Mechanical alloying techniques have been used to produce BN nanorods based on elemental boron powders and nitrogen gas mixed in a container at room temperature. To explore the possible increments in the amount of the obtained nanorods, different containers have been used (stainless steel and tungsten carbide). Also different element additions to the initial mixture, such as Si and Fe have been tested. The results indicate that the Fe and Si additions enhance the BN nanorods production and reduce the presence of oxygen in these materials.
Keywords

Nanorods, Mechanical alloying, Boron nitride, Characterization, Electron microscopy.
Introduction

Fullerene-related materials such as carbon nanotubes have been the centre of extensive research [1]. The formation of nanotubular structures have also been found in several other systems such as: MoS2 [2], BxCyNz [3] and BN [4]. BN nanotubes are promising tubular structures for use in electronic devices because of the special semiconducting properties [5]. Different methods have been recently reported in the literature for synthesizing these BN nanostructure crystalline materials. These include techniques such as: plasma arc discharge [4], laser ablation [6] and catalytic decomposition [7]. Also, BN nanotubes have been obtained from a substitution reaction of carbon nanotubes at 1773 K [8]. These methods require either high power lasers or high temperature even sometimes subsequent annealing of the obtained compounds [9]. Ball milling techniques have also been used for this purpose. Thus, for example, room temperature ball milling of elemental boron in ammonia gas followed by annealing at a relatively low temperature has been used to produce BN nanotubes [10]. Multiple walled BN nanotubes and nanorods have recently been obtained using a mechanical alloying technique at room temperature [11]. However, the presence of these BN nanostructures were scarce and not frequently found in the ball milled powders. In this investigation, the effect of the container nature and the effects of some particular element additions to the milled powder mixture, on the BN nanorod production have been explored. Stainless steel and tungsten carbide containers have been used in the experimental ball mill arrangements. Also, additions of Si and Fe to the original mixture (boron powder and nitrogen gas), have been explored.
Experimental

Boron powder (99.8%) with particle sizes of approximately 1μ was ball milled at room temperature using a SPEX ball mill (8000D). High purity hydrogen was used as the milling atmosphere. Balls and containers (volume 270 ml.) of steel and tungsten carbide were used. Small amounts of sample were taken at specific milling times (3 and 8 h.), keeping the weight ratio of 30:1. Fe (99.9%) and Si (98.5%) were added to the boron powders (2 wt%), when the tungsten carbide container was used. The mechanically milled powders were characterized using X ray diffraction patterns and transmission electron microscopy. The X-ray experiments were carried out in a Siemens D-5000 instrument using CuKα radiation (Nickel filter) and the TEM observations in a Philips Tecnai F20 microscope. The TEM observations of the powder samples were obtained using holey carbon coated copper grids.