in this paper using MTS Nanoindenter XP with a Berkovich tip. The load–displacement curve of zeolite FER was obtained. According to continuous stiffness measurement (CSM) technique and the calculation method given by W.C. Oliver, the hardness and the elastic modulus of zeolite FER were found to be around 1 GPa and 10 GPa, respectively. Finally, the mechanical properties of large zeolite FER single crystal were compared with SiO2 standard sample. D 2005 Elsevier B.V. All rights reserved. Keywords: Zeolite FER; Single crystal; Mechanical properties; Hardness; Elastic module
1. Introduction Zeolites are periodic, microporous materials that are generally composed of aluminosilicate tetrahedral frameworks. They have channel and cage dimensions ranging between 0.2 and 2.0 nm [1]. Zeolites are widely applied in catalysis, ion exchange and gas separation of chemistry industry. In addition, they are also used as novel optical electronic and magnetic materials. Zeolites exhibit some unusual physical properties. Woodcock and Lightfoot [2] have found the negative thermal expansion in the siliceous zeolites chabazite and ITQ-4. Although the research of physical properties of zeolites is attracting a lot of attention among researchers, little study on
T Corresponding authors. X.F. Shu is to be contacted at Research Institute of Applied Mechanics, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China. Tel.: +86 351 6014455; fax: +86 351 6018320. J.X. Dong, Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China. Tel.: +86 351 6010550 8; fax: +86 351 6010908. E-mail addresses: [email protected] (X.F. Shu)8 [email protected] (J.X. Dong). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.12.055
the mechanical properties of zeolite single crystal has been performed systematically, mainly due to the difficulty in preparation for samples of larger size single crystal (100 Am or larger). Furthermore, these samples have too small sizes (5 mm or less) to measure its mechanical properties by standard mechanical testing instruments. However, it is useful to study the mechanical properties of zeolites for the strength design in their wide range applications. For example, heterogeneous catalysts are exposed to strong compression and shear stresses during the formation of the final catalyst pellet, either through size reduction operations, palletizing or during the extrusion of the final product [3]. Zeolites are subjected to ball milling as a means of enhancing the selectivity for base catalyzed reactions [4]. It has been supposed that some zeolites, such as zeolite MFI, zeolite AET, zeolite THO and so on, may show auxetic property [5]. Wang et al. [6] researched mechanical properties of zeolite ZSM-5 (MFI) single crystal in 2002. They measured Young’s modulus of zeolite ZSM-5 by a self-designed micro-deformation tester. The tester can be used only for the samples of size greater than 200 Am. This excluded the measurement of the samples with specified sizes and shapes,
1596
J. Lin et al. / Materials Letters 59 (2005) 1595–1597
10 days. Then zeolite FER was obtained after separating the solid and liquid. X-ray powder diffractometer (RIGAKU D/max 2500, 40 kV, 100 mA) was used for measuring the phase of samples. A scanning electron microscope (JEOL JSM35C) was employed for observing the morphology and size of crystals.
e.g. flaky zeolite ferrierite (FER) single crystal because it is only 3–5 Am thick. The instrumented nanoindentation testing provides a common method for measuring mechanical properties of materials on small scales. It can be used as long as the dimensions of investigated materials are no less than 20 Am. The method has very high precision in measurement. Many materials, such as aluminum, tungsten quartz, soda-lime glass, fused silica and sapphire, etc., have been measured by means of indentation experiments [7]. However, the technique has not been applied in the determination of mechanical properties of zeolites. Ferrierite (FER) is a medium-pore-type zeolite, containing a two-dimensional network of 10-MR pores (4.35.5 2) and 8-MR (3.45.5 2) intersecting channels [8]. It has been widely used as catalysts in such chemical reactions as nbutene isomerization [9] or NOx reduction [10]. In this paper, the single crystal of zeolite FER was synthesized by near non-aqueous method, which has been reported by Kuperman et al. [11]. The mechanical properties of zeolite FER were measured using MTS Nanoindenter XP. The values of the hardness and elastic modulus of zeolite FER were quantified.
