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Properties of powders produced by electrical explosions of copper–nickel alloy wires
Materials Letters 61 (2007) 3247 – 3250 www.elsevier.com/locate/matlet
Properties of powders produced by electrical explosions of copper–nickel alloy wires Y.S. Kwon a , V.V. An b , A.P. Ilyin b , D.V. Tikhonov b,⁎ a
Research Center for Machine Parts and Materials Processing, University of Ulsan, Republic of Korea b High Voltage Research Institute at Tomsk Polytechnic University, Russian Federation Received 1 June 2006; accepted 10 November 2006 Available online 29 November 2006
Abstract The phase and element compositions of surface and near-surface layers of particles in powders produced in gaseous argon by electric explosion of Cu–Ni alloy wires were studied. It was established that powders produced from Cu–Ni alloys are phase heterogeneous. Their size distribution function is three-modal. Their dispersivity increases with the increase of the energy input into a conductor. The principal phase stabilizing in electroexplosion end-products from alloys Cu–Ni23 and Cu–Ni45 is intermetallic compound Cu0.81Ni0.19. Apparently, the metal phases of copper or nickel are located in the central areas of the particles. A mechanism of particle formation during electrical explosion of wires was proposed. © 2006 Elsevier B.V. All rights reserved. Keywords: Electrical explosion of wires; Cu–Ni alloy; Surface layers; Particles
1. Introduction Electrical explosion of wires (EEW) is a promising method for producing a number of materials with new properties [1]. The key factor of the electroexplosive method of producing nanopowders (NP) lies in wire fast dispersion (t ∼ 1–3 μs) by a powerful electric current pulse. The process is characterized by a high current density ( j > 1010 À/m2) and fast metal heating (∼ 1010 K/s) up to high temperatures (T > 104 K) [2]. Previously, the morphology, phase composition and oxidation dynamics of powders produced by electrical explosions of brass wires were studied. The brass alloy consisted of copper and more fusible zinc [3]. It was found that particles of these powders are phase-inhomogeneous. The surface of the particles is coated with zinc oxide. The increase of the energy input into the wire is accompanied by an increase in the dispersivity of the powders and in the initial α-phase zinc-depletion. Thus, the surface of the particles produced during explosions of brass wires is enriched in the more low-melting and more fugitive component zinc. In this work, experimental results characteriz⁎ Corresponding author. E-mail address: [email protected] (D.V. Tikhonov). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.11.047
ing powders produced from Cu–Ni alloys are presented. Such alloys are widely used for various applications: settings, coins, corrosion-proof pieces of sea crafts, and tribotechnics. Nickel is a more refractory component (T = 1453 °C) in comparison with copper (T = 1083 °C). Much experimental work on the mechanisms of wire destruction during EEW and on formation of nanopowder particles is known [2,4,7]. At the same time, there is no agreement on the mechanisms of formation of the particles. The purpose of the present work was to study the formation of the disperse composition of powders. The work was also aimed at determining the phase formation and redistribution of Cu and Ni atoms between the surface and volume of the particles during dispersion and cooling of electrical explosion products. 2. Experimental procedure Cu–Ni alloy (6, 12, 23 and 45 wt.% Ni) wires of 0.3 mm in diameter were used. Explosions were carried out in argon at a pressure 1.5 · 105 Pa using the experimental setup shown schematically in Fig. 1. The setup was vacuumized up to 100–200 Pa, before it was filled. One of the main parameters
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Fig. 1. Structural scheme of the experimental setup. 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.
influencing the properties of the produced nanopowder is the specific energy input into the wire W/Ws [4] (where W is the energy input into the wire, Ws is the sublimation energy of the wire). The energy input into the wire was calculated from oscillograms of current and electrical parameters of the circuit using a known technique [5]. The energy input into the conductor was experimentally adjusted by varying the voltage of the capacitive storage. In other cases, powder samples were prepared at the same charge voltage, whereas the content of Cu–Ni alloy components was varied. The powder settled in a special collector and passivated in an oxygen-controlled argon atmosphere, and then was analyzed. An X-ray diffractometer DRON-3.0 was used to determine the phase composition of the powders. The element composition of the particle surface was studied by X-ray photoelectric spectroscopy (XRS) using a scanning microscope JSM-840 (Jeol). The average particle diameter was determined by nitrogen low-temperature adsorption (BET method). Particle-size distribution functions were plotted by converting data obtained from an analyzer Mastersizer 2000 (Malvern). 3. Results and discussion According to the experimental data (Fig. 2), the powders are polydisperse and the particles have a spherical form. In given experiments, all EEW products were analyzed, unlike in previous studies where only individual fractions were tested [6,8]. It should be noted that
Fig. 2. SEM photograph of nanopowder produced from alloy Cu–Ni23.
