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Stability of Mullite Protective Coatings for Silicon‐Based Ceramics
Author(s) -
Krishnamurthy Ramanathan,
Sheldon Brian W.,
Haynes J. Allen
Publication year - 2005
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2005.00169.x
Subject(s) - mullite , materials science , ceramic , coating , silicon , diffusion , composite material , transient (computer programming) , volatilisation , ionic bonding , chemical engineering , mineralogy , thermodynamics , ion , metallurgy , chemistry , physics , organic chemistry , computer science , engineering , operating system
Silicon‐based ceramics are prone to severe oxidation and volatilization problems in the presence of water vapor. To address these issues, mullite has been investigated in recent years as a possible protective coating material. To analyze the stability of such coatings, a multi‐species diffusion model for ionic species is developed. Onsager reciprocity is assumed for the mobility coefficients and the resulting moving boundary problem is solved numerically. The formulation also accounts for substantial Si volatilization away from the outer surface of the coating. This model is used to analyze an initial transient leading to the formation of an internal silica layer, a second transient period that follows this silica formation, and a steady‐state regime that can only be attained if Si diffusion is sufficiently fast.