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Preparation and electromagnetic performance of coating of multiwall carbon nanotubes with iron nanogranule
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 288 (2005) 397–402 www.elsevier.com/locate/jmmm
Preparation and electromagnetic performance of coating of multiwall carbon nanotubes with iron nanogranule X. Shen, R.Z. Gong, Y. Nie, J.H. Nie Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, PR China Received 8 January 2004; received in revised form 17 September 2004 Available online 28 November 2004
Abstract A method to prepare one-dimensional nanocomposites based on coating of multiwall carbon nanotubes (MWNTs) with iron nanogranule was proposed. TEM micrographs show that the outer diameters of purified MWNTs are 13 nm. MWNTs through pyrolysis of carbonyl method can increase to 35 nm. The dynamic electromagnetic parameters of composites were measured in the 2–18 GHz range. At 2 GHz, the m0 ; m00 ; 0 and 00 of the composites are 2.64, 1.63, 12 and 2.04, respectively. These characteristic electromagnetic properties may be used for microwave absorbing material. As the reaction temperature is 180 C, the compatibility of deposition rate and chemsorption rate is helpful in obtaining a better coating layer on MWNTs. It was also found that supercritical drying technology can eliminate surface tension and keep the structure of the one-dimensional nanocomposites. r 2004 Elsevier B.V. All rights reserved. PACS: 75.75.+a; 75.47.De; 85.75.Dd Keywords: Carbon nanotubes; Pyrolysis of carbonyl; One-dimensional nanocomposites; Chemsorption; Coating
1. Introduction Carbon nanotubes as one-dimensional nanomaterial, feature high intensity, excellent flexibility, low density and promising electromagnetic properties. The potential applications of carbon nanoCorresponding author. Faculty of Material Science & Chemical Engineering, China University of Geosciences, Wuhan 430074, China. Tel.: +86 27 8754 7337; fax: +86 27 8754 7337. E-mail addresses: [email protected], [email protected] (X. Shen).
tubes have extended to nanoscale electronic device [1,2] tip of scanning probe microscope [3], electrode material [4,5] and polymer composites [6,7]. Since many metals can be deposited on almost any substrate after previous activation, by electroless plating [8], the carbon nanotubes as templates could be encapsulated by a thin layer of metal. Shen Zeng-min et al. [7] have studied coating of carbon nanotubes with nickel through electroless deposition technique. The maximum absorbing peak of the microwave absorbing composites containing carbon nanotubes reaches 22.8 dB at
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.08.035
ARTICLE IN PRESS 398
X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
11.4 GHz, while for nickel-coated carbon nanotubes it is 11.85 dB at 14 GHz. The absorbing peak of the composite transfers from 11.4 to 14 GHz and the absorbing peak becomes broader. It may be speculated that the ferromagnetic materialcoated carbon nanotubes can be of interest for microwave absorbing materials. However, the method we used differs greatly from the above report. In this paper, the purification, modification of self-assembled monolayers, chemsorption and chemical deposition of carbonyl iron [9] are selected to achieve iron-coated multiwall carbon nanotubes (MWNTs). The one-dimensional nanocomposites may be used as microwave absorbing materials.
2. Experiments The MWNTs used in this work are produced by the catalytic decomposition of acetylene over mesoporous silica containing cobalt nanoparticles embedded in the pores, which were prepared by a sol–gel process. As the carbon nanotubes have low chemical reactivity and a large curvature, the nanotubes were subjected to oxidation treatment to modify the surface chemistry. The carbon nanotubes were suspended in an aqueous solution of 0.54 mol/L NH4 F and kept in a water bath of 60 C for 30 min, and were then rinsed with distilled water and filtrated. Then modification of self-assembled monolayers was accomplished by dispersing them in an ethanol solution containing 0.3 vol% 3-aminopropyltriethoxy-silane for 12 h, and rinsing with distilled water and ethanol subsequently. The treated MWNTs and Fe(CO)5 were then introduced into the reactor of pyrolysis of carbonyl, which contains 100 ml N,N-Dimethyl formamide, and isolated from the air. In order to increase the number of activated sites, it is essential for a nonionic surfactant (Tween-20) to increase the wettability and dispersivity of MWNTs before coating. While refluxing in an oil bath of 180 C. Fe(CO)5 transforms the mixture of Fem (CO)n and gradually decomposes as carbonyl iron deposit, which appear as polycrystallites. The released CO gas is absorbed in an aqueous
solution of 0.5 mol/L KMnO4 : The chemsorption of iron on the surfaces of MWNTs are achieved by bonding iron to the external pendant amino group of the self-assembled monolayers. Finally, onedimensional nanocomposites are produced through centrifugal effect, filtration and supercritical drying method.
