NH_x/OH Surface Groups in Commercial Si_3N_4 Powders Analyzed by Diffuse Reflectance Infrared Fourier Transform (DRIFT) Spectroscopy

摘要

NH_x/OH surface groups of four different commercial silicon nitride powders produced by two different methods: diimide precipitation and carbothermal reduction with different nitriding media were determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The results show that for both methods the nitriding media has a profound effect on the powders surface composition. In silicon nitride powders produced using NH_3 as nitriding media in both methods, surface hydrogen content in the form of NH_x/OH groups is larger than for a powder using N_2 in the carbothermal reduction process. The intensity of NH and NH_2 groups identified and quantified by DRIFT (this work) correlate with the amounts of N_2 desorbed molecules above 1300 deg C and NH_3 desorbed molecules below 1300 deg C, measured by temperature programmed desorption mass spectroscopy (TPDMS) for the same powders, respectively. It is concluded that the NH structures form part of the surface layer.