Combustion SynThesis Of Molybdenum Silicides And Borosilicides For Ultrahigh-Temperature Structural Applications

Author

Mohammad Shafiul Alam, University of Texas at El PasoFollow

Date of Award

2014-01-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

Evgeny Shafirovich

Abstract

Molybdenum silicides and borosilicides are promising structural materials for gas-turbine power plants. A major challenge, however, is to simultaneously achieve high oxidation resistance and acceptable mechanical properties at high temperatures. For example, molybdenum disilicide (MoSi₂) has excellent oxidation resistance and poor mechanical properties, while Mo-rich silicides such as Mo₅Si₃ (called T₁) have much better mechanical properties but poor oxidation resistance. One approach is based on the fabrication of MoSi₂−T₁ composites that combine high oxidation resistance of MoSi₂ and good mechanical properties of T₁. Another approach involves the addition of boron to Mo-rich silicides for improving their oxidation resistance through the formation of a borosilicate surface layer. In particular, Mo₅SiB₂ (called T₂) phase is considered as an attractive material. In the Thesis, MoSi₂−T₁ composites and materials based on T₂ phase are obtained by mechanically activated SHS. Use of SHS compaction (quasi-isostatic pressing) significantly improves oxidation resistance of the obtained MoSi₂−T₁ composites. Combustion of Mo−Si−B mixtures for the formation of T₂ phase becomes possible if the composition is designed for the addition of more exothermic reactions leading to the formation of molybdenum boride. These mixtures exhibit spin combustion, the characteristics of which are in good agreement with the spin combustion theory. Oxidation resistance of the obtained Mo−Si−B materials is independent on the concentration of Mo phase in the products so that the materials with a higher Mo content are preferable because of better mechanical properties. Also, T₂ phase has been obtained by the chemical oven combustion synThesis technique.

Language

en

Provenance

Received from ProQuest

Copyright Date

2014

File Size

70 pages

File Format

application/pdf

Rights Holder

Mohammad Shafiul Alam

Recommended Citation

Alam, Mohammad Shafiul, "Combustion SynThesis Of Molybdenum Silicides And Borosilicides For Ultrahigh-Temperature Structural Applications" (2014). Open Access Theses & Dissertations. 1190.
https://scholarworks.utep.edu/open_etd/1190