CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 39 (2013) 8531–8535 Short communication Effect of sintering atmosphere on the densification behavior of hot pressed TiN ceramics Jia-Xiang Xue, Hai-Tao Liu, Yun Tang, Chang-Ming Xu, Guo-Jun Zhang n State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Shanghai 200050, China Received 5 February 2013; received in revised form 17 March 2013; accepted 18 March 2013 Available online 23 March 2013 Abstract Using nano-sized starting powders, TiN ceramics were hot pressed under different sintering atmospheres, which were nitrogen, argon and vacuum (5 Pa). The effects of sintering atmosphere on the densification process and microstructures of TiN ceramics were investigated. At 1500 1C, ceramics densified under vacuum demonstrated higher density compared with nitrogen and argon, owing to the high nitrogen vacancy concentration which came from the dissociation of TiN under vacuum circumstance. At 1600 1C, however, the densification process under vacuum will be hindered because of the decomposition of TiN. Combining a lower sintering temperature, smaller grain size and higher grain boundary concentration, the argon atmosphere is more suitable for fabrication of TiN ceramics as nuclear materials. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Hot pressing; Densification; Nonstoichiometry; Sintering atmosphere; Titanium nitride (TiN) 1. Introduction To reduce the toxicity of the nuclear waste and enhance the safety of nuclear power, the Gen IV systems have been developed during the last few years [1,2]. Both the gas-cooled fast nuclear reactor (GFR) and accelerator driven sub-critical system (ADS) are planned to transmute transuranium elements using inert matrix fuels (IMF) to optimize the burn up of nuclear fuel. The IMF need to work either at very high temperature or require fast neutron spectra [1–4]. Recent reports show that titanium nitride (TiN), one transition metal nitride, is proposed as an attractive candidate material as IMF due to a combination of excellent physical and chemical properties, including high melting temperature, low neutron absorption cross-section, high thermal conductivity at high temperature, extreme hardness, good corrosion resistance and its superior solubility of minor actinide (MA: Np, Am, Cm) elements [5–10]. For the densification of TiN ceramics, owing to the high melting point, strong covalent bonding and low self-diffusion coefficient, high sintering temperature and pressure are usually essential to obtain densified products. But considering the application in nuclear system, a lower sintering temperature is needed for the densification because some of the actinide nitride, such as AmN, has a tendency to decompose and evaporate at higher temperature [11]. So densification of TiN ceramics at a relatively lower sintering temperature is a new challenge for TiN ceramics used as IMF. TiN belongs to the cubic system, which is similar to the cubic face-centered lattice of NaCl, and it shows a remarkably broad range of nonstoichiometry by a fairly wide homogeneity range (TiN x , where 0.37 o x o 1.2) [12]. For transition metal nitride, for example, the ZrN ceramics, it has been reported that the changes of the sintering atmosphere can produce nitrogen vacancies, which accelerates densification process of the substoichiometric ZrN x ceramics [13,14]. So in the present work, besides using the nano-sized TiN powders as starting materials to enhance the densification, we tried to densify TiN ceramics by carrying out different sintering atmospheres and studied the effects of the atmosphere on hot pressed TiN ceramics, which included the nonstoichiometry tailoring, densification enhancement and microstructure evolution. 2. Experimental procedure Commercial nano-sized TiN (titanium nitride, D 50 =20 nm, specific surface area by BET about 35.7 m 2 /g, purity 99%, www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.03.062 n Corresponding author. Tel.: +86 21 52411080; fax: +86 21 52413122. E-mail address: gjzhang@mail.sic.ac.cn (G.-J. Zhang).