Formation of self-supporting porous graphite structures by Spark Plasma Sintering of nickel–amorphous carbon mixtures Boris B. Bokhonov a , Dina V. Dudina a,n , Arina V. Ukhina a , Michail A. Korchagin a , Natalia V. Bulina a , Vyacheslav I. Mali b , Alexander G. Anisimov b a Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze Street, 18, Novosibirsk 630128, Russian Federation b Lavrentiev Institute of Hydrodynamics SB RAS, Lavrentiev Avenue, 15, Novosibirsk 630090, Russian Federation article info Article history: Received 23 April 2014 Received in revised form 22 July 2014 Accepted 16 September 2014 Available online 19 September 2014 Keywords: A. Metals C. Electron microscopy C. X-ray diffraction D. Microstructure abstract Graphitization of amorphous carbon in the presence of nickel has been reported for various configura- tions of the metal–carbon interface; however, no study has been performed to evaluate a possibility of forming self-supporting networks by sintering of the in situ formed graphite. In this work, we have shown that Spark Plasma Sintering (SPS) of nickel–amorphous carbon mixtures containing 50 vol% of Ni at 1000 °C results in the formation of networks formed by sintered graphite platelets 50–200 nm thick and 0.3–2 μm in diameter. Upon selective dissolution of nickel, a self-supporting porous 3D skeleton was revealed in 20 mm-diameter compacts. Starting from the mechanically milled Ni–C mixture, porous graphite of uniform microstructure and containing submicron pores was obtained. A model study has been performed, in which a thin amorphous carbon film graphitized during annealing and formed a continuous graphite film with micron-sized grains covering an area of 2 cm  2 cm of the surface of a Ni foil. We discuss the role of the in situ formation of graphite by nickel-assisted graphitization in the formation of networks consisting of well sintered platelets during the SPS and the design possibilities of porous carbon materials produced by phase separation in nickel–graphite composites. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Low-temperature graphitization of amorphous carbon in the presence of nickel has been known and utilized for several decades [1–5]. It is generally accepted that nickel acts as a graphitization catalyst by enabling the dissolution–precipitation formation mechanism of graphite. The initial interaction of carbon with nickel leads to the formation of either solid solutions or nickel carbide, a metastable phase [6]. Depending on the target size and morphology of the graphite product, different configura- tions of the Ni/C interface are used in conducting the graphitiza- tion process. In order to produce graphene structures, nickel films are used as substrates [5]. Graphite-encapsulated nickel nanopar- ticles can be obtained in the mechanically milled and annealed mixtures of nickel and soot powders [4]. Although the graphitiza- tion process of amorphous carbon has been described for various relative contents of the phases and configurations of the Ni/C interface, the aspects of sintering of graphite grains in nickel– graphite composites thus obtained have been rather scarcely addressed. Of particular interest are composites containing comparable volume contents of the phases, which can form continuous networks. Such composites can be fabricated by solid-state consolidation of powders [7], whose structure has been tailored in a way that facilitates the formation of networks of the phases by inter-particle necking and sintering during consolida- tion. One of the directions of the microstructural design of these composites can be based on varying the length scale, on which the networks of the phases interpenetrate each other. The connectivity of the networks can be studied by selectively dissolving one of the phases to reveal the network formed by the other phase. Selective removal of copper from the surface of the TiB 2 –43 vol% Cu composite pellets of 94–98% relative density consolidated by Spark Plasma Sintering (SPS) and shock compac- tion resulted in the formation of a porous nano-grained titanium diboride layer that maintained its integrity [7]. The same proce- dure of selective dissolution of copper applied to conventionally sintered TiB 2 –43 vol% Cu compacts, which were only 64% dense, did not allow obtaining a layer adherent to the compact. Similarly, the targeted preparation of porous materials is possible if one of the phases is selectively dissolved [8–11]. Recently, we proposed a novel and simple preparation route of nanoporous silver, which is based on selective dissolution of Fe or Ni from Ag–50 vol% Fe and Ag–50 vol% Ni nanocomposites in the powder state and Spark Plasma Sintered compacts [11]. The nanocomposite structure in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jpcs Journal of Physics and Chemistry of Solids http://dx.doi.org/10.1016/j.jpcs.2014.09.007 0022-3697/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. Fax: þ7 383 332 28 47. E-mail address: dina1807@gmail.com (D.V. Dudina). Journal of Physics and Chemistry of Solids 76 (2015) 192–202