Three-component ceramic coating for silica insulation

Claim 1

An insulating structure for withstanding repeated exposure to cyclical temperature changes of from about -250° F. to about 2,500° F., said structure comprising a substrate having thereon a moisture-impervious ceramic laminate coating which comprises: a. a barrier layer consisting essentially of fused silica, said barrier layer adhered to said substrate; b. an emissivity layer consisting essentially of a high silica glass and an emissivity agent selected from the group of silicon carbide, nickel oxide, chrome oxide, cobalt oxide, nickel-chrome spinel, silicon nitride, calcined mixed oxides of iron, chrome and cobalt, and mixtures thereof, with the weight ratio of high silica glass to emissivity agent being from about 50:1 to about 4:1; and c. an overglaze layer consisting essentially of a high silica glass and a borosilicate glass having a composition of from about 70 to about 87 wt.% SiO 2 , from about 10 to about 20 wt.% B 2 O 3 , from about 2 to about 5 wt.% Na.sub. 2 O and from about 1 to about 5 wt.% Al 2 O 3 , with the weight ratio of high silica glass to borosilicate glass being from about 3:1 to about 19:1.

Claim 8

A method of rendering impervious to moisture a substrate which comprises sequentially applying to said substrate and firing at a temperature of from about 1,700° F. to about 2,500° F. a. a barrier coating consisting essentially of a fused silica slip having from about 80 to about 90 wt.% solids; b. an emissivity coating consisting essentially of a high silica glass, an emissivity agent selected from the group of silicon carbide, nickel oxide, chrome oxide, cobalt oxide, nickel-chrome spinel, silicon nitride, calcined mixed oxides of iron, chrome and cobalt and mixtures thereof, and an effective amount of a suspension agent in an aqueous slurry containing from about 10 to about 90 wt.% solids, with the weight ratio of high silica glass to emissivity agent being from about 50:1 to about 4:1; and c. an overglaze coating consisting essentially of a high silica glass, a borosilicate glass having a composition of from about 70 to about 87 wt.% SiO 2 , from about 10 to about 20 wt.% B 2 O 3 , from about 2 to about 5 wt.% Na 2 O, and from about 1 to about 5 wt.% Al 2 O 3 , and an effective amount of a suspension agent in an aqueous slurry containing from about 10 to about 90 wt.% solids, with the weight ratio of high silica glass to borosilicate glass being from about 3:1 to about 19:1.

Claim 9

A method of rendering impervious to moisture a substrate which comprises sequentially applying to said substrate and firing at a temperature of from about 1,700° F. to about 2,500° F. a. a barrier coating consisting essentially of a fused silica slip having from about 80 to about 90 wt.% solids; b. an emissivity coating consisting essentially of a high silica glass, an emissivity agent selected from the group of silicon carbide, nickel oxide, chrome oxide, cobalt oxide, nickel-chrome spinel, silicon nitride, calcined mixed oxides of iron, chrome and cobalt and mixtures thereof, and an effective amount of a suspension agent in an aqueous slurry containing from about 10 to about 90 wt.% solids, with the weight ratio of high silica glass to emissivity agent being from about 50:1 to about 4:1; and c. an overglaze coating consisting essentially of a high silica glass, a borosilicate glass having a composition of from about 70 to about 87 wt.% SiO 2 , from about 10 to about 20 wt.% B 2 O 3 , from about 2 to about 5 wt.% Na 2 O, and from about 1 to about 5 wt.% Al 2 O 3 , and an effective amount of a suspension agent in an aqueous slurry containing from about 10 to about 90 wt.% solids, with the weight ratio of high silica glass to borosilicate glass being from about 3:1 to about 19:1.