Accelerated sintering of SiC Nanopowder with Stacking Disorder-Order Transformation
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Accelerated sintering of SiC Nanopowder with Stacking Disorder-Order Transformation Kenshiro Shirai1, Takeshi A. Yamamoto1, Manshi Ohyanagi1, Zuhair A. Munir2 1 High-Tech Research Center, Ryukoku University, Seta, Otsu, 520-2194, Japan 2 Facility for Advanced Combustion Synthesis (FACS), Department of Chemical Engineering and Materials Science, University of California, Davis California, USA ABSTRACT Consolidation of SiC nanopowder with stacking disordered structure was accelerated by o milling with the AlN as the additive. SiC powders without the additive was sintered at 1900 C to a density of 99%. The grain size of the sintered material was approximately 500 nm. On the other hand, with AlN as additive, the sintering temperature to reach a density of 98% was reduced to o 1700 C by the addition of 3.0 mol% AlN. The grain size of this material was less than 100 nm. The effect of AlN addition on SiC sintering with disorder-order transformation was evaluated by shrinkage profile, XRD analysis, and TEM observation. INTRODUCTION Present and potential technological structural applications of silicon carbide are the consequence of its unusual properties which include low density, chemical stability, and high strength at high temperatures. In addition, silicon carbide has recently been considered for device applications because of its attractive electronic properties [1-5]. As a wide-gap semiconductor, it has received considerable attention as a material for high-power devices, including radar and microwave applications under extreme conditions. Its high temperature strength, high thermal conductivity, and low nuclear activation, make it attractive for these applications [6-10]. Since o the sintering of SiC requires high temperatures> 2000 C [11,12], it is difficult to accomplish without extensive grain growth. Sintering additives of Al2O3 and a B-C mixture have been used to lower the sintering temperature and hence control grain growth [13-16]. However, the precipitation of these additives in the grain boundary often leads to a decrease in the mechanical and thermoelectrical properties of the sintered product. We have recently shown that SiC nanopowders with stacking disordered structure prepared by mechanical alloying (MA), could be consolidated without sintering additives by the spark plasma sintering (SPS) method [17-20]. The relative density of SiC powder synthesized by o planetary ball milling increased abruptly to 95 % when sintering was carried out at 1675 C, and o to 98 % when sintering was done at 1700 C. We have shown that the consolidation of nanostructured SiC to high relative densities (up to 98 %) is due to densification enhanced by a disorder-order transformation [17-20]. We also observed a dependence of sintering behavior on the material used for the milling balls and vial, implying a possible dependence of the ordering process on impurity contamination. However, the nature of the impurities could not be determined by XRD analysis due to the low level of its occurrence [21]. In this work, we
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