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Self-catalytic growth of aluminum borate nanowires
Chemical Physics Letters 375 (2003) 632–635 www.elsevier.com/locate/cplett
Self-catalytic growth of aluminum borate nanowires Yuming Liu, Qunqing Li, Shoushan Fan
*
Department of Physics, Tsinghua-Foxconn Nanotechnology Research Center, Tsinghua University, Beijing 100084, China Received 3 April 2003; in final form 27 May 2003
Abstract Aluminum borate (Al4 B2 O9 ) nanowires are synthesized by directly heating a mixture of Al and B2 O3 powder at 850 °C. The nanowires synthesized are single-crystal with lengths about several micrometers and diameters ranging from 20 to 100 nm. The transmission electron microscopy (TEM) images show that Al particles are at the tips of some nanowires, which indicates a vapor–liquid–solid (VLS) growth mechanism. Boron oxide dissociates metal Al powder to prevent it from aggregating and simultaneously reacts with aluminum to produce aluminum borate. A self-catalytic growth mechanism of the aluminum borate nanowires is proposed. Ó 2003 Elsevier Science B.V. All rights reserved.
1. Introduction One-dimensional nanoscale materials, such as nanotubes [1], nanowires [2], and nanobelts [3], have attracted much attention because of their interesting properties for understanding fundamental physical concepts and for potential applications [4,5]. Alumina and aluminum borate are remarkable ceramics with enhanced mechanical properties, chemical stability, and potential applications in high-temperature composites [6–9]. Reports about nanowires as to alumina (Al2 O3 ) nanowires and aluminum borate (Al18 B4 O33 ) nanowires have been made recently [10–13]. But all the reactions take place at a temperature over 1000 °C. Here, we are representing a very simple
*
Corresponding author. Fax: +86-10-62789851. E-mail address: [email protected] (S. Fan).
method to synthesize at a pretty low temperature another kind of aluminum borate (Al4 B2 O9 ) nanowires, which has never been reported yet according to as far as our knowledge is concerned.
2. Experimental Al and B2 O3 powders are mixed well at a weight ratio of 27:70 and homogenized in an agate pestle and mortar. An alumina boat containing the powder mixture is placed in the central hot zone inside an alumina tube and heated at 850 °C for 1 h, then cooled to room temperature. An argon flow with 30 standard cubic centimeters per minute (sccm) passes through the quartz tube during the whole process. The originally tough product will come into fine hoar powder after a drop of water added and then is collected easily. The product is examined by X-ray diffraction (XRD, D/max-rB)
0009-2614/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0009-2614(03)00930-8
Y. Liu et al. / Chemical Physics Letters 375 (2003) 632–635
with Cu-Ka radiation, and its morphologies and microscopic composition are characterized by scanning electron microscopy (SEM, JEM-6301F) and transmission electron microscopy (TEM, HP800) equipped with an energy dispersive spectrometry system (EDS). High-resolution TEM (HRTEM) is carried out by a TEM (JEM-200CX) operated at 200 kV.
3. Results and discussions Fig. 1 shows a SEM overview image and a XRD pattern of the obtained sample. Due to the SEM image, in spite of a quantity of nanowires obtained, the most of the sample is granular impurity. XRD pattern shows that the majority of the sample is hydroxide boron and aluminum, which must be the residual reactant (the hydroxide boron is due to the reaction of boron oxide and
Fig. 1. (a) SEM overview image of the sample with a quantity of nanowires and impurities. (b) XRD pattern shows that the main compositions of the sample are B(OH)3 and Al.
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H2 O). We believe that the aluminum and the hydroxide boron are just the impurities found in the SEM image and the intensities of the peaks associated with the nanowires in XRD pattern are too weak to be observed because of the smaller quantities compared with the impurities. To confirm this idea, the sample is put into HCl solution to eliminate aluminum and hydroxide boron. The reaction is very intense with an abundant gas which must be hydrogen discharged. The deposition is washed carefully with distilled water and filtrated. The obtained deposition is characterized by TEM and XRD diffraction. Fig. 2 shows the XRD pattern of the sample obtained after its being treated by HCl solution. The XRD pattern shows that the sample is aluminum borate (Al4 B2 O9 ) (JCPDS 09-0158 and JCPDS 29-0010) with little aluminum oxide (Al2 O3 ) (JCPDS 82-1467). No aluminum peaks exist, and a peak of hydroxide boron marked with star symbol still can be found but is much lower than that in Fig. 1b. Although aluminum oxide peaks can be found in the XRD pattern, the quantity of aluminum oxide nanowires is much less according to the HRTEM statistics. TEM image (Fig. 3a) shows that the sample is mainly composed of straight nanowires and hardly any impurity is found. The nanowires have lengths of several micrometers and diameters ranging from 20 to hundred of nanometers. The selected area electron diffraction pattern taken from a single nanowire shows the nanowires are single-crystal. Fig. 3b shows a typical electron diffraction pattern indexed as an orthorhombic Al4 B2 O9 phase with
Fig. 2. XRD pattern of the sample after treatment by HCl solution. The reflection peaks of Al4 B2 O9 and Al2 O3 are marked by their indices. The peak marked by star symbol is due to B(OH)3 which is not completely eliminated.
