Abstract: Described is a process for the refinement of a quartz powder, comprising the step of separating microparticles of refractory minerals, in particular minerals containing rare earth metal compounds, from the quartz powder by an elutriation step.

Abstract: An apparatus for the continuous production of hollow quartz-glass ingots, comprising a) a crucible or refractory tank for providing a softened quartz-glass mass having a dieorifice in the bottom of the crucible or refractory tank; b) a mandrel vertically drawing off the softened quartz-glass mass through a die toprovide a hollow quartz-glass ingot; and c) a cutting section for on-line cutting of the hollow quartz-glass ingot to a specificlength, characterized in that the apparatus comprises active means for cooling the internalsurface of the hollow quartz-glass ingot prior to the cutting station.

Abstract: An apparatus for the continuous production of hollow quartz-glass ingots, comprising a) a crucible or refractory tank for providing a softened quartz-glass mass having a dieorifice in the bottom of the crucible or refractory tank; b) a mandrel vertically drawing off the softened quartz-glass mass through a die toprovide a hollow quartz-glass ingot; and c) a cutting section for on-line cutting of the hollow quartz-glass ingot to a specificlength, characterized in that the apparatus comprises active means for cooling the internalsurface of the hollow quartz-glass ingot prior to the cutting station.

Abstract: The present invention relates to a continuous method for the production of hollow quartz-glass ingots and an apparatus for said method, whereby the hollow quartz-glass ingots are cooled on the internal surface.

Abstract: Described is a process for the refinement of a quartz powder, comprising the step of separating microparticles of refractory minerals, in particular minerals containing rare earth metal compounds, from the quartz powder by an elutriation step.

Abstract: A method and apparatus for manufacturing a quartz glass ingot of large cross-sectional area by continuous flame-fusion whereby on-line crack-free cutting of the ingot is ensured by using the internal heat of the ingot to permit equilibration of the internal and surface temperatures while passing through one or more annealing chambers, thus ensuring controlled cooling to temperature at which it is possible to cut the ingot with a water-cooled saw.

Abstract: The present invention relates to a continuous method for the production of hollow quartz-glass ingots and an apparatus for said method, whereby the hollow quartz-glass ingots are cooled on the internal surface.

Abstract: One aspect relates to a method for the production of synthetic quartz glass. Moreover, one aspect relates to a polyalkylsiloxane compound, which includes certain specifications with respect to chlorine content, metallic impurities content, and residual moisture, as well as the use thereof for the production of synthetic quartz glass. One aspect also relates to a synthetic quartz glass that can be obtained according to the method of one embodiment.

Abstract: Hollow ingots of transparent synthetic vitreous silica glass of external diameter greater than 400 mm and internal diameter greater than 300 mm are disclosed. The ingots are substantially free from bubbles or inclusions greater than 100 ?m in diameter, have no more than 100 ppB of any individual metallic impurity, and have chlorine concentration less than 5 ppM. Also disclosed are methods for producing such ingots, in which a porous soot body of density greater than 0.4 g/cm3 is deposited on an oxidation resistant mandrel. The soot body is dehydrated on a mandrel comprising graphite, carbon fiber reinforced carbon, silicon carbide, silicon impregnated silicon carbide, silicon carbide-coated graphite or vitreous silica, either under vacuum or in the presence of a reducing gas, and then sintered to transparent pore-free glass under vacuum or in an atmosphere of helium.

Abstract: One aspect relates to a method for the production of synthetic quartz glass. Moreover, one aspect relates to a polyalkylsiloxane compound, which includes certain specifications with respect to chlorine content, metallic impurities content, and residual moisture, as well as the use thereof for the production of synthetic quartz glass. One aspect also relates to a synthetic quartz glass that can be obtained according to the method of one embodiment.

Abstract: Processes for the manufacture of a hollow cylindrical porous body of synthetic vitreous silica soot by outside vapor deposition on a mandrel are described, in which the temperature of the mandrel is controlled to be substantially constant throughout the deposition process. In preferred embodiments, the mandrel is composed of metal or metal alloy. Hollow ingots of pure or doped synthetic vitreous silica glass manufactured by such processes are also described.