Fig. 3. Scheme of the scattering of EEW products. 1 — High voltage electrode; 2 — grounded electrode; 3 — wire feeding mechanism; 4 — roll with wire; 5 — wire position.
the full particle diameter distribution is three-modal due to a wire destruction mechanism and to subsequent cooling of the initial EEW products. Primarily the conductor is split into a gaseous phase and overheated metal droplets (Fig. 3). In the first stage of scattering, the gaseous phase moves away from the axis of the conductor faster than the droplets. Physically, this process represents a flow of droplets of an overheated liquid in a gaseous stream. At the time evaporation of metal from the surface of the droplets, cooling of both the droplets and the gaseous phase occurs. The formation of the droplets is connected to a breakage of chemical bonds between atoms of metals and is accompanied by an electron thermoemission. As a result, the droplets are positively charged, whereas the gaseous phase is negatively charged. Since the gaseous phase is a less dense medium, it is decelerated faster. Therefore, the droplets catch up and penetrate the gaseous phase during further scattering. Processes of relaxation and temperature pull down of both constituents occur, so that the second flow of the droplets by gaseous products occurs at lower temperatures. At that time, the formation of particles occurs both by condensation of the gaseous phase on the surface of the liquid droplets and by condensation on nuclei in the gaseous phase (Fig. 4). Particles of 0.3–1.0 μm in diameter and the finest particles of 0.1–0.15 μm in diameter, respectively, are formed due to these processes. The formation of large spherical particles (diameter 1–10 μm) is related to a so-called end-effect: destruction of the conductor ends at lower current density [9]. Thus, a three-modal particle-size distribution is obtained during electrical explosion of wires. The increase of the specific energy W/Wc input into conductors is accompanied by an increase of the powder dispersivity (Table 1). In such a way, the dispersivity of the powder produced from alloy Cu–Ni45 increases a little bit faster than that of the powder produced from Cu–Ni23 alloy. When increasing W/Wc from 0.9 up to 1.8, the specific surface area increases from 2.9 m2/g up to 5.6 m2/g and up to 6.7 m2/g for the EEW products of Cu–Ni23 and Cu–Ni45 alloys, respectively. This can be explained by the higher Ni content in Cu–Ni45 compared to Cu–Ni23 and by the higher melting temperature of nickel in contrast with that of copper. It is well-known that the increase of metal melting temperature leads to a higher dispersivity of EEW
Fig. 4. Scheme of the formation of the particles by condensation of the gas phase on metal droplets (1) and by condensation on the charged centers (2).
