Silica coating composition, process of coating metal therewith and article produced thereby

Claim 1

IN A PROCESS FOR FORMING AN ADHERENT SILICA COATING ON A METAL THE STEPS COMPRISING COATING THE METAL WITH AN AQUEOUS DISPERSION IN WHICH WATER IS THE ONLY CONTINUOUS PHASE, THE DISPERSION COMPRISING (A) AS DISPERSED ORGANIC FILM-FORMER WHICH IS A CARBOXYLIC, POLYANIONIC POLYMER CONTAINING A SUFFICIENT PROPORTION OF CARBOXYL GROUPS THAT THE AMMONIUM SALT OF THE POLYMER IS AT LEAST 1% BY WEIGHT SOLUBLE IN WATER AT 25*C. AND PH 6.5, THE POLYMER BEING REMOVABLE WITHOUT CARBONIZATION BY HEATING AT A TEMPERATURE BELOW 700*F., AND BEING ONE WHICH DRIES TO A SOLID AND (B) COLLOIDALLY DISPERSED, NONRETICULATED, AMORPHOUS SILICA PARTICLES HAVING AN AVERAGE SIZE OF 3 TO 150 MILLIMICRONS, THE CONCENTRATION OF SILICA IN THE DISPERSION BEING FROM 1 TO 50% BY WEIGHT, THE TOTAL TOTAL SOLIDS CONTENT OF THE DISPERSION BEING UP TO 70% BY WEIGHT, AND THE INITIAL PROPORTION OF REMOVABLE FILM-FORMER BEING ABOUT 5% TO 100% BY WEIGHT BASED ON THE WEIGHT OF SILICA, DRYING THE COATING, AND HEATING THE COATING AT A TEMPERATURE ABOVE THAT AT WHICH THE FILMFORMER IS REMOVED AND BELOW THE MELTING POINT OF THE METAL.