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Characteristics of nanopowders produced by wire electrical explosion of tinned copper conductor in argon
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Materials Letters 62 (2008) 3143 – 3145 www.elsevier.com/locate/matlet
Characteristics of nanopowders produced by wire electrical explosion of tinned copper conductor in argon Y.S. Kwon a , A.P. Ilyin b , D.V. Tikhonov b,⁎, G.V. Yablunovsky b , V.V. An b a
Research Center for Machine Parts and Materials Processing, University of Ulsan, San-29, Moogu-2 Dong, Nam-Ku. Ulsan 680-749, Republic of Korea b High Voltage Research Institute at Tomsk Polytechnic University, 2a, Lenin Ave., 634028, Tomsk, Russia Received 13 June 2007; accepted 6 February 2008 Available online 13 February 2008
Abstract The end products of electrical explosion of copper wires coated with a thin tin layer were studied. Depositing tin (~ 1 wt.%) on the surface of the copper wire did not have a considerable effect on the relation between the sample dispersity and the input energy. When increasing the input energy, the tin content in surface and near-surface layers of the nanoparticles reduces sharply within 1.1–1.3 W/Ws. Decreasing the input energy increases the oxidation onset temperature by ~ 20 °C when heating Cu (Sn) nanopowders unlike the copper nanopowders without additives. The main phase in the powders is crystallized copper. © 2008 Elsevier B.V. All rights reserved. Keywords: Wire electrical explosion; Surface layers; Nanoparticles
1. Introduction Brasses are widely used as antifriction alloys [1]. Recently copper–tin alloys were used as metal-cladding additives to different oils [2]. At the same time, the system Cu–Sn is not only a solid solution where intermetallic compounds can form under certain conditions. Furthermore, the brass–metal pair will have completely different characteristics during friction. The purpose of this work is to establish phase formation regularities, redistribution of Cu and Sn atoms between the surface and volume of particles during wires electrical explosion (WEE), and cooling products. The nanopowders were produced by electrical explosion of copper wires coated with tin in gaseous argon. Previously the morphology, phase composition and oxidation dynamics of brass (63 wt.% copper) nanopowders were studied [3]. It was found that the phase composition of the nanopowder particles is heterogeneous. When increasing the input energy (W/Ws), the surface is covered with zinc
⁎ Corresponding author. Tel.: +7 3822 419101; fax: +7 3822 418560. E-mail addresses: [email protected] (Y.S. Kwon), [email protected] (D.V. Tikhonov). 0167-577X/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.02.006
oxide, the dispersivity of the nanopowder increases and the part of the initial zinc-depleted α-phase increases. 2. Experimental procedure The samples of the nanopowders were produced using the experimental set-up UFP-4 which is schematically presented in Fig. 1.
Fig. 1. Structural scheme of the experimental set-up. 1 — Explosion chamber with a wire feeding mechanism; 2 — discharger; 3 — capacity storage; 4 — charger; 5 — vacuum system; 6 — gas filling system; 7 — system for separation of explosion products from gas; 8 — control panel.
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Table 1 Fabrication conditions of nanopowders from Cu(Sn) wire Sample no.
Voltage U0, kV
Capacity, μF
Length of the wire, 1, mm
Specific energy input into the wire, W/Ws
Specific energy of the arc stage, Wa/Ws
Average-surface diameter, μm
Specific surface area, m2/g
1. 2. 3. 4. 5. 6. 7.⁎
26 24 22 20 18 16 26
2.28 2.28 2.28 2.28 2.28 2.28 2.01
82 82 82 82 82 82 80
1.86 1.61 1.37 1.19 0.98 0.82 1.74
0.33 0.20 0.07 0 0 0 0.35
0.08 0.09 0.08 0.12 0.16 0.18 0.06
9.1 8.2 8.2 5.9 4.8 4.1 10.2
The set-up is equipped with an automatic gadget for the wire moving in the interelectrode space where the destruction of the wire by electric current impulse occurs during 1–2 μs. For the producing of nanopowders, 0.298 mm copper wire (RF GOST 16-705-492-2005) with the Cu content 99.93% coated with 2 μm of tin was used. For the experiment, 6 samples of nanopowder were produced at different values of the input energy into the wire and the arc stage energy. The input energy of electrical explosion and the arc stage energy were changed by regulating the voltage (U0) applied to the section of the exploded wire (l). The fabrication conditions of nanopowders are presented in Table 1. Wire electrical explosions were carried out in argon at pressure 1.5 · 105 Pa. The repetition frequency of explosions was 0.7 Hz. After passivation in argon with controlled air access, the samples were analyzed. The thermal analysis (derivatograph Q1000) was used to determine parameters of the chemical reactivity of the nanopowders. The average diameter of powder particles was measured using low temperature nitrogen adsorption (BET method). The energy input into the wire was calculated from the current oscillograms and the circuit electrical parameters of the circuit using a known technique [4].
