热障涂层陶瓷层材料LnMgAl11O19(Ln=La,Nd)粉体的性能

用共沉淀法制备LaMgAl₁₁O₁₉粉体，证明了提高沉淀温度和pH值可使前驱粉体的性能明显提高。应用差热分析和X射线法研究了磁铅石相的生成温度和粉体的结晶度；使用Scherrer 公式并结合XRD谱计算了晶粒尺寸；用扫描电镜观察了各工艺参数的前驱粉体在1500℃时效5 h后的形貌；使用Malvern ZEN3600粒度仪和Manual measurement软件分析了粉体硬团聚的尺寸分布；用Nd₂O₃, Gd₂O₃, Sm₂O₃替代La₂O₃，研究了制备多种镁基六铝酸盐粉体的可行性。结果表明：在pH值为11.5、沉淀温度为60℃条件下制备的前驱粉体，其完全相变为纯LaMgAl₁₁O₁₉粉体的初始温度为1440℃，比在常温下沉淀的前驱粉体降低了150℃，磁铅石相的生成效率明显提高。在1500℃时效5 h的粉体其晶粒为纳米尺度。提高沉淀温度和pH值有利于减小晶粒尺寸和降低粉体的热导率。采用相同工艺参数可制备出纯NdMgAl₁₁O₁₉粉体，其晶粒尺寸略大于LaMgAl₁₁O₁₉粉体的尺寸。

Preparation and Performance of LnMgAl11O19(Ln=La,Nd) Powders for Thermal Barrier Coating

Powders of LaMgAl₁₁O₁₉ (lanthanum magnesium hexaaluminate) were synthesized via a two-step process, i.e. chemical co-deposition for precursor powders and then high-temperature calcination for final products. The quality of the precursor powders could be improved significantly by proper adjusting the co-deposition parameters such as increasing the deposition temperature and pH value. The formation temperature of magnetoplumbite-phase, the crystallinity and grain size of the prepared powders were characterized by differential thermal analysis and X-ray diffraction. The morphology of powders calcined at 1500℃ for 5 hours for various precursors was examined by scanning electron microscope, while their grain size distribution was inspected by Malvern ZEN3600 and Manual measurement. The feasibility of preparation of various magnesium hexaaluminate was tried by replacing La₂O₃ with Nd₂O₃, Gd₂O₃ or Sm₂O₃ respectively. The results show that the precursor powders, co-deposited from solution with pH=11.5 at 60℃, could be transformed into powders of plain LaMgAl₁₁O₁₉-phase after calcination at 1440℃, which was 150℃ lower than those co-deposited at room temperature. The powders calcined at 1500℃ for 5 hours were nano-sized, while rising the deposition temperature and pH value may be beneficial to decrease the grain size, therewith decrease the thermal conductivity of powders. Besides the grain size of NdMgAl₁₁O₁₉ powders prepared with the same process parameters was slightly larger than that of LaMgAl₁₁O₁₉ powders.