3. Results and discussion As in Fig. 1(c), the high-magnification TEM images of MWNTs after pretreatment show that the inner and outer diameters of the tubes are 3.8 and 13 nm, respectively. Fig. 1(a) and (b) show that the diameters of the iron-coated MWNTs by using pyrolysis of carbonyl method increased from 13 to 35 nm. The results indicate that a layer of iron deposition is able to form on the surfaces of the MWNTs. The surface of the coated MWNTs seems very smooth, but several voids in the coated layer are discovered by intensive TEM observations. Perhaps the uneven dispersion of chemsorption centers on pretreated MWNTs would induce nonuniform growth or deposition layer at different parts of MWNTs. As the deposition rate is higher than 12.2 mg/(cm2 h), the normal growth rate of iron is higher than the lateral growth rate. The iron deposit is formed as spherical grains, which appear to be very closely packed crystallites. The results indicate that the iron nanoparticles tend to aggregate on the outer surfaces of the MWNTs. It is noticed that the deposited layer is sensitive to the reaction temperature, which subsequently influences the reaction rate and chemsorption process. If the reaction temperature is higher than 220 C, the deposition rate in contrast to the chemsorption rate is higher, so that the aggregation tendency would be more serious. When the reaction temperature is lower than 160 C, the reaction cannot proceed. At 180 C, low deposition rate is helpful in obtaining a better coating layer on MWNTs. In addition, low stirring speed is subject to adsorbing iron nanogranule. Energy dispersion X-ray (EDX) analysis (Fig. 2) shows that the major component in the coated layer is iron, with a little silicon element, which mainly derives from the catalyst for preparing
ARTICLE IN PRESS X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
399
500
Fe(Ka)
Counts
400 300 200 100
Si(Ka) 0 2
4
6
8
10
12
14
e/Kev Fig. 2. EDX pattern of iron-coated MWNTs.
Fig. 3. Electron diffraction pattern of the iron-coated MWNTs.
Fig. 1. TEM micrographs of iron-coated MWNTs: (a) magnified 58 k times, (b) magnified 600 k times and (c) Highmagnification TEM micrographs of MWNTs after pretreatment.
MWNTs. Electron diffraction experiments (Fig. 3) also confirm mainly polycrystalline iron shown in the pattern besides graphite. In order to reduce the conglomeration of the iron-coated MWNTs in the drying process, several methods are employed. First, the coated nanotubes are washed with ethanol and dried at 85 C under vacuum condition. Fig. 4(a) shows that the
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X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402 8
Ms
6
Mr
M(emµ)
4
mHc
2 0 -2 -4 -6 -8 -1000
-500
0
500
1000
H(KOe)
ε
Fig. 5. Static hysteresis curves for iron-coated MWNTs.
13 12 11 10 9 8 7 6 5 4 3 2 1 0
ε′
ε″
0
2
4
6
8
10 12 f/GHz
14
16
18
20
Fig. 6. Dependence of e0 ; e00 on frequency.
Fig. 4. SEM micrographs of iron-coated under different drying conditions: (a) 85 C and vacuum, (b) 600 C and N2 atmosphere and (c) supercritical drying technology.
conglomeration is obvious. Second, the coated nanotubes are dried in vacuum sintering furnace under N2 atmosphere at 600 C for 12 h and cooled. Fig. 4(b) shows that the conglomeration still occurs. Third, a new type of drying technology [10], which makes use of supercritical fluids is adopted. As temperature and pressure, respectively, reach 250 C and 7 MPa, ethanol media becomes supercritical fluids. The ethanol and water in the coated MWNTs are gradually discharged at equilibrium conditions. Simultaneously, the residual ethanol and water of fluids are exorcised by nitrogen, and then the coated
ARTICLE IN PRESS X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
tively. The complex permeability and permittivity of composites are a good match. These characteristic electromagnetic properties, resulting from the nanometer size effect, can be applied to the microwave absorbing material.
