ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
A mechanistic model that interprets the transition in oxidation behavior of zirconiumdiboride as the temperature is varied from 600°C to 2500°C is presented. Available thermodynamicdata and literature data for vapor pressures, oxygen permeability in boria, and viscosity of boriawere used to evaluate the model. Three regimes and the temperatures of transition between themwere identified. In the intermediate temperature regime, viz., 1000ºC to 1800ºC, goodcorrespondence was obtained between theory and experiments for weight gain, recession, and scalethickness as functions of temperature and oxygen partial pressure. In this regime, the rate-limitingstep is the diffusion of dissolved oxygen through a film of liquid boria in capillaries at the base ofthe oxidation product. At lower temperatures, an external boria scale forms, but it was not found tocontribute significantly to oxidation resistance. Comparison with literature data on recession is verygood, but weight gain is predicted to be higher than experimentally observed unless flow of viscousboria is included. At higher temperatures, the boria is lost by evaporation, and the oxidation rate islimited by diffusion of molecular oxygen through the capillaries between nearly columnar blocks ofthe oxide MO2.; this regime is soon followed by a rapid acceleration of recession due tovaporization of the oxide MO2 itself
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/20/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.595-598.823.pdf
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