Abstract: An apparatus and method are provided for sintering a hollow cylindrical body of porous synthetic silica. The apparatus comprises a hollow mandrel for supporting the body in a horizontal position, and the mandrel is housed within a vacuum furnace having heating elements arranged to surround the body circumferentially along its entire length. The method includes supporting the body on a hollow horizontally-oriented mandrel in a vacuum furnace in which heating elements are disposed surrounding the body, and heating the body by means of the elements to a sintering temperature.

Abstract: Methods are described for manufacturing silica-based glass, in which silica precursor material is supplied to a synthesis flame in the form of an emulsion. The methods involve the steps of: forming an emulsion of an aqueous phase in a non-aqueous liquid silica precursor material; supplying the emulsion as a spray of droplets into a synthesis flame, whereby the precursor material is converted in the flame into a silica-containing soot; and collecting the soot on a substrate, either as a porous soot body for subsequent consolidation to glass or directly as a substantially pore-free glass.

Abstract: Processes for the manufacture of a hollow cylindrical porous body of synthetic vitreous silica soot by outside vapour deposition on a mandrel are described, in which the temperature of the mandrel is controlled to be substantially constant throughout the deposition process. In preferred embodiments, the mandrel is composed of metal or metal alloy. Hollow ingots of pure or doped synthetic vitreous silica glass manufactured by such processes are also described.

Abstract: Hollow ingots of transparent synthetic vitreous silica glass of external diameter greater than 400 mm and internal diameter greater than 300 mm are disclosed. The ingots are substantially free from bubbles or inclusions greater than 100 ?m in diameter, have no more than 100 ppB of any individual metallic impurity, and have chlorine concentration less than 5 ppM. Also disclosed are methods for producing such ingots, in which a porous soot body of density greater than 0.4 g/cm3 is deposited on an oxidation resistant mandrel. The soot body is dehydrated on a mandrel comprising graphite, carbon fibre reinforced carbon, silicon carbide, silicon impregnated silicon carbide, silicon carbide-coated graphite or vitreous silica, either under vacuum or in the presence of a reducing gas, and then sintered to transparent pore-free glass under vacuum or in an atmosphere of helium.

Abstract: Methods are described for manufacturing silica-based glass, in which silica precursor material is supplied to a synthesis flame in the form of an emulsion. The methods involve the steps of: forming an emulsion of an aqueous phase in a non-aqueous liquid silica precursor material; supplying the emulsion as a spray of droplets into a synthesis flame, whereby the precursor material is converted in the flame into a silica-containing soot; and collecting the soot on a substrate, either as a porous soot body for subsequent consolidation to glass or directly as a substantially pore-free glass.

Abstract: A process for the manufacture of a substantially bubble-free article of synthetic vitreous silica free from localised variations in refractive index (striae) and suitable for optical applications, wherein an ingot of synthetic vitreous silica containing unacceptable bubbles is submitted to a first heat treatment process consisting of hot isostatic pressing at a temperature in the range 1,250° C. to 1,500° C. at a pressure in the range 10 MPa to 250 MPa, followed by a second heat treatment process at a pressure in the range 0.01 to 1 MPa and at a temperature in the range 1,550° C. to 1,850° C.

Abstract: A method and apparatus for the manufacture of synthetic vitreous silica ingots involves the production of a melt of synthetic vitreous silica in a crucible (35) within a refractory furnace (31), and the continuous withdrawal of an ingot (43) through an orifice (40) in the wall of the crucible. The silica may be deposited in the crucible by a synthesis burner (33), which may also serve to maintain the silica above its sintering temperature. The emerging ingot is supported by an arrangement of moveable clamps (44).

Abstract: Disclosed is a quartz glass product of enhanced opacity manufactured by fusion of silica particles, the opacity being enhanced by the reaction of an organosilicon additive in the course of the fusion process. A method of enhancing the opacity of a quart glass product by fusing silica particles in the presence of an organosilicon additive is also disclosed.

Abstract: A linear burner for the synthesis of silica by vapor-phase reaction of a silicon-containing feedstock in a flame comprises at least five slots opening to an exit face (52a) of the burner and extending side-by-side in the elongate direction of the linear burner, and includes means (P1-P10) to supply a separate gas flow to each of said slots. An assembly of separator plates (52) is disposed between opposed casing parts (50, 51), which assembly defines the slots. At least one of the casing parts (50, 51) defines at least part of a respective plenum chamber (54) for each gas flow, each plenum chamber (54) communicating with a different one of said slots in the separator assembly. The invention also extends to a method of operating such a linear burner.