Process for preparing coated silica particles and product obtained thereby

Claim 1

A COMPOSITION COMPRISING SILICA IN THE FORM OF PULVERULENT AGGREGATES OF SUBSTANTIALLY SPHERICAL, ULTIMATE PARTICLES, THE COMPOSITON BEING SUBSTANTIALLY IDENTICAL WITH THE PRODUCT PRODUCED BY A PROCESS INCLUDING THE STEPS OF BUILDING UP THE SIZE OF ULTIMATE SILICA PARTICLES IN AN AQUEOUS SILICA SOL BY ADDING REACTIVE SILICA THERETO AT A PH OF 8 TO 11 AND A TEMPERATURE OF ABOUT 60 TO 100* C., THE REACTIVE SILICA BEING FRESHLY PREPARED BY NEUTRALIZING SODIUM SILICATE WITH AN ACID, UNTIL THE PARTICLES IN THE SOL ARE IN THE SIZE RANGE OF 15 TO 130 MILLIMICRONS, THE PARTICLES BEING SO DENSE THAT THEIR SURFACE AREAS AS DETERMINED BY NITROGEN ADSPORPTION IS NOT MORE THAN ABOUT 30 PER CENT GREATER THAN THEIR SURFACE AREA AS COMPUTED FROM THE APPARENT PARTICLE SIZE DETERMINED FROM AN ELECTRON MICROGRAPH OF THE PARTICLES, AND MIXING IN SOLUTION IN THE SOL OF BUILTUP PARTICLES AN ORGANIC NITROGEN COMPOUND HAVING A CARBON CHAIN OF AT LEAST 10 CARBON ATOMS IN THE PROPORTION OF ABOUT FROM 0.1 TO 10.0 PER CENT BY WEIGHT, BASED ON THE SILICA, WHEREBY THE SILICA IS PRECIPITATED.