Method of manufacturing granulated silica powder, method of manufacturing vitreous silica crucible

A method of manufacturing a vitreous silica crucible having a transparent layer using waste vitreous silica containing a large amount of bubbles, the method comprising:

• providing waste vitreous silica containing a large amount of bubbles generated in the manufacturing process of a crucible, said waste vitreous silica containing 15 ppm or less of a mineralizer,
• pulverizing the waste vitreous silica to form silica fine powder having an average particle diameter between 10 μm or more and 100 μm or less, said average particle diameter being set to remove most bubbles trapped in the waste vitreous silica,
• granulating the silica fine powder to obtain granulated silica powder having an average particle diameter of 200 to 600 μm, without organic components under helium atmosphere, and
• forming a transparent vitreous silica layer by fusing the granulated silica powder, wherein substantially all bubbles are removed while the granulated silica powder is fused, followed by cooling,
• wherein the transparent vitreous silica layer is formed by forming a silica powder layer by depositing the granulated silica powder on the bottom and the side of a rotating mold, and fusing the silica powder layer by arc fusing the silica powder layer followed by cooling to vitrify it;
• wherein the transparent vitreous silica layer is formed by subjecting the silica powder layer to a reduced pressure of −50 kPa or more and less than −95 kPa while fusing the silica powder layer.