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Y. Liu et al. / Chemical Physics Letters 375 (2003) 632–635
Fig. 3. TEM characterizations on aluminum borate. (a) Low magnification TEM photo of the sample after treatment. (b) A typical selected area electron diffraction pattern and (c) corresponding HRTEM image taken from an Al4 B2 O9 nanowire.
, b ¼ 15:26 A , lattice constants of a ¼ 14:74 A recorded from [ c ¼ 5:56 A 1 0 0] zone axis. The d-spacings of (0 0 1) planes are clearly resolved in the corresponding lattice fringes (Fig. 3c). So the impurities of aluminum and hydroxide boron are eliminated by the treatment, and much pure aluminum borate nanowires are obtained. The TEM observations also show that several aluminum borate nanowires grow from a same particle (Fig. 4a) in the sample before HCl solution treatment. The EDS analysis (Fig. 4b) reveals that the particle contains Al (the elements before Na cannot be found using our equipment, and copper is found because of the carbon-coated copper grid). If the sample has been purified, this phenomenon cannot be observed, which confirms that the particle contains metal Al because the aluminum particle will react with HCl solution during the purification treatment. The phenomenon of particles are at the tips of the nanowires strongly indicates that the growth mechanism of nanowires is vapor–solid–liquid (VLS) growth [14,15]. But to obtain the nuclei which are necessary for VLS growth of nanowires, special catalyst is usually added, such as Fe2 O3 supported by Al2 O3 . In our experiment, no such catalysts are added in the reactant. Recently, some nanowires have been synthesized by self-catalytic growth [16,17]. In this growth mechanism, some liquid-state metal, such
Fig. 4. (a) TEM image show that several nanowires have a same particle at their tips. (b) EDS spectra from the particle reveal that the particle contains element aluminum.
as Sn and Ga, can serve as a liquid nucleus for VLS growth of the nanowires. Here, we also consider that the growth of aluminum borate nanowires is a self-catalytic VLS growth with metal Al serving as the nuclei. The possible reaction process is discussed as follows. In our method, the reaction temperature is 850 °C. During the process, B2 O3 will melt first at about 450 °C and Al powder may be dispersed into molten B2 O3 and well dissociated. So when Al begins to melt at about 660 °C, it will become small liquid droplets but not aggregation. All these small Al droplets will serve as the nuclei for the growth just like the Fe2 O3 catalysts used in VLS growth. Then Al will react with B2 O3 and vapor components of Al2 O and B2 O2 could occur. The Al droplets absorb the vapor component and subsequently yield Al4 B2 O9 which dissolves in the Al droplets. When a supersaturated solution is
Y. Liu et al. / Chemical Physics Letters 375 (2003) 632–635
achieved, Al4 B2 O9 will crystallize at some favored sites of the Al droplets. Then the Al droplets become smaller and smaller while the reaction continues, and the nanowires are synthesized. Because Al droplets serve as both nuclei and reactant, the lengths and the diameters of the nanowires will depend on the size of Al droplets. The Al droplets in the reaction have a large range in diameters from several hundreds of nanometer to several tens of micrometers, so the nanowires fabricated have not uniform diameters and lengths. In this growth process, the Al4 B2 O9 nanowires can crystallize at some sites of a same big Al droplet simultaneously sometimes and several nanowires grow from a same particle. All these are consistent with the TEM observation. In self-catalytic growth process, dissociation of the metal to prevent complete crust formation is very important [16]. In this experiment, B2 O3 can dissociate metal Al into small liquid droplets so that the production is not to be big agglomeration but nanowires.
4. Conclusion In summary, Al4 B2 O9 nanowires are synthesized in bulk quantities by self-catalytic VLS growth at lower temperature. The Al4 B2 O9 nanowires are single crystals. B2 O3 dissociates metal Al into small droplets. Metal Al droplets are the nuclei to absorb the vapor component produced by the reaction between B2 O3 and Al for the growth of nanowires. A self-catalytic growth mechanism has been discussed.