3.0
iron-coated MWNTs
2.5
µ′
2.0 1.5
4. Conclusion
1.0 0.5 0
2
4
6
8
10
12
14
16
18
20
f/GHz 1.8
iron-coated MWNTs
1.6 1.4 1.2
µ″
401
1.0 0.8 0.6 0.4 0.2 0
2
4
6
8
10
12
14
16
18
20
f/GHz Fig. 7. Dependence of m0 ; m00 on frequency.
MWNTs are cooled to room temperature in a N2 atmosphere. Fig. 4(b) shows that the iron-coated MWNTs are uniform and highly dispersive. The result indicates that supercritical drying technology can eliminate surface tension and maintain the structure of the solid nanomaterial during drying. We determine the hysteresis curves at room temperature with vibrating sample magnetometer, and the result is presented in Fig. 5. From this figure we can see that the saturation magnetization and coercive force for the coated carbon nanotubes are 538.5 Gs and 3470 A m1 ; respectively. This result indicates that it is a soft magnetic material and the coercive force is low. In addition, the dynamic electromagnetic parameters (Figs. 6 and 7) are also determined by vector network analyzer. At 2 GHz, the m0 ; m00 ; 0 and 00 of the composites are 2.64, 1.63, 12 and 2.04, respec-
The main conclusion from this work may be summarized as follows: 1. A new one-dimensional nanocomposite based on the coating of MWNTs templates with iron is prepared by pyrolysis of carbonyl method. 2. The surface pretreatments of the MWNTs are indispensible steps before coating. The uniform and highly dense dispersion of chemsorption centers after pretreatment are the crucial aspects for an excellent coated metal layer on MWNTs. The deposited layer is sensitive to the reaction temperature, which influences the reaction rate and chemsorption rate. A low deposition rate is helpful in obtaining a better coating layer on the MWNTs. 3. The experimental result indicates that supercritical drying technology can eliminate surface tension and maintain the structure of the onedimensional nanocomposites during drying. The modification of self-assembled monolayers, reaction temperatures and proportionality of the reactant are found to be critical for getting better electromagnetic performance. The ironcoated MWNTs may be useful for microwave absorbing materials fields.
Acknowledgement The financial support of this research project was from the spaceflight innovation foundation. References [1] F. Service Robert, Science 292 (5514) (2001) 45. [2] Zhang Zhen-Hua, Peng Jing-Cui, Acta Phys. Sinica 50 (6) (2000) 1150.
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X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
[3] C.V. Nguyen, R.M.D. Stevens, A. Cassell, et al., Nanotechnology 12 (3) (2001) 363. [4] Ma Ren-zhi, Wei Bing-qing, Xu Cai-lu, et al., Sci. in China (Ser. E-Technological Sci.) 43 (2) (2000) 178. [5] C. Niu, E.K. Sichel, R. Hoch, et al., Appl. Phys. Lett. 70 (11) (1997) 1480. [6] C. Stephan, T.P. Nguyen, B. Lahr, et al., J. Mater. Res. 17 (2) (2002) 396.
[7] Shen Zeng-min, Zhao Dong-lin, New Carbon Mater. 16 (1) (2001) 1. [8] Chen Xiao-hua, Yan Yong-hong, Zhang Gao-min, et al., Microfabrication Technol. 2 (1999) 17. [9] Ni Yan, Zhao Zhen-sheng, He Hua-hui, J. Huazhong Univ. Sci. Tech. 29 (7) (2001) 75. [10] A. Tsutsumi, S. Nakamoto, T.A. Mineo, Power Technol. 85 (2) (1995) 275.
