Sub-Micrometer Particles Produced by a Low-Powered AC Electric Arc in Liquids

Copyright © 2012 American Scientific Publishers All rights reserved Printed in the United States of America

Journal of Nanoscience and Nanotechnology Vol. 12, 604–609, 2012

Sub-Micrometer Particles Produced by a Low-Powered AC Electric Arc in Liquids Jacek A. Jaworski1 2 ∗ and Eric Fleury2

RESEARCH ARTICLE

1

H. Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Krakow, Poland 2 Center for High Temperature Energy Materials, Korea Institute of Science and Technology (KIST), 39-1 Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Korea The article presents the report of the production of composites of sub-micrometer metal particles in matrix consisted of the metal compounds by means of an AC electric arc in water and paraffin solutions using electrodes carbon–metal and metal–metal (metal: Ni, Fe, Co, Cu). The advantage of this method is the low electric power (from 5 to 10 W) needed in comparison to standard DC Delivered by Ingenta to: arc-discharge methods (0.8 to 3 kW). This method enables the production of particles from conKorea Institute of Scienceand & Technology (KIST) ductive material also in wide range of temperature in solvent which could be either transparent IP : 161.122.24.184 to light or opaque. Moreover the solvent can be electrolyte or insulating liquid. The microstructure Fri, 16 by Mar 2012 06:24:29 of the composite layer was investigated scanning electron microscopy (SEM), Electron Probe Microanalysis (EPMA) and X-ray. During particles production in water metal oxides were created. Additionally using cobalt–copper, nickel–copper as couple electrodes, insoluble in water copper (II) hydroxide crystal grains were created additionally which crystals shape was depended on transition metal. For iron–copper couple electrodes system the copper (II) hydroxide was not formed. Experiments with sequence production of Ni and Fe particles with C electrode assisting in molten paraffin let to obtain both Ni and Fe particles surrounded by paraffin. After solidification the material was insulator but if locally magnetic field influenced on the liquid solution in that place after solidification a new composite was created which was electric current conductor with resistivity around 0.1  · m, was attracted by magnetic field and presented magneto resistance around 0.4% in changing magnetic field in a range 150 mT. After mixing the concentrated paraffin with normal paraffin resistivity of the mixture increased and it became photosensitive and created small voltage under light influence.

Keywords: Nanoparticle, Microparticle, Electric Discharge, Sub-Microparticle, Paraffin, Water, Magneto Resistance, Conductivity, Photovoltaics.

1. INTRODUCTION Substances containing two or more different nanoscale materials are of increasing interest in present day research because of their unique properties. These nanoparticles have many applications in a number of fields, including nanoelectronic devices, molecular recognition, biomedical applications, and optical devices.1 2 There exist various methods to synthesize nanoparticles either by physical, chemical or mechanical processes.2 3 The manufacturing of nanomaterials can be achieved by two distinct approaches that are based on the “bottom up” approach consisting in growing nanoparticles atoms by atoms2 or by reduction of bulk material into nanoparticles called “top down” approach.2 The second group of important materials applied in industry since dozens years included ∗

Author to whom correspondence should be addressed.

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particles with sub-micrometer size. Submicrometer particles are interesting as ingredients to produce bulk products from sintered powders or as starting materials for solid based 3D printers.4 As in the production of nanoparticles, various methods can be used to manufacturing submicrometer particles, from chemical way,5 6 pulverization7 and mechanical communition by milling to electrical discharge.8 9 They are also produced, as byproduct during industrial processes and are usually treated as air pollution which need to be removed from atmosphere because of their adverse impact on health.10–12 This paper described a novel solution of the physical “top down” methods based on sputtering by an electric arc in a liquid solution. The AC electric discharge technique for the production of metallic nano- and sub-micrometer particles in liquids is easy, effective, inexpensive and could be undertaken in various types of environments such as gases and liquids which could be ion insulators 1533-4880/2012/12/604/006

doi:10.1166/jnn.2012.5351

Jaworski and Fleury

Sub-Micrometer Particles Produced by a Low-Powered AC Electric Arc in Liquids

or electrolytes. The performance of this method is very important for future industrial application. Experiments presented in the paper focused on the production of new materials containing nano- and submicrometer particles with new mechanical, electrical and magnetic properties. These new materials with submicrometer particles can be used in 3D printers to produce spatial objects by addition of successive layers of material of the specified geometry, with high resolution. Experiments were performed in two different liquids: water and paraffin. The scheme for the particles prepared in water was as follows: the particles were made by electric arc and next concentrated by evaporating water. In the case of paraffin only the magnetic particles were produced and collected using a permanent magnet.

