College of Mechanical and Electronic Engineering , Northwest A&F University , Xinong Road 22 , Yangling , Shaanxi 712100 , China.
ACS Appl Mater Interfaces. 2018 Apr 11;10(14):11852-11861. doi: 10.1021/acsami.7b16952. Epub 2018 Mar 28.
Silicon nitride (SiN) products with different nanostructure morphologies and different phases for SiN ceramic with high thermal conductivity were synthesized by a direct nitriding method. NaCl and NHCl 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 NHCl content was 3 wt %, and the maximum α-SiN 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), NHCl decomposition and the generation of stacked amorphous SiN occurs; in the second stage (900-1450 °C), NaCl melts and SiN generates; and in the third stage (>1450 °C), α-SiN → β-SiN 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 NHCl facilitated the evaporation of Si powders and the decomposition of AlO from porcelain boat and furnace tube, which resulted in the mixing of N, O, AlO, and Si vapors and generated Al Si O nanowires with rough surfaces and lead to thin SiN nanowires, nanobranches by the vapor-solid (VS), vapor-liquid-solid (VLS), and the double-stage VLS base and VS tip growth mechanisms.
通过直接氮化法合成了具有不同纳米结构形态和不同相的氮化硅（SiN）产品，以提高 SiN 陶瓷的导热率。将 NaCl 和 NHCl 添加到原始 Si 粉末中，并在 100 mL/min 的氮气流量下进行反应。通过 X 射线衍射、场发射扫描电子显微镜和高分辨率透射电子显微镜系统地表征了产物的相组成和形态。在 1450°C 时，NaCl 含量为 30wt%，NHCl 含量为 3wt%，最大α-SiN 含量为 96wt%。通过分析反应方案，可以将 Si 氮化过程分为三个阶段：第一阶段（25-900°C），NHCl 分解并产生堆叠的非晶态 SiN；第二阶段（900-1450°C），NaCl 熔化并产生 SiN；第三阶段（>1450°C），α-SiN→β-SiN 相变和 NaCl 蒸发。产物由两层组成：上层为包含不同纳米结构的纳米线薄层，下层主要由蓬松、块状和短针状产物组成。NaCl 和 NHCl 的引入促进了 Si 粉末的蒸发以及瓷舟和炉管中 AlO 的分解，从而导致 N、O、AlO 和 Si 蒸气的混合，并产生具有粗糙表面的 Al Si O 纳米线，导致 SiN 纳米线、纳米枝晶通过气相-固相等（VS）、气相-液相-固相等（VLS）和双阶段 VLS 基底和 VS 尖端生长机制生成。
