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High-Temperature Isothermal Oxidation of Ultra-High Temperature Ceramics Using Thermal Gravimetric Analysis.
- Source :
-
Journal of the American Ceramic Society . Feb2016, Vol. 99 Issue 2, p619-626. 8p. - Publication Year :
- 2016
-
Abstract
- Oxidation of ZrB2 + SiC composites is investigated using isothermal measurements to study the effects of temperature, time, and gas flow on oxidation behavior and microstructural evolution. A test method called dynamic nonequilibrium thermal gravimetric analysis (DNE-TGA), which eliminates oxidation during the heating ramp, has been developed to monitor mass change from the onset of an isothermal hold period (15 min) as a function temperature (1000°C-1600°C) and gas flow (50 and 200 mL/min). In comparing isothermal to nonisothermal TGA measurements, the scale thicknesses from isothermal tests are up to 4 times greater, indicating that oxidation kinetics are faster for isothermal testing, where the oxide scale thickness is 110 μm after 15 min at 1600°C in air. Isothermal oxidation followed parabolic kinetics with a mass gain that is temperature dependent from 1000°C-1600°C. The mass gain increased from ~5 to 45 g/m2 and parabolic rate constants increased from 0.037 to 2.2 g2/m4·s over this temperature range. The effect of flow velocity on oxidation is not significant under the given laminar flow environment where the gas boundary layer is calculated to be 4 mm. These values are consistent with diffusion of oxygen through the glass-ceramic surface layer as rate limiting. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00027820
- Volume :
- 99
- Issue :
- 2
- Database :
- Academic Search Index
- Journal :
- Journal of the American Ceramic Society
- Publication Type :
- Academic Journal
- Accession number :
- 112684785
- Full Text :
- https://doi.org/10.1111/jace.14001