A study of pest oxidation in polycrystalline MoSi sub 2

Journal Article · Thu Oct 01 04:00:00 EDT 1992 · Journal of Materials Research; (United States)

DOI:https://doi.org/10.1557/JMR.1992.2747· OSTI ID:7080998

McKamey, C G; Tortorelli, P F; DeVan, J H; Carmichael, C A ^[1]

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1. Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6115 (United States)

MoSi{sub 2} is a promising high temperature material with low density (6.3 g/cm{sup 3}), high melting point (2020 {degree}C), and good oxidation resistance at temperatures to about 1900 {degree}C. However, in the intermediate temperature range between 400 and 600 {degree}C, it is susceptible to a pest'' reaction which causes catastrophic disintegration by a combination of oxidation and fracture. In this study, we have used polycrystalline MoSi{sub 2}, produced by arc-casting of the pure elements and by cold and hot pressing of alloy powders, to characterize the pest reaction and to determine the roles of composition, grain or phase boundaries, and physical defects on the oxidation and fracture of specimens exposed to air at 500 {degree}C. It was found that pest disintegration occurs through transport of oxygen into the interior of the specimen along pre-existing cracks and/or pores, where it reacts to form MoO{sub 3} and SiO{sub 2}. The internal stress produced during the formation of MoO{sub 3} results in disintegration to powder. Near the stoichiometric ratio, the susceptibility to pest disintegration increases with increasing molybdenum content and with decreasing density. Silicon-rich alloys were able to form protective SiO{sub 2} and showed no indication of disintegration, even at densities as low as 60%.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 7080998
• Journal Information: Journal of Materials Research; (United States), Journal Name: Journal of Materials Research; (United States) Vol. 7:10; ISSN JMREE; ISSN 0884-2914
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360205* -- Ceramics
Cermets
& Refractories-- Corrosion & Erosion
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CRYSTAL STRUCTURE
CRYSTALS
FAILURES
FRACTURES
GRAIN BOUNDARIES
MICROSTRUCTURE
MOLYBDENUM COMPOUNDS
MOLYBDENUM SILICIDES
OXIDATION
POLYCRYSTALS
REFRACTORY METAL COMPOUNDS
SILICIDES
SILICON COMPOUNDS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TRANSITION ELEMENT COMPOUNDS