Abstract: Cup-shaped porous silica preforms suitable for manufacture of large 24-inch crucibles used in Czochralski crystal-growing furnaces are produced by a unique electrophoretic casting process using a high-purity aqueous silica slip or slurry having a predetermined particle-size distribution, an average particle size of from 6 to 10 microns and a solids content of from 80 to 85 percent by weight. The slurry contains an electrolyte, such as ammonium hydroxide, has a pH of from 7.5 to 8.5, and can be wet milled at a pH of at least 7 in such manner as to provide the micronized silica particles with excellent electrophoretic mobility, thereby providing a superb process for economical mass production of large pure silica preforms using safe voltages, such as 20 to 40 volts. The electrophoretic casting apparatus can be of the type shown in FIGS.

Abstract: Cup-shaped porous silica preforms suitable for manufacture of large 24-inch crucibles used in Czochralski crystal-growing furnaces are produced by a unique electrophoretic casting process using a high-purity aqueous silica slip or slurry having a predetermined particle-size distribution, an average particle size of from 6 to 10 microns and a solids content of from 80 to 85 percent by weight. The slurry contains an electrolyte, such as ammonium hydroxide, has a pH of from 7.5 to 8.5, and can be wet milled at a pH of at least 7 in such manner as to provide the micronized silica particles with excellent electrophoretic mobility, thereby providing a superb process for economical mass production of large pure silica preforms using safe voltages, such as 20 to 40 volts. The electrophoretic casting apparatus can be of the type shown in FIGS.

Abstract: A number of unique processes are disclosed for manufacture of sintered high-purity quartz glass products in which a shaped silica body or preform is made from an aqueous slurry of micronized silica particles by gel casting, slip casting or electrophoretic deposition. The silica particles may comprise a major portion by weight of crystalline silica. In one embodiment of the invention the sintered quartz glass is transparent, substantially bubble-free and suitable for scientific or optical uses. In another embodiment the porous silica preform is fired in steam to increase the hydroxyl content and then nitrided in a nitrogen-hydrogen reducing atmosphere. A minute amount of chemically-combined nitrogen in the high-purity quartz glass is sufficient to provide a tremendous improvement in physical properties and an incredible increase in the resistance to devitrification.

Abstract: The application discloses a number of unique sintered quartz glass products together with new silica compositions and processes for making and using such products. Nitrided clear and opaque nitrided quartz products are disclosed having incredible physical properties resulting from the incorporation of very small, but effective, amounts (e.g., 25 ppm or more) of chemically bound nitrogen. Opaque quartz glass heat shields with remarkable resistance to transmission of infrared radiation are disclosed which can have a high bubble population density, such as 80 to 120 per mm2. These heat shields make possible remarkable improvement in the performance of tube furnaces and other reactors used in processing silicon wafers and other electronic components.

Abstract: A number of unique processes are disclosed for manufacture of sintered high-purity quartz glass products in which a shaped silica body or preform is made from an aqueous slurry of micronized silica particles by gel casting, slip casting or electrophoretic deposition. The silica particles may comprise a major portion by weight of crystalline silica. In one embodiment of the invention the sintered quartz glass is transparent, substantially bubble-free and suitable for scientific or optical uses. In another embodiment the porous silica preform is fired in steam to increase the hydroxyl content and then nitrided in a nitrogen-hydrogen reducing atmosphere. A minute amount of chemically-combined nitrogen in the high-purity quartz glass is sufficient to provide a tremendous improvement in physical properties and an incredible increase in the resistance to devitrification.

Abstract: Unique cristobalite-seeded quartz glass crucibles and cores admirably suited for Cz crystal growing and D.S. metal casting are formed by slip casting using a slurry containing a quartz refractory composition comprising silica particles with an average particle size of from 1 to 10 microns and a minute but effective amount of micronized dispersible particles of a unique crystallization aid, such as basic aluminum acetate, which provides the glass with at least 0.005 percent by weight of evenly dispersed metallic ions. The metallic ions provide the quartz glass with nucleation sites so that heating of the glass to a temperature of from 1200.degree. C. to 1250.degree. C. permits formation of a high concentration of evenly dispersed cristobalite nuclei in the glass without causing excessive devitrification prior to cooling of the seeded glass. The desired nucleation sites can also be provided by using micronized particles of alpha quartz or alpha cristobalite.