Disperse Spherical Single-crystal α-Al₂O₃ Particles And Their Composite

α-Al2O3 has been exploited in applications ranging from ceramic fillers, bioceramics, to transparent armour, and transparent sodium vapour lamp envelopes, due to its unique mechanical, optical, electrical, biological properties. One of the most important application of α-Al2O3 spheres is to be utilized as filling material for improving polymers properties and broadening polymer’s applications field. Compared with conventional Al2O3 particles, α-Al2O3 spheres have more excellent dispersion of the fillers in PMMA matrix, owing to its low viscosity and high symmetry characteristics. Generally, transition aluminas transformed to α-Al2O3 occurs at a high temperature, leading to exaggerated grain growth and vermicular microstructure, which limit the application of α-Al2O3 particles. Therefore, it is quite significant to prepare dispersed α-Al2O3 spheres by reducing the phase transition temperature from the perspective of commercial or academic. Hence, we report a new approach to fabricate single-crystal α-Al2O3 spheres with good dispersion and narrow size distributions by introducing α-Fe2O3 as seed and isolating phase. Furthermore, we prepared α-Al2O3 spheres/reducing graphene oxide(r GO-Al2O3) hybrid fillers to enhance the thermal stability of PMMA composites.(1) In this work, we develop a simple method for the fabrication of dispersed and single-crystal α-Al2O3 spheres by co-precipitation-isolation phase method. A study of the microstructure of the Al2O3 particles was accomplished through transmission electron microscopy(TEM), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The TEM, SEM and XRD results show that the α-Al2O3 particles are dispersed, small in size, and spherical in shape. And we have fabricated different samples with average sizes of 116, 125, and 130 nm, respectively. The influence of α-Fe2O3 served as seed and isolating phase on the phase transformation of the alumina precursor, particle morphology, size, and agglomeration degree was investigated.(2) PMMA composites filled with r GO-Al2O3 with outstanding thermal stability have been prepared by simple solution mixing method. The GO-Al2O3 hybrids were synthesized through in-situ processes. And then freeze-dried and low-temperature have been maintained to achieve reduction of r GO-Al2O3 hybridfillers. The results of SEM and thermogravimetric analysis(TG) show that the incorporation of r GO-Al2O3 hybrid fillers not only improve the dispersion of the fillers in PMMA matrix, but also enhance the thermal stability of PMMA composites as compared with the pure PMMA. Meanwhile, the thermal stability of PMMA composites with r GO-Al2O3 hybrid fillers were systematically studied in this dissertation. The enhanced thermal stability was observed in the PMMA composites filled with r GO-Al2O3 hybridfillers, and the related mechanism was discussed.