Electromagnetic wave-transparent porous silicon nitride ceramic prepared by gel-casting combined with in-situ nitridation reaction |
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Affiliation: | 1. Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, PR China;2. Engineering Academic of People''s Liberation Army, Xuzhou 221004, PR China |
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Abstract: | To achieve the balance between mechanical properties and electromagnetic wave-transparent properties of porous silicon nitride (Si3N4), the key is to form an interlocking microstructure constituted by columnar β-Si3N4 crystals. This structure can be realized by liquid-phase sintering. However, grain boundaries which affect high temperature properties and volume shrinkage during sintering are inevitable. We proposed a strategy to realize this structure by gel-casting of β-Si3N4 whisker (Si3N4w) and Si powder followed by in-situ nitridation of Si. To achieve chemically-stable slurry containing micro-sized Si with low viscosity, a novel formulation was developed. Two key structural parameters of the interlocking Si3N4w network, i.e., density of the Si3N4w skeleton and inter-whisker bonding mode, were adjusted by composition of raw materials and nitridation temperature. The flexural strength, dielectric constant and loss of the porous ceramics are 44.9 MPa, 2.7 and 2 × 10?3, when the volume fraction of Si3N4w/Si is 5 and the nitriding temperature is 1400 °C. |
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Keywords: | Porous silicon nitride ceramics Reaction bonded silicon nitride Gel-casting Dielectric properties |
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