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Rollers made of silicon nitride ceramic are sometimes used in high-end skateboard Bearings , due to the material's shock and heat-resistant characteristics. Also used an ignition source for domestic gas appliances, Hot Surface Ignition. Crystal structure of silicon nitride There exist 3 crystallographic structures of silicon nitride (Si3N4), 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 condition. The γ phase can only be synthesized under extremely high pressure and it is third hardest materials, following the diamond and the cubic boron nitride (BN). See crystallographic structure of the α- and β- Si3N4 in and γ phase Si3N4 in [http://beamteam.usask.ca/member8.htm α- and β-Si3N4 have hexagonal structures, 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 α-Si3N4 and β-Si3N4, respectively. The AB layer is the same in the α and β phases, and the CD layer in the α phase is related to AB by a c-glide plane. The Si3N4 tetrahedra in β-Si3N4 are interconnected in such a way 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. {Link without Title} |
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