Finely divided silica product and its method of preparation

Claim 1

IN A PROCESS FOR THE MANUFACTURE OF FINELY DIVIDED SILICA PRODUCTS WHEREIN AN AQUEOUS SOLUTION OF SODIUM SILICATE HAVING A WEIGHT PERCENT RATIO OF NA2O TO SIO2 WITHIN THE RANGE OF FROM ABOUT 2:1 TO 1:4 AND A SODIUM SILICATE CONCENTRATION OF FROM ABOUT 0.5 TO 30% SIO2 IS CONTACTED WITH A COACERVATING AGENT CAPABLE OF CLUSTERING AQUEOUS SODIUM SILICATE SOLUTIONS AND AN INSOLUBILIZING AGENT CONSISTING OF AN ACIDIC MATERIAL HAVING AN ANION OF AN ACID STRONGER THAN SILICIC ACID AND CAPABLE OF PRECIPITATING SUBSTANTIALLY PURE SILICA FROM THE MIXTURE, THE IMPROVEMENT WHICH COMPRISES: (A) INTRODUCING SAID COACERVATING AGENT IN A QUANTITY WITHIN THE RANGE OF 20-500% OF THE EQUILIBRIUM OPALESCENCE RATIO, (B) INTRODUCING THE INSOLUBILIZING AGENT IN A QUANTITY SUFFICIENT TO PRICIPITATE GEL-FREE SILICA, (C) MAINTAINING THE ENVIRONMENTAL CONDITIONS SUBSTANTIALLY UNIFORM IN THE ABOVE MIXTURE WHILE THE FINELY DIVIDED SILICA PRODUCTS ARE IN FORMATION BY; (D) MIXING SAID COACERVATING AGENT WITH SAID SODIUM SILICATE SOLUTION NOT LATER THAN SAID INSOLUBILIZING AGENT IS MIXED THEREWITH, (E) COMPLETING THE MIXING IN OF THE INSOLUBILIZING AGENT BEFORE THE APPEARANCE OF ANY SUBSTANTIAL AMOUNT OF A SILICA PRECIPITATE, AND IN ANY EVENT WITHIN A PERIOD NOT SUBSTANTIALLY EXCEEDING FIVE SECONDS, (F) FOLLOWING COMPLETION OF THE MIXING IN OF THE INSOLUBILIZING AGENT, RECOVERING THE FINELY DIVIDED SILICA THEREBY PRODUCED.