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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]