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

点击翻译按钮获取中文摘要

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.