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Improving dispersion of nanometer-size diamond particles by acoustic cavitation
Ultrasonics 44 (2006) e473–e476 www.elsevier.com/locate/ultras
Improving dispersion of nanometer-size diamond particles by acoustic cavitation Takeyoshi Uchida
b
a,*
, Akiko Hamano b, Norimichi Kawashima b, Shinichi Takeuchi b
a Post Graduate School, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama, Kanagawa 225-8502, Japan Faculty of Biomedical Engineering, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama, Kanagawa 225-8502, Japan
Available online 2 June 2006
Abstract A novel acoustic-dispersion method for fine diamond particles was developed. Two samples of nanometer-sized diamond particles were used. They had primary particle sizes of 5 nm (ND5) and 150 nm (ND150). Disaggregation of agglomerated particles using ultrasound and surface modification of ND5 and ND150 were investigated. The ND5 and ND150 particles aggregated to secondary particles, having sizes on the order of micrometers. The surfaces of ND5 and ND150 particle were modified due to chemical reactions and the particles were disaggregated by acoustic cavitation. The ND5 particles were disaggregated to give an average particle size of about 100 nm by ultrasound exposure with average acoustic intensities higher than 800 W/m2. The agglomerated ND150 particles with size of 15 lm were disaggregated to reach an average particle size of about 300 nm by ultrasound exposure with an average acoustic intensity higher than 2000 W/m2. The surfaces of ND5 and ND150 particles were found to be modified with hydroxyl groups resulting from acoustic cavitation. This could lead to a well dispersed solution of nanometer-sized diamond particles in water. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Acoustic cavitation; Nanometer-sized diamond particles; Particle dispersion technique; Active oxygen species
1. Introduction The circumferential texturing of the surface of a hard disk is very important and its texturing profiles markedly affect the final magnetic properties in longitudinal magnetic recording. The texturing aims (1) to avoid adhesion between the magnetic head and the disk surface and (2) to eliminate slight undulations and projections to obtain a suitable surface roughness. Consequently, a proper abrasive is required for texturing that (1) does not damage the surface by scratching, (2) gives uniform texturing lines, and (3) precisely controls the surface roughness of the textured surface. To meet these requirements, the abrasive should have a narrow particle size distribution and be well dis-
*
Corresponding author. Fax: +81 45 972 5972. E-mail address: [email protected] (T. Uchida).
0041-624X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ultras.2006.05.026
persed in water. High precision polishing requires an abrasive of fine particle size. Generally, the smaller the particle diameter of the abrasive, the greater is the difficulty with which the abrasive is dispersed uniformly in water. Due to the increased surface energy, the particles agglomerate more easily. The abrasive, when used in an agglomerated state, can scratch the substrate. Dispersion stability is a very important factor in the performance of polishing. Abrasives such as diamond particle suspension are used for high precision polishing of silicon wafers, quartz wafers and glass hard disks, etc. Recently, fine diamond particles have been used for high precision polishing of hard disks [1,2]. In particular, nanometer high precision polishing is also required for manufacturing hard disks with an ultrahigh recording density. Although various types of dispersants and dispersion equipments have been developed to improve the dispersibility and dispersion stability of diamond particles, they
e474
T. Uchida et al. / Ultrasonics 44 (2006) e473–e476
could not modify the essential surface properties of the particles. Since the methods have some problems concerning particle dispersion characteristics, reproducibility and polishing efficiency, it is important to improve the dispersion and dispersion stability of nanometer-sized diamond particles. When water is irradiated with ultrasound, acoustic cavitation occurs, which then causes the generation of active oxygen species and shock waves [3–5]. A reaction field of high temperature and high pressure is formed in the water tank. We propose a novel dispersion method for nanometer-sized diamond particles by ultrasound exposure. Recently, sonochemistry has been investigated in some industries. Studies on the reduction of the particle size of inorganic substances by ultrasound have been reported [6–8]. Many of these studies used an ultrasound horn in their ultrasound exposure system. When using the ultrasound horn, aqueous suspensions were contaminated by erosion from the horn. The purpose of this study was to disaggregate nanometer-sized diamond particles without erosion by forming a standing wave acoustic field in the water tank. We also attempt the simultaneous surface modification of nanometer-sized diamond by ultrasound exposure. 2. Experimental Fig. 1 shows the experimental apparatus used in this study. A stainless steel vibrating disk (2 mm thick, 180 mm diameter) with a bolt-clamped Langevin-type transducer (BLT) attached to the disk was placed in the bottom of a water tank (70 mm long, 70 mm wide, and 140 mm high). The Langevin-type transducer consists of piezoelectric plates that are sandwiched between two duraluminum vibrating plates. The Langevin transducer has a fundamental frequency at 40 kHz and a bandwidth of l0 kHz. However, it has many higher harmonic modes at
Diamond particle suspension
Langevin type Vibrating disk
Power amplifier
transducer
Function generator
Fig. 1. Experimental system of surface modification and disaggregation of diamond particles by ultrasound exposure.
