Solution plasma synthesis of bimetallic nanoparticles

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Mar 12, 2015 - Genki Saito1, Yuki Nakasugi1, Toru Yamashita2 and Tomohiro ... 2 Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan.

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Solution plasma synthesis of bimetallic nanoparticles

This content has been downloaded from IOPscience. Please scroll down to see the full text. 2014 Nanotechnology 25 135603 (http://iopscience.iop.org/0957-4484/25/13/135603) View the table of contents for this issue, or go to the journal homepage for more

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Nanotechnology Nanotechnology 25 (2014) 135603 (7pp)

doi:10.1088/0957-4484/25/13/135603

Solution plasma synthesis of bimetallic nanoparticles Genki Saito1 , Yuki Nakasugi1 , Toru Yamashita2 and Tomohiro Akiyama1 1

Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo 060-8628, Japan 2 Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan E-mail: [email protected] Received 28 November 2013, revised 25 January 2014 Accepted for publication 3 February 2014 Published 4 March 2014

Abstract

This paper describes the facile solution plasma synthesis of bimetallic nanoparticles, including solid solution alloys (Ni–Cu and Ni–Cr system), eutectic alloys of Sn–Pb, and intermetallic alloys (SnSb and Ni3 Sn), by using metallic alloy wire as the cathode and Pt wire as the anode. In the typical process, the cathode was melted by the local-concentration of current, upon applying a DC voltage between the two electrodes immersed in the electrolyte. The solid solution alloys of Ni–Cu and Ni–Cr prepared in this study have a uniform distribution of composition. On the other hand, the uniformity in the composition of the eutectic Sn–Pb alloy depends on the microstructure of the electrode. The use of quenched electrode with small crystal grains favors the formation of Sn–Pb alloy nanoparticles, in which the Sn-rich and Pb-rich phases coexist in each particle. The formation of intermetallic SnSb and Ni3 Sn alloy nanoparticles is accompanied by the formation of colloidal oxide. These results demonstrate that the solution plasma technique is applicable not only for the synthesis of pure metals but can also be used for the synthesis of various alloy nanoparticles. Keywords: alloy nanoparticle, solid solution alloys, eutectic, intermetallic, solution plasma, solder, bimetallic nanoparticles, nanoalloy (Some figures may appear in colour only in the online journal)

1. Introduction

used as solders. Lately, studies have reported the formation of Sn–Pb and Sn–Bi nanoparticles embedded in Al matrix [8, 9]. Furthermore, nanoparticles of intermetallic compounds such as SnSb, Cu6 Sn5 , and Ni3 Sn4 have been reported to increase the energy density of Li ion batteries [10, 11]. For such applications, SnSb alloy nanoparticles have been synthesized via co-precipitation [12, 13], high-energy ball milling [11, 14] and mixing melt-spun [15]. In the past decade, laser irradiation [16–18], microwave [19, 20], and plasma [21–29] in solution have been extensively used for the synthesis of nanoparticles. These methods offer the following advantages: (1) use of simple equipment without the stringent need of vacuum chamber, (2) no requirement of gas supply, (3) use of readily available precursors, (4) facile separation of the products in solution. To this end, several reports have demonstrated the use of plasma and microwave methods to synthesize various metallic nanoparticles, includ-

Bimetallic alloy nanoparticles have attracted increased attention because of their novel and complex properties, which are distinct from those of the pure elemental nanoparticles and bulk alloys [1]. Depending on the solubility or miscibility of atoms in the solid state, alloys may be solid solution, eutectic alloy, and intermetallic alloy. Among the various solid solutions, Ni–Cu nanocrystal is an attractive material that is being extensively used as a catalyst in fuel cells [2], glucose sensors [3], and magnetic materials [4]. Thus far, Ni–Cu nanoparticles have been synthesized via hydrothermal reaction [2], hydrazine reduction [5], polymeric precursor method [4], microemulsion method [6], and chemical vapor deposition [7] using metallic chloride [2, 4–6], sulfate [6], and acetylacetonate [7] as precursors. Meanwhile, Sn-based eutectic alloys such as Sn–Pb, Sn–Bi, and Sn–Zn, are being 0957-4484/14/135603+07$33.00

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Nanotechnology 25 (2014) 135603

