ChemInform Abstract: Constitution of Mullite Glasses Produced by Ultra-Rapid Quenching of Plasma-Sprayed Melts.
Abstract
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ChemInform Abstract
Title glasses are prepared by melting spray-dried powders of pure . alpha.-Al2O3 (0.68 μm particle size) and quartz (1.92 μm) corresponding to 3:2 mullite composition in a nitrogen-plasma flame followed by quenching in water. As shown by XRD, optical microscopy, SEM, and TEM, the as-quenched hollow, porous spherules of ≤100 . mu.m particle size consist of mullite glass in addition to some residual α-Al2O3 and quartz and small amounts of newly formed mullite. The amount of mullite glass, composed of a network of (SiO) tetrahedra and (AlO)-octahedra, -pentahedra, and -tetrahedra, can be increased to >90 wt.% by double plasma quenching of the material. According to the 29Si and 27Al NMR data, the structure is very similar to those of metakaolinite, type I mullite precursors and other melt- quenched glasses of the Al2O3-SiO2 system.
