Formation of Different Si 3 N 4 Nanostructures by Salt-Assisted Nitridation

• Published in: ACS applied materials & interfaces 2018-04, Vol.10 (14), p.11852-11861
• Main Authors: Liu, Xiongzhang, Guo, Ran, Zhang, Sengjing, Li, Qingda, Saito, Genki, Yi, Xuemei, Nomura, Takahiro
• Format: Article
• Language: English
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.7b16952

Silicon nitride (Si N ) products with different nanostructure morphologies and different phases for Si N ceramic with high thermal conductivity were synthesized by a direct nitriding method. NaCl and NH Cl were added to raw Si powders, and the reaction was carried out under a nitrogen gas flow of 100 mL/min. The phase composition and morphologies of the products were systemically characterized by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. At 1450 °C, the NaCl content was 30 wt %, the NH Cl content was 3 wt %, and the maximum α-Si N content was 96 wt %. The process of Si nitridation can be divided into three stages by analyzing the reaction schemes: in the first stage (25-900 °C), NH Cl decomposition and the generation of stacked amorphous Si N occurs; in the second stage (900-1450 °C), NaCl melts and Si N generates; and in the third stage (>1450 °C), α-Si N → β-Si N phase change and the evaporation of NaCl occurs. The products are made of two layers: a thin upper layer of nanowires containing different nanostructures and a lower layer mainly comprising fluffy, blocky, and short needlelike products. The introduction of NaCl and NH Cl facilitated the evaporation of Si powders and the decomposition of Al O from porcelain boat and furnace tube, which resulted in the mixing of N , O , Al O, and Si vapors and generated Al Si O nanowires with rough surfaces and lead to thin Si N nanowires, nanobranches by the vapor-solid (VS), vapor-liquid-solid (VLS), and the double-stage VLS base and VS tip growth mechanisms.