Molecular Modeling of High-Temperature Oxidation of Refractory Borides
Abstract
Refractory diboride with silicon carbide additive has a unique oxide scale structure with two condensed oxide phases (solid + liquid), and demonstrates oxidation resistance superior to either monolithic diboride or silicon carbide. We rationalize that this is because the silica-rich liquid phase can retreat outward to remove the high SiO gas volatility region, while still holding onto the zirconia skeleton mechanically by capillary forces, to form a "solid pillars, liquid roof" scale architecture and maintain barrier function. Basic assessment of the oxygen carriers in the borosilicate liquid in oxygen-rich condition is performed based on first-principles calculations. It is estimated from entropy and mobility arguments that above a critical temperature Tc~ 1500C the dominant oxygen carriers should be network defects, such as peroxyl linkage or oxygen deficient centers, instead of molecular O2 as in the Deal-Grove model. These network defects will lead to sub-linear dependence of the oxidation rate with external oxygen partial pressure.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 2008
- Accession Number
- ADA482170
Entities
People
- Ju Li
Organizations
- Ohio State University