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Single crystalline α-Si 3 N 4 nanowhiskers were synthesized by direct nitridation of the NH 3 -pretreated silicon powders under N 2 /H 2 atmosphere without adding any catalysts. The phase composition and microstructure of the as-obtained products were investigated. It is shown that the NH 3 pretreatment has a great influence on the phase and microstructure of the products. With NH 3 pretreatment, single crystalline α-Si 3 N 4 nanowhiskers were obtained. Whereas, the dominant β-Si 3 N 4 particles were formed without NH 3 pretreatment. The isolated α-Si 3 N 4 crystal nuclei and the relatively thick oxide layer were formed on the surface of the silicon particles after pretreating by NH 3. The growth of the α-Si 3 N 4 nanowhiskers is obeyed the vapor-solid (VS) mechanism. [ABSTRACT FROM AUTHOR]

Silicon oxynitride nanopowders were successfully prepared by thermal explosion of the Si and SiO 2 mixed powders with the different particle sizes in various molar ratio (x / y = 2.0, 1.5) under N 2 , supplemented by the subsequent gravity separation strategy. The effects of Si/SiO 2 molar ratio, preheating temperature and insulation time on the phase composition of the as-oxynitrided products in the thermal explosion strategy were investigated. Meanwhile, the effects of sedimentation time on the phase composition and oxygen content of the as-obtained products in the gravity separation strategy were also discussed. It is shown that the by-products are absent in the as-oxynitrided products with a 1.5:1 M ratio. Prolonging the insulation time or preheating temperature is beneficial to improve the content of Si 2 N 2 O phase with a 2.0:1 M ratio. All the by-product phases are disappeared in the as-oxynitrided products with a 2.0:1 M ratio after sedimentation treatment of 120 s. The as-obtained silicon oxynitride nanopowders with 58% of recovery and 16.2% of oxygen content are close to the theoretical stoichiometric ratio of Si 2 N 2 O. The preparation mechanism of silicon oxynitride nanopowders was proposed. [ABSTRACT FROM AUTHOR]

In this work, millimeter-scale Si 3 N 4 @SiO x core-shell structure nanowires were synthesized using the direct nitridation method without the use of catalysts. The silicon powders used as raw materials were pretreated at 1300 °C for 3 h under ammonia. The ammonia was then converted into a nitrogen/hydrogen gas mixture and heated at 1350 °C for another 5 h. The morphology and structure of the as-obtained nanowires were investigated in detail. The Si 3 N 4 @SiO x nanowires with a core-shell structure were composed of a crystalline α-Si 3 N 4 core and an amorphous SiO x shell. The formation of the α-Si 3 N 4 core nanowire is due to the reaction of the N 2 gas with the byproduct SiO gas. However, the formation of the amorphous SiO x shell is related to the deposition location of the samples. For the inner part of the samples, the SiO x shell derives from the deposition of the byproduct SiO gas at 1350 °C, while the SiO x shell of the external part of the samples likely derives from the oxidation of the silicon nitride core during the cooling process. [ABSTRACT FROM AUTHOR]