Y.S. Kwon et al. / Materials Letters 61 (2007) 3247–3250 Table 1 Specific surface area of Cu–Ni(23) and Cu–Ni(45) alloy powders as a function of the specific energy input into the conductor
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Table 3 Dependence of deflection of Ni content in the surface and near-surface layers of the particles from a value specific energy input into the wire (XRD data)
Alloy
W/Ws
ãs, m2/g
Alloy
W/Ws
Δ[Ni], %
Cu–Ni23%
0.90 1.20 1.47 1.70 1.80 0.87 1.11 1.34 1.52 1.76
2.9 3.5 4.2 4.6 5.6 2.9 3.2 4.7 5.7 6.3
Cu–Ni23%
0.90 1.20 1.47 1.70 1.80 0.87 1.11 1.34 1.52 1.76
6.1 3.0 4.3 3.5 2.7 −4.8 −5.3 −4.3 −3.2 −1.4
Cu–Ni45%
products [10]. At the same energy input into the wire, the higher dispersivity is characterized for a nanopowder produced from the more refractory metal. When cooling EEW products, the particles of refractory metal pass faster into the solid state, and their liquid-droplet coalescence ends. The alloy components were previously found to be redistributed between the surface layers and the volume of the particles [3,11,12]. The degree of redistribution depends on the specific energy input into the conductor. In the case of tin–lead alloy, the surface and near-surface layers of the particles are enriched in the more refractory component — lead [11]. For the Cu–Ni alloys, a multidirectional redistribution of initial components (Table 2) is observed. The Cu–Ni6 and Cu–Ni12 alloys are enriched in nickel from the surface and near-surface layers of the particles. At the same time, the particles of Cu–Ni23 and Cu–Ni45 alloys are depleted in nickel. When increasing the specific energy input into conductors from Cu–Ni23 and Cu–Ni45 alloys, the element composition of the surface and near-surface layers of the particles for both alloys tends to the initial composition of the conductors (Table 3). According to the XRD analysis of the powders, the observed reflexions correspond to the Cu0.81Ni0.19 phase [13], whereas copper and nickel reflexions were not detected. Those phases of solid substances are mainly stabilized in EEW end-products that possess a lower X-ray density [12], i.e., the lattice parameter is increased. When cooling the nanoparticles, crystalline phases stabilize with the maximal lattice parameter, e.g., gamma-iron forms during electrical explosions of iron wires. If metal does not possess polymorphism, the lattice is characterized by static displacements of atoms with regard to the equilibrium state. Stabilization of the phases with a lower X-ray density is caused by a stretching effect occurring during the cooling of the particles and by the primary crystallization of the surface and nearsurface layers. Stabilization of solid phases with lower X-ray densities becomes energetically more favorable. There are two intermetallic compounds in the Cu–Ni system: Cu0.81Ni0.19 and Cu3.8Ni. However, only the Cu0.81Ni0.19 phase is stabilized in the EEW end-products. This is probably connected to the lower X-ray density of this phase. Table 2 Deviation of the Ni content in surface and near-surface layers of particles from that of initial conductors according to XPS data Alloy
Δ[NI], %
Cu–Ni6 Cu–Ni12 Cu–Ni23 Cu–Ni45
7.42 4.65 −0.88 −7.30
For alloys Cu–Ni6 and Cu–Ni12, W/Ws =0.9; Cu–Ni23 — 2.3 W/Ws; Cu–Ni45 — 0.7 W/Ws).
Cu–Ni45%
Comparing the XRD data of the powders with the element composition data of the surface and near-surface layers of the particles, one can assume that intermetallic compound Cu0.81Ni0.19 is predominantly concentrated in the surface and near-surface layers of the particles. Copper and nickel, which were not part to the intermetallide structure, are predominantly concentrated in the central areas of the particles. Such arrangement of metal phases and their shielding by an intermetallic compound allows the explanation of the absence of copper and nickel reflexions in the X-ray pattern.
4. Conclusions 1. With increasing energy input into the conductor, the ratio between copper and nickel in the surface and near-surface layers of the particles tends towards that in the initial conductor. 2. According to the XRD data, the principal phase stabilized in the end-products of electrical explosion of conductors from alloys Cu–Ni23 and Cu–Ni45 is the intermetallic compound Cu0.81Ni0.19 and, apparently, the copper or nickel phases located in the central areas of the particles. 3. With the increase of the specific energy input into the conductor, the dispersivity of the powders from Cu–Ni45 alloy increases faster than that of powders from Cu–Ni23 alloy. It can be explained by the different nickel contents of the alloys. 4. Irrespective of the Ni content in Cu–Ni alloys in the studied range of Ni concentrations (6–45 wt.%), the intermetallic compound Cu0.81Ni0.19, which has apparently a lower X-ray density, is formed on the surface of the particles. References [1] I.D. Morokhov, Physics and Chemistry of Ultradispersed Systems, Science, Moscow, 1987, pp. 5–9. [2] V.A. Burtsev, N.V. Kalinin, A.V. Luchinskii, Electric Explosion of Conductors and its Application in Electrophysical Plants, Energoatomizdat, Moscow, 1990. [3] A.P. Lyashko, G.G. Savel'ev, D.V. Tikhonov, Morphology, phase composition and oxidation of powders produced by electrical explosion of brass wires, Phizika i khimia obrabotki materialov (Physics and Chemistry of Materials Processing) (6) (1992) 127–130. [4] M.I. Lerner, Control over formation of highly dispersed particles under conditions of electrical explosion of conductors. A thesis for a degree of candidate of technical sciences. Tomsk Polytechnic Institute (1988). [5] I.F. Kvartshava, V.V. Bondarenko, A.A. Pljutto, et al., Oscillogram calculation of energy of electrical explosion of wires, Zh. tekh. fiz. 31 (5) (1956) 745–751.
