Introduction Silicon-based ceramics and composites are being used to improve the performance of gas turbine engines while reducing emissions.  These ceramics are susceptible to corrosion in the high-temperature, high-pressure combustion environment limiting their usefulness.  Oxide ceramic environmental barrier coatings are being developed to protect these materials from corrosion, however, silica forms between the coating and the SiC and Si3N4 substrate. The silica is a weak link in the system thus research has been initiated to explore ceramics that form zircon (ZrSiO4) and mullite (Al6Si2O13).  The similar thermal and mechanical properties of these oxides to the SiC and Si3N4 substrates can effectively eliminate spalling and limit corrosion associated with silica formation.   Experimental The ceramic mixtures were prepared in stoichiometric quantities and wet ball milled with appropriate media for an intimate distribution of powder The mixtures were hot pressed into 3.81 cm diameter cylindrical specimens The specimens were then ground and cut into coupons 1.17 x 1.17 x 0.254 cm3 The specimens were cleaned, weighed and annealed at different temperatures and time intervals

Room Temperature X-Ray Diffraction Data Collection

Crystal Structure X-ray Diffraction Pattern Crystal System Cubic a=b=c=4.3582Å a=ß=y=90º F43/m Hexagonal a=b=7.6608 Å c=2.9110 Å a=ß=90º y=120º P63/m Tetragonal a=b=6.6120 Å c=5.9940 Å a=ß=y=90º I41/amd Orthorhombic a=7.5473 Å b=7.6928 Å c=2.8893 Å a=ß=y=90º Pbam * Si and Al2 are shared sites   Future Work Combine Silicon Carbide particulate with zircon, mullite and corundum as three different batches.  Also, zirconium silicide will be mixed with silicon carbide and silicon nitride as two batches.  After pressing, the samples will be placed in a steam unit at high pressure  and temperature where the environment will closely model that of a gas turbine engine. Silicon nitride and silicon carbide will be coated with similar compositions using chemical vapor deposition to provide a protective barrier.

Zircon forms more readily at 1350ºC versus 950ºC and less annealing time is required Acknowledgements Research is co-sponsored by the Office of Industrial Technologies, Continuous Fiber Ceramic Components program and by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies as part of the High Temperature Materials Laboratory User Program.  Oak Ridge National Laboratory is managed by Lockheed Martin Energy Research Corporation for the U.S. Department of Energy under contract DE-AC05-96-OR22464.