Provided is a method for producing a synthetic opaque quartz glass where flame processing can be performed in high purity with a simple way and even a large sized one can be produced, and the synthetic opaque quartz glass. A method for producing a synthetic opaque quartz glass which comprises the step of heating and burning a quartz glass porous body under a pressure of from 0.15 MPa to 1000 MPa at a temperature of from 1200 C. The quartz glass porous body is prepared by depositing quartz glass particles which are produced by hydrolyzing a silicon compound with an oxyhydrogen flame.

In one method for producing opaque quartz glass, a green body is produced from a slip containing fine, amorphous SiO.sub.2 particles and coarse SiO.sub.2 reinforcement bodies and the green body is sintered by way of a sintering treatment into a blank made from the opaque quartz glass. The reinforcement bodies with a specific density D.sub.K1 are here embedded in a SiO.sub.2 matrix with a specific glass density D.sub.M. Starting from this, in order to provide a blank of opaque quartz glass that is less susceptible to cracking and illustrates homogeneous transmission even in the case of small wall thicknesses, in one aspect sinterable reinforcement bodies are used, the specific density D.sub.K0 of which prior to the sintering treatment is lower than the specific glass density D.sub.M, and which due to the sintering treatment reach the specific density D.sub.K1 which differs from the specific glass density D.sub.M by less than 10%.

An alkali-free glass substrate contains, as represented by mass % based on oxides: 54% to 68% of SiO.sub.2; 10% to 25% of Al.sub.2O.sub.3; 0.1% to 5.5% of B.sub.2O.sub.3; and 8% to 26% of MgO+CaO+SrO+BaO. The alkali-free glass substrate has -OH of 0.15 mm.sup.1 to 0.35 mm.sup.1, and a Cl content of 0.15 to 0.3 mass %. A bubble growth index I of the alkali-free glass substrate given by the following formula is 320 or more: I=590.5[-OH]+874.1[Cl]5.7[B.sub.2O.sub.3]33.3. In the formula, [-OH] is -OH of the alkali-free glass substrate in mm.sup.1, [Cl] is the Cl content of the alkali-free glass substrate in mass %, and [B.sub.2O.sub.3] is a B.sub.2O.sub.3 content of the alkali-free glass substrate in mass %.

A body, such as a lamp body, includes a tubular element. At least one conductor is introduced into the tubular element and a glass material surrounds the conductor. The glass material forms a seal between the tubular element and the conductor. The glass material comprises a sintered glass, such as a sintered glass ring, and may completely surround the conductor.

A spherical inorganic oxide powder wherein a volume-based cumulative 50% diameter D50 is 4-55 ?m; and in a cross-section of a cured body containing an epoxy resin and the spherical inorganic oxide powder at a mass ratio of 2:1, when a total of 5000 particles with a maximum diameter of 51 ?m or larger are observed in a field of view at 100? magnification using a scanning electron microscope, a total number of air bubbles having a maximum diameter of 1 ?m or larger and smaller than 10 ?m is 40 or fewer and a total number of air bubbles having a maximum diameter of 10 ?m or larger is 30 or fewer.

A glass tube for sealing a metal includes a glass that contains, in terms of mass %, 50% or more of SiO.sub.2+B.sub.2O.sub.3, 0% to 10% of Al.sub.2O.sub.3, 3% to 20% of RO (R is an alkali-earth metal), and 11% to 22% of R.sub.2O (R is an alkali metal), and that has 10 l/g or less of an amount of CO.sub.2 emitted when heated from a room temperature to 1100 C.

A diffuser material of synthetically produced, pore-containing quartz glass and a method for the manufacture of a molded body consisting fully or in part thereof. The diffuser material has a chemical purity of at least 99.9% SiO.sub.2, a cristobalite content of not more than 1%, and a density in the range of 2.0 to 2.18 g/cm.sup.3. Starting therefrom, to indicate a diffuser material which is improved with respect to diffuse reflectivity with Lambertian behavior over a wide wavelength range, high material homogeneity and UV radiation resistance, the quartz glass has a hydroxyl group content in the range of at least 200 wt. ppm and at least 80% of the pores have a maximum pore dimension of less than 20 m.

In one method for producing opaque quartz glass, a green body is produced from a slip containing fine, amorphous SiO.sub.2 particles and coarse SiO.sub.2 reinforcement bodies and the green body is sintered by way of a sintering treatment into a blank made from the opaque quartz glass. The reinforcement bodies with a specific density D.sub.K1 are here embedded in a SiO.sub.2 matrix with a specific glass density D.sub.M. Starting from this, in order to provide a blank of opaque quartz glass that is less susceptible to cracking and illustrates homogeneous transmission even in the case of small wall thicknesses, in one aspect sinterable reinforcement bodies are used, the specific density D.sub.K0 of which prior to the sintering treatment is lower than the specific glass density D.sub.M, and which due to the sintering treatment reach the specific density D.sub.K1 which differs from the specific glass density D.sub.M by less than 10%.

To provide opaque quartz glass having no water absorbing properties and being excellent in infrared light shielding properties, and a method for its production. In the production of opaque quartz glass of the present invention, a fine amorphous silica powder and a pore forming agent are mixed, then molded and heated at a predetermined temperature, to obtain opaque quartz glass wherein contained pores are closed pores, the average pore size of pores is from 5 to 20 m, and the content density of pores is high, whereby the heat shielding properties are high.

To provide opaque quartz glass having no water absorbing properties and being excellent in infrared light shielding properties, and a method for its production. In the production of opaque quartz glass of the present invention, a fine amorphous silica powder and a pore forming agent are mixed, then molded and heated at a predetermined temperature, to obtain opaque quartz glass wherein contained pores are closed pores, the average pore size of pores is from 5 to 20 m, and the content density of pores is high, whereby the heat shielding properties are high.