PRODUCTION OF HIGH PURITY SILICA POWDER AND HIGH PURITY SILICA POWDER PRODUCED BY THIS METHOD

摘要

PROBLEM TO BE SOLVED: To obtain a silica powder of ultrahigh purity, especially with specified or smaller concn. of iron elements by treating a high purity water-contg. silica gel produced from an alkali silicate soln. with an inorg. acid at a specified or lower temp., treating the silica gel with nitric acid, hydrochloric acid or a mixture of them at a specified or higher temp., and then calcining at a specified or higher temp. ;SOLUTION: After a silica gel is treated with an inorg. acid at 80°C, the gel is treated with nitric acid or hydrochloric acid or a mixture of them at ≥80°C and calcined at ≥1000°C. It is preferable to use different inorg. acids for a first stage and a second stage. When the concn. of iron elements dissolved by the inorg. acid treatment in the second stage exceeds 10 ng per one gram of silicon dioxide in the water-contg. silica gel, the acid is newly exchanged and the treatment is repeated to control the concn. of the iron elements to ≤10 ng. By this method, a silica gel with ≥80 ppb iron element conc, is obtd. The obtd. silica powder is useful for as source material of semiconductor member, as the filler of a sealing agent used for LSIs, and as the source material for the production of crucibles to draw single crystals.;COPYRIGHT: (C)1999,JPO