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 cm3.

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: A high-purity transparent silica glass containing Fe, Na and K impurities each in an amount of 0.01-0.3 ppm, and an OH group in an amount of 0-3 ppm; among the Fe impurities, the content of metallic Fe having a valency of +0 being not larger than 0.1 ppm. This transparent silica glass exhibits, even when it is maintained at 900-1,400.degree. C. for at least 20 hours, an extinction coefficient of not larger than 0.009 at a wavelength of 400 nm, and does not become colored as visually examined. The silica glass is made by a process wherein powdery silica filled in a mold cavity is melted at 1,700.degree. C. or higher, characterized in that the melting is conducted in a graphite mold having a porous high-purity graphite layer provided on the mold inner surface so that the filled silica is not contacted with the mold; said porous layer having a bulk density of 0.1-1.5 g/cm.sup.3, and the content of each of Fe, Na and K impurities in the porous layer being not larger than 1 ppm.

Abstract: Pure transparent quartz glass is provided by molding powdery amorphous silica into an article, converting the molded powdery amorphous silica into crystalline silica of high-temperature type cristobalite structure, and then fusing the crystalline silica, the quartz glass containing impurities respectively at a content of not higher than 1 ppm, and an OH group at a content of not higher than 20 ppm, and having a viscosity of 10.sup.12.0 poise or more at 1200.degree. C. The quartz glass is transparent and has high purity, and is excellent in high temperature viscosity characteristics. The quartz glass can be produced at a low cost.

Abstract: The high-purity, opaque quartz glass containing 3.times.10.sup.6 -9.times.10.sup.6 of closed cells having an average size of 20-40 .mu.m per 1 cm.sup.3, a ratio of closed cells having sizes of 100 .mu.m or more to the whole of cells being 1% or less, thereby showing 5% or less of linear transmittance for near infrared rays (.lambda.=900 nm) at a thickness of 1 mm is produced by compacting amorphous silica powder having an average particle size of 0.5-10 .mu.m, in which each of impurities selected from Li, Na, K, Fe, Ti and Al is 1 ppm or less, if any, and sintering the resultant green body at 1730.degree.-1850.degree. C.

Abstract: An electrostatic precipitator includes charging, inertia and collection sections, which are arranged in the order mentioned along the direction of gas flow containing therein particles to be removed. The charging section includes a parallel electrode and a discharging electrode located between the parallel plates, and, thus, the particles floating in the gas passing through the charging section become charged and partly agglomerated. The inertia section includes a deflector plate arranged at a predetermined angle thereby causing the gas flow to change its course of action locally to have the particles impinge on the deflector plate due to inertia. The collection section includes a trough which is formed continuous with the deflector plate with its mouth opened against the gas flow.

Abstract: A nonporous flexible sound insulating sheet is provided which is composed of 50 to 90 wt.% of a nonwoven lead fiber fabric and 10 to 50 wt.% of a vinyl chloride polymer reinforcing material. The reinforcing material fills the spaces between individual lead fibers of the nonwoven fabric to secure the individual lead fibers in their places. The lead fibers are substantially uniformly distributed in the nonwoven fabric and are disposed such that the axes of the lead fibers extend, as a whole, substantially at random in all directions, and such that the lead fibers are not exposed on the surface of the sound insulating sheet. The sound insulation sheet has a thickness of 0.3 to 2.0 mm and a specific gravity of 2.0 to 6.5.

Abstract: An apparatus for producing a multiple layer conjugate fiber having a housing with a rotary cylinder plug and a stationary spinning plate. The housing is provided with at least two polymer feed inlets and the rotary cylinder plug contains at least two grooves along the outer periphery and passageways in communication with the grooves which open out at the lower surface of the rotary plug. The spinning plate contains a plurality of spinning orifices that are positioned and lined up with the passageways of the rotary cylinder plug. Means are provided for forming a limited space or multiple laminar chamber.

Abstract: A spun-type yarn having a unique configuration and useful properties is manufactured by a novel process which comprises forming a ribbon-shaped fiber bundle being substantially free from twists and composed of randomly oriented continuous filaments, each of which comprises random bends and loops along its length, and then false twisting the ribbon-shaped bundle to consolidate it into a yarn. In the false-twisting, some of the filaments are broken.