Silica glass crucible

Abstract

A silica glass crucible is disclosed comprising an aluminum-doped inner wall layer. An aluminum-doped layer can be formed on an outer wall portion. The inner layer is non-homogeneously doped with aluminum to promote silica crystallization. The non-homogeneous silica grain mixture contains aluminum and can be aluminum-doped and aluminum-free silica grains or, alternatively, aluminum-coated coarse quartz grain. The crucible is made by introducing into a rotating crucible mold bulk silica grain to form a bulky wall including a bottom wall and a side wall. After heating the interior of the mold to fuse the bulk silica grains, an inner silica grain, doped with aluminum, is introduced. The heat at least partially melts the inner silica grain, allowing it to fuse to the wall to form an inner layer. The crucible is cooled, and the fused silica grains form nuclei of crystalline silica within the inner layer.

The invention claimed is:  
     
         1 . A crucible comprising: 
 a wall including a bottom wall and side wall;    an aluminum-doped layer formed on an inner portion of said wall; and    an aluminum-doped layer formed on an outer portion of said wall.    
     
     
         2 . The crucible of  claim 1 , wherein the aluminum-doped outer layer is substantially an outer layer of the side wall.  
     
     
         3 . The crucible of  claim 1 , wherein the inner layer is in the range of 0.2-1.2 mm deep.  
     
     
         4 . The crucible of  claim 1 , wherein the inner layer is doped with aluminum in the range of about 50-500 ppm.  
     
     
         5 . The crucible of  claim 1 , wherein the outer layer is no more than substantially 0.5-2.5 mm deep.  
     
     
         6 . The crucible of  claim 1 , wherein the outer layer is doped with aluminum in the range of about 100-500 ppm.  
     
     
         7 . The crucible of  claim 1 , wherein a portion of the side wall interposed between the outer layer and the inner layer is free of aluminum doping.  
     
     
         8 . The crucible of  claim 1 , wherein a portion of the bottom wall interposed between the outer layer and the inner layer is free of aluminum doping.  
     
     
         9 . A method for making a silica glass crucible, comprising: 
 introducing into a rotating crucible mold outer silica grain doped with aluminum to form an outer layer;    introducing into said mold bulk silica grain consisting essentially of quartz grain to form a bulky wall including a bottom wall and a side wall;    heating the interior of the mold; and    introducing into said mold inner silica grain doped with aluminum, wherein the heat fuses said outer and bulk silica grains and at least partially melts said inner silica grain and fuses said at least partially molten inner silica grain to the bulk wall to form an inner layer.    
     
     
         10 . The method of  claim 9 , further comprising cooling the fused silica grains so as to form within the inner layer a plurality of nuclei of crystalline silica.  
     
     
         11 . The method of  claim 10 , wherein cooling comprises maintaining the crucible in the range of 400-600° C. for approximately 25 minute.  
     
     
         12 . The method of  claim 10 , wherein cooling comprises maintaining the crucible in the range of 1400-1600° C. for approximately one minute.  
     
     
         13 . The method of  claim 9 , wherein the outer layer is formed substantially on the side wall.  
     
     
         14 . The method of  claim 9 , wherein a selected thickness of the inner layer is in the range of 0.2-1.2 mm.  
     
     
         15 . The method of  claim 9 , wherein the inner silica grain is doped with aluminum in the range of 50-500 ppm.  
     
     
         16 . The method of  claim 9 , wherein the outer silica grain is doped with aluminum in the range of 100-500 ppm.  
     
     
         17 . A silica glass crucible, comprising: 
 a wall including a bottom wall and a side wall;    an homogeneously aluminum-doped layer formed on the inner portion of said wall;    wherein said layer has a depth in the range of 0.2-0.5 mm and is doped with aluminum in the range of about 50-500 ppm.    
     
     
         18 . The crucible of  claim 17 , wherein the inner layer is doped with aluminum in the range of about 80-160 ppm.  
     
     
         19 . The crucible of  claim 17 , wherein the inner layer is doped with aluminum in the range of about 100-120 ppm.  
     