Journal of Magnetism and Magnetic Materials 288 (2005) 397–402 www.elsevier.com/locate/jmmm
Preparation and electromagnetic performance of coating of multiwall carbon nanotubes with iron nanogranule X. Shen, R.Z. Gong, Y. Nie, J.H. Nie Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, PR China Received 8 January 2004; received in revised form 17 September 2004 Available online 28 November 2004
Abstract A method to prepare one-dimensional nanocomposites based on coating of multiwall carbon nanotubes (MWNTs) with iron nanogranule was proposed. TEM micrographs show that the outer diameters of purified MWNTs are 13 nm. MWNTs through pyrolysis of carbonyl method can increase to 35 nm. The dynamic electromagnetic parameters of composites were measured in the 2–18 GHz range. At 2 GHz, the m0 ; m00 ; 0 and 00 of the composites are 2.64, 1.63, 12 and 2.04, respectively. These characteristic electromagnetic properties may be used for microwave absorbing material. As the reaction temperature is 180 C, the compatibility of deposition rate and chemsorption rate is helpful in obtaining a better coating layer on MWNTs. It was also found that supercritical drying technology can eliminate surface tension and keep the structure of the one-dimensional nanocomposites. r 2004 Elsevier B.V. All rights reserved. PACS: 75.75.+a; 75.47.De; 85.75.Dd Keywords: Carbon nanotubes; Pyrolysis of carbonyl; One-dimensional nanocomposites; Chemsorption; Coating
1. Introduction Carbon nanotubes as one-dimensional nanomaterial, feature high intensity, excellent flexibility, low density and promising electromagnetic properties. The potential applications of carbon nanoCorresponding author. Faculty of Material Science & Chemical Engineering, China University of Geosciences, Wuhan 430074, China. Tel.: +86 27 8754 7337; fax: +86 27 8754 7337. E-mail addresses: [email protected], [email protected] (X. Shen).
tubes have extended to nanoscale electronic device [1,2] tip of scanning probe microscope [3], electrode material [4,5] and polymer composites [6,7]. Since many metals can be deposited on almost any substrate after previous activation, by electroless plating [8], the carbon nanotubes as templates could be encapsulated by a thin layer of metal. Shen Zeng-min et al. [7] have studied coating of carbon nanotubes with nickel through electroless deposition technique. The maximum absorbing peak of the microwave absorbing composites containing carbon nanotubes reaches 22.8 dB at
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.08.035
ARTICLE IN PRESS 398
X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
11.4 GHz, while for nickel-coated carbon nanotubes it is 11.85 dB at 14 GHz. The absorbing peak of the composite transfers from 11.4 to 14 GHz and the absorbing peak becomes broader. It may be speculated that the ferromagnetic materialcoated carbon nanotubes can be of interest for microwave absorbing materials. However, the method we used differs greatly from the above report. In this paper, the purification, modification of self-assembled monolayers, chemsorption and chemical deposition of carbonyl iron [9] are selected to achieve iron-coated multiwall carbon nanotubes (MWNTs). The one-dimensional nanocomposites may be used as microwave absorbing materials.
2. Experiments The MWNTs used in this work are produced by the catalytic decomposition of acetylene over mesoporous silica containing cobalt nanoparticles embedded in the pores, which were prepared by a sol–gel process. As the carbon nanotubes have low chemical reactivity and a large curvature, the nanotubes were subjected to oxidation treatment to modify the surface chemistry. The carbon nanotubes were suspended in an aqueous solution of 0.54 mol/L NH4 F and kept in a water bath of 60 C for 30 min, and were then rinsed with distilled water and filtrated. Then modification of self-assembled monolayers was accomplished by dispersing them in an ethanol solution containing 0.3 vol% 3-aminopropyltriethoxy-silane for 12 h, and rinsing with distilled water and ethanol subsequently. The treated MWNTs and Fe(CO)5 were then introduced into the reactor of pyrolysis of carbonyl, which contains 100 ml N,N-Dimethyl formamide, and isolated from the air. In order to increase the number of activated sites, it is essential for a nonionic surfactant (Tween-20) to increase the wettability and dispersivity of MWNTs before coating. While refluxing in an oil bath of 180 C. Fe(CO)5 transforms the mixture of Fem (CO)n and gradually decomposes as carbonyl iron deposit, which appear as polycrystallites. The released CO gas is absorbed in an aqueous
solution of 0.5 mol/L KMnO4 : The chemsorption of iron on the surfaces of MWNTs are achieved by bonding iron to the external pendant amino group of the self-assembled monolayers. Finally, onedimensional nanocomposites are produced through centrifugal effect, filtration and supercritical drying method.
