Abstract
Cr2O3 is a common nucleating agent useful for forming ceramics from oxide glasses. In this study we have used a variety of synchrotron radiation techniques to examine the atomic structure, crystallinity and microstructure of a magnesium alumino-silicate glass ceramic whose composition is close to that of the mineral cordierite, Mg2Al4Si5O18. X-ray Absorption spectra on the Cr K-edge have been performed with samples that were heat treated at different temperatures and times to examine the metamorphosis of the nucleating site. This study reveals that Cr3+ is always octahedrally coordinated with oxygen. In addition, the second nearest neighbour environment changes from an amorphous, single shell of Al/Si, but upon crystallisation, develops into a well ordered Al/Mg shell indicative of the formation of a dilute Cr spinel phase. Powder X-ray Diffraction (XRD) patterns, however, reveal that the major phase initially precipitated (approximately 900°C) is a stuffed quartz and from the lattice parameters that the composition is SiO2-rich. With prolonged heat treatment a small quantity of a spinel phase emerges whose composition from its lattice parameter is close to MgAl2O4. Combined Small Angle X-ray Scattering (SAXS) and XRD establish that devitrification at these temperatures is associated with particles about 250A in size, on average. Energy dispersive powder diffraction patterns were collected in situ to observe changes in crystallinity with temperature and time. From these measurements the stuffed quartz phase identified at 900°C is found to be intermediate, being eventually replaced at higher temperatures by cordierite with a small quantity of spinel.
Original language | English |
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Title of host publication | MRS Proceedings |
Place of Publication | Pittsburgh, PA |
Publisher | Materials Research Society |
Pages | 39-44 |
Number of pages | 6 |
Volume | 307 |
ISBN (Print) | 1558992030 |
DOIs | |
Publication status | Published - Apr 1993 |
Externally published | Yes |
Event | Materials Research Society Spring Meeting - San Francisco, CA, USA Duration: 12 Apr 1993 → 15 Apr 1993 |
Other
Other | Materials Research Society Spring Meeting |
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City | San Francisco, CA, USA |
Period | 12/04/93 → 15/04/93 |