     
         20 . A method for making a silica glass crucible, comprising: 
 introducing into a rotating crucible mold bulk silica grain consisting essentially of pure silica grain to form a bulk grain wall having a bottom wall and a side wall;    heating the interior of the mold;    introducing into said mold inner silica grain doped with aluminum, wherein the heat fuses said bulk silica grain and at least partially melts said inner silica grain and fuses said at least partially molten inner silica grain to the bulk grain wall to form a homogeneously aluminum-doped inner layer.    
     
     
         21 . The method of  claim 20 , further comprising cooling so as to form within the inner layer a plurality of nuclei of crystalline silica.  
     
     
         22 . The method of  claim 21 , wherein cooling comprises maintaining the crucible in the range of 400-600° C. for approximately 25 minute.  
     
     
         23 . The method of  claim 21 , wherein cooling comprises maintaining the crucible in the range of 1400-1600° C. for approximately one minute.  
     
     
         24 . The method of  claim 20 , wherein a selected thickness of the inner layer is in the range of 0.2-0.5 mm.  
     
     
         25 . The method of  claim 20 , wherein the inner silica grain is doped with aluminum in the range of 50-500 ppm.  
     
     
         26 . The crucible of  claim 20 , wherein the inner layer is doped with aluminum in the range of about 80-160 ppm.  
     
     
         27 . The crucible of  claim 20 , wherein the inner layer is doped with aluminum in the range of about 100-120 ppm.  
     
     
         28 . A silica glass crucible comprising: 
 a wall including a bottom wall and a side wall; and    a layer non-homogeneously doped with aluminum formed on an inner portion of said wall to promote crystallization of silica.    
     
     
         29 . The crucible of  claim 28 , wherein the inner layer has an average aluminum doping of 30-100 ppm and a depth in the range of greater than 0.2 mm to 1.5 mm.  
     
     
         30 . The crucible of  claim 28 , wherein the inner layer has a thickness of substantially 0.3-0.7 mm.  
     
     
         31 . A method for making a silica glass crucible, comprising: 
 introducing into a rotating crucible mold bulk silica grain to form a bulk grain wall having a bottom wall and a side wall, said bulk silica grain consisting essentially of pure silica grain;    heating the interior of the mold;    introducing into said mold a non-homogeneous combination of silica grain containing aluminum, wherein the heat fuses said bulk silica grain and wherein the heat at least partially melts said non-homogeneous silica grain and fuses said at least partially molten non-homogeneous silica grain to the wall to form an inner layer.    
     
     
         32 . The method of  claim 31 , further comprising cooling so as to form within the inner layer a plurality of nuclei of crystalline silica.  
     
     
         33 . The method of  claim 32 , wherein cooling comprises maintaining the crucible in the range of 400-600° C. for approximately 25 minute.  
     
     
         34 . The method of  claim 32 , wherein cooling comprises maintaining the crucible in the range of 1400-1600° C. for approximately one minute.  
     
     
         35 . The method of  claim 31 , wherein the non-homogeneous combination of silica grain containing aluminum is comprised of a mixture of aluminum-doped silica grain and non-doped silica grain.  
     
     
         36 . The method of  claim 35 , wherein the aluminum-doped silica grain is doped with at least 80 ppm to approximately 160 ppm aluminum.  
     
     
         37 . The method of  claim 35 , wherein the aluminum-doped silica grain is doped with approximately 90 ppm to 110 ppm aluminum.  
     
     
         38 . The method of  claim 35 , wherein the non-doped silica grain is natural quartz grain containing less than approximately 18 ppm aluminum.  
     
     
         39 . The method of  claim 35 , wherein the non-doped silica grain is synthetic silica grain containing less than approximately 1 ppm aluminum and less than approximately 5 ppm of total metallic impurities.  
     
     
         40 . The method of  claim 31 , wherein the non-homogeneous combination of silica grain containing aluminum is coarse quartz grain coated with aluminum and wherein at least approximately 20% of the coarse quartz grains are larger than approximately 200 μm in grain size.  
     
     
         41 . The crucible of  claim 40 , wherein at least approximately 50% of the coarse quartz grains are larger than approximately 200 μm in grain size.  
     
     
         42 . The method of  claim 31 , wherein the inner layer has a thickness of substantially 0.2-1.5 mm.  
     
     
         43 . The method of  claim 31 , wherein the inner layer has a thickness of substantially 0.3-0.7 mm.