BCl3-NH3-H2-N2前驱体化学气相沉积法制备氮化硼涂层

以BCl₃-NH₃-H₂-N₂为前驱体系统, 在垂直放置的热壁反应器中利用化学气相沉积工艺制备氮化硼(BN)涂层, 分析了工艺参数对沉积速率的影响, 通过扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和X射线衍射技术(XRD)分析了碳化硅纤维表面BN涂层的形貌和微观结构, 提出了BN沉积过程中主要的气相和表面反应, 以及关键气相组分。研究结果显示：在600~850℃的范围内, 随着沉积温度的升高, BN沉积速率逐渐加快, 同一温度下, 沉积区域内BN沉积速率沿气流方向逐渐减缓, 表明气相组分在气流方向逐渐消耗; 随着系统压力的提高, BN沉积速率先加快后减缓, 表明沉积过程由表面反应控制转变为质量传输控制; 随滞留时间延长, 距气体入口1~3 cm处, BN的沉积速率逐渐增大, 而距气体入口4~5 cm处, 沉积速率先增大后逐渐变小。SEM照片显示碳化硅纤维表面BN涂层光滑致密, XPS结果表明主要成分为BN及氧化产物B₂O₃, XRD图谱表明热处理前BN为无定形态, 1200℃热处理后BN的结晶度提高, 并向六方形态转变。BN的沉积是由BCl₃和NH₃反应所生成的中间气相组分Cl₂BNH₂、ClB(NH₂)₂和B(NH₂)₃来实现的。

Preparation of Boron Nitride Coating from BCl3-NH3-H2-N2 Precursor by Chemical Vapor Deposition

Boron nitride (BN) coatings were prepared using BCl₃-NH₃-H₂-N₂ precursor system by chemical vapor deposition process in a vertically-placed hot wall reactor. The effect of processing parameters on the deposition rates was analyzed. The morphology and microstructure of the BN coating on the surface of the silicon carbide fiber were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscope (XPS) and X-ray diffraction (XRD) . The dominant gas-surface reactions and crucial gas-phase components during BN deposition process were established. The results show that the deposition rates of BN increase gradually with the elevating deposition temperature from 600℃ to 850℃. And at a defined temperature, the deposition rates of BN gradually decrease along the gases flow direction in the deposition area, indicating that the gas-phase components are gradually consumed along the gases flow direction. The deposition rates of BN increase firstly and then decrease with the increase of system pressures, which suggests that the deposition process change from surface reactions control to mass transfer control. The BN deposition rates increase at 1-3 cm away from gases inlet, but decrease after increase firstly at 4-5 cm away from gases inlet as the residence time getting longer. SEM results show that BN coating on the surface of silicon carbide fiber is relatively smooth and dense. The chemical compositions of coating determined by XPS are BN and B₂O₃. XRD results indicate that the deposited BN at 650℃is amorphous. After heat-treatment at 1200℃ for 2 h, it transformed into the hexagonal BN(h-BN). The deposition of BN is achieved by the intermediate gas-phase species composed of Cl₂BNH₂, ClB(NH₂)₂ and B(NH₂)₃ which were generated by the reaction of BCl₃ and NH₃.