Fig. 2. Typical derivatogram of nanopowder of Cu (Sn) (DTA and TG) at heating in air.
3. Results and discussion According to the experimental data, the average-surface diameter of the particles decreases when increasing the charge voltage (U0) and reaches its minimum 0.08 μm at charge voltage equal and more than 22 kV (Table 1). The phase composition of the powders was studied using an X-ray diffractometer DRON-3.0 with CuKα radiation. The Xray patterns showed the presence of reflections corresponding to the copper crystal phase that approximately coincides with the JCPDS data. The presence of copper oxide phases was found out: copper (II) oxide for all samples and copper (I) oxide for samples 2 and 3. No shift in reflex positions was observed, and no reflections of tin or Cu–Sn intermetallic compound were detected. The presence of the phase Cu2O reflexes can be concerned with a higher chemical reactivity of the particles of samples 2 and 3 during passivation. Perhaps, this contributed to the formation of the high-temperature phase of copper oxide Cu2O. The oxidation process at temperature up to 500 °C is characterized by two stages. This is preceded by a stage of desorption of sorbed gases and decomposition of unstable compounds that is typical for other nanopowders produced by WEE. The chemical reactivity of the samples of the powders Cu (Sn) was analyzed using a previously developed procedure [5] during heating in air. Fig. 2 shows a typical derivatogram for these powders. Sample 7 was produced from the preceding set of samples that were made of a copper wire without any additives. This is an analogue of sample 1 according to the fabrication parameters. The oxidation onset temperature (Ts) with a relative error ±2 °C was measured with the
Fig. 3. Dependence of the Fe and Sn contents in the surface and near-surface layers of nanopowder particles on the specific energy input into a wire (probing area 0.1 mm2).
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due to competitive diffusion during cooling of liquid metal particles when scattering the explosion products.
4. Conclusion
Fig. 4. The Fe and Sn content in the surface and near-surface layers of single particles of different diameters depending on the energy input into the conductor.
Piloyan's method [6]. This temperature (Ts) is a test on the chemical and phase composition of the nanoparticle surface. For the samples produced at low input energy (samples 5 and 6), Ts is 15–20 °C higher than that for samples 1 and 2. The oxidation onset temperature of samples 1 and 2 is almost coincident with Ts of the copper sample without tin additive (sample 7). The analysis of the particles surface at the depth of ~ 5 nm was carried out by using XPS microanalysis on the scanning microscope Jeol-840 by means a built-in device “Link”. The following regularity is observed for a small probing area: when increasing W/Ws the tin content on the surface of the powder particles decreases from 0.81 to 0.005 wt.% (Fig. 3). At first, the Fe impurity content drops from 0.59 to 0.007 wt.%, and then it rises up to 0.89 wt.%. The minimum Fe content is at energy 1.37 W/Ws. It was previously found [7] that when exploding simultaneously wires of different metals, the surface and near-surface layers of powder nanoparticles are enriched with the volatile metal or the metal that has a lower atom diffusion coefficient near the crystallization point of the particles. This enrichment is explained by the phenomenon of stable diffusion during cooling of scattered wire explosion products that results in redistribution of elements in final products of electric explosion. At the same time, tin was not found during general probing of the samples (probing area 1.2 mm2). The Fe content varies from 0.005 to 0.85 wt.%. For some particles of the powder, the tin content in the surface and near-surface layers does not vary with the increase in the input energy W/Ws. The Fe content rises from 0.007 to 0.6 wt.%. (Fig. 4) when the energy increases from 0.82 to 1.86 W/Ws. The surface of the particles of approximately 1, 1–5 and 10 μm in diameter does not contain more than 0.009 wt.% of tin atoms. As explained previously [7], this is related to redistribution of elements