2.2. Sample preparation and testing The typical zeolite FER samples were imbedded in an epoxy resin cylinder. The surface of the cylinder that contained zeolite FER samples was polished for measurement. MTS Nanoindenter XP was used to measure the mechanical properties of zeolite FER sample. When a Berkovich tip applied force to the sample, the load and the displacement were monitored continuously using an Atomic Force Microscope. The hardness and elastic modulus can be gained according to continuous contact stiffness measurement (CSM) technique [12,13] and the calculation method of Oliver and Pharr [7].
3. Results and discussion 2. Experiment As mentioned above, the Berkovich indenter was used in the experiment. It is a three-sided pyramidal tip. This tip geometry has been used as the standard for nanoindentation due to its high precision and accuracy in measurement. The Berkovich tip has sharper angles and a higher aspect ratio, the radius of curvature can be much smaller than that for a Vickers tip. So it is suitable for shallow indents. A Vickers indenter is a four-sided pyramidal tip. It is good for very large load work. Other indenter, such as a Cube-corner tip, is often used for light load scratching or fracture toughness. A Conical tip is used for indenting in very soft materials and scratch testing.
2.1. Sample synthesis and characterization Large zeolite FER single crystals with dimensions of about 290180 Am were prepared in a near non-aqueous solvent according to the method of Kuperman et al. Due to the lack of the availability of organic hydrofluor compounds, a solution of hydrogen fluoride and pyridine was used in our experiment. The solution of HF (40%, 1.3 ml), pyridine (98%), n-propylamine (98%) and fused silica (99%) were poured into a 25 ml autoclave with Teflon. The autoclave was put into an oven and kept at 180 8C for
a)
b) 25
Load (mN)
20 15 10 5 0 0
200
400
600
800 1000 1200
Displacement (nm)
Displacement (nm)
Fig. 1. Load–displacement curves of zeolite FER and SiO2 standard sample. (a) Load–displacement curve of zeolite FER. (b) Load–displacement curve of SiO2.
J. Lin et al. / Materials Letters 59 (2005) 1595–1597 Table 1 Comparison of hardness and elastic modulus of zeolite FER and SiO2 standard sample Hardness (GPa) Elastic modulus (GPa)
Zeolite FER
SiO2
1 10
10 100
Fig. 1a shows the load–displacement curve for zeolite FER single crystal sample. During the loading stage of the process, the total penetration depth is the summation of the elastic and plastic depths. It can be seen that zeolite FER is a kind of nonlinear elastoplastic material. Unload curve presents the extent of elastic recovery of zeolite FER. The hardness and elastic modulus can be calculated from the load–displacement data shown in Fig. 1a. The three key quantities are the peak load, the displacement at peak load and the initial unloading contact stiffness, i.e. the slope of the initial portion of the unloading curve. It should be noted that the contact stiffness is measured only at peak load for nonlinear unloading curve according to Pharr [14]. With CSM technique employed, the contact stiffness is measured continuously during loading and continuous hardness and elastic modulus can be obtained. SiO2 is used as a standard sample when using MTS Nanoindenter XP [15]. Fig. 1b shows the load–displacement curve of SiO2 standard sample. Unload began from the peak depth of 1030 nm. The displacement of SiO2 recovered to 530 nm, while that of zeolite FER recovered to 750 nm. This means that SiO2 shows better elastic property. In addition, peak load was only 22 mN for zeolite FER and 125 mN for SiO2 in the same displacement of 1030 nm. It obviously can tell the differences between the hardness of zeolite FER and SiO2. The main reason can be analyzed from their crystal framework structure. There are micro-pores in zeolite FER single crystals. Contrarily, SiO2 has dense structure. A porous material may be softer and a sample with dense structure may be harder. This can explain why zeolite FER is softer and SiO2 is harder. The hardness and elastic modulus values for zeolite FER and SiO2 are listed in Table 1 and it can be found that elastic modulus of SiO2 was also much larger than zeolite FER.
1597
4. Conclusions Nanoindentation is a common instrument for accurately measuring mechanical properties of small scale materials. The mechanical properties of large zeolite FER single crystals were measured by universal instrument—MTS Nanoindenter XP. The load–displacement data were recorded continuously. Hardness and elastic modulus were measured, making use of CSM technique and Oliver’s method, as 1 GPa and 10 GPa, respectively. This technique is a potential method researching mechanical properties of zeolites.
Acknowledgements This paper was sponsored by NSFC (20373047, 10372067) and LNM; authors thank Dr. Taihua Zhang for his help in the experiment.
