Title page for ETD etd-52698-1790

Type of Document Master's Thesis
Author Majumdar, Nandita N.
Author's Email Address nmajumda@vt.edu
URN etd-52698-1790
Title Development of Low Expansion Glaze Coatings on As Fired Si3N4 to Enhance Room Temperature Flexural Strength
Degree Master of Science
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Hirschfeld, Deidre A. Committee Chair
Brown, Jesse J. Jr. Committee Member
Gordon, Ronald S. Committee Member
  • silicon nitride
  • glaze coatings
  • room temperature flexural strength
Date of Defense 1998-06-19
Availability unrestricted
Silicon nitride (Si3N4) has the potential for use in various high-performance applications.

However, surface defects such as voids/pits are commonly present on as processed Si3N4. When

subjected to external forces, fracture originates at such flaws. To reduce or eliminate surface

flaws, machining operations are required which constitute a major proportion of production costs.

In order to offer an inexpensive alternative to machining and also to enhance the room

temperature flexural strength of as fired Si3N4, low expansion glaze coatings of lithium

aluminosilicate (LAS) and magnesium aluminosilicate (MAS) compositions were developed.

Homogeneous and crack-free glaze coatings were successfully formed on as processed Si3N4.

This ensured formation of compressive surface stresses on the as fired Si3N4 which, in turn, led to

the reduction of the effects of surface flaws. When compared to the uncoated as fired Si3N4, both

the glaze coatings helped achieve greater flexural strength. Analyses of the two glazes indicated

better strength for the MAS coating compared to the LAS. Wear tests revealed that the MAS

glaze exhibited higher wear resistance than the LAS glaze. These differences were attributed to

the ability of the magnesium aluminosilicate glaze to achieve greater surface smoothness and

better adherence to the substrate than the lithium aluminosilicate.

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