1. Depositing tin (~ 1 wt.%.) on the surface of a copper wire did not have a considerable effect on the relation between the sample dispersity and the input energy. The dispersity of the investigated samples almost agrees with that of the copper powders without tin. 2. According to the X-ray phase analysis, the CuO content decreases with the increase of the input energy (dispersity). For the maximal dispersity samples (1 and 3), the formation of high-temperature oxide Cu2O is observed. The main phase in the powders is crystallized copper reflexes in the Xray patterns coincide with the reference (JCPDS card index). 3. With the decrease in the input energy, the oxidation onset temperature of Cu (Sn) nanopowders increases by ~ 20 °C during heating in contrast to the copper nanopowders without additives. 4. The experiments showed that the temperature after the end of heat evolution is the same for the entire set of samples. This coincides with the temperature of the end of heat evolution for the copper nanopowder without additives and equals 500 °C. It is worth to note that the minimum mass gain is observed for sample 1 during oxidation. The sample was produced at the maximum input energy. The only reactivity parameter that is symbate to the value of the input energy is the oxidation rate of powder samples. 5. With the increase of the input energy, the tin content in surface and near-surface layers of nanoparticles decreases sharply within 1.1–1.3 W/Ws. According to the microanalysis, the Fe impurity content decreases at 1.37 W/Ws and then increases up to 0.89 wt.% (sample 1) with the increase of the input energy. References [1] Yu. M. Lahtin, V.P. Leontyeva, Materiology, Mechanical engineering, Moscow, 1980. [2] I.V. Frishberg, L.V. Zolotuhina, V.V. Harlamov, MiTOM 7 (2000) 21–23. [3] A.P. Lyashko, G.G. Savel'ev, D.V. Tikhonov, FHOM 6 (1992) 127–130. [4] I.F. Kvartshava, V.V. Bondarenko, A.A. Pljutto, A.A. Chernov, ZTF 31 (5(2)) (1956) 745–751. [5] A.P. Ilyin, A.A. Gromov, G.V. Yablunovsky, FGV 37 (4) (2001) 58–62. [6] Ya. Shestak, The Theory of the Thermal Analysis, World, Moscow, 1987. [7] D.V. Tikhonov, Electroexplosive Production of Nanopowders of Complex Composition. A thesis for a degree of candidate of technical sciences. Tomsk Polytechnic University 2000.
Materials Letters 62 (2008) 3143 – 3145 www.elsevier.com/locate/matlet
Characteristics of nanopowders produced by wire electrical explosion of tinned copper conductor in argon Y.S. Kwon a , A.P. Ilyin b , D.V. Tikhonov b,⁎, G.V. Yablunovsky b , V.V. An b a
Research Center for Machine Parts and Materials Processing, University of Ulsan, San-29, Moogu-2 Dong, Nam-Ku. Ulsan 680-749, Republic of Korea b High Voltage Research Institute at Tomsk Polytechnic University, 2a, Lenin Ave., 634028, Tomsk, Russia Received 13 June 2007; accepted 6 February 2008 Available online 13 February 2008
Abstract The end products of electrical explosion of copper wires coated with a thin tin layer were studied. Depositing tin (~ 1 wt.%) on the surface of the copper wire did not have a considerable effect on the relation between the sample dispersity and the input energy. When increasing the input energy, the tin content in surface and near-surface layers of the nanoparticles reduces sharply within 1.1–1.3 W/Ws. Decreasing the input energy increases the oxidation onset temperature by ~ 20 °C when heating Cu (Sn) nanopowders unlike the copper nanopowders without additives. The main phase in the powders is crystallized copper. © 2008 Elsevier B.V. All rights reserved. Keywords: Wire electrical explosion; Surface layers; Nanoparticles
1. Introduction Brasses are widely used as antifriction alloys [1]. Recently copper–tin alloys were used as metal-cladding additives to different oils [2]. At the same time, the system Cu–Sn is not only a solid solution where intermetallic compounds can form under certain conditions. Furthermore, the brass–metal pair will have completely different characteristics during friction. The purpose of this work is to establish phase formation regularities, redistribution of Cu and Sn atoms between the surface and volume of particles during wires electrical explosion (WEE), and cooling products. The nanopowders were produced by electrical explosion of copper wires coated with tin in gaseous argon. Previously the morphology, phase composition and oxidation dynamics of brass (63 wt.% copper) nanopowders were studied [3]. It was found that the phase composition of the nanopowder particles is heterogeneous. When increasing the input energy (W/Ws), the surface is covered with zinc
⁎ Corresponding author. Tel.: +7 3822 419101; fax: +7 3822 418560. E-mail addresses: [email protected] (Y.S. Kwon), [email protected] (D.V. Tikhonov). 0167-577X/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.02.006
oxide, the dispersivity of the nanopowder increases and the part of the initial zinc-depleted α-phase increases. 2. Experimental procedure The samples of the nanopowders were produced using the experimental set-up UFP-4 which is schematically presented in Fig. 1.
