Alumina-based protective coating for ceramic materials
AssigneeThe Boeing Company
InventorsMichael E. Rorabaugh, Charles W. Newquist, Juris Verzemnieks
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Abstract
A coated ceramic has alumina as an amorphous residue from an alumina sol containing alumina powder or and, optionally, a high emittance powder. The alumina powder alters the rheology and wetting characteristics of the sol to aid in forming the residue and increases the alumina concentration (% solids) in the residue. The high emittance powder radiates heat out of the residue and away from the ceramic when the coated ceramic is heated, such as during orbital reentry.
Claims20
A coated ceramic suitable for use as a flexible insulating blanket at temperatures at least about 1800-2300.degree. F. comprising:
- (a) a ceramic substrate;
- (b) an alumina surface coating on the substrate, wherein the coating is formed by applying a sol to the substrate to produce an amorphous alumina residue;
- (c) an effective amount of alumina powder in the coating being added to the sol to thicken and to stabilize the sol and to improve wetting of the sol on the substrate;
- (d) optionally, an effective amount of cement in the coating added to the sol to improve bonding between the coating and the substrate;
- and
- (e) optionally, a high emittance powder carried in the sol to radiate heat from the coating.
An alumina sol for coating alumina, aluminosilicate, or aluminoborosilicate fibers to protect the fibers from becoming brittle when exposed to an oxidative atmosphere at elevated temperatures, comprising:
- (a) a molecular dispersion of alumina in an aqueous carrier;
- (b) a high emittance powder in the carrier to thicken the sol to improve its application and to provide radiation of thermal energy at elevated temperatures;
- and
- (c) alumina powder for thickening the sol to improve its wetting of the fibers.
A method for preventing embrittlement of aluminoborosilicate fibers when exposed to elevated temperatures in an oxidative atmosphere, comprising the steps of:
- (a) coating the fibers with an alumina surface coating by exposing the fibers to an alumina sol;
- (b) optionally, adding alumina powder to the sol to form a sol--powder mixture for thickening the sol to improve wetting of the fibers with the sol--powder mixture and for increasing the concentration of alumina in the coating;
- and
- (c) optionally, adding a high emittance powder in the sol so that the coating radiates heat quickly when the coated fiber is heated.
Dependencies are inferred from the claim text.