iia elements and the lanthanide series elements the group iia elements include but are not limited magnesium calcium strontium and barium the group iii elements include but are not limited to yttrium and lanthanum the lanthanide series includes cerium ytterbium and other elements having an atomic number from 58 through 71 oxides of these elements either alone or in combination can be used to stabilize zirconia based coatings a widely used thermal barrier coating is yttria stabilized zirconia ysz having preferably about 6 8 weight percent yttria though it is foreseeable that other ceramic materials could be used a suitable thickness range for the ysz top coat 114 is about 12 5 to about 1250 u03bcm about 0 0005 to about 0 050 inch with a preferred range of about 125 to about 750 u03bcm about 0 005 to about 0 030 inch depending on the particular application the mechanism for the degradation of the silicon component of silicon carbide as well as silicon and other silicon compounds in a hot corrosive hydrous environment is the formation of volatile silicon monoxide sio and silicon hydroxide si oh x products it being understood that carbon will form co and co 2 upon exposure to an oxidizing environment the diffusivity of oxidants in the ysz topcoat 114 is generally very high therefore in order to protect the silicon containing substrate 104 the coating system must include additional layers 106 107 beneath the ysz top coat 114 that individually or in.