Novel synthesis and thermal property analysis of MgO–Nd 2 Zr 2 O 7 composite Linggen Kong a , Ji Zhang b , Yoshitaka Maeda c , Mark G. Blackford a , Sean Li b , Gerry Triani a , Daniel J. Gregg a,n a Institute of Materials Engineering, Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia b School of Materials Science and Engineering, UNSW Australia, Kensington, 2 High Street, Sydney, NSW 2052, Australia c Department of Mechanical Engineering, Nagaoka University of Technology, Nagaoka city, Niigata Prefecture, Japan article info Article history: Received 16 March 2016 Received in revised form 22 June 2016 Accepted 27 July 2016 Keywords: Novel aqueous solution process MgO-Nd 2 Zr 2 O 7 Thermal properties abstract MgO-Nd 2 Zr 2 O 7 composites with ratios of 50–70 vol% MgO were produced via a one-pot combustion synthesis. A suite of characterization techniques, including X-ray diffraction, scanning and transmission electron microscopy were employed to investigate the structural properties while dilatometry, si- multaneous thermal analysis and laser flash analysis were used to characterize the thermal properties of the composites. Dense pellets were produced after sintering at 1400 °C with grain sizes between 200 and 500 nm for both phases. The thermal properties of the composites are similar to those produced using standard methods. The composite with 70 vol% MgO was found to have the highest thermal conductivity below 1000 °C, while above this temperature the thermal conductivity was found to be similar and independent of MgO content. This novel synthesis route produces materials which show significant improvements in homogeneity with smaller particle sizes when compared to current standard synthesis techniques without significantly reducing thermal conductivity. & 2016 Elsevier Ltd All rights reserved. 1. Introduction The global stockpiles of plutonium were estimated to be around 505 t at the end of 2014 and growing steadily, and they represent a proliferation concern [1]. Inert matrix fuel (IMF) materials offer the advantage of burning surplus plutonium and other minor ac- tinides (MA) produced from the fuel cycle in current light water reactors with minimal production of further actinides [2,3]. In an IMF, plutonium (or other MA) is embedded in a uranium-free matrix so as to burn it without breeding any new plutonium by neutron capture in U-238 [4]. This concept of actinide burning uses a non-fertile matrix such as ZrO 2 to provide a more efficient consumption of plutonium compared to that in mixed uranium and plutonium oxide fuel (MOX). Potentially this once-through cycle U-free IMF strategy utilizes the energetic value of plutonium as well as reduces the radiotoxicity and proliferation risk of nu- clear waste. There is extensive literature on various materials for use as IMFs for burning plutonium [5–7] and candidates to be used as IMF materials must meet strict material performance require- ments. These include high temperature stability, irradiation sta- bility, high thermal conductivity, low neutron capture cross-sec- tion for the non-MA elements, good resistance to corrosion in hot aqueous solution, and good compatibility with reactor coolant [8– 10]. The centerline temperature of the composite IMF pellets for this application would be expected to be in the 1000–1500 °C range. A composite material of magnesia (MgO) and pyrochlore structured ceramic (A 2 B 2 O 7 ) is a leading candidate among those oxides studied for use as IMF materials [3,7,11–16]. MgO possesses a high melting point (2827 °C), high thermal conductivity (13 W K 1 m 1 at 1000 °C), good neutronic properties, and good radiation resistance [17], however it cannot incorporate plutonium or MA within its crystal structure. Pyrochlore (A 2 B 2 O 7 ) is a cor- rosion resistant [18], radiation tolerant phase [19] capable of in- corporating plutonium and MA within its crystal structure [20] and is in itself a candidate nuclear waste form for the incorpora- tion of Pu and MA [7,19,21], however its thermal conductivity is relatively low [15,22]. As a result, the combination of MgO and pyrochlore provides an IMF candidate that has attracted sub- stantial interest in recent years [3,7,11–16]. The conventional method to produce Nd 2 Zr 2 O 7 with the pyr- ochlore structure is the solid-state mechanical mixing of single metal oxide material, followed by high temperature calcination [12,14]. However, it is difficult to produce pyrochlore powder with homogeneous composition, thus multiple milling steps are re- quired to overcome this drawback. In order to improve the uni- formity of the materials, several wet-chemistry routes have been investigated for the preparation of the pyrochlore phase. All wet Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ceramint Ceramics International http://dx.doi.org/10.1016/j.ceramint.2016.07.187 0272-8842/& 2016 Elsevier Ltd All rights reserved. n Corresponding author. Please cite this article as: L. Kong, et al., Novel synthesis and thermal property analysis of MgO–Nd 2 Zr 2 O 7 composite, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.07.187i Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