Title page for ETD etd-32798-1377


Type of Document Master's Thesis
Author Nguyen, Thierry Huu Chi
Author's Email Address nguyent@vt.edu
URN etd-32798-1377
Title CMZP and Mg-doped Al2TiO5 Thin film Coatings for High Temperature Corrosion Protection of Si3N4 Heat Exchangers
Degree Master of Science
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Brown, Jesse J. Jr. Committee Chair
Kampe, Stephen L. Committee Member
Love, Brian J. Committee Member
Keywords
  • alkali corrosion
  • silicon nitride
  • coatings
Date of Defense 1998-04-21
Availability unrestricted
Abstract
Silicon nitride (Si3N4) is a potentially good ceramic material for industrial heat exchangers. However, at elevated temperatures and in coal combustion atmospheres its lifetime is severely reduced by oxidation. To increase its corrosion resistance, the formation of a protective oxidation barrier layer was promoted by the deposition of oxide thin films. Homogeneous and crack-free oxide coatings of calcium magnesium zirconium phosphate (CMZP) and magnesium doped aluminum titanate (Mg-doped Al2TiO5) were successfully deposited on Si3N4 using the sol-gel and dip-coating technique. Coated and uncoated samples were then exposed to a sodium containing atmosphere at 1000*C for 360 hours to simulate typical industrial environment conditions. Structural post-exposure analyses based on weight loss measurements and mechanical tests indicated better corrosion resistance and strength retention for CMZP coated Si3N4 compared to as received and Mg-doped Al2TiO5 coated Si3N4. This difference was attributed to the protective nature of the corrosion layer, which in the case of CMZP, significantly impeded the inward diffusion of oxygen to the Si3N4 surface.
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