Fig. 1. Structural scheme of the experimental set-up. 1 — Explosion chamber with a wire feeding mechanism; 2 — discharger; 3 — capacity storage; 4 — charger; 5 — vacuum system; 6 — gas filling system; 7 — system for separation of explosion products from gas; 8 — control panel.
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Table 1 Fabrication conditions of nanopowders from Cu(Sn) wire Sample no.
Voltage U0, kV
Capacity, μF
Length of the wire, 1, mm
Specific energy input into the wire, W/Ws
Specific energy of the arc stage, Wa/Ws
Average-surface diameter, μm
Specific surface area, m2/g
1. 2. 3. 4. 5. 6. 7.⁎
26 24 22 20 18 16 26
2.28 2.28 2.28 2.28 2.28 2.28 2.01
82 82 82 82 82 82 80
1.86 1.61 1.37 1.19 0.98 0.82 1.74
0.33 0.20 0.07 0 0 0 0.35
0.08 0.09 0.08 0.12 0.16 0.18 0.06
9.1 8.2 8.2 5.9 4.8 4.1 10.2
The set-up is equipped with an automatic gadget for the wire moving in the interelectrode space where the destruction of the wire by electric current impulse occurs during 1–2 μs. For the producing of nanopowders, 0.298 mm copper wire (RF GOST 16-705-492-2005) with the Cu content 99.93% coated with 2 μm of tin was used. For the experiment, 6 samples of nanopowder were produced at different values of the input energy into the wire and the arc stage energy. The input energy of electrical explosion and the arc stage energy were changed by regulating the voltage (U0) applied to the section of the exploded wire (l). The fabrication conditions of nanopowders are presented in Table 1. Wire electrical explosions were carried out in argon at pressure 1.5 · 105 Pa. The repetition frequency of explosions was 0.7 Hz. After passivation in argon with controlled air access, the samples were analyzed. The thermal analysis (derivatograph Q1000) was used to determine parameters of the chemical reactivity of the nanopowders. The average diameter of powder particles was measured using low temperature nitrogen adsorption (BET method). The energy input into the wire was calculated from the current oscillograms and the circuit electrical parameters of the circuit using a known technique [4].
Fig. 2. Typical derivatogram of nanopowder of Cu (Sn) (DTA and TG) at heating in air.
3. Results and discussion According to the experimental data, the average-surface diameter of the particles decreases when increasing the charge voltage (U0) and reaches its minimum 0.08 μm at charge voltage equal and more than 22 kV (Table 1). The phase composition of the powders was studied using an X-ray diffractometer DRON-3.0 with CuKα radiation. The Xray patterns showed the presence of reflections corresponding to the copper crystal phase that approximately coincides with the JCPDS data. The presence of copper oxide phases was found out: copper (II) oxide for all samples and copper (I) oxide for samples 2 and 3. No shift in reflex positions was observed, and no reflections of tin or Cu–Sn intermetallic compound were detected. The presence of the phase Cu2O reflexes can be concerned with a higher chemical reactivity of the particles of samples 2 and 3 during passivation. Perhaps, this contributed to the formation of the high-temperature phase of copper oxide Cu2O. The oxidation process at temperature up to 500 °C is characterized by two stages. This is preceded by a stage of desorption of sorbed gases and decomposition of unstable compounds that is typical for other nanopowders produced by WEE. The chemical reactivity of the samples of the powders Cu (Sn) was analyzed using a previously developed procedure [5] during heating in air. Fig. 2 shows a typical derivatogram for these powders. Sample 7 was produced from the preceding set of samples that were made of a copper wire without any additives. This is an analogue of sample 1 according to the fabrication parameters. The oxidation onset temperature (Ts) with a relative error ±2 °C was measured with the
Fig. 3. Dependence of the Fe and Sn contents in the surface and near-surface layers of nanopowder particles on the specific energy input into a wire (probing area 0.1 mm2).