55 kHz, 75 kHz, 85 kHz, 100 kHz, 135 kHz, and 155 kHz. We measured the frequency characteristics of the input impedance of the BLT and found that the best impedance matching between the transducer and electric circuits was at 155 kHz, which was then used for the experimental measurements. A suspension of diamond particles was exposed to ultrasound using the ultrasound exposure system and a standing wave acoustic field was subsequently formed. The output signal of a function generator (HP 8116A) was amplified using a power amplifier (ENI 2100L) with a gain of 50 dB and applied to the BLT. Two diamond particles samples were used in this study. They consist of particles having a nominal particle sizes of 5 nm (ND5) and 150 nm (ND150). ND5 is expected to be used as an abrasive and as a solid lubricant in the future. ND150 has already been used for polishing the substrate of a hard disk. Many processes are required for disaggregating ND150 to obtain primary size particles. Both ND5 and ND150 were aggregated. The size of aggregated particles for ND5 was about 5 lm and that of those for ND150 was about 15 lm. To 500 ml of distilled water was added 30 mg of the diamond powder and the suspension was stirred fully. The height of the diamond suspension in the water tank was about 100 mm. The diamond suspension was then exposed to ultrasound at 155 kHz for 20 min. 3. Results and discussion 3.1. Experimental condition We tried to disaggregate the aggregated diamond particles by shock waves of acoustic cavitation and high ultrasonic power. Active oxygen species were generated by acoustic cavitation. The surface of diamond particles was modified by the chemical reaction of active oxygen species, as described below. A standing wave was formed in the water tank in Fig. 1 for the stable generation of acoustic cavitation. Diamond particles were disaggregated and their surface was stably modified by trapping cavitation bubbles at the antinodes of sound pressure in the standing wave acoustic field. Fig. 2 shows the frequency characteristics of the light intensity of sonochemical luminescence measured using a photomultiplier. Sonochemical luminescence is a typical sonochemical reaction that occurs between luminol anion and active oxygen species triggered by acoustic cavitation. A high light intensity was observed under the conditions that active oxygen species reactively generate. The highest light intensity of sonochemical luminescence was observed at 155 kHz. The operating frequency of 155 kHz was then used in this study. 3.2. Acoustic intensity and active oxygen species The acoustic field in the water tank was measured by a hydrophone (TORAY, H5C-001) scanning the horizontal
T. Uchida et al. / Ultrasonics 44 (2006) e473–e476
1.2 Relative amount of DMPO-OH
Count of photon×106 counts/s
6 5 4 3 2 1
1 0.8 0.6 0.4 0.2 0
0 0
100 Frequency (kHz)
200
plane at the distance of 10 mm from the acoustic radiation surface of the stainless steel vibrating disk. The measured horizontal plane was located at the antinode of the standing wave acoustic field. The maximum sound pressure and average acoustic intensity were measured. Fig. 3 shows the relationship between the voltage applied to the BLT and the average acoustic intensity. Fig. 3 shows the measured data and the regression curve calculated by least-square method. The average acoustic intensity was obtained as the average of measured acoustic intensities at each point in the measured horizontal plane. The purpose of this study was to disaggregate and modify the surface of ND5 and ND150 by shock waves and active oxygen species generated by ultrasound exposure. The relationship between the average acoustic intensity in the water tank and the amount of generated active oxygen species was investigated with the spin-trap method using electron spin resonance (ESR) spectroscopy. 5,5Dimethyl-1-pyrroline-N-oxide (DMPO) was used as a spin-trap agent. Fig. 4 shows the relationship between the
1000
2000
3000
4000
5000
Fig. 4. Relationship between the average acoustic intensity and the peak under the area of DMPO-OH spectrum.
