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A water-resistant porcelain enamel coating and method of making the same is provided. The porcelain enamel coating is prepared using a borosilicate glass frit, and mill additions of silica and a zirconia compound. The mixture is applied to a metal substrate and fired, resulting in a water-resistant

A water-resistant porcelain enamel coating and method of making the same is provided. The porcelain enamel coating is prepared using a borosilicate glass frit, and mill additions of silica and a zirconia compound. The mixture is applied to a metal substrate and fired, resulting in a water-resistant coating that resists cracking and crazing. The coating is particularly useful in water heaters. In one embodiment, the coating comprises a fine zirconia compound having a median particle size of less than 10 microns.

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1. A method of manufacturing water-resistant porcelain enamel coating, the method comprising:providing ground glass;adding mill additions to the ground glass to form a mixture, wherein the mill additions comprise silica and a zirconia compound;applying the mixture to a metal substrate to form a coat

1. A method of manufacturing water-resistant porcelain enamel coating, the method comprising:providing ground glass;adding mill additions to the ground glass to form a mixture, wherein the mill additions comprise silica and a zirconia compound;applying the mixture to a metal substrate to form a coated substrate; andfiring the coated substrate to form the water-resistant porcelain enamel coating, wherein the silica and zirconia compound mill additions comprise at least about 25 and less than about 70 parts by weight per hundred parts by weight ground glass. 2. The method of claim 1 wherein the ground glass is provided by grinding a glass system. 3. The method of claim 1 wherein the ground glass comprises a sodium borosilicate glass. 4. The method of claim 1 wherein the zirconia compound comprises zircon (ZrO 2 .SiO 2 ) or zirconia (ZrO 2 ). 5. The method of claim 1 wherein the mixture comprises from about 15 to about 50 parts by weight of the silica mill addition per hundred parts by weight of the ground glass. 6. The method of claim 1 wherein the mixture comprises at least about 10 parts by weight of the zirconia compound mill addition per hundred parts by weight of the ground glass. 7. The method of claim 1 wherein the mill additions further comprise a clay. 8. The method of claim 1 wherein the metal substrate comprises steel. 9. The method of claim 1 wherein the metal substrate is a water heater. 10. The method of claim 1 wherein the coated substrate is fired at a temperature of about 1000 to about 1700° F. (538-927° C.). 11. The method of claim 1 wherein the coated substrate is fired at a temperature of about 1550 to about 1650° F. (843-899° C.). 12. The method of claim 1 wherein the ground glass comprises:about 52 weight percent SiO 2 ,about 17 weight percent Na 2 O,about 10 weight percent ZrO 2 ,less than about 4.1 weight percent F 2 ,less than about 0.005 weight percent CaO, andgreater than about 4.1 weight percent Li 2 O. 13. A method of manufacturing a water-resistant porcelain enamel coating suitable for use on a water heater, the method comprising:providing a ground borosilicate glass;adding mill additions to the ground glass to form a mixture, wherein the mill additions comprise (a) a zirconia compound constituting at least about 10 parts by weight per hundred parts by weight ground glass and (b) a silica compound;applying the mixture to a water heater; and firing the water heater at a temperature of about 1000° F. to about 1700° F. to form the water-resistant porcelain enamel coating. 14. The method of claim 13 wherein the zirconia compound comprises zircon (ZrO 2 .SiO 2 ) or zirconia (ZrO 2 ). 15. The method of claim 13 wherein the mixture comprises from about 15 to about 50 parts by weight of the silica compound mill addition and from about 10 to about 30 parts by weight of the zirconia compound mill addition per 100 parts by weight of the ground glass. 16. A method of manufacturing a water-resistant porcelain enamel coating, the method comprising:providing ground glass;adding mill additions to the ground glass to form a mixture, wherein the mill additions comprise silica and a zirconia compound and wherein the mixture comprises at least about 15 parts and less than about 60 parts by weight of the silica mill addition per hundred parts by weight of the ground glass;applying the mixture to a metal substrate to form a coated substrate; andfiring the coated substrate at a temperature of about 1000 to 1700° F. (538-927° C.) to form the water-resistant porcelain enamel coating. 17. The method of claim 16, wherein the metal substrate is a portion of a water heater. 