Processing of Silicon nitride


Silicon nitride. A cleaner alternative is spark plasma sintering, where heating is conducted rapidly (seconds) by passing pulses of electric current through the compacted powder. Dense silicon nitride compacts have been obtained by this technique at temperatures 1500–1700 °C. Three crystallographic structures of silicon nitride (Si3N4) exist, designated as α, β, and γ phases. The α and β phases are the most common forms of Si3N4 and can be produced under normal pressure conditions. The γ phase can only be synthesized under high pressures and temperatures and has a hardness of 35 GPa. The α- and β-Si3N4 have trigonal (Pearson symbol hP28, space group P31c, No. 159) and hexagonal (hP14, P63, No. 173) structures, respectively, which are built up by corner-sharing SiN4 tetrahedra. They can be regarded as consisting of layers of silicon and nitrogen atoms in the sequence ABAB... or ABCDABCD... in β-Si3N4 and α-Si3N4. The Si3N4 tetrahedra in β-Si3N4 are interconnected so that tunnels are formed, running parallel with the c-axis of the unit cell. Due to the c-glide plane that relates AB to CD, the α structure contains cavities instead of tunnels. The cubic γ-Si3N4 is often designated as c modification in the literature, in analogy with the cubic modification of boron nitride (c-BN). It has a spinel-type structure in which two silicon atoms each coordinate six nitrogen atoms octahedrally, and one silicon atom coordinates four nitrogen atoms tetrahedrally. If you are looking for high quality, high purity, and cost-effective Silicon nitride, or if you require the latest price, please email contact mis-asia.

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