Novel synthesis of nitride powders by microwave-assisted combustion
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A novel and simple microwave-assisted combustion procedure for the synthesis of a number of technologically important metal nitrides was demonstrated. The method involves the combustion reaction of a porous metal powder compact with N2 gas in the microwave field and provides phase-pure metal nitride products (consisting of fine particles, fibers, and whiskers) within minutes. The ignition and combustion temperatures of the reaction were found to vary as a function of compaction pressure. The microwave-prepared nitrides were characterized using x-ray diffraction, scanning electron microscopy energy dispersive spectroscopy, thermogravimetric analysis, and infrared spectroscopy. The present microwave-assisted hybrid-heating procedure allows the preparation of nitrides with good crystallinity, structural uniformity, and phase purity, and appears to have general applicability for the preparation of metal nitrides (using the respective metals or even their oxides).
I. INTRODUCTION
Metal nitrides possess very high thermal, mechanical, and chemical stability.1 Several nitrides are also characterized by low densities and are therefore of great technological interest for light-weight applications. Titanium nitride (TiN) is a well-known diffusion barrier for aluminum interconnect metallization in very large-scale integration (VLSI) device technology.2 It is also used as a gold-colored hard coating on many tool parts.3 Aluminum nitride (AlN) has attracted much attention in recent years for its excellent dielectric properties, high thermal conductivity, high-temperature machinability, and good electrical resistivity.4,5 AlN is also an electronic substrate material due to this good thermal compatibility and nonreactivity with silicon.6 Vanadium nitride (VN) is an important industrial catlayst known for its selectivity and stability.7 Gallium nitride (GaN) is one of the most promising wide-band-gap (3.38 eV) materials for shortwavelength optoelectronic devices and has potential for applications in high-temperature electronics and in realizing blue-ultraviolet lasers. Commercial nitride powders are synthesized via either carbothermal8 or direct nitridation9 of metals. The conventional procedures for the synthesis of these important nitrides, however, are often plagued by extremely long reaction times (several hours to even days) caused by slow diffusion rates in solids and
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J. Mater. Res., Vol. 15, No. 4, Apr 2000 Downloaded: 14 Jul 2014
usually involve many cumbersome steps. They often require the use of atomized metal powders (involving risk of explosions),10 laser heating at high pressures,11 very precise temperature-programmed reaction controls,12 heating of the respective oxides for several hours in a continuous flow of ammonia,13 and so on. Besides these, other methods on laboratory-scale synthesis have been reported, such as decomposition of expensive organometallic compounds,14 prolonged reduction and nitridation of m
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