Patent ID: 8596095

Claim:
A method for preparing a synthetic quartz glass ingot by a direct process, comprising vapor phase hydrolyzing or oxidatively decomposing a silane compound or a siloxane compound in a burner flame to form fine particles of silica, depositing the silica particles on a target and concurrently melting and vitrifying the particles to form and grow a synthetic quartz glass ingot on the target while the target is moved back and forth, said method further comprising the steps of: (i) continuously feeding the silane compound or the siloxane compound at a predetermined rate, (ii) keeping the flame in constant contact with an overall front of the ingot, (iii) repeating the back and forth movement of the target in an axial direction along an ingot growth direction, wherein a difference between backward and forward travel distance is 0.1 to 5 mm, so that the back and forth movement of the target has a cycle time of up to 10 minutes and is repeating at a predetermined speed of 0.10 to 0.39 mm/sec, and (iv) maintaining a face shape of the growing ingot unchanged by adjusting the feed rate of the silane compound or the siloxane compound and controlling an ingot growth rate to 5 to 30 mm/hr.