Rapid communicationOpen-celled porous Cu prepared by replication of NaCl space-holders
Introduction
Porous metals have been developed in various fields of industry and are expected as novel engineering materials in the last decades [1], [2], [3], [4]. These special materials possess unique combinations of properties such as light-weight and excellent sound absorption due to the existence of a large number of pores that can lead to viscous attenuation of sounds [5], high impact energy absorption arising from their large strains under relative low stresses [6], [7], and high damping originating from the vibration of cell walls and the friction of cracks [8], as well as high gas permeability [9], etc. According to the connections of pores, porous metals can be categorized as close-celled and open-celled. In most cases, the functions such as filtration, separation, and sound or energy absorption require open-celled morphologies. Thus, porous metals with open-celled morphologies have wider applications in functional structures [10].
Up to now, numerous techniques have been developed to produce porous Cu, such as directional solidification, electrodeposition or vapor deposition, powder metallurgy, etc. [10], [11], [12], [13]. Among which, directional solidification is especially suitable for producing coralloid porous Cu, while its relative low porosity and low open cell rate limit its application in the preparation of open-celled porous Cu [10], [11]. For electrodeposition and vapor deposition, however, there are still some restrictions to the morphologies of the resultant porous Cu, since the morphology parameters like pore size, pore shape and porosity are determined to a large extend by their precursor materials [10]. These restrictions in morphologies can lead to a limited range of properties and thus less wide applications. It is therefore necessary to develop more flexible techniques to offer a wider range of structures and properties.
Powder metallurgy technique possesses unique advantages in preparation of porous metals [12], [13], [14]. In which sintering-dissolution process (SDP) is a promising route for manufacturing open-celled porous metals [14], [15]. The most outstanding technical advantage of SDP is much wider range of structure parameters, thus providing more opportunities for resultant porous metals to meet the desired behaviors. However, in the literature there has shown very little respect to the preparation of porous Cu via SDP. And the NaCl particles have not been used as space-holders for the preparation of porous Cu, either, because the melting point of NaCl (801 °C) is far below that of Cu (1083 °C). Nevertheless, it is interesting to note that using NaCl as space-holders possesses numerous advantages such as low cost, fast dissolution in water, reduced corrosive attack of metal during dissolution, free of toxicity, in addition to significant widening of structure parameters such as porosity, pore shape, pore size and homogeneity of pore distribution, etc. [4]. It is therefore necessary to explore preparation of porous Cu using NaCl as space-holders, with the aim of expanding the range of structures and applications of the porous Cu.
Section snippets
Experimental procedure
The as-received raw materials are electrolytic Cu powders and domestic NaCl particles as shown in Fig. 1. The 200 mesh electrolytic Cu powders exhibit a typical dendritic shape, while NaCl particles are cuboidal in shape and around 0.75 mm in size. To avoid the rupture of NaCl particles at high sintering temperatures the NaCl particles were heated to 400 °C holding for 2 h before use to remove the water and then graded through a series sieves. The electrolytic Cu powders and NaCl particles were
Results and discussion
Fig. 2 shows the typical morphologies of the porous Cu with a porosity of 71.3% and an average pore size of 0.75 mm. Homogenous distribution in Cu matrix of interconnected pores can be clearly seen. Both the shape and size of solid NaCl particles are well replicated, and accordingly resulting in cuboidal cross-sectional shape of the pores, suggesting that effective bonding between Cu particles had been achieved before NaCl melted at 801 °C, and the final sintering temperature will not affect the
Conclusions
In the present study, an open-celled porous Cu has been successfully prepared by replication of NaCl space-holders via a sintering-dissolution technique for the first time. Resultant material exhibits uniformly distributed and interconnected pores. It is proposed that a compaction pressure range of 250–300 MPa and a sintering temperature range of 940–960 °C allow the achievement of effective bonding between Cu powders without crushing the NaCl particles and losing liquid metal.
Quasi-static
Acknowledgements
This work was supported by the Key Program of Natural Science Foundation of Tianjin (Project No. 09JCZDJC22200), Natural Science Foundation of Hebei Province (Project No. E2009000060).
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