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Accession Number:
ADA331930
Title:
Sonochemical Synthesis of Molybdenum Disilicide (MoSi2).
Descriptive Note:
Final rept. 1 Apr 93-Dec 96,
Corporate Author:
WASHINGTON UNIV ST LOUIS MO
Report Date:
1997-10-22
Pagination or Media Count:
105.0
Abstract:
Two successful solution phase synthesis methods were developed for the preparation of Nanocrystalline MoSi particles. The first method consisted of coreducing molybdenum and silicon halides by NaK alloy in an ultrasonically agitated hydrocarbon solvent followed by thermal processing at lOOO deg C under vacuum to eliminate byproduct salts. The second method was the reaction of MoCl3 and Si in the solid state. These reactants underwent an ignition at approximately 500 deg C that resulted in the evolution of SiCl4 and the formation of MoSi crystallites. Nanoparticles were compacted using a range of proess variables. A micromechanism based model was developed for nanoparticle densification during uniaxial and hydrostatic pressing. The model takes into account the effects on densification of agglomeration, bulk and surface impurities, fewer dislocations per particle, low-stability of dislocations due to fine size, and other factors unique to nanoparticle systems. A good agreement of model predictions with experimental data was observed for a wide range of material and processing variables. Significant strength increases were observed for nanocrystalline MoSi2. However, the expected improvements in fracture toughness and ductility were not observed presumably because of high levels of carbon and oxygen in the particles and residual porosity in the compacts.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
