Combustion synthesis of boron nitride powder
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Combustion synthesis of boron nitride powder Chyi-Ching Hwang and Shyan-Lung Chunga) Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan, 70101, Republic of China (Received 1 March 1997; accepted 9 May 1997)
A combustion synthesis (SHS) process developed in our previous study for the synthesis of Si3 N4 has been tested for the synthesis of boron nitride (BN) powder. Boron and NaN3 powders were used as the reactants. In addition to ammonium halides, KHF2 , FeCl3 , NaNH2 , or a mixture of 50 mol % FeCl3 and 50 mol % NaNH2 was added to the reactants to examine their catalytic effect. These powders were mixed and pressed into a cylindrical compact. The compact was wrapped up with an igniting agent (i.e., Mg 1 Fe3 O4 ) and the synthesis reaction was triggered by the combustion of the igniting agent. It was found that only those reagents containing both halogen and hydrogen can exert effectively the catalytic effect. The BN powder as-synthesized is mostly in the form of agglomerated fine particles (0.1–1 mm in diameter) and is hexagonal in crystalline structure. Effects of various experimental parameters on the product yield were investigated. A possible reaction mechanism was proposed, which explains the effects of the experimental parameters on the synthesis reaction.
I. INTRODUCTION
The use of boron nitride in various fields of technology is constantly growing because of its excellent physical and chemical properties. Hexagonal boron nitride (h-BN) has been acknowledged as one of the best materials for refractories, lubricants, and electrical insulators. Cubic boron nitride (c-BN) is a superhard material and has a great potential for application as cutting tools, grinding, and abrasive materials.1–3 In this work, we investigate the use of the combustion synthesis (SHS) method for the production of BN powder. The SHS method, originally developed in the former USSR,4 has been applied to synthesis of various high-temperature materials including ceramics, intermetallics, and composites.5 It has many potential advantages such as low-processing cost, energy efficiency, and high production rate.6 In our previous study,7 a SHS process was developed for the synthesis of AlN powder by using Al and NaN3 as the reactants. By wrapping up the reactant compact with aluminum foil and an igniting agent (i.e., Ti 1 C), high product conversions were achieved at low nitrogen pressures (
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