Weight loss and gas evolution during sintering of silicon nitride powders synthesized by silica reduction and imide deco
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Weight loss and gas evolution during sintering of silicon nitride powders synthesized by silica reduction and imide decomposition Yasuhiro Goto and Yoshiyuki Ohnumaa) Materials and Devices Research Laboratories, Research and Development Center, Toshiba Corporation, 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210, Japan (Received 11 June 1997; accepted 2 March 1998)
The relationships among weight loss, gas evolution, and other changes during sintering were investigated for silicon nitride powders synthesized by silica reduction and imide decomposition. Small weight losses were detected for all powders at low temperatures (below 1400 ±C), and large weight losses were found to occur for the silica-reduction powders at high temperatures (1400– 1800 ±C). Only CO was detected in the sampled gases during sintering, and CO evolution peaks were seen at around 900– 1200 (broad), 1400, and 1600 ±C. The main deposited material around the samples was SiO. The weight losses at low temperatures were thought to be caused by evaporation of residual binder or adsorbed substances. The main causes of the large weight losses at high temperatures were thought to be CO and SiO evolutions, and CO evolution at around 1600 ±C probably originated from the liquid phase accompanied by a – Si3 N4 to b – Si3 N4 transformation. I. INTRODUCTION Three methods are generally used to synthesize silicon nitride (Si3 N4 ) powders: silicon nitridation,1 silica reduction,2– 4 and imide decomposition.5 –7 In the siliconnitridation method, Si is directly converted to Si3 N4 by nitrogen or ammonia. In the silica-reduction method, Si3 N4 is synthesized by a two-step process; reduction of SiO2 by carbon followed by nitridation by N2 . In the imidedecomposition method, SiCl4 is reacted with NH3 to form silicon diimide [Si(NH)2 ], which is then decomposed to form amorphous silicon nitride. The amorphous powder is crystallized by heat treatment. Many studies8 –12 have focused on the influences of powder properties on sinterability, microstructures, and mechanical properties. There has been, however, little research on the effects of the method of synthesis of the powders on the various changes that occur during sintering, e.g., weight changes, densification, phase transformation, and evolution of gaseous phases. In this study, the details of the changes and the relationships between changes, especially that between weight loss and gas evolution during sintering, were investigated for powders synthesized by both silica reduction and imide decomposition. II. EXPERIMENTAL PROCEDURES A. Sample preparation Commercial-grade silicon nitride powders synthesized by silica reduction (A-100, Toshiba Ceramics Co. Ltd., Tokyo, Japan) and by imide decomposition (E-10, Ube a)
Present address: Yamagata Technical High School, Yamagata 990, Japan.
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 12, Dec 1998
Downloaded: 17 Mar 2015
Industries Ltd., Tokyo, Japan) were used in this study. The properties and impuritie
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