Influence Of Phase Transformation On γ-Al₂O₃ Sintering Behavior

Thermal Dilatometer, X-ray Diffraction(XRD), Dynamic Laser Scattering(DLS) Scanning Electron Microscope(SEM), and Fourier Transform Infrared Radiation(FT-IR) were used to analysis the densification process, microstructure evolution and phase transformation in the sintering stage of nano γ-Al₂O₃. The influence of phase transformation on both the densification and the changes of the particle size were analyzed.The sintering curves of γ-Al_O3 samples with 1²Î¼m and 10⁵0nm were compared. In the entire sintering process, the nanometer sample shrinkage speed was larger than that of the micron sample, and the contraction completed temperature was lower. At the same time, the shrinkage quantity can reach 23.28%. The phase transformation took place in the range of 900 1170℃ for nanometer sample and 960 1230℃ for micron sample. The shrinkage rate was 11.28% for nanometer sample and 12.32 % for micron sample during the phase transformation stage.The densification process and microstructure change of nanometer γ-Al₂O₃ were analyzed. In the initial period of sintering, γ→δ→θ transformation contributed little to the shrinkage. In the intermediate stage of 950℃, alpha phase transformation caused the volume diffusion resistance reduce, the sintering driving force increasing led to the densification speeding up. In the later period, crystal growth was rapid, and densification was enhanced. The pore ratio decreased with the temperature increasing. A lot of pores with different shapes which size above 200nm were closed within crystal at the end of sintering. Crystal shape changed from circle granular to inferior circle granular, short columnar and anomaly polygon granular.The phase transformation influenced the densification process. In the range of 950℃¹170℃, the θ→a transformation belongs to non-isotropically nuclear process. New phase nuclear formation and growth happened in the same process, which made the grain size distribute in the scope of 50 300nm. Afer phase transformation, heterogeneous microstructure caused many pores in the grains.The changes of grain size related to the phase transformation. The particle size decreased along with the formation of new phase, while the grain size ascended with the new phase growth. Corresponding to the formation of three new phases, the particle size reduced with temperature elevating.