Abstract: The invention provides a method for manufacturing a large scale quartz glass slab ingot in a flame hydrolysis reaction in a furnace, including the steps of rotating the furnace, depositing a fused silica on a furnace bed, and extending the deposit outwardly by heating and rotation of the furnace, thereby a quartz glass slab ingot is obtained. A quartz glass burner is installed at the ceiling of the furnace, hydrogen gas supplied to the burner flows down along the tapered wall of the oxygen chamber and is ejected into the outer casing. Part of the hydrogen gas is deflected to the center of the burner and mixed with the oxygen just after the ejection from the oxygen gas nozzles. Thereby, the flame is formed smoothly and the thermal efficiency is improved. The flame becomes wide enough and the silica powder transported by the hydrogen gas is uniformly fused by the flame and heat capacity of the fused silica.

Abstract: Highly durable silica glass comprising silica having incorporated therein aluminum and at least one element (M) selected from group 2A elements, group 3A elements and group 4A elements of the periodic table. Preferably, the sum of aluminum and element (M) is at least 30 atomic % based on the amount of total metal elements in the silica glass, and the atomic ratio of aluminum to element (M) is in the range of 0.05 to 20. The silica glass has a high purity and exhibits enhanced durability while good processability and machinability, and reduced dusting property are kept, and the glass is suitable for members of a semiconductor production apparatus or liquid crystal display production apparatus using a halogenated gas and/or its plasma.

Abstract: Highly durable silica glass containing 0.01% to 2% by weight of at least one element selected from magnesium, calcium, strontium, barium, yttrium, hafnium and zirconium. The silica glass is produced by melting a powdery material comprising a finely divided silica powder and a finely divided zirconium-containing substance by oxyhydrogen flame or plasma are to form an accumulated molten material layer, and extending the molten material layer outwardly in radial directions.

Abstract: An abrasive molding composed of a mass of inorganic particles, said mass having pores intervening among the inorganic particles, which molding has abrasive area to be placed in frictional contact with an article to be abraded, and non-abrasive area on a abrading surface of the abrasive molding. The abrasive area has exposed pores having a diameter of not larger than 1 &mgr;m, the total area of said exposed pores having a diameter of not larger than 1 &mgr;m occupying below 15% of the total area of abrasive area, and the non-abrasive area occupies 20% to 60% of the sum of the abrasive area and the non-abrasive area.

Abstract: An opaque silica glass article comprising a transparent portion and an opaque portion, wherein the opaque portion has an apparent density of 1.70-2.15 g/cm3 and contains 5×104-5×106 bubbles per cm3, said bubbles having an average diameter of 10-100 &mgr;m; and the transparent portion has an apparent density of 2.19-2.21 g/cm3 and the amount of bubbles having a diameter of at least 100 &mgr;m in the transparent portion is not more than 1×103 per cm. The opaque silica glass article is made by a process wherein a mold is charged with a raw material for forming the opaque portion, which is a mixture comprising a silica powder with a small amount of a silicon nitride powder, and a raw material for forming the transparent portion so that the two raw materials are located in the positions corresponding to the opaque and the transparent portions, respectively, of the silica glass article to be produced; and the raw materials are heated in vacuo to be thereby vitrified.

Abstract: An opaque silica glass article comprising a transparent portion and an opaque portion, wherein the opaque portion has an apparent density of 1.70-2.15 g/cm3 and contains 5×104−5×106 bubbles per cm3, said bubbles having an averaged diameter of 10-100 &mgr;m; and the transparent portion has an apparent density of 2.19-2.21 g/cm3 and the amount of bubbles having a diameter of at least 100 &mgr;m in the transparent portion is not more than 1×103 per cm3. The opaque silica glass article is made by a process wherein a mold is charged with a raw material for forming the opaque portion, which is a mixture comprising a silica powder with a small amount of a silicon nitride powder, and a raw material for forming the transparent portion so that the two raw materials are located in the positions corresponding to the opaque and the transparent portions, respectively, of the silica glass article to be produced; and the raw materials are heated in vacuo to be thereby vitrified.