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[6] Yu.A. Kotov, N.A. Yavorovsky, Study of the particles formed during electrical explosion of conductors, Phizika i khimiya obrabotki materialov (Physics and chemistry of material processing) (4) (1978) 24–29. [7] M.M. Martynyuk, Role of vaporization and boiling of liquid metal during electrical explosion of wires, Zh. tekh. fiz. 4 (6) (1974) 1262–1270. [8] Yu.F. Ivanov, M.N. Osmonoliev, V.S. Sedoi, Production of ultra-fine powders and their use in high energetic compositions, Propellants Explos. Pyrotech. 28 (6) (2003) 319–333. [9] V.M. Volkov, I.A. Shaykevich, Studying of configuration end-effect of wire electric explosion, Izv. vuzov. Fizika (News of Higher Education. Physics) (7(158)) (1975) 138–139. [10] I. Hiroshi, M. Umakoashi, Preparation of fine metallic and ceramic particles by the wire explosion method, Funsai Micrometrics (37) (1993) 124–135.
[11] A.P. Ilyin, D.V. Tikhonov, Morphology, phase and chemical composition of powders produced by electrical explosion of conductors from tin–lead alloy, Phizika i khimia obrabotki materialov (Physics and Chemistry of Materials Processing) (3) (2001) 68–71. [12] D.V. Tikhonov, Electroexplosive production of nanopowders of complex composition. A thesis for a degree of candidate of technical sciences, Tomsk Polytechnic University, 2000. [13] JCPDS-International Centre for Diffraction Data, PCPDFWIN version 1.30, 1997.
Properties of powders produced by electrical explosions of copper–nickel alloy wires Y.S. Kwon a , V.V. An b , A.P. Ilyin b , D.V. Tikhonov b,⁎ a
Research Center for Machine Parts and Materials Processing, University of Ulsan, Republic of Korea b High Voltage Research Institute at Tomsk Polytechnic University, Russian Federation Received 1 June 2006; accepted 10 November 2006 Available online 29 November 2006
Abstract The phase and element compositions of surface and near-surface layers of particles in powders produced in gaseous argon by electric explosion of Cu–Ni alloy wires were studied. It was established that powders produced from Cu–Ni alloys are phase heterogeneous. Their size distribution function is three-modal. Their dispersivity increases with the increase of the energy input into a conductor. The principal phase stabilizing in electroexplosion end-products from alloys Cu–Ni23 and Cu–Ni45 is intermetallic compound Cu0.81Ni0.19. Apparently, the metal phases of copper or nickel are located in the central areas of the particles. A mechanism of particle formation during electrical explosion of wires was proposed. © 2006 Elsevier B.V. All rights reserved. Keywords: Electrical explosion of wires; Cu–Ni alloy; Surface layers; Particles
1. Introduction Electrical explosion of wires (EEW) is a promising method for producing a number of materials with new properties [1]. The key factor of the electroexplosive method of producing nanopowders (NP) lies in wire fast dispersion (t ∼ 1–3 μs) by a powerful electric current pulse. The process is characterized by a high current density ( j > 1010 À/m2) and fast metal heating (∼ 1010 K/s) up to high temperatures (T > 104 K) [2]. Previously, the morphology, phase composition and oxidation dynamics of powders produced by electrical explosions of brass wires were studied. The brass alloy consisted of copper and more fusible zinc [3]. It was found that particles of these powders are phase-inhomogeneous. The surface of the particles is coated with zinc oxide. The increase of the energy input into the wire is accompanied by an increase in the dispersivity of the powders and in the initial α-phase zinc-depletion. Thus, the surface of the particles produced during explosions of brass wires is enriched in the more low-melting and more fugitive component zinc. In this work, experimental results characteriz⁎ Corresponding author. E-mail address: [email protected] (D.V. Tikhonov). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.11.047
ing powders produced from Cu–Ni alloys are presented. Such alloys are widely used for various applications: settings, coins, corrosion-proof pieces of sea crafts, and tribotechnics. Nickel is a more refractory component (T = 1453 °C) in comparison with copper (T = 1083 °C). Much experimental work on the mechanisms of wire destruction during EEW and on formation of nanopowder particles is known [2,4,7]. At the same time, there is no agreement on the mechanisms of formation of the particles. The purpose of the present work was to study the formation of the disperse composition of powders. The work was also aimed at determining the phase formation and redistribution of Cu and Ni atoms between the surface and volume of the particles during dispersion and cooling of electrical explosion products. 2. Experimental procedure Cu–Ni alloy (6, 12, 23 and 45 wt.% Ni) wires of 0.3 mm in diameter were used. Explosions were carried out in argon at a pressure 1.5 · 105 Pa using the experimental setup shown schematically in Fig. 1. The setup was vacuumized up to 100–200 Pa, before it was filled. One of the main parameters