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Acknowledgements This work is supported by the National Natural Science Foundation of China and the State Key Project of Fundamental Research of China.
References [1] S. Iijima, Nature 354 (1991) 56. [2] W. Han, S.S. Fan, Q.Q. Li, Y.D. Hu, Science 277 (1997) 1287. [3] Z.W. Pan, Z.R. Dai, Z.L. Wang, Science 291 (2001) 1947. [4] A.P. Alivisatos, Science 271 (1996) 933. [5] M.S. Gudiksen, L.J. Lauhon, J. Wang, D.C. Smith, C.M. Lieber, Nature 415 (2002) 617. [6] G. Das, Ceram. Eng. Sci. Proc. 5 (1995) 977. [7] L.M. Peng, S.J. Zhu, Z.Y. Ma, J. Mi, F.G. Wang, H.R. Chen, D.O. Northwood, Mater. Sci. Eng. A 265 (1999) 63. [8] M. Touratier, A. Beakon, J.Y. Chatellier, Compos. Sci. Technol. 44 (1992) 369. [9] D. Jaque, O. Enguita, J.G. Sole, A.D. Jiang, Z.D. Luo, Appl. Phys. Lett. 76 (2000) 2176. [10] V. Valcarcel, A. Souto, G. Francisco, Adv. Mater. 10 (1998) 138. [11] C.C. Tang, S.S. Fan, P. Li, M. Lamy de la Chapelle, H.Y. Dang, J. Cryst. Growth 224 (2001) 117. [12] J. Zhou, S.Z. Deng, J. Chen, J.C. She, N.S. Xu, Chem. Phys. Lett. 365 (2002) 505. [13] R. Ma, Y. Bando, T. Soto, Appl. Phys. Lett. 81 (2002) 3467. [14] Y. Wu, P. Yang, J. Am. Chem. Soc. 123 (2001) 3165. [15] X.F. Duan, J.F. Wang, C.M. Lieber, Appl. Phys. Lett. 76 (2000) 1116. [16] S. Sharma, M.K. Sunkara, J. Am. Chem. Soc. 124 (2002) 12288. [17] Y.Q. Chen, X.F. Cui, K. Zhang, D.Y. Pan, S.Y. Zhang, B. Wang, J.G. Hou, Chem. Phys. Lett. 369 (2003) 16.
Self-catalytic growth of aluminum borate nanowires Yuming Liu, Qunqing Li, Shoushan Fan
*
Department of Physics, Tsinghua-Foxconn Nanotechnology Research Center, Tsinghua University, Beijing 100084, China Received 3 April 2003; in final form 27 May 2003
Abstract Aluminum borate (Al4 B2 O9 ) nanowires are synthesized by directly heating a mixture of Al and B2 O3 powder at 850 °C. The nanowires synthesized are single-crystal with lengths about several micrometers and diameters ranging from 20 to 100 nm. The transmission electron microscopy (TEM) images show that Al particles are at the tips of some nanowires, which indicates a vapor–liquid–solid (VLS) growth mechanism. Boron oxide dissociates metal Al powder to prevent it from aggregating and simultaneously reacts with aluminum to produce aluminum borate. A self-catalytic growth mechanism of the aluminum borate nanowires is proposed. Ó 2003 Elsevier Science B.V. All rights reserved.
1. Introduction One-dimensional nanoscale materials, such as nanotubes [1], nanowires [2], and nanobelts [3], have attracted much attention because of their interesting properties for understanding fundamental physical concepts and for potential applications [4,5]. Alumina and aluminum borate are remarkable ceramics with enhanced mechanical properties, chemical stability, and potential applications in high-temperature composites [6–9]. Reports about nanowires as to alumina (Al2 O3 ) nanowires and aluminum borate (Al18 B4 O33 ) nanowires have been made recently [10–13]. But all the reactions take place at a temperature over 1000 °C. Here, we are representing a very simple
*
Corresponding author. Fax: +86-10-62789851. E-mail address: [email protected] (S. Fan).
method to synthesize at a pretty low temperature another kind of aluminum borate (Al4 B2 O9 ) nanowires, which has never been reported yet according to as far as our knowledge is concerned.