the transparency of the environment.17 Moreover in this new method the solvent can be either electrolyte or insulating liquid. These attributes distinguishes this production method from others. Of course, the drawback could be aggressiveness of the environment used in this method which could deteriorate the electrodes. The production of particles in water was undertaken at room temperature. The nano- and sub-micrometer sized metal particles were created from tiny drops of liquid metal evaporated from the metal electrode under AC electric arc discharge and cooled in the liquid environment. The upper part of the suspension was decanted three days before been extracted and the water was subsequently evaporated onto a glass substrate. For paraffin, experiments were performed only with Fe, Ni and C electrodes. The microstructure of the composite layer was investigated

2. EXPERIMENTAL DETAILS AND RESULTS 2.1. Synthesis Method and CharacterizationDelivered

by Ingenta to: Korea Institute of Science & Technology (KIST) Sub-micrometer metal particles were manufactured by IP : 161.122.24.184 means of an AC electric arc in water and paraffin solu16 Mar 2012 06:24:29 tions using pair of electrodes carbon–metal orFri, metal–metal

(b)

AC current

(c)

Fixed electrode

Vibrating electrode

Liquid

Fig. 1. liquid.

Sketch of the device used for the production of the particles in

J. Nanosci. Nanotechnol. 12, 604–609, 2012

Fig. 2. Particles produced from C and Co couple electrodes: (a) Particles of Co surrounded by CoO foam, (b) EDX analysis of a particle, (c) analysis of the surrounded foam.

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(metal: Ni, Fe, Co, Cu) by means of a device schematically shown on a Figure 1. The device consists of two electrodes supplied by AC current of 5 to 10 A with voltage 1 V. The electrodes are immersed in the liquid and a contact between these electrodes is established periodically with a frequency of about 2 Hz creating an electric arc. The advantage of this method is the low electric power applied. The range of power was from 5 to 10 W in comparison to standard DC arc-discharge methods where the power can be hundred times larger e.g., from 0.8 to 3 kW.8 9 This method enables the production of particles from conductive materials in wide range of temperatures for the liquid surrounding the electrodes. Another advantage of this method over others such as laser ablation manufacturing is its insensitivity to the optical transparency medium. The laser ablation method is known to be very dependent on

(a)

Sub-Micrometer Particles Produced by a Low-Powered AC Electric Arc in Liquids

Jaworski and Fleury

foams and pure metal particles, the analyses indicated additionally the presence of copper (II) hydroxide crystal grains, those crystals shapes were found to be dependent on the nature of the transition metal used for the counter 2.2. Particles Production in Water electrode. However, it is noticed that in the case of iron– copper couple electrode system, the copper (II) hydroxide For experiments performed using carbon as one electrode did not form (Fig. 3). It could be connected with iron elecand a transition metal for the second electrode, it was tropotential (−0.44) which is almost two times higher than found that the metal particles were covered by a thin layer that of Co (−0.28) and Ni (−0.24). of oxide and surrounded by metal oxide foam (Fig. 2). EPMA measurements for particles prepared using Ni–Fe Figure 2 shows results obtained for Co and C couple eleccouple electrodes indicated only the occurrence of Ni partrodes. Although not shown, similar results were obtained ticles surrounded by Ni and Fe oxides and hydroxides. for nickel-carbon and iron-carbon couple electrodes. PracA possible explanation for this behavior could be as sugtically all carbon avulsed from the carbon electrode was gested above that iron being more reactive than nickel burnt out into carbon oxides and only traces could be reacted with oxygen. detected on the surface of the metal particles and their surThe results indicate that water is not a good medium roundings. A larger amount of carbon was detected at the for the production of metallic particles by means of elecsurface of the particles (Fig. 2(b)) in comparison to that in tric discharge because of the high reactivity of the metallic the foam (Fig. 2(c)). This suggests that the surface of parparticles.to: In addition, the particle production rate is very ticles are rapidly cooled and protected by the Delivered formation ofby Ingenta low and these metallic particles are surrounded by a large protective oxide owing to the presence of the surrounding Korea Institute of Science & Technology (KIST) quantity of by-product that should be removed. In general, water. IP : 161.122.24.184 the produced metallic particles and oxides and hydroxides For experiments with copper-cobalt or Fri, copper-nickel 16 Mar 2012 06:24:29 couple electrode, except for the presence of metal oxide were insulators however some of them presented trace of

Int. [a.u.]

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by scanning electron microscopy (SEM), Electron Probe Microanalysis (EPMA) and X-ray diffraction (XRD).

