GB2141423A

GB2141423A - Infra-red transparent selenium-containing glass

Info

Publication number: GB2141423A
Application number: GB08316580A
Authority: GB
Inventors: Valery Viktorovich Melnikov; Valentina Fedorovna Kokorina
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-06-17
Filing date: 1983-06-17
Publication date: 1984-12-19
Also published as: GB2141423B; GB8316580D0

Abstract

The glass comprises 7 to 27% of arsenic, 1 to 6% of antimony, 13 to 29% of iodine, 46 to 68% of selenium, and optionally tellurium, preferably in an amount of 1 to 6% (all the above percentages being by weight).

Description

SPECIFICATION Infra-red transparent, selenium-containing glass The present invention is concerned with glasses suitable for use in infra-red optics.

There are known infra-red transparent glasses, such as "chalcogenide" glasses containing arsenic, germanium, selenium and sulphur. (See USSR Author's Certificate 140544). Such glasses generally have a softening point of 200 to 300 C, which means they are unsuitable for uses where low melting points are required (e.g. below 100 C), such as lens cements.

It is known to make lens cements from glasses containing arsenic, sulphur, thallium and antimony, but the presence of sulphur limits the transparency to infra-red radiation and the presence of thallium causes the materials to tend to crystallize. (See USSR Author's Certificate 617399).

It is further known to make a vitreous lens cementing melt from a composition comprising 10 to 60% by weight arsenic, 10 to 80% sulphur, 2 to 60% iodine and 2 to 15% of antimony (see USSR Author's Certificate 267791). Typical properties of such a cement are refractive index 2.2; transparency range 1 to 13.5 microns, and a cementing temperature of 130 C.

The transparency range is insufficient when it is desired to operate at longer wavelengths (e.g. in the RF range); also the low refractive index means that the cement is unsuitable for cementing optical components of high refractive index.

We have now developed an improved infra-red transparent glass, which has a high refractive index and transparency both in the infra-red and RF ranges. The glass according to the invention comprises: 7 to 27% by weight of arsenic, 1 to 6% by weight of antimony, 13 or 14 to 29% by weight of iodine, and 46 to 68% by weight of selenium.

Glasses according to the invention generally have a low forming temperature (below 100 C) and do not crystallise during heat treatment. They also have good chemical durability and can be used to provide good optical contact between surfaces, without attacking the surfaces.

In order to increase the refractive index and inhibit crystallisation during heat treatment, the glass preferably contains tellurium, preferably in an amount of 1 to 6% by weight because less than 1% gives little increase in refractive index, while more than 6% might cause a tendency for the glass to crystallise. When tellurium is present, the amount of selenium is preferably 47 to 62% by weight.

As indicated, the composition according to the invention contains 46 or 48 to 68% of selenium; less than this amount causes the glass to tend to crystallise and more than 68% impairs the thermoplastic properties of the glass.

A particularly preferred composition comprises: 24 to 27% by weight of arsenic, 2 to 5% by weight of antimony, 13 to 16% by weight of iodine, 55 to 57% by weight of selenium, and 2to 4% by weight of tellurium.

The accompanying drawing shows the transmittance curves (in the infra-red and RF ranges) for various thicknesses of glass according to the invention. Curve 1 corresponds to a thickness of 30 microns (in this case the glass is transparent up to a wavelength of 25 microns); curves 2 and 3 correspond to thicknesses of 10 and 20 mm, respectively (the glass being transparent up to a wavelength of 18 microns).

In the RF range, at a frequency of 3.5 x 1 010Hz (8 mm range), the dielectric constant is E 7.2 and the loss tangent tg 3 is 5 x 10-4. The refractive index of such a glass is about 2.25 (without tellurium - with tellurium the refractive index may be increased up to 2.40).

Glasses according to the invention may be made by the vacuum technique, in which arsenic, antimony, iodine, selenium and tellurium taken in desired quantities are placed in a quartz ampoule which is evacuated by a vacuum pump to a vacuum of 10-2Pa and soldered-up by a gas torch. The ampoule containing the batch is then placed in an electric furnace and heated during 12 hours to 700 + 100C under stirring. After the melting is completed and the furnace has cooled down to 300 t 1 00C, the ampoule containing the substance is tempered to room temperature (200C). The quartz ampoule is then broken and the glass ingot is withdrawn.