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Y.S. Kwon et al. / Materials Letters 61 (2007) 3247–3250
Fig. 1. Structural scheme of the experimental setup. 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.
influencing the properties of the produced nanopowder is the specific energy input into the wire W/Ws [4] (where W is the energy input into the wire, Ws is the sublimation energy of the wire). The energy input into the wire was calculated from oscillograms of current and electrical parameters of the circuit using a known technique [5]. The energy input into the conductor was experimentally adjusted by varying the voltage of the capacitive storage. In other cases, powder samples were prepared at the same charge voltage, whereas the content of Cu–Ni alloy components was varied. The powder settled in a special collector and passivated in an oxygen-controlled argon atmosphere, and then was analyzed. An X-ray diffractometer DRON-3.0 was used to determine the phase composition of the powders. The element composition of the particle surface was studied by X-ray photoelectric spectroscopy (XRS) using a scanning microscope JSM-840 (Jeol). The average particle diameter was determined by nitrogen low-temperature adsorption (BET method). Particle-size distribution functions were plotted by converting data obtained from an analyzer Mastersizer 2000 (Malvern). 3. Results and discussion According to the experimental data (Fig. 2), the powders are polydisperse and the particles have a spherical form. In given experiments, all EEW products were analyzed, unlike in previous studies where only individual fractions were tested [6,8]. It should be noted that
Fig. 2. SEM photograph of nanopowder produced from alloy Cu–Ni23.
Fig. 3. Scheme of the scattering of EEW products. 1 — High voltage electrode; 2 — grounded electrode; 3 — wire feeding mechanism; 4 — roll with wire; 5 — wire position.
the full particle diameter distribution is three-modal due to a wire destruction mechanism and to subsequent cooling of the initial EEW products. Primarily the conductor is split into a gaseous phase and overheated metal droplets (Fig. 3). In the first stage of scattering, the gaseous phase moves away from the axis of the conductor faster than the droplets. Physically, this process represents a flow of droplets of an overheated liquid in a gaseous stream. At the time evaporation of metal from the surface of the droplets, cooling of both the droplets and the gaseous phase occurs. The formation of the droplets is connected to a breakage of chemical bonds between atoms of metals and is accompanied by an electron thermoemission. As a result, the droplets are positively charged, whereas the gaseous phase is negatively charged. Since the gaseous phase is a less dense medium, it is decelerated faster. Therefore, the droplets catch up and penetrate the gaseous phase during further scattering. Processes of relaxation and temperature pull down of both constituents occur, so that the second flow of the droplets by gaseous products occurs at lower temperatures. At that time, the formation of particles occurs both by condensation of the gaseous phase on the surface of the liquid droplets and by condensation on nuclei in the gaseous phase (Fig. 4). Particles of 0.3–1.0 μm in diameter and the finest particles of 0.1–0.15 μm in diameter, respectively, are formed due to these processes. The formation of large spherical particles (diameter 1–10 μm) is related to a so-called end-effect: destruction of the conductor ends at lower current density [9]. Thus, a three-modal particle-size distribution is obtained during electrical explosion of wires. The increase of the specific energy W/Wc input into conductors is accompanied by an increase of the powder dispersivity (Table 1). In such a way, the dispersivity of the powder produced from alloy Cu–Ni45 increases a little bit faster than that of the powder produced from Cu–Ni23 alloy. When increasing W/Wc from 0.9 up to 1.8, the specific surface area increases from 2.9 m2/g up to 5.6 m2/g and up to 6.7 m2/g for the EEW products of Cu–Ni23 and Cu–Ni45 alloys, respectively. This can be explained by the higher Ni content in Cu–Ni45 compared to Cu–Ni23 and by the higher melting temperature of nickel in contrast with that of copper. It is well-known that the increase of metal melting temperature leads to a higher dispersivity of EEW
Fig. 4. Scheme of the formation of the particles by condensation of the gas phase on metal droplets (1) and by condensation on the charged centers (2).
