ELECTROLESS DEPOSITION OF OXIDATION RESISTANT HIGH TEMPERATURE COATINGS IN MOLTEN SALT

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2021-9-10

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Ömür, İshak Emre

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Molybdenum and molybdenum alloy (TZM) can be protected against oxygen in hightemperature environment by developing silicide coating on their surface without damaging their mechanical properties. In this study, molybdenum di-silicide was coated on pure molybdenum and its alloy (TZM) surfaces using a molten salt method. NaCl-KCl-NaF eutectic composition was used as salt mixture, and Na2SiF6 and silicon powder were added to the system as silicon source. X-ray diffraction (XRD), Inductively Coupled Plasma – Mass Spectrometer (ICP-MS) and scanning electron microscope (SEM) were used for characterization of the silicide coatings. Effects of operating temperature and time on coating thickness for both pure molybdenum and TZM alloy were studied. Also, effect of silicon sources; Na2SiF6 and silicon powder, on thickness of silicide layer was investigated. While higher operating temperature had limited effect on coating thickness for pure molybdenum samples, thicker coatings were obtained at lower temperatures for TZM alloy samples. Also, longer operating time slightly increased coating thickness for pure molybdenum substrates, however; it had a significant effect for TZM alloy samples for 4 hours of processing time. Although amount of silicon sources in salt mixture had no effect on coating thickness for pure molybdenum samples, amount of silicon in salt mixture had an enormous effect for TZM alloy samples. Also, molybdenum di-silicide coated TZM alloy samples were tested at high-temperature oxygen environment, and it was proved that silicide coating is protective against oxidation by forming silica.

Subject Keywords

Molten salt, high-temperature coatings, molybdenum di-silicide coatings, oxidation, crystallography

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https://hdl.handle.net/11511/94244

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

İ. E. Ömür, “ELECTROLESS DEPOSITION OF OXIDATION RESISTANT HIGH TEMPERATURE COATINGS IN MOLTEN SALT,” M.S. - Master of Science, Middle East Technical University, 2021.