High-Temperature Isothermal Oxidation of Ultra-High Temperature Ceramics Using Thermal Gravimetric Analysis

Melia Miller-Oana, Erica L. Corral

Research output: Contribution to journalArticle

7 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)619-626
Number of pages8
JournalJournal of the American Ceramic Society
Volume99
Issue number2
DOIs
StatePublished - Feb 1 2016

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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