Optimal synthesis and characterization of Ag nanofluids by electrical explosion of wires in liquids
© Ju Park et al; licensee Springer. 2011
Received: 30 October 2010
Accepted: 15 March 2011
Published: 15 March 2011
Silver nanoparticles were produced by electrical explosion of wires in liquids with no additive. In this study, we optimized the fabrication method and examined the effects of manufacturing process parameters. Morphology and size of the Ag nanoparticles were determined using transmission electron microscopy and field-emission scanning electron microscopy. Size and zeta potential were analyzed using dynamic light scattering. A response optimization technique showed that optimal conditions were achieved when capacitance was 30 μF, wire length was 38 mm, liquid volume was 500 mL, and the liquid type was deionized water. The average Ag nanoparticle size in water was 118.9 nm and the zeta potential was -42.5 mV. The critical heat flux of the 0.001-vol.% Ag nanofluid was higher than pure water.
As noble metal materials, silver nanoparticles exhibit significantly distinct physical, chemical, and biological properties. Silver nanoparticles have attracted attention in a wide range of application fields [1–4]. Their unique properties result from particles on the nanoscale that are monodispersed and unagglomerated.
Nanofluids, dispersed nanoscale particles suspended in a base fluid , have drawn tremendous interest from scientific and industrial communities because of their unique properties. They have been used in many industrial applications such as heat transfer, automotive, electronic, biomedical device manufacturing, and others [6–10]. In particular, nanofluids have gained interest as heat transfer fluids. Due to the high thermal conductivity of nanoscale metal particles, metal-nanofluids may significantly enhance thermal transport capabilities. Nanofluids have shown the most promise as coolants because they enhance critical heat flux [CHF] [11–13].
Previous works on electrical explosion of wires
Karioris and Fish 
Au, Ag, Al, Cu, Fe, W, Mo, Ni, Th, U, Pt, Mg, Pb, Sn, Ta
Al, Ni, Au, Pt
Voltage: 0-30 kV
where W is the energy deposited in the wire, v is the voltage, and i(τ) is the time integration.
Parameters that can influence the properties of particles synthesized by EEWL include electrical circuit parameters (voltage, capacitance, inductance); the amount of energy deposited in the wire; the properties of the exploding wire (diameter, length, defects); sublimation of the metal; and properties of the liquid (viscosity, thermal conductivity, breakdown strength).
In this study, we produced and characterized pure Ag nanofluids by EEWL. We examined the energy deposition in the wire under various conditions and focused on controlled particle size and stability. To identify the effects of key parameters in EEWL, we designed the experiments using Minitab and observed the Ag particle size, morphology, and dispersibility in nanofluids. For applications such as cooling system for electronics and nuclear reactors, it is important to increase the CHF. Thus, to determine potential for increased CHF, we used the pool boiling test of the Ag nanofluids. Finally, to decrease the particle size and improve the dispersibility of Ag nanofluids, we optimized the processing parameters for EEWL using a response optimization technique [ROT].
The Ag wire (0.1 mm in diameter) was installed in the cylinder filled with the liquids. The capacitor was charged to 3 kV and the current flowed through the wire when the spark-gap switch was closed. High-temperature plasma was generated by the electrical energy deposited in the wire and was condensed by the basic fluids. A self-integrated Rogowsky coil and a high-voltage probe were used to measure the current and voltage waveforms, respectively.
Summary of experimental parameters
7.5 μF, 30 μF
2.8 mm, 3.8 mm
Deionized water, Ethanol
500 mL, 1,000 mL
We analyzed the effects of the energy deposited in the exploding wire on the size and shape of the Ag nanoparticles. The morphology was observed by high-resolution transmission electron microscopy [TEM]. The size and zeta potential of the nanoparticles were measured using a submicron size and zeta potential measuring system (Nano ZS, Malvern, Worcestershire WR14 1XZUK, UK). Adsorption spectra were analyzed using UV/Vis spectroscopy. Design of experiments [DOE] was performed to optimize the control factors for EEWL.
Manufacturing of Ag nanofluids
Average particle size and zeta potential of Ag nanofluids produced by EEWL in deionized water
Average particle size (nm)
Zeta potential (mV)
Figure 6b shows the coagulation of Ag nanoparticles, which was likely a result of three potential processes. First, agglomeration may have occurred during handling or processing due to the high specific surface area of the nanoparticles. Second, it may have occurred during the drying process of sample preparation. Finally, it may have occurred during condensation.
Average particle size and zeta potential of Ag nanofluids
Average particle size (nm)
Zeta potential (mV)
Liquid volume (mL)
In this study, we produced Ag nanofluids by electrical explosion of wires in liquids. By optimizing control parameters, we decreased the particle size under fast explosion conditions and long plasma duration with low-viscosity media. Low viscosity decreased the particle size and dispersion stability due to greater expansion in the plasma volume. The process was optimized by ROT when capacitance was 30 μF, wire length was 38 mm, liquid volume was 500 mL, and the liquid type was deionized water. For the repeated experiment, the average particle size of the Ag nanoparticles in water was 118.9 nm and the zeta potential was -42.5 mV. The CHF of the 0.001-vol.% Ag nanofluid was higher than that of pure water.
This research was partly supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0023511) and the Fostering of Regional Strategic Industry Program though the Ministry of Knowledge Economy (70007094).
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