Browsing by Author "Zangvil, A"

Now showing 1 - 2 of 2

Effect of zirconia content on the oxidation behavior of silicon carbide/zirconia/mullite composites
(1998-09-01)
Tsai, CY
;
Lin, CC
;
Zangvil, A
;
Li, AK
;
材料科學與工程學系
The oxidation of hot-pressed SiC-particle (SiCp)/zirconia (ZrO2)/mullite composites with various ZrO2 contents, exposed in air isothermally at 1000 degrees and 1200 degrees C for up to 500 h, was investigated; an emphasis was placed on the effects of the ZrO2 content on the oxidation behavior. A clear critical volume fraction of ZrO2 existed for exposures at either 1000 degrees or 1200 degrees C: the oxidation rate increased dramatically at ZrO2 contents of >20 vol%. The sharp transition in the oxidation rate due to the variation of ZrO2 content could be explained by the percolation theory, when applied to the oxygen diffusivity in a randomly distributed two-phase medium. Morphologically, the composites with ZrO2 contents greater than the critical value showed a large oxidation zone, whereas the composites with ZrO2 contents less than the critical value revealed a much-thinner oxidation zone. The results also indicated that the formation of zircon (ZrSiO4) at 1200 degrees C, through the reaction between ZrO2 and the oxide product, could reduce the oxidation rate of the composite.
Phase evolution in silicon carbide-whisker-reinforced mullite/zirconia composite during long-term oxidation at 1000 degrees to 1350 degrees C
(2000-07-01)
Lin, CC
;
Zangvil, A
;
Ruh, R
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A composite consisting of 30 wt% SiC whiskers and a mullite-based matrix (mullite-32.4 wt% ZrO2-2.2 wt% MgO) was isothermally exposed in air at 1000 degrees-1350 degrees C, for up to 1000 h, Microstructural evolution in the oxidized samples was investigated using X-rap diffractometry and analytical transmission electron microscopy. Amorphous SiO2, formed through the oxidation of SIC whiskers, was devitrified into cristobalite at T greater than or equal to 1200 degrees C and into quartz at 1000 degrees C. At T greater than or equal to 1200 degrees C, the reaction between ZrO2 and SiO2 resulted in zircon, and prismatic secondary mullite grains mere formed via a solution-reprecipitation mechanism in severely oxidized regions. Ternary compounds, such as sapphirine and cordierite, also mere found after long-term exposure at T greater than or equal to 1200 degrees C.