Laser processing issues of nanosized intermetallic Fe–Sn and metallic Sn particles
Highlights
► Intermetallic Fe–Sn and metallic Sn nanoparticles synthesized by laser pyrolysis. ► Fe(CO)5 and Sn(CH3)4 were used as precursors. ► FeSn2, Sn and Fe3SnC phases were identified by XRD. ► Complex core–shell structural characteristics were found by HRTEM analysis. ► Higher magnetization was found in samples with increased Fe/Sn atomic ratio.
Introduction
Due to finite size effects, metallic/intermetallic nanoparticles display a range of novel electronic, magnetic and chemical properties which are distinct from the corresponding bulk materials. Of much recent interest are bimetallic compound/alloys [1], as promising magnetic materials with high resistance against oxidation. Research of novel alloys is encouraged by challenges to discover new types of materials whose properties should be strongly dependent on the preparation methods.
In the last few years Sn-based intermetallics (including Fe–Sn) were intensely investigated for Li-ion batteries composite electrodes [2], [3]. These alloys are considered to have higher specific capacity and greater density than graphite, leading to Li-ion batteries with higher energy density. Iron was chosen because it does not form alloys with Li, so it might form an inactive matrix for the tin atoms. It was found that FeSn2 exhibits the best electrochemical activity and superior cycling performance [4]. It is known that tin is commonly used as a base metal for soldering. Other recent research direction of high interest refers to the use of new Sn-based nanocomposites for lead-free solder alloys [5], [6].
Fe–Sn intermetallics were most often obtained by mechanical alloying in a ball planetary mill [7]. Preparing nanosized Sn particles is difficult and has only been accomplished in a few cases. More common synthesis techniques for Sn based nanostructured compounds are the vapor deposition-based techniques, the chemical reduction of tin salts and also the thermal decomposition of inorganic or organic precursors in a reductive atmosphere [8]. In our previous studies [9] we have reported on the single step synthesis of SnO2-based nanoparticles using the pyrolysis of tetramethyl tin (TMT) sensitized with ethylene mixtures. By introducing iron pentacarbonyl in the reactive mixture, simultaneous iron doping occurred. Controlled Fe/Sn atomic ratios were used in order to prepare Fe-doped SnO2-based nanopowders.
Here we further explore the laser-induced gas phase decomposition of selected volatile organometallics for the formation and optimization of a novel range of morphologically less known nano-structured Sn (single phase) and bimetallic Fe–Sn materials. In the laser pyrolysis process, ethylene was used as sensitizer. The present study concerns low concentration Fe doped iron–tin nanocomposites which is a domain rarely approached in the literature. The investigated structural and magnetic characteristics are discussed.
Section snippets
Experimental
The laser pyrolysis technique adapted to the synthesis of Sn-based nanoparticles has been described in detail earlier [10]. The admission of the gases to the reaction chamber implies a nozzle with two concentric tubes. In case of the intermetallic Fe–Sn nanoparticles, Sn(CH3)4 and Fe(CO)5, as gas phase precursors are simultaneously allowed to emerge into the flow reactor where they are orthogonally crossed by the CO2 laser beam (100 W nominal power, λ = 10.6 μm). In case of the synthesis of
Results and discussions
Table 1 and Table 2 list the experimental parameters and the elemental content of the samples as determined by the EDAX analysis, respectively. Thus, the elemental content (in at%) of the as-synthesized samples in carbon, oxygen, tin and iron is displayed in Table 2, together with their Fe/Sn atomic ratios. Their values range from 0.69 to 1.64 and were obtained by the control of Fe(CO)5 and Sn(CH3)4 flows, respectively (the Fe concentration increases from about 23 at% (sample TF2) to 33 at%
Conclusions
Controlled Fe/Sn atomic ratios, ranging from 0.69 to 1.64 were obtained for the prepared Fe–Sn nanopowders by the control of Fe(CO)5 and Sn(CH3)4 flows, respectively. At the incorporation of Fe into the lattice XRD studies evidence three main phases: the metallic Sn phase, the intermetallic FeSn2 phase and, to a much lesser extent, the cubic ternary carbide Fe3SnC. Complex core–shell structural characteristics were found by HRTEM analysis. The temperature dependent 57Fe Mossbauer spectroscopy
Acknowledgments
This research was supported by the Projects IDEI-431/2007 and IDEI 80/5.10.2011-PNCD2 Program of the Romanian Ministry of Education, Research, Youth and Sport.
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