50 45 40 35 30 25 20 15 10 5 500 0 450 400 350 300 250 200 150 100 50 50 0 45 40 35 30 25 20 15 10 5 0

Co-Cu

Cu(OH)2

Ni-Cu

Cu(OH)2

Fe-Cu

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Θ [deg] Fig. 3. Particles produced from Cu–Co, Ni–Cu and Fe–Cu couple electrodes. The top pictures shows XRD spectrum and SEM image of particles produced with Cu and Co electrodes, the middle–Cu and Ni electrodes and the bottom–Cu and Fe electrodes. Magnification of the top and central SEM image is 50,000× and the bottom one–200,000×.

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electrical conductivity just after drying. This suggests that right after drying the metallic particles oxidized during exposition to air. To preserve properties such as electrical conductivity, the particles should be dried and kept in neutral environment.

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Interesting results were obtained for composites produced with a mixture of iron and nickel particles. The procedure for the production of the composites was as described above. The iron particles were firstly produced and in a second step the nickel particles were synthesized in the iron paraffin suspension. The solution was also kept at 90  C for a few hours in order to let the heaviest parti2.3. Particles Production in Paraffin cles sinking down to the bottom of the solution by gravity effect. The paraffin collected from the surface of the solidThe synthesis of metallic particles was performed in  ified solution was black, nonmagnetic and insulating. The molten paraffin at a temperature of 90 C, using Fe–Fe, paraffin collected by the permanent magnet with magnetiNi–Ni, Ni–Fe, Ni–C, Fe–C couple electrodes. The best zation near 345 mT was conductive and magnetic and very results for the production of these particles were obtained easy to make into shape at a temperature around 50  C. for metal-carbon couple electrodes. When two metalEPMA analyses of the Ni and Fe particles produced with lic couple electrodes were used, they sometimes welded C counter electrode are shown in Figure 4 with both Ni together which perturbed the particle production. However and Fe particles distributed in the surrounded paraffin. This this effect does not occur when the manufacturing prokind of composite was found to be an electrical conduccess made use of metal–carbon couple electrodes. A reftor with a resistivity of around 0.1  · m. It also presented erence sample was prepared by mixing pure paraffin with magneto-resistance higher than the composite containing graphite powder in a mass ratio 1:1. The reference sample by Ingenta Delivered only ironto: particles with value near approximately 0.4% was prepared based on a procedure described in of a Polish Korea Institute Science & Technology (KIST) under a magnetic field of about 150 mT. The resistance patent.18 In that patent, it was indicated that whenIPthe vol: 161.122.24.184 was also found to increase as the applied magnetic field ume fraction of soot in a paraffin—soot composite Fri, 16varied Mar 2012 06:24:29 increased. The resistance of the composite could be varied from a few percent to 50%, the resistivity of the composite by adjusting the volume fraction of particles in the parafdecreased from a few M · m to 30  · m. In this work, fin which would enable a modification of the properties graphite, not soot, was used to produce the reference samfrom conductor to semiconductor until insulator. Furtherple. It is noticed that the reference sample produced in this more, the composite with a resistivity ranging from 7 ·m work was grey and was not conductive. to 150  · m presented photo-galvanic effect; a generated During the production of iron particles, the transparent voltage of millivolts was observed to be dependent upon paraffin became black and opaque. At the end of the prothe material resistivity and the intensity of light. The light cess, the solution was kept at 90  C for a few hours in from a fluorescent lamp with a power 24 W placed at order to let the heaviest particles sinking down to the bota distance 10 cm generated in a 2 cm2 sample supported tom of the solution by gravity effect. The paraffin collected by iron frame displayed a voltage of around 9 mV. from a surface of the solidified solution was black, nonThis type of materials is potentially interesting for magnetic and insulating. When a permanent magnet with the new generation of 3D printers. Black colour protects magnetization near 345 mT was placed near the surface against deep penetration of the laser beam into the medium of the solution, the produced material changed to become and the magnetic properties can be helpful for layer creconductive and magnetic, which was very easy to achieve ation by application of a magnetic field. The Figure 5 at a temperature around 50  C since the material is malshows a schematic of a future 3D printer that can use leable. Its resistivity was measured to be around 0.2  · m these new particle-based composite. It bases on a Stereo and it was found to slightly increase as the magnetic field Lithography Apparatus (SLA) solution, process using phowas increased from 0 to 150 mT. The increase of the tosensitive resin cured by a laser that traces the part’s resistance was on an order of 0.1%. cross sectional geometry layer by layer. The electromagIn the following step, the composite mixture was mixed net collects submicro and nanoparticles of Fe and Ni. The with the reference sample in a volume ratio 6:1 and it was magnetic field is chosen in such way that only one layer observed that the resistivity of the new composite grew of particles is collected on the surface. The laser beam, to around 5  · m. The sample was still magnetic and as it is in the case of SLA method, welds the first crossadditionally generated electric current when exposed to section of the built object from this layer of particles. visual light. The light from a fluorescent lamp with power After finishing of first layer the electromagnet is switched 24 W placed at a distance 10 cm generated in a 2 cm2 off, the inchworm motor move down the electromagnet sample supported by iron generated a voltage of around on a distance corresponding to the thickness of one parti0.5 mV. In addition it was observed that if a small amount cle layer. The first welded layer falls down with the elecof pure paraffin was added to the iron-paraffin composite, tromagnet on the distance of thickness of the layer and the results were not altered which indicated that the dopagain the electromagnet starts, collects fresh particles from ing by graphite powder does not influence significantly the the suspension. When the second layer is ready the laser beam welds the second cross-section of the built object. properties of the paraffin-iron composite.