Y.S. Kwon et al. / Materials Letters 62 (2008) 3143–3145
3145
due to competitive diffusion during cooling of liquid metal particles when scattering the explosion products.
4. Conclusion
Fig. 4. The Fe and Sn content in the surface and near-surface layers of single particles of different diameters depending on the energy input into the conductor.
Piloyan's method [6]. This temperature (Ts) is a test on the chemical and phase composition of the nanoparticle surface. For the samples produced at low input energy (samples 5 and 6), Ts is 15–20 °C higher than that for samples 1 and 2. The oxidation onset temperature of samples 1 and 2 is almost coincident with Ts of the copper sample without tin additive (sample 7). The analysis of the particles surface at the depth of ~ 5 nm was carried out by using XPS microanalysis on the scanning microscope Jeol-840 by means a built-in device “Link”. The following regularity is observed for a small probing area: when increasing W/Ws the tin content on the surface of the powder particles decreases from 0.81 to 0.005 wt.% (Fig. 3). At first, the Fe impurity content drops from 0.59 to 0.007 wt.%, and then it rises up to 0.89 wt.%. The minimum Fe content is at energy 1.37 W/Ws. It was previously found [7] that when exploding simultaneously wires of different metals, the surface and near-surface layers of powder nanoparticles are enriched with the volatile metal or the metal that has a lower atom diffusion coefficient near the crystallization point of the particles. This enrichment is explained by the phenomenon of stable diffusion during cooling of scattered wire explosion products that results in redistribution of elements in final products of electric explosion. At the same time, tin was not found during general probing of the samples (probing area 1.2 mm2). The Fe content varies from 0.005 to 0.85 wt.%. For some particles of the powder, the tin content in the surface and near-surface layers does not vary with the increase in the input energy W/Ws. The Fe content rises from 0.007 to 0.6 wt.%. (Fig. 4) when the energy increases from 0.82 to 1.86 W/Ws. The surface of the particles of approximately 1, 1–5 and 10 μm in diameter does not contain more than 0.009 wt.% of tin atoms. As explained previously [7], this is related to redistribution of elements
1. Depositing tin (~ 1 wt.%.) on the surface of a copper wire did not have a considerable effect on the relation between the sample dispersity and the input energy. The dispersity of the investigated samples almost agrees with that of the copper powders without tin. 2. According to the X-ray phase analysis, the CuO content decreases with the increase of the input energy (dispersity). For the maximal dispersity samples (1 and 3), the formation of high-temperature oxide Cu2O is observed. The main phase in the powders is crystallized copper reflexes in the Xray patterns coincide with the reference (JCPDS card index). 3. With the decrease in the input energy, the oxidation onset temperature of Cu (Sn) nanopowders increases by ~ 20 °C during heating in contrast to the copper nanopowders without additives. 4. The experiments showed that the temperature after the end of heat evolution is the same for the entire set of samples. This coincides with the temperature of the end of heat evolution for the copper nanopowder without additives and equals 500 °C. It is worth to note that the minimum mass gain is observed for sample 1 during oxidation. The sample was produced at the maximum input energy. The only reactivity parameter that is symbate to the value of the input energy is the oxidation rate of powder samples. 5. With the increase of the input energy, the tin content in surface and near-surface layers of nanoparticles decreases sharply within 1.1–1.3 W/Ws. According to the microanalysis, the Fe impurity content decreases at 1.37 W/Ws and then increases up to 0.89 wt.% (sample 1) with the increase of the input energy. References [1] Yu. M. Lahtin, V.P. Leontyeva, Materiology, Mechanical engineering, Moscow, 1980. [2] I.V. Frishberg, L.V. Zolotuhina, V.V. Harlamov, MiTOM 7 (2000) 21–23. [3] A.P. Lyashko, G.G. Savel'ev, D.V. Tikhonov, FHOM 6 (1992) 127–130. [4] I.F. Kvartshava, V.V. Bondarenko, A.A. Pljutto, A.A. Chernov, ZTF 31 (5(2)) (1956) 745–751. [5] A.P. Ilyin, A.A. Gromov, G.V. Yablunovsky, FGV 37 (4) (2001) 58–62. [6] Ya. Shestak, The Theory of the Thermal Analysis, World, Moscow, 1987. [7] D.V. Tikhonov, Electroexplosive Production of Nanopowders of Complex Composition. A thesis for a degree of candidate of technical sciences. Tomsk Polytechnic University 2000.