References [1] E.C. Moloy, L.P. Davila, J.F. Shackelford, A. Navrotsky, Microporous and Mesoporous Materials 54 (2002) 1. [2] D.A. Woodcock, P. Lightfoot, Chemistry of Materials 11 (1999) 2508. [3] Z. Wang, R.F. Lobo, J. Lambros, Microporous and Mesoporous Materials 57 (2003) 1. [4] J.H. Xie, S. Kaliaguine, Applied Catalysis. A, General 148 (1997) 415. [5] J.N. Grima, R. Jackson, K.E. Evans, Advanced Materials 12 (2000) 1912. [6] Z. Wang, J. Lambros, R.F. Lobo, Journal of Materials Science 37 (2002) 2491. [7] W.C. Oliver, G.M. Pharr, Journal of Materials Research 7 (1992) 1564. [8] R.B. Khomane, B.D. Kulkarni, R.K. Ahedi, Journal of Colloid and Interface Science 236 (2001) 208. [9] L. Domokos, L. Lefferts, K. Seshan, J.A. Lercher, Journal of Molecular Catalysis. A, Chemical 162 (2000) 147. [10] Consuelo Montes de Correa, Fernando Co´rdoba, Felipe Bustamante, Microporous and Mesoporous Materials 40 (2000) 149. [11] A. Kuperman, S. Nadimi, S. Oliver, G.A. Ozin, J.M. Garce´s, M.M. Olken, Nature 365 (1993) 239. [12] J.B. Pethica, W.C. Oliver, Physica Scripta 19 (1987) 61. [13] G.M. Pharr, W.C. Oliver, F.R. Brotzen, Journal of Materials Research 7 (1992) 613. [14] G.M. Pharr, Materials Science and Engineering, A 253 (1998) 151. [15] T.H. Zhang, Y.M. Yang, Advances in Mechanics 32 (2002) 349.
The experimental determination of mechanical properties of zeolite ferrierite crystal J. Lina, X.F. Shua,T, J.X. Dongb,T a
Research Institute of Applied Mechanics, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China
b
Received 29 April 2004; accepted 14 December 2004 Available online 2 February 2005
Abstract Large zeolite ferrierite (FER) single crystal was synthesized according to the method of A. Kuperman et al. in a near non-aqueous solvent. The mechanical properties of zeolite FER single crystal were measured in this paper using MTS Nanoindenter XP with a Berkovich tip. The load–displacement curve of zeolite FER was obtained. According to continuous stiffness measurement (CSM) technique and the calculation method given by W.C. Oliver, the hardness and the elastic modulus of zeolite FER were found to be around 1 GPa and 10 GPa, respectively. Finally, the mechanical properties of large zeolite FER single crystal were compared with SiO2 standard sample. D 2005 Elsevier B.V. All rights reserved. Keywords: Zeolite FER; Single crystal; Mechanical properties; Hardness; Elastic module
1. Introduction Zeolites are periodic, microporous materials that are generally composed of aluminosilicate tetrahedral frameworks. They have channel and cage dimensions ranging between 0.2 and 2.0 nm [1]. Zeolites are widely applied in catalysis, ion exchange and gas separation of chemistry industry. In addition, they are also used as novel optical electronic and magnetic materials. Zeolites exhibit some unusual physical properties. Woodcock and Lightfoot [2] have found the negative thermal expansion in the siliceous zeolites chabazite and ITQ-4. Although the research of physical properties of zeolites is attracting a lot of attention among researchers, little study on
T Corresponding authors. X.F. Shu is to be contacted at Research Institute of Applied Mechanics, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China. Tel.: +86 351 6014455; fax: +86 351 6018320. J.X. Dong, Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, PR China. Tel.: +86 351 6010550 8; fax: +86 351 6010908. E-mail addresses: [email protected] (X.F. Shu)8 [email protected] (J.X. Dong). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.12.055
the mechanical properties of zeolite single crystal has been performed systematically, mainly due to the difficulty in preparation for samples of larger size single crystal (100 Am or larger). Furthermore, these samples have too small sizes (5 mm or less) to measure its mechanical properties by standard mechanical testing instruments. However, it is useful to study the mechanical properties of zeolites for the strength design in their wide range applications. For example, heterogeneous catalysts are exposed to strong compression and shear stresses during the formation of the final catalyst pellet, either through size reduction operations, palletizing or during the extrusion of the final product [3]. Zeolites are subjected to ball milling as a means of enhancing the selectivity for base catalyzed reactions [4]. It has been supposed that some zeolites, such as zeolite MFI, zeolite AET, zeolite THO and so on, may show auxetic property [5]. Wang et al. [6] researched mechanical properties of zeolite ZSM-5 (MFI) single crystal in 2002. They measured Young’s modulus of zeolite ZSM-5 by a self-designed micro-deformation tester. The tester can be used only for the samples of size greater than 200 Am. This excluded the measurement of the samples with specified sizes and shapes,
1596
J. Lin et al. / Materials Letters 59 (2005) 1595–1597
10 days. Then zeolite FER was obtained after separating the solid and liquid. X-ray powder diffractometer (RIGAKU D/max 2500, 40 kV, 100 mA) was used for measuring the phase of samples. A scanning electron microscope (JEOL JSM35C) was employed for observing the morphology and size of crystals.
