Method of preparing silicon dioxide

Claim 1

A PROCESS FOR RECOVERING AT TEMPERATURES BELOW ABOUT 600*C. FINELY-DIVIDED SILICON DIOXIDE HAVING AN AVERAGE PARTICLE DIAMETER WITHIN THE RANGE OF 2 TO 200 MU FROM THE HYDROGEN FLUORIDE-CONTAINING GASEOUS REACTION PRODUCT OBTAINED BY REACTING SILICON TETRAFLUORIDE WITH WATER IN THE GASEOUS PHASE AT TEMPERATURES ABOVE ABOUT 600*C. WHILE INHIBITING REVERSE REACTION OF THE SILICON DIOXIDE WITH HYDROGEN FLUORIDE TO PRODUCE SILICON TETRAFLUORIDE AND WATER, WHICH COMPRISES (1) DILUTING THE REACTION PRODUCT WITH AN INERT GAS HAVING A LOWER TEMPERATURE THAN THE REACTION PRODUCT IN A VOLUME TO INHIBIT SAID REVERSE REACTION OF SILICON DIOXIDE WITH HYDROGEN FLUORIDE, SIMULTANEOUSLY REDUCE THE TEMPERATURE OF THE REACTION PRODUCT TO BELOW 600*C., AND THEREBY MAINTAIN THE AVERAGE SILICON DIOXIDE PARTICLE SIZE DIAMETER WITHIN THE RANGE FROM 2 TO 200 MU; AND (2) RECOVERING SUCH SILICON DIOXIDE FROM THE REACTION PRODUCT.