Optimization of Chemical Vapor Deposition Parameters for Fabrication of Oxidation‐Resistant Mullite Coatings on Silicon Nitride

Abstract

Fabrication of mullite (3Al2O3·2SiO2) coatings by chemical vapor deposition (CVD) using AlCl3–SiCl4–H2–CO2 gas mixtures was studied. The resultant CVD mullite coating microstructures were sensitive to gas‐phase composition and deposition temperature. Chemical thermodynamic calculations performed on the AlCl3–SiCl4–H2–CO2 system were used to predict an equilibrium CVD phase diagram. Results from the thermodynamic analysis, process optimization, and effects of various process parameters on coating morphology are discussed. Dense, adherent crystalline CVD mullite coatings ∼2 μm thick were successfully grown on Si3N4 substrates at 1000°C and 10.7 kPa total pressure. The resultant coatings were 001 textured and contained well‐faceted grains ∼0.3–0.5 μm in size.

Characterization of Chemical Vapor‐Deposited (CVD) Mullite+CVD Alumina+Plasma‐Sprayed Tantalum Oxide Coatings on Silicon Nitride Vanes After an Industrial Gas Turbine Engine Field Test

“…Mullite coatings (0.5–5 μm thick with an Al:Si ratio of 2.8–3.0) were deposited directly onto the as‐received Si 3 N 4 vanes at 1050°C and 10.6 KPa (80 Torr) for 120 min, using a laboratory‐scale, horizontal, hot‐wall CVD reactor flowing SiCl 4 , AlCl 3 , H 2 , and CO 2 13–15 . X‐ray diffraction of control coupons indicated crystalline mullite coatings with a 001 texture.…”

Suspension Development for Electrophoretic Deposition of Mullite Coating

“…Mullite has attracted the most interest as a protective coating for SiC or Si 3 N 4 ceramics due to its low coefficient of thermal expansion (CTE), chemical compatibility with Si-based ceramics, and good adherence, and currently it is receiving more attention as a diffusion barrier between Si-based materials and more complex aluminosilicate environmental barrier coatings [5]. A variety of methods have been developed to prepare mullite coating including CVD [6], plasma spraying [7] and slurry dip process [8]. For the plasma sprayed mullite coating, it contains a significant amount of metastable amorphous phase and a subsequent exposure to a temperature above 1000 o C will cause the crystallization of the amorphous phase.…”

Synthesis of Al2O3–SiO2 Films by Ar/O2 Plasma-Enhanced CVD from Alkoxide Precursors

“…[6][7][8][9][10][11][12][13][14] The disadvantage of using these chloride precursors is that chlorine is hazardous and may cause exhaust pollution. Alkoxide solutions are also important precursors as they have the advantages of low cost, no emission of halogen pollutants, and ease of handling.…”