e.g. flaky zeolite ferrierite (FER) single crystal because it is only 3–5 Am thick. The instrumented nanoindentation testing provides a common method for measuring mechanical properties of materials on small scales. It can be used as long as the dimensions of investigated materials are no less than 20 Am. The method has very high precision in measurement. Many materials, such as aluminum, tungsten quartz, soda-lime glass, fused silica and sapphire, etc., have been measured by means of indentation experiments [7]. However, the technique has not been applied in the determination of mechanical properties of zeolites. Ferrierite (FER) is a medium-pore-type zeolite, containing a two-dimensional network of 10-MR pores (4.35.5 2) and 8-MR (3.45.5 2) intersecting channels [8]. It has been widely used as catalysts in such chemical reactions as nbutene isomerization [9] or NOx reduction [10]. In this paper, the single crystal of zeolite FER was synthesized by near non-aqueous method, which has been reported by Kuperman et al. [11]. The mechanical properties of zeolite FER were measured using MTS Nanoindenter XP. The values of the hardness and elastic modulus of zeolite FER were quantified.
2.2. Sample preparation and testing The typical zeolite FER samples were imbedded in an epoxy resin cylinder. The surface of the cylinder that contained zeolite FER samples was polished for measurement. MTS Nanoindenter XP was used to measure the mechanical properties of zeolite FER sample. When a Berkovich tip applied force to the sample, the load and the displacement were monitored continuously using an Atomic Force Microscope. The hardness and elastic modulus can be gained according to continuous contact stiffness measurement (CSM) technique [12,13] and the calculation method of Oliver and Pharr [7].
3. Results and discussion 2. Experiment As mentioned above, the Berkovich indenter was used in the experiment. It is a three-sided pyramidal tip. This tip geometry has been used as the standard for nanoindentation due to its high precision and accuracy in measurement. The Berkovich tip has sharper angles and a higher aspect ratio, the radius of curvature can be much smaller than that for a Vickers tip. So it is suitable for shallow indents. A Vickers indenter is a four-sided pyramidal tip. It is good for very large load work. Other indenter, such as a Cube-corner tip, is often used for light load scratching or fracture toughness. A Conical tip is used for indenting in very soft materials and scratch testing.
2.1. Sample synthesis and characterization Large zeolite FER single crystals with dimensions of about 290180 Am were prepared in a near non-aqueous solvent according to the method of Kuperman et al. Due to the lack of the availability of organic hydrofluor compounds, a solution of hydrogen fluoride and pyridine was used in our experiment. The solution of HF (40%, 1.3 ml), pyridine (98%), n-propylamine (98%) and fused silica (99%) were poured into a 25 ml autoclave with Teflon. The autoclave was put into an oven and kept at 180 8C for
a)
b) 25
Load (mN)
20 15 10 5 0 0
200
400
600
800 1000 1200
Displacement (nm)
Displacement (nm)
Fig. 1. Load–displacement curves of zeolite FER and SiO2 standard sample. (a) Load–displacement curve of zeolite FER. (b) Load–displacement curve of SiO2.