average acoustic intensity in the water tank and the relative amount of DMPO-OH that was formed. The relative amount of generated DMPO-OH by ultrasound exposure was calculated from the ESR spectrum. Generation of active oxygen species (OH) by acoustic cavitation was confirmed at 155 kHz. The amount of generated active oxygen species (OH) increased with increasing average acoustic intensity in the water tank as shown in Fig. 4. Thus, active oxygen species (OH)were generated at average acoustic intensities higher than about 800 W/m2. 3.3. Disaggregation and surface modification After ultrasound exposure, changes in the size distribution for ND5 and ND150 were measured using a size distribution measuring system (BeckmanCoulter, LS230). Fig. 5 and Table 1 show the relationship between the average acoustic intensity in the water tank and the average particle size for ND5 and ND150. Substances on the diamond particle surface after ultrasound exposure were examined using a Fourier-transform infrared photometer
20 Average particle size (micron)
4000
3000 y = 0.7357x2.0339
2000
R2 = 0.9983 1000 Regression curve 0
0
Average acoustic intensity (W/m2)
Fig. 2. Frequency characteristics of the light intensity of sonochemical luminescence in the water tank of the ultrasound exposure system using a photomultiplier.
Average acoustic intensity (W/m2)
e475
0
20 40 Applied voltage (V)
60
Fig. 3. Relationship between the amplitude of voltage applied to transducer and the average acoustic intensity in the water tank of the ultrasound system.
15 ND150 10
ND5
5
0 0
2000
4000
6000
8000
Average acoustic intensity (W/m2)
Fig. 5. Relationship between the average acoustic intensity and the average particle size for ND5 and ND150, expressed in micrometers.
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T. Uchida et al. / Ultrasonics 44 (2006) e473–e476
Table 1 Relationship between average particle sizes of sonicated diamond particles by ultrasound exposure and average intensity of ultrasound Average acoustic intensity (W/m2)
ND5 (lm)
ND150 (lm)
0 210 860 2300 7900
5.1 1.04 0.42 0.12
15.4 14.4 5 0.65 0.32
Transmittance (a.u.)
Without sonication
With sonication
and Table 1. For ND5 an average particle size of 100 nm was obtained after ultrasound exposure with an average acoustic intensity greater than 800 W/m2, while for ND150 an average particle size of 300 nm was obtained after ultrasound exposure with average acoustic intensities greater than 2000 W/m2. Figs. 4 and 5 show that the average particle sizes of ND5 and ND150 were decreased by ultrasound vibrating power and shock waves by acoustic cavitation with average acoustic intensities higher than 800 W/m2. Typical valleys are usually observed near 3400 cm 1 in the infrared absorption spectra of substances with hydroxyl groups [9]. The valleys observed in the infrared absorption spectra of the sonicated ND5 and ND150 were located near 3400 cm 1 as shown in Figs. 6 and 7. Then, ultrasound exposure caused a chemical modification through the introduction of hydroxyl groups on the surface of ND5 and ND150. The hydroxyl groups produced a dispersed solution of nanometer-sized diamond particles in water. 4. Summary
4000
3500
3000
2500 2000 1500 Wavenumber (cm-1)
1000
500
Fig. 6. Infrared absorption spectra of ND5 with and without sonication.
Transmittance (a.u.)
