Journal of Alloys and Compounds 482 (2009) 110–113 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom A study on mechanochemical behavior of B 2 O 3 –Al system to produce alumina-based nanocomposite E. Mohammad Sharifi a , F. Karimzadeh a,b,∗ , M.H. Enayati a,b a Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran b Nanotechnology and Advanced Materials Institute, Isfahan University of Technology, Isfahan 84156-83111, Iran article info Article history: Received 8 February 2009 Received in revised form 5 April 2009 Accepted 7 April 2009 Available online 21 April 2009 Keywords: Ceramics Nanostructured materials Mechanochemical processing abstract One possible route for producing the fine and homogenous distribution of hard particles in composite microstructure is the mechanochemical processing in which high-energy ball milling promotes the reac- tion in a mixture of reactive powders. In this study mechanochemical reaction of B 2 O 3 and Al powder during ball milling was studied. The phase transformation and microstructure of powder particles dur- ing ball milling were investigated by X-ray diffractometry and scanning electron microscopy. The results showed that during ball milling the B 2 O 3 –Al reacted with a combustion mode producing Al 2 O 3 –AlB 12 nanocomposite. The crystallite size of Al 2 O 3 and AlB 12 was 40 and 25nm, respectively. This structure appeared to be stable upon annealing. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In recent years, there has been increased interest in the scope of ceramic–ceramic composites. The main objective for research in this field is to develop a new generation of ceramic materials with a higher strength and better toughness [1,2]. Alumina-based ceramic composites reinforced with carbides, borides and nitrides have been widely developed in order to produce an alternative mate- rial for cutting tools [3–5]. Studies have shown that the addition of some hard particles, in the amount of 20–40 wt.%, can improve toughness, strength and also thermal shock resistance of the mono- lithic matrix [6–9]. Moreover the dispersion of hard particles in the matrix produces a pinning effect that reduces alumina crystallite growth, which in turn improves the mechanical properties of the material [10,11]. It has been pointed out that producing nanosized microstructure is an effective way to overcome the brittleness of ceramics [12]. Several techniques such as self-propagating high temperature synthesis (SHS) and mechanochemical synthesis have been devel- oped to produce a wide array of ceramic matrix composites. Among these methods, mechanochemical synthesis; that is, chem- ical reactions induced by high-energy ball milling, is well known for fabrication of novel materials such as nanocomposites [13]. High-energy ball milling can enhance the kinetics of reactions ∗ Corresponding author at: Department of Materials Engineering, Isfahan Univer- sity of Technology, Daneshgah Blv., Isfahan 84156-83111, Iran. Tel.: +98 311 3915744; fax: +98 311 3912752. E-mail address: Karimzadeh f@cc.iut.ac.ir (F. Karimzadeh). of components and as a result can induce chemical reactions in powder mixtures at room temperature or at least at much lower temperatures. This technique can lead to formation of interpen- etrating phase composites with nanosized microstructures. An important characteristic of such phases is that they exhibit prop- erties and performance much improved over their conventional microcrystalline counterparts [14]. Boride dispersed alumina composite has several potential appli- cations including neutron absorber and armor materials [15]. By now, no data have been reported on the use of mechanically induced aluminothermic reduction of boron oxide for the preparation of boride dispersed alumina matrix nanocomposite. The study of the aluminothermic reduction of boron oxide is not only of practical importance in the preparation of alumina matrix composites but also of theoretical interest. In this work, formation of Al 2 O 3 –AlB 12 nanocomposite powder was investigated by utilizing mechanochemical process starting from B 2 O 3 and Al powder mixtures. In meantime, the structural evolution during mechanochemical process was studied. 2. Experimental B2O3 (99% purity) and Al (99.5% purity) powders with stoichiometric composi- tion were mixed according to reaction (1): 13Al + 6B2O3 = 6Al2O3 + AlB12 (1) The weight percentage of AlB12 in reaction (1) is about 20%. Ball milling of powder mixture was carried out in a planetary ball mill at room temperature and under argon atmosphere. The ball milling media were hardened chromium steel vial (150 ml) with five steel balls (20 mm). The ball-to-powder weight ratio and the rotational speed of vial were 10:1 and 500rpm, respectively. The milling was interrupted at selected times and a small amount of powder was 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.04.051