Accession Number:

ADA277224

Title:

Sodium Sulfate Corrosion of Silicon Carbide Fiber-Reinforced Lithium Aluminosilicate Glass-Ceramic Matrix Composites

Descriptive Note:

Master's thesis

Corporate Author:

NAVAL POSTGRADUATE SCHOOL MONTEREY CA

Personal Author(s):

Report Date:

1993-12-01

Pagination or Media Count:

71.0

Abstract:

Sodium sulfate hot corrosion of a SiC fiber-reinforced lithium aluminosilicate LAS glass-ceramic matrix composite was studied using Scanning Electron Microscope SEM and X-ray Diffraction XRD. Changes in the microstructural chemical composition of the specimens were investigated. The samples provided by Naval Air Warfare Center NAWC, Warminster, PA were grouped as follows 1 as-received, 2 Na2SO4 salt-coated and heat-treated in oxygen, 3 noncoated and heat-treated in oxygen, 4 Na2S4. Salt-coated and heat- treated in argon, and 5 noncoated and heat-treated in argon. Heat treatment was performed by NAWC for 100 hours at 900 deg C. Experimental data obtained indicated that the presence of Na2SO4 in an oxidative environment resulted in rapid corrosion of the matrix and SiC fibers and in the latter rings of SiO2 replaced what had previously been SiC. There was very limited degradation of the fibers and matrix exposed at the surface in the noncoated sample heat-treated in oxygen and in the salt-coated sample heat-treated in argon. A significant reduction in the amount of mullite in the matrices of all heat-treated samples was observed. Mullite dissolved into either the glassy phase or into the Beta- spodumene matrix. Lastly, the presence of distinct magnesium silicate crystalline phases in the salt-coated and heat-treated in oxygen sample implies that the MgO at the surface reacted with the SiO2 in the matrix. SiC Fiber- reinforced composites, Lithium aluminosilicate glass ceramics.

Subject Categories:

  • Laminates and Composite Materials

Distribution Statement:

APPROVED FOR PUBLIC RELEASE