Facile synthesis and characterization of reduced graphene oxide/copper composites using freeze-drying and spark plasma sintering
Introduction
Copper-based composites have received considerable attention in recent years due to their potential candidates as bearing, electrical sliding contacts, resistance welding electrodes, and so on [1], [2]. As an attractive reinforcement medium, carbon materials like graphite, carbon nanotubes and carbon fibres have been extensively investigated due to their excellent mechanical, thermal, electrical and tribological properties [1], [3]. Especially, they exhibit many significant enhancements to the properties of the Cu matrix such as strength, electrical conductivity and wear resistance [2], [4], [5]. Still, exploring new carbon reinforcements and investigating their contribution to various properties are important to Cu-based composites.
Graphene, with a unique two-dimensional layer of sp2-hybridized carbon atoms, possesses high Young's modulus (1 TPa) [6], high fracture strength (125 GPa) [6] and extreme thermal conductivity (5000 Wm−1 K−1) [7]. It has recently attracted tremendous attention as a reinforcing agent for developing a wide range of metal matrix composites [8], [9]. Thereinto, only a very few researchers attempted to fabricate graphene/Cu composites using different methods, such as high-ratio differential speed rolling technique, CVD-grown and chemical reduction [9], [10], [11]. However, most of the previous reports focused on the rGO/Cu nanocomposites with low rGO contents (<0.2 wt%) using the chemical reduction of copper ions and GO [9], [12]. The introduction of rGO exhibited excellent interfacial bonding and improved wear resistance [9], [12]. In this paper, we explored a combined methodology based on freeze-drying and spark plasma sintering to facilely fabricate bulk Cu-based composites with 2.5 and 5.0 wt% contents of rGO. Microstructural characteristic of the resultant composites was investigated in detail, and the compressive property and strengthening mechanisms were also discussed.
Section snippets
Experimental procedure
Firstly, GO was prepared from purified natural graphite by a modified Hummer's method [13]. The purified GO was dispersed in water to make a 20 mg/ml suspension. Cu–2.5rGO (wt%) and Cu–5.0rGO (wt%) composites, referred respectively to as composites #1 and #2 hereafter, were synthesized in this work. Fig. 1 shows the schematic illustration of the fabrication process of rGO/Cu composites. 32.7 ml and 65.4 ml GO aqueous dispersions were respectively used for the fabrication of composites #1 and #2.
Results and discussion
Fig. 2a shows the XRD patterns of the freeze-dried composite powders and pure Cu powder. In each specimen, the diffraction peaks at 2θ=43.3°, 50.4° and 74.2° were indexed to the (111), (200) and (220) planes of the face-centered cubic (fcc) Cu (JCPDS 85-1326). No characteristic peaks of rGO were detected possibly due to the low concentration of rGO. The result of XRD (Fig. 2b) and FT-IR (Fig. 2c) together with GO indicated that the rGO was separated and collected in the freeze-dried composite
Conclusion
The rGO/Cu composites were successfully fabricated by the combination of freeze-drying and spark plasma sintering. The GO was effectively reduced by the addition of N2H4·H2O in the GO/Cu mixtures. As-sintered rGO/Cu composites exhibited both agglomerated and dispersed states of rGO distribution in the Cu matrix. The compressive 0.2% yield strength of the composites with 2.5 and 5.0 wt% additions reached 109.4 and 121.2 MPa respectively, and exhibited significantly higher strength than those of
Acknowledgment
This work was supported by National Natural Science Foundation of China (51503177) and Talent Introduction Project of Yancheng Institute of Technology (No. kjc2015016).
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