Stock material or miscellaneous articles – Hollow or container type article – Glass – ceramic – or sintered – fused – fired – or calcined metal...
Patent
1996-05-07
1998-04-07
Zirker, Daniel
Stock material or miscellaneous articles
Hollow or container type article
Glass, ceramic, or sintered, fused, fired, or calcined metal...
428 434, 428426, 65 172, 65 173, C03B 1906, C03B 2000, B01J 300, H01L 2102
Patent
active
057362068
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention pertains to a molded body of quartz glass which has at least one surface region of transparent quartz glass, the exposed surface of which is smooth, with a surface microroughness of less than 8 .mu.m.
The invention also pertains to a process for the production of a molded body of quartz glass with at least one surface region of transparent quartz glass, the surface of which is smooth, with a surface microroughness of less than 8 .mu.m.
Japanese Registered Design Publication No. 58-12280 (published on Jan. 26, 1983) describes a molded body of quartz glass which has at least one surface region of transparent quartz glass, the exposed surface of which is smooth and has a surface roughness of less than 2 .mu.m. A flange ring of transparent quartz glass is fused onto the flange of a base consisting of opaque, bubble-containing quartz glass; the exposed surface of the ring is polished again to achieve the desired low surface roughness and then flame-glazed to produce a smooth surface. It is extremely expensive to produce a molded body with a structure of this kind, because each flange ring must be cut individually from a transparent quartz glass plate, which entails a considerable amount of cutting waste in addition to other problems. Fusing a transparent quartz glass flange ring of this kind onto a flange of opaque quartz glass, furthermore, is extremely risky because of the possibility of shrinkage and/or the development of internal stresses between the two grades of quartz glass. Aside from this, the production method is also highly labor-intensive. Nor does the flame-glazing of the exposed surface of the flange of the molded body of opaque quartz glass lead to the desired result, because, although a smooth surface resistant to acid treatment is obtained, the bubbles of the quartz glass remain behind as holes of considerable size in the exposed surface.
SUMMARY OF THE INVENTION
The invention is based on the task of creating a molded body of quartz glass of the type characterized above which has a simple structure, which can be produced inexpensively, and which eliminates the need to stock or to produce supplemental components.
The invention is based on the additional task of offering a process for the production of these molded bodies which can be implemented easily and which eliminates almost all of the material waste.
The molded body includes a base, the base material of which has a chemical purity of at least 99.9% and a cristobalite content of no more than 1%, which is gas-impermeable and opaque and contains pores. At which, a wall thickness of 1 mm, the base material has nearly constant direct spectral transmission of less than 10% in the wavelength range of .lambda.=190 nm to .lambda.=2,650 nm; and a density of at least 2.15 g/cm.sup.3. The transparent surface region is formed from the base material by subjecting it to a heat treatment at a temperature of more than 1,650.degree. C., the thickness of the transparent layer being at least 0.5 mm, the direct spectral transmission of the transparent layer being at least 60% in the wavelength range of .lambda.=600 nm to .lambda.=2,650 nm for a layer thickness of 1 mm.
It is advantageous for the molded body to consist of a single base.
Preferably at least 80% of the pores of the base material have a maximum pore dimension of less than 20 .mu.m; it is advantageous for the maximum pore dimension to be less than 10 .mu.m. The pore content of the base material is in the range of 0.5-2.5% per unit volume.
Because the molded body is formed from a base consisting of a base material with specified characteristics, stresses are almost completely eliminated, because the density of the opaque, porous base material and the density of the base material made transparent by the heat treatment do not differ essentially from each other. Because of the low percentage of pores per unit volume in the base material, the base material which has been transformed into transparent material also fails to show any significant amount of shrin
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patent: 4956208 (1990-09-01), Uchikawa et al.
patent: 5330941 (1994-07-01), Yaba et al.
patent: 5389582 (1995-02-01), Loxley et al.
Englisch Wolfgang
Hellmann Dietmar
Moritz Stephan
Heraeus Quarzglas GmbH
Zirker Daniel
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