Development of High Thermal Conductivity Silicon Nitride Ceramics Using Rare-Earth Metal Complexes as the Precursors for Sintering Aids

1.稀土金属配合物的合成及合适的溶剂选择CN-为配体，在Y ~（3+）水溶液中，以不含氧原子的CN-为配体，在任何条件下都只生成氢氧化物，研究了氰基配合物的合成。以艾德（艾德）为溶剂，成功地合成了[Y（艾德）3]C13配合物，证实了该配合物具有很强的吸湿性，发现非水溶剂CH 3CN能溶解YC 13。以其为溶剂，使用化学计量的ED合成了[Y（艾德）3]C13溶液。将氮化硅和烧结助剂粉末与溶液混合并随后干燥，这是一种均匀添加配合物的新方法。氮化硅烧结体的制备及其评价添加[Y（艾德）3] Cl 3作为“脱氧烧结助剂”，制备了氮化硅烧结体。然而，它们显示出非常低的烧结密度，约60%。发现使用麦克斯韦关系式估计的致密烧结体的热导率高于没有“脱氧烧结助剂”的那些。XRD分析表明样品中存在Y_2Si_3N_6。在1800℃热压烧结得到致密的烧结体，在1850℃退火完成相变。这导致了烧结体的显著膨胀，这可能是由于复合体在完全分解之前致密化.第四族元素的氮化物和碳化物的影响通过添加第四族元素的氮化物和碳化物制备的氮化硅烧结体进行了评价。虽然热力学计算预测只有ZrN和HfN可以作为MX（M=Ti、Zr或Hf，X=N或C）中的“脱氧烧结助剂”，但所有烧结体的热导率均低于不含MX的烧结体。发现IV族元素氮化物显著改善了致密化。

1. Synthesis of rare-earth metal complexes, and search for appropriate solventsSelecting CN-as a ligand without oxygen atom, the synthesis of cyano complex was examined from an aqueous solution of Y3+, which produced only hydroxides in any conditions. Selecting ethylene diamine (ED), the [Y(ED)3]C13 complex was successfully synthesized using ED itself as a solvent, which was confirmed to be highly hygroscopic.It was found that a non-aqueous solvent CH3CN dissolved YC13. Using it as a solvent, a [Y(ED)3]C13 solution was synthesized using a stoichiometric amount of ED. Powders of Silicon nitride and sintering aids were mixed with the solution and were subsequently dried, which was a new method for homogeneously adding the complex.2. Fabrication of silicon nitride sintered bodies and their evaluationAdding [Y(ED)3]C13 as a "de-oxygen sintering aid", silicon nitride sintered bodies were fabricated. However, they showed very low sintered densities about 60 %. Estimated thermal conductivities of dense sintered bodies using the Maxwell relationship were found to be higher than those without "de-oxygen sintering aid". The XRD showed the existence of Y2Si3N6 which had never reported. The dense sintered body fabricated by hot-pressing at 1800℃ was annealed at 1850℃ to finish the phase transformation. This resulted in significant swelling of sintered body, which would be due to the densification before the complete decomposition of complex.3. Effect of the nitrides and carbides of the group IV elementsSilicon nitride sintered bodies fabricated by adding the nitrides and carbides of the group IV elements were evaluated. Although the thermodynamic calculations predicted that only the ZrN and HfN could act as the "de-oxygen sintering aid" among MX (M=Ti, Zr or Hf, X=N or C), all the sintered bodies showed lower thermal conductivities than those without MX. It was found that the group IV element nitrides significantly improved densification.