Without sonication
With sonication
We investigated a novel dispersion method for fine diamond particles using ultrasound exposure. ND5 and ND150 were used as nanometer-sized diamond particles in this study. The average particle size for ND5 and ND150 decreased in an ultrasonic standing wave. When the average acoustic intensity in the water tank increased over about 800 W/m2, the average particle size of ND5 decreased from 5 lm to 100 nm. When the average acoustic intensity in the water tank increased beyond 2 kW/m2, the average particle size of ND150 decreased from 15 lm to 300 nm. Ultrasound exposure caused a chemical modification through the introduction of hydroxyl groups on the surface of ND5 and ND150. References
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1) Fig. 7. Infrared absorption spectra of ND150 with and without sonication.
(JEOL, FT/IR-460). Figs. 6 and 7 show the infrared absorption spectra of ND5 and ND150 with and without sonication, respectively. The average particle sizes for ND5 and ND150 decreased after ultrasound exposure as shown in Fig. 5
[1] T. Uchida, A. Hamano, N. Kawashima, S. Takeuchi, Jpn. J. Appl. Phys. 44 (2005) 4553. [2] T. Uchida, T. Sato, S. Takeuchi, N. Kuramochi, N. Kawasima, Jpn. J. Appl. Phys. 42 (2003) 2967. [3] T.J. Mason, Ultrason. Sonochem. 10 (2003) 175. [4] J.P. Lorimer, T.J. Mason, Ultrason. Sonochem. 2 (1995) S79. [5] K.S. Suslick, Sonochemistry, Science 247 (1997) 1439. [6] L.A. Perez-Maqueda, F. Franco, M.A. Aviles, J. Poyato, J.L. PerezRodriguez, Clay. Clay. Miner. 51 (2003) 701. [7] I. Lapides, S. Yariv, J. Mater. Sci. 39 (2004) 5209. [8] L.A. Perez-Maqueda, J.M. Blanes, J. Pascual, J.L. Perez-Rodriguez, J. Eur. Ceram. Soc. 24 (2004) 2793. [9] T. Murakami, M. Takahashi, N. Kawashima, Chem. Lett. 2000 (2000) 1312.
Improving dispersion of nanometer-size diamond particles by acoustic cavitation Takeyoshi Uchida
b
a,*
, Akiko Hamano b, Norimichi Kawashima b, Shinichi Takeuchi b
a Post Graduate School, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama, Kanagawa 225-8502, Japan Faculty of Biomedical Engineering, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama, Kanagawa 225-8502, Japan
Available online 2 June 2006
Abstract A novel acoustic-dispersion method for fine diamond particles was developed. Two samples of nanometer-sized diamond particles were used. They had primary particle sizes of 5 nm (ND5) and 150 nm (ND150). Disaggregation of agglomerated particles using ultrasound and surface modification of ND5 and ND150 were investigated. The ND5 and ND150 particles aggregated to secondary particles, having sizes on the order of micrometers. The surfaces of ND5 and ND150 particle were modified due to chemical reactions and the particles were disaggregated by acoustic cavitation. The ND5 particles were disaggregated to give an average particle size of about 100 nm by ultrasound exposure with average acoustic intensities higher than 800 W/m2. The agglomerated ND150 particles with size of 15 lm were disaggregated to reach an average particle size of about 300 nm by ultrasound exposure with an average acoustic intensity higher than 2000 W/m2. The surfaces of ND5 and ND150 particles were found to be modified with hydroxyl groups resulting from acoustic cavitation. This could lead to a well dispersed solution of nanometer-sized diamond particles in water. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Acoustic cavitation; Nanometer-sized diamond particles; Particle dispersion technique; Active oxygen species
1. Introduction The circumferential texturing of the surface of a hard disk is very important and its texturing profiles markedly affect the final magnetic properties in longitudinal magnetic recording. The texturing aims (1) to avoid adhesion between the magnetic head and the disk surface and (2) to eliminate slight undulations and projections to obtain a suitable surface roughness. Consequently, a proper abrasive is required for texturing that (1) does not damage the surface by scratching, (2) gives uniform texturing lines, and (3) precisely controls the surface roughness of the textured surface. To meet these requirements, the abrasive should have a narrow particle size distribution and be well dis-
*
Corresponding author. Fax: +81 45 972 5972. E-mail address: [email protected] (T. Uchida).
