Formation of TiB 2 by volume combustion and mechanochemical process Eda Bilgi a , H. Erdem C ¸ amurlu b , Barıs ¸ Akgu ¨n a , Yavuz Topkaya a , Naci Sevinc ¸ a, * a Department of Metallurgical and Materials Engineering, Middle East Technical University, I ˙ no ¨nu ¨ Bulvarı, 06531 Ankara, Turkey b Department of Mechanical Engineering, Akdeniz University, Dumlupınar Bulvarı, 07058 Antalya, Turkey Received 25 December 2006; received in revised form 24 April 2007; accepted 1 May 2007 Available online 5 May 2007 Abstract Titanium diboride was produced both by volume combustion synthesis (VCS) and by mechanochemical synthesis (MCP) through the reaction of TiO 2 ,B 2 O 3 and Mg. VCS products, expected to be composed of TiB 2 and MgO, were found to contain also side products such as Mg 2 TiO 4 , Mg 3 B 2 O 6 , MgB 2 and TiN. HCl leaching was applied to the reaction products with the objective of removing MgO and the side products. Formation of TiN could be prevented by conducting the VCS under an argon atmosphere. Mg 2 TiO 4 did not form when 40% excess Mg was used. Wet ball milling of the products before leaching was found to be effective in removal of Mg 3 B 2 O 6 during leaching in 1 M HCl. When stoichiometric starting mixtures were used, all of the side products could be removed after wet ball milling in ethanol and leaching in 5 M HCl when pure TiB 2 was obtained with a molar yield of 30%. Pure TiB 2 could also be obtained at a molar yield of 45.6% by hot leaching of VCS products at 75 8C in 5 M HCl, omitting the wet ball milling step. By MCP, products containing only TiB 2 and MgO were obtained after 15 h of ball milling. Leaching in 0.5 M HCl for 3 min was found to be sufficient for elimination of MgO. Molar yield of TiB 2 was 89.6%, much higher than that of VCS. According to scanning electron microscope analyses, the TiB 2 produced had average grain size of 0.27  0.08 mm. # 2007 Elsevier Ltd. All rights reserved. Keywords: A. Ceramics; B. Chemical synthesis; C. X-ray diffraction 1. Introduction Titanium diboride (TiB 2 ) is a transition-metal boride which has important chemical, electrical, thermal and mechanical properties. It is the most stable among the several titanium–boron compounds [1]. It has high hardness, high electrical conductivity, thermal stability, high melting point [2] and high wear resistance [3,4]. It is chemically inert to molten metals [5]. Due to these attractive properties, it is utilized in variety of applications including cutting tools, wear resistant parts [6], armors [7], and as a cathode material in electrolytic production of aluminum [8]. It also finds application as a grain refining agent in aluminum castings and in production of vacuum metallization boats [9,10]. There are a number of methods for production of TiB 2 . It can be produced through a solid state reaction between titanium and boron [11]. It is produced from oxides by carbothermic [12] or metallothermic [13,14,5] reduction processes. Fused salt electrolysis [15–17], vapor phase deposition [18] and mechanochemical synthesis [19,20] are other techniques for production of titanium diboride. www.elsevier.com/locate/matresbu Materials Research Bulletin 43 (2008) 873–881 * Corresponding author. Tel.: +90 3122102537; fax: +90 3122102518. E-mail address: nsevinc@metu.edu.tr (N. Sevinc ¸). 0025-5408/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2007.05.001