3. Results and discussion As in Fig. 1(c), the high-magnification TEM images of MWNTs after pretreatment show that the inner and outer diameters of the tubes are 3.8 and 13 nm, respectively. Fig. 1(a) and (b) show that the diameters of the iron-coated MWNTs by using pyrolysis of carbonyl method increased from 13 to 35 nm. The results indicate that a layer of iron deposition is able to form on the surfaces of the MWNTs. The surface of the coated MWNTs seems very smooth, but several voids in the coated layer are discovered by intensive TEM observations. Perhaps the uneven dispersion of chemsorption centers on pretreated MWNTs would induce nonuniform growth or deposition layer at different parts of MWNTs. As the deposition rate is higher than 12.2 mg/(cm2 h), the normal growth rate of iron is higher than the lateral growth rate. The iron deposit is formed as spherical grains, which appear to be very closely packed crystallites. The results indicate that the iron nanoparticles tend to aggregate on the outer surfaces of the MWNTs. It is noticed that the deposited layer is sensitive to the reaction temperature, which subsequently influences the reaction rate and chemsorption process. If the reaction temperature is higher than 220 C, the deposition rate in contrast to the chemsorption rate is higher, so that the aggregation tendency would be more serious. When the reaction temperature is lower than 160 C, the reaction cannot proceed. At 180 C, low deposition rate is helpful in obtaining a better coating layer on MWNTs. In addition, low stirring speed is subject to adsorbing iron nanogranule. Energy dispersion X-ray (EDX) analysis (Fig. 2) shows that the major component in the coated layer is iron, with a little silicon element, which mainly derives from the catalyst for preparing
ARTICLE IN PRESS X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
399
500
Fe(Ka)
Counts
400 300 200 100
Si(Ka) 0 2
4
6
8
10
12
14
e/Kev Fig. 2. EDX pattern of iron-coated MWNTs.
Fig. 3. Electron diffraction pattern of the iron-coated MWNTs.
Fig. 1. TEM micrographs of iron-coated MWNTs: (a) magnified 58 k times, (b) magnified 600 k times and (c) Highmagnification TEM micrographs of MWNTs after pretreatment.
MWNTs. Electron diffraction experiments (Fig. 3) also confirm mainly polycrystalline iron shown in the pattern besides graphite. In order to reduce the conglomeration of the iron-coated MWNTs in the drying process, several methods are employed. First, the coated nanotubes are washed with ethanol and dried at 85 C under vacuum condition. Fig. 4(a) shows that the
ARTICLE IN PRESS 400
X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402 8
Ms
6
Mr
M(emµ)
4
mHc
2 0 -2 -4 -6 -8 -1000
-500
0
500
1000
H(KOe)
ε
Fig. 5. Static hysteresis curves for iron-coated MWNTs.
13 12 11 10 9 8 7 6 5 4 3 2 1 0
ε′
ε″
0
2
4
6
8
10 12 f/GHz
14
16
18
20
Fig. 6. Dependence of e0 ; e00 on frequency.
Fig. 4. SEM micrographs of iron-coated under different drying conditions: (a) 85 C and vacuum, (b) 600 C and N2 atmosphere and (c) supercritical drying technology.
conglomeration is obvious. Second, the coated nanotubes are dried in vacuum sintering furnace under N2 atmosphere at 600 C for 12 h and cooled. Fig. 4(b) shows that the conglomeration still occurs. Third, a new type of drying technology [10], which makes use of supercritical fluids is adopted. As temperature and pressure, respectively, reach 250 C and 7 MPa, ethanol media becomes supercritical fluids. The ethanol and water in the coated MWNTs are gradually discharged at equilibrium conditions. Simultaneously, the residual ethanol and water of fluids are exorcised by nitrogen, and then the coated
ARTICLE IN PRESS X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
tively. The complex permeability and permittivity of composites are a good match. These characteristic electromagnetic properties, resulting from the nanometer size effect, can be applied to the microwave absorbing material.