0041-624X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ultras.2006.05.026
persed in water. High precision polishing requires an abrasive of fine particle size. Generally, the smaller the particle diameter of the abrasive, the greater is the difficulty with which the abrasive is dispersed uniformly in water. Due to the increased surface energy, the particles agglomerate more easily. The abrasive, when used in an agglomerated state, can scratch the substrate. Dispersion stability is a very important factor in the performance of polishing. Abrasives such as diamond particle suspension are used for high precision polishing of silicon wafers, quartz wafers and glass hard disks, etc. Recently, fine diamond particles have been used for high precision polishing of hard disks [1,2]. In particular, nanometer high precision polishing is also required for manufacturing hard disks with an ultrahigh recording density. Although various types of dispersants and dispersion equipments have been developed to improve the dispersibility and dispersion stability of diamond particles, they
e474
T. Uchida et al. / Ultrasonics 44 (2006) e473–e476
could not modify the essential surface properties of the particles. Since the methods have some problems concerning particle dispersion characteristics, reproducibility and polishing efficiency, it is important to improve the dispersion and dispersion stability of nanometer-sized diamond particles. When water is irradiated with ultrasound, acoustic cavitation occurs, which then causes the generation of active oxygen species and shock waves [3–5]. A reaction field of high temperature and high pressure is formed in the water tank. We propose a novel dispersion method for nanometer-sized diamond particles by ultrasound exposure. Recently, sonochemistry has been investigated in some industries. Studies on the reduction of the particle size of inorganic substances by ultrasound have been reported [6–8]. Many of these studies used an ultrasound horn in their ultrasound exposure system. When using the ultrasound horn, aqueous suspensions were contaminated by erosion from the horn. The purpose of this study was to disaggregate nanometer-sized diamond particles without erosion by forming a standing wave acoustic field in the water tank. We also attempt the simultaneous surface modification of nanometer-sized diamond by ultrasound exposure. 2. Experimental Fig. 1 shows the experimental apparatus used in this study. A stainless steel vibrating disk (2 mm thick, 180 mm diameter) with a bolt-clamped Langevin-type transducer (BLT) attached to the disk was placed in the bottom of a water tank (70 mm long, 70 mm wide, and 140 mm high). The Langevin-type transducer consists of piezoelectric plates that are sandwiched between two duraluminum vibrating plates. The Langevin transducer has a fundamental frequency at 40 kHz and a bandwidth of l0 kHz. However, it has many higher harmonic modes at
Diamond particle suspension
Langevin type Vibrating disk
Power amplifier
transducer
Function generator
Fig. 1. Experimental system of surface modification and disaggregation of diamond particles by ultrasound exposure.
