Patent ID: 7341797

Claim:
A protective coating on a silicon-containing surface, the protective coating consisting essentially of barium oxide, strontia, alumina, and silica, and incidental impurities so as to have a barium-strontium aluminosilicate composition, the protective coating having an outer surface region consisting essentially of one or more stoichiometric crystalline phases of barium-strontium aluminosilicate and being substantially free of a nonstoichiometric second crystalline phase of barium-strontium aluminosilicate that contains an approximately equimolar ratio of BaO/SrO, Al 2 O 3 , and SiO 2 , the protective coating having a second region beneath the outer surface region that consists essentially of the one or more stoichiometric crystalline phases of barium-strontium aluminosilicate and the nonstoichiometric second crystalline phase of barium-strontium aluminosilicate.