G Saito et al

ing Au [22, 23], Ag [19] and Pt [19], from the metal ions in solution. Typically, metallic rods, plates, and powders have been used as the starting materials for the synthesis of Au [20, 21, 24], Ag [24], Ni [21, 25, 26] nanoparticles via solution plasma method. In addition, alloy nanoparticles have also been synthesized using this method. For example, solid solution alloy of Pt–Au nanoparticles have been synthesized from H2 PtCl6 , NaAuCl4 , and HClO4 solutions [27]. Similarly, FePt intermetallic nanoparticles were synthesized in molten LiCl–KCl–CsCl electrolyte containing metallic ions of Fe and Pt [28]. Pootawang et al reported the formation of Ag/Pt bimetallic nanocomposites via electrode erosion, taking advantage of the effects of electric arc at the cathode (Ag rod) and sputtering at the anode (Pt rod) [29]. Furthermore, Zhang et al demonstrated the synthesis of Ag–Au alloy nanoparticles in solution by laser irradiation of a metal powder suspension [18]. However, to the best of our knowledge, synthesis of nanoparticles using alloy electrode as a raw material has not been reported in the literature. Herein, we have investigated the synthesis of alloy nanoparticles from alloy electrode of solid solution alloy, eutectic alloy, and intermetallic compound. In the case of eutectic alloy, we have also analyzed the effect of the crystal grain size of the electrode on the morphology of the synthesized nanoparticles.

Figure 1. Schematic diagram of the plasma electrolysis apparatus

used for the experimental synthesis of nanoparticles. The cathode was an alloy wire or stick, in which an exposed portion acted as an electrode, whereas the anode was formed from a platinum wire that was bent into a half-round mesh. The distance between both electrodes was kept at 30 mm, as shown in the corresponding cubic diagram.

a surface area that was 50 times larger than that of the cathode. The distance between the two electrodes was maintained at 30 mm. The plasma was generated around the cathode by applying an appropriate voltage using a direct-current (DC) power supply (ZX800H, Takasago). We have previously reported the production of metallic Ni nanoparticles using a 0.1 M NaOH solution [25]. Therefore, in the case of the Ni-based solid solution alloy, 0.1 M NaOH was used as the electrolyte with an applied voltage of 160 V. On the other hand, in the case of the Sn–based eutectic or intermetallic alloy, a 0.1 M KCl electrolyte solution and an applied voltage of 150 V were used, as Sn readily dissolves in alkaline solutions. The temperature of the solution was recorded every 5 s at the position 10 mm below the surface by using a polymer-coated thermistor thermometer (Ondotori TR-71Ui, T&D). The current and voltage were recorded every 2 s using a DC power supply. The alloys synthesized in this study were observed by using scanning transmission electron microscope (STEM, HD-2000, Hitachi High-Technologies) and field-emission scanning electron microscope (FE-SEM, JSM-7010FA, JEOL). The composition of the alloys was determined by energy dispersive x-ray analysis (EDX) using the genesis microanalysis system (EDAX) attached to the STEM. In addition, the alloys were further characterized by x-ray diffraction (XRD) using Miniflex II (Rigaku) diffractometer.

2. Experimental details 2.1. Materials and methods

In the case of solid solution alloy, metallic wires of Cu–43%Ni constantan wire (Ni 42.6 wt%, Cu 56.6 wt%, Mn 0.8 wt%), Cu– 66%Ni monel wire (Ni 66.3 wt%, Cu 31.3 wt%, Fe 1.5 wt%, Mn 0.9 wt%), Ni–21%Cr nichrome wire (Cr 20.6 wt%, Ni 78.3 wt%, Si 1.1 wt%), and Ni–9%Cr chromel wire (Cr 8.9 wt%, Ni 91.1 wt%) of diameter 1.0 mm were used as the raw materials for the synthesis of nanoparticles. For eutectic alloy nanoparticles, Sn–35%Pb tin–lead solder (Pb 35 wt%, Sn 65 wt%), Bi–30%Sn alloy (Sn 30 wt%, Bi 70 wt%), and Sn–25%Zn alloy were used as raw materials. The Sn–25%Zn alloy was prepared by mixing pre-determined quantities of pure Sn and Zn. Furthermore, we investigated the effect of crystal grain size of the electrode on the properties of the synthesized nanoparticles. For this, Sn–35%Pb, Bi–30%Sn, and Sn–25%Zn alloys were heated up to their melting point, followed by quenching with ice water. The intermetallic SnSb alloy was prepared by melting Sn and Sb grains in a crucible. The Cu5 Sn6 and Ni3 Sn alloys were synthesized by arc melting. The obtained bulk alloys were cut into thin sticks of diameter

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