Y.S. Kwon et al. / Materials Letters 61 (2007) 3247–3250 Table 1 Specific surface area of Cu–Ni(23) and Cu–Ni(45) alloy powders as a function of the specific energy input into the conductor
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Table 3 Dependence of deflection of Ni content in the surface and near-surface layers of the particles from a value specific energy input into the wire (XRD data)
Alloy
W/Ws
ãs, m2/g
Alloy
W/Ws
Δ[Ni], %
Cu–Ni23%
0.90 1.20 1.47 1.70 1.80 0.87 1.11 1.34 1.52 1.76
2.9 3.5 4.2 4.6 5.6 2.9 3.2 4.7 5.7 6.3
Cu–Ni23%
0.90 1.20 1.47 1.70 1.80 0.87 1.11 1.34 1.52 1.76
6.1 3.0 4.3 3.5 2.7 −4.8 −5.3 −4.3 −3.2 −1.4
Cu–Ni45%
products [10]. At the same energy input into the wire, the higher dispersivity is characterized for a nanopowder produced from the more refractory metal. When cooling EEW products, the particles of refractory metal pass faster into the solid state, and their liquid-droplet coalescence ends. The alloy components were previously found to be redistributed between the surface layers and the volume of the particles [3,11,12]. The degree of redistribution depends on the specific energy input into the conductor. In the case of tin–lead alloy, the surface and near-surface layers of the particles are enriched in the more refractory component — lead [11]. For the Cu–Ni alloys, a multidirectional redistribution of initial components (Table 2) is observed. The Cu–Ni6 and Cu–Ni12 alloys are enriched in nickel from the surface and near-surface layers of the particles. At the same time, the particles of Cu–Ni23 and Cu–Ni45 alloys are depleted in nickel. When increasing the specific energy input into conductors from Cu–Ni23 and Cu–Ni45 alloys, the element composition of the surface and near-surface layers of the particles for both alloys tends to the initial composition of the conductors (Table 3). According to the XRD analysis of the powders, the observed reflexions correspond to the Cu0.81Ni0.19 phase [13], whereas copper and nickel reflexions were not detected. Those phases of solid substances are mainly stabilized in EEW end-products that possess a lower X-ray density [12], i.e., the lattice parameter is increased. When cooling the nanoparticles, crystalline phases stabilize with the maximal lattice parameter, e.g., gamma-iron forms during electrical explosions of iron wires. If metal does not possess polymorphism, the lattice is characterized by static displacements of atoms with regard to the equilibrium state. Stabilization of the phases with a lower X-ray density is caused by a stretching effect occurring during the cooling of the particles and by the primary crystallization of the surface and nearsurface layers. Stabilization of solid phases with lower X-ray densities becomes energetically more favorable. There are two intermetallic compounds in the Cu–Ni system: Cu0.81Ni0.19 and Cu3.8Ni. However, only the Cu0.81Ni0.19 phase is stabilized in the EEW end-products. This is probably connected to the lower X-ray density of this phase. Table 2 Deviation of the Ni content in surface and near-surface layers of particles from that of initial conductors according to XPS data Alloy
Δ[NI], %
Cu–Ni6 Cu–Ni12 Cu–Ni23 Cu–Ni45
7.42 4.65 −0.88 −7.30
For alloys Cu–Ni6 and Cu–Ni12, W/Ws =0.9; Cu–Ni23 — 2.3 W/Ws; Cu–Ni45 — 0.7 W/Ws).