55 kHz, 75 kHz, 85 kHz, 100 kHz, 135 kHz, and 155 kHz. We measured the frequency characteristics of the input impedance of the BLT and found that the best impedance matching between the transducer and electric circuits was at 155 kHz, which was then used for the experimental measurements. A suspension of diamond particles was exposed to ultrasound using the ultrasound exposure system and a standing wave acoustic field was subsequently formed. The output signal of a function generator (HP 8116A) was amplified using a power amplifier (ENI 2100L) with a gain of 50 dB and applied to the BLT. Two diamond particles samples were used in this study. They consist of particles having a nominal particle sizes of 5 nm (ND5) and 150 nm (ND150). ND5 is expected to be used as an abrasive and as a solid lubricant in the future. ND150 has already been used for polishing the substrate of a hard disk. Many processes are required for disaggregating ND150 to obtain primary size particles. Both ND5 and ND150 were aggregated. The size of aggregated particles for ND5 was about 5 lm and that of those for ND150 was about 15 lm. To 500 ml of distilled water was added 30 mg of the diamond powder and the suspension was stirred fully. The height of the diamond suspension in the water tank was about 100 mm. The diamond suspension was then exposed to ultrasound at 155 kHz for 20 min. 3. Results and discussion 3.1. Experimental condition We tried to disaggregate the aggregated diamond particles by shock waves of acoustic cavitation and high ultrasonic power. Active oxygen species were generated by acoustic cavitation. The surface of diamond particles was modified by the chemical reaction of active oxygen species, as described below. A standing wave was formed in the water tank in Fig. 1 for the stable generation of acoustic cavitation. Diamond particles were disaggregated and their surface was stably modified by trapping cavitation bubbles at the antinodes of sound pressure in the standing wave acoustic field. Fig. 2 shows the frequency characteristics of the light intensity of sonochemical luminescence measured using a photomultiplier. Sonochemical luminescence is a typical sonochemical reaction that occurs between luminol anion and active oxygen species triggered by acoustic cavitation. A high light intensity was observed under the conditions that active oxygen species reactively generate. The highest light intensity of sonochemical luminescence was observed at 155 kHz. The operating frequency of 155 kHz was then used in this study. 3.2. Acoustic intensity and active oxygen species The acoustic field in the water tank was measured by a hydrophone (TORAY, H5C-001) scanning the horizontal
T. Uchida et al. / Ultrasonics 44 (2006) e473–e476
1.2 Relative amount of DMPO-OH
Count of photon×106 counts/s
6 5 4 3 2 1
1 0.8 0.6 0.4 0.2 0
0 0
100 Frequency (kHz)
200
plane at the distance of 10 mm from the acoustic radiation surface of the stainless steel vibrating disk. The measured horizontal plane was located at the antinode of the standing wave acoustic field. The maximum sound pressure and average acoustic intensity were measured. Fig. 3 shows the relationship between the voltage applied to the BLT and the average acoustic intensity. Fig. 3 shows the measured data and the regression curve calculated by least-square method. The average acoustic intensity was obtained as the average of measured acoustic intensities at each point in the measured horizontal plane. The purpose of this study was to disaggregate and modify the surface of ND5 and ND150 by shock waves and active oxygen species generated by ultrasound exposure. The relationship between the average acoustic intensity in the water tank and the amount of generated active oxygen species was investigated with the spin-trap method using electron spin resonance (ESR) spectroscopy. 5,5Dimethyl-1-pyrroline-N-oxide (DMPO) was used as a spin-trap agent. Fig. 4 shows the relationship between the
1000
2000
3000
4000
5000
Fig. 4. Relationship between the average acoustic intensity and the peak under the area of DMPO-OH spectrum.
average acoustic intensity in the water tank and the relative amount of DMPO-OH that was formed. The relative amount of generated DMPO-OH by ultrasound exposure was calculated from the ESR spectrum. Generation of active oxygen species (OH) by acoustic cavitation was confirmed at 155 kHz. The amount of generated active oxygen species (OH) increased with increasing average acoustic intensity in the water tank as shown in Fig. 4. Thus, active oxygen species (OH)were generated at average acoustic intensities higher than about 800 W/m2. 3.3. Disaggregation and surface modification After ultrasound exposure, changes in the size distribution for ND5 and ND150 were measured using a size distribution measuring system (BeckmanCoulter, LS230). Fig. 5 and Table 1 show the relationship between the average acoustic intensity in the water tank and the average particle size for ND5 and ND150. Substances on the diamond particle surface after ultrasound exposure were examined using a Fourier-transform infrared photometer
20 Average particle size (micron)
4000
3000 y = 0.7357x2.0339
2000
R2 = 0.9983 1000 Regression curve 0
0
Average acoustic intensity (W/m2)
Fig. 2. Frequency characteristics of the light intensity of sonochemical luminescence in the water tank of the ultrasound exposure system using a photomultiplier.
Average acoustic intensity (W/m2)
e475
0
20 40 Applied voltage (V)
60
Fig. 3. Relationship between the amplitude of voltage applied to transducer and the average acoustic intensity in the water tank of the ultrasound system.
