Free-formed quartz glass ingots and method for making the same

Abstract

A method to form quartz glass ingots of ultra low contamination and defect levels by firing a high-purity quartz form as the feedstock, wherein the quartz glass ingot is free-formed on a platen rotating concentrically with the feedstock quartz article.

1 . A quartz glass article in the form of a blank, ingot, or a plate, having a total defect concentration of less than 150 defects per cm 3  and a hydroxyl concentration of less than 150 ppm.  
     
     
         2 . The quartz glass article of  claim 1 , having a defect concentration of less than 150 defects per cm 3  and a hydroxyl concentration of less than 50 ppm.  
     
     
         3 . The quartz glass article of  claim 1 , having a defect concentration of less than 50 defects per cm 3  and a hydroxyl concentration of less than 150 ppm.  
     
     
         4 . The quartz glass article of  claim 1 , having a defect concentration of less than 50 defects per cm 3  and a hydroxyl concentration of less than 50 ppm.  
     
     
         5 . The quartz glass article of  claim 1 , wherein the quartz glass article is made in a process wherein a fabricated quartz glass article is used as feedstock, and wherein the quartz feedstock is selected from at least one of rods and tubings.  
     
     
         6 . The quartz glass article of  claim 5 , wherein the quartz glass feedstock is at least a fabricated quartz glass article having a high silica content of greater than 85% SiO2.  
     
     
         7 . The quartz glass article of  claim 5 , wherein said quartz glass feedstock has a hydroxyl impurity concentration and wherein the hydroxyl concentration of said quartz glass article is less than 30 ppm higher than the hydroxyl concentration of the quartz glass feedstock.  
     
     
         8 . The quartz glass article of  claim 5 , wherein at least a quartz glass rod is used as the feedstock, and wherein the quartz glass rod is drawn directly from a rod making process.  
     
     
         9 . The quartz glass article of  claim 5 , wherein the quartz glass feedstock comprises a plurality of quartz rod segments being joined and fused prior to being used as the feedstock.  
     
     
         10 . The quartz glass article of  claim 5 , wherein the quartz glass feedstock is a rod having a solid cross-section and a circular cross-sectional shape.  
     
     
         11 . The quartz glass article of  claim 5 , wherein the quartz glass feedstock has a diameter between 1 and 100 mm.  
     
     
         12 . The quartz glass article of  claim 12 , wherein the quartz glass feedstock has a diameter between 20 and 50 mm.  
     
     
         13 . The quartz glass article of  claim 5 , in the form of an ingot.  
     
     
         14 . The quartz glass article of  claim 14 , wherein the ingot is made in a process wherein a fabricated quartz glass article in the form of a rod having a diameter between 1 and 100 mm is used as feedstock, and wherein the quartz glass ingot has a diameter ranging from 2 to 100 times the diameter of the rod feedstock.  
     
     
         15 . The quartz glass article of  claim 15 , wherein the quartz glass ingot has a diameter ranging from 5 to 50 times the diameter of the rod feedstock.  
     
     
         16 . The quartz glass article of  claim 14 , wherein said ingot has an outer diameter between 6 inches and 24 inches and a height between 6 inches and 48 inches.  
     
     
         17 . The quartz glass article of  claim 1 , wherein said quartz glass article is an ingot, and wherein said ingot is made in a process comprising the steps of: 
 feeding a quartz glass rod as a feedstock into a furnace containing a platen rotating in axially symmetry to the quartz glass feedstock;    heating the quartz glass rod to a flow temperature for the quartz glass rod to flow;    flow-forming the quartz glass ingot on the rotating platen in the absence of a container or mold.    
     
     
         18 . The quartz glass article of  claim 18 , wherein the axial symmetry has a maximum eccentricity of no more than one feedstock diameter between the axes of the feedstock and the ingot.  
     
     
         19 . The quartz glass article of  claim 18 , wherein the quartz glass ingot is formed at a rate between about 5 and 50 pounds per hour.  
     
     
         20 . The quartz glass article of  claim 20 , wherein the quartz glass ingot is formed at a rate between 10 and 20 pounds per hour.  
     
     
         21 . The quartz glass article of  claim 18 , wherein the rod feedstock is continuously drawn from a melt held at a temperature between 1800° C. and 2500° C., for a period of 1 to 10 hours.  
     
     
         22 . The quartz glass article of  claim 18 , wherein the quartz glass feedstock comprises a plurality of quartz rod segments being joined and fused prior to being used as the feedstock, for a continuous linear feed into the process.  
     
     
         23 . The quartz glass article of  claim 18 , wherein a heat source is used to apply heat either indirectly or directly onto the quartz glass feedstock, and wherein the heat source is at least one selected from the group consisting of: resistive heating, RF heating, microwave heating, laser heating, electron beam heating, plasma torch heating, zone heating, induction heating, and burner.  
     
     
         24 . The quartz glass article of  claim 24 , wherein the heat source is an oxy-fuel burner.  
     
     
         25 . The quartz glass article of  claim 24 , wherein the heat source is at least one selected from the group consisting of: a single top center burner, multiple side burners, and multiple top-side burners.  
     
     
         26 . A quartz glass article in the form of an ingot having a center core and an outer portion having outer diameter between 6 inches and 24 inches, wherein the center core has a diameter of at least ½ the outer diameter and with a total defect concentration of less than 150 defects per cm 3  and a hydroxyl concentration of less than 150 ppm.  
     
     
         27 . A process for manufacturing a quartz glass ingot, comprising the steps of: 
 providing a fabricated quartz glass article as a feedstock,    feeding the fused quartz glass feedstock into a furnace containing a platen rotating in axial symmetry to the quartz glass feedstock,    heating the fused quartz glass feedstock to a temperature sufficient for the quartz feedstock to melt, thus forming the quartz glass ingot on the rotating platen in the absence of a container or mold.    
     
     
         28 . The process of  claim 28 , further comprising the step of annealing the fabricated quartz glass article prior to feeding the quartz glass article as feedstock to the furnace.  
     
     
         29 . The process of  claim 28 , further comprising the step of fusing a plurality of quartz rod segments into a fabricated quartz glass article prior to feeding the quartz glass article as feedstock to the furnace.  
     
     
         30 . The process of  claim 28 , wherein the axial symmetry has a maximum eccentricity of no more than one feedstock diameter between the axes of the feedstock and the ingot.  
     
     
         31 . The process of  claim 28 , wherein the quartz feedstock is selected from at least one of rods and tubings.  
     
     
         32 . The process of  claim 28 , wherein the quartz glass ingot is formed at a rate between about 5 and 50 pounds per hour.  
     
     
         33 . The process of  claim 34 , wherein the quartz glass ingot is formed at a rate between 10 and 20 pounds per hour.  
     
     
         34 . The process of  claim 28 , wherein a heat source is used to apply heat either indirectly or directly onto the quartz glass feedstock, and wherein the heat source is at least one selected from the group consisting of: resistive heating, RF heating, microwave heating, laser heating, electron beam heating, plasma torch heating, zone heating, induction heating, and burner.  
     
     
         35 . The quartz glass article of claim  36 , wherein the heat source is at least one selected from the group consisting of: a single top center burner, multiple side burners, and multiple top-side burners.