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Reaction between Refractory Metals and Insulating Nitrides at High Temperature

1970; Ceramic Society of Japan; Volume: 78; Issue: 893 Linguagem: Inglês

10.2109/jcersj1950.78.27

1884-2127

Toshiyuki SATA, Teruo Urano,

Metal and Thin Film Mechanics

Some nitrides, BN, AIN and Si3N4, are used as electric insulators up to moderate temperature. The difficult problems occured when they were to be employed at higher temperatures than 2000°C. The reactions between those insulators and conductors of refractory metals, tungsten and tantalum, were investigated up to 2100°C in a tungsten furnace under argon atmosphere.In all of the power reactions of W with BN with various compositions at 1100° to 2000°C for 2 hrs., W2B was first formed, followed by WB, W2B5 and WB4 stepwisely, and nitrogen gas was released. Between Ta and BN (50-50 molar composition), TaN, TaB and small amount of TaB2 were formed. In the reactions between metals and AIN (50-50 molar composition) for 2 hrs., W did not react, but Ta formed TaN over 1600°C. Vaporisation Al and AlN were observed considerably with elevating temperature. In the reactions between metals and Si3N4 (50-50 molar composition) for 2 hrs., W3Si2 and WSi2, and TaN and TaSi2 were formed, but vaporisation of Si3N4 was observed over 1400°C.In the reaction between sintered pellets of W and BN, reaction layers of W2B and WB were confirmed on the original W by means of XMA. Here kinetics of formation of W2B from W and BN were investigated at the temperatures from 1270° to 1360°C by means of the TGA. By the method of J. H. Sharp et al., the curve of a reaction yield α with a reduced time t/t0.5 showed that the reaction rate was controlled by the phase-boundary reaction. An activation energy of this reaction was determined to be 87.0±17.0kcal/mole from the Arrhenius plots, and this value is larger than the activation energy 64.0±6.3kcal/mole of diffusion of B in W2B given by A. P. Epik.Insulating properties of BN for W leads dropped at higher temperature than 1500°C owing to the formation of conducting borides. Tungsten borides were easily oxidized in air in the range of 400° to 600°C. Their resistivities have a order of 10-5 ohm-cm as metallic conductor. W2B was weak paramagnetic, and WB and W2B5 were diamagnetic.