18. The method of claim 1, wherein the zirconia compound has a median particle size, and the median particle size is less than about 10 microns. 19. The method of claim 16, wherein the zirconia compound has a median particle size, and the median particle size is less than about 10 microns. 20. A method of m anufacturing a water-resistant porcelain enamel coating, the method comprising:adding mill additions to ground glass to form a mixture, wherein the mill additions comprise a zirconia compound;applying the mixture to a substrate; andfiring the coated substrate to form the water-resistant porcelain enamel coating, at least a portion of the coating regularly contacting water. 21. The method of claim 20, wherein the zirconia compound has a median particle size of less than about 100 microns. 22. The method of claim 20, wherein the median particle size is less than about 10 microns. 23. The method of claim 20, wherein the median particle size is about 0.1 to 10 microns. 24. The method of claim 20, wherein the median particle size is about 0.1 to 5 microns. 25. The method of claim 20, wherein the median particle size is about 0.3 to 4 microns. 26. The method of claim 20, wherein the zirconia compound mill additions comprise up to about 60 parts by weight per 100 parts ground glass. 27. The method of claim 20, wherein the zirconia compound mill additions comprise about 10 to about 60 parts by weight per 100 parts ground glass. 28. The method of claim 20, wherein the zirconia compound mill additions comprise up to about 90 parts by weight per 100 parts ground glass. 29. The method of claim 28, wherein the zirconia compound mill additions comprise about 35 to 75 parts by weight per 100 parts ground glass. 30. The method of claim 20, wherein zirconia compound mill additions comprise up to about 120 parts by weight per 100 parts by weight ground glass. 31. The method of claim 30, wherein the zirconia compound mill additions comprise about 30 to 100 parts by weight per 100 parts by weight ground glass. 32. The method of claim 20, wherein the substrate is at least a portion of a water heater. 33. The method of claim 20, wherein the portion of the water heater is an internal portion of the water heater, and the coating contacts water in the water heater. 34. The method of claim 20, wherein the mixture comprises up to about 120 parts by weight fine zirconia compound per about 100 parts by weight ground glass. 35. The method of claim 20, wherein the mixture comprises about 10 to about 80 parts by weight fine zirconia compound per about 100 parts by weight ground glass. 36. The method of claim 20, wherein the mill additions further comprise silica. 37. The method of claim 36, wherein the mixture comprises at least about 20 and less than about 120 parts by weight zirconia compound and silica per hundred parts by weight ground glass. 38. The method of claim 26, wherein the firing occurs at a temperature from about 1000° F. to about 1700° F. 39. The method of claim 20, wherein the zirconia compound comprises at least one of zircon (ZrO 2 .SiO 2 ), zirconia (ZrO 2 ), and a combination thereof. 40. A method of manufacturing a water-resistant porcelain enamel coating, the method comprising:adding a zirconia compound and silica to ground glass to form a mixture;applying the mixture to a metal substrate to form a coated substrate; andfiring the coated substrate to form the water-resistant porcelain enamel coating, wherein the mixture comprises at least about 20 and less than about 100 parts by weight zirconia compound and silica per hundred parts by weight ground glass. 41. The method of claim 40, wherein the zirconia compound has a median particle size, and the median particle size is less than about 10 microns. 42. The method of claim 40, wherein the mixture comprises at least about 20 and less than about 100 parts by weight zirconia compound and silica per hundred parts by weight ground glass. 43. The method of claim 40, wherein the firing occurs at a temperature from about 1000° F. to about 1700° F. 44. The method of claim 40, wherein fine zirconia compound comprises at least one of zircon (ZrO 2 .SiO 2 ), zirconia (ZrO 2 ), and a combination thereof. 45. The method of claim 40, wherein the substrate is steel. 46. The met hod of claim 40, wherein the substrate is at least a portion of a water heater. 47. The method o claim 46, wherein the portion of the water heater is an internal portion of the water heater and the coating contacts water in the water heater. 48. The method of claim 40, wherein the zirconia compound mill additions comprise at least about 10 and less than about 120 parts by weight per hundred parts by weight ground glass. 49. The method of claim 40, wherein at least a portion of the coating regularly contacts water.