Burner and method for the manufacture of synthetic quartz glass

Abstract

A burner for use in the manufacture of synthetic quartz glass is provided, which comprises a main burner ( 7 ) comprising a multi-tube assembly ( 1 ) including a center tube ( 2 ) for feeding a silica-forming compound, a first enclosure tube ( 3 ) surrounding the center tube for feeding a combustion-supporting gas, and a second enclosure tube ( 4 ) surrounding the first enclosure tube for feeding a combustible gas; a tubular shell ( 5 ) surrounding the multi-tube assembly for feeding a combustible gas; and a plurality of nozzles ( 6 ) disposed within the tubular shell for feeding a combustion-supporting gas. A double-tube assembly ( 8 ) is disposed so as to surround the forward opening of the main burner ( 7 ) for feeding a combustion-supporting gas. Synthetic quartz glass ingots having high optical homogeneity are produced.

1 . A burner for use in the manufacture of synthetic quartz glass, comprising 
 a main burner comprising a multi-tube assembly of a three or more tube construction including a center tube for feeding a silica-forming compound, a first enclosure tube surrounding the center tube for feeding a combustion-supporting gas, and a second enclosure tube surrounding the first enclosure tube for feeding a combustible gas; a tubular shell surrounding the multi-tube assembly for feeding a combustible gas; and a plurality of nozzles disposed within the tubular shell for feeding a combustion-supporting gas, the main burner defining a forward opening, and    a double-tube assembly surrounding at least the forward opening of the main burner.    
   
   
       2 . The burner of  claim 1 , wherein said double-tube assembly includes an outer tube and an inner tube disposed within the outer tube, said outer tube surrounds the forward opening of the main burner and projects further forward, said inner tube has a forward end which is disposed in register with or backward of the forward opening of the main burner.  
   
   
       3 . The burner of  claim 1 , wherein said double-tube assembly defines therein a passage for a combustion-supporting gas.  
   
   
       4 . The burner of  claim 1 , wherein the total cross-sectional area of gas discharge ports of the plurality of nozzles disposed in the tubular shell accounts for 5% to 20% of the cross-sectional area of a gas discharge region between the multi-tube assembly and the tubular shell.  
   
   
       5 . A method for the manufacture of a synthetic quartz glass ingot using a burner comprising a main burner comprising a multi-tube assembly of a three or more tube construction including a center tube, a first enclosure tube surrounding the center tube, and a second enclosure tube surrounding the first enclosure tube, a tubular shell surrounding the multi-tube assembly, and a plurality of nozzles disposed within the tubular shell, the main burner defining a forward opening, and a double-tube assembly surrounding at least the forward opening of the main burner; said method comprising the steps of: 
 placing the burner to face a quartz glass target mounted on a rotating support,    feeding a silica-forming compound to the center tube, a combustion-supporting gas to the first enclosure tube and the nozzles, a combustible gas to the second enclosure tube and the tubular shell, and a combustion-supporting gas to the double-tube assembly,    forming an oxyhydrogen flame from the combustion-supporting gas and the combustible gas for subjecting the silica-forming compound to vapor phase hydrolysis or oxidative decomposition to form silica fines,    depositing the silica fines on the target, and    melting and vitrifying the deposited silica into quartz glass.    
   
   
       6 . The method of  claim 5 , wherein the silica-forming compound is a silane or siloxane, the combustion-supporting gas is oxygen, the combustible gas is hydrogen, 
 the silica-forming compound and oxygen are fed to the burner such that the molar amount of the silica-forming compound is at least 1.3 times the stoichiometry of oxygen, and    the molar ratio of the amount of actually fed oxygen to the stoichiometry of oxygen needed for the silica-forming compound and hydrogen fed to the burner is from 0.6 to 1.3.    
   
   
       7 . The method of  claim 5 , wherein the combustion-supporting gas is fed through the double-tube assembly at a flow velocity of 0.5 to 1.3 m/sec.  
   
   
       8 . The method of  claim 5 , wherein the ingot has a diameter of at least 150 mm.