Flame synthesis of aluminate glass microspheres
Various compositions of CaO–Al2O3, pure silica, and Y2O3–Al2O3 glass microspheres ∼10 μm in size have been prepared by flame synthesis in a CH4/O2 flame from oxide precursors using equipment built in-house. The microspheres were mostly amorphous, however, with increasing alumina content some crystalline phases were detected: these phases were grossite (CaAl4O7) in the Al2O3–CaO system, and α-Al2O3 and YAG (Y3Al5O12) in the Al2O3–Y2O3 system. The glasses were infrared transparent in the wavelength range 4000–1300 cm–1. Some bulk samples of some of the compositions were prepared by hot pressing of microspheres at a temperature between the glass transition temperature and the onset of crystallisation temperature. Densification proceeds by plastic flow. Despite being nearly fully dense the bulk glasses were opaque and milky white. Possible reasons for the lack of transparency include the presence of light scattering residual porosity or incorporation of water during quenching into glass structure. The method opens new possibilities for synthesis of bulk glasses with specific properties, which cannot be prepared by traditional melting and cooling of the melt, due to their high crystallisation tendency.
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Document Type: Research Article
Publication date: December 1, 2010