Cu–Ni45%
Comparing the XRD data of the powders with the element composition data of the surface and near-surface layers of the particles, one can assume that intermetallic compound Cu0.81Ni0.19 is predominantly concentrated in the surface and near-surface layers of the particles. Copper and nickel, which were not part to the intermetallide structure, are predominantly concentrated in the central areas of the particles. Such arrangement of metal phases and their shielding by an intermetallic compound allows the explanation of the absence of copper and nickel reflexions in the X-ray pattern.
4. Conclusions 1. With increasing energy input into the conductor, the ratio between copper and nickel in the surface and near-surface layers of the particles tends towards that in the initial conductor. 2. According to the XRD data, the principal phase stabilized in the end-products of electrical explosion of conductors from alloys Cu–Ni23 and Cu–Ni45 is the intermetallic compound Cu0.81Ni0.19 and, apparently, the copper or nickel phases located in the central areas of the particles. 3. With the increase of the specific energy input into the conductor, the dispersivity of the powders from Cu–Ni45 alloy increases faster than that of powders from Cu–Ni23 alloy. It can be explained by the different nickel contents of the alloys. 4. Irrespective of the Ni content in Cu–Ni alloys in the studied range of Ni concentrations (6–45 wt.%), the intermetallic compound Cu0.81Ni0.19, which has apparently a lower X-ray density, is formed on the surface of the particles. References [1] I.D. Morokhov, Physics and Chemistry of Ultradispersed Systems, Science, Moscow, 1987, pp. 5–9. [2] V.A. Burtsev, N.V. Kalinin, A.V. Luchinskii, Electric Explosion of Conductors and its Application in Electrophysical Plants, Energoatomizdat, Moscow, 1990. [3] A.P. Lyashko, G.G. Savel'ev, D.V. Tikhonov, Morphology, phase composition and oxidation of powders produced by electrical explosion of brass wires, Phizika i khimia obrabotki materialov (Physics and Chemistry of Materials Processing) (6) (1992) 127–130. [4] M.I. Lerner, Control over formation of highly dispersed particles under conditions of electrical explosion of conductors. A thesis for a degree of candidate of technical sciences. Tomsk Polytechnic Institute (1988). [5] I.F. Kvartshava, V.V. Bondarenko, A.A. Pljutto, et al., Oscillogram calculation of energy of electrical explosion of wires, Zh. tekh. fiz. 31 (5) (1956) 745–751.
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[6] Yu.A. Kotov, N.A. Yavorovsky, Study of the particles formed during electrical explosion of conductors, Phizika i khimiya obrabotki materialov (Physics and chemistry of material processing) (4) (1978) 24–29. [7] M.M. Martynyuk, Role of vaporization and boiling of liquid metal during electrical explosion of wires, Zh. tekh. fiz. 4 (6) (1974) 1262–1270. [8] Yu.F. Ivanov, M.N. Osmonoliev, V.S. Sedoi, Production of ultra-fine powders and their use in high energetic compositions, Propellants Explos. Pyrotech. 28 (6) (2003) 319–333. [9] V.M. Volkov, I.A. Shaykevich, Studying of configuration end-effect of wire electric explosion, Izv. vuzov. Fizika (News of Higher Education. Physics) (7(158)) (1975) 138–139. [10] I. Hiroshi, M. Umakoashi, Preparation of fine metallic and ceramic particles by the wire explosion method, Funsai Micrometrics (37) (1993) 124–135.
[11] A.P. Ilyin, D.V. Tikhonov, Morphology, phase and chemical composition of powders produced by electrical explosion of conductors from tin–lead alloy, Phizika i khimia obrabotki materialov (Physics and Chemistry of Materials Processing) (3) (2001) 68–71. [12] D.V. Tikhonov, Electroexplosive production of nanopowders of complex composition. A thesis for a degree of candidate of technical sciences, Tomsk Polytechnic University, 2000. [13] JCPDS-International Centre for Diffraction Data, PCPDFWIN version 1.30, 1997.