Microwave assisted synthesis of technologically important transition metal silicides
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Microwave assisted synthesis of technologically important transition metal silicides B. Vaidhyanathan and K. J. Raoa) Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore –560 012, India (Received 1 November 1996; accepted 25 March 1997)
A novel, simple, clean, and fast microwave assisted method of preparing important transition metal silicides (MoSi2 , WSi2 , CoSi2 , and TiSi2 ) has been described. Amorphous carbon is used both as a microwave susceptor and as a preventer of oxidation.
I. INTRODUCTION
Transition metal silicides form a rich category of inorganic materials with their technologically important properties. MoSi2 is used for making heating elements in high temperature furnaces, interconnecting contacts in integrated circuits, as structural material in aircraft engine hot-section components, etc.1–3 This high temperature engineering material has other important merits such as excellent oxidation resistance, high melting point (2303 K), high electrical conductivity, and low density.4 WSi2 can be easily alloyed with other high melting silicides and can be used as a potential structural material. CoSi2 is used for metallization and circuit path formation in integrated circuit devices5 because of its very low electrical resistance. TiSi2 is a potential microelectronic circuit material. The conventional methods of preparation of these intermetallic compounds are extremely tedious and rather involved; like direct reaction of fused high purity constituents for several hours in vacuum, reaction of arc melted pure metals, laser pulse treatment of metallic mixture, rigorous mechanical alloying, plasma heating or self propagating high temperature synthesis, etc.6–9 The present article reports a simple, novel, and fast method of synthesis of these important transition metal silicides using microwave irradiation. The preparation can be so organized that the products can be directly used as heating elements, as targets for thin film preparation, etc. It has been realized recently that microwave radiation can be used to accelerate a variety of chemical reactions and products of good structural uniformity have been obtained.10–16 The great advantages of microwave heating appear to be the very short time scales involved in the preparation and the selectivity in energy transfer from the microwave field. It is found that a number of oxides (e.g., V2 O5 , WO3 , Cr2 O3 , and CuO) and a few halides (e.g., AgI and CuI) absorb energy from microwaves very efficiently and can be heated to 1000 K
a)
Author to whom correspondence should be addressed. J. Mater. Res., Vol. 12, No. 12, Dec 1997
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or more.17,18 However, the use of microwaves is not possible when none of the reactants is a good microwave susceptor. In such cases a chemically inert microwave coupling material can be successfully employed as a secondary heater (i.e., as an in situ inert heating source) in the microwave field to initiate the
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