J. Lin et al. / Materials Letters 59 (2005) 1595–1597 Table 1 Comparison of hardness and elastic modulus of zeolite FER and SiO2 standard sample Hardness (GPa) Elastic modulus (GPa)
Zeolite FER
SiO2
1 10
10 100
Fig. 1a shows the load–displacement curve for zeolite FER single crystal sample. During the loading stage of the process, the total penetration depth is the summation of the elastic and plastic depths. It can be seen that zeolite FER is a kind of nonlinear elastoplastic material. Unload curve presents the extent of elastic recovery of zeolite FER. The hardness and elastic modulus can be calculated from the load–displacement data shown in Fig. 1a. The three key quantities are the peak load, the displacement at peak load and the initial unloading contact stiffness, i.e. the slope of the initial portion of the unloading curve. It should be noted that the contact stiffness is measured only at peak load for nonlinear unloading curve according to Pharr [14]. With CSM technique employed, the contact stiffness is measured continuously during loading and continuous hardness and elastic modulus can be obtained. SiO2 is used as a standard sample when using MTS Nanoindenter XP [15]. Fig. 1b shows the load–displacement curve of SiO2 standard sample. Unload began from the peak depth of 1030 nm. The displacement of SiO2 recovered to 530 nm, while that of zeolite FER recovered to 750 nm. This means that SiO2 shows better elastic property. In addition, peak load was only 22 mN for zeolite FER and 125 mN for SiO2 in the same displacement of 1030 nm. It obviously can tell the differences between the hardness of zeolite FER and SiO2. The main reason can be analyzed from their crystal framework structure. There are micro-pores in zeolite FER single crystals. Contrarily, SiO2 has dense structure. A porous material may be softer and a sample with dense structure may be harder. This can explain why zeolite FER is softer and SiO2 is harder. The hardness and elastic modulus values for zeolite FER and SiO2 are listed in Table 1 and it can be found that elastic modulus of SiO2 was also much larger than zeolite FER.
1597
4. Conclusions Nanoindentation is a common instrument for accurately measuring mechanical properties of small scale materials. The mechanical properties of large zeolite FER single crystals were measured by universal instrument—MTS Nanoindenter XP. The load–displacement data were recorded continuously. Hardness and elastic modulus were measured, making use of CSM technique and Oliver’s method, as 1 GPa and 10 GPa, respectively. This technique is a potential method researching mechanical properties of zeolites.
Acknowledgements This paper was sponsored by NSFC (20373047, 10372067) and LNM; authors thank Dr. Taihua Zhang for his help in the experiment.
References [1] E.C. Moloy, L.P. Davila, J.F. Shackelford, A. Navrotsky, Microporous and Mesoporous Materials 54 (2002) 1. [2] D.A. Woodcock, P. Lightfoot, Chemistry of Materials 11 (1999) 2508. [3] Z. Wang, R.F. Lobo, J. Lambros, Microporous and Mesoporous Materials 57 (2003) 1. [4] J.H. Xie, S. Kaliaguine, Applied Catalysis. A, General 148 (1997) 415. [5] J.N. Grima, R. Jackson, K.E. Evans, Advanced Materials 12 (2000) 1912. [6] Z. Wang, J. Lambros, R.F. Lobo, Journal of Materials Science 37 (2002) 2491. [7] W.C. Oliver, G.M. Pharr, Journal of Materials Research 7 (1992) 1564. [8] R.B. Khomane, B.D. Kulkarni, R.K. Ahedi, Journal of Colloid and Interface Science 236 (2001) 208. [9] L. Domokos, L. Lefferts, K. Seshan, J.A. Lercher, Journal of Molecular Catalysis. A, Chemical 162 (2000) 147. [10] Consuelo Montes de Correa, Fernando Co´rdoba, Felipe Bustamante, Microporous and Mesoporous Materials 40 (2000) 149. [11] A. Kuperman, S. Nadimi, S. Oliver, G.A. Ozin, J.M. Garce´s, M.M. Olken, Nature 365 (1993) 239. [12] J.B. Pethica, W.C. Oliver, Physica Scripta 19 (1987) 61. [13] G.M. Pharr, W.C. Oliver, F.R. Brotzen, Journal of Materials Research 7 (1992) 613. [14] G.M. Pharr, Materials Science and Engineering, A 253 (1998) 151. [15] T.H. Zhang, Y.M. Yang, Advances in Mechanics 32 (2002) 349.