15 ND150 10
ND5
5
0 0
2000
4000
6000
8000
Average acoustic intensity (W/m2)
Fig. 5. Relationship between the average acoustic intensity and the average particle size for ND5 and ND150, expressed in micrometers.
e476
T. Uchida et al. / Ultrasonics 44 (2006) e473–e476
Table 1 Relationship between average particle sizes of sonicated diamond particles by ultrasound exposure and average intensity of ultrasound Average acoustic intensity (W/m2)
ND5 (lm)
ND150 (lm)
0 210 860 2300 7900
5.1 1.04 0.42 0.12
15.4 14.4 5 0.65 0.32
Transmittance (a.u.)
Without sonication
With sonication
and Table 1. For ND5 an average particle size of 100 nm was obtained after ultrasound exposure with an average acoustic intensity greater than 800 W/m2, while for ND150 an average particle size of 300 nm was obtained after ultrasound exposure with average acoustic intensities greater than 2000 W/m2. Figs. 4 and 5 show that the average particle sizes of ND5 and ND150 were decreased by ultrasound vibrating power and shock waves by acoustic cavitation with average acoustic intensities higher than 800 W/m2. Typical valleys are usually observed near 3400 cm 1 in the infrared absorption spectra of substances with hydroxyl groups [9]. The valleys observed in the infrared absorption spectra of the sonicated ND5 and ND150 were located near 3400 cm 1 as shown in Figs. 6 and 7. Then, ultrasound exposure caused a chemical modification through the introduction of hydroxyl groups on the surface of ND5 and ND150. The hydroxyl groups produced a dispersed solution of nanometer-sized diamond particles in water. 4. Summary
4000
3500
3000
2500 2000 1500 Wavenumber (cm-1)
1000
500
Fig. 6. Infrared absorption spectra of ND5 with and without sonication.
Transmittance (a.u.)
Without sonication
With sonication
We investigated a novel dispersion method for fine diamond particles using ultrasound exposure. ND5 and ND150 were used as nanometer-sized diamond particles in this study. The average particle size for ND5 and ND150 decreased in an ultrasonic standing wave. When the average acoustic intensity in the water tank increased over about 800 W/m2, the average particle size of ND5 decreased from 5 lm to 100 nm. When the average acoustic intensity in the water tank increased beyond 2 kW/m2, the average particle size of ND150 decreased from 15 lm to 300 nm. Ultrasound exposure caused a chemical modification through the introduction of hydroxyl groups on the surface of ND5 and ND150. References
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1) Fig. 7. Infrared absorption spectra of ND150 with and without sonication.
(JEOL, FT/IR-460). Figs. 6 and 7 show the infrared absorption spectra of ND5 and ND150 with and without sonication, respectively. The average particle sizes for ND5 and ND150 decreased after ultrasound exposure as shown in Fig. 5
[1] T. Uchida, A. Hamano, N. Kawashima, S. Takeuchi, Jpn. J. Appl. Phys. 44 (2005) 4553. [2] T. Uchida, T. Sato, S. Takeuchi, N. Kuramochi, N. Kawasima, Jpn. J. Appl. Phys. 42 (2003) 2967. [3] T.J. Mason, Ultrason. Sonochem. 10 (2003) 175. [4] J.P. Lorimer, T.J. Mason, Ultrason. Sonochem. 2 (1995) S79. [5] K.S. Suslick, Sonochemistry, Science 247 (1997) 1439. [6] L.A. Perez-Maqueda, F. Franco, M.A. Aviles, J. Poyato, J.L. PerezRodriguez, Clay. Clay. Miner. 51 (2003) 701. [7] I. Lapides, S. Yariv, J. Mater. Sci. 39 (2004) 5209. [8] L.A. Perez-Maqueda, J.M. Blanes, J. Pascual, J.L. Perez-Rodriguez, J. Eur. Ceram. Soc. 24 (2004) 2793. [9] T. Murakami, M. Takahashi, N. Kawashima, Chem. Lett. 2000 (2000) 1312.