✍ Scribed by M. Holmström; T. Chartier; P. Boch
No coin nor oath required. For personal study only.
Mullite ceramics have rather modest mechanical properties at room temperature. However, the strength and fracture toughness can be improved by adding ZrO 2, i.e. through transformationtoughening mechanisms.
The present study has been devoted to the preparation of mullite and ZrO2-mullite composites by reaction sintering. The starting materials are A1203, SiO 2 and ZrO 2 powders. The zirconia is a "pure" grade with no stabilizing additives. Its particle size is small (less than 0.5 I~m) to avoid the spontaneous tetragonal to monoclinic transformation.
The kinetics of reaction and sintering have been studied, and the microstructural characteristics of sintered materials have been determined for three compositions: ZrO2-free mullite, 5vol.%ZrO 2mullite, and 15vol.%ZrO2-mullite. In all cases, fully reacted and nearly dense samples can be obtained by sintering at 1620 °C for 2 h or more. Both densification and reaction kinetics are accelerated in ZrO2-mullite compared with ZrO2-free mullite. Zircon (ZrSi04) can be detected as a transitory phase in the ZrO 2-containing materials.
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