In order that the present invention may be more fully understood, the following Examples are given by way of illustration only.

Example 1 A batch containing 149.60 g of arsenic, 27.00 g of antimony, 281.60 g of iodine, 499.30 g of selenium and 42.50 g of tellurium was placed in a quartz ampoule which was evacuated by a vacuum pump to 10-2Pa and soldered-up by a gas torch. The ampoule containing the batch was then placed in an electric furnace and heated for 12 hours consecutively to 300, 500 and 700"C under stirring. After the melting was completed and the furnace cooled down to 300"C the ampoule with the glass was tempered to room temperature (20 C). The ampoule was then broken, and the glass ingot was withdrawn. The glass yield was 1 kg.

The resulting glass had a forming temperature about 150or, and a refractive index 2.40, and it could be used for making high-refractive optical components of various types transparent in the infra-red and in the R.F. range.

Examples 2 to 7 Example 1 was repeated using materials and conditions as set out in the following Table.

The product of Example 2 had good thermal stability (forming temperature 190"C) and could be used for making high refractive index optical components transparent in the infra-red and RF ranges.

The product of Example 3 had a low forming temperature (30-40"C) high refractive index (2.35) and good thermoplastic properties. The glass could be used for providing an optical contact with high refractive objects having a limited thermal stability. Owing to the low softening point this glass should be stored ata lower temperature (5-10 C).

The product of Example 4 had good thermal stability (forming temperature is 120"C) and high refractive index and it could be used for making high-refractive optical components transparent in the infra-red and in the RF range.

The product of Example 5 did not contain tellurium so that its refractive index was as low as 2.25. The glass had good thermal stability (forming temperature was 1 00 C) and could be used for making optical components transparent in the infra-red and in the RF range.

The absence of tellurium in the product of Example 6 resulted in lowering its refractive index to 2.30. The glass had good thermal stability (forming temperature was 1 10"C) and could be used for making optical components transparent in the infra-red and in the RF range.

The absence of tellurium in the product of Example 7 resulted in a reduction of the refractive index to 2.27.

The glass had poor thermal stability (forming temperature was 50-60 C) and good thermoplastic properties.

This made it possible to use the glass for providing an optical contact with surfaces of various samples which had similar refractive indices.

This glass may also be used as lens cement for cementing together optical components transparent in the infra-red and in the RF range.

TABLE Example Composition of glass in % by weight Forming temperature Refractive As Sb I Se Te OC index 1 14.96 2.70 28.16 49.93 4.25 150 2.40 2 26.07 5.65 14.72 47.64 5.92 190 2.40 3 7.07 1.14 28.81 61.91 1.07 30-40 2.35 4 24.65 2.35 14.07 55.81 3.12 120 2.40 5 19.16 3.67 28.64 48.53 - 100 2.25 6 9.89 5.08 17.38 67.65 - 110 2.30 7 11.12 2.98 27.78 58.12 - 50-60 2.27 The glass according to the invention has good thermoplasticity, low tendency to crystallization in the range of heattreatment temperatures, good adhesion to various materials (crystals, organic materials, optical glasses and the like), low forming temperature (up to 1000C). These properties enable the glass according to the invention to be used for providing an optical contact with the surfaces of samples made of a large variety of materials. In addition, the glass may be used for making both standard and tailored optical components such as lenses, optical filters, prisms, optical cells and the like. The glass according to the invention may also be used as a lens cement for cementing together optical components which are transparent in both the infra-red and the RF range.

Claims

1. An infra-red transparent glass which comprises: 7 to 27% by weight of arsenic, 1 to 6% by weight of antimony, 13 or 14 to 29% by weight of iodine, and 46 to 68% by weight of selenium.

2. A glass according to claim 1,which also contains tellurium.

3. A glass according to claim 2, in which the amount of tellurium is 1 to 6% by weight.

4. A glass according to claim 2, which comprises: 24 to 27% by weight of arsenic, 2 to 5% by weight of antimony, 13 to 16% by weight of iodine, 55 to 57% by weight of selenium, and 2 to 4% by weight of tellurium.

5. An infra-red transparent glass, substantially as herein described in any of the Examples.