3.0
iron-coated MWNTs
2.5
µ′
2.0 1.5
4. Conclusion
1.0 0.5 0
2
4
6
8
10
12
14
16
18
20
f/GHz 1.8
iron-coated MWNTs
1.6 1.4 1.2
µ″
401
1.0 0.8 0.6 0.4 0.2 0
2
4
6
8
10
12
14
16
18
20
f/GHz Fig. 7. Dependence of m0 ; m00 on frequency.
MWNTs are cooled to room temperature in a N2 atmosphere. Fig. 4(b) shows that the iron-coated MWNTs are uniform and highly dispersive. The result indicates that supercritical drying technology can eliminate surface tension and maintain the structure of the solid nanomaterial during drying. We determine the hysteresis curves at room temperature with vibrating sample magnetometer, and the result is presented in Fig. 5. From this figure we can see that the saturation magnetization and coercive force for the coated carbon nanotubes are 538.5 Gs and 3470 A m1 ; respectively. This result indicates that it is a soft magnetic material and the coercive force is low. In addition, the dynamic electromagnetic parameters (Figs. 6 and 7) are also determined by vector network analyzer. At 2 GHz, the m0 ; m00 ; 0 and 00 of the composites are 2.64, 1.63, 12 and 2.04, respec-
The main conclusion from this work may be summarized as follows: 1. A new one-dimensional nanocomposite based on the coating of MWNTs templates with iron is prepared by pyrolysis of carbonyl method. 2. The surface pretreatments of the MWNTs are indispensible steps before coating. The uniform and highly dense dispersion of chemsorption centers after pretreatment are the crucial aspects for an excellent coated metal layer on MWNTs. The deposited layer is sensitive to the reaction temperature, which influences the reaction rate and chemsorption rate. A low deposition rate is helpful in obtaining a better coating layer on the MWNTs. 3. The experimental result indicates that supercritical drying technology can eliminate surface tension and maintain the structure of the onedimensional nanocomposites during drying. The modification of self-assembled monolayers, reaction temperatures and proportionality of the reactant are found to be critical for getting better electromagnetic performance. The ironcoated MWNTs may be useful for microwave absorbing materials fields.
Acknowledgement The financial support of this research project was from the spaceflight innovation foundation. References [1] F. Service Robert, Science 292 (5514) (2001) 45. [2] Zhang Zhen-Hua, Peng Jing-Cui, Acta Phys. Sinica 50 (6) (2000) 1150.
ARTICLE IN PRESS 402
X. Shen et al. / Journal of Magnetism and Magnetic Materials 288 (2005) 397–402
[3] C.V. Nguyen, R.M.D. Stevens, A. Cassell, et al., Nanotechnology 12 (3) (2001) 363. [4] Ma Ren-zhi, Wei Bing-qing, Xu Cai-lu, et al., Sci. in China (Ser. E-Technological Sci.) 43 (2) (2000) 178. [5] C. Niu, E.K. Sichel, R. Hoch, et al., Appl. Phys. Lett. 70 (11) (1997) 1480. [6] C. Stephan, T.P. Nguyen, B. Lahr, et al., J. Mater. Res. 17 (2) (2002) 396.
[7] Shen Zeng-min, Zhao Dong-lin, New Carbon Mater. 16 (1) (2001) 1. [8] Chen Xiao-hua, Yan Yong-hong, Zhang Gao-min, et al., Microfabrication Technol. 2 (1999) 17. [9] Ni Yan, Zhao Zhen-sheng, He Hua-hui, J. Huazhong Univ. Sci. Tech. 29 (7) (2001) 75. [10] A. Tsutsumi, S. Nakamoto, T.A. Mineo, Power Technol. 85 (2) (1995) 275.