Sub-Micrometer Particles Produced by a Low-Powered AC Electric Arc in Liquids

Jaworski and Fleury

Delivered by Ingenta to: Korea Institute of Science & Technology (KIST) IP : 161.122.24.184 Fri, 16 Mar 2012 06:24:29

RESEARCH ARTICLE

Fig. 4. EPMA pictures showing Ni and Fe particles surrounded by paraffin. The CP picture shows an image of the material in the SEM mode. The picture Ni indicates nickel particles positions and the picture Fe–iron particles positions (Magnification–2000×).

Because of the opaqueness of the liquid only the top layer will be welded. As it is in the SLA method, the process involved the repeated welding of successive layers until accomplishment of the entire object.

Laser

Laser beam

Electromagnet

Inchworm motor

3. CONCLUSIONS The results presented in this article demonstrated the successful production of sub-micrometer particles by means of a new AC electric discharge technique in water and paraffin. For experiments performed in water, the metallic sub-micrometer and nano-particles were found to be surrounded by oxides and hydroxides. To circumvent the formation of hydroxide, composites composed of submicrometer particles with electro-magnetic properties were prepared using paraffin as a medium. Because of its electrical conductivity and magnetic properties as well as the ductility for temperatures below approximately 50  C, this new type of composite can be used in various technologies and branches of industry. The photo-sensitivity measured from visible light could be used as a new kind of photodetector. However the most promising application for this type of the composite material consisted of particles embedded in paraffin is believed to be as source of submicrometer sized particles for the new generation of 3D printers.

Fe-Ni –paraffin composite

Fig. 5. Model of 3D printer. The electromagnet collects submicro and nanoparticles of Fe and Ni and the laser beam weld first layer of them. Next the electromagnet is switched off, the inchworm motor move down the electromagnet with the first welded layer and again the electromagnet starts, collects particles and the laser beam weld them to next layer.

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Acknowledgments: Dr. Jaworski thanks the Korean Federation of Science and Technology for rewarding with the Brain Pool fellowship. The author acknowledges the financial support by the by 21st Frontier Program CNMT (#2010K000265) of the Korean Ministry of Education Science and Technology. J. Nanosci. Nanotechnol. 12, 604–609, 2012

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10. S.-L. Huang, M.-K. Hsu, and C.-C. Chan, Environ. Health Perspect. 111, 478 (2003). 11. D. R. Smith, J. A. Campbel, and K. K. Nielson, Atmos Environ. 13, 607 (1979). 12. R. L. Davison, D. F. S. Natusch, J. R. Wallace, and C. A. Evans, Environ. Sci. Technol. 9, 862 (1975). 13. J. Takahara, S. Yamagishi, H. Taki, A. Morimoto, and T. Kobayashi, Opt. Lett. 22, 475 (1997). 14. I. D. Nikolov, K. Kurihara, and K. Goto, Nanotechnology 14, 946 (2003). 15. H. Choi, D. F. P. Pile, S. Nam, G. Bartal, and X. Zhang, Opt. Ex. 17, 7519 (2009). 16. R. F. Oulton, V. J. Sorger, T. Zentgraf, R.-M. Ma, Ch. Gladden, L. Dai, G. Bartal, and X. Zhang, Nature 461, 629 (2009). 17. K. Kawaguchi, J. Jaworski, Y. Ishikawa, T. Sasaki, and N. Koshizaki, J. Magn. Magn. Mater. 310, 2369 (2007). 18. C. Biuro Studiów I Projektów Budownictwa Wodnego “Hydroprojekt,” “Electrical model for the study of physical phenomena by analogy, a production method of the material for manufacture such models and a method of production these models” (in Polish) Polish patent no. PL 41604 (1958).

Delivered by Ingenta to: Korea Institute of Science & Technology (KIST) Received: 5 November 2010. Accepted: 11 February 2011. IP : 161.122.24.184 Fri, 16 Mar 2012 06:24:29

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