2. Experimental Al and B2 O3 powders are mixed well at a weight ratio of 27:70 and homogenized in an agate pestle and mortar. An alumina boat containing the powder mixture is placed in the central hot zone inside an alumina tube and heated at 850 °C for 1 h, then cooled to room temperature. An argon flow with 30 standard cubic centimeters per minute (sccm) passes through the quartz tube during the whole process. The originally tough product will come into fine hoar powder after a drop of water added and then is collected easily. The product is examined by X-ray diffraction (XRD, D/max-rB)
0009-2614/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0009-2614(03)00930-8
Y. Liu et al. / Chemical Physics Letters 375 (2003) 632–635
with Cu-Ka radiation, and its morphologies and microscopic composition are characterized by scanning electron microscopy (SEM, JEM-6301F) and transmission electron microscopy (TEM, HP800) equipped with an energy dispersive spectrometry system (EDS). High-resolution TEM (HRTEM) is carried out by a TEM (JEM-200CX) operated at 200 kV.
3. Results and discussions Fig. 1 shows a SEM overview image and a XRD pattern of the obtained sample. Due to the SEM image, in spite of a quantity of nanowires obtained, the most of the sample is granular impurity. XRD pattern shows that the majority of the sample is hydroxide boron and aluminum, which must be the residual reactant (the hydroxide boron is due to the reaction of boron oxide and
Fig. 1. (a) SEM overview image of the sample with a quantity of nanowires and impurities. (b) XRD pattern shows that the main compositions of the sample are B(OH)3 and Al.
633
H2 O). We believe that the aluminum and the hydroxide boron are just the impurities found in the SEM image and the intensities of the peaks associated with the nanowires in XRD pattern are too weak to be observed because of the smaller quantities compared with the impurities. To confirm this idea, the sample is put into HCl solution to eliminate aluminum and hydroxide boron. The reaction is very intense with an abundant gas which must be hydrogen discharged. The deposition is washed carefully with distilled water and filtrated. The obtained deposition is characterized by TEM and XRD diffraction. Fig. 2 shows the XRD pattern of the sample obtained after its being treated by HCl solution. The XRD pattern shows that the sample is aluminum borate (Al4 B2 O9 ) (JCPDS 09-0158 and JCPDS 29-0010) with little aluminum oxide (Al2 O3 ) (JCPDS 82-1467). No aluminum peaks exist, and a peak of hydroxide boron marked with star symbol still can be found but is much lower than that in Fig. 1b. Although aluminum oxide peaks can be found in the XRD pattern, the quantity of aluminum oxide nanowires is much less according to the HRTEM statistics. TEM image (Fig. 3a) shows that the sample is mainly composed of straight nanowires and hardly any impurity is found. The nanowires have lengths of several micrometers and diameters ranging from 20 to hundred of nanometers. The selected area electron diffraction pattern taken from a single nanowire shows the nanowires are single-crystal. Fig. 3b shows a typical electron diffraction pattern indexed as an orthorhombic Al4 B2 O9 phase with
Fig. 2. XRD pattern of the sample after treatment by HCl solution. The reflection peaks of Al4 B2 O9 and Al2 O3 are marked by their indices. The peak marked by star symbol is due to B(OH)3 which is not completely eliminated.
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Y. Liu et al. / Chemical Physics Letters 375 (2003) 632–635
Fig. 3. TEM characterizations on aluminum borate. (a) Low magnification TEM photo of the sample after treatment. (b) A typical selected area electron diffraction pattern and (c) corresponding HRTEM image taken from an Al4 B2 O9 nanowire.
, b ¼ 15:26 A , lattice constants of a ¼ 14:74 A recorded from [ c ¼ 5:56 A 1 0 0] zone axis. The d-spacings of (0 0 1) planes are clearly resolved in the corresponding lattice fringes (Fig. 3c). So the impurities of aluminum and hydroxide boron are eliminated by the treatment, and much pure aluminum borate nanowires are obtained. The TEM observations also show that several aluminum borate nanowires grow from a same particle (Fig. 4a) in the sample before HCl solution treatment. The EDS analysis (Fig. 4b) reveals that the particle contains Al (the elements before Na cannot be found using our equipment, and copper is found because of the carbon-coated copper grid). If the sample has been purified, this phenomenon cannot be observed, which confirms that the particle contains metal Al because the aluminum particle will react with HCl solution during the purification treatment. The phenomenon of particles are at the tips of the nanowires strongly indicates that the growth mechanism of nanowires is vapor–solid–liquid (VLS) growth [14,15]. But to obtain the nuclei which are necessary for VLS growth of nanowires, special catalyst is usually added, such as Fe2 O3 supported by Al2 O3 . In our experiment, no such catalysts are added in the reactant. Recently, some nanowires have been synthesized by self-catalytic growth [16,17]. In this growth mechanism, some liquid-state metal, such
Fig. 4. (a) TEM image show that several nanowires have a same particle at their tips. (b) EDS spectra from the particle reveal that the particle contains element aluminum.
as Sn and Ga, can serve as a liquid nucleus for VLS growth of the nanowires. Here, we also consider that the growth of aluminum borate nanowires is a self-catalytic VLS growth with metal Al serving as the nuclei. The possible reaction process is discussed as follows. In our method, the reaction temperature is 850 °C. During the process, B2 O3 will melt first at about 450 °C and Al powder may be dispersed into molten B2 O3 and well dissociated. So when Al begins to melt at about 660 °C, it will become small liquid droplets but not aggregation. All these small Al droplets will serve as the nuclei for the growth just like the Fe2 O3 catalysts used in VLS growth. Then Al will react with B2 O3 and vapor components of Al2 O and B2 O2 could occur. The Al droplets absorb the vapor component and subsequently yield Al4 B2 O9 which dissolves in the Al droplets. When a supersaturated solution is
Y. Liu et al. / Chemical Physics Letters 375 (2003) 632–635
achieved, Al4 B2 O9 will crystallize at some favored sites of the Al droplets. Then the Al droplets become smaller and smaller while the reaction continues, and the nanowires are synthesized. Because Al droplets serve as both nuclei and reactant, the lengths and the diameters of the nanowires will depend on the size of Al droplets. The Al droplets in the reaction have a large range in diameters from several hundreds of nanometer to several tens of micrometers, so the nanowires fabricated have not uniform diameters and lengths. In this growth process, the Al4 B2 O9 nanowires can crystallize at some sites of a same big Al droplet simultaneously sometimes and several nanowires grow from a same particle. All these are consistent with the TEM observation. In self-catalytic growth process, dissociation of the metal to prevent complete crust formation is very important [16]. In this experiment, B2 O3 can dissociate metal Al into small liquid droplets so that the production is not to be big agglomeration but nanowires.
4. Conclusion In summary, Al4 B2 O9 nanowires are synthesized in bulk quantities by self-catalytic VLS growth at lower temperature. The Al4 B2 O9 nanowires are single crystals. B2 O3 dissociates metal Al into small droplets. Metal Al droplets are the nuclei to absorb the vapor component produced by the reaction between B2 O3 and Al for the growth of nanowires. A self-catalytic growth mechanism has been discussed.
635
Acknowledgements This work is supported by the National Natural Science Foundation of China and the State Key Project of Fundamental Research of China.
References [1] S. Iijima, Nature 354 (1991) 56. [2] W. Han, S.S. Fan, Q.Q. Li, Y.D. Hu, Science 277 (1997) 1287. [3] Z.W. Pan, Z.R. Dai, Z.L. Wang, Science 291 (2001) 1947. [4] A.P. Alivisatos, Science 271 (1996) 933. [5] M.S. Gudiksen, L.J. Lauhon, J. Wang, D.C. Smith, C.M. Lieber, Nature 415 (2002) 617. [6] G. Das, Ceram. Eng. Sci. Proc. 5 (1995) 977. [7] L.M. Peng, S.J. Zhu, Z.Y. Ma, J. Mi, F.G. Wang, H.R. Chen, D.O. Northwood, Mater. Sci. Eng. A 265 (1999) 63. [8] M. Touratier, A. Beakon, J.Y. Chatellier, Compos. Sci. Technol. 44 (1992) 369. [9] D. Jaque, O. Enguita, J.G. Sole, A.D. Jiang, Z.D. Luo, Appl. Phys. Lett. 76 (2000) 2176. [10] V. Valcarcel, A. Souto, G. Francisco, Adv. Mater. 10 (1998) 138. [11] C.C. Tang, S.S. Fan, P. Li, M. Lamy de la Chapelle, H.Y. Dang, J. Cryst. Growth 224 (2001) 117. [12] J. Zhou, S.Z. Deng, J. Chen, J.C. She, N.S. Xu, Chem. Phys. Lett. 365 (2002) 505. [13] R. Ma, Y. Bando, T. Soto, Appl. Phys. Lett. 81 (2002) 3467. [14] Y. Wu, P. Yang, J. Am. Chem. Soc. 123 (2001) 3165. [15] X.F. Duan, J.F. Wang, C.M. Lieber, Appl. Phys. Lett. 76 (2000) 1116. [16] S. Sharma, M.K. Sunkara, J. Am. Chem. Soc. 124 (2002) 12288. [17] Y.Q. Chen, X.F. Cui, K. Zhang, D.Y. Pan, S.Y. Zhang, B. Wang, J.G. Hou